Publications by authors named "John H Arnold"

62 Publications

Adding Continuous Vital Sign Information to Static Clinical Data Improves the Prediction of Length of Stay After Intubation: A Data-Driven Machine Learning Approach.

Respir Care 2020 Sep;65(9):1367-1377

Department of Pediatrics, Harvard Medical School, Boston, Massachusetts.

Background: Bedside monitors in the ICU routinely measure and collect patients' physiologic data in real time to continuously assess the health status of patients who are critically ill. With the advent of increased computational power and the ability to store and rapidly process big data sets in recent years, these physiologic data show promise in identifying specific outcomes and/or events during patients' ICU hospitalization.

Methods: We introduced a methodology designed to automatically extract information from continuous-in-time vital sign data collected from bedside monitors to predict if a patient will experience a prolonged stay (length of stay) on mechanical ventilation, defined as >4 d, in a pediatric ICU.

Results: Continuous-in-time vital signs information and clinical history data were retrospectively collected for 284 ICU subjects from their first 24 h on mechanical ventilation from a medical-surgical pediatric ICU at Boston Children's Hospital. Multiple machine learning models were trained on multiple subsets of these subjects to predict the likelihood that each of these subjects would experience a long stay. We evaluated the predictive power of our models strictly on unseen hold-out validation sets of subjects. Our methodology achieved model performance of >83% (area under the curve) by using only vital sign information as input, and performances of 90% (area under the curve) by combining vital sign information with subjects' static clinical data readily available in electronic health records. We implemented this approach on 300 independently trained experiments with different choices of training and hold-out validation sets to ensure the consistency and robustness of our results in our study sample. The predictive power of our approach outperformed recent efforts that used deep learning to predict a similar task.

Conclusions: Our proposed workflow may prove useful in the design of scalable approaches for real-time predictive systems in ICU environments, exploiting real-time vital sign information from bedside monitors. (ClinicalTrials.gov registration NCT02184208.).
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http://dx.doi.org/10.4187/respcare.07561DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7906608PMC
September 2020

Distribution of Ventilation Measured by Electrical Impedance Tomography in Critically Ill Children.

Respir Care 2020 May 28;65(5):590-595. Epub 2020 Jan 28.

Department of Health Professions, Liberty University, School of Health Sciences, Lynchburg, Virginia.

Background: Electrical impedance tomography (EIT) is a noninvasive, portable lung imaging technique that provides functional distribution of ventilation. We aimed to describe the relationship between the distribution of ventilation by mode of ventilation and level of oxygenation impairment in children who are critically ill. We also aimed to describe the safety of EIT application.

Methods: A prospective observational study of EIT images obtained from subjects in the pediatric ICU. Images were categorized by whether the subjects were on intermittent mandatory ventilation (IMV), continuous spontaneous ventilation, or no positive-pressure ventilation. Images were categorized by the level of oxygenation impairment when using [Formula: see text]/[Formula: see text]. Distribution of ventilation is described by the center of ventilation.

Results: Sixty-four images were obtained from 25 subjects. Forty-two images obtained during IMV with a mean ± SD center of ventilation of 55 ± 6%, 14 images during continuous spontaneous ventilation with a mean ± SD center of ventilation of 48.1 ± 11%, and 8 images during no positive-pressure ventilation with a mean ± SD center of ventilation of 47.5 ± 10%. Seventeen images obtained from subjects with moderate oxygenation impairment with a mean ± SD center of ventilation of 59.3 ± 1.9%, 12 with mild oxygenation impairment with a mean ± SD center of ventilation of 52.6 ± 2.3%, and 4 without oxygenation impairment with a mean ± SD center of ventilation of 48.3 ± 4%. There was more ventral distribution of ventilation with IMV versus continuous spontaneous ventilation ( = .009), with IMV versus no positive-pressure ventilation ( = .01) cohorts, and with moderate oxygenation impairment versus cohorts without oxygenation impairment ( = .009). There were no adverse events related to the placement and use of EIT in our study.

Conclusions: Children who had worse oxygen impairment or who received controlled modes of ventilation had more ventral distribution of ventilation than those without oxygen impairment or the subjects who were spontaneously breathing. The ability of EIT to detect changes in the distribution of ventilation in real time may allow for distribution-targeted mechanical ventilation strategies to be deployed proactively; however, future studies are needed to determine the effectiveness of such a strategy.
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http://dx.doi.org/10.4187/respcare.07076DOI Listing
May 2020

Noninvasive Ventilation Is Interrupted Frequently and Mostly Used at Night in the Pediatric Intensive Care Unit.

Respir Care 2020 Mar 24;65(3):341-346. Epub 2019 Sep 24.

Division of Critical Care Medicine, Department of Anesthesiology, Critical Care and Pain Medicine, Boston Children's Hospital, Boston, Massachusetts.

Background: Noninvasive ventilation (NIV) is commonly used to support children with respiratory failure, but detailed patterns of real-world use are lacking. The aim of our study was to describe use patterns of NIV via electronic medical record (EMR) data.

Methods: We performed a retrospective electronic chart review in a tertiary care pediatric ICU in the United States. Subjects admitted to the pediatric ICU from 2014 to 2017 who were mechanically ventilated were included in the study.

Results: The median number of discrete device episodes, defined as a time on support without interruption, was 20 (interquartile range [IQR] 8-49) per subject. The median duration of bi-level positive airway pressure (BPAP) support prior to interruption was 6.3 h (IQR 2.4-10.4); the median duration of CPAP was 6 h (IQR 2.1-10.4). Interruptions to BPAP had a median duration of 6.3 h (IQR 2-15.5); interruptions to CPAP had a median duration of 8.6 h (IQR 2.2-16.8). Use of NIV followed a diurnal pattern, with 44% of BPAP and 42% of CPAP subjects initiating support between 7:00 pm and midnight, and 49% of BPAP and 46% of CPAP subjects stopping support between 5:00 am and 10:00 am.

Conclusions: NIV was frequently interrupted, and initiation and discontinuation of NIV follows a diurnal pattern. Use of EMR data collected for routine clinical care allowed the analysis of granular details of typical use patterns. Understanding NIV use patterns may be particularly important to understanding the burden of pediatric ICU bed utilization for nocturnal NIV. To our knowledge, this is the first study to examine in detail the use of pediatric NIV and to define diurnal use and frequent interruptions to support.
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http://dx.doi.org/10.4187/respcare.06883DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7119185PMC
March 2020

Empirical Probability of Positive Response to PEEP Changes and Mechanical Ventilation Factors Associated With Improved Oxygenation During Pediatric Ventilation.

Respir Care 2019 Oct 14;64(10):1193-1198. Epub 2019 May 14.

Department of Bioengineering, Northeastern University, Boston, Massachusetts.

Background: PEEP is titrated to improve oxygenation during mechanical ventilation. It is clinically desirable to identify factors that are associated with a clinical improvement or deterioration following a PEEP change. However, these factors have not been adequately described in the literature. Therefore, we aimed to quantify the empirical probability of PEEP changes having a positive effect upon oxygenation, compliance of the respiratory system (C), and the ratio of dead space to tidal volume (V/V). Further, clinical factors associated with positive response during pediatric mechanical ventilation are described.

Methods: Mechanically ventilated pediatric subjects in the ICU were eligible for inclusion in the study. During PEEP increases (PEEP), a responder was defined as having an improved S /F ratio; non-responders demonstrated a worsening S /F ratio in the following hour. When PEEP was decreased (PEEP), a responder was anyone who maintained or increased the S /F ratio; non-responders demonstrated a worsening S /F ratio. Features from continuous mechanical ventilation variables were extracted, and differences between responders and non-responders were identified.

Results: 286 PEEP change cases were eligible for analysis in 76 subjects. For PEEP cases, the empirical probability of positive response was 56%, 67%, and 54% for oxygenation, C, and V/V, respectively. The median S /F increase was 13. For PEEP, the empirical probability of response was 46%, 53%, and 46% for oxygenation, C, and V/V, respectively. PEEP responders had higher F requirements (70.8 vs 52.5%, < .001), mean airway pressure (14.0 vs 12.9 cm HO, = .03), and oxygen saturation index (9.9 vs 7.5, = .002) versus non-responders. For PEEP, V/V was lower in responders (0.46 vs 0.50, = .031).

Conclusions: In children requiring mechanical ventilation, the responder rate was modest for both PEEP and PEEP cases. These data suggest that PEEP titration often does not have the desired clinical effect, and predicting which patients will manifest a positive response is complex, requiring more sophisticated means of assessing individual subjects.
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http://dx.doi.org/10.4187/respcare.06707DOI Listing
October 2019

Time versus treatment: interpreting longitudinal data analysis of treprostinil.

J Pediatr 2019 03 14;206:304-305. Epub 2018 Dec 14.

Boston Children's Hospital Harvard Medical School Boston, Massachusetts.

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http://dx.doi.org/10.1016/j.jpeds.2018.11.034DOI Listing
March 2019

Equilibration Time Required for Respiratory System Compliance and Oxygenation Response Following Changes in Positive End-Expiratory Pressure in Mechanically Ventilated Children.

Crit Care Med 2018 05;46(5):e375-e379

Department of Bioengineering, Northeastern University, Boston, MA.

Objectives: Increases in positive end-expiratory pressure are implemented to improve oxygenation through the recruitment and stabilization of collapsed alveoli. However, the time it takes for a positive end-expiratory pressure change to have maximum effect upon oxygenation and pulmonary compliance has not been adequately described in children. Therefore, we sought to quantify the time required for oxygenation and pulmonary system compliance changes in children requiring mechanical ventilation.

Design: Retrospective analysis of continuous data.

Settings: Multidisciplinary ICU of a pediatric university hospital.

Patients: Mechanically ventilated pediatric subjects.

Interventions: A case was eligible for analysis if during a 90-minute window following an increase in positive end-expiratory pressure, no other changes to the ventilator were made, ventilator and physiologic data were continuously available and a positive oxygenation response was observed. Time to 90% (T90) of the maximum change in oxygenation and compliance was computed. Differences between oxygenation and compliance T90 were compared using a paired t test. The effect of severity of illness (by oxygen saturation index) upon oxygenation and compliance was analyzed.

Measurements And Main Results: A total of 200 subjects were enrolled and 1,150 positive end-expiratory pressure change cases were analyzed. Of these, 54 subjects with 171 positive end-expiratory pressure change case were included in the analysis (67% were responders).Changes in dynamic compliance (T90 = 38 min) preceded changes in oxygenation (T90 = 71 min; p < 0.001). Oxygenation response differed depending on severity of illness quantified by oxygen saturation index; lung dysfunction was associated with a longer response time (p = 0.001).

Conclusions: T90 requires 38 and 71 minutes for dynamic pulmonary compliance and oxygenation, respectively; the latter was directly observed to be dependent upon severity of illness. To our knowledge, this is the first report of oxygenation and compliance equilibration data following positive end-expiratory pressure increases in pediatric mechanically ventilated subjects.
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http://dx.doi.org/10.1097/CCM.0000000000003001DOI Listing
May 2018

Dexmedetomidine in the PICU: Can We Get More for Less?

Pediatr Crit Care Med 2017 09;18(9):893-894

Department of Anesthesiology, Perioperative and Pain Medicine, Division of Critical Care Medicine, Boston Children's Hospital, Harvard Medical School, Boston, MA.

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http://dx.doi.org/10.1097/PCC.0000000000001240DOI Listing
September 2017

The Quality of Quality Metrics-Reply.

Respir Care 2017 02;62(2):254-255

Department of Anesthesiology, Perioperative, and Pain Medicine Division of Critical Care Medicine Boston Children's Hospital Pediatric Anesthesia Harvard Medical School Boston, Massachusetts.

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http://dx.doi.org/10.4187/respcare.05408DOI Listing
February 2017

Daily Goals Formulation and Enhanced Visualization of Mechanical Ventilation Variance Improves Mechanical Ventilation Score.

Respir Care 2017 Mar 10;62(3):268-278. Epub 2017 Jan 10.

Department of Anesthesiology, Perioperative and Pain Medicine, Division of Critical Care Medicine, Boston Children's Hospital, Boston, Massachusetts.

Background: The systematic implementation of evidence-based practice through the use of guidelines, checklists, and protocols mitigates the risks associated with mechanical ventilation, yet variation in practice remains prevalent. Recent advances in software and hardware have allowed for the development and deployment of an enhanced visualization tool that identifies mechanical ventilation goal variance. Our aim was to assess the utility of daily goal establishment and a computer-aided visualization of variance.

Methods: This study was composed of 3 phases: a retrospective observational phase (baseline) followed by 2 prospective sequential interventions. Phase I intervention comprised daily goal establishment of mechanical ventilation. Phase II intervention was the setting and monitoring of daily goals of mechanical ventilation with a web-based data visualization system (T3). A single score of mechanical ventilation was developed to evaluate the outcome.

Results: The baseline phase evaluated 130 subjects, phase I enrolled 31 subjects, and phase II enrolled 36 subjects. There were no differences in demographic characteristics between cohorts. A total of 171 verbalizations of goals of mechanical ventilation were completed in phase I. The use of T3 increased by 87% from phase I. Mechanical ventilation score improved by 8.4% in phase I and 11.3% in phase II from baseline ( = .032). The largest effect was in the low risk V category, with a 40.3% improvement from baseline in phase I, which was maintained at 39% improvement from baseline in phase II ( = .01). mechanical ventilation score was 9% higher on average in those who survived.

Conclusions: Daily goal formation and computer-enhanced visualization of mechanical ventilation variance were associated with an improvement in goal attainment by evidence of an improved mechanical ventilation score. Further research is needed to determine whether improvements in mechanical ventilation score through a targeted, process-oriented intervention will lead to improved patient outcomes. (ClinicalTrials.gov registration NCT02184208.).
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http://dx.doi.org/10.4187/respcare.04873DOI Listing
March 2017

Categorization in Mechanically Ventilated Pediatric Subjects: A Proposed Method to Improve Quality.

Respir Care 2016 Sep 14;61(9):1168-78. Epub 2016 Jun 14.

Department of Anesthesiology, Perioperative, and Pain Medicine, Division of Critical Care Medicine, Boston Children's Hospital and Pediatric Anesthesia, Harvard Medical School, Boston, Massachusetts.

Background: Thousands of children require mechanical ventilation each year. Although mechanical ventilation is lifesaving, it is also associated with adverse events if not properly managed. The systematic implementation of evidence-based practice through the use of guidelines and protocols has been shown to mitigate risk, yet variation in care remains prevalent. Advances in health-care technology provided the ability to stream data about mechanical ventilation and therapeutic response. Through these advances, a computer system was developed to enable the coupling of physiologic and ventilation data for real-time interpretation. Our aim was to assess the feasibility and utility of a newly developed patient categorization and scoring system to objectively measure compliance with standards of care.

Methods: We retrospectively categorized the ventilation and oxygenation statuses of subjects within our pediatric ICU utilizing 15 rules-based algorithms. Targets were predetermined based on generally accepted practices. All patient categories were calculated and presented as a percent score (0-100%) of acceptable ventilation, acceptable oxygenation, barotrauma-free, and volutrauma-free states.

Results: Two hundred twenty-two subjects were identified and analyzed encompassing 1,578 d of mechanical ventilation. Median age was 3 y, median ideal body weight was 14.7 kg, and 63% were male. The median acceptable ventilation score was 84.6%, and the median acceptable oxygenation score was 70.1% (100% being maximally acceptable). Potential for ventilator-induced lung injury was broken into 2 components: barotrauma and volutrauma. There was very little potential for barotrauma, with a median barotrauma-free state of 100%. Median potential for a volutrauma-free state was 56.1%.

Conclusions: We demonstrate the first patient categorization system utilizing a coordinated data-banking system and analytics to determine patient status and a surveillance of mechanical ventilation quality. Further research is needed to determine whether interventions such as visual display of variance from goal and patient categorization summaries can improve outcomes. (ClinicalTrials.gov registration NCT02184208.).
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http://dx.doi.org/10.4187/respcare.04723DOI Listing
September 2016

The effects of lung recruitment maneuvers on exhaled breath condensate pH.

J Breath Res 2015 Sep 3;9(3):036009. Epub 2015 Sep 3.

Boston Children's Hospital, 300 Longwood Ave, Farley 019, Boston, MA 02115, USA.

Exhaled breath condensate (EBC) pH serves as a surrogate marker of airway lining fluid (ALF) pH and can be used to evaluate airway acidification (AA). AA is known to be present in acute respiratory distress syndrome (ARDS) and can be evaluated via continuous EBC pH measurement during mechanical ventilation. Lung recruitment maneuvers (LRMs) are utilized in the treatment of ARDS, however, their impact on EBC pH has never been explored. Here we described the acute effects of two commonly used LRMs on EBC pH. In a prospective, non-randomized, serial exposure study, 10 intubated pediatric subjects with acute respiratory distress syndrome sequentially underwent: a period of baseline ventilation, sustained inflation (SI) maneuver of 40 cm H2O for 40 s, open lung ventilation, staircase recruitment strategy (SRS) (which involves a systematic ramping of plateau pressures in 5 cm H2O increments, starting at 30 cm H2O), and PEEP titration. Maximum lung recruitment during the SRS is defined as a PaO2 + PaCO2 of  >400 mmHg. Following lung recruitment, PEEP titration was conducted from 20 cm H2O in 2 cm H2O decrements until a PaO2 + PaCO2 was  <380 and then increased by 2 cm H2O. EBC pH, arterial blood gases, lung mechanics, hemodynamics, and function residual capacity were obtained following each phase of the LRM and observational period. Seven out of 10 patients were able to reach maximum lung recruitment. Baseline EBC pH (6.38   ±   0.37) did not correlate with disease severity defined by PaO2/FiO2 ratio or oxygenation index (OI). Average EBC pH differed between phases and decreased after LRM (p = 0.001). EBC pH is affected by LRMs. EBC acidification following LRMs may represent a washout effect of opening acidic lung units and ventilating them or acute AA resulting from LRM.
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http://dx.doi.org/10.1088/1752-7155/9/3/036009DOI Listing
September 2015

High-Frequency Oscillatory Ventilation in Pediatric Acute Lung Injury: A Multicenter International Experience.

Crit Care Med 2015 Dec;43(12):2660-7

1Department of Anesthesiology, Perioperative and Pain Medicine, Division of Critical Care Medicine, Boston Children's Hospital, Harvard Medical School, Boston, MA. 2Children's Medical Center of Dallas, Dallas, TX. 3Neonatal and Pediatric Intensive Care Unit, Department of Pediatrics, University Hospital of Geneva, Geneva, Switzerland. 4Czech Technical University in Prague, Kladno, Czech Republic. 5Department of Pediatric Intensive Care, Wilhelmina Children's Hospital, University Medical Center Utrecht, Utrecht, The Netherlands. 6Pediatric Intensive Care, Queen Paola Children's Hospital, Antwerp, Belgium. 7Division of Pediatric Intensive Care, Department of Pediatrics, VU University Medical Center, Amsterdam, The Netherlands. 8The Hospital for Sick Children, Toronto, ON, Canada.

Objective: We aim to describe current clinical practice, the past decade of experience and factors related to improved outcomes for pediatric patients receiving high-frequency oscillatory ventilation. We have also modeled predictive factors that could help stratify mortality risk and guide future high-frequency oscillatory ventilation practice.

Design: Multicenter retrospective, observational questionnaire study.

Setting: Seven PICUs.

Patients: Demographic, disease factor, and ventilatory and outcome data were collected, and 328 patients from 2009 to 2010 were included in this analysis.

Interventions: None.

Measurement And Main Results: Patients were classified into six cohorts based on underlying diagnosis. We used univariate analysis to identify factors associated with mortality risk and multivariate logistic regression to identify independent predictors of mortality risk. An oxygenation index greater than 35 and immunocompromise exhibited the greatest predictive power (p < 0.0001) for increased mortality risk, and respiratory syncytial virus was associated with lowest mortality risk (p = 0.003). Differences in mortality risk as a function of oxygenation index were highly dependent on primary underlying condition. A trend toward an increase in oscillator amplitude and frequency was observed when compared with historical data.

Conclusions: Given the number of centers and subjects included in the database, these findings provide a robust description of current practice regarding the use of high-frequency oscillatory ventilation for pediatric hypoxic respiratory failure. Patients with severe hypoxic respiratory failure and immunocompromise had the highest mortality risk, and those with respiratory syncytial virus had the lowest. A means of identifying the risk of 30-day mortality for subjects can be obtained by identifying the underlying disease and oxygenation index on conventional ventilation preceding the initiation of high-frequency oscillatory ventilation.
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http://dx.doi.org/10.1097/CCM.0000000000001278DOI Listing
December 2015

Mechanical ventilation guided by electrical impedance tomography in experimental acute lung injury.

Crit Care Med 2013 May;41(5):1296-304

Department of Anesthesiology, Perioperative and Pain Medicine, Division of Critical Care Medicine, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.

Objective: To utilize real-time electrical impedance tomography to guide lung protective ventilation in an animal model of acute respiratory distress syndrome.

Design: Prospective animal study.

Setting: Animal research center.

Subjects: Twelve Yorkshire swine (15 kg).

Interventions: Lung injury was induced with saline lavage and augmented using large tidal volumes. The control group (n = 6) was ventilated using ARDSnet guidelines, and the electrical impedance tomography-guided group (n = 6) was ventilated using guidance with real-time electrical impedance tomography lung imaging. Regional electrical impedance tomography-derived compliance was used to maximize the recruitment of dependent lung and minimize overdistension of nondependent lung areas. Tidal volume was 6 mL/kg in both groups. Computed tomography was performed in a subset of animals to define the anatomic correlates of electrical impedance tomography imaging (n = 5). Interleukin-8 was quantified in serum and bronchoalveolar lavage samples. Sections of dependent and nondependent regions of the lung were fixed in formalin for histopathologic analysis.

Measurements And Main Results: Positive end-expiratory pressure levels were higher in the electrical impedance tomography-guided group (14.3 cm H₂O vs. 8.6 cm H₂O; p < 0.0001), whereas plateau pressures did not differ. Global respiratory system compliance was improved in the electrical impedance tomography-guided group (6.9 mL/cm H₂O vs. 4.7 mL/cm H₂O; p = 0.013). Regional electrical impedance tomography-derived compliance of the most dependent lung region was increased in the electrical impedance tomography group (1.78 mL/cm H₂O vs. 0.99 mL/cm H₂O; p = 0.001). Pao₂/FIO₂ ratio was higher and oxygenation index was lower in the electrical impedance tomography-guided group (Pao₂/FIO₂: 388 mm Hg vs. 113 mm Hg, p < 0.0001; oxygentation index, 6.4 vs. 15.7; p = 0.02) (all averages over the 6-hr time course). The presence of hyaline membranes (HM) and airway fibrin (AF) was significantly reduced in the electrical impedance tomography-guided group (HMEIT 42% samples vs. HMCONTROL 67% samples, p < 0.01; AFEIT 75% samples vs. AFCONTROL 100% samples, p < 0.01). Interleukin-8 level (bronchoalveolar lavage) did not differ between the groups. The upper and lower 95% limits of agreement between electrical impedance tomography and computed tomography were ± 16%.

Conclusions: Electrical impedance tomography-guided ventilation resulted in improved respiratory mechanics, improved gas exchange, and reduced histologic evidence of ventilator-induced lung injury in an animal model. This is the first prospective use of electrical impedance tomography-derived variables to improve outcomes in the setting of acute lung injury.
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http://dx.doi.org/10.1097/CCM.0b013e3182771516DOI Listing
May 2013

Interaction of dependent and non-dependent regions of the acutely injured lung during a stepwise recruitment manoeuvre.

Physiol Meas 2013 Feb 25;34(2):163-77. Epub 2013 Jan 25.

Department of Anesthesiology, Perioperative and Pain Medicine, Boston Children's Hospital, Boston, MA, USA.

The benefit of treating acute lung injury with recruitment manoeuvres is controversial. An impediment to settling this debate is the difficulty in visualizing how distinct lung regions respond to the manoeuvre. Here, regional lung mechanics were studied by electrical impedance tomography (EIT) during a stepwise recruitment manoeuvre in a porcine model with acute lung injury. The following interaction between dependent and non-dependent regions consistently occurred: atelectasis in the most dependent region was reversed only after the non-dependent region became overdistended. EIT estimates of overdistension and atelectasis were validated by histological examination of lung tissue, confirming that the dependent region was primarily atelectatic and the non-dependent region was primarily overdistended. The pulmonary pressure-volume equation, originally designed for modelling measurements at the airway opening, was adapted for EIT-based regional estimates of overdistension and atelectasis. The adaptation accurately modelled the regional EIT data from dependent and non-dependent regions (R(2) > 0.93, P < 0.0001) and predicted their interaction during recruitment. In conclusion, EIT imaging of regional lung mechanics reveals that overdistension in the non-dependent region precedes atelectasis reversal in the dependent region during a stepwise recruitment manoeuvre.
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http://dx.doi.org/10.1088/0967-3334/34/2/163DOI Listing
February 2013

Comparison of 2 lung recruitment strategies in children with acute lung injury.

Respir Care 2013 Aug 4;58(8):1280-90. Epub 2012 Dec 4.

Department of Cardiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.

Background: Lung recruitment maneuvers are frequently used in the treatment of children with lung injury. Here we describe a pilot study to compare the acute effects of 2 commonly used lung recruitment maneuvers on lung volume, gas exchange, and hemodynamic profiles in children with acute lung injury.

Methods: In a prospective, non-randomized, crossover pilot study, 10 intubated pediatric subjects with lung injury sequentially underwent: a period of observation; a sustained inflation (SI) maneuver of 40 cm H2O for 40 seconds and open-lung ventilation; a staircase recruitment strategy (SRS) (which utilized 5 cm H2O increments in airway pressure, from a starting plateau pressure of 30 cm H2O and PEEP of 15 cm H2O); a downwards PEEP titration; and a 1 hour period of observation with PEEP set 2 cm H2O above closing PEEP.

Results: Arterial blood gases, lung mechanics, hemodynamics, and functional residual capacity were recorded following each step of the study and following each increment of the SRS. Both SI and SRS were effective in raising PaO2 and functional residual capacity. During the SRS maneuver we noted significant increases in dead-space ventilation, a decrease in carbon dioxide elimination, an increase in PaCO2, and a decrease in compliance of the respiratory system. Lung recruitment was not sustained following the decremental PEEP titration.

Conclusions: SRS is effective in opening the lung in children with early acute lung injury, and is hemodynamically well tolerated. However, attention must be paid to PaCO2 during the SRS. Even minutes following lung recruitment, lungs may derecruit when PEEP is lowered beyond the closing pressure.
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http://dx.doi.org/10.4187/respcare.01808DOI Listing
August 2013

Reversal of dependent lung collapse predicts response to lung recruitment in children with early acute lung injury.

Pediatr Crit Care Med 2012 Sep;13(5):509-15

From the Division of Critical Care Medicine, Children's Hospital Boston, Harvard Medical School, Boston, MA, USA.

Objective: To describe the resolution of regional atelectasis and the development of regional lung overdistension during a lung-recruitment protocol in children with acute lung injury.

Design: Prospective interventional trial.

Setting: Pediatric intensive care unit.

Patients: Ten children with early (<72 hrs) acute lung injury.

Interventions: Sustained inflation maneuver (positive airway pressure of 40 cm H2O for 40 secs), followed by a stepwise recruitment maneuver (escalating plateau pressures by 5 cm H2O every 15 mins) until physiologic lung recruitment, defined by PaO2 + PaCO2 ≥400 mm Hg, was achieved. Regional lung volumes and mechanics were measured using electrical impedance tomography.

Measurements And Main Results: Patients that responded to the stepwise lung-recruitment maneuver had atelectasis in 54% of the dependent lung regions, while nonresponders had atelectasis in 10% of the dependent lung regions (p = .032). In the pressure step preceding physiologic lung recruitment, a significant reversal of atelectasis occurred in 17% of the dependent lung regions (p = .016). Stepwise recruitment overdistended 8% of the dependent lung regions in responders, but 58% of the same regions in nonresponders (p < .001). Lung compliance in dependent lung regions increased in responders, while compliance in nonresponders did not improve. In contrast to the stepwise recruitment maneuver, the sustained inflation did not produce significant changes in atelectasis or oxygenation: atelectasis was only reversed in 12% of the lung (p = .122), and there was only a modest improvement in oxygenation (27 ± 14 mm Hg, p = .088).

Conclusions: Reversal of atelectasis in the most dependent lung region preceded improvements in gas exchange during a stepwise lung-recruitment strategy. Lung recruitment of dependent lung areas was accompanied by considerable overdistension of nondependent lung regions. Larger amounts of atelectasis in dependent lung areas were associated with a positive response to a stepwise lung-recruitment maneuver.
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http://dx.doi.org/10.1097/PCC.0b013e318245579cDOI Listing
September 2012

Whither lung EIT: where are we, where do we want to go and what do we need to get there?

Physiol Meas 2012 May 24;33(5):679-94. Epub 2012 Apr 24.

Systems and Computer Engineering, Carleton University, Ottawa, Canada.

Breathing moves volumes of electrically insulating air into and out of the lungs, producing conductivity changes which can be seen by electrical impedance tomography (EIT). It has thus been apparent, since the early days of EIT research, that imaging of ventilation could become a key clinical application of EIT. In this paper, we review the current state and future prospects for lung EIT, by a synthesis of the presentations of the authors at the 'special lung sessions' of the annual biomedical EIT conferences in 2009-2011. We argue that lung EIT research has arrived at an important transition. It is now clear that valid and reproducible physiological information is available from EIT lung images. We must now ask the question: How can these data be used to help improve patient outcomes? To answer this question, we develop a classification of possible clinical scenarios in which EIT could play an important role, and we identify clinical and experimental research programmes and engineering developments required to turn EIT into a clinically useful tool for lung monitoring.
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http://dx.doi.org/10.1088/0967-3334/33/5/679DOI Listing
May 2012

Isoflurane for life-threatening bronchospasm: a 15-year single-center experience.

Respir Care 2012 Nov 13;57(11):1857-64. Epub 2012 Mar 13.

Division of Pediatric Critical Care Medicine, Department of Pediatrics, Duke Children's Hospital, Duke University Medical Center, Durham, NC 27710, USA.

Background: Children with severe bronchospasm requiring mechanical ventilation may become refractory to conventional therapy. In these critically ill patients, isoflurane is an inhaled anesthetic agent available in some centers to treat bronchospasm. We hypothesized that isoflurane is safe and would lead to improved gas exchange in children with life-threatening bronchospasm refractory to conventional therapy.

Methods: A retrospective review was conducted and included mechanically ventilated children treated with isoflurane in a quaternary pediatric ICU for life-threatening bronchospasm, from 1993 to 2007. Demographic, blood gas, ventilator, and outcome data were collected.

Results: Thirty-one patients, with a mean age of 9.5 years (range 0.4-23 years) were treated with isoflurane, from 1993 to 2007. Mean time to initiation of isoflurane after intubation was 13 hours (0-120 h), and the mean maximum isoflurane dose was 1.1% (0.3-2.5%). Mean duration of isoflurane administration was 54.5 hours (range 1-181 h), with a total mean duration of mechanical ventilation of 252 hours (range 16-1,444 h). Isoflurane led to significant improvement in pH and P(CO(2)) within 4 hours of initiation (P ≤ .001). Complications during isoflurane administration included hypotension requiring vasoactive infusions in 24 (77%), arrhythmia in 3 (10%), neurologic side effects in 3 (10%), and pneumothorax in 1 (3%) patient.

Conclusions: Isoflurane led to improvement in pH and P(CO(2)) within 4 hours in this series of mechanically ventilated patients with life-threatening bronchospasm. The majority of patients in this series developed hypotension, but there was a low incidence of other side effects related to isoflurane administration. Isoflurane appears to be an effective therapy in patients with life-threatening bronchospasm refractory to conventional therapy. However, further investigation is warranted, given the uncertain overall impact of isoflurane in this context.
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http://dx.doi.org/10.4187/respcare.01605DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3825849PMC
November 2012

A unified approach for EIT imaging of regional overdistension and atelectasis in acute lung injury.

IEEE Trans Med Imaging 2012 Mar 10;31(3):834-42. Epub 2012 Jan 10.

Department of Anesthesiology, Perioperative and Pain Medicine, Children’s Hospital Boston, Harvard Medical School, Boston, MA 02115, USA.

Patients with acute lung injury or acute respiratory distress syndrome (ALI/ARDS) are vulnerable to ventilator-induced lung injury. Although this syndrome affects the lung heterogeneously, mechanical ventilation is not guided by regional indicators of potential lung injury. We used electrical impedance tomography (EIT) to estimate the extent of regional lung overdistension and atelectasis during mechanical ventilation. Techniques for tidal breath detection, lung identification, and regional compliance estimation were combined with the Graz consensus on EIT lung imaging (GREIT) algorithm. Nine ALI/ARDS patients were monitored during stepwise increases and decreases in airway pressure. Our method detected individual breaths with 96.0% sensitivity and 97.6% specificity. The duration and volume of tidal breaths erred on average by 0.2 s and 5%, respectively. Respiratory system compliance from EIT and ventilator measurements had a correlation coefficient of 0.80. Stepwise increases in pressure could reverse atelectasis in 17% of the lung. At the highest pressures, 73% of the lung became overdistended. During stepwise decreases in pressure, previously-atelectatic regions remained open at sub-baseline pressures. We recommend that the proposed approach be used in collaborative research of EIT-guided ventilation strategies for ALI/ARDS.
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http://dx.doi.org/10.1109/TMI.2012.2183641DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7176466PMC
March 2012

Quality of life of pediatric cardiac patients who previously required extracorporeal membrane oxygenation.

Pediatr Crit Care Med 2012 Jul;13(4):428-34

Department of Cardiology, Children's Hospital Boston, Harvard Medical School, Boston, MA, USA.

Objectives: We sought to assess quality of life of pediatric cardiac extracorporeal membrane oxygenation survivors. We hypothesized that these patients would have decreased quality of life when compared to that of a general U.S. population sample.

Design: Cross-sectional study.

Setting: Patient homes and Children's Hospital Boston.

Patients: Cardiac extracorporeal membrane oxygenation survivors currently 5-18 yrs old.

Interventions: None.

Measurements And Main Results: Quality of life was assessed by parent proxy report using the Child Health Questionnaire Parent Form 50 and was compared to that of a general U.S. population sample and other cardiac populations. Factors associated with lower quality of life were sought. Physical summary scores for 41 cardiac extracorporeal membrane oxygenation survivors were lower than the mean of the general population sample (42.4 ± 16.4 vs. 53.0 ± 8.8; p < .001) but similar to those of children with Fontan physiology or an automatic implantable cardioverter defibrillator. Psychosocial summary scores in extracorporeal membrane oxygenation patients were not different from those of the general population (48.2 ± 11.8 vs. 51.2 ± 9.1; p = .11) or of other cardiac samples. Postcardiotomy extracorporeal membrane oxygenation, more noncardiac operations, total intensive care and hospital days, noncardiac medical conditions, medications, and the need for physical, occupational, or speech therapy were associated with low physical summary scores. More noncardiac operations, noncardiac medical conditions, and the need for special education, physical, occupational, or speech therapy were associated with low psychosocial summary scores.

Conclusions: In pediatric cardiac extracorporeal membrane oxygenation survivors, the physical component of health-related quality of life is lower than that of the general population but similar to that of patients with complex cardiac disease, whereas psychosocial quality of life is similar to that of the general population and of other pediatric cardiac populations.
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http://dx.doi.org/10.1097/PCC.0b013e318238ba21DOI Listing
July 2012

A spontaneous breathing trial with pressure support overestimates readiness for extubation in children.

Pediatr Crit Care Med 2011 Nov;12(6):e330-5

Department of Anesthesia, Children's Hospital, Boston, MA, USA.

Objective: To evaluate the performance of an extubation readiness test based on a spontaneous breathing trial using pressure support.

Design: Retrospective chart review.

Setting: Pediatric intensive care unit.

Patients: All infants and children admitted to the pediatric intensive care unit requiring intubation from July 2007 to December 2008 were eligible for this study.

Interventions: Routine use of an extubation readiness test using pressure support set according to endotracheal tube size to determine completion of weaning and readiness for extubation.

Measurements And Main Results: A total of 755 extubation readiness tests were performed in 538 patients with a pass rate of 83%. Of 500 children who passed the extubation readiness test and were extubated without planned noninvasive ventilation use, the extubation failure rate was 11.2% (5.8% required reintubation). Extubation failure was defined as need for noninvasive ventilation or reintubation within 24 hrs of planned extubation. Logistic regression analysis revealed a significant association between duration of mechanical ventilation and extubation failure. Children ventilated for over 48 hrs had an 18.5% failure rate despite passing an extubation readiness test before extubation and the extubation readiness test was not a significant predictor of extubation success. Most extubation failures were the result of inadequate gas exchange attributable to lower respiratory tract dysfunction.

Conclusions: A spontaneous breathing trial using pressure support set at higher levels for smaller endotracheal tubes overestimates readiness for extubation in children and contributes to a higher failed extubation rate. The objective data obtained during an extubation readiness test may help to identify patients who will benefit from extubation to noninvasive ventilation.
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http://dx.doi.org/10.1097/PCC.0b013e3182231220DOI Listing
November 2011

Pediatric respiratory diseases: 2011 update for the Rogers' Textbook of Pediatric Intensive Care.

Pediatr Crit Care Med 2011 May;12(3):325-38

Section of Critical Care Medicine, The Children's Hospital, Denver, CO, USA.

Objectives: To review articles relevant to the field of pediatric respiratory disease that were published after the 2008 Rogers' Textbook of Pediatric Intensive Care.

Data Sources: The authors searched the PubMed database (http://www.ncbi.nlm.nih.gov/sites/entrez) from the National Library of Medicine for citations from the pediatric and adult literature relevant to pediatric status asthmaticus, bronchiolitis, pneumonia, acute lung injury, acute respiratory distress syndrome, and neonatal respiratory failure. The authors also searched the reference lists of key primary publications and recent review articles, and queried the National Institutes of Health's ClinicalTrials.gov Web site (www.clinicaltrials.gov) to obtain information about ongoing clinical trials for acute lung injury. The authors had knowledge of new publications in the field of respiratory monitoring, which were considered for inclusion in the review.

Study Selection And Data Extraction: The authors reviewed the promising articles and the decision to include any article in the review was based on its potential to inform pediatric intensive care practice or future research.

Data Synthesis: Articles in six categories were selected for inclusion: status asthmaticus, bronchiolitis, pneumonia, acute lung injury/acute respiratory distress syndrome, respiratory monitoring, and neonatal respiratory failure.

Conclusions: There have been important new developments relevant to the pathogenesis and management of pediatric respiratory diseases. In particular, new insights into the causal pathways of respiratory syncytial virus-induced airways disease can potentially lead to novel therapies. Computed tomography imaging of the injured lung during mechanical ventilation has opened new avenues for future research directed at testing new treatments in acute lung injury subpopulations defined according to lung mechanics. Promising new monitoring techniques may play a supporting role in the conduct of these studies. Finally, evidence from the neonatal literature recently has shown how the course and future consequences of respiratory failure in this population may be modified through more widespread use of noninvasive support.
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http://dx.doi.org/10.1097/PCC.0b013e3182152661DOI Listing
May 2011

Electrocardiographic guidance for the placement of gastric feeding tubes: a pediatric case series.

Respir Care 2011 Apr 21;56(4):467-71. Epub 2011 Jan 21.

Department of Respiratory Care, Children's Hospital Boston, Boston, Massachusetts, USA.

Background: The placement of nasal or oral gastric tubes is one of the most frequently performed procedures in critically ill children; tube malposition, particularly in the trachea, is an important complication. Neurally adjusted ventilatory assist (NAVA) ventilation (available only on the Servo-i ventilator, Maquet Critical Care, Solna, Sweden) requires a proprietary-design catheter (Maquet Critical Care, Solna, Sweden) with embedded electrodes that detect the electrical activity of the diaphragm (EA(di)). The EA(di) catheter has the potential benefit of confirming proper positioning of a gastric catheter, based on and the EA(di) waveforms.

Methods: In a case series study, our multidisciplinary team used EA(di) guidance for immediate, real-time confirmation of proper nasal or oral gastric tube placement in 20 mechanically ventilated pediatric patients who underwent 23 oral or nasal gastric tube placements. The catheters were placed with our standard practice, with the addition of a team member monitoring the EA(di) waveforms. As the tube passes down the esophagus and posterior to the heart, a characteristic EA(di) pattern is identified and the position of the atrial signal confirms correct placement of the gastric tube. If the EA(di) waveforms indicate incorrect placement, the tube is repositioned until the proper EA(di) waveform pattern is obtained. Then proper tube placement is reconfirmed via auscultation over the stomach while air is injected into the catheter, checking the pH of fluid suctioned from the catheter (gastric pH indicates correct positioning), and/or radiograph.

Results: The group's median age was 3 years (range 4 d to 16 y). All 20 patients had successful gastric catheter placement. The EA(di) catheter provided characteristic patterns for correctly placed tubes, tubes malpositioned above or below the gastroesophageal junction, and curled tubes. Proper catheter position was confirmed via radiograph and/or gastric pH in all 20 patients.

Conclusions: EA(di) guidance helps confirm proper gastric catheter position, is equivalent to our standard practice for confirming gastric catheter placement, and may reduce the need for radiographs and improve patient safety by avoiding catheter malpositions.
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http://dx.doi.org/10.4187/respcare.00886DOI Listing
April 2011

Electrical activity of the diaphragm during extubation readiness testing in critically ill children.

Pediatr Crit Care Med 2011 Nov;12(6):e220-4

Department of Anesthesiology, Perioperative and Pain Medicine, Children's Hospital, Boston, MA, USA.

Objectives: To investigate the electrical activity of the diaphragm during extubation readiness testing.

Design: Prospective observational trial.

Setting: A 29-bed medical-surgical pediatric intensive care unit.

Patients: Mechanically ventilated children between 1 month and 18 yrs of age.

Interventions: Twenty patients underwent a standardized extubation readiness test using a minimal pressure support ventilation strategy. A size-appropriate multiple-array esophageal electrode (electrical diaphragmatic activity catheter), which doubled as a feeding tube, was inserted. The electrical diaphragmatic activity, ventilatory parameters, and spirometry measurements were recorded with the Servo-i ventilator (Maquet, Solna, Sweden). Measurements were obtained before the extubation readiness test and 1 hr into the extubation readiness test.

Measurements And Main Results: During extubation readiness testing, the ratio of tidal volume to delta electrical diaphragmatic activity was significantly lower in those patients who passed the extubation readiness test compared to those who failed the extubation readiness test (extubation readiness test, pass: 24.8 ± 20.9 mL/μV vs. extubation readiness test, fail: 67.2 ± 27 mL/μV, respectively; p = .02). Delta electrical diaphragmatic activity correlated significantly with neuromuscular drive assessed by airway opening pressure at 0.1 secs (before extubation readiness test: r = .591, p < .001; during extubation readiness test: r = .682, p < .001). Eight out of 20 patients had ventilator dys-synchrony identified with electrical diaphragmatic activity during extubation readiness testing.

Conclusions: Patients who generate higher diaphragmatic activity in relation to tidal volume may have better preserved diaphragmatic function and a better chance of passing the extubation readiness test as opposed to patients who generate lower diaphragmatic activity in relation to tidal volume, indicating diaphragmatic weakness. Electrical activity of the diaphragm also may be a useful adjunct to assess neuromuscular drive in ventilated children.
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http://dx.doi.org/10.1097/PCC.0b013e3181fe28fcDOI Listing
November 2011

Factors associated with survival in pediatric extracorporeal membrane oxygenation--a single-center experience.

J Pediatr Surg 2010 Oct;45(10):1995-2003

Division of Critical Care Medicine (Anesthesia), Children's Hospital Boston, Boston, MA 02115, USA.

Aim: We aimed to examine outcomes of extracorporeal membrane oxygenation (ECMO) therapy in the pediatric population and identify pre-ECMO and on-ECMO characteristics that are associated with survival.

Methods: We retrospectively reviewed the ECMO records at our institution between 1999 and 2008 and selected pediatric patients who were cannulated for respiratory failure or hemodynamic instability resistant to conventional interventions. We recorded details of pre-ECMO clinical characteristics, including blood gas variables and mechanical ventilatory support, and details of ECMO therapy including survival off ECMO and to hospital discharge. Predictors of survival were analyzed using logistic regression modeling and a prediction algorithm was developed.

Results: Of the 445 ECMO runs, data from 58 consecutive patients were analyzed: 57% were successfully decannulated, and 48% survived to discharge from the hospital. The cohort included 32 (55%) female patients, 22 postoperative patients (38%), and 15 (26%) with an immunosuppressive condition, with a median age of 5 years and weight 19.5 kg, The mean duration of pre-ECMO respiratory support was 3 days, in the form of high-frequency oscillatory ventilation (n = 28, 48%) and conventional mechanical ventilation (n = 13, 22%). The median duration (interquartile range) of ECMO support was 142 hours (60, 321) or 5.9 days. Pre-ECMO pH above 7.2 (P < .001) and oxygenation index below 35 (P = .021) were associated with the highest survival rates. Pre-ECMO PaCO(2) and duration of mechanical ventilation were not associated with survival.

Conclusions: Based on our results, ECMO therapy should be considered early in children with oxygenation index greater than 35 with worsening metabolic status. The restriction of ECMO based on ventilator days alone needs to be revisited in this era of lung protective ventilation.
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http://dx.doi.org/10.1016/j.jpedsurg.2010.05.028DOI Listing
October 2010

Regional overdistension identified with electrical impedance tomography in the perflubron-treated lung.

Physiol Meas 2010 Aug 21;31(8):S85-95. Epub 2010 Jul 21.

Division of Critical Care Medicine, Department of Anesthesiology, Perioperative and Pain Medicine, Children's Hospital Boston, Harvard Medical School, Boston, MA, USA.

Regional lung overdistension occurring during high frequency oscillatory ventilation (HFOV) and partial liquid ventilation (PLV) was investigated in a prospective animal trial using 18 mechanically ventilated Yorkshire swine under general anesthesia. Lung injury was induced with saline lavage and augmented using large tidal volumes. Electrical impedance tomography (EIT) and regional lung histopathology were used to identify regional lung overdistension during HFOV. Lung injury was quantified using a histopathologic lung injury score. The animals were randomized to three groups (n = 6 animals in each group): a control group and two dose groups of perfluorooctyl bromide (PFOB) (PFOB-Lo 1.5 ml kg(-1) and PFOB-Hi 3 ml kg(-1)). The animals were transitioned from conventional ventilation to HFOV, and a slow inflation-deflation maneuver was performed by changing mean airway pressure (Paw) by 5 cmH(2)O every 15 min to a maximum Paw of 40 cmH(2)O. In dependent lung areas, the PFOB-Hi (3 ml kg(-1)) group, in comparison with the control group, was associated with significantly greater alveolar overdistension seen on lung histopathology (P < 0.001 compared to control), a decreased mean impedance (P < 0.05 compared to the control group) and a decreased ventilation-induced impedance change during HFOV (P < 0.05 compared to the control group). We conclude that treatment with PFOB-Hi during HFOV compared to a control group in an animal model of lung injury led to regional overdistension of dependent lung areas, as evidenced by increased alveolar overdistension on lung histopathology, decreased mean lung impedance and decreased HFOV-induced regional lung volume changes as measured by EIT.
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http://dx.doi.org/10.1088/0967-3334/31/8/S07DOI Listing
August 2010

Towards lung EIT image segmentation: automatic classification of lung tissue state from analysis of EIT monitored recruitment manoeuvres.

Physiol Meas 2010 Aug 21;31(8):S31-43. Epub 2010 Jul 21.

Department of Bioengineering, Univerisity of Strathclyde, Rottenrow, Glasgow G4 0NW, UK.

There is emerging evidence that the ventilation strategy used in acute lung injury (ALI) makes a significant difference in outcome and that an inappropriate ventilation strategy may produce ventilator-associated lung injury. Most harmful during mechanical ventilation are lung overdistension and lung collapse or atelectasis. Electrical impedance tomography (EIT) as a non-invasive imaging technology may be helpful to identify lung areas at risk. Currently, no automated method is routinely available to identify lung areas that are overdistended, collapsed or ventilated appropriately. We propose a fuzzy logic-based algorithm to analyse EIT images obtained during stepwise changes of mean airway pressures during mechanical ventilation. The algorithm is tested on data from two published studies of stepwise inflation-deflation manoeuvres in an animal model of ALI using conventional and high-frequency oscillatory ventilation. The timing of lung opening and collapsing on segmented images obtained using the algorithm during an inflation-deflation manoeuvre is in agreement with well-known effects of surfactant administration and changes in shunt fraction. While the performance of the algorithm has not been verified against a gold standard, we feel that it presents an important first step in tackling this challenging and important problem.
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http://dx.doi.org/10.1088/0967-3334/31/8/S03DOI Listing
August 2010

Regional lung volume changes during high-frequency oscillatory ventilation.

Pediatr Crit Care Med 2010 Sep;11(5):610-5

Division of Critical Care Medicine, Children's Hospital Boston, Harvard Medical School, Boston, MA, USA.

Objective: To investigate regional lung volume changes occurring during an inflation-deflation maneuver using high-frequency oscillatory ventilation.

Design: Prospective animal trial.

Setting: Animal research laboratory.

Subjects: Six Yorkshire swine.

Interventions: Electrical impedance tomography was used to quantify regional ventilation during high-frequency oscillatory ventilation. The electrical impedance tomography-derived center of ventilation was used to describe the distribution of regional ventilation, whereas spectral analysis was used to describe regional ventilation-induced impedance changes. Lung injury was induced using surfactant lavage. Animals were transitioned to high-frequency oscillatory ventilation and a slow inflation-deflation maneuver was performed by changing mean airway pressure by 5 cm H2O every 15 mins to a maximum mean airway pressure of 40 cm H2O.

Measurements And Main Results: The induction of lung injury was associated with a significant shift of the center of ventilation toward nondependent areas and an increase in shunt fraction (p < .001). During the following inflation-deflation maneuver using high-frequency oscillatory ventilation, inflation was associated with a shift of the center of ventilation from nondependent to dependent areas. Center of ventilation was significantly correlated with the shunt fraction (p < .001). Analyzing different lung layers along the gravitational axis separately, nondependent lung areas showed significantly decreased regional ventilation-induced impedance changes at higher pressures, suggesting overdistension, whereas dependent lung areas showed increased impedance changes, suggesting recruitment. The reverse was observed during deflation (all p < .05).

Conclusions: The center of ventilation during high-frequency oscillatory ventilation correlated with oxygenating efficiency as measured by the shunt fraction. Lung recruitment during high-frequency oscillatory ventilation produced a significant shift of regional ventilation toward dependent areas of the lung and led to overdistension of nondependent areas.
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http://dx.doi.org/10.1097/PCC.0b013e3181c51690DOI Listing
September 2010

Respiratory distress associated with inadequate mechanical ventilator flow response in a neonate with congenital diaphragmatic hernia.

Respir Care 2010 Mar;55(3):342-5

Respiratory Care Department, Children's Hospital Boston, Boston, Massachusetts 02115, USA.

The incidence of congenital diaphragmatic hernia has been reported as 0.17-0.66 per 1,000 births. Despite advances in neonatal intensive care, congenital diaphragmatic hernia is associated with high mortality and morbidity. We report a neonate who was born with a left congenital diaphragmatic hernia and underwent surgical repair. The lack of ventilator flow response and flow cycling was identified via interpretation of the ventilator graphic and clinical assessment. Presumably, the ventilator failed to respond to the patient's peak inspiratory flow demand, despite the clinician's setting the highest peak flow available. A time-cycled pressure-limited mode with adjustable peak flow rate was the only option that met the infant's flow requirement, and alleviated the respiratory distress. This clinical finding follows bench research that raises the concern that so called "cradle-to-grave" ventilators may not optimally support all neonates.
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March 2010