Accurate measurement of oxygen consumption in children undergoing cardiac catheterization

Cardiac Output Estimation in the Intensive Care Unit

BACKGROUND

Cardiac output (CO) is a quintessential property of the cardiovascular system, one whose estimation is vital to patient care in critical illness. The most common techniques for assessing CO, thermodilution (TD) and the estimated Fick (eFick) approximation, force tradeoffs that motivate a need for new methods.

OBJECTIVES

The purpose of this study was to novel CO estimators to fill key gaps in critical care medicine.

METHODS

Machine learning was used to estimate CO from physiology measurements made during routine clinical care in the intensive care unit (ICU) or cardiac catheterization lab. Models were trained and validated using a curated set of 13,172 ground-truth measurements of TD-CO from 4,825 patients. Model performance was evaluated using regression metrics, trajectory analysis, classification accuracy, and ΔCO tracking.

RESULTS

Three established eFick models all performed poorly in the ICU because their static estimates of oxygen consumption could not track the dynamics of critical illness. In the postcardiac surgery intensive care unit, the best eFick model erred in its CO predictions by 30% (mean absolute percentage error [MAPE]) with a coefficient of determination (R2) of -1.5. The best model derived here, labeled CORE (Catheter Optimized caRdiac output Estimation), predicted CO with an MAPE of 14% (P < 0.001 vs eFick) and an R2 of 0.58. These estimates could be calculated from measurements obtained with either a pulmonary artery catheter or a central venous catheter. The CORE model was also robust to the presence of moderate or severe tricuspid regurgitation, achieving an MAPE of 16% and R2 of 0.65 relative to a ground-truth determined by the direct Fick technique with measured oxygen consumption.

CONCLUSIONS

CO models that account for dynamic physiology in ICU patients were more accurate than widely used eFick models and more versatile than TD. The performance of these models combined with their adaptation to vascular access, broad applicability, ease of use, and ease of deployment should enable them to benefit patients across diverse ICU settings.

Oxygen Delivery During Cardiopulmonary Bypass in Pediatric Patients With Congenital Heart Disease: Association With Postoperative Acute Kidney Injury

OBJECTIVE

This study was designed to investigate the distribution of nadir oxygen delivery (DO2), mean DO2, and area under ideal DO2 (AUiDO2) among categorized age groups of pediatric patients and their associations with postoperative cardiac surgery-associated (CSA) acute kidney injury (AKI) and clinical outcomes.

DESIGN

Retrospective cohort study.

SETTING

A tertiary teaching hospital.

PARTICIPANTS

Patients aged <15 years with congenital heart disease who underwent cardiac surgery between May 2018 and May 2022.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Nadir DO2, mean DO2, and AUiDO2 were defined as the lowest DO2, average DO2, and dose of decrement combining the intensity and duration of DO2 less than the calculated ideal DO2, respectively. The primary outcome was CSA-AKI occurrence within 48 hours postoperatively. Secondary outcomes included maximum serum lactate levels (Lacmax) for the first 24 hours after pediatric cardiac intensive care unit admission. Of 479 patients, 147 (30.7%) developed AKI. Nadir DO2 and AUiDO2 were not significantly different between patients with CSA-AKI and those without CSA-AKI (p = 0.115 and p = 0.12, respectively). However, the mean DO2 was significantly higher in patients with CSA-AKI (p = 0.025). After adjusting for potential confounders, no significant differences were observed in the odds for CSA-AKI based on increments in nadir DO2, mean DO2, or AUiDO2. In contrast, nadir DO2 and mean DO2 were significantly associated with Lacmax in both univariate and multivariable regression analyses.

CONCLUSION

DO2-related values during cardiopulmonary bypass were not associated with CSA-AKI in pediatric patients with congenital heart disease. However, nadir DO2 and mean DO2 were significantly associated with postoperative serum lactate levels.

Measured Oxygen Consumption During Pediatric Cardiac Catheterization is More Accurate than Assumed Oxygen Consumption

When calculating cardiac index (C.I.) by the Fick method, oxygen consumption (VO2) is often unknown, so assumed values are typically used. This practice introduces a known source of inaccuracy into the calculation. Using a measured VO2 (mVO2) from the CARESCAPE E-sCAiOVX module provides an alternative that may improve accuracy of C.I. calculations. Our aim is to validate this measurement in a general pediatric catheterization population and compare its accuracy with assumed VO2 (aVO2). mVO2 was recorded for all patients undergoing cardiac catheterization with general anesthesia and controlled ventilation during the study period. mVO2 was compared to the reference VO2 (refVO2) determined by the reverse Fick method using cardiac MRI (cMRI) or thermodilution (TD) as a reference standard for measurement of C.I. when available. 193 VO2 measurements were obtained, including 71 with a corresponding cMRI or TD measure of cardiac index for validation. mVO2 demonstrated satisfactory concordance and correlation with the TD- or cMRI-derived refVO2 (ρc = 0.73, r2 = 0.63) with a mean bias of - 3.2% (SD ± 17.3%). Assumed VO2 demonstrated much weaker concordance and correlation with refVO2 (ρc = 0.28, r2 = 0.31) with a mean bias of + 27.5% (SD ± 30.0%). Subgroup analysis of patients < 36 months of age demonstrated that error in mVO2 was not significantly different from that observed in older patients. Many previously reported prediction models for assuming VO2 performed poorly in this younger age range. Measured oxygen consumption using the E-sCAiOVX module is significantly more accurate than assumed VO2 when compared to TD- or cMRI-derived VO2 in a pediatric catheterization lab.

Associations of systemic oxygen consumption with age and body temperature under general anesthesia: retrospective cohort study

BACKGROUND

Body temperature (BT) is thought to have associations with oxygen consumption (VO2). However, there have been few studies in which the association between systemic VO2 and BT in humans was investigated in a wide range of BTs. The aims of this study were 1) to determine the association between VO2 and age and 2) to determine the association between VO2 and BT.

METHODS

This study was a retrospective study of patients who underwent surgery under general anesthesia at a tertiary teaching hospital. VO2 was measured by the Dräger Perseus A500 anesthesia workstation (Dräger Medical, Lubeck, Germany). The associations of VO2 with age and BT were examined using spline regression and multivariable regression analysis with a random effect.

RESULTS

A total of 7,567 cases were included in this study. A linear spline with one knot shows that VO2 was reduced by 2.1 ml/kg/min with one year of age (p < 0.001) among patients less than 18 years of age and that there was no significant change in VO2 among patients 18 years of age or older (estimate: 0.014 ml/kg/min, p = 0.08). VO2 in all bands of BT < 36.0 °C was not significantly different from VO2 in BT >  = 36 °C and < 36.5 °C. Multivariable linear regression analysis showed that compared with VO2 in BT >  = 36 °C and < 36.5 °C as a reference, VO2 levels were significantly higher by 0.57 ml/kg/min in BT >  = 36.5 °C and < 37 °C (p < 0.001), by 1.8 ml/kg/min in BT >  = 37 °C and < 37.5 °C (p < 0.001), by 3.6 ml/kg/min in BT >  = 37.5 °C and < 38 °C (p < 0.001), by 4.9 ml/kg/min in BT >  = 38 °C and < 38.5 °C (p < 0.001), and by 5.7 ml/kg/min in BT >  = 38.5 °C (p < 0.001). The associations between VO2 and BT were significantly different among categorized age groups (p = 0.03).

CONCLUSIONS

VO2 increases in parallel with increase in body temperature in a hyperthermic state but remains constant in a hypothermic state. Neonates and infants, who have high VO2, may have a large systemic organ response in VO2 to change in BT.

Hypoxemia in Young Children Undergoing One-lung Ventilation: A Retrospective Cohort Study

BACKGROUND

One-lung ventilation in children remains a specialized practice with low case numbers even at tertiary centers, preventing an assessment of best practices. The authors hypothesized that certain case factors may be associated with a higher risk of intraprocedural hypoxemia in children undergoing thoracic surgery and one-lung ventilation.

METHODS

The Multicenter Perioperative Outcomes database and a local quality improvement database were queried for documentation of one-lung ventilation in children 2 months to 3 yr of age inclusive between 2010 and 2020. Patients undergoing vascular or other cardiac procedures were excluded. All records were reviewed electronically for the presence of hypoxemia, oxygen saturation measured by pulse oximetry (Spo2) less than 90% for 3 min or more continuously, and severe hypoxemia, Spo2 less than 90% for 5 min or more continuously during one-lung ventilation. Records were also assessed for hypercarbia, end-tidal CO2 greater than 60 mmHg for 5 min or more or a Paco2 greater than 60 on arterial blood gas. Covariates assessed for association with these outcomes included age, weight, American Society of Anesthesiologists (Schaumburg, Illinois) Physical Status 3 or greater, duration of one-lung ventilation, preoperative Spo2 less than 98%, bronchial blocker versus endobronchial intubation, left operative side, video-assisted thoracoscopic surgery, lower tidal volume ventilation (tidal volume less than or equal to 6 ml/kg plus positive end expiratory pressure greater than or equal to 4 cm H2O for more than 80% of the duration of one-lung ventilation), and type of procedure.

RESULTS

Three hundred six cases from 15 institutions were included for analysis. Hypoxemia and severe hypoxemia occurred in 81 of 306 (26%) patients and 56 of 306 (18%), respectively. Hypercarbia occurred in 153 of 306 (50%). Factors associated with lower risk of hypoxemia in multivariable analysis included left operative side (odds ratio, 0.45 [95% CI, 0.251 to 0.78]) and bronchial blocker use (odds ratio, 0.351 [95% CI, 0.177 to 0.67]). Additionally, use of a bronchial blocker was associated with a reduced risk of severe hypoxemia (odds ratio, 0.290 [95% CI, 0.125 to 0.62]).

CONCLUSIONS

Use of a bronchial blocker was associated with a lower risk of hypoxemia in young children undergoing one-lung ventilation.

EDITOR’S PERSPECTIVE

Anesthesia Management for Pediatrics with Congenital Heart Diseases Who Undergo Cardiac Catheterization in China

Objectives

The goal of this study was to summarize anesthesia management for pediatrics with congenital heart diseases who undergo cardiac catheterization procedure in China.

Methods

The relevant articles were identified through computerized searches in the CNKI, Wanfang, VIP, and PubMed databases through May 2020, using different combinations of keywords: “congenital heart diseases,” “pediatric,” “children,” “anesthesia,” “cardiac catheterization,” “interventional therapy,” “interventional treatment,” “interventional examination,” and “computed tomography.”

Results

The database searches identified 48 potentially qualified articles, of which 25 (9,738 patients in total) were determined to be eligible and included. The authors collect data from the article information. Anesthesia methods included endotracheal intubation or laryngeal mask ventilation general anesthesia, monitored anesthesia care, and combined with sacral canal block. Anesthesia-related complications occurred in 7.41% of the patients and included dysphoria, respiratory depression, nausea, vomiting, cough, increased respiratory secretion, and airway obstruction. The incidence of procedure-related complications was 12.14%, of which the most common were arrhythmia and hypotension.

Conclusions

For pediatric patients with congenital heart diseases who undergo cardiac catheterization procedures in China, arrhythmia and hypotension are the most common procedure-related complications. Monitored anesthesia care is the commonly used anesthesia methods, and dysphoria, cough, nausea, vomiting, and respiratory depression are frequent complications associated with anesthesia.

A Device for the Quantification of Oxygen Consumption and Caloric Expenditure in the Neonatal Range

BACKGROUND

The accurate measurement of oxygen consumption (VO2) and energy expenditure (EE) may be helpful to optimize the treatment of critically ill patients. However, current techniques are limited in their ability to accurately quantify these end points in infants due to a low VO2, low tidal volume, and rapid respiratory rate. This study describes and validates a new device intended to perform in this size range.

METHODS

We created a customized device that quantifies inspiratory volume using a pneumotachometer and concentrations of oxygen and carbon dioxide gas in the inspiratory and expiratory limbs. We created a customized algorithm to achieve precise time alignment of these measures, incorporating bias flow and compliance factors. The device was validated in 3 ways. First, we infused a certified gas mixture (50% oxygen/50% carbon dioxide) into an artificial lung circuit, comparing measured with simulated VO2 and carbon dioxide production (VCO2) within a matrix of varying tidal volume (4-20 mL), respiratory rate (20-80 bpm), and fraction of inspired oxygen (0.21-0.8). Second, VO2, VCO2, and EE were measured in Sprague Dawley rats under mechanical ventilation and were compared to simultaneous Douglas bag collections. Third, the device was studied on n = 14 intubated, spontaneously breathing neonates and infants, comparing measured values to Douglas measurements. In all cases, we assessed for difference between the device and reference standard by linear regression and Bland-Altman analysis.

RESULTS

In vitro, the mean ± standard deviation difference between the measured and reference standard VO2 was +0.04 ± 1.10 (95% limits of agreement, -2.11 to +2.20) mL/min and VCO2 was +0.26 ± 0.31 (-0.36 to +0.89) mL/min; differences were similar at each respiratory rate and tidal volume measured, but higher at fraction of inspired oxygen of 0.8 than at 0.7 or lower. In rodents, the mean difference was -0.20 ± 0.55 (-1.28 to +0.89) mL/min for VO2, +0.16 ± 0.25 (-0.32 to +0.65) mL/min for VCO2, and -0.84 ± 3.29 (-7.30 to +5.61) kcal/d for EE. In infants, the mean VO2 was 9.0 ± 2.5 mL/kg/min by Douglas method and was accurately measured by the device (bias, +0.22 ± 0.87 [-1.49 to +1.93] mL/kg/min). The average VCO2 was 8.1 ± 2.3 mL/kg/min, and the device exhibited a bias of +0.33 ± 0.82 (-1.27 to +1.94) mL/kg/min. Mean bias was +2.56% ± 11.60% of the reading for VO2 and +4.25% ± 11.20% of the reading for VCO2; among 56 replicates, 6 measurements fell outside of the 20% error range, and no patient had >1 of 4 replicates with a >20% error in either VO2 or VCO2.

CONCLUSIONS

This device can measure VO2, VCO2, and EE with sufficient accuracy for clinical decision-making within the neonatal and pediatric size range, including in the setting of tachypnea or hyperoxia.

Evolution of the concept of oxygen transport in the critically ill, with a focus on children after cardiopulmonary bypass

The concept of oxygen transport, defined as the relation between oxygen consumption (VO2) and delivery (DO2), is of fundamental importance in critically ill patients. The past 200 years have witnessed a stepwise progressive improvement in the understanding of pathophysiological disturbances in the balance of DO2 and VO2 in critically ill patients including those after cardiopulmonary bypass surgery. Intermittent spectacular technological achievements have accelerated the rate of progress. Therapeutic advances have been particularly impressive during the recent decades. Examination of the relation between DO2 and VO2 provides a useful framework around which the care of the critically ill may be developed. Until now, only a few groups have used this framework to examine children after cardiopulmonary bypass. The key topics that will be covered in this review article are the evolution of the concept from its early development to its present, increasingly sophisticated, role in the management of critically ill patients, with a focus on children after cardiopulmonary bypass surgery.

Inaccuracy of a continuous arterial pressure waveform monitor when used for congenital cardiac catheterization

OBJECTIVE

To determine the accuracy of a continuous cardiac output monitor (FloTrac sensor) for measuring cardiac index in children with congenital heart disease undergoing cardiac catheterization. Cardiac index is a critical hemodynamic parameter measured during catheterizations in children with congenital heart disease. This has been challenging to measure accurately and many clinicians rely on predictive equations for calculating cardiac index.

DESIGN

Prospective, nonrandomized trial.

SETTING

Tertiary care congenital heart center.

PATIENTS

Consecutive participants ≤18 years old undergoing clinically indicated cardiac catheterizations from September 2014 through August 2015.

INTERVENTIONS

Oxygen consumption was measured using the Vmax Encore 229 monitor attached to the ventilator circuit. The FloTrac transducer with third generation software was connected to a pigtail catheter in the descending aorta and cardiac index was obtained.

OUTCOME MEASURES

Cardiac index by the Fick equation using measured oxygen consumption was compared to cardiac index from the FloTrac sensor using paired t-test and Bland-Altman analysis.

RESULTS

39 participants (median age 5.1 years, 1.5-18.3, 64% female) were studied. Cardiac index by FloTrac was higher than cardiac index by Fick (6.4 ± 3.4 vs 3.7 ± 1.2 L/min/m² , P < .001). Bland-Altman analysis showed a consistent overestimation of cardiac index by FloTrac which worsened as cardiac index increased (mean bias 2.7 L/min/m² , 95% limits of agreement -4.2, 9.5).

CONCLUSIONS

The results of this study show that the FloTrac sensor provides cardiac index measures which are not accurate enough to justify use in children with congenital heart disease undergoing catheterization. Further studies may allow for modifications of the algorithms to obtain more accurate cardiac index in this population.

Bone-Specific Alkaline Phosphatase in Patients Who Have Undergone the Fontan Operation

Bone-specific alkaline phosphatase (BALP) is produced by osteoblasts. A recent series noted a positive association between cardiac index (CI) and BALP in patients with Fontan circulation. CI is low at baseline in these patients, and small decreases in CI may result in diverting of blood away from bone. We prospectively enrolled 15 patients (males ≤ 14 yo, females ≤ 12 yo) who had previously undergone Fontan operation and were undergoing cardiac catheterization. Serum BALP was measured at catheterization, and analysis performed to evaluate association between age-/gender-specific BALP z-score and CI as well as other patient variables. The median age at catheterization was 5.6 years (3.1-13.1), and time from Fontan was 1.5 years (0.1-12.1). The median superior vena cava saturation (SVC) was 65 % (52-74), median average between SVC and inferior vena cava (IVC) saturations was 62.5 % (51-70), and median CI was 3.8 L/min/m(2) (2.0-8.4). The median BALP was 65 IU/L and BALP z-score was -2.1 (-3.2 to 0.9). BALP z-score was not associated with CI (ρ = -0.1, p = 0.7), but a positive correlation was noted with the average of SVC and IVC saturation (ρ = 0.5, p = 0.052) and with SVC saturation (ρ = 0.4, p = 0.07), both nearly reaching statistical significance. In our cohort of children with Fontan circulation undergoing catheterization, BALP z-score was not associated with CI, but an association with estimates of mixed venous saturation was noted that nearly reached statistical significance. We hypothesize that BALP is a marker of oxygen delivery in those with Fontan circulation and may represent a valuable biomarker in this population.

Diagnostic Cardiac Catheterization in the Pediatric Population

Although the utility of diagnostic cardiac catheterization in the clinical setting has diminished over the last years, due to the emergence of noninvasive imaging modalities, such as echocardiography, magnetic resonance imaging and computed tomography, catheterization for diagnostic reasons still constitutes a valuable tool in certain parts in the workup of pediatric heart disease. As a result, awareness of the main aspects of diagnostic catheterization is of great importance for the clinical cardiologist. In this article, the main variables measured and the main actions performed during diagnostic cardiac catheterization in children are discussed.

Anesthesia and the pediatric cardiac catheterization suite: a review

Advances in technology over the last couple of decades have caused a shift in pediatric cardiac catheterization from a primary focus on diagnostics to innovative therapeutic interventions. These improvements allow patients a wider range of nonsurgical options for treatment of congenital heart disease. However, these therapeutic modalities can entail higher risk in an already complex patient population, compounded by the added challenges inherent to the environment of the cardiac catheterization suite. Anesthesiologists caring for children with congenital heart disease must understand not only the pathophysiology of the disease but also the effects the anesthetics and interventions have on the patient in order to provide a safe perioperative course. It is the aim of this article to review the latest catheterization modalities offered to patients with congenital heart disease, describe the unique challenges presented in the cardiac catheterization suite, list the most common complications encountered during catheterization and finally, to review the literature regarding different anesthetic drugs used in the catheterization lab.

A new predictive equation for oxygen consumption in children and adults with congenital and acquired heart disease

OBJECTIVE

To develop a new predictive equation for oxygen consumption (VO2) in children and adults with congenital and acquired heart disease.

METHODS

We retrospectively reviewed data from 502 consecutive patients (age 0-59 years) undergoing cardiac catheterisation with measured VO2 (M-VO2) and compared M-VO2 with VO2 from the LaFarge equations (LF-VO2) in patients <3 years (Group 1) and ≥3 years (Group 2). Factors associated with inaccurate LF-VO2 were used to develop a new predictive equation, which was prospectively validated in 100 consecutive patients (age 0-59 years).

RESULTS

LF-VO2 was inaccurate in 42% of Group 1 (n=201) and 13% of Group 2 (n=301). Multivariable predictors of inaccurate LF-VO2 included age (OR 0.41, p=0.01) and single ventricle anatomy (OR 2.98, p=0.03) in Group 1 and anaemia (OR 0.84, p<0.001) in Group 2. Critical illness was borderline significant in both groups. The new predictive equation for VO2:[Formula: see text] Intraclass correlation between M-VO2 and the new predictive equation was good (r=0.53), whereas LF-VO2 was not (r=0.17). Bland-Altman analysis comparing M-VO2 with the new equation and with LF-VO2 demonstrated superiority of the new equation (mean bias 2.5 mL/min/m(2) vs -5.0 mL/min/m(2); limits of agreement -51.6, 56.5 vs -82.1, 72).

CONCLUSIONS

VO2 derived from the LaFarge equations is frequently inaccurate, particularly in younger patients, and will lead to erroneous haemodynamic calculations. We developed and prospectively validated a new VO2 predictive equation for use in patients of all ages with congenital and acquired heart disease.

Validation of the Innocor device for noninvasive measurement of oxygen consumption in children and adults

Outpatient measurements of oxygen consumption (VO2) and cardiac output (CO) are valuable in the management of pediatric cardiac disease. Current methods are inaccurate and cumbersome or require invasive procedures. New devices to measure these variables in adults have not been rigorously tested for children. The Innocor system uses a photoacoustic analyzer to measure gas content for noninvasive measurement of VO2 and CO. This study sought to validate Innocor-derived VO2 measurements in children and adults by comparing them against the gold standard Douglas bag method. Subjects were tested in an outpatient setting. Adaptations were made for pediatric patients based on weight. Resting VO2 measurements were obtained simultaneously by the Innocor system and Douglas bag during 3 min. The study enrolled 31 children (mean age, 12.2 years; range, 7-17 years, 17 girls) and 29 adults (mean age, 36.7 years; range, 19-57 years; 17 women). Strong correlation between the two techniques was seen for both the adults (R (2) = 0.88) and the children (R (2) = 0.82). The average discrepancy between the Innocor and Douglas bag measurements was 1.7 % (range, 0.6-19.1 %) for the adults, and 5.4 % (range, 0.1-32.2 %) for the children. The discrepancy was more than 15 % for 17 % of the adults and 22 % of the children, with the Innocor device tending to overestimate VO2 in children compared with the Douglas bag. This trend was not seen in adults. The Innocor system has excellent correlation with the Douglas bag and shows promise for noninvasive measurement of VO2 and CO in the school-age pediatric population.