Higher Dead Space Is Associated With Increased Mortality in Critically Ill Children

Noninvasive Surrogate for Physiologic Dead Space Using the Carbon Dioxide Ventilatory Equivalent: Testing in a Single-Center Cohort, 2017-2023

OBJECTIVES

We sought to evaluate the association between the carbon dioxide ( co2 ) ventilatory equivalent (VEq co2 = minute ventilation/volume of co2 produced per min), a marker of dead space that does not require a blood gas measurement, and mortality risk. We compared the strength of this association to that of physiologic dead space fraction (V D /V t = [Pa co2 -mixed-expired P co2 ]/Pa co2 ) as well as to other commonly used markers of dead space (i.e., the end-tidal alveolar dead space fraction [AVDSf = (Pa co2 -end-tidal P co2 )/Pa co2 ], and ventilatory ratio [VR = (minute ventilation × Pa co2 )/(age-adjusted predicted minute ventilation × 37.5)]).

DESIGN

Retrospective cohort data, 2017-2023.

SETTING

Quaternary PICU.

PATIENTS

One hundred thirty-one children with acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

All dead space markers were calculated at the same 1-minute timepoint for each patient within the first 72 hours of using invasive mechanical ventilation. The 131 children had a median (interquartile range, IQR) age of 5.8 (IQR 1.4, 12.6) years, oxygenation index (OI) of 7.5 (IQR 4.6, 14.3), V D /V t of 0.47 (IQR 0.38, 0.61), and mortality was 17.6% (23/131). Higher VEq co2 ( p = 0.003), V D /V t ( p = 0.002), and VR ( p = 0.013) were all associated with greater odds of mortality in multivariable models adjusting for OI, immunosuppressive comorbidity, and overall severity of illness. We failed to identify an association between AVDSf and mortality in the multivariable modeling. Similarly, we also failed to identify an association between OI and mortality after controlling for any dead space marker in the modeling. For the 28-day ventilator-free days outcome, we failed to identify an association between V D /V t and the dead space markers in multivariable modeling, although OI was significant.

CONCLUSIONS

VEq co2 performs similarly to V D /V t and other surrogate dead space markers, is independently associated with mortality risk, and may be a reasonable noninvasive surrogate for V D /V t .

Arterial to end-tidal carbon dioxide gap and its characterization in mechanically ventilated adults in the emergency department

PURPOSE

To evaluate early measurement of the arterial to end-tidal carbon dioxide (PaCO2-PetCO2) gap, a surrogate for physiologic dead space, and its association with clinical outcomes in intubated adults in the emergency department (ED).

MATERIALS AND METHODS

Observational cohort study of invasively mechanically ventilated adults in an academic medical center (years 2009 to 2016). The association of the PaCO2-PetCO2 gap was evaluated with respect to clinical outcomes; the primary outcome was in-hospital mortality.

RESULTS

519 patients were included. 325 (63%) patients had an elevated (>5 mmHg) PaCO2-PetCO2. Patients with an elevated PaCO2-PetCO2 were significantly older, had higher APACHE II scores, more frequently had chronic obstructive pulmonary disease (COPD), had lower arterial oxygen to fraction of inspired oxygen (P:F) ratios, and were more likely to be intubated for exacerbation of COPD or sepsis. There was no difference in mortality for patients with an elevated PaCO2-PetCO2 (25% vs 26%) in unadjusted analysis (p = 0.829) or adjusted analysis (aOR = 0.81 [95% CI: 0.53-1.26]), as compared to a non-elevated PaCO2-PetCO2.

CONCLUSIONS

An elevated PaCO2-PetCO2 gap is common in the post-intubation period in the ED, but not significantly associated with clinical outcomes.

Capnometry after an inspiratory breath hold, PLAT CO2 , as a surrogate for P aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ in mild to moderate pediatric acute respiratory distress syndrome: A feasibility study

OBJECTIVE

Accurate and reliable noninvasive methods to estimate gas exchange are necessary to guide clinical decisions to avoid frequent blood samples in children with pediatric acute respiratory distress syndrome (PARDS). We aimed to investigate the correlation and agreement between end-tidalP CO 2 ${P}_{{\mathrm{CO}}_{2}}$ measured immediately after a 3-s inspiratory-hold (PLAT CO2 ) by capnometry andP aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ measured by arterial blood gases (ABG) in PARDS.

DESIGN

Prospective cohort study.

SETTING

Seven-bed Pediatric Intensive Care Unit, Hospital El Carmen de Maipú, Chile.

PATIENTS

Thirteen mechanically ventilated patients aged ≤15 years old undergoing neuromuscular blockade as part of management for PARDS.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

All patients were in volume-controlled ventilation mode. The regular end-tidalP CO 2 ( P ETCO 2 ) ${P}_{{\mathrm{CO}}_{2}}({P}_{{\mathrm{ETCO}}_{2}})$ (without the inspiratory hold) was registered immediately after the ABG sample. An inspiratory-hold of 3 s was performed for lung mechanics measurements, recordingP ETCO 2 ${P}_{{\mathrm{ETCO}}_{2}}$ in the breath following the inspiratory-hold. (PLAT CO2 ). End-tidal alveolar dead space fraction (AVDSf) was calculated as[ ( P aCO 2 - P ETCO 2 ) / P aCO 2 ] $[({P}_{{\mathrm{aCO}}_{2}}\mbox{--}{P}_{{\mathrm{ETCO}}_{2}})/{P}_{{\mathrm{aCO}}_{2}}]$ and its surrogate (S)AVDSf as[ ( PLAT CO 2 - P ETCO 2 ) / PLAT CO 2 ] $[{(}_{\mathrm{PLAT}}{\mathrm{CO}}_{2}\mbox{--}{P}_{{\mathrm{ETCO}}_{2}}){/}_{\mathrm{PLAT}}{\mathrm{CO}}_{2}]$ . Measurements ofP aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ were considered the gold standard. We performed concordance correlation coefficient (ρc), Spearman's correlation (rho), and Bland-Altmann's analysis (mean difference ± SD [limits of agreement, LoA]). Eleven patients were included, with a median (interquartile range) age of 5 (2-11) months. Tidal volume was 5.8 (5.7-6.3) mL/kg, PEEP 8 (6-8), driving pressure 10 (8-11), and plateau pressure 17 (17-19) cm H2 O. Forty-one paired measurements were analyzed.P aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ was higher thanP ETCO 2 ${P}_{{\mathrm{ETCO}}_{2}}$ (52 mmHg [48-54] vs. 42 mmHg [38-45], p < 0.01), and there were no significant differences with PLAT CO2 (50 mmHg [46-55], p > 0.99). The concordance correlation coefficient and Spearman's correlation betweenP aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ and PLAT CO2 were robust (ρc = 0.80 [95% confidence interval [CI]: 0.67-0.90]; and rho = 0.80, p < 0.001.), and forP ETCO 2 ${P}_{{\mathrm{ETCO}}_{2}}$ were weak and strong (ρc = 0.27 [95% CI: 0.15-0.38]; and rho = 0.63, p < 0.01). The bias between PLAT CO2 andP aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ was -0.4 ± 3.5 mmHg (LoA -7.2 to 6.4), and betweenP ETCO 2 ${P}_{{\mathrm{ETCO}}_{2}}$ andP aCO 2 ${P}_{{\mathrm{aCO}}_{2}}$ was -8.5 ± 4.1 mmHg (LoA -16.6 to -0.5). The correlation between AVDSf and (S)AVDSf was moderate (rho = 0.55, p < 0.01), and the mean difference was -0.5 ± 5.6% (LoA -11.5 to 10.5).

CONCLUSION

This pilot study showed the feasibility of measuring end-tidal CO2 after a 3-s end-inspiratory breath hole in pediatric patients undergoing controlled ventilation for ARDS. Encouraging preliminary results warrant further study of this technique.

The end-tidal alveolar dead space fraction for risk stratification during the first week of invasive mechanical ventilation: an observational cohort study

BACKGROUND

The end-tidal alveolar dead space fraction (AVDSf = [PaCO₂-P_ETCO₂]/PaCO₂) is a metric used to estimate alveolar dead space. Higher AVDSf on the first day of mechanical ventilation is associated with mortality and fewer ventilator-free days. It is not clear if AVDSf is associated with length of ventilation in survivors, how AVDSf performs for risk stratification beyond the first day of ventilation, or whether AVDSf adds predictive value to oxygenation (oxygenation index [OI]) or severity of illness (Pediatric Risk of Mortality [PRISM III]) markers.

METHODS

Retrospective single-center observational cohort study of children and young adults receiving invasive mechanical ventilation. In those with arterial or capillary blood gases, AVDSf was calculated at the time of every blood gas for the first week of mechanical ventilation.

RESULTS

There were 2335 children and young adults (median age 5.8 years [IQR 1.2, 13.2]) enrolled with 8004 analyzed AVDSf values. Higher AVDSf was associated with mortality and longer length of ventilation in survivors throughout the first week of ventilation after controlling for OI and PRISM III. Higher OI was not associated with increased mortality until ≥ 48 h of ventilation after controlling for AVDSf and PRISM III. When using standardized variables, AVDSf effect estimates were generally higher than OI for mortality, whereas OI effect estimates were generally higher than AVDSf for the length of ventilation in survivors. An AVDSf > 0.3 was associated with a higher mortality than an AVDSf < 0.2 within each pediatric acute respiratory distress syndrome severity category. The maximum AVDSf within 12 h of intensive care unit admission demonstrated good risk stratification for mortality (AUC 0.768 [95% CI 0.732, 0.803]). AVDSf did not improve mortality risk stratification when added to PRISM III but did improve mortality risk stratification when added to the gas exchange components of PRISM III (minimum 12-h PaO₂ and maximum 12-h PCO₂) (p < 0.00001).

CONCLUSIONS

AVDSf is associated with mortality and length of ventilation in survivors throughout the first week of invasive mechanical ventilation. Some analyses suggest AVDSf may better stratify mortality risk than OI, whereas OI may better stratify risk for prolonged ventilation in survivors than AVDSf.

Understanding clinical and biological heterogeneity to advance precision medicine in paediatric acute respiratory distress syndrome

Paediatric acute respiratory distress syndrome (PARDS) is a heterogeneous clinical syndrome that is associated with high rates of mortality and long-term morbidity. Factors that distinguish PARDS from adult acute respiratory distress syndrome (ARDS) include changes in developmental stage and lung maturation with age, precipitating factors, and comorbidities. No specific treatment is available for PARDS and management is largely supportive, but methods to identify patients who would benefit from specific ventilation strategies or ancillary treatments, such as prone positioning, are needed. Understanding of the clinical and biological heterogeneity of PARDS, and of differences in clinical features and clinical course, pathobiology, response to treatment, and outcomes between PARDS and adult ARDS, will be key to the development of novel preventive and therapeutic strategies and a precision medicine approach to care. Studies in which clinical, biomarker, and transcriptomic data, as well as informatics, are used to unpack the biological and phenotypic heterogeneity of PARDS, and implementation of methods to better identify patients with PARDS, including methods to rapidly identify subphenotypes and endotypes at the point of care, will drive progress on the path to precision medicine.

Alveolar dead space fraction is not associated with early RV systolic dysfunction in pediatric ARDS

PRIMARY HYPOTHESIS

We hypothesized that higher alveolar dead space fraction (AVDSf) at pediatric acute respiratory distress syndrome (PARDS) onset would be associated with right ventricular (RV) systolic dysfunction within the first 24 h of PARDS.

STUDY DESIGN AND METHODS

We performed a retrospective single-center cohort study of PARDS patients with clinically obtained echocardiograms within 24 h. Primary exposure was AVDSf at PARDS onset. Primary outcome was RV systolic dysfunction as defined by RV global longitudinal strain (GLS) (>-18%). Secondary outcomes included pulmonary hypertension (PH) and RV systolic dysfunction as defined by other echocardiogram parameters, and measures of oxygenation. Unadjusted and adjusted logistic and linear regression were used to investigate AVDSf associations with outcomes.

RESULTS

Ninety-one patients were included: median age 6.2 years, 46% female, and 65% with moderate or severe PARDS. Median AVDSf was 0.2 (interquartile range [IQR] 0.0-0.3), 33% had RV dysfunction, and 21% had PH. Unadjusted and adjusted logistic regression showed no association between AVDSf and RV systolic dysfunction or PH by any echocardiographic measure, but unadjusted and adjusted linear regression did show an association between AVDSf and PaO2 /FiO2 .

CONCLUSION

AVDSf at PARDS onset was not associated with RV systolic dysfunction or PH within 24 h but was associated with PaO2 /FiO2 ratio and may be more reflective of pulmonary causes of ventilation-perfusion mismatch. Future investigations should focus on clarifying the clinical utility of AVDSf in relation to existing metrics throughout the course of PARDS.

Pathobiology, Severity, and Risk Stratification of Pediatric Acute Respiratory Distress Syndrome: From the Second Pediatric Acute Lung Injury Consensus Conference

OBJECTIVES

To review the literature for studies published in children on the pathobiology, severity, and risk stratification of pediatric acute respiratory distress syndrome (PARDS) with the intent of guiding current medical practice and identifying important areas for future research related to severity and risk stratification.

DATA SOURCES

Electronic searches of PubMed and Embase were conducted from 2013 to March 2022 by using a combination of medical subject heading terms and text words to capture the pathobiology, severity, and comorbidities of PARDS.

STUDY SELECTION

We included studies of critically ill patients with PARDS that related to the severity and risk stratification of PARDS using characteristics other than the oxygenation defect. Studies using animal models, adult only, and studies with 10 or fewer children were excluded from our review.

DATA EXTRACTION

Title/abstract review, full-text review, and data extraction using a standardized data collection form.

DATA SYNTHESIS

The Grading of Recommendations Assessment, Development, and Evaluation approach was used to identify and summarize relevant evidence and develop recommendations for clinical practice. There were 192 studies identified for full-text extraction to address the relevant Patient/Intervention/Comparator/Outcome questions. One clinical recommendation was generated related to the use of dead space fraction for risk stratification. In addition, six research statements were generated about the impact of age on acute respiratory distress syndrome pathobiology and outcomes, addressing PARDS heterogeneity using biomarkers to identify subphenotypes and endotypes, and use of standardized ventilator, physiologic, and nonpulmonary organ failure measurements for future research.

CONCLUSIONS

Based on an extensive literature review, we propose clinical management and research recommendations related to characterization and risk stratification of PARDS severity.

Monitoring in Pediatric Acute Respiratory Distress Syndrome: From the Second Pediatric Acute Lung Injury Consensus Conference

OBJECTIVES

Monitoring is essential to assess changes in the lung condition, to identify heart-lung interactions, and to personalize and improve respiratory support and adjuvant therapies in pediatric acute respiratory distress syndrome (PARDS). The objective of this article is to report the rationale of the revised recommendations/statements on monitoring from the Second Pediatric Acute Lung Injury Consensus Conference (PALICC-2).

DATA SOURCES

MEDLINE (Ovid), Embase (Elsevier), and CINAHL Complete (EBSCOhost).

STUDY SELECTION

We included studies focused on respiratory or cardiovascular monitoring of children less than 18 years old with a diagnosis of PARDS. We excluded studies focused on neonates.

DATA EXTRACTION

Title/abstract review, full-text review, and data extraction using a standardized data collection form.

DATA SYNTHESIS

The Grading of Recommendations Assessment, Development and Evaluation approach was used to identify and summarize evidence and develop recommendations. We identified 342 studies for full-text review. Seventeen good practice statements were generated related to respiratory and cardiovascular monitoring. Four research statements were generated related to respiratory mechanics and imaging monitoring, hemodynamics monitoring, and extubation readiness monitoring.

CONCLUSIONS

PALICC-2 monitoring good practice and research statements were developed to improve the care of patients with PARDS and were based on new knowledge generated in recent years in patients with PARDS, specifically in topics of general monitoring, respiratory system mechanics, gas exchange, weaning considerations, lung imaging, and hemodynamic monitoring.

Dead space ratio as a tool in nitric oxide weaning: a study in pulmonary hypertensive disease

OBJECTIVES

To describe the association between successful weaning of inhaled nitric oxide and trends in dead space ratio during such weans in patients empirically initiated on nitric oxide therapy out of concern of pulmonary hypertensive crisis.

PATIENTS

Children in a cardiac intensive care unit initiated on inhaled nitric oxide out of clinical concern for pulmonary hypertensive crisis retrospectively over 2 years.

MEASUREMENTS AND MAIN RESULTS

Twenty-seven patients were included, and nitric oxide was successfully discontinued in 23/27. These patients exhibited decreases in dead space ratio (0.18 versus 0.11, p = 0.047) during nitric oxide weaning, and with no changes in dead space ratio between pre- and post-nitric oxide initiation (p = 0.88) and discontinuation (p = 0.63) phases. These successful patients had a median age of 10 months [4.0, 57.0] and had a pre-existent diagnosis of CHD in 6/23 and pulmonary hypertension in 2/23. Those who failed nitric oxide discontinuation trended with a higher dead space ratio at presentation (0.24 versus 0.10), were more likely to carry a prior diagnosis of pulmonary hypertension (50% versus 8.7%), and had longer mechanical ventilation days (5 versus 12).

CONCLUSIONS

Patients empirically placed on nitric oxide out of concern of pulmonary hypertensive crisis and successfully weaned off showed unchanged or decreased dead space ratio throughout the initiation to discontinuation phases of nitric oxide therapy. Trends in dead space ratio may aid in determining true need for nitric oxide and facilitate effective weaning. Further studies are needed to directly compare trends between success and failure groups.

Continuous noninvasive blood gas estimation in critically ill pediatric patients with respiratory failure

Patients supported by mechanical ventilation require frequent invasive blood gas samples to monitor and adjust the level of support. We developed a transparent and novel blood gas estimation model to provide continuous monitoring of blood pH and arterial CO₂ in between gaps of blood draws, using only readily available noninvasive data sources in ventilated patients. The model was trained on a derivation dataset (1,883 patients, 12,344 samples) from a tertiary pediatric intensive care center, and tested on a validation dataset (286 patients, 4030 samples) from the same center obtained at a later time. The model uses pairwise non-linear interactions between predictors and provides point-estimates of blood gas pH and arterial CO₂ along with a range of prediction uncertainty. The model predicted within Clinical Laboratory Improvement Amendments of 1988 (CLIA) acceptable blood gas machine equivalent in 74% of pH samples and 80% of PCO₂ samples. Prediction uncertainty from the model improved estimation accuracy by 15% by identifying and abstaining on a minority of high-uncertainty samples. The proposed model estimates blood gas pH and CO₂ accurately in a large percentage of samples. The model's abstention recommendation coupled with ranked display of top predictors for each estimation lends itself to real-time monitoring of gaps between blood draws, and the model may help users determine when a new blood draw is required and delay blood draws when not needed.

Volumetric Capnography in Pediatric Extracorporeal Membrane Oxygenation: A Case Series

The kinetics of carbon dioxide elimination (VCO2) may be used as a surrogate for pulmonary blood flow. As such, we can apply a novel use of volumetric capnography to assess hemodynamic stability in patients requiring extracorporeal membrane oxygenation (ECMO). We report our experience of pediatric patients requiring ECMO support who were monitored using volumetric capnography. We describe the use of VCO2 and its association with successful decannulation. This is a prospective observational study of pediatric patients requiring ECMO support at The Children's Hospital at Montefiore from 2017 to 2019. A Respironics NM3 monitor was applied to each patient. Demographics, hemodynamic data, blood gases, and VCO2 (mL/min) data were collected. Data were collected immediately prior to and after decannulation. Over the course of the study period, seven patients were included. Predecannulation VCO2 was higher among patients who were successfully decannulated than nonsurvivors (109 [35, 230] vs. 12.4 [7.6, 17.2] mL/min), though not statistically significant. Four patients (57%) survived without further mechanical support; two (29%) died, and one (14%) was decannulated to Berlin. Predecannulation VCO2 appears to correlate with hemodynamic stability following decannulation. This case series adds to the growing literature describing the use of volumetric capnography in critical care medicine, particularly pediatric patients requiring ECMO. Prospective studies are needed to further elucidate the use of volumetric capnography and optimal timing for ECMO decannulation.

Prediction and types of dead-space fraction during exercise in male chronic obstructive pulmonary disease patients

A high dead space (VD) to tidal volume (VT) ratio during peak exercise (VD/VTpeak) is a sensitive and consistent marker of gas exchange abnormalities; therefore, it is important in patients with chronic obstructive pulmonary disease (COPD). However, it is necessary to use invasive methods to obtain VD/VTpeak, as noninvasive methods, such as end-tidal PCO2 (PETCO2peak) and PETCO2 adjusted with Jones' equation (PJCO2peak) at peak exercise, have been reported to be inconsistent with arterial PCO2 at peak exercise (PaCO2peak). Hence, this study aimed to generate prediction equations for VD/VTpeak using statistical techniques, and to use PETCO2peak and PJCO2peak to calculate the corresponding VD/VTpeaks (i.e., VD/VTpeakETVD/VTpeakJ).A total of 46 male subjects diagnosed with COPD who underwent incremental cardiopulmonary exercise tests with PaCO2 measured via arterial catheterization were enrolled. Demographic data, blood laboratory tests, functional daily activities, chest radiography, two-dimensional echocardiography, and lung function tests were assessed.In multivariate analysis, diffusing capacity, vital capacity, mean inspiratory tidal flow, heart rate, and oxygen pulse at peak exercise were selected with a predictive power of 0.74. There were no significant differences in the PCO2peak values and the corresponding VD/VTpeak values across the three types (both p = NS).In subjects with COPD, VD/VTpeak can be estimated using statistical methods and the PETCO2peak and PJCO2peak. These methods may have similar predictive power and thus can be used in clinical practice.

Oxygenation Defects, Ventilatory Ratio, and Mechanical Power During Severe Pediatric Acute Respiratory Distress Syndrome: Longitudinal Time Sequence Analyses in a Single-Center Retrospective Cohort

OBJECTIVES

Our understanding of pediatric acute respiratory distress syndrome is based on information from studies reporting intermittent, serial respiratory data. We have analyzed a high-resolution, longitudinal dataset that incorporates measures of hypoxemia severity, metrics of lung mechanics, ventilatory ratio, and mechanical power and examined associations with survival after the onset of pediatric acute respiratory distress syndrome.

DESIGN

Single-center retrospective cohort, 2013-2018.

SETTING

Tertiary surgical/medical PICU.

PATIENTS

Seventy-six cases of severe pediatric acute respiratory distress syndrome, determined according to the Pediatric Acute Lung Injury Consensus Conference criteria.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The high-resolution database included continuous monitoring of ventilatory data (0.03 Hz) for up to 14 days after the diagnosis of pediatric acute respiratory distress syndrome or until extubation or death (n = 26). In the 12,128 hours of data during conventional mechanical ventilation, we used generalized estimating equations to compare groups, accounting for any effect of time. We identified an association between survival and faster rate of improvement in delta pressure (peak inspiratory pressure minus positive end-expiratory pressure; p = 0.028). Nonsurvival was associated with higher daily Pediatric Logistic Organ Dysfunction-2 scores (p = 0.005) and more severe hypoxemia metrics (p = 0.005). Mortality was also associated with the following respiratory/pulmonary metrics (mean difference [95% CI]): positive end-expiratory pressure level (+2.0 cm H2O [0.8-3.2 cm H2O]; p = 0.001), peak inspiratory pressure level (+3.0 cm H2O [0.5-5.5 cm H2O]; p = 0.022), respiratory rate (z scores +2.2 [0.9-3.6]; p = 0.003], ventilatory ratio (+0.41 [0.28-0.55]; p = 0.0001], and mechanical power (+5 Joules/min [1-10 Joules/min]; p = 0.013). Based on generalized linear mixed modeling, mechanical power remained associated with mortality after adjustment for normal respiratory rate, age, and daily Pediatric Logistic Organ Dysfunction-2 score (+3 Joules/breath [1-6 Joules/breath]; p = 0.009).

CONCLUSIONS

Mortality after severe pediatric acute respiratory distress syndrome is associated with the severity of organ dysfunction, oxygenation defects, and pulmonary metrics including dead space and theoretical mechanical energy load.

Twenty-four-hour mechanical power variation rate is associated with mortality among critically ill patients with acute respiratory failure: a retrospective cohort study

Objectives

Defined as the energy applied to the respiratory system by ventilator, mechanical power (MP) of ventilation reflects the risk of ventilation-induced lung injury. This study aims to explore the relationship between dynamic changes in MP and prognosis in critically ill patients.

Methods

This was a single-centre retrospective cohort study. Patients receiving mechanical ventilation with acute respiratory failure (ARF) and MP > 10 J/min on admission in the ICU were included. MP (J/min) was calculated as 0.098 × minute ventilation (L/min) × [(peak inspiratory pressure + positive end-expiratory pressure)/2] and the MP variation rate (%) as ([baseline MP − 24-h MP]/baseline MP) × 100. Patients were divided into two groups according to whether MP decreased 24 h after admission (MP-improved group defined as 24-h MP variation rate > 0% vs. MP-worsened group defined as 24-h MP variation rate ≤ 0%).

Results

In total, 14,463 patients were screened between January 2015 and June 2020, and finally, a study cohort of 602 patients was obtained. The MP-improved group had a lower ICU mortality rate than the MP-worsened group (24% vs. 36%; p = 0.005). The 24-h MP variation rate was associated with ICU mortality after adjusting for confounders (odds ratio, 0.906 [95% CI 0.833–0.985]; p = 0.021), while baseline MP (p = 0.909) and 24-h MP (p = 0.059) were not. All MP components improved in the MP-improved group, while minute ventilation and positive end-expiratory pressure contributed to the increase in MP in the MP-worsened group.

Conclusions

The 24-h MP variation rate was an independent risk factor for ICU mortality among ARF patients with elevated MP. Early decreases in MP may provide prognostic benefits in this population.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-021-01691-4.

Alveolar Dead-Space Fraction and Arterial Saturation Predict Postoperative Course in Fontan Patients

OBJECTIVES

Fontan surgery, the final surgical stage in single ventricle palliation, redirects systemic venous blood into the pulmonary circulation for gas exchange. A decrease in pulmonary blood flow can lead to major complications and grave outcomes. Alveolar dead-space fraction represents the portion of inhaled air that does not participate in gas exchange and hence quantifies ventilation-perfusion abnormalities in the lung. Increased alveolar dead-space fraction has been associated with prolonged mechanical ventilation and worse outcome after congenital heart surgery. The association of alveolar dead-space fraction with clinical outcomes in patients undergoing Fontan operation has not been reported.

INTERVENTIONS

None.

DESIGN, SETTING, AND PATIENTS

A retrospective charts review of all pediatric patients who underwent Fontan surgery during June 2010-November 2018 in a tertiary-care pediatric hospital. Associations between alveolar dead-space fraction and arterial oxyhemoglobin saturation to a composite outcome (surgical or catheter-based intervention, extracorporeal membrane oxygenation use, prolonged ventilation, prolonged hospital length of stay, or death) were explored. Secondary endpoints were parameters of severity of illness, chest drainage duration, and length of stay.

MEASUREMENTS AND MAIN RESULTS

Of 128 patients undergoing Fontan operation, 34 met criteria for composite outcome. Alveolar dead-space fraction was significantly higher in the composite (0.33 ± 0.14) versus control (0.25 ± 0.26; p = 0.016) group. Alveolar dead-space fraction greater than or equal to 0.29 indicated a 37% increase in risk to meet composite criteria. Admission arterial oxygen saturation was significantly lower in composite versus control group (93.4% vs 97.1%; p = 0.005). Alveolar dead-space fraction was significantly associated with increased durations of mechanical ventilation, ICU length of stay, duration of thoracic drainage, and parameters of severity of illness.

CONCLUSIONS

Alveolar dead-space fraction and arterial saturation may predict complicated postoperative course in patients undergoing the Fontan operation.

Biomarkers in pediatric acute respiratory distress syndrome

Pediatric acute respiratory distress syndrome (PARDS) is a heterogenous process resulting in a severe acute lung injury. A single indicator does not exist for PARDS diagnosis. Rather, current diagnosis requires a combination of clinical and physiologic variables. Similarly, there is little ability to predict the path of disease, identify those at high risk of poor outcomes or target therapies specific to the underlying pathophysiology. Biomarkers, a measured indicator of a pathologic state or response to intervention, have been studied in PARDS due to their potential in diagnosis, prognostication and measurement of therapeutic response. Additionally, PARDS biomarkers show great promise in furthering our understanding of specific subgroups or endotypes in this highly variable disease, and thereby predict which patients may benefit and which may be harmed by PARDS specific therapies. In this chapter, we review the what, when, why and how of biomarkers in PARDS and discuss future directions in this quickly changing landscape.

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.

Pulmonary Dead Space Fraction and Extubation Success in Children After Cardiac Surgery

OBJECTIVES

1) Determine the correlation between pulmonary dead space fraction and extubation success in postoperative pediatric cardiac patients; and 2) document the natural history of pulmonary dead space fractions, dynamic compliance, and airway resistance during the first 72 hours postoperatively in postoperative pediatric cardiac patients.

DESIGN

A retrospective chart review.

SETTING

Cardiac ICU in a quaternary care free-standing children's hospital.

PATIENTS

Twenty-nine with balanced single ventricle physiology, 61 with two ventricle physiology.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We collected data for all pediatric patients undergoing congenital cardiac surgery over a 14-month period during the first 72 hours postoperatively as well as prior to extubation. Overall, patients with successful extubations had lower preextubation dead space fractions and shorter lengths of stay. Single ventricle patients had higher initial postoperative and preextubation dead space fractions. Two-ventricle physiology patients had higher extubation failure rates if the preextubation dead space fraction was greater than 0.5, whereas single ventricle patients had similar extubation failure rates whether preextubation dead space fractions were less than or equal to 0.5 or greater than 0.5. Additionally, increasing initial dead space fraction values predicted prolonged mechanical ventilation times. Airway resistance and dynamic compliance were similar between those with successful extubations and those who failed.

CONCLUSIONS

Initial postoperative dead space fraction correlates with the length of mechanical ventilation in two ventricle patients but not in single ventricle patients. Lower preextubation dead space fractions are a strong predictor of successful extubation in two ventricle patients after cardiac surgery, but may not be as useful in single ventricle patients.

Measurement of Dead Space Fraction Upon ICU Admission Predicts Length of Stay and Clinical Outcomes Following Bidirectional Cavopulmonary Anastomosis

OBJECTIVES

Increased alveolar dead space fraction has been associated with prolonged mechanical ventilation and increased mortality in pediatric patients with respiratory failure. The association of alveolar dead space fraction with clinical outcomes in patients undergoing bidirectional cavopulmonary anastomosis for single ventricle congenital heart disease has not been reported. We describe an association of alveolar dead space fraction with postoperative outcomes in patients undergoing bidirectional cavopulmonary anastomosis.

DESIGN

In a retrospective case-control study, we examined for associations between alveolar dead space fraction ([PaCO2 - end-tidal CO2]/PaCO2), arterial oxyhemoglobin saturation, and transpulmonary gradient upon postoperative ICU admission with a composite primary outcome (requirement for surgical or catheter-based intervention, death, or transplant prior to hospital discharge, defining cases) and several secondary endpoints in infants following bidirectional cavopulmonary anastomosis.

SETTINGS

Cardiac ICU in a tertiary care pediatric hospital.

PATIENTS

Patients undergoing bidirectional cavopulmonary anastomosis at our institution between 2011 and 2016.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of 191 patients undergoing bidirectional cavopulmonary anastomosis, 28 patients were cases and 163 were controls. Alveolar dead space fraction was significantly higher in the case (0.26 ± 0.09) versus control group (0.17 ± 0.09; p < 0.001); alveolar dead space fraction at admission was less than 0.12 in 0% of cases and was greater than 0.28 in 35% of cases. Admission arterial oxyhemoglobin saturation was significantly lower in the case (77% ± 12%) versus control group (83% ± 9%; p < 0.05). Sensitivity and specificity for future case versus control assignment was best when prebidirectional cavopulmonary anastomosis risk factors, admission alveolar dead space fraction (AUC, 0.74), and arterial oxyhemoglobin saturation (AUC, 0.65) were combined in a summarial model (AUC, 0.83). For a given arterial oxyhemoglobin saturation, the odds of becoming a case increased on average by 181% for every 0.1 unit increase in alveolar dead space fraction. Admission alveolar dead space fraction and arterial oxyhemoglobin saturation were linearly associated with prolonged ICU length of stay, hospital length of stay, duration of mechanical ventilation, and duration of thoracic drainage (p < 0.001 for all).

CONCLUSIONS

Following bidirectional cavopulmonary anastomosis, alveolar dead space fraction in excess of 0.28 or arterial oxyhemoglobin saturation less than 78% upon ICU admission indicates an increased likelihood of requiring intervention prior to hospital discharge. Increasing alveolar dead space fraction and decreasing arterial oxyhemoglobin saturation are associated with increased lengths of stay.

Mechanical Ventilation and Decision Support in Pediatric Intensive Care

Respiratory support is required in most children in the pediatric intensive care unit. Decision-support tools (paper or electronic) have been shown to improve the quality of medical care, reduce errors, and improve outcomes. Computers can assist clinicians by standardizing descriptors and procedures, consistently performing calculations, incorporating complex rules with patient data, and capturing relevant data. This article discusses computer decision-support tools to assist clinicians in making flexible but consistent, evidence-based decisions for equivalent patient states.

Evaluating the Performance of the Pediatric Acute Lung Injury Consensus Conference Definition of Acute Respiratory Distress Syndrome

OBJECTIVE

The Pediatric Acute Lung Injury Consensus Conference has developed a pediatric-specific definition of acute respiratory distress syndrome, which is a significant departure from both the Berlin and American European Consensus Conference definitions. We sought to test the external validity and potential impact of the Pediatric Acute Lung Injury Consensus Conference definition by comparing the number of cases of acute respiratory distress syndrome and mortality rates among children admitted to a multidisciplinary PICU when classified by Pediatric Acute Lung Injury Consensus Conference, Berlin, and American European Consensus Conference criteria.

DESIGN

Retrospective cohort study.

SETTING

Tertiary care, university-affiliated PICU.

PATIENTS

All patients admitted between March 2009 and April 2013 who met inclusion criteria for acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of 4,764 patients admitted to the ICU, 278 (5.8%) met Pediatric Acute Lung Injury Consensus Conference pediatric acute respiratory distress syndrome criteria with a mortality rate of 22.7%. One hundred forty-three (32.2% mortality) met Berlin criteria, and 134 (30.6% mortality) met American European Consensus Conference criteria. All patients who met American European Consensus Conference criteria and 141 (98.6%) patients who met Berlin criteria also met Pediatric Acute Lung Injury Consensus Conference criteria. The 137 patients who met Pediatric Acute Lung Injury Consensus Conference but not Berlin criteria had an overall mortality rate of 13.1%, but 29 had severe acute respiratory distress syndrome with 31.0% mortality. At acute respiratory distress syndrome onset, there was minimal difference in mortality between mild or moderate acute respiratory distress syndrome by both Berlin (32.4% vs 25.0%, respectively) and Pediatric Acute Lung Injury Consensus Conference (16.7% vs 18.6%, respectively) criteria, but higher mortality for severe acute respiratory distress syndrome (Berlin, 43.6%; Pediatric Acute Lung Injury Consensus Conference, 37.0%). Twenty-four hours after acute respiratory distress syndrome onset, the presence of severe acute respiratory distress syndrome (using either Berlin or Pediatric Acute Lung Injury Consensus Conference) was associated with nearly 50% mortality.

CONCLUSIONS

Applying the Pediatric Acute Lung Injury Consensus Conference definition of acute respiratory distress syndrome has the potential to significantly increase the number of acute respiratory distress syndrome patients identified, with a lower overall mortality rate. However, severe acute respiratory distress syndrome is associated with extremely high mortality, particularly if present at 24 hours after initial diagnosis.

Comparing the Effect of Adaptive Support Ventilation (ASV) and Synchronized Intermittent Mandatory Ventilation (SIMV) on Respiratory Parameters in Neurosurgical ICU Patients

BACKGROUND

Various modes of mechanical ventilation have different effects on respiratory variables. Lack of patients' neuro-ventilatory coordination and increasing the work of breathing are major disadvantages in mechanically ventilated patients.

OBJECTIVES

This study is conducted to compare the respiratory parameters differences in Adaptive support ventilation (ASV) and synchronized intermittent mandatory ventilation (SIMV) modes in neurosurgical ICU patients.

METHODS

In a crossover study, patients under mechanical ventilation in neurosurgical ICU were enrolled. The patients alternatively experienced two types of ventilations for 30 minutes (adaptive support ventilation and synchronized intermittent mandatory ventilation). The respiratory parameters (tidal volume, respiratory rate, airway pressure, lung compliance, end-tidal carbon dioxide, peripheral oxygenation and respiratory dead space), hemodynamic variables, every 10 minutes and arterial blood gas analysis at the end of each 30 minutes were recorded. Results were compared and analyzed with SPSS v.19.

RESULTS

Sixty patients were involved in this study. In ASV mode, values including peak airway pressure (P-peak), end-tidal carbon dioxide (EtCO2), tidal volume and respiratory dead space were significantly lower than SIMV mode. Although the mean value for dynamic compliance had no significant difference in the two types of ventilation, it was better in ASV mode.

CONCLUSIONS

ASV mode compared with SIMV mode can lead to improve lung compliance and respiratory dead space.

Alveolar Dead Space Fraction Discriminates Mortality in Pediatric Acute Respiratory Distress Syndrome

OBJECTIVES

Physiologic dead space is associated with mortality in acute respiratory distress syndrome, but its measurement is cumbersome. Alveolar dead space fraction relies on the difference between arterial and end-tidal carbon dioxide (alveolar dead space fraction = (PaCO2 - PetCO2) / PaCO2). We aimed to assess the relationship between alveolar dead space fraction and mortality in a cohort of children meeting criteria for acute respiratory distress syndrome (both the Berlin 2012 and the American-European Consensus Conference 1994 acute lung injury) and pediatric acute respiratory distress syndrome (as defined by the Pediatric Acute Lung Injury Consensus Conference in 2015).

DESIGN

Secondary analysis of a prospective, observational cohort.

SETTING

Tertiary care, university affiliated PICU.

PATIENTS

Invasively ventilated children with pediatric acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of the 283 children with pediatric acute respiratory distress syndrome, 266 had available PetCO2. Alveolar dead space fraction was lower in survivors (median 0.13; interquartile range, 0.06-0.23) than nonsurvivors (0.31; 0.19-0.42; p < 0.001) at pediatric acute respiratory distress syndrome onset, but not 24 hours after (survivors 0.12 [0.06-0.18], nonsurvivors 0.14 [0.06-0.25], p = 0.430). Alveolar dead space fraction at pediatric acute respiratory distress syndrome onset discriminated mortality with an area under receiver operating characteristic curve of 0.76 (95% CI, 0.66-0.85; p < 0.001), better than either initial oxygenation index or PaO2/FIO2. In multivariate analysis, alveolar dead space fraction at pediatric acute respiratory distress syndrome onset was independently associated with mortality, after adjustment for severity of illness, immunocompromised status, and organ failures.

CONCLUSIONS

Alveolar dead space fraction at pediatric acute respiratory distress syndrome onset discriminates mortality and is independently associated with nonsurvival. Alveolar dead space fraction represents a single, useful, readily obtained clinical biomarker reflective of pulmonary and nonpulmonary variables associated with mortality.