A Continuous Noninvasive Method to Assess Mixed Venous Oxygen Saturation: A Proof-of-Concept Study in Pigs

Validation of the capnodynamic method to calculate mixed venous oxygen saturation in postoperative cardiac patients

BACKGROUND

Cardiac output and mixed venous oxygen saturation are key variables in monitoring adequate oxygen delivery and have typically been measured using pulmonary artery catheterisation. The capnodynamic method measures effective pulmonary blood flow utilising carbon dioxide kinetics in ventilated patients. Combined with breath-by-breath measurements of carbon dioxide elimination, a non-invasive approximation of mixed venous oxygen saturation can be calculated.

METHODS

This study primarily investigated the agreement between mixed venous oxygen saturation calculated using the capnodynamic method and blood gas analysis of mixed venous blood sampled via a pulmonary artery catheter in 47 haemodynamically stable postoperative cardiac patients. Both measurements were synchronised and performed during alveolar recruitment by stepwise changes to the level of positive end-expiratory pressure. Simultaneously, we studied the agreement between effective pulmonary blood flow and thermodilution cardiac output. The Bland-Altman method for repeated measurements and calculation of percentage error were used to examine agreement. Measurements before and after alveolar recruitment were analysed by a paired t test. The study hypothesis for agreement was a limit of difference of ten percentage points between mixed venous oxygen saturation using the capnodynamic algorithm vs. catheter blood gas analysis.

RESULTS

Capnodynamic calculation of mixed venous saturation compared to blood gas analysis showed a bias of -0.02 [95% CI - 0.96-0.91] % and limits of agreement at 8.8 [95% CI 7.7-10] % and - 8.9 [95% CI -10-- 7.8] %. The percentage error was < 20%. The effective pulmonary blood flow compared to thermodilution showed a bias of - 0.41 [95% CI - 0.55-- 0.28] l.min-1 and limits of agreement at 0.56 [95% CI 0.41-0.75] l.min-1 and - 1.38 [95% CI - 1.57--1.24] l.min-1. The percentage error was < 30%. Only effective pulmonary blood flow increased by 0.38 [95% CI 0.20-0.56] l.min-1 (p < 0.01) after alveolar recruitment.

CONCLUSIONS

In this study, minimal bias and limits of agreement < 10% between mixed venous oxygen saturation calculated by the capnodynamic method and pulmonary arterial blood gas analysis confirmed the agreement hypothesis in stable postoperative patients. The effective pulmonary blood flow agreed with thermodilution cardiac output, while influenced by pulmonary shunt flow.

Capnodynamic assessment of mixed venous oxygen saturation in a porcine experimental endotoxemic model

Sepsis continues to be a major cause of death and illness globally, posing significant challenges for healthcare professionals. In the pursuit of more accurate and timely monitoring tools, the concept of capnodynamically derived mixed venous oxygen saturation (Capno-SvO2) has emerged as a promising method. Capno-SvO2 provides a non-invasive way to assess and track SvO2 and could serve as an additional tool alongside more invasive methods like the pulmonary artery catheter. This could potentially be of great value in the care of critically ill patients with sepsis, where alternative minimal invasive monitoring methods may vary in reliability. The aim of the current study was to compare capno-SvO2 against values obtained through pulmonary artery blood sample CO-oximetry and continuous fiberoptic SvO2 monitoring, using a well-established porcine experimental sepsis model. Anesthetized pigs were exposed to a standardized endotoxin infusion sepsis protocol, followed by a series of maneuvers typically applied in sepsis care. Simultaneous recordings were done throughout the experiment for all three monitoring methods. Bland-Altman analysis corrected for repeated measurements was used to assess the agreement of absolute values between the paired recording of CO-oximetry and Capno-SvO2 as well as between CO-oximetry and fiberoptic SvO2. The ability of Capno-SvO2 and fiberoptic SvO2 to track changes was assessed by concordance rate. A total of 10 animals and 275 paired datapoints were included in the study. The majority of the animals displayed pronounced hemodynamical instability in response to endotoxin exposure and subsequent treatment interventions. Analysis of all paired data points showed a bias between Capno-SvO2 and CO-oximetry SvO2 of + 1% with 95% limits of agreement of -14% to + 17%. The corresponding numbers for fiberoptic SvO2 and CO-oximetry SvO2 were -4% and -15% to + 8%. The concordance rate as compared to CO-oximetry, were 97% and 93% for Capno-SvO2 and fiberoptic SvO2, respectively. In this experimental sepsis model, continuous, non-invasive Capno-SvO2 generates average absolute values comparable to the gold standard CO-oximetry albeit with relatively wide limits of agreement. Capno-SvO2 displayed a concordance rate of 97% against CO-oximetry and exhibits better trending ability compared to invasive fiberoptic SvO2.

Validation of a Novel Method for Noninvasive Mixed Venous Oxygen Saturation Monitoring in Anesthetized Children

BACKGROUND

Mixed venous oxygen saturation (SvO 2 ) is a critical variable in the assessment of oxygen supply and demand but is rarely used in children due to the invasive nature of pulmonary artery catheters. The aim of this prospective, observational study was to investigate the accuracy of noninvasively measured SvO 2 acquired by the novel capnodynamic method, based on differential Fick equation (Capno-SvO 2 ), against gold standard CO-oximetry.

METHODS

Capno-SvO 2 was compared to SvO 2 measured by pulmonary artery blood gas CO-oximetry in children undergoing cardiac catheter interventions and subjected to moderate hemodynamic challenges. Bland-Altman analysis was used to describe the agreement of absolute values between CO-oximetry and Capno-SvO 2 , and a concordance rate was calculated to evaluate the ability of Capno-SvO 2 to track change.

RESULTS

Twenty-five procedures were included in the study. Capno-SvO 2 showed a bias toward CO-oximetry of +3 percentage points; upper and lower limits of agreement were +11 percentage points (95% confidence interval [CI], 9-14) and -5 percentage points (95% CI, -8 to -3), respectively. The concordance rate was 92% (95% CI, 89-96).

CONCLUSIONS

In conclusion, this first clinical application of a novel concept for noninvasive SvO 2 monitoring without the need for a pulmonary artery catheter indicates that Capno-SvO 2 generates absolute values and trending capacity in close agreement with the gold standard reference method.

Noninvasive tracking of mixed venous oxygen saturation via near-infrared spectroscopy cerebral oximetry: a retrospective observational study

Although previous studies have shown correlation between regional cerebral oxygen saturation (rScO2) and mixed venous oxygen saturation (SvO2), there is a lack of pragmatic information on the clinical applicability of these findings, such as tracking ability. We retrospectively analyzed continuous intraoperative recordings of rScO2 and SvO2 obtained from a pulmonary artery catheter and either of two near-infrared spectroscopy (NIRS) devices (INVOS 5100C, Medtronic; O3, Masimo) during off-pump cardiopulmonary bypass (OPCAB) surgery in adult patients. The ability of rScO2 to track SvO2 was quantitatively evaluated with 5 min interval changes transformed into relative values. The analysis included 176 h of data acquired from 48 subjects (26 and 22 subjects for INVOS and O3 dataset, respectively). The area under ROC of the left-rScO2 for detecting change of SvO2 ≥ 10% in INVOS and O3 datasets were 0.919 (95% CI 0.903-0.936) and 0.852 (95% CI 0.818-0.885). The concordance rates between the interval changes of left-rScO2 and SvO2 in INVOS and O3 datasets were 90.6% and 91.9% with 10% exclusion zone. rScO2 can serve as a noninvasive tool for detecting changes in SvO2 levels, a critical hemodynamic measurement.

Standardized blood volume changes monitored by capnodynamic hemodynamic variables: An experimental comparative study in pigs

BACKGROUND

The capnodynamic method, based on Volumetric capnography and differential Fick mathematics, assess cardiac output in mechanically ventilated subjects. Capnodynamic and established hemodynamic monitoring parameters' capability to depict alterations in blood volume were investigated in a model of standardized hemorrhage, followed by crystalloid and blood transfusion.

METHODS

Ten anesthetized piglets were subjected to controlled hemorrhage (450 mL), followed by isovolemic crystalloid bolus and blood re-transfusion. Intravascular blood volume, and all hemodynamic variables, were determined twice after each intervention. The investigated hemodynamic variables were: cardiac output and stroke volume for capnodynamics and pulse contour analysis, respectively, pulse pressure and stroke volume variability and mean arterial pressure. One-way ANOVA and Tukey's test for multiple comparisons were used to identify significant changes. Trending was assessed by correlation and concordance.

RESULT

Concordance against intravascular volume changes for capnodynamic cardiac output and stroke volume were 96 and 94%, with correlations r = .78 and .68, (p < .0001) with significant changes for 6 and 5 of the 6 measuring points, respectively. Mean arterial pressure and pulse pressure variation had a concordance of 85% and 87%, r = .67 (p < .0001) and r = -.45 (p < .0001), respectively, and both changed significantly for 3 of 6 measuring points. Pulse contour stroke volume variation, stroke volume and cardiac output, showed concordance and correlation of 76%, r = -.18 (p = .11), 63%, r = .28 (p = .01) and 50%, r = .31 (p = .007), respectively and significant change for 1, 1 and 0 of the measuring points, respectively.

CONCLUSION

Capnodynamic cardiac output and stroke volume did best depict the changes in intravascular blood volume. Pulse contour parameters did not follow volume changes in a reliable way.

Capnodynamics - noninvasive cardiac output and mixed venous oxygen saturation monitoring in children

Hemodynamic monitoring in children is challenging for many reasons. Technical limitations in combination with insufficient validation against reference methods, makes reliable monitoring systems difficult to establish. Since recent studies have highlighted perioperative cardiovascular stability as an important factor for patient outcome in pediatrics, the need for accurate hemodynamic monitoring methods in children is obvious. The development of mathematical processing of fast response mainstream capnography signals, has allowed for the development of capnodynamic hemodynamic monitoring. By inducing small changes in ventilation in intubated and mechanically ventilated patients, fluctuations in alveolar carbon dioxide are created. The subsequent changes in carbon dioxide elimination can be used to calculate the blood flow participating in gas exchange, i.e., effective pulmonary blood flow which equals the non-shunted pulmonary blood flow. Cardiac output can then be estimated and continuously monitored in a breath-by-breath fashion without the need for additional equipment, training, or calibration. In addition, the method allows for mixed venous oxygen saturation (SvO₂) monitoring, without pulmonary artery catheterization. The current review will discuss the capnodyamic method and its application and limitation as well as future potential development and functions in pediatric patients.

Capnodynamics-Measuring cardiac output via ventilation

Recent studies have identified stable hemodynamics as a contributing factor to improve outcome in pediatric anesthesia. So far, most of the hemodynamic monitoring methods applied in children have been complex to apply and often not satisfactory validated. Standard mainstream carbon dioxide analysis in combination with real-time mathematical analysis of the measured capnography data has enabled the development of dynamic capnography, a non-invasively cardiac output monitoring method that can be applied without user practice or need for calibrations. Capnodynamic cardiac output assessment has been extensively validated against gold standard reference methods, both in experimental and clinical settings. This review will describe the principle behind dynamic capnography measurement of cardiac output and mixed venous oxygen saturation. Additionally, the methods limitations and challenges when applied in children will be delineated.

Blood pressure and flow in pediatric anesthesia: An educational review

During recent years, a lot of interest has been focused on blood pressure in the context of pediatric anesthesia, trying to define what is normal in relation to age and what numeric values that should be regarded as hypotension, needing active intervention. However, blood pressure is mainly measured as a proxy for flow, that is, cardiac output. Thus, just focusing on specific blood pressure numbers may not necessarily be very useful or appropriate. The aim of this educational review is to put the issue of intraoperative blood pressure in the context of pediatric anesthesia in further perspective.

Comparison between capnodynamic and thermodilution method for cardiac output monitoring during major abdominal surgery: An observational study

BACKGROUND

Cardiac output (CO) monitoring is the basis of goal-directed treatment for major abdominal surgery. A capnodynamic method estimating cardiac output (COEPBF) by continuously calculating nonshunted pulmonary blood flow has previously shown good agreement and trending ability when evaluated in mechanically ventilated pigs.

OBJECTIVES

To compare the performance of the capnodynamic method of CO monitoring with transpulmonary thermodilution (COTPTD) in patients undergoing major abdominal surgery.

DESIGN

Prospective, observational, method comparison study. Simultaneous measurements of COEPBF and COTPTD were performed before incision at baseline and before and after increased (+10 cmH2O) positive end-expiratory pressure (PEEP), activation of epidural anaesthesia and intra-operative events of hypovolemia and low CO. The first 25 patients were ventilated with PEEP 5 cmH2O (PEEP5), while in the last 10 patients, lung recruitment followed by individual PEEP adjustment (PEEPadj) was performed before protocol start.

SETTING

Karolinska University Hospital, Stockholm, Sweden.

PATIENTS

In total, 35 patients (>18 years) scheduled for major abdominal surgery with advanced hemodynamic monitoring were included in the study.

MAIN OUTCOME MEASURES AND ANALYSIS

Agreement and trending ability between COEPBF and COTPTD at different clinical moments were analysed with Bland--Altman and four quadrant plots.

RESULTS

In total, 322 paired values, 227 in PEEP5 and 95 in PEEPadj were analysed. Respectively, the mean COEPBF and COTPTD were 4.5 ± 1.0 and 4.8 ± 1.1 in the PEEP5 group and 4.9 ± 1.2 and 5.0 ± 1.0 l min-1 in the PEEPadj group. Mean bias (levels of agreement) and percentage error (PE) were -0.2 (-2.2 to 1.7) l min-1 and 41% for the PEEP5 group and -0.1 (-1.7 to 1.5) l min-1 and 31% in the PEEPadj group. Concordance rates during changes in COEPBF and COTPTD were 92% in the PEEP5 group and 90% in the PEEPadj group.

CONCLUSION

COEPBF provides continuous noninvasive CO estimation with acceptable performance, which improved after lung recruitment and PEEP adjustment, although not interchangeable with COTPTD. This method may become a tool for continuous intra-operative CO monitoring during general anaesthesia in the future.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT03444545.

Non-invasive capnodynamic mixed venous oxygen saturation during major changes in oxygen delivery

Mixed venous oxygen saturation (SvO₂) is an important variable in anesthesia and intensive care but currently requires pulmonary artery catheterization. Recently, non-invasive determination of SvO₂ (Capno-SvO₂) using capnodynamics has shown good agreement against CO-oximetry in an animal model of modest hemodynamic changes. The purpose of the current study was to validate Capno-SvO₂ against CO-oximetry during major alterations in oxygen delivery. Furthermore, evaluating fiberoptic SvO₂ for its response to the same challenges. Eleven mechanically ventilated pigs were exposed to oxygen delivery changes: increased inhaled oxygen concentration, hemorrhage, crystalloid and blood transfusion, preload reduction and dobutamine infusion. Capno-SvO₂ and fiberoptic SvO₂ recordings were made in parallel with CO-oximetry. Respiratory quotient, needed for capnodynamic SvO₂, was measured by analysis of mixed expired gases. Agreement of absolute values between CO-oximetry and Capno-SvO₂ and fiberoptic SvO₂ respectively, was assessed using Bland–Altman plots. Ability of Capno- SvO₂ and fiberoptic SvO₂ to detect change compared to CO-oximetry was assessed using concordance analysis. The interventions caused significant hemodynamic variations. Bias between Capno-SvO₂ and CO-oximetry was + 3% points (95% limits of agreements – 7 to + 13). Bias between fiberoptic SvO₂ and CO-oximetry was + 1% point, (95% limits of agreements − 7 to + 9). Concordance rate for Capno-SvO₂ and fiberoptic SvO₂ vs. CO-oximetry was 98% and 93%, respectively. Capno-SvO₂ generates absolute values close to CO-oximetry. The performance of Capno-SvO₂ vs. CO-oximetry was comparable to the performance of fiberoptic SvO₂ vs. CO-oximetry. Capno-SvO₂ appears to be a promising tool for non-invasive SvO₂ monitoring.

Cardiac Output Assessments in Anesthetized Children: Dynamic Capnography Versus Esophageal Doppler

BACKGROUND

The objective of this study was to compare esophageal Doppler cardiac output (COEDM) against the reference method effective pulmonary blood flow cardiac output (COEPBF), for agreement of absolute values and ability to detect change in cardiac output (CO) in pediatric surgical patients. Furthermore, the relationship between these 2 methods and noninvasive blood pressure (NIBP) parameters was evaluated.

METHODS

Fifteen children American Society of Anesthesiology (ASA) I and II (median age, 8 months; median weight, 9 kg) scheduled for surgery were investigated in this prospective observational cohort study. Baseline COEPBF/COEDM/NIBP measurements were made at positive end-expiratory pressure (PEEP) 3 cm H2O. PEEP was increased to 10 cm H2O and COEPBF/COEDM/NIBP was recorded after 1 and 3 minutes. PEEP was then lowered to 3 cm H2O, and all measurements were repeated after 3 minutes. Finally, 20-µg kg-1 intravenous atropine was given with the intent to increase CO, and all measurements were recorded again after 5 minutes. Paired recordings of COEDM and COEPBF were examined for agreement and trending ability, and all parameters were analyzed for their responses to the hemodynamic challenges.

RESULTS

Bias between COEDM and COEPBF (COEDM - COEPBF) was -17 mL kg-1 min-1 (limits of agreement, -67 to +33 mL kg-1 min-1) with a mean percentage error of 32% (95% confidence interval [CI], 25-37) and a concordance rate of 71% (95% CI, 63-80). The hemodynamic interventions caused by PEEP manipulations resulted in significant decrease in COEPBF absolute numbers (155 mL kg-1 min-1 [95% CI, 151-159] to 127 mL kg-1 min-1 [95% CI, 113-141]) and a corresponding relative decrease of 18% (95% CI, 14-22) 3 minutes after application of PEEP 10. No corresponding decreases were detected by COEDM. Mean arterial pressure showed a relative decrease with 5 (95% CI, 2-8) and 6% (95% CI, 2-10) 1 and 3 minutes after the application of PEEP 10, respectively. Systolic arterial pressure showed a relative decrease of 5% (95% CI, 2-10) 3 minutes after application of PEEP 10. None of the recorded parameters responded to atropine administration except for heart rate that showed a 4% relative increase (95% CI, 1-7, P = .02) 5 minutes after atropine.

CONCLUSIONS

COEDM was unable to detect the reduction of CO cause by increased PEEP, whereas COEPBF and to a minimal extent NIBP detected these changes in CO. The ability of COEPBF to react to minor reductions in CO, before noticeable changes in NIBP are seen, suggests that COEPBF may be a potentially useful tool for hemodynamic monitoring in mechanically ventilated children.