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

Increased physiologic dead space fraction is associated with mortality after comprehensive stage 2 operation

OBJECTIVE

Our objective was to assess the predictive value of physiologic dead space fraction for mortality in patients undergoing the comprehensive stage 2 operation.

METHODS

This was a single-centre retrospective observational study conducted at a quaternary free-standing children's hospital specialising in hybrid palliation of single ventricle cardiac disease. 180 patients underwent the comprehensive stage 2 operation. 76 patients (42%) underwent early extubation, 59 (33%) standard extubation, and 45 (25%) delayed extubation. We measured time to extubation, post-operative outcomes, length of stay and utilised Fine gray models, Youden's J statistic, cumulative incidence function, and logistic regression to analyse outcomes.

RESULTS

Delayed extubation group suffered significantly higher rates of mortality (31.1% vs. 6.8%), cardiac arrest (40.0% vs. 10.2%), stroke (37.8% vs. 11.9%), and need for catheter (28.9% vs. 5.1%) and surgical intervention (24.4% vs. 8.5%) (P < 0.001). Physiologic dead space fraction was significantly higher in the delayed extubation group and in non-survivors with a value of 0.3, which was found to be the discriminatory point by Youden's J statistic. For a 0.1 unit increase in physiologic dead space fraction on post-operative day 1, the odds of a patient expiring increase by a factor of 2.26 (95% CI 1.41-3.97, p < 0.001) and by a factor of 3.79 (95% CI 1.65-11.7, p 0.01) on post-operative day 3.

CONCLUSIONS

Delayed extubation impacts morbidity and mortality in patients undergoing the comprehensive stage 2 operation. Increased physiologic dead space fraction in the first 60 hours after arrival to the ICU is associated with higher mortality.

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.

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.

The Use of Alveolar Dead Space Fraction to Predict Postoperative Outcomes after Pediatric Cardiac Surgery: A Retrospective Study

Patients with congenital heart disease (CHD) that have surgical repair with cardiopulmonary bypass (CPB) reflect a unique population with multiple pulmonary and systemic factors that may contribute to increased alveolar dead space and low cardiac output syndrome. This study aimed to assess and compare changes in the alveolar dead space fraction (AVDSf) in the immediate postoperative period with outcomes in children with CHD who underwent repair on CPB. A single-center retrospective review study of critically ill children with CHD, younger than 18 years of age admitted to the Pediatric Intensive Care Unit (PICU) after undergoing surgical repair on CPB and received invasive mechanical ventilation for at least 24 h. One hundred and two patients were included in the study. Over the first 24 h, mean AVDSf was significantly higher in patients who had longer hospital length of stay (LOS) (> 21 days) p = 0.02, and longer duration of invasive mechanical ventilation (DMV) (> 170 h) p = 0.01. Cross-sectional analyses at 23-24 h revealed that AVDSf > 0.25 predicts mortality and DMV (p = 0.03 and P = 0.02 respectively); however, it did not predict prolonged hospital LOS. For every 0.1 increase in the AVDSf, the odds of mortality, DMV, and hospital LOS increased by 4.9 [95% CI = 1.45-16.60, p = 0.002], 2.06 [95% CI = 1.14-3.71, p = 0.01], and 1.43[95% CI = 0.84-2.45, p = 0.184], respectively. The area under the ROC curve at 23-24 h for AVDSf was 0.868 to predict mortality as an outcome. AVDSf > 0.25 at 23-24 h postoperatively was an independent predictor of mortality with sensitivity and specificity of 83% and 80%, respectively and was superior to other commonly used surrogates of cardiac output. In the immediate postoperative period of pediatric patients with CHD, high AVDSf is associated with longer hospital length of stay and duration of invasive mechanical ventilation. Increased AVDSf values at 23-24 h postoperatively is associated with mortality in patients with CHD exposed to CPB.

Superior Cavopulmonary Connection: Its Physiology, Limitations, and Anesthetic Implications

The superior cavopulmonary connection (SCPC) or "bidirectional Glenn" is an integral, intermediate stage in palliation of single ventricle patients to the Fontan procedure. The procedure, normally performed at 3 to 6 months of life, increases effective pulmonary blood flow and reduces the ventricular volume load in patients with single ventricle (parallel circulation) physiology. While the SCPC, with or without additional sources of pulmonary blood flow, cannot be considered a long-term palliation strategy, there are a subset of patients who require SCPC palliation for a longer interval than the typical patient. In this article, we will review the physiology of SCPC, the consequences of prolonged SCPC palliation, and modes of failure. We will also discuss strategies to augment pulmonary blood flow in the presence of an SCPC. The anesthetic considerations in SCPC patients will also be discussed, as these patients may present for noncardiac surgery from infancy to adulthood.

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.

Atrial function in Fontan patients assessed by CMR: Relation with exercise capacity and long-term outcomes

OBJECTIVE

To assess the role of atrial function on exercise capacity and clinical events in Fontan patients.

DESIGN

We included 96 Fontan patients from 6 tertiary centers, aged 12.8 (IQR 10.1-15.6) years, who underwent cardiac magnetic resonance imaging and cardiopulmonary exercise testing within 12 months of each other from 2004 to 2017. Intra-atrial lateral tunnel (ILT) and extracardiac conduit (ECC) patients were matched 1:1 with regard to age, gender and dominant ventricle. The pulmonary venous atrium was manually segmented in all phases and slices. Atrial function was assessed by volume-time curves. Furthermore, atrial longitudinal and circumferential feature tracking strain was assessed. We determined the relation between atrial function and exercise capacity, assessed by peak oxygen uptake and VE/VCO₂ slope, and events (mortality, listing for transplant, re-intervention, arrhythmia) during follow-up.

RESULTS

Atrial maximal and minimal volumes did not differ between ILT and ECC patients. ECC patients had higher reservoir function (21.1 [16.4-28.0]% vs 18.2 [10.9-22.2]%, p = .03), lower conduit function and lower total circumferential strain (13.8 ± 5.1% vs 18.0 ± 8.7%, p = .01), compared to ILT patients. Only for ECC patients, a better late peak circumferential strain rate predicted better VE/VCO₂ slope. No other parameter of atrial function predicted peak oxygen uptake or VE/VCO₂ slope. During a median follow-up of 6.2 years, 42 patients reached the composite end-point. No atrial function parameters predicted events during follow-up.

CONCLUSIONS

ECC patients have higher atrial reservoir function and lower conduit function. Atrial function did not predict exercise capacity or events during follow-up.