Non-invasive metabolic monitoring of patients under anaesthesia by continuous indirect calorimetry—an in vivo trial of a new method

Perioperative estimations of oxygen consumption from LiDCO™plus-derived cardiac output and Ca-cvO2 difference: Relationship with measurements by indirect calorimetry in elderly patients undergoing major abdominal surgery

BACKGROUND

Feasible estimations of perioperative changes in oxygen consumption (VO2) could enable larger studies of its role in postoperative outcomes. Current methods, either by reverse Fick calculations using pulmonary artery catheterisation or metabolic by breathing gas analysis, are often deemed too invasive or technically requiring. In addition, reverse Fick calculations report generally lower values of oxygen consumption.

METHODS

We investigated the relationship between perioperative estimations of VO2 (EVO2), from LiDCO™plus-derived (LiDCO Ltd, Cambridge, UK) cardiac output and arterial-central venous oxygen content difference (Ca-cvO2), with indirect calorimetry (GVO2) by QuarkRMR (COSMED srl. Italy), using data collected 2017-2018 during a prospective observational study on perioperative oxygen transport in 20 patients >65 years during epidural and general anaesthesia for open pancreatic or liver resection surgery. Eighty-five simultaneous intra- and postoperative measurements at different perioperative stages were analysed for prediction, parallelity and by traditional agreement assessment.

RESULTS

Unadjusted bias between GVO2 and EVO2 indexed for body surface area was 26 (95% CI 20 to 32) with limits of agreement (1.96SD) of -32 to 85 ml min-1m-2. Correlation adjusted for the bias was moderate, intraclass coefficient(A,1) 0.51(95% CI 0.34 to 0.65) [F (84,84) = 3.07, P<0.001]. There was an overall association between GVO2 and EVO2, in a random coefficient model [GVO2 = 73(95% CI 62 to 83) + 0.45(95% CI 0.29 to 0.61) EVO2 ml min-1m-2, P<0.0001]. GVO2 and EVO2 changed in parallel intra- and postoperatively when normalised to their respective overall means.

CONCLUSION

Based on this data, estimations from LiDCO™plus-derived cardiac output and Ca-cvO2 are not reliable as a surrogate for perioperative VO2. Results were in line with previous studies comparing Fick-based and metabolic measurements but limited by variability of data and possible underpowering. The parallelity at different perioperative stages and the prediction model can provide useful guidance and methodological tools for future studies on similar methods in larger samples.

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 (ρ_c = 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 (ρ_c = 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.

The effects of general anaesthesia on oxygen consumption: A meta-analysis guiding future studies on perioperative oxygen transport

BACKGROUND

Increased oxygen extraction, the ratio of consumption to delivery, has been associated with poor outcome after surgery. Oxygen consumption (VO2) can change in several ways in the perioperative period, but is seldom monitored directly in routine care. This study investigates the effects of general anaesthesia on VO2.

METHODS

We searched PubMed, EMBASE, and Cochrane Library 1946-2018 for studies including VO2 measurements before and after anaesthesia induction. Quality was assessed by Cochrane risk of bias tool and NIH Quality Assessment tool for before-and-after studies. Changes in VO2 after anaesthesia induction were pooled in a random effects model meta-analysis with standardized mean differences transformed to absolute changes of VO2. Changes in VO2 after surgical incision and after recovery from anaesthesia were analysed as secondary outcomes in the included studies.

RESULTS

Twenty-four studies including 453 patients were analysed for VO2 changes induced by anaesthesia. Studies were published during 1969-2000 and mean age of patients ranged 28-70 years. VO2 decreased after anaesthesia induction by -65 (-75; -55, 95% CI) mL min^-1 and indexed VO2 (VO2I) by -33 (-38; -28, 95% CI) mL min^-1  m^-2 . After surgical incision and in the post-operative period VO2 increased again. Heterogeneity was considerable among the studies and the overall quality of evidence was very low.

CONCLUSIONS

General anaesthesia probably reduces oxygen consumption but the effect estimate is uncertain. Given the limited generalizability and low quality of the available evidence, new studies in modern perioperative settings and in today's older high-risk surgical patient populations are needed.

In Vivo Validation of the M-COVX® Metabolic Monitor in Patients under Anaesthesia

A practical method of breath-by-breath monitoring of metabolic gas exchange has been developed by GE Healthcare/Datex Ohmeda and incorporated into existing anaesthetic and critical care monitoring systems (M-COVX®). This device relates flow measurements made at the mouth by pneumotachograph to measurements of inspired and expired gas composition by matching the two waveforms thereby allowing continuous, breath-by-breath monitoring of an intubated patient's oxygen uptake and carbon dioxide production. Given that there is a paucity of data comparing this new device against methods more widely used clinically, we tested the device on 11 patients undergoing cardiopulmonary bypass surgery. Using a standard anaesthetic machine (Datex Ohmeda Excel 210 SE) with a semi-closed circle absorber system, oxygen uptake was measured at the mouth continuously throughout the operation at approximately six-second intervals. The data were compared against the reverse Fick method and against standard indirect calorimetry using the Haldane transformation. When compared to the calculated reverse Fick oxygen uptake, a mean difference of +16.5% was found pre-bypass and +9.9% post-bypass, consistent with uptake of oxygen by lung tissue, which is not taken into account by the reverse Fick method. Measurements made comparing the M-COVX metabolic monitor against standard Haldane showed a mean difference of +5.1% pre-bypass and –2.1% post-bypass. Given the ease with which this device can be incorporated into existing anaesthetic monitoring systems and its accuracy in measuring oxygen uptake, the M-COVX module is an attractive addition to existing perioperative monitoring.

Comparison of Minimally and More Invasive Methods of Determining Mixed Venous Oxygen Saturation

OBJECTIVE

To investigate the accuracy of a minimally invasive, 2-step, lookup method for determining mixed venous oxygen saturation compared with conventional techniques.

DESIGN

Single-center, prospective, nonrandomized, pilot study.

SETTING

Tertiary care hospital, university setting.

PARTICIPANTS

Thirteen elective cardiac and vascular surgery patients.

INTERVENTIONS

All participants received intra-arterial and pulmonary artery catheters. Minimally invasive oxygen consumption and cardiac output were measured using a metabolic module and lithium-calibrated arterial waveform analysis (LiDCO; LiDCO, London), respectively. For the minimally invasive method, Step 1 involved these minimally invasive measurements, and arterial oxygen content was entered into the Fick equation to calculate mixed venous oxygen content. Step 2 used an oxyhemoglobin curve spreadsheet to look up mixed venous oxygen saturation from the calculated mixed venous oxygen content. The conventional "invasive" technique used pulmonary artery intermittent thermodilution cardiac output, direct sampling of mixed venous and arterial blood, and the "reverse-Fick" method of calculating oxygen consumption.

MEASUREMENTS AND MAIN RESULTS

LiDCO overestimated thermodilution cardiac output by 26%. Pulmonary artery catheter-derived oxygen consumption underestimated metabolic module measurements by 27%. Mixed venous oxygen saturation differed between techniques; the calculated values underestimated the direct measurements by between 12% to 26.3%, this difference being statistically significant.

CONCLUSION

The magnitude of the differences between the minimally invasive and invasive techniques was too great for the former to act as a surrogate of the latter and could adversely affect clinical decision making.

[Monitoring oxygen consumption in energy metabolism in pediatric anesthesia: clinical utility]

OBJECTIVES

To determine changes in oxygen consumption as a marker of energy metabolism during general inhaled anesthesia in pediatric patients and to identify factors that might influence consumption.

MATERIAL AND METHODS

Prospective, observational, double-blind study in children under inhaled anesthesia in spontaneous ventilation. We monitored heart rate electrocardiogram, noninvasive blood pressure, respiratory frequency, carbon dioxide (CO2) end-expiratory pressure, oxygen saturation by pulse oximetry, state entropy, response entropy, esophageal temperature, and (by indirect calorimetry) oxygen consumption and the respiratory quotient. Capillary blood was extracted every 5 minutes to determine lactate concentration.

RESULTS

Thirty-six patients (ASA 1-2) between 5 and 11 years old were included. Mean (SD) oxygen consumption was 0.6 (0.12) mL x kg(-1)min(-1) at baseline, 5.3 (03) mL x kg(-1) min(-1) during maintenance of anesthesia, and 8.1 (1.1) mL x kg(-1) min(-1) on awakening. A progressive increase was detected in lactic acid concentration, from a baseline mean of 0.8 (0.1) mmol/L to 2.2 (0.9) mmol/L half an hour later; the change was unrelated to oxygen consumption. After correcting the flow of normal saline solution to 0.9%, a significant increase in oxygen consumption (P < .05) was detected. Factors that were significantly correlated (P < 0.1 and r of +/- 0.95) were temperature (oxygen consumption decreased > 10% for each degree centigrade decrease), inspired oxygen fraction > 0.8; sharp changes in the expired CO2 fraction exceeding 2 standard deviations (+/- 6), use of nitrous oxide in the gas mix (inspired nitrous oxide fraction > 20%), the length of the sampling line, and increased respiratory frequency. A model with 3 factors was constructed to explain the kinetics of oxygen consumption during anesthesia.

CONCLUSIONS

Oxygen consumption monitoring may provide an indirect indicator of homeostatic changes during surgery. The ideal system for carrying out such monitoring during anesthesia remains to be found, and the values to guide the anesthesiologist in deciding whether or not to intervene immediately still need to be determined.

Arterial oxygenation and one-lung anesthesia

PURPOSE OF REVIEW

In the presence of the obligatory shunt during one-lung ventilation, arterial oxygenation is determined by the magnitude of the shunt in addition to the oxygen content of the mixed venous blood coursing through that shunt. The present discussion aims to heighten awareness of factors determining arterial oxygenation during one-lung anesthesia, other than the magnitude of the shunt and dependent lung low-ventilation perfusion units.

RECENT FINDINGS

A convenient way to increase mixed venous and thereby arterial oxygenation is to raise cardiac output. While this approach has achieved some success when increasing cardiac output from low levels, other studies have highlighted limitations of this approach when cardiac output attains very high levels. The effect of anesthesia techniques on the relationship between oxygen consumption and cardiac output could also explain unanswered questions regarding the pathophysiology of arterial oxygenation during one-lung anesthesia.

SUMMARY

The effects of anesthesia techniques on oxygen consumption, cardiac output and therefore mixed venous oxygenation can significantly affect arterial oxygenation during one-lung anesthesia. While pursuing increases in cardiac output may, under limited circumstances, benefit arterial oxygenation during one-lung ventilation, this approach is not a panacea and does not obviate the necessity to optimize dependent lung volume.