Increasing tidal volumes and pulmonary overdistention adversely affect pulmonary vascular mechanics and cardiac output in a pediatric swine model

A multimodal stacked ensemble model for cardiac output prediction utilizing cardiorespiratory interactions during general anesthesia

This study examined the possibility of estimating cardiac output (CO) using a multimodal stacking model that utilizes cardiopulmonary interactions during general anesthesia and outlined a retrospective application of machine learning regression model to a pre-collected dataset. The data of 469 adult patients (obtained from VitalDB) with normal pulmonary function tests who underwent general anesthesia were analyzed. The hemodynamic data in this study included non-invasive blood pressure, plethysmographic heart rate, and SpO2. CO was recorded using Vigileo and EV1000 (pulse contour technique devices). Respiratory data included mechanical ventilation parameters and end-tidal CO2 levels. A generalized linear regression model was used as the metalearner for the multimodal stacking ensemble method. Random forest, generalized linear regression, gradient boosting machine, and XGBoost were used as base learners. A Bland-Altman plot revealed that the multimodal stacked ensemble model for CO prediction from 327 patients had a bias of - 0.001 L/min and - 0.271% when calculating the percentage of difference using the EV1000 device. Agreement of model CO prediction and measured Vigileo CO in 142 patients reported a bias of - 0.01 and - 0.333%. Overall, this model predicts CO compared to data obtained by the pulse contour technique CO monitors with good agreement.

Analysis of the effect of CPAP on hemodynamics using clinical data and a theoretical model: CPAP therapy decreases cardiac output mechanically but increases it via afterload reduction

BACKGROUND

Noninvasive positive pressure ventilation (NIPPV) has been established as an effective treatment for heart failure. Positive airway pressure such as continuous positive airway pressure (CPAP) increases cardiac output (CO) in some patients but decreases it in others. However, the mechanism behind such unpredictable responses remains undetermined.

METHODS AND RESULTS

We measured hemodynamic parameters of 38 cases using Swan-Ganz catheter before and after CPAP in chronic heart failure status. In those whose CO increased by CPAP, pulmonary vascular resistance (PVR) was significantly decreased and SpO2 significantly increased, but the other parameters were not changed. On the other hand, PVR was not changed, but systemic vascular resistance (SVR) was increased in those whose CO decreased by CPAP. To explain this phenomenon, we simulated the cardiovascular system using a cardiac model of time-varying elastance. In this model, it was indicated that CPAP decreases CO irrespective of cardiac function or filling status under constant PVR condition. However, when reduction of PVR by CPAP was taken into account, an increase in CO was expected especially in the hypervolemic and low right ventricle (RV) systolic function cases.

CONCLUSIONS

CPAP would increase CO only where PVR can be reduced by CPAP therapy, especially in the case with hypervolemia and/or low RV systolic function. Understanding the underlying mechanism should help identify the patients for whom NIPPV would be effective.

Association of small adult ventilation bags with return of spontaneous circulation in out of hospital cardiac arrest

INTRODUCTION

Little is known about the impact of tidal volumes delivered by emergency medical services (EMS) to adult patients with out-of-hospital cardiac arrest (OHCA). A large urban EMS system changed from standard adult ventilation bags to small adult bags. We hypothesized that the incidence of return of spontaneous circulation (ROSC) at the end of EMS care would increase after this change.

METHODS

We performed a retrospective analysis evaluating adults treated with advanced airway placement for nontraumatic OHCA between January 1, 2015 and December 31, 2021. We compared rates of ROSC, ventilation rate, and mean end tidal carbon dioxide (ETCO2) by minute before and after the smaller ventilation bag implementation using linear and logistic regression.

RESULTS

Of the 1,994 patients included, 1,331 (67%) were treated with a small adult bag. ROSC at the end of EMS care was lower in the small bag cohort than the large bag cohort, 33% vs 40% (p = 0.003). After adjustment, small bag use was associated with lower odds of ROSC at the end of EMS care [OR 0.74, 95% CI 0.61 - 0.91]. Ventilation rates did not differ between cohorts. ETCO2 values were lower in the large bag cohort (33.2 ± 17.2 mmHg vs. 36.9 ± 19.2 mmHg, p < 0.01).

CONCLUSION

Use of a small adult bag during OHCA was associated with lower odds of ROSC at the end of EMS care. The effects on acid base status, hemodynamics, and delivered minute ventilation remain unclear and warrant additional study.

Analysis of cerebral Interleukin-6 and tumor necrosis factor alpha patterns following different ventilation strategies during cardiac arrest in pigs

Hypoxia-induced neuroinflammation after cardiac arrest has been shown to be mitigated by different ventilation methods. In this prospective randomized animal trial, 35 landrace pigs were randomly divided into four groups: intermittent positive pressure ventilation (IPPV), synchronized ventilation 20 mbar (SV 20 mbar), chest compression synchronized ventilation 40 mbar (CCSV 40 mbar) and a control group (Sham). After inducing ventricular fibrillation, basic life support (BLS) and advanced life support (ALS) were performed, followed by post-resuscitation monitoring. After 6 hours, the animals were euthanized, and direct postmortem brain tissue samples were taken from the hippocampus (HC) and cortex (Cor) for molecular biological investigation of cytokine mRNA levels of Interleukin-6 (IL-6) and tumor necrosis factor alpha (TNFα). The data analysis showed that CCSV 40 mbar displayed low TNFα mRNA-levels, especially in the HC, while the highest TNFα mRNA-levels were detected in SV 20 mbar. The results indicate that chest compression synchronized ventilation may have a potential positive impact on the cytokine expression levels post-resuscitation. Further studies are needed to derive potential therapeutic algorithms from these findings.

Methods for calculating ventilation rates during resuscitation from out-of-hospital cardiac arrest

OBJECTIVE

Ventilation control is important during resuscitation from out-of-hospital cardiac arrest (OHCA). We compared different methods for calculating ventilation rates (VR) during OHCA.

METHODS

We analyzed data from the Pragmatic Airway Resuscitation Trial, identifying ventilations through capnogram recordings. We determined VR by: 1) counting the number of breaths within a time epoch ("counted" VR), and 2) calculating the mean of the inverse of measured time between breaths within a time epoch ("measured" VR). We repeated the VR estimates using different time epochs (10, 20, 30, 60 sec). We defined hypo- and hyperventilation as VR <6 and >12 breaths/min, respectively. We assessed differences in estimated hypo- and hyperventilation with each VR measurement technique.

RESULTS

Of 3,004 patients, data were available for 1,010. With the counted method, total hypoventilation increased with longer time epochs ([10-s epoch: 75 sec hypoventilation] to [60-s epoch: 97 sec hypoventilation]). However, with the measured method, total hypoventilation decreased with longer time epochs ([10-s epoch: 223 sec hypoventilation] to [60-s epoch: 150 sec hypoventilation]). With the counted method, the total duration of hyperventilation decreased with longer time epochs ([10-s epochs: 35 sec hyperventilation] to [60-s epoch: 0 sec hyperventilation]). With the measured method, total hyperventilation decreased with longer time epochs ([10-s epoch: 78 sec hyperventilation] to [60-s epoch: 0 sec hyperventilation]). Differences between the measured and counted estimates were smallest with a 60-s time epoch.

CONCLUSIONS

Quantifications of hypo- and hyperventilation vary with the applied measurement methods. Measurement methods are important when characterizing ventilation rates in OHCA.

Improving Ventilation Rates During Pediatric Cardiopulmonary Resuscitation

BACKGROUND

Excessive ventilation at rates of 30 breaths per minute (bpm) or more during cardiopulmonary resuscitation (CPR) decreases venous return and coronary perfusion pressure, leading to lower survival rates in animal models. A review of our institution's pediatric CPR data revealed that patients frequently received excessive ventilation.

METHODS

We designed a multifaceted quality improvement program to decrease the incidence of clinically significant hyperventilation (≥30 bpm) during pediatric CPR. The program consisted of provider education, CPR ventilation tools (ventilation reminder cards, ventilation metronome), and individual CPR team member feedback. CPR events were reviewed pre- and postintervention. The first 10 minutes of each CPR event were divided into 20 second epochs, and the ventilation rate in each epoch was measured via end-tidal carbon dioxide waveform. Individual epochs were classified as within the target ventilation range (<30 bpm) or clinically significant hyperventilation (≥30 bpm). The proportion of epochs with clinically significant hyperventilation, as well as median ventilation rates, were analyzed in the pre- and postintervention periods.

RESULTS

In the preintervention period (37 events, 699 epochs), 51% of CPR epochs had ventilation rates ≥30 bpm. In the postintervention period (24 events, 426 epochs), the proportion of CPR epochs with clinically significant hyperventilation decreased to 29% (P < .001). Median respiratory rates decreased from 30 bpm (interquartile range 21-36) preintervention to 21 bpm (interquartile range 12-30) postintervention (P < .001).

CONCLUSIONS

A quality improvement initiative grounded in improved provider education, CPR team member feedback, and tools focused on CPR ventilation rates was effective at reducing rates of clinically significant hyperventilation during pediatric CPR.

High PEEP Levels during CPR Improve Ventilation without Deleterious Haemodynamic Effects in Pigs

Background: Invasive ventilation during cardiopulmonary resuscitation (CPR) is very complex due to unique thoracic pressure conditions. Current guidelines do not provide specific recommendations for ventilation during ongoing chest compressions regarding positive end-expiratory pressure (PEEP). This trial examines the cardiopulmonary effects of PEEP application during CPR. Methods: Forty-two German landrace pigs were anaesthetised, instrumented, and randomised into six intervention groups. Three PEEP levels (0, 8, and 16 mbar) were compared in high standard and ultralow tidal volume ventilation. After the induction of ventricular fibrillation, mechanical chest compressions and ventilation were initiated and maintained for thirty minutes. Blood gases, ventilation/perfusion ratio, and electrical impedance tomography loops were taken repeatedly. Ventilation pressures and haemodynamic parameters were measured continuously. Postmortem lung tissue damage was assessed using the diffuse alveolar damage (DAD) score. Statistical analyses were performed using SPSS, and p values <0.05 were considered significant. Results: The driving pressure (Pdrive) showed significantly lower values when using PEEP 16 mbar than when using PEEP 8 mbar (p = 0.045) or PEEP 0 mbar (p < 0.001) when adjusted for the ventilation mode. Substantially increased overall lung damage was detected in the PEEP 0 mbar group (vs. PEEP 8 mbar, p = 0.038; vs. PEEP 16 mbar, p = 0.009). No significant differences in mean arterial pressure could be detected. Conclusion: The use of PEEP during CPR seems beneficial because it optimises ventilation pressures and reduces lung damage without significantly compromising blood pressure. Further studies are needed to examine long-term effects in resuscitated animals.

Airway Strategy and Ventilation Rates in the Pragmatic Airway Resuscitation Trial

BACKGROUND

We sought to describe ventilation rates during out-of-hospital cardiac arrest (OHCA) resuscitation and their associations with airway management strategy and outcomes.

METHODS

We analyzed continuous end-tidal carbon dioxide capnography data from adult OHCA enrolled in the Pragmatic Airway Resuscitation Trial (PART). Using automated signal processing techniques, we determined continuous ventilation rate for consecutive 10-second epochs after airway insertion. We defined hypoventilation as a ventilation rate <6 breaths/min. We defined hyperventilation as a ventilation rate >12 breaths/min. We compared differences in total and percentage post-airway hyper- and hypoventilation between airway interventions (laryngeal tube (LT) vs. endotracheal intubation (ETI). We also determined associations between hypo-/hyperventilation and OHCA outcomes (ROSC, 72-hour survival, hospital survival, hospital survival with favorable neurologic status).

RESULTS

Adequate post-airway capnography were available for 1,010 (LT n=714, ETI n=296) of 3,004 patients. Median ventilation rates were: LT 8.0 (IQR 6.5-9.6) breaths/min, ETI 7.9 (6.5-9.7) breaths/min. Total duration and percentage of post-airway time with hypoventilation were similar between LT and ETI: median 1.8 vs. 1.7 minutes, p=0.94; median 10.5% vs. 11.5%, p=0.60. Total duration and percentage of post-airway time with hyperventilation were similar between LT and ETI: median 0.4 vs. 0.4 minutes, p=0.91; median 2.1% vs. 1.9%, p=0.99. Hypo- and hyperventilation exhibited limited associations with OHCA outcomes.

CONCLUSION

In the PART Trial, EMS personnel delivered post-airway ventilations at rates satisfying international guidelines, with only limited hypo- or hyperventilation. Hypo- and hyperventilation durations did not differ between airway management strategy and exhibited uncertain associations with OCHA outcomes.

Cardiovascular and Gas Exchange Effects of Individualized Positive End-Expiratory Pressures in Cats Anesthetized With Isoflurane

Objectives

To compare the effects of four levels of end-expiratory pressure [zero (ZEEP) and three levels of positive end-expiratory pressure (PEEP)] on the cardiovascular system and gas exchange of cats anesthetized with isoflurane and mechanically ventilated for 3 h with a tidal volume of 10 ml/kg.

Study Design

Prospective, randomized, controlled trial.

Animals

Six healthy male neutered purpose-bred cats.

Methods

Anesthesia was induced with isoflurane and maintained at 1.3 minimum alveolar concentration. PEEP of maximal respiratory compliance (PEEP_maxCrs) was identified in a decremental PEEP titration, and cats were randomly ventilated for 3 h with one of the following end-expiratory pressures: ZEEP, PEEP_maxCrs minus 2 cmH₂O (PEEP_maxCrs−2), PEEP_maxCrs, and PEEP_maxCrs plus 2 cmH₂O (PEEP_maxCrs+2). Cardiovascular and gas exchange variables were recorded at 5, 30, 60, 120, and 180 min (T5 to T180, respectively) of ventilation and compared between and within ventilation treatments with mixed-model ANOVA followed by Dunnet's and Tukey's tests (normal distribution) or Friedman test followed by the Dunn's test (non-normal distribution). Significance to reject the null hypothesis was considered p < 0.05.

Results

Mean arterial pressure (MAP—mmHg) was lower in PEEP_maxCrs+2 [63 (49–69); median (range)] when compared to ZEEP [71 (67–113)] at T5 and stroke index (ml/beat/kg) was lower in PEEP_maxCrs+2 (0.70 ± 0.20; mean ± SD) than in ZEEP (0.90 ± 0.20) at T60. Cardiac index, oxygen delivery index (DO₂I), systemic vascular resistance index, and shunt fraction were not significantly different between treatments. The ratio between arterial partial pressure and inspired concentration of oxygen (PaO₂/FIO₂) was lower in ZEEP than in the PEEP treatments at various time points. At T180, DO₂I was higher when compared to T5 in PEEP_maxCrs. Dopamine was required to maintain MAP higher than 60 mmHg in one cat during PEEP_maxCrs and in three cats during PEEP_maxCrs+2.

Conclusion

In cats anesthetized with isoflurane and mechanically ventilated for 3 h, all levels of PEEP mildly improved gas exchange with no significant difference in DO₂I when compared to ZEEP. The PEEP levels higher than PEEP_maxCrs−2 caused more cardiovascular depression, and dopamine was an effective treatment. A temporal increase in DO₂I was observed in the cats ventilated with PEEP_maxCrs. The effects of these levels of PEEP on respiratory mechanics, ventilation-induced lung injury, as well as in obese and critically ill cats deserve future investigation for a better understanding of the clinical use of PEEP in this species.

Prehospital Cardiac Arrest Airway Management: An NAEMSP Position Statement and Resource Document

Airway management is a critical component of out-of-hospital cardiac arrest (OHCA) resuscitation. Multiple cardiac arrest airway management techniques are available to EMS clinicians including bag-valve-mask (BVM) ventilation, supraglottic airways (SGAs), and endotracheal intubation (ETI). Important goals include achieving optimal oxygenation and ventilation while minimizing negative effects on physiology and interference with other resuscitation interventions. NAEMSP recommends:Based on the skill of the clinician and available resources, BVM, SGA, or ETI may be considered as airway management strategies in OHCA.Airway management should not interfere with other key resuscitation interventions such as high-quality chest compressions, rapid defibrillation, and treatment of reversible causes of the cardiac arrest.EMS clinicians should take measures to avoid hyperventilation during cardiac arrest resuscitation.Where available for clinician use, capnography should be used to guide ventilation and chest compressions, confirm and monitor advanced airway placement, identify return of spontaneous circulation (ROSC), and assist in the decision to terminate resuscitation.

Lung ultrasound predicts histological lung injury in a neonatal model of acute respiratory distress syndrome

RATIONALE

Point-of-care ultrasound (POCUS) is used to evaluate pulmonary edema in adults with acute respiratory distress syndrome (ARDS). Its use has not been validated in neonatal models.

OBJECTIVES

We compared an in vivo lung ultrasound score against clinical and histological markers of acute lung injury, in a neonatal animal model, hypothesizing that POCUS would sensitively diagnose early acute lung injury in neonates and discern its severity.

METHODS

Fifteen anesthetized, ventilated 3-day-old neonatal piglets were divided into controls, moderate lung injury, or severe lung injury by graded treatment with oleic acid. Degree of lung injury was quantified at baseline, immediately after oleic acid administration, and 1 hour after the evolution of acute lung injury, by blood gases, ventilation parameters and calculated oxygenation deficit; hemodynamic indices by echocardiography, and lung ultrasound obtained in an 8-region grid of anterior and posterior zones, semi-quantitatively analyzed by a blinded observer. Lungs were inflation-fixed postmortem at last mean airway pressure, for histological assessment.

RESULTS

Acute lung injury manifested in oleic acid-treated groups as dose-dependent capillary leak causing intravascular depletion and cardiac failure, hypoxemia with increasing intrapulmonary shunt fraction, decreased lung compliance, and resistance. Ultrasound scores of anterior regions distinguished moderate from severe injury; scores in posterior regions reached maximum values immediately after lung injury. POCUS score correlated with calculated intrapulmonary shunt fraction (R²  = .65) and with histological injury score (R²  = .61), P < .01.

CONCLUSION

We conclude that POCUS may be valuable in neonates for early quantification of acute lung injury or ARDS; and that nondependent ultrasound regions clearly distinguish severity of pulmonary edema.

Manual ventilation quality is improved with a real-time visual feedback system during simulated resuscitation

INTRODUCTION

Manual ventilations during cardiac arrest are frequently performed outside of recommended guidelines. Real-time feedback has been shown to improve chest compression quality, but the use of feedback to guide ventilation volume and rate has not been studied. The purpose of this study was to determine whether the use of a real-time visual feedback system for ventilation volume and rate improves manual ventilation quality during simulated cardiac arrest.

METHODS

Teams of 2 emergency medical technicians (EMTs) performed two 8-min rounds of cardiopulmonary resuscitation (CPR) on a manikin during a simulated cardiac arrest scenario with one EMT performing ventilations while the other performed compressions. The EMTs switched roles every 2 min. During the first round of CPR, ventilation and chest compression feedback was disabled on a monitor/defibrillator. Following a 20-min rest period and a brief session to familiarize the EMTs with the feedback technology, the trial was repeated with feedback enabled. The primary outcome variables for the study were ventilations and chest compressions within target. Ventilation rate (target, 8-10 breaths/minute) and tidal volume (target, 425-575 ml) were measured using a novel differential pressure-based flow sensor. Data were analyzed using paired t tests.

RESULTS

Ten teams of 2 EMTs completed the study. Mean percentages of ventilations performed in target for rate (41% vs. 71%, p < 0.01), for volume (31% vs. 79%, p < 0.01), and for rate and volume together (10% vs. 63%, p < 0.01) were significantly greater with feedback.

CONCLUSION

The use of a novel visual feedback system for ventilation quality increased the percentage of ventilations in target for rate and volume during simulated CPR. Real-time feedback to perform ventilations within recommended guidelines during cardiac arrest should be further investigated in human resuscitation.

Prevalence and Outcomes of Pediatric In-Hospital Cardiac Arrest Associated With Pulmonary Hypertension

OBJECTIVES

In adult in-hospital cardiac arrest, pulmonary hypertension is associated with worse outcomes, but pulmonary hypertension-associated in-hospital cardiac arrest has not been well studied in children. The objective of this study was to determine the prevalence of pulmonary hypertension among children with in-hospital cardiac arrest and its impact on outcomes.

DESIGN

Retrospective single-center cohort study.

SETTING

PICU of a quaternary care, academic children's hospital.

PATIENTS

Children (<18 yr old) receiving greater than or equal to 1 minute of cardiopulmonary resuscitation (cardiopulmonary resuscitation) for an index in-hospital cardiac arrest with an echocardiogram in the 48 hours preceding in-hospital cardiac arrest, excluding those with cyanotic congenital heart disease.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of 284 in-hospital cardiac arrest subjects, 57 (20%) had evaluable echocardiograms, which were analyzed by a cardiologist blinded to patient characteristics. Pulmonary hypertension was present in 20 of 57 (35%); nine of 20 (45%) had no prior pulmonary hypertension history. Children with pulmonary hypertension had worse right ventricular systolic function, measured by fractional area change (p = 0.005) and right ventricular global longitudinal strain (p = 0.046); more right ventricular dilation (p = 0.010); and better left ventricular systolic function (p = 0.001). Children with pulmonary hypertension were more likely to have abnormal baseline functional status and a history of chronic lung disease or acyanotic congenital heart disease and less likely to have sepsis or acute kidney injury. Children with pulmonary hypertension were more likely to have an initial rhythm of pulseless electrical activity or asystole and were more frequently treated with inhaled nitric oxide (80% vs 32%; p < 0.001) at the time of cardiopulmonary resuscitation. On multivariable analysis, pulmonary hypertension was not associated with event survival (14/20 [70%] vs 24/37 [65%]; adjusted odds ratio, 1.30 [CI95, 0.25-6.69]; p = 0.77) or survival to discharge (8/20 [40%] vs 10/37 [27%]; adjusted odds ratio, 1.17 [CI95, 0.22-6.44]; p = 0.85).

CONCLUSIONS

Pulmonary hypertension physiology preceding pediatric in-hospital cardiac arrest may be more common than previously described. Among this cohort with a high frequency of inhaled nitric oxide treatment during cardiopulmonary resuscitation, pulmonary hypertension was not associated with survival outcomes.

A method for translational rat ex vivo lung perfusion experimentation

The application of ex vivo lung perfusion (EVLP) has significantly increased the successful clinical use of marginal donor lungs. While large animal EVLP models exist to test new strategies to improve organ repair, there is currently no rat EVLP model capable of maintaining long-term lung viability. Here, we describe a new rat EVLP model that addresses this need, while enabling the study of lung injury due to cold ischemic time (CIT). The technique involves perfusing and ventilating male Lewis rat donor lungs for 4 h before transplanting the left lung into a recipient rat and then evaluating lung function 2 h after reperfusion. To test injury within this model, lungs were divided into groups and exposed to different CITs (i.e., 20 min, 6 h, 12 h, 18 h and 24 h). Experiments involving the 24-h-CIT group were prematurely terminated due to the development of severe edema. For the other groups, no differences in the ratio of arterial oxygen partial pressure to fractional inspired oxygen ([Formula: see text]/[Formula: see text]) were observed during EVLP; however, lung compliance decreased over time in the 18-h group (P = 0.012) and the [Formula: see text]/[Formula: see text] of the blood from the left pulmonary vein 2 h after transplantation was lower compared with 20-min-CIT group (P = 0.0062). This new model maintained stable lung function during 4-h EVLP and after transplantation when exposed to up to 12 h of CIT.

Effectiveness of Manual Ventilation in Intubated Helicopter Emergency Services-Transported Trauma Patients

BACKGROUND

Helicopter Emergency Medical Services agencies frequently transport intubated patients to definitive care. No evidence exists to determine the type of ventilation in this population. Practice varies amongst programs from bag-valve-mask to mechanical ventilation.

STUDY OBJECTIVE

Evaluate the effectiveness of bag-valve ventilation in intubated trauma patients. We hypothesized manual ventilation provides adequate support to maintain physiologic ETCO₂.

METHODS

From June to December 2015, twenty patients were enrolled in this prospective, observational study. Included were endotracheally intubated trauma patients transported by this HEMS program. Excluded were interfacility transports, non-scene calls, and patients with supraglottic devices. ETCO₂ was recorded every 30 seconds during the flight. As a descriptive pilot study, power was not considered.

RESULTS

20 patients provided over 500 cumulative minutes of manual ventilation data. The percentage of cumulative time spent with adequate oxygen saturations was 83.6%. The percentage of cumulative time spent with adequate ETCO₂ was 48.7%, with 34.6% of time spent under and 16.7% above this range.

CONCLUSION

Manual ventilation maintained a physiologic ETCO₂ only 16.7% of the time. Significant variability existed, resulting in intermittent hypoxia and hyperventilation. Prior research linked such events to increased morbidity and mortality. Further studies are warranted to compare manual against mechanically ventilated patients.

A Cross-Over Trial Comparing Conventional to Compression-Adjusted Ventilations with Metronome-Guided Compressions

Introduction:

Hyperventilation during cardiopulmonary resuscitation (CPR) negatively affects cardiopulmonary physiology. Compression-adjusted ventilations (CAVs) may allow providers to deliver ventilation rates more consistently than conventional ventilations (CVs). This study sought to compare ventilation rates between these two methods during simulated cardiac arrest.

Null Hypothesis:

That CAV will not result in different rates than CV in simulated CPR with metronome-guided compressions.

Methods:

Volunteer Basic Life Support (BLS)-trained providers delivered bag-valve-mask (BVM) ventilations during simulated CPR with metronome-guided compressions at 100 beats/minute. For the first 4-minute interval, volunteers delivered CV. Volunteers were then instructed on how to perform CAV by delivering one breath, counting 12 compressions, and then delivering a subsequent breath. They then performed CAV for the second 4-minute interval. Ventilation rates were manually recorded. Minute-by-minute ventilation rates were compared between the techniques.

Results:

A total of 23 volunteers were enrolled with a median age of 36 years old and with a median of 14 years of experience. Median ventilation rates were consistently higher in the CV group versus the CAV group across all 1-minute segments: 13 vs 9, 12 vs 8, 12 vs 8, and 12 vs 8 for minutes one through four, respectively (P &lt;.01, all). Hyperventilation (&gt;10 breaths per minute) occurred 64% of the time intervals with CV versus one percent with CAV (P &lt;.01). The proportion of time which hyperventilation occurred was also consistently higher in the CV group versus the CAV group across all 1-minute segments: 78% vs 4%, 61% vs 0%, 57% vs 0%, and 61% vs 0% for minutes one through four, respectively (P &lt;.01, all).

Conclusions:

In this simulated model of cardiac arrest, CAV had more accurate ventilation rates and fewer episodes of hyperventilation compared with CV.

Nikolla DA, Kramer BJ, Carlson JN. A cross-over trial comparing conventional to compression-adjusted ventilations with metronome-guided compressions. Prehosp Disaster Med. 2019;34(2):220–223

Minimal Change in Cardiac Index With Increasing PEEP in Pediatric Acute Respiratory Distress Syndrome

Objective: To determine if increasing positive end expiratory pressure (PEEP) leads to a change in cardiac index in children with Pediatric Acute Respiratory Distress Syndrome ranging from mild to severe. Design: Prospective interventional study. Setting: Multidisciplinary Pediatric Intensive Care Unit in a University teaching hospital. Patients: Fifteen intubated children (5 females, 10 males) with a median age of 72 months (IQR 11, 132) and a median weight of 19.3 kg (IQR 7.5, 53.6) with a severity of Pediatric Acute Respiratory Distress Syndrome that ranged from mild to severe with a median lung injury score of 2.3 (IQR 2.0, 2.7). Measurements: Cardiac index (CI) and stroke volume (SV) were measured on baseline ventilator settings and subsequently with a PEEP 4 cmH₂O higher than baseline. Change in CI and SV from baseline values was evaluated using Wilcoxon signed rank test. Results: A total of 19 paired measurements obtained. The median baseline PEEP was 8 cmH₂O (IQR 8, 10) Range 6-14 cmH₂O. There was no significant change in cardiac index or stroke volume with change in PEEP. Baseline median CI 4.4 L/min/m² (IQR 3.4, 4.8) and PEEP 4 higher median CI of 4.3 L/min/m² (IQR 3.6, 4.8), p = 0.65. Baseline median SV 26 ml (IQR 13, 44) and at PEEP 4 higher median SV 34 ml (IQR 12, 44) p = 0.63. Conclusion: There is no significant change in cardiac index or stroke volume with increasing PEEP by 4 cmH₂O in a population of children with mild to severe PARDS. Clinical Trial Registration: The study is registered on Clinical trails.gov under the Identifier: NCT02354365.

The pulsatile component of left atrial pressure has little effect on pulmonary artery impedance estimation in normal rats

Pulmonary artery impedance (PAZ) that measures the pulsatile properties of the vasculature provides diagnostic and prognostic information in patients with pulmonary vascular diseases. While downstream pressure [i.e., left atrial (LA) pressure] should be considered when calculating static properties of pulmonary vasculature, PAZ is commonly estimated without taking into account the pulsatile component of LA pressure. We examined whether PAZ can be estimated with reasonable accuracy without using LA pressure. Pulmonary artery (PA) flow, PA pressure, and LA pressure were measured under irregular pacing in eight normal Sprague-Dawley rats. PAZ was estimated by analyzing a one-input, one-output system (I1O1 analysis) that does not include LA pressure, and a two-input, one-output system (I2O1 analysis) that includes LA pressure. Using a tube and 3-element Windkessel model, PAZ was parameterized as peripheral resistance (RP ), arterial compliance (CP ), characteristic impedance (ZC ), and transmission time to the reflection site (TD ). These parameters were not significantly different between the I1O1 and I2O1 analyses (RP : 0.286 ± 0.040 vs. 0.274 ± 0.038 mmHg·min/mL, CP : 0.352 ± 0.049 vs. 0.343 ± 0.041 mL/mmHg, ZC : 0.115 ± 0.005 vs. 0.117 ± 0.005 mmHg·min/mL, TD : 13.2 ± 1.8 vs. 12.9 ± 1.7 msec). In conclusion, the I1O1 analysis that does not use LA pressure estimates PAZ with reasonable accuracy compared with the I2O1 analysis that uses LA pressure in normal rats. Our finding that the pulsatile component of LA pressure contributes little to PAZ estimation may justify the clinical use of the I1O1 analysis.

Efficacy of Manual Ventilation Techniques During Cardiopulmonary Resuscitation in Dogs

The efficacy of ventilation of dogs during cardiopulmonary resuscitation (CPR) with a tight fitting face mask or mouth-to-nose rescue breathing has not been evaluated. Twenty-four purpose bred research dogs: Dogs were randomized to be ventilated by cuffed orotracheal tube, tight fitting face mask, mouth-to-nose breathing or compressions only during CPR (n = 6 in all groups). Orotracheal tube and face mask ventilation was performed on room air. Chest compressions were performed during the experimental procedure. Arterial blood gases were performed prior to euthanasia (baseline), at 3 min and at 6 min of CPR. PaO₂ and PaCO₂ were compared for each time point and each group. There was no difference in PaO₂ or PaCO₂ between groups at baseline. At 6 min all groups had a significantly higher PaCO₂ (P ≤ 0.005) and the facemask and compression only groups had a significantly lower PaO₂ (P < 0.02) when compared to the orotracheal tube group. There was no difference between the PaO₂ of the mouth-to-nose group compared to the orotracheal tube group at 3 or 6 min. Gastric distension, regurgitation, gas leakage around the mouth, and ineffective breaths were all noted in both the face mask and mouth-to-nose group. The results of this study supports that orotracheal intubation is the preferred technique for ventilation during CPR in dogs. When orotracheal intubation is not possible, face mask ventilation or mouth-to-nose ventilation would be reasonable alternatives. When oxygen supplementation is available, face mask ventilation is likely to be superior. Appropriate training for both face mask and mouth-to-nose ventilation techniques is recommended.

The past, present, and future of ventilation during cardiopulmonary resuscitation

PURPOSE OF REVIEW

To evaluate the past and present literature on ventilation during out of hospital cardiac arrest, highlighting research that has informed current guidelines.

RECENT FINDINGS

Previous studies have studied what are optimal compression-to-ventilation ratios, ventilation rates, and methods of ventilation. Continuous chest compression cardiopulmonary resuscitation (CPR) has not shown to provide a significant survival benefit over the traditional 30 : 2 CPR. The optimal ventilation rate is recommended at 8 to 10 breaths per minute. Methods such as capnography and thoracic impedance are being used to evaluate ventilation in research studies.

SUMMARY

Future out of hospital cardiac arrest studies are still exploring how to optimize the delivery of ventilation during the initial stages of resuscitation. More prospective studies focusing on ventilation are needed to inform guidelines.

Cardiopulmonary physiology: why the heart and lungs are inextricably linked

Because the heart and lungs are confined within the thoracic cavity, understanding their interactions is integral for studying each system. Such interactions include changes in external constraint to the heart, blood volume redistribution (venous return), direct ventricular interaction (DVI), and left ventricular (LV) afterload. During mechanical ventilation, these interactions can be amplified and result in reduced cardiac output. For example, increased intrathoracic pressure associated with mechanical ventilation can increase external constraint and limit ventricular diastolic filling and, therefore, output. Similarly, high intrathoracic pressures can alter blood volume distribution and limit diastolic filling of both ventricles while concomitantly increasing pulmonary vascular resistance, leading to increased DVI, which may further limit LV filling. While LV afterload is generally considered to decrease with increased intrathoracic pressure, the question arises if the reduced LV afterload is primarily a consequence of a reduced LV preload. A thorough understanding of the interaction between the heart and lungs can be complicated but is essential for clinicians and health science students alike. In this teaching review, we have attempted to highlight the present understanding of certain salient aspects of cardiopulmonary physiology and pathophysiology, as well as provide a resource for multidisciplined health science educators and students.

Ventilation modalities in infants with congenital diaphragmatic hernia

Neonates with congenital diaphragmatic hernia are among the more complex patients to support with mechanical ventilation. They have particular features that add to the difficulties already present in the neonatal patient. A ventilation strategy tailored to the patient's underlying physiology rather than mode of ventilation is a crucial issue for clinicians treating these delicate patients.

Comparison of different inspiratory triggering settings in automated ventilators during cardiopulmonary resuscitation in a porcine model

BACKGROUND

Mechanical ventilation via automated in-hospital ventilators is quite common during cardiopulmonary resuscitation. It is not known whether different inspiratory triggering sensitivity settings of ordinary ventilators have different effects on actual ventilation, gas exchange and hemodynamics during resuscitation.

METHODS

18 pigs enrolled in this study were anaesthetized and intubated. Continuous chest compressions and mechanical ventilation (volume-controlled mode, 100% O2, respiratory rate 10/min, and tidal volumes 10ml/kg) were performed after 3 minutes of ventricular fibrillation. Group trig-4, trig-10 and trig-20 (six pigs each) were characterized by triggering sensitivities of 4, 10 and 20 (cmH2O for pressure-triggering and L/min for flow-triggering), respectively. Additionally, each pig in each group was mechanically ventilated using three types of inspiratory triggering (pressure-triggering, flow-triggering and turned-off triggering) of 5 minutes duration each, and each animal matched with one of six random assortments of the three different triggering settings. Blood gas samples, respiratory and hemodynamic parameters for each period were all collected and analyzed.

RESULTS

In each group, significantly lower actual respiratory rate, minute ventilation volume, mean airway pressure, arterial pH, PaO2, and higher end-tidal carbon dioxide, aortic blood pressure, coronary perfusion pressure, PaCO2 and venous oxygen saturation were observed in the ventilation periods with a turned-off triggering setting compared to those with pressure- or flow- triggering (all P<0.05), except when compared with pressure-triggering of 20 cmH2O (respiratory rate 10.5[10/11.3]/min vs 12.5[10.8/13.3]/min, P = 0.07; coronary perfusion pressure 30.3[24.5/31.6] mmHg vs 27.4[23.7/29] mmHg, P = 0.173; venous oxygen saturation 46.5[32/56.8]% vs 41.5[33.5/48.5]%, P = 0.575).

CONCLUSIONS

Ventilation with pressure- or flow-triggering tends to induce hyperventilation and deteriorating gas exchange and hemodynamics during CPR. A turned-off patient triggering or a pressure-triggering of 20 cmH2O is preferred for ventilation when an ordinary inpatient hospital ventilator is used during resuscitation.

Real-time tidal volume feedback guides optimal ventilation during simulated CPR

PURPOSE

We performed this study to investigate whether real-time tidal volume feedback increases optimal ventilation and decreases hyperventilation during manikin-simulated cardiopulmonary resuscitation (CPR).

BASIC PROCEDURES

We developed a new real-time tidal volume monitoring device (TVD) which estimated tidal volume in real time using a magnetic flowmeter. The TVD was validated with a volume-controlled mechanical ventilator with various tidal volumes. We conducted a randomized, crossover, manikin-simulation study in which 14 participants were randomly divided into a control (without tidal volume feedback, n = 7) and a TVD group (with real-time tidal volume feedback, n = 7) and underwent manikin simulation. The optimal ventilation was defined as 420-490 mL of tidal volumes for a 70-kg adult manikin. After 2 weeks of the washout period, the simulation was repeated via the participants' crossover.

MAIN FINDINGS

In the validation study, 97.6% and 100% of the difference ratios in tidal volumes between the mechanical ventilator and TVD were within ±1.5% and ±2.5%, respectively. During manikin-simulated CPR, TVD use increased the proportion of optimal ventilation per person. Its median values (range) of the control group and the TVD group were 37.5% (0.0-65.0) and 87.5% (65.0-100.0), respectively, P < .001). TVD use also decreased hyperventilation. The proportions of hyperventilation in the control group and the TVD group were 25.0% vs 8.9%, respectively (P < .001).

PRINCIPAL CONCLUSIONS

Real-time tidal volume feedback using the new TVD guided the rescuers to provide optimal ventilation and to avoid hyperventilation during manikin-simulated CPR.

Development of a servo pump system for in vivo loading of pathological pulmonary artery impedance on the right ventricle of normal rats

Pulmonary artery (PA) impedance provides detailed information on right ventricular (RV) afterload in pulmonary hypertension (PH). This study aimed to examine PA impedance in a rat model of monocrotaline-induced PH (MCT-PH) and to develop an experimental system for in vivo loading of pathological PA impedance on the RV of normal rats. PA impedance was quantified in normal ( n = 10) and MCT-PH rats ( n = 10) using a three-element Windkessel (3-WK) model. Compared with normal rats, MCT-PH rats had higher characteristic impedance ( ZC) and peripheral pulmonary resistance ( RP) ( ZC: 0.121 ± 0.039 vs. 0.053 ± 0.017 mmHg·min·ml−1, P < 0.001; RP: 0.581 ± 0.334 vs. 0.252 ± 0.105 mmHg·min·ml−1, P = 0.013) and lower pulmonary artery compliance ( CP) (0.242 ± 0.131 vs. 0.700 ± 0.186 ml/mmHg, P < 0.001). In another group of 10 normal rats, a computer-controlled servo pump was connected to the left PA for loading PA impedance with parameters in pathological ranges designed by the 3-WK model. Activation of the servo pump decreased the error of measured vs. target PA impedance (modulus: from 0.047 ± 0.020 without pump activation to 0.019 ± 0.007 with pump activation, P < 0.001; phase: 0.085 ± 0.028 to 0.043 ± 0.012 radians, P < 0.001). In conclusion, MCT-PH increases ZCand RPand decreases CP. Our servo pump system, which is capable of imposing arbitrary PA impedance with pathological parameters, may offer a unique opportunity to delineate the pathological significance of PA impedance in PH.

Low tidal volume ventilation ameliorates left ventricular dysfunction in mechanically ventilated rats following LPS-induced lung injury

Background

High tidal volume ventilation has shown to cause ventilator-induced lung injury (VILI), possibly contributing to concomitant extrapulmonary organ dysfunction. The present study examined whether left ventricular (LV) function is dependent on tidal volume size and whether this effect is augmented during lipopolysaccharide(LPS)-induced lung injury.

Methods

Twenty male Wistar rats were sedated, paralyzed and then randomized in four groups receiving mechanical ventilation with tidal volumes of 6 ml/kg or 19 ml/kg with or without intrapulmonary administration of LPS. A conductance catheter was placed in the left ventricle to generate pressure-volume loops, which were also obtained within a few seconds of vena cava occlusion to obtain relatively load-independent LV systolic and diastolic function parameters. The end-systolic elastance / effective arterial elastance (Ees/Ea) ratio was used as the primary parameter of LV systolic function with the end-diastolic elastance (Eed) as primary LV diastolic function.

Results

Ees/Ea decreased over time in rats receiving LPS (p = 0.045) and high tidal volume ventilation (p = 0.007), with a lower Ees/Ea in the rats with high tidal volume ventilation plus LPS compared to the other groups (p < 0.001). Eed increased over time in all groups except for the rats receiving low tidal volume ventilation without LPS (p = 0.223). A significant interaction (p < 0.001) was found between tidal ventilation and LPS for Ees/Ea and Eed, and all rats receiving high tidal volume ventilation plus LPS died before the end of the experiment.

Conclusions

Low tidal volume ventilation ameliorated LV systolic and diastolic dysfunction while preventing death following LPS-induced lung injury in mechanically ventilated rats. Our data advocates the use of low tidal volumes, not only to avoid VILI, but to avert ventilator-induced myocardial dysfunction as well.

Reliability and accuracy of the thoracic impedance signal for measuring cardiopulmonary resuscitation quality metrics

AIM

To determine the accuracy and reliability of the thoracic impedance (TI) signal to assess cardiopulmonary resuscitation (CPR) quality metrics.

METHODS

A dataset of 63 out-of-hospital cardiac arrest episodes containing the compression depth (CD), capnography and TI signals was used. We developed a chest compression (CC) and ventilation detector based on the TI signal. TI shows fluctuations due to CCs and ventilations. A decision algorithm classified the local maxima as CCs or ventilations. Seven CPR quality metrics were computed: mean CC-rate, fraction of minutes with inadequate CC-rate, chest compression fraction, mean ventilation rate, fraction of minutes with hyperventilation, instantaneous CC-rate and instantaneous ventilation rate. The CD and capnography signals were accepted as the gold standard for CC and ventilation detection respectively. The accuracy of the detector was evaluated in terms of sensitivity and positive predictive value (PPV). Distributions for each metric computed from the TI and from the gold standard were calculated and tested for normality using one sample Kolmogorov-Smirnov test. For normal and not normal distributions, two sample t-test and Mann-Whitney U test respectively were applied to test for equal means and medians respectively. Bland-Altman plots were represented for each metric to analyze the level of agreement between values obtained from the TI and gold standard.

RESULTS

The CC/ventilation detector had a median sensitivity/PPV of 97.2%/97.7% for CCs and 92.2%/81.0% for ventilations respectively. Distributions for all the metrics showed equal means or medians, and agreements >95% between metrics and gold standard was achieved for most of the episodes in the test set, except for the instantaneous ventilation rate.

CONCLUSION

With our data, the TI can be reliably used to measure all the CPR quality metrics proposed in this study, except for the instantaneous ventilation rate.

Elevated positive end-expiratory pressure decreases cardiac index in a rhesus monkey model

RATIONALE

Clinicians are often concerned that higher positive end-expiratory pressure (PEEP) will decrease cardiac index (CI). PEEP affects CI through multiple inter-related mechanisms. The adult Rhesus monkey is an excellent model to study cardiopulmonary interaction due to similar pulmonary and chest wall compliances to human infants.

OBJECTIVE

Our goal was to examine the impact of increasing PEEP on CI in Rhesus monkeys as a model for critically ill children.

METHODS

Prospective, experimental animal study. Nine healthy anesthetized, intubated Rhesus monkeys were allowed to breathe spontaneously at a PEEP of 0, 5, 10, and 15 cm H2O while CI was measured with an ultrasonic Doppler (USCOM).

MEASUREMENTS AND MAIN RESULTS

Cardiac index decreased between PEEP levels of 5 and 15 cm H2O. The mean decrease in CI for the entire cohort of monkeys was 18% (p < 0.01) with a range of -11 to 49%. Stroke volume and oxygen delivery also decreased between PEEP levels of 5 and 15 cm H2O (p < 0.01).

CONCLUSION

Between PEEP levels of 5 and 15 cm H2O, there was a decrease in CI, stroke volume, and oxygen delivery in intubated Rhesus monkeys. A plausible mechanism is that over-distention of normally compliant lungs at increased PEEP resulted in decreased preload to the right ventricle, outweighing the potentially beneficial decrease in left ventricular afterload or pulmonary vascular resistance. Further investigation is warranted, particularly in children with lung injury, who have historically benefited from increased PEEP levels without over-distention.

Cardiac index and oxygen delivery during low and high tidal volume ventilation strategies in patients with acute respiratory distress syndrome: a crossover randomized clinical trial

INTRODUCTION

The beneficial effect of low tidal volume (TV) ventilation strategy on mortality in patients with acute respiratory distress syndrome (ARDS) has been attributed to the protective effect on ventilator-induced lung injury, and yet its effect on cardiovascular function might also play an important role. The aim of this study was to assess whether low TV ventilation improves cardiac output and oxygen delivery compared with high TV ventilation strategy in patients with ARDS.

METHODS

In this crossover randomized clinical trial 16 ARDS patients were recruited in an intensive care unit at a university-affiliated hospital. Each patient was ventilated for 30 min with low (6 mL/kg) and 30 min with high (12 mL/kg) TV. The two experimental periods, applied in random order and with allocation concealment, were separated by 30 min of basal ventilation. Minute ventilation was constantly maintained by appropriate respiratory rate changes.

RESULTS

Compared with high TV ventilation, low TV ventilation showed decreased pH (7.37 vs. 7.41, P = 0.001) and increased PaCO₂ (49 vs. 43 mmHg; P = 0.002). Cardiac index and oxygen delivery index were increased with low compared with high TV ventilation (3.9 vs. 3.5 L.min⁻¹.m⁻², P = 0.012, and 521 vs. 463 mL.min⁻¹.m⁻², P = 0.002, respectively), while oxygen extraction ratio decreased (0.36 vs. 0.44, P = 0.027). In four patients oxygen extraction ratio was >0.5 during high TV but not during low TV strategy. The magnitude of the change in cardiac index was positively associated with PaCO₂ variation (P = 0.004), while it was unrelated to the magnitude of changes in TV and airway pressure. The decrease of cardiac index was predicted by PaCO₂ reduction, with and area under ROC curve of 0.72.

CONCLUSIONS

Our findings suggest that a low TV ventilation strategy increases cardiac index and oxygen delivery, thus supporting the hypothesis that the beneficial effect of low TV ventilation in patients with ARDS could be partially explained by hemodynamic improvement. In other words, low tidal volume ventilation could be protective also for the cardiovascular system and not only for the lung. The slight increase of PaCO₂ during low TV ventilation seems to predict the increase of cardiac index.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00713713.

Advances in monitoring and management of pediatric acute lung injury

This article focuses on the respiratory management and monitoring of pediatric acute lung injury (ALI) as a specific cause for respiratory failure. Definitive, randomized, controlled trials in pediatrics to guide optimal ventilatory management are few. The only adjunct therapy that has been proved to improve clinical outcome is low tidal volume ventilation, but only in adult patients. Careful monitoring of the patient's respiratory status with airway graphic analysis and capnography can be helpful. Definitive data are needed in the pediatric population to assist in the care of infants, children, and adolescents with ALI to improve survival and functional outcome.

Association Between Postresuscitation Partial Pressure of Arterial Carbon Dioxide and Neurological Outcome in Patients With Post–Cardiac Arrest Syndrome

Background—

Partial pressure of arterial CO 2 (Pa co 2 ) is a regulator of cerebral blood flow after brain injury. Recent guidelines for the management of cardiac arrest recommend maintaining Pa co 2 at 40 to 45 mm Hg after successful resuscitation; however, there is a paucity of data on the prevalence of Pa co 2 derangements during the post–cardiac arrest period and its association with outcome.

Methods and Results—

We analyzed a prospectively compiled and maintained cardiac arrest registry at a single academic medical center. Inclusion criteria are as follows: age ≥18, nontrauma arrest, and comatose after return of spontaneous circulation. We analyzed arterial blood gas data during 0 to 24 hours after the return of spontaneous circulation and determined whether patients had exposure to hypocapnia and hypercapnia (defined as Pa co 2 ≤30 mm Hg and Pa co 2 ≥50 mm Hg, respectively, based on previous literature). The primary outcome was poor neurological function at hospital discharge, defined as Cerebral Performance Category ≥3. We used multivariable logistic regression, with multiple sensitivity analyses, adjusted for factors known to predict poor outcome, to determine whether post–return of spontaneous circulation hypocapnia and hypercapnia were independent predictors of poor neurological function. Of 193 patients, 52 (27%) had hypocapnia only, 63 (33%) had hypercapnia only, 18 (9%) had both hypocapnia and hypercapnia exposure, and 60 (31%) had no exposure; 74% of patients had poor neurological outcome. Hypocapnia and hypercapnia were independently associated with poor neurological function, odds ratio 2.43 (95% confidence interval, 1.04–5.65) and 2.20 (95% confidence interval, 1.03–4.71), respectively.

Conclusions—

Hypocapnia and hypercapnia were common after cardiac arrest and were independently associated with poor neurological outcome. These data suggest that Pa co 2 derangements could be potentially harmful for patients after resuscitation from cardiac arrest.

Quantifying the effect of cardiopulmonary resuscitation quality on cardiac arrest outcome: a systematic review and meta-analysis

Background- Evidence has accrued that cardiopulmonary resuscitation quality affects cardiac arrest outcome. However, the relative contributions of chest compression components (such as rate and depth) to successful resuscitation remain unclear. Methods and Results- We sought to measure the effect of cardiopulmonary resuscitation quality on cardiac arrest outcome through systematic review and meta-analysis. We searched for any clinical study assessing cardiopulmonary resuscitation performance on adult cardiac arrest patients in which survival was a reported outcome, either return of spontaneous circulation or survival to admission or discharge. Of 603 identified abstracts, 10 studies met inclusion criteria. Effect sizes were reported as mean differences. Missing data were resolved by author contact. Estimates were segregated by cardiopulmonary resuscitation metric (chest compression rate, depth, no-flow fraction, and ventilation rate), and a random-effects model was applied to estimate an overall pooled effect. Arrest survivors were significantly more likely to have received deeper chest compressions than nonsurvivors (mean difference, 2.44 mm; 95% confidence interval, 1.19-3.69 [P<0.001]; n=6 studies; I(2)=0.0%; P for heterogeneity=0.9). Likewise, survivors were significantly more likely to have received chest compression rates closer to 85 to 100 compressions per minute (cpm) than nonsurvivors (absolute mean difference from 85 cpm, -4.81 cpm; 95% confidence interval, -8.19 to -1.43 [P=0.005]; from 100 cpm, -5.04 cpm; 95% confidence interval, -8.44 to -1.65 [P=0.004]; n=6 studies; I(2)<49%; P for heterogeneity >0.2). No significant difference in no-flow fraction (n=7 studies) or ventilation rate (n=4 studies) was detected between survivors and nonsurvivors. Conclusions- Deeper chest compressions and rates closer to 85 to 100 cpm are significantly associated with improved survival from cardiac arrest.

Impact of implementing 5 potentially better respiratory practices on neonatal outcomes and costs

OBJECTIVE

We implemented 5 potentially better practices to limit mechanical ventilation (MV), supplemental oxygen, and bronchopulmonary dysplasia in newborn infants born before 33 weeks' gestation.

METHODS

The methods used in this study included (1) exclusive use of bubble continuous positive airway pressure (bCPAP), (2) provision of bCPAP in the delivery room, (3) strict intubation criteria, (4) strict extubation criteria, and (5) prolonged CPAP to avoid supplemental oxygen. We excluded outborn infants and those with major anomalies and obstetric complications from analysis.

RESULTS

Demographics were similar in 61 infants born before and 60 born after implementation. For infants born at 26 to 32(6/7) weeks' gestation, intubation (first 72 hours) decreased from 52% to 11% (P < .0001) and surfactant use decreased from 48% to 14% (P=.0001). In all infants, the mean ± SD fraction of inspired oxygen requirement (first 24 hours) decreased from 0.27 ± 0.08 to 0.24 ± 0.05 (P=.0005), days of oxygen decreased from 23.5 ± 44.5 to 9.3 ± 22.0 (P=.04), and days of MV decreased from 8.8 ± 27.8 to 2.2 ± 6.2 (P=.005). Hypotension decreased from 33% to 15% (P=.03). The percentage of infants with bronchopulmonary dysplasia was 17% before and 8% after (P=.27). Nurse staffing ratios remained unchanged.

CONCLUSIONS

Implementation of these potentially better practices reduced the need for MV, surfactant, and supplemental oxygen as well as reduced hypotension among infants born before 33 weeks' gestation without adverse consequences. The costs for equipment and surfactant were lower.

Volume loading reduces pulmonary vascular resistance in ventilated animals with acute lung injury: evaluation of RV afterload

During mechanical ventilation, increased pulmonary vascular resistance (PVR) may decrease right ventricular (RV) performance. We hypothesized that volume loading, by reducing PVR, and, therefore, RV afterload, can limit this effect. Deep anesthesia was induced in 16 mongrel dogs (8 oleic acid-induced acute lung injury and 8 controls). We measured ventricular pressures, dimensions, and stroke volumes during positive end-expiratory pressures of 0, 6, 12, and 18 cmH2O at three left ventricular (LV) end-diastolic pressures (5, 12, and 18 mmHg). Oleic acid infusion (0.07 ml/kg) increased PVR and reduced respiratory system compliance ( P < 0.05). With positive end-expiratory pressure, PVR was greater at a lower LV end-diastolic pressure. Increased PVR was associated with a decreased transseptal pressure gradient, suggesting that leftward septal shift contributed to decreased LV preload, in addition to that caused by external constraint. Volume loading reduced PVR; this was associated with improved RV output and an increased transseptal pressure gradient, which suggests that rightward septal shift contributed to the increased LV preload. If PVR is used to reflect RV afterload, volume loading appeared to reduce PVR, thereby improving RV and LV performance. The improvement in cardiac output was also associated with reduced external constraint to LV filling,; since calculated PVR is inversely related to cardiac output, increased LV output would reduce PVR. In conclusion, our results, which suggest that PVR is an independent determinant of cardiac performance, but is also dependent on cardiac output, improve our understanding of the hemodynamic effects of volume loading in acute lung injury.

Heart failure treatment in the intensive care unit in children

Although pediatric heart failure is generally a chronic, progressive disorder, recovery of ventricular function may occur with some forms of cardiomyopathy. Guidelines for the management of chronic heart failure in adults and children have recently been published by the International Society for Heart and Lung Transplantation the American College of Cardiology, and the American Heart Association. The primary aim of heart failure therapy is to reduce symptoms, preserve long-term ventricular performance, and prolong survival primarily through antagonism of the neurohormonal compensatory mechanisms. Because some medications may be detrimental during an acute decompensation, physicians who manage these patients as inpatients must be knowledgeable about the medications and therapeutic goals of chronic heart failure treatment. Understanding the mechanisms of chronic heart failure may foster improved understanding of the treatment of decompensated heart failure.

VTCO2 and dynamic compliance-guided lung recruitment in surfactant-depleted piglets: a computed tomography study

OBJECTIVE

Using computed tomography (CT) as reference, our primary objectives were to test if maximal tidal elimination of carbon dioxide (VTCO2) could be used as a marker of "optimal recruitment," indicating maximal available lung tissue for gas exchange and if a decrease in dynamic compliance (Cdyn) indicated the beginning of lung collapse during a downward positive end-expiratory pressure (PEEP) titration.

DESIGN

Prospective laboratory animal investigation.

SETTING

Clinical physiology research laboratory.

SUBJECTS

Six piglets undergoing lung lavage.

INTERVENTIONS

Saline-lavaged piglets were initially ventilated without PEEP at a tidal volume (VT) of 10 mL/kg followed by baseline ventilation at end-inspiratory pressure (EIP) 25 cm H2O and PEEP 6 cm H2O. PEEP was increased to 12 or 15 cm H2O. Then EIP was increased in steps of 5 cm H2O and the EIP where VTCO2 peaked or leveled off was assumed to define optimally recruited lungs. A downward PEEP titration followed from 12 or 15 to 4 cm H2O in steps of 1 cm H2O. First decline of Cdyn was assumed to define onset of lung collapse. VTCO2 and Cdyn were continuously recorded and CT scans iterated for each change of ventilation. "Open-lung PEEP" was set 2 cm H2O above PEEP at the first Cdyn decline and was used for a final period of "open-lung ventilation."

MEASUREMENTS AND MAIN RESULTS

CT images showed recruited lungs at peak VTCO2 and that a minimal amount of normally aerated lung was added by further increase in EIP. Cdyn declined just before CT scans indicated lung collapse. Compared with baseline, the target VT of 10 mL/kg was achieved at lower EIP and pressure amplitude (EIP-PEEP) during the final open-lung ventilation with more normally aerated and fewer collapsed lungs. Cdyn was doubled after recruitment.

CONCLUSIONS

The lung recruitment maneuver was effective and lungs optimally recruited at maximal VTCO2. A fall in Cdyn indicated lung collapse during downward PEEP titration as confirmed by CT.

Ventilation during resuscitation efforts for out-of-hospital primary cardiac arrest

PURPOSE OF REVIEW

To discuss recent findings surrounding the role of ventilation during cardiopulmonary resuscitation for individuals with out-of-hospital primary cardiac arrest.

RECENT FINDINGS

Active assisted ventilation during primary cardiac arrest may not always be beneficial and, in some circumstances, may lead to worse outcomes. By interrupting chest compressions and thereby decreasing vital organ perfusion, rescue breathing may be deleterious. In addition to the time required to administer breaths, the delay due to the insertion of advanced airways, even by well trained individuals, is often extensive. Furthermore, once intubation is completed, excessive hyperventilation occurs frequently, even by recently trained medical providers. Although most experts agree that excessive ventilation is harmful during out-of-hospital cardiac resuscitation, the optimal rate, tidal volume, timing, and technique of ventilation is still unknown. There is increasing evidence that, in patients with witnessed arrests and a shockable rhythm, the optimal form of ventilation is passive oxygen insufflation.

SUMMARY

Assisted ventilation during the initial provision of cardiopulmonary resuscitation is less important than previously believed. It is hypothesized that, by training prehospital medical providers to utilize passive oxygen insufflation for individuals with primary cardiac arrest, critical organ perfusion will increase and, therefore, survival after out-of-hospital cardiac arrest will improve.

Technique for prolonged normothermic ex vivo lung perfusion

BACKGROUND

The inhibition of cellular metabolism induced by hypothermia obviates the possibility of substantial reparative processes occurring during organ preservation. The aim of this study was to develop a technique of extended (12-hour) ex vivo lung perfusion (EVLP) at normothermia for assessment and protective maintenance of the donor lung.

METHODS

Six double-lung blocks from 35-kg pigs and 5 single human lungs were subjected to 12 hours of normothermic EVLP using acellular Steen Solution. In the animal studies, the left lung was transplanted into recipients at the end of EVLP and reperfused for 4 hours to evaluate the impact of prolonged EVLP on post-transplant lung function. A protective mode of mechanical ventilation with controlled perfusion flows and pressures in the pulmonary vasculature were employed during EVLP. Lung oxygenation capacity (DeltaPo(2)), pulmonary vascular resistance and airway pressures were evaluated in the system. Red blood cells were added to the perfusate to a hematocrit of 20% at the end of human lung EVLP to study lung functional assessment with and without cells.

RESULTS

Lung function was stable during 12 hours of EVLP. This stability during prolonged normothermic EVLP translated into excellent post-transplant lung function (Pao(2)/Fio(2): 527 +/- 22 mm Hg), low edema formation (wet/dry ratio: 5.24 +/- 0.38) and preserved lung histology after transplantation. The acellular perfusion assessment of lung function accurately correlated with post-transplant graft function.

CONCLUSIONS

Twelve hours of EVLP at physiologic temperatures using an acellular perfusate is achievable and maintains the donor lungs without inflicting significant added injury. This system can be used to assess, maintain and treat injured donor lungs.

Ventilatory management during routine general anaesthesia

Intraoperative hypoxaemia and postoperative respiratory complications remain the challenges of modern anaesthetic practice. Anaesthesia causes both depression of respiratory centres and profound changes of respiratory mechanics. Most anaesthetized patients consequently require mechanical ventilation and supplemental oxygen. Recent data suggest that intraoperative respiratory management of a patient can affect postoperative outcome. In this review, we briefly describe the mechanisms responsible for the impairment of intraoperative gas exchange and provide guidelines to prevent or manage hypoxaemia. Moreover, we discuss several aspects of mechanical ventilation that can be employed to improve patients' outcome.

Hemodynamic effects of levobupivacaine after pediatric caudal anesthesia evaluated by transesophageal doppler

BACKGROUND

The aim of this study is to determine if there are significant differences in hemodynamic effects between combined general-regional anesthesia using levobupivacaine 0.25% 2 ml x kg(-1) via the caudal route in comparison with balanced general anesthesia using continuous infusion of remifentanil in young children undergoing genitourinary surgery.

PATIENTS AND METHODS

62 ASA I-II pediatric patients (12 female, 50 male) aged 6 months to 7 years undergoing genitourinary surgery were included in the study. Patients were randomly allocated into one of two groups of 31 patients each. Group Caud received caudal blockade with levobupivacaine 0.25% 2 mg x kg(-1) in combined general-regional anesthesia and Group Gen received balanced general anesthesia with remifentanil. The noninvasive hemodynamic parameters were measured in each group 5 min after induction of general anesthesia or caudal block (Tcaud), after further 5 min coincident with skin incision (Tsi), 10 min after skin incision (T10i), at the end of surgical procedure (Tend). The time between Tcaud and Tsi was 10 min and the measurements during the interval time T10i-Tend were performed every 15 min according to the duration of surgical procedures.

RESULTS

There was a decrease in all measured hemodynamic parameters at skin incision. The decreases occurred in both groups with those in the caudal group occurring at skin incision and those in the balanced anesthesia group occurring at 10 min after skin incision. These variations showed no significant differences for any of the stated outcomes; neither between the groups at each time point nor in the caudal in comparison with baseline measurements.

CONCLUSIONS

Using transesophageal Doppler no differences in hemodynamic parameters could be detected between balanced general anesthesia with either caudal levobupivacaine or remifentanil infusion. Both techniques showed good hemodynamic stability with only minor changes from baseline over time which are unlikely to be of clinical significance except possibly in patients with preexisting cardiovascular compromise. Other studies with noninvasive monitoring in a larger population are required to better understand the consequences of caudal blockade on CO and on regional blood flow in infants.

Influence of ventilation strategies on survival in severe controlled hemorrhagic shock

OBJECTIVE

To investigate the effect of different ventilation settings on hemodynamic stability in severe controlled hemorrhagic shock.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

Research laboratory in a university hospital.

SUBJECTS

Approximately 35-45 kg domestic pigs.

INTERVENTIONS

Twenty-four domestic pigs were bled 45 mL/kg (estimated 65% of their calculated blood volume) and then ventilated with either 0 cm H2O positive end-expiratory pressure and a respiratory rate of 14 ventilations/min (positive end-expiratory pressure 0 respiratory rate 14), or with 5 cm H2O positive end-expiratory pressure, a respiratory rate of 28 ventilations/min, and a tidal volume reduced by half (positive end-expiratory pressure 5 respiratory rate 28), or with 5 cm H2O positive end-expiratory pressure and a respiratory rate of 14 ventilations/min (positive end-expiratory pressure 5 respiratory rate 14). After 1 hr study phase surviving animals, received fluid resuscitation and were monitored for further 1 hr.

MEASUREMENTS AND MAIN RESULTS

Pulmonary variables, hemodynamic variables, and short-term survival. There were no significant differences in mean arterial blood pressure and cardiac index after hemorrhage. After 20 mins of different ventilation strategies mean arterial blood pressure was 40 +/- 3 mm Hg in the positive end-expiratory pressure 0 respiratory rate 14 group, vs. 24 +/- 6 mm Hg the positive end-expiratory pressure 5 respiratory rate 28 group (p < 0.05) vs. 19 +/- 3 mm Hg in the positive end-expiratory pressure 5 respiratory rate 14 group (p < 0.01). Cardiac index was 65 +/- 5 mL/min/kg in the positive end-expiratory pressure 0 respiratory rate 14 group vs. 37 +/- 5 mL/min/kg in the positive end-expiratory pressure 5 respiratory rate 28 group(p < 0.01) and 20 +/- 3 mL/min/kg in the positive end-expiratory pressure 5 respiratory rate 14 group (p < 0.01). Mean airway pressure and positive end-expiratory pressure correlated strongly with mean arterial blood pressure and cardiac index. None of the positive end-expiratory pressure 0 respiratory rate 14 animals died in the study phase, whereas six of seven positive end-expiratory pressure 5 respiratory rate 28 animals, and all seven positive end-expiratory pressure 5 respiratory rate 14 animals died.

CONCLUSIONS

In this porcine model of severe hemorrhagic shock, reduction of positive end-expiratory pressure was the most important ventilation strategy component influencing hemodynamic stability. Reducing mean airway pressure by decreasing tidal volumes and increasing respiratory rates seemed to have less influence on cardiopulmonary function and survival than 0 cm H2O positive end-expiratory pressure.

Airway management for the uninitiated

The 21(st) century has witnessed burgeoning interest in airway management. Pertinent basic sciences are covered in numerous texts and lectures. This article presents clinical information required to perform airway management. It serves as a primer for those interested in learning airway management skills. It does not replace extensive practice under the tutelage of expert airway managers.