Dead Space Fraction Research Articles

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

BackgroundThe end-tidal alveolar dead space fraction (AVDSf = [PaCO2−PETCO2]/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.MethodsRetrospective 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.ResultsThere 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).ConclusionsAVDSf 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.

965: THE ASSOCIATION BETWEEN VENTILATORY EFFICIENCY, A NONINVASIVE DEAD SPACE METRIC, AND MORTALITY

Introduction: Higher dead space is associated with increased mortality and prolonged mechanical ventilation in children and adults with acute respiratory distress syndrome (ARDS). Dead space assessment typically requires measurement of PCO2. Ventilatory efficiency (minute ventilation/VCO2) may be a useful non-invasive continuous dead space surrogate with prognostic value. Methods: Prospective observational cohort study. Mechanically ventilated children with ARDS were monitored with volumetric capnography. The first simultaneous measurements of ventilatory efficiency, physiologic dead space (VD/VT=[PCO2-PeCO2]/PCO2), the end-tidal alveolar dead space fraction (AVDSf=[PCO2-PETCO2]/PCO2), and oxygenation index (OI) within the first 72h of mechanical ventilation were used in the analysis. Results: There were 80 enrolled children. Median VD/VT was 0.46 (IQR 0.38, 0.58) and OI was 7.5 (IQR 4.6, 14.2). Mortality was 19%. The correlation between VD/VT and ventilatory efficiency (rs=0.68, p< 0.001) and VD/VT and AVDSf (rs=0.74, p< 0.001) were high. The correlation between AVDSf and ventilatory efficiency was lower (rs=0.48, p< 0.001). After controlling for OI and severity of illness (PRISM III) in separate multivariable models, higher VD/VT (per 0.1 increase, OR 1.66 [95% CI 1.04, 2.64], p=0.035), ventilatory efficiency (per 0.01, OR 1.69 [95% CI 1.10, 2.59], p=0.017), and AVDSf (per 0.1, OR 1.88 (95% CI 1.05, 3.38), p=0.035) were all associated with increased mortality. However, VD/VT, ventilatory efficiency, and AVDSf were not independently associated with fewer 28-day ventilator free days (VFD) or longer length of mechanical ventilation in survivors (LMV) after controlling for OI and PRISM III. OI was not associated with mortality after controlling for any of the dead space terms (all p>0.15) and PRISM III, but was independently associated with fewer 28-day VFDs (all p< 0.03) and longer LMV (all p< 0.01). Conclusions: Higher ventilatory efficiency, a continuous non-invasive measure of dead space that does not rely on blood gas measurement, is highly correlated with VD/VT and is independently associated with increased mortality in children with acute hypoxemic respiratory failure. Dead space metrics appear more strongly associated with mortality while OI appears more strongly associated with length of ventilation.

887: INFLUENCE OF INFLAMMATORY MARKERS AND ACUTE PHASE REACTANTS ON PULMONARY DEAD SPACE IN COVID-19 ARDS

Introduction: Ventilatory ratio (VR) is a bedside index of impaired ventilation that can be used as a surrogate marker for pulmonary dead space fraction (VD/VT). Vasculopathy is hypothesized to increase VD/VT in patients with acute respiratory distress syndrome (ARDS) due to COVID-19. The purpose of this study was to investigate associations between VR and markers of inflammation in critically ill COVID-ARDS patients. Methods: We conducted a retrospective study of patients admitted to an intensive care unit due to SARS-CoV-2 infection. All subjects required invasive mechanical ventilation and met the Berlin criteria for ARDS. Clinical lab values were collected at two timepoints: 2-8 hours after intubation (T1) and 2-24 hours before tracheostomy (T2). VR was split into high (VR>2) and low (VR< 2) groups. Comparisons were performed using student’s t, Mann-Whitney, and z tests for difference in proportions with ⍺=0.05. Results: Of the 139 subjects enrolled at T1, 67 (48%) had high VR (>2), with an overall mean VR of 2.08. High VR was significantly associated with leukocyte count (WBC) (13.3 vs. 10.6 x10^9/L, p=0.004), and platelet count (284 vs 248 x10^9/L, p=0.003). There was no association between VR status and procalcitonin (p=0.08), d-dimer (p=0.73), fibrinogen (p=0.38), CRP (p=0.22), and ferritin (p=0.33). Since certain markers had non-Gaussian distributions, we determined threshold values. D-dimer over 500 ng/mL was associated with higher VR (2.3 vs. 1.8, p=0.004) and procalcitonin over 0.5 ng/mL was moderately associated with higher VR (2.2 vs 1.9, p=0.052). CRP >181 μg/mL (the median) and ferritin values >1.5x the upper limit of normal were not associated with VR (p=0.30 and p=0.26, respectively). To enrich the dataset, we pooled data from T1 and T2 and treated each as an independent sample. In this pooled analysis, high VR was associated with higher platelet count (282 vs. 253, p=0.046), and higher procalcitonin (3.464 vs. 0.964, p=0.032). There were no significant associations with VR and d-dimer (p=0.88), fibrinogen (p=0.54), CRP (p=0.20), and ferritin (p=0.76) in the pooled data. Conclusions: Ventilatory ratio appears to be associated with higher levels of some inflammatory markers including WBC, platelets, d-dimer, and procalcitonin in COVID-ARDS patients.

Early decrease of ventilatory ratio after prone position ventilation may predict successful weaning in patients with acute respiratory distress syndrome: A retrospective cohort study.

Previous studies usually identified patients who benefit the most from prone positioning by oxygenation improvement. However, inconsistent results have been reported. Physiologically, pulmonary dead space fraction may be more appropriate in evaluating the prone response. As an easily calculated bedside index, ventilatory ratio (VR) correlates well with pulmonary dead space fraction. Hence, we investigated whether the change in VR after prone positioning is associated with weaning outcomes at day 28 and to identify patients who will benefit the most from prone positioning. This retrospective cohort study was performed in a group of mechanically ventilated, non-COVID ARDS patients who received prone positioning in the ICU at Zhongda hospital, Southeast University. The primary outcome was the rate of successful weaning patients at day 28. Arterial blood gas results and corresponding ventilatory parameters on five different time points around the first prone positioning were collected, retrospectively. VR responders were identified by Youden's index. Competing-risk regression models were used to identify the association between the VR change and liberation from mechanical ventilation at day 28. One hundred and three ARDS patients receiving prone positioning were included, of whom 53 (51%) successfully weaned from the ventilator at day 28. VR responders were defined as patients showing a decrease in VR of greater than or equal to 0.037 from the baseline to within 4 h after prone. VR responders have significant longer ventilator-free days, higher successful weaning rates and lower mortality compared with non-responders at day 28. And a significant between-group difference exists in the respiratory mechanics improvement after prone (P < 0.05). A linear relationship was also found between VR change and compliance of the respiratory system (Crs) change after prone (r = 0.32, P = 0.025). In the multivariable competing-risk analysis, VR change (sHR 0.57; 95% CI, 0.35-0.92) was independently associated with liberation from mechanical ventilation at day 28. Ventilatory ratio decreased more significantly within 4 h after prone positioning in patients with successful weaning at day 28. VR change was independently associated with liberation from mechanical ventilation at day 28.

Therapeutic Effects of Respiratory Muscle Training in Patients with Chronic Obstructive Pulmonary Disease

<h3>Research Objectives</h3> To investigate the improvement of cognition, lung function, clinical scores, and diaphragmatic muscle performance after respiratory muscle training in populations of chronic obstructive pulmonary disease (COPD) comorbid with mild cognitive impairment. <h3>Design</h3> This is a prospective randomized study with eight weeks of intervention. <h3>Setting</h3> Participants were recruited from a tertiary referral center, and they were instructed to perform training at home with telephonic supervision every week. <h3>Participants</h3> The inclusion criteria included: (1) a diagnosis of COPD, and (2) an mini mental state examination (MMSE) score between 23 and 27. The exclusion criteria were: (1) being unable to follow respiratory muscle training instructions or complete the questionnaires of our study due to cognitive impairment; (2) difficulty in completing cardiopulmonary exercise testing (CPET) due to high-risk cardiopulmonary diseases or orthopedic conditions; (3) a body mass index (BMI) of ≥30. Finally, 28 patients received both inspiratory and expiratory muscle training and 20 patients received inspiratory muscle training only. <h3>Interventions</h3> Participants were randomized into the full training (inspiratory plus expiratory muscle training) or the simple training group (inspiratory muscle training only) for a total of eight weeks. <h3>Main Outcome Measures</h3> Diaphragmatic thickness fraction and excursion examined through ultrasound; scores of MMSE, the COPD assessment test (CAT) and modified Medical Research Council (mMRC) scale; percentage of predicted FVC, FEV1, FEV1/FVC, DLCO, and DLCO/VA examined by pulmonary function test; dead space fraction (Vd/Vt) and minute ventilation to CO2 output (VE/VCO2) slope examined by CPET; and distance walked and changes in oxygen saturation and perceived exertion during six-minute walking test. <h3>Results</h3> Respiratory muscle training significantly improved the diaphragmatic thickness fraction and excursion, lung functions, MMSE, CAT and mMRC scores. The difference between the full training and simple training group was not significant. Patients with FEV1>30% had more improvement in diaphragmatic thickness than those with FEV1< 30%. <h3>Conclusions</h3> Expiratory muscle training could provide no further benefit to inspiratory muscle training. Additional study recruiting more patients with FEV< 30% could better validate our study results in clinical settings. <h3>Author(s) Disclosures</h3> Nothing to be disclosed.

Dead space fraction for treatment guidance and prognosis evaluation of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a common cause of critical illness and high mortality from respiratory failure. Increased dead space fraction (VD/VT) was independently associated with lung injury and mortality of ARDS. VD/VT is readily obtained by bedside measurements of arterial blood gas and end-tidal carbon dioxide. Early attention and application of VD/VT as an indicator will help to better understand the pathophysiological of ARDS, guide clinical treatment, and better assess the severity and clinical prognosis of the disease.

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

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. 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. 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 . 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.

Physiological response to prone positioning in intubated adults with COVID-19 acute respiratory distress syndrome: a retrospective study

BackgroundCOVID-19 related acute respiratory distress syndrome (ARDS) has specific characteristics compared to ARDS in other populations. Proning is recommended by analogy with other forms of ARDS, but few data are available regarding its physiological effects in this population. This study aimed to assess the effects of proning on oxygenation parameters (PaO2/FiO2 and alveolo-arterial gradient (Aa-gradient)), blood gas analysis, ventilatory ratio (VR), respiratory system compliance (CRS) and estimated dead space fraction (VD/VT HB). We also looked for variables associated with treatment failure.MethodsRetrospective monocentric study of intubated COVID-19 ARDS patients managed with an early intubation, low to moderate positive end-expiratory pressure and early proning strategy hospitalized from March 6 to April 30 2020. Blood gas analysis, PaO2/FiO2, Aa-gradient, VR, CRS and VD/VT HB were compared before and at the end of each proning session with paired t-tests or Wilcoxon tests (p < 0.05 considered as significant). Proportions were assessed using Fischer exact test or Chi square test.ResultsForty-two patients were included for a total of 191 proning sessions, median duration of 16 (5–36) hours. Considering all sessions, PaO2/FiO2 increased (180 [148–210] vs 107 [90–129] mmHg, p < 0.001) and Aa-gradient decreased (127 [92–176] vs 275 [211–334] mmHg, p < 0.001) with proning. CRS (36.2 [30.0–41.8] vs 32.2 [27.5–40.9] ml/cmH2O, p = 0.003), VR (2.4 [2.0–2.9] vs 2.3 [1.9–2.8], p = 0.028) and VD/VT HB (0.72 [0.67–0.76] vs 0.71 [0.65–0.76], p = 0.022) slightly increased. Considering the first proning session, PaO2/FiO2 increased (186 [165–215] vs 104 [94–126] mmHg, p < 0.001) and Aa-gradient decreased (121 [89–160] vs 276 [238–321] mmHg, p < 0.001), while CRS, VR and VD/VT HB were unchanged. Similar variations were observed during the subsequent proning sessions. Among the patients who experienced treatment failure (defined as ICU death or need for extracorporeal membrane oxygenation), fewer expressed a positive response in terms of oxygenation (defined as increase of more than 20% in PaO2/FiO2) to the first proning (67 vs 97%, p = 0.020).ConclusionProning in COVID-19 ARDS intubated patients led to an increase in PaO2/FiO2 and a decrease in Aa-gradient if we consider all the sessions together, the first one or the 4 subsequent sessions independently. When considering all sessions, CRS increased and VR and VD/VT HB only slightly increased.

Cardiorespiratory effects of different intraabdominal pressures in sheep: An experimental study.

Increased intraabdominal pressure (IAP) during laparoscopy can reduce venous return, but changes in respiratory system mechanics and their effect in left cardiac function are not well documented. This study evaluated the effects of different IAPs on respiratory mechanics and cardiac function in 10 healthy nonpregnant adult Santa Ines ewes randomly submitted to a crossover study using different IAPs: 0 mm Hg (G1), 10 mm Hg (G2), 12 mmHg (G3), and 15 mmHg (G4). Animals were anesthetized and mechanically ventilated (VT =15 ml/kg; positive end-expiratory pressure=3 cmH2 O; FiO2 =1.0). Pneumoperitoneum was induced by Hasson's trocar cannula. Variables were measured at INITIAL (IAP, 0 mmHg) and FINAL time points for each IAP after 1 h. At FINAL, driving airway pressure (ΔP,RS ), and percentage fraction of dead space (Vd/Vt) were higher in G3 and G4 than G1 (p=0.002, difference in means [MD] 4.60, 95% CI: 7.91-1.28, and p < 0.001, MD 5.4, 95% CI: 8.7-2.0; p=0.016, MD -9.5, 95% CI: -17.9 to -1.2; and p=0.027, MD -8.7, 95% CI: -17.1 to -0.4). The ejection fraction and fractional shortening were lower in G3 (p=0.039, MD -11.38, 95% CI: -0.07--22.68; p=0.015, MD -13.05, 95% CI: -1.74--24.36) and G4 (p=0.039, MD -9.94, 95% CI: -0.07 to -19.80; p=0.015, MD -11.43, 95%CI: -1.57 to -21.30, respectively) than G2. In G3, the maximum pulmonary flow velocity correlated negatively with ΔP,RS (r=-0.740; p=0.018), and Vd/Vt correlated positively with ΔP,RS (r=0.738, p=0.046). At IAP of 12 and 15 mm Hg impaired respiratory system mechanics, reduced left cardiac function and no change in maximum pulmonary artery flow velocity were detected. Therefore, respiratory mechanics should be monitored as an interplay to reduce left cardiac function.

Hierarchical stratification of the factors related to exertional dyspnoea and exercise intolerance in male COPD patients

Background The order and extent of interactions across the factors affecting exertional dyspnoea (ED) and exercise intolerance (EI) in patients with chronic obstructive pulmonary disease (COPD) are not clear. We hypothesized that lung and non-lung variables were the primary variables, ED was the secondary variable and EI was the tertiary variable. Methods Data on demographics, blood tests, cardiac imaging, lung function tests and invasive dead space fractions (VD/VT) during incremental exercise test of 46 male COPD subjects were obtained. These variables were categorized by factor analysis and pair-wise correlation analysis was conducted. The best factor of each category was selected and then multivariate regression was conducted. Results Peak tidal inspiratory flow (VT/TIpeak), VD/VTpeak and tidal lung expansion capability, and resting diffusing capacity of the lungs (DLCO)% predicted were the primary pulmonary factors most related to ED, whereas body mass index (BMI), haemoglobin and cholesterol levels were the primary non-pulmonary factors. In multivariate regression analysis, VT/TIpeak, VD/VTpeak and DLCO% were the primary factors most related to ED (r 2 = 0.69); ED was most related to EI (r = −0.74 to −0.83). Conclusion Using hierarchical stratification and statistical methods may improve understanding of the pathophysiology of ED and EI in patients with COPD. KEY MESSAGES The pathophysiology of exertional dyspnoea (ED) and exercise intolerance (EI) in chronic obstructive pulmonary disease (COPD) is complex. The order and extent of interactions across factors are not clear. In multivariate regression analysis, we found that tidal inspiratory flow, dead space fraction and resting diffusing capacity of the lungs % but not the non-pulmonary factors affected ED. Using correlation coefficients, we further found that ED was the secondary variable and EI was the tertiary variable. Hierarchical stratification of the important factors associated with ED and EI in patients with COPD clarifies their relationships and could be incorporated into management programmes and outcome studies for these patients.

Development and validation of a model to calculate anesthetic agent consumption from inspired and end-expired concentrations, minute ventilation, fresh gas flow and dead space ventilation.

Anesthetic agent consumption is often calculated as the product of fresh gas flow (FGF) and vaporizer dial setting (FVAP). Because FVAP of conventional vaporizers is not registered in automated anesthesia records, retrospective agent consumption studies are hampered. The current study examines how FVAP can be retrospectively calculated from the agent's inspired (FIN) and end-expired concentration (FET), FGF, and minute ventilation (MV). Theoretical analysis of agent mass balances in the circle breathing reveals FVAP = [FIN - (dead space fraction * FIN + (1 - dead space fraction) * FET) * (1 - FGF/MV)]/(1-(1 - FGF/MV)). FIN, FET, FGF and MV are routinely monitored, but dead space fraction is unknown. Dead space fraction for sevoflurane, desflurane, and isoflurane was therefore determined empirically from an unpublished data set of 161 patient containing FVAP, FIN, FET, MV and FGF ranging from 0.25 to 8 L/min delivered via an ADU® (GE, Madison, WI, USA). Dead space fraction for each agent was determined empirically by having Excel's solver function calculate the value of dead space fraction that minimized the sum of the squared differences between dialed FVAP and predicted FVAP. With dead space fraction known, the model was then prospectively tested for sevoflurane in O2/air using data collected over the course of two weeks with one FLOW-i (Getinge, Solna, Sweden) and one Zeus workstation (Dräger, Lübeck, Germany). Because both workstations use an electronically controlled vaporizer/injector, the dialed FVAP were available to allow the calculation of median performance error (MDPE) and median absolute performance error (MDAPE). MDPE and MDAP are reported as median and interquartiles. The empirical dead space fraction for isoflurane, sevoflurane, and desflurane were 0.59, 0.49, and 0.66, respectively. For prospective testing, a total of 149.4h of useful data were collected from 78 patient with the Zeus and Flow-i combined, with FGF ranging from 0.18 to 8 L/min. The model predicted dialed FVAP well, with a MDPE of -1 (-11, 6) % and MDAPE of 8 (4, 17) %. FVAP can be retrospectively calculated from FIN, FET, FGF, and MV plus an agent specific dead space fraction factor with a degree of error that we believe suffices for retrospective sevoflurane consumption analyses. Performance with other agents and N2O awaits further validation.

Vasculopathy and Increased Vascular Congestion in Fatal COVID-19 and Acute Respiratory Distress Syndrome.

Rationale: The leading cause of death in coronavirus disease 2019 (COVID-19) is severe pneumonia, with many patients developing acute respiratory distress syndrome (ARDS) and diffuse alveolar damage (DAD). Whether DAD in fatal COVID-19 is distinct from other causes of DAD remains unknown. Objective: To compare lung parenchymal and vascular alterations between patients with fatal COVID-19 pneumonia and other DAD-causing etiologies using a multidimensional approach. Methods: This autopsy cohort consisted of consecutive patients with COVID-19 pneumonia (n = 20) and with respiratory failure and histologic DAD (n = 21; non-COVID-19 viral and nonviral etiologies). Premortem chest computed tomography (CT) scans were evaluated for vascular changes. Postmortem lung tissues were compared using histopathological and computational analyses. Machine-learning-derived morphometric analysis of the microvasculature was performed, with a random forest classifier quantifying vascular congestion (CVasc) in different microscopic compartments. Respiratory mechanics and gas-exchange parameters were evaluated longitudinally in patients with ARDS. Measurements and Main Results: In premortem CT, patients with COVID-19 showed more dilated vasculature when all lung segments were evaluated (P = 0.001) compared with controls with DAD. Histopathology revealed vasculopathic changes, including hemangiomatosis-like changes (P = 0.043), thromboemboli (P = 0.0038), pulmonary infarcts (P = 0.047), and perivascular inflammation (P < 0.001). Generalized estimating equations revealed significant regional differences in the lung microarchitecture among all DAD-causing entities. COVID-19 showed a larger overall CVasc range (P = 0.002). Alveolar-septal congestion was associated with a significantly shorter time to death from symptom onset (P = 0.03), length of hospital stay (P = 0.02), and increased ventilatory ratio [an estimate for pulmonary dead space fraction (Vd); p = 0.043] in all cases of ARDS. Conclusions: Severe COVID-19 pneumonia is characterized by significant vasculopathy and aberrant alveolar-septal congestion. Our findings also highlight the role that vascular alterations may play in Vd and clinical outcomes in ARDS in general.

Correlation between dead space fraction and pulmonary ultrasound score in patients with acute respiratory distress syndrome and its prognostic value

To investigate the correlation between dead space fraction and lung ultrasound score (LUS) and their prognostic value in patients with acute respiratory distress syndrome (ARDS). The data of 98 patients with ARDS treated in the intensive care unit (ICU) of the First Affiliated Hospital of Jinzhou Medical University from January to December 2020 were collected and analyzed. The gender, age, acute physiology and chronic health evaluation II (APACHE II), oxygenation index, dead space fraction and LUS score immediately and 24, 48, 72 and 96 hours after ICU admission and 28-day outcomes of all patients were collected. Pearson correlation was used to analyze the correlation between dead space fraction and LUS score. Binary Logistic regression was performed to analyze whether the dead space fraction and LUS score could be the risk factors of the prognosis in patients with ARDS. Receiver operator characteristic curve (ROC) was used to analyze the predictive effect of dead space fraction and LUS score on 28-day mortality in patients with ARDS. A total of 98 patients with ARDS were included, of which 76 cases survived and 22 cases died within 28 days. With the prolongation of ICU stay, the dead space fraction and LUS score in the survival group increased first and then decreased. The dead space fraction and LUS score in the death group continued to increase to 96 hours, and were significantly higher than those in the survival group (dead space fraction: 0.569±0.019 vs. 0.491±0.021, LUS score: 20.09±2.39 vs. 15.13±1.91, both P < 0.05). There was a positive correlation between the dead space fraction and LUS score at 48, 72 and 96 hours in ICU (r values were 0.200, 0.471 and 0.677, all P < 0.05). Binary Logistic regression analysis showed that dead space fraction and LUS score were independent risk factors affecting the prognosis of patients with ARDS [dead space fraction: odds ratio (OR) was 69.064, 95% confidence interval (95%CI) was 22.680-123.499, P = 0.008; LUS score: OR was 4.790, 95%CI was 1.609-14.261, P = 0.005]. The results of ROC curve analysis showed that the dead space fraction at 48, 72 and 96 hours after ICU admission could be used to predict the 28-day mortality of patients with ARDS, the sensitivity was 59.1%, 90.9% and 95.5%, and the specificity was 89.5%, 80.3% and 98.7%. The area under the curve (AUC) of dead space fraction predicting 28-day mortality was 0.802, 0.952 and 0.998, all P < 0.01. The LUS score of 72 hours and 96 hours in ICU could be used to predict the 28-day mortality of patients with ARDS, the sensitivity was 77.3%, 77.3% and 100.0%, and the specificity was 68.4%, 88.2% and 80.3%, respectively. The AUC of the LUS score to predict the 28-day mortality of patients were 0.935 and 0.959, both P < 0.01. There was significant correlation between dead space fraction and LUS score, both of which were risk factors of 28-day mortality and be used to evaluate the 28-day prognosis of patients with ARDS.

Impairment in Preextubation Alveolar Gas Exchange Is Associated With Postextubation Respiratory Support Needs in Infants After Cardiac Surgery

OBJECTIVES:To determine if indices of alveolar gas exchange preextubation predict postextubation respiratory support needs as well as the need for escalation of therapies following infant cardiac surgery.DESIGN:Retrospective chart review.SETTING:Pediatric cardiac ICU in a quaternary-care teaching hospital.PATIENTS:Infants less than 1 year old who underwent biventricular repair from January 2015 to December 2017.INTERVENTIONS:None.MEASUREMENTS AND MAIN RESULTS:Preextubation alveolar-arterial gradient, oxygenation index, oxygen saturation index, Pao2/Fio2 ratio, and dead space ventilation (analyzed with both end-tidal carbon dioxide gradient and dead space fraction) were evaluated for each patient. All but dead space ventilation were associated with a higher level of noninvasive respiratory support immediately postextubation. Furthermore, impaired preextubation gas exchange was independently associated with escalation of respiratory support within the first 48-hour postextubation.CONCLUSIONS:Validated measures of alveolar gas exchange can be used as a tool to assess postextubation respiratory support needs including the risk of escalation of respiratory support in the first 48-hour postextubation. Prospective study with implementation of extubation guidelines, both for readiness and determination of early postextubation support, is needed to validate these findings.

Pulmonary Dead Space Fraction: A Predictive Factor for Transplant Suitability in Clinical Ex Vivo Lung Perfusion

<h3>Purpose</h3> Dead space fraction (DSF) correlates with disease severity in cases of pulmonary embolism (PE) and lung injury, and with mortality in acute respiratory distress syndrome. We sought to determine the relationship between DSF and donor lung transplant suitability during clinical ex vivo lung perfusion (EVLP). <h3>Methods</h3> DSF was calculated in 80 consecutive double lung cases undergoing acellular EVLP from 6/2019 to 8/2021 in our department. 53 cases were judged suitable for transplant. End-tidal CO₂ and CO₂ levels in perfusate were measured, and DSF stratified into quartiles (Q1, lowest; Q4, highest). DSF was calculated using the following formula: (PCO₂ in left atrium - End tidal CO₂) / PCO₂ in left atrium. <h3>Results</h3> Tobacco use history correlated with significantly higher DSF (vs. no tobacco use history, (<i>p</i> < 0.05). Presence of PE also correlated with higher DSF (<i>p</i> < 0.05). Lungs in the highest DSF quartile (Q4) displayed significantly higher peak airway pressure, lower PaO₂/FiO₂, and lower dynamic compliance during EVLP (<i>p</i> < 0.01, each; <b>Figure A-D</b>). The Q4 DSF group also had higher lung weight following EVLP (<i>p</i> < 0.05). Transplant suitability decreased with higher DSF; 85% (17/20 cases) of Q1, 85% (17/20 cases) of Q2, 60% (12/20 cases) of Q3, and 35% (7/20 cases) of Q4 (<i>p</i> < 0.01, <b>Figure E</b>) lungs were suitable for transplant. Of the 53 EVLP cases transplanted, 30-day recipient survival was 98% and the incidence of Grades 0, 1, 2, and 3 primary graft dysfunction at 72 hours was 19%, 57%, 13%, and 6%, respectively with 3 ungradable cases. <h3>Conclusion</h3> In human lungs undergoing acellular EVLP, higher DSF correlates with decreased transplant suitability. Further studies are needed to establish mechanisms by which high DSF contributes to lower transplant suitability.

The Association Between Alveolar Dead Space Fraction and Mortality in Pediatric Acute Respiratory Distress Syndrome: A Prospective Cohort Study.

BackgroundAlveolar dead-space fraction (AVDSF), the volume of alveolar gas that does not participate in gas exchange, has been reported to predict mortality and morbidity in adults with acute respiratory distress syndrome (ARDS). This study aims to characterize AVDSF in patients with pediatric ARDS (PARDS), to determine its association with clinical outcomes and examine the validity of a previously studied cutoff (AVDSF > 0.25).MethodsThis was a prospective cohort study performed in the setting of a lung protective mechanical ventilation protocol. AVDSF was calculated by the equation: AVDSF = [partial pressure of arterial carbon dioxide (PaCO2) – end tidal carbon dioxide (etCO2)]/PaCO2. Receiver operating curve and Youden index were used to identify an AVDSF cutoff associated with mortality, which characterized “high or low AVDSF” groups. Correlation between AVDSF and clinical indices of severity were determined [including daily oxygenation index (OI), admission Pediatric Index of Mortality 2 (PIM 2) and Pediatric Logistic Organ Dysfunction (PELOD) scores]. The primary outcome, mortality in PARDS patients, was compared between the high and low AVDSF groups and analyzed in a multivariable logistic regression adjusting for inotrope use and PIM 2 score. Secondary outcomes included 28-day ventilator-free (VFD) and intensive care unit-free (IFD) days.ResultsSixty-nine PARDS patients with a median (interquartile range) age of 4.5 (0.8, 10.6) years were included in this analysis. Daily AVDSF correlated with daily OI (R2 = 0.10; p < 0.001). Mean AVDSF over the first 7 days of PARDS correlated with PIM 2 (R2 = 0.10; p = 0.010) and PELOD (R2 = 0.12; p = 0.004) scores. The greatest area under the curve identified an AVDSF cutoff of 0.22, which was close to the previously suggested 0.25. The high AVDSF group had higher mortality [7/19 (36.8%) vs. 5/50 (10.0%); p = 0.009] and lower VFD [2 (0, 18) vs. 21 (15, 24); p = 0.007] and IFD [0 (0, 16) vs. 16 (5, 21); p = 0.013]. In the multivariable model, being in the high AVDSF group [adjusted odds ratio 4.67 (95% CI: 1.12, 19.39)] was significantly associated with mortality.ConclusionsHigh AVDSF was independently associated with increased mortality and decreased VFD and IFD. AVDSF may be complementary to oxygenation indices in risk stratifying PARDS and warrant further study.

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.

Neural respiratory drive in chronic thromboembolic pulmonary hypertension: Effect of balloon pulmonary angioplasty

Excessive ventilation (V̇E) during exercise, ascribed to heightened neural ventilatory drive and/or to increased “wasted” ventilation, is a feature of chronic thromboembolic pulmonary hypertension (CTEPH). In selected CTEPH patients, balloon pulmonary angioplasty (BPA) allows near-normalization of resting haemodynamic parameters but does not allow excess exercise hyperventilation to normalize. Neural ventilatory drive can be estimated by studying how arterial PCO2 (PaCO2), end-tidal PCO2 (PETCO2), V̇E and CO2 output (V̇CO2) change across the exercise-to-recovery transition during a cardiopulmonary exercise test. Increased “wasted” ventilation can be quantified by the physiological dead space fraction of tidal volume (VD/VT) calculated with the Enghoff simplification of the Bohr equation. These measurements were made before and after BPA in 22 CTEPH patients without significant cardiac and/or pulmonary comorbidities. Our observations suggest that before BPA, excessive hyperventilation was secondary to both heightened neural ventilatory drive and increased “wasted” ventilation; after BPA, measurements made across the exercise-to-recovery transition suggest that heightened neural ventilatory drive was no longer present.

Expiratory high-frequency percussive ventilation: a novel concept for improving gas exchange

BackgroundAlthough high-frequency percussive ventilation (HFPV) improves gas exchange, concerns remain about tissue overdistension caused by the oscillations and consequent lung damage. We compared a modified percussive ventilation modality created by superimposing high-frequency oscillations to the conventional ventilation waveform during expiration only (eHFPV) with conventional mechanical ventilation (CMV) and standard HFPV.MethodsHypoxia and hypercapnia were induced by decreasing the frequency of CMV in New Zealand White rabbits (n = 10). Following steady-state CMV periods, percussive modalities with oscillations randomly introduced to the entire breathing cycle (HFPV) or to the expiratory phase alone (eHFPV) with varying amplitudes (2 or 4 cmH2O) and frequencies were used (5 or 10 Hz). The arterial partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2) were determined. Volumetric capnography was used to evaluate the ventilation dead space fraction, phase 2 slope, and minute elimination of CO2. Respiratory mechanics were characterized by forced oscillations.ResultsThe use of eHFPV with 5 Hz superimposed oscillation frequency and an amplitude of 4 cmH2O enhanced gas exchange similar to those observed after HFPV. These improvements in PaO2 (47.3 ± 5.5 vs. 58.6 ± 7.2 mmHg) and PaCO2 (54.7 ± 2.3 vs. 50.1 ± 2.9 mmHg) were associated with lower ventilation dead space and capnogram phase 2 slope, as well as enhanced minute CO2 elimination without altering respiratory mechanics.ConclusionsThese findings demonstrated improved gas exchange using eHFPV as a novel mechanical ventilation modality that combines the benefits of conventional and small-amplitude high-frequency oscillatory ventilation, owing to improved longitudinal gas transport rather than increased lung surface area available for gas exchange.

Effects of an open lung ventilatory strategy on lung gas exchange during laparoscopic surgery.

In general anaesthesia, early collapse of poorly ventilated lung segments with low alveolar ventilation-perfusion ratios occurs and may lead to postoperative pulmonary complications after abdominal surgery. An 'open lung' ventilation strategy involves lung recruitment followed by 'individualised' positive end-expiratory pressure titrated to maintain recruitment of low alveolar ventilation-perfusion ratio lung segments. There are limited data in laparoscopic surgery on the effects of this on pulmonary gas exchange. Forty laparoscopic bowel surgery patients were randomly assigned to standard ventilation or an 'open lung' ventilation intervention, with end-tidal target sevoflurane of 1% supplemented by propofol infusion. After peritoneal insufflation, stepped lung recruitment was performed in the intervention group followed by maintenance positive end-expiratory pressure of 12-15 cmH2O adjusted to maintain dynamic lung compliance at post-recruitment levels. Baseline gas and blood samples were taken and repeated after a minimum of 30 minutes for oxygen and carbon dioxide and for sevoflurane partial pressures using headspace equilibration. The sevoflurane arterial/alveolar partial pressure ratio and alveolar deadspace fraction were unchanged from baseline and remained similar between groups (mean (standard deviation) control group = 0.754 (0.086) versus intervention group = 0.785 (0.099), P = 0.319), while the arterial oxygen partial pressure/fractional inspired oxygen concentration ratio was significantly higher in the intervention group at the second timepoint (control group median (interquartile range) 288 (234-372) versus 376 (297-470) mmHg in the intervention group, P = 0.011). There was no difference between groups in the sevoflurane consumption rate. The efficiency of sevoflurane uptake is not improved by open lung ventilation in laparoscopy, despite improved arterial oxygenation associated with effective and sustained recruitment of low alveolar ventilation-perfusion ratio lung segments.