Comparison of metabolic monitors in critically ill, ventilated patients

Substrate utilization of carbohydrates, fat, and protein in the late acute phase of critically ill surgical patients: A retrospective longitudinal study

BACKGROUND AND AIMS

Tailoring nutrition to measured energy expenditure (EE) and provision of adequate protein amounts, is considered gold standard for critically ill patients. There are currently no recommendations to measure specific substrate utilization or to adapt nutrition accordingly.

METHODS

In this retrospective longitudinal study, we analyzed results of 316 simultaneous measurements of indirect calorimetry (IC) and urinary urea nitrogen (UUN) in 191 mechanically ventilated, critically ill patients, admitted to the surgical intensive care unit (SICU) in a tertiary medical center. We calculated substrate utilization, compared it to administered nutrition, investigated factors that may influence it and tested the added value of routine UUN measurements over IC alone.

RESULTS

The mean total EE, measured using the indirect calorimetry module, was 1600 ± 451 kcal/day The mean daily fat, carbohydrates and protein oxidation were 118.3 ± 63.9 g, 53.3 ± 114.1 g and 64.7 ± 36.0 g, respectively, accounting for 68.8 % ± 31.4 %, 14.2 % ± 29.6 % and 17.0 % ± 8.6 % of the total EE. Fasting and noradrenaline administration were the only factors that influenced substrate utilization, resulting in higher fat and lower carbohydrate utilization (p < 0.045 for all). There were significant differences between percentage of substrate utilization and supply, with average differences of +28.5 % for fat, -38 % for carbohydrates and +1.9 % for protein (p < 0.006 for all).

CONCLUSIONS

SICU patients demonstrated very high fat utilization and lower than expected carbohydrate utilization, that differed significantly from amounts supplied. Further prospective studies are needed to elucidate the clinical impact of these findings.

Energy Expenditure, a New Tool for Monitoring Surgical Stress in Colorectal Oncological Patients: A Prospective, Monocentric Study

BACKGROUND

Surgical stress response in colorectal surgery consists of a neurohormonal and an immunological response and influences oncological outcomes. The intensity of surgical trauma influences mortality, morbidity, and metastasis' occurrence in colorectal neoplasia. Energy expenditure (EE) stands for the body's energy consumed to keep its homeostasis and can be either calculated or measured by direct or indirect calorimetry.

AIM

The present study attempted to evaluate surgical stress response using EE measurement and compare it to the postoperative cortisol dynamic.

METHODS

A prospective, monocentric study was conducted over a period of one year in the Anesthesiology Department including 21 patients from whom serum cortisol values were collected in the preoperative period and on the first postoperative day, and EE was measured and recorded every 15 minutes throughout surgery using the indirect calorimetry method. The study compared EE values' dynamic registered 30 minutes after intubation and 30 minutes before extubating (after abdominal closure) to cortisol perioperative dynamic.

RESULTS

We enrolled 21 patients and 84 measurements were recorded, 42 probes of serum cortisol and 42 measurements of EE. The mean value of the first measurement of serum cortisol was 13.60±3.6 µg and the second was 16.21±6.52 µg. The average value of the first EE recording was 1273.9±278 kcal and 1463.4±398.2 kcal of the second recording. The bivariate analysis performed showed a good correlation between cortisol variation and EE's variation (Spearman coefficient=0.666, p<0.001, CI=0.285, 0.865). In nine cases (42.85%), cortisol value at 24 hours reached the baseline or below the baselines preoperative value. In eight cases (38.09%), patients' EE at the end of the surgery was lower than that recorded at the beginning of the surgery.

CONCLUSIONS

Intraoperative EE variation correlated well with cortisol perioperative dynamic and stood out in this study as a valuable and accessible predictor of surgical stress in colorectal surgery.

Two-hour indirect calorimetry measurement as a predictor of 24-hour energy expenditure in critically ill surgical patients: A longitudinal study

BACKGROUND

Measuring energy expenditure (EE) by indirect calorimetry (IC) has become the gold standard tool for critically ill patients to define energy targets and tailor nutrition. Debate remains as to the optimal duration of measurements or the optimal time of day in which to perform IC.

METHODS

In this retrospective longitudinal study, we analyzed results of daily continuous IC in 270 mechanically ventilated, critically ill patients admitted to the surgical intensive care unit in a tertiary medical center and compared measurements performed at different hours of the day.

RESULTS

A total of 51,448 IC hours was recorded, with an average 24-h EE of 1523 ± 443 kcal/day. Night shift (00:00-8:00) was found to have significantly lower EE measurements (mean, 1499 ± 439 kcal/day) than afternoon (16:00-00:00; mean, 1526 ± 435 kcal/day) and morning (8:00-16:00; mean, 1539 ± 462 kcal/day) measurements (P < 0.001 for all). The bi-hourly time frame that most closely resembled the daily mean was 18:00-19:59, with a mean of 1521 ± 433 kcal/day. Daily EE measurements of the continuous IC at days 3-7 of admission showed a trend toward a daily increase in 24-h EE, but the difference was not statistically significant (P = 0.081).

CONCLUSIONS

Periodic measurements of EE can differ slightly when performed at various hours of the day, but the error range is small and may not necessarily have a clinical impact. When continuous IC is not available, a 2-h EE measurement between 18:00 and 19:59 can serve as a reasonable alternative.

A novel prediction equation of resting energy expenditure for Japanese septic patients

Estimating nutrient consumption and administering appropriate nutritional therapy is essential for improving clinical outcomes in critically ill patients. Various equations, such as the Harris-Benedict equation, have been developed to estimate the required calories. Previous equations, however, targeted Westerners, whose physical characteristics are likely different from those of Asians. Hence, it is unclear whether these equations can be used for Asian patients. This study focused specifically on sepsis patients admitted to a single Japanese ICU, and aimed to develop novel equations to estimate their total energy expenditure. A total of 95 sepsis patients were included in this study. We measured resting energy expenditure (REE) by using indirect calorimetry, and created equations to calculate basal metabolic rate (BMR) using height, weight and age as variables. REE was predicted by multiplying BMR by the novel equation with the stress factor of 1.4. The prediction error of our novel equations were smaller than those of other conventional equations. We further confirmed the accuracy of our equations and that they were unaffected by patient age and disease severity by using data obtained from another patient group. The current study suggested that these equations might allow accurate estimation of the total energy expenditure and proper management of nutritional therapy in Asian sepsis patients.

Assessment of Metabolic and Nutritional Imbalance in Mechanically Ventilated Multiple Trauma Patients: From Molecular to Clinical Outcomes

The critically ill polytrauma patient is characterized by a series of metabolic changes induced by inflammation, oxidative stress, sepsis, and primary trauma, as well as associated secondary injuries associated. Metabolic and nutritional dysfunction in the critically ill patient is a complex series of imbalances of biochemical and genetic pathways, as well as the interconnection between them. Therefore, the equation changes in comparison to other critical patients or to healthy individuals, in which cases, mathematical equations can be successfully used to predict the energy requirements. Recent studies have shown that indirect calorimetry is one of the most accurate methods for determining the energy requirements in intubated and mechanically ventilated patients. Current research is oriented towards an individualized therapy depending on the energy consumption (kcal/day) of each patient that also takes into account the clinical dynamics. By using indirect calorimetry, one can measure, in real time, both oxygen consumption and carbon dioxide production. Energy requirements (kcal/day) and the respiratory quotient (RQ) can be determined in real time by integrating these dynamic parameters into electronic algorithms. In this manner, nutritional therapy becomes personalized and caters to the patients’ individual needs, helping patients receive the energy substrates they need at each clinically specific time of treatment.

Reliability of, and Agreement Between, two Breath-by-Breath Indirect Calorimeters at Varying Levels of Inspiratory Oxygen

BACKGROUND

Indirect calorimetry (IC) is considered the accurate way of measuring energy expenditure (EE). IC devices often apply the Haldane transformation, introducing errors at inspiratory oxygen fraction (FiO₂ ) >60%. The aim was to assess measurement reliability and agreement between an unevaluated IC (device 2) (Beacon Caresystem, Mermaid Care A/S, Noerresundby, Denmark) not using Haldane transformation and an IC that does (device 1) (Ecovx, GE, Helsinki, Finland) at varying FiO₂ .

METHODS

Twenty healthy male subjects participated, with 16 completing the study (33 ± 9 years, 83.3 ± 16 kg, 1.83 ± 0.08 m). Subjects were mechanically ventilated in pressure support (3cmH₂ O; positive end-expiratory pressure: 3cmH₂ O) at FiO₂ of 21%, 50%, 85%, and 21% for 15 minutes at each FiO₂ . Mean EE, oxygen consumption (VO₂ ), and CO₂ production (VCO₂ ) were compared within and between devices across FiO₂ levels.

RESULTS

Device 2 showed within-device EE significant differences at 21% vs 50% FiO₂ and device 1 for VCO₂ at 50% vs. 85% FiO₂ . For all variables, both devices showed reliable measurements at 21% and 50% FiO₂ , but at 85%, FiO₂ bias and limits of agreement increased. Between devices, there were significant differences for EE at both 21% and 85% FiO₂ for VO₂ and for VCO₂ at 85% FiO₂ .

CONCLUSION

Both systems measured EE, VO₂ , and VCO₂ at 21%-85% FiO₂ reliably but with bias at 85% FiO₂ . The devices were in agreement at 21% and 50% FiO₂ , but further studies need to confirm accuracy at high FiO₂ .

Indirect calorimetry in critically ill mechanically ventilated patients: Comparison of E-sCOVX with the deltatrac

BACKGROUND & AIMS

Indirect calorimetry is recommended to measure energy expenditure (EE) in critically ill, mechanically ventilated patients. The most validated system, the Deltatrac® (Datex-Ohmeda, Helsinki, Finland) is no longer in production. We tested the agreement of a new breath-by-breath metabolic monitor E-sCOVX® (GE healthcare, Helsinki, Finland), with the Deltatrac. We also compared the performance of the E-sCOVX to commonly used predictive equations.

METHODS

We included mechanically ventilated patients eligible to undergo indirect calorimetry. After a stabilization period, EE was measured simultaneously with the Deltatrac and the E-sCOVX for 2 h. Agreement and precision of the E-sCOVX was tested by determining bias, limits of agreement and agreement rates compared to the Deltatrac. Performance of the E-sCOVX was also compared to four predictive equations: the 25 kcal/kg, Penn State University 2003b, Faisy, and Harris-Benedict equation.

RESULTS

We performed 29 measurements in 16 patients. Mean EE-Deltatrac was 1942 ± 274 kcal/day, and mean EE-E-sCOVX was 2177 ± 319 kcal/day (p < 0.001). E-sCOVX overestimated EE with a bias of 235 ± 149 kcal/day, being 12.1% of EE-Deltatrac. Limits of agreement were -63 to +532 kcal/day. The 10% and 15% agreement rates of EE-E-sCOVX compared to the Deltatrac were 34% and 72% respectively. The bias of E-sCOVX was lower than the bias of the 25 kcal/kg-equation, but higher than bias of the other equations. Agreement rates for E-sCOVX were similar to the equations. The Faisy-equation had the highest 15% agreement rate.

CONCLUSION

The E-sCOVX metabolic monitor is not accurate in estimating EE in critically ill mechanically ventilated patients when compared to the Deltatrac, the present reference method. The E-sCOVX overestimates EE with a bias and precision that are clinically unacceptable.

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.

Effect of FiO2 in the measurement of VO2 and VCO2 using the E-COXV metabolic monitor

OBJECTIVE

We evaluated the effect of changes in FiO₂ on the bias and accuracy of the determination of oxygen consumption (V˙O₂) and carbon dioxide production (V˙CO₂) using the E-COVX monitor in patients with mechanical ventilation.

DESIGN

Descriptive of concordance.

SETTING

Intensive Care Unit.

PATIENTS OR PARTICIPANTS

Patients with mechanical ventilation.

INTERVENTIONS

We measured V˙O₂ and V˙CO₂ using the E-COVX monitor. Values recorded were the average in 5min. Two groups of 30 patients. We analyzed: 1) the reproducibility in the measurement of V˙O₂ and V˙CO₂ at FiO₂ 0.4, and 2) the effect of the changes in FiO₂ on the measurement of V˙O₂ and V˙CO₂. Statistical analysis was performed using Bland and Altman test.

VARIABLES OF MAIN INTEREST

Bias and accuracy.

RESULTS

1) FiO₂ 0.4 reproducibility: The bias in the measurement of V˙O₂ and V˙CO₂ was 1.6 and 2.1mL/min, respectively, and accuracy was 9.7 to -8.3% and 7.2 to -5.2%, respectively, and 2) effect of FiO₂ on V˙O₂: The bias of V˙O₂ measured at FiO₂ 0.4 and 0.6 was -4.0mL/min and FiO₂ 0.4 and 0.8 was 5.2mL/min. Accuracy between FiO₂ 0.4 and 0.6 was 11.9 to -14.1%, and between FiO₂ 0.4 and 0.8 was 43.9 to -39.7%.

CONCLUSIONS

The E-COVX monitor evaluates V˙O₂ and V˙CO₂ in critical patients with mechanical ventilation with a clinically acceptable accuracy until FiO₂ 0.6.

The influence of metabolic imbalances and oxidative stress on the outcome of critically ill polytrauma patients: a review

The critically ill polytrauma patient presents with a series of associated pathophysiologies secondary to the traumatic injuries. The most important include systemic inflammatory response syndrome (SIRS), sepsis, oxidative stress (OS), metabolic disorders, and finally multiple organ dysfunction syndrome (MODS) and death. The poor outcome of these patients is related to the association of the aforementioned pathologies. The nutrition of the critically ill polytrauma patient is a distinct challenge because of the rapid changes in terms of energetic needs associated with hypermetabolism, sepsis, SIRS, and OS. Moreover, it has been proven that inadequate nutrition can prolong the time spent on a mechanical ventilator and the length of stay in an intensive care unit (ICU). A series of mathematical equations can predict the energy expenditure (EE), but they have disadvantages, such as the fact that they cannot predict the EE accurately in the case of patients with hypermetabolism. Indirect calorimetry (IC) is another method used for evaluating and monitoring the energy status of critically ill patients. In this update paper, we present a series of pathophysiological aspects associated with the metabolic disaster affecting the critically ill polytrauma patient. Furthermore, we present different non-invasive monitoring methods that could help the intensive care physician in the adequate management of this type of patient.

New generation indirect calorimeters for measuring energy expenditure in the critically ill: a rampant or reticent revolution?

To lower the risk of incorrectly feeding critically ill patients, indirect calorimetry (IC) is proposed as the most ideal method to evaluate energy expenditure and to establish caloric goals. New IC devices are progressively introduced but validation of this new generation remains challenging and arduous.

Clinical Guide for the Use of Metabolic Carts: Indirect Calorimetry--No Longer the Orphan of Energy Estimation

Critically ill patients often require nutrition support, but accurately determining energy needs in these patients is difficult. Energy expenditure is affected by patient characteristics such as weight, height, age, and sex but is also influenced by factors such as body temperature, nutrition support, sepsis, sedation, and therapies. Using predictive equations to estimate energy needs is known to be inaccurate. Therefore, indirect calorimetry measurement is considered the gold standard to evaluate energy needs in clinical practice. This review defines the indications, limitations, and pitfalls of this technique and gives practice suggestions in various clinical situations.

Metabolic monitoring in the intensive care unit: a comparison of the Medgraphics Ultima, Deltatrac II, and Douglas bag collection methods

BACKGROUND

The accuracy of oxygen consumption measurement by indirect calorimeters is poorly validated in mechanically ventilated intensive care patients where multiple confounders exist. This study sought to compare the Medgraphics Ultima (MGU) and Deltatrac II (DTII) devices, and the Douglas bag (DB) technique in mechanically ventilated patients at rest.

METHODS

Prospective comparison of oxygen consumption measurement using three indirect calorimetry techniques in stable, resting mechanically ventilated patients at rest. Oxygen consumption (VO2), carbon dioxide production (VCO2), resting energy expenditure (REE), and respiratory quotient (RQ) were recorded breath-by-breath by the MGU over a 30-75 min period. During this time, simultaneous measurements were taken using the DTII, the DB, or both.

RESULTS

While there was no systematic error (bias) between measurements made by the three techniques (VO2: MGU vs DTII 3.6%, MGU vs DB 3.3%), the limits of agreement were wide (VO2: MGU vs DTII 33%, MGU vs DB 54%).

CONCLUSIONS

Resting oxygen consumption values in stable mechanically ventilated patients measured by the three techniques showed acceptable bias but poor precision. There is an important clinical and research need to develop new indirect calorimeters specifically tailored to measure oxygen consumption during mechanical ventilation.

Nutrition Monitoring in the PICU

The ideal set of variables for nutritional monitoring that may correlate with patient outcomes has not been identified. This is particularly difficult in the PICU patient because many of the standard modes of nutritional monitoring, although well described and available, are fraught with difficulties. Thus, repeated anthropometric and laboratory markers must be jointly analyzed but individually interpreted according to disease and metabolic changes, in order to modify and monitor the nutritional treatment. In addition, isotope techniques are neither clinically feasible nor compatible with the multiple measurements needed to follow progression. On the other hand, indirect alternatives exist but may have pitfalls, of which the clinician must be aware. Risks exist for both overfeeding and underfeeding of PICU patients so that an accurate monitoring of energy expenditure, using targeted indirect calorimetry, is necessary to avoid either extreme. This is very important, since the monitoring of the nutritional status of the critically ill child serves as a guide to early and effective nutritional intervention.

Energy estimation and measurement in critically ill patients

The estimation of caloric needs of critically ill patients is usually based on energy expenditure (EE), while current recommendations for caloric intake most often rely on a fixed amount of calories. In fact, during the early phase of critical illness, caloric needs are probably lower than EE, as a substantial proportion of EE is covered by the non-inhibitable endogenous glucose production. Hence, the risk of overfeeding is higher during the early phase than the late phase, while the risk of underfeeding is higher during the late phase of critical illness. Therefore, an accurate measurement of EE can be helpful to prevent early overfeeding and late underfeeding. Available techniques to assess EE include predictive equations, calorimetry, and doubly labeled water, the reference method. The available predictive equations are often inaccurate, while indirect calorimetry is difficult to perform for several reasons, including a shortage of reliable devices and technical limitations. In this review, the authors intend to discuss the different techniques and the influence of the method used on the interpretation of the results of clinical studies.

Relationship between energy expenditure, nutritional status and clinical severity before starting enteral nutrition in critically ill children

The objective of the present study was to investigate the relationship between energy expenditure (EE), biochemical and anthropometric nutritional status and severity scales in critically ill children. We performed a prospective observational study in forty-six critically ill children. The following variables were recorded before starting nutrition: age, sex, diagnosis, weight, height, risk of mortality according to the Paediatric Risk Score of Mortality (PRISM), the Revised Paediatric Index of Mortality (PIM2) and the Paediatric Logistic Organ Dysfunction (PELOD) scales, laboratory parameters (albumin, total proteins, prealbumin, transferrin, retinol-binding protein, cholesterol and TAG, and nitrogen balance) and EE measured by indirect calorimetry. The results showed that there was no relationship between EE and clinical severity evaluated using the PRISM, PIM2 and PELOD scales or with the anthropometric nutritional status or biochemical alterations. Finally, it was concluded that neither nutritional status nor clinical severity is related to EE. Therefore, EE must be measured individually in each critically ill child using indirect calorimetry.

The effects of endotracheal suctioning on the accuracy of oxygen consumption and carbon dioxide production measurements and pulmonary mechanics calculated by a compact metabolic monitor

BACKGROUND

Open endotracheal suctioning (ETS), which is performed regularly in mechanically ventilated patients to remove obstructive secretions, can cause an immediate decrease in dynamic compliance and expired tidal volume and result in inadequate or inaccurate sidestream respiratory monitoring, necessitating prolonged periods of stabilization of connected metabolic monitors. We investigated the immediate effect of open ETS on the accuracy of oxygen consumption (VO2) and carbon dioxide production (VCO2) measurements and calculated lung mechanics, respiratory quotient, and resting energy expenditure in mechanically ventilated children without severe lung pathology, when using a compact modular metabolic monitor (E-COVX) continuously recording patient spirometry and gas exchange measurements.

METHODS

Open ETS was performed when clinically indicated in 11 children mechanically ventilated for sepsis or head injury. A total of 2800 pulmonary 1-min gas exchange measurements were recorded in 28 ETS instances for 50 consecutive minutes before and 50 min after the standardized procedure.

RESULTS

Pulmonary mechanics and indirect calorimetry did not differ between pre- and postsuction sets of measurements. Pre- and postsuction VO2, VCO2, dynamic airway resistance, dynamic compliance, and expiratory minute ventilation remained stable from 5 to 55 min after tracheal suctioning and did not differ among different ventilatory modes. Average paired differences of sequential pre- and postsuction VO2, VCO2, respiratory quotient, and resting energy expenditure were -0.6%, -1%, -0.1%, and -0.3%. Ratio differences between the first and the second periods of measurements (1-25 vs 26-50 sets of 1-min measurements) did not differ in the two groups.

CONCLUSIONS

Pulmonary mechanics and indirect calorimetry measurements are not influenced after uneventful open ETS in well-sedated patients. The E-COVX is able to reliably record spirometry and metabolic indices as early as 5 min after suctioning at different ventilator modes.

Laboratory validation of the M-COVX metabolic module in measurement of oxygen uptake

A practical method of breath-by-breath monitoring of metabolic gas exchange has previously been developed by GE Healthcare and can now be easily incorporated into existing anaesthetic and critical care monitoring (M-COVX). Previous research using this device has shown good accuracy and precision between the M-COVX measurements and a traditional measurement of gas uptake at the mouth and also against the reverse Fick method during cardiac surgery and critical care, but its accuracy in the paediatric situation and across a range of ventilatory settings awaits validation. We tested the M-COVX metabolic monitor in the laboratory comparing its measurement to a traditional Haldane transformation across a wide range of oxygen consumption values, from 50 ml/minute to just under 300 ml/minute, typical of those expected in anaesthetised adults and children. The M-COVX device showed acceptable accuracy with an overall mean bias of -3.3% (range -15.1 to +4.2%, P = 0.21). Excellent linearity was found, by y = 0.96x + 0.5 ml/minute, r = 0.99. The device showed acceptable robustness to ventilatory changes examined, including changes in respiratory rate, I:E ratio, FiO2 up to 75% and simulated spontaneous breathing. However any induced leak from around the simulated endotracheal tube caused a significant error in paediatric scenarios.

Influence of different ventilator modes on Vo(2) and Vco(2) measurements using a compact metabolic monitor

OBJECTIVE

We assessed the influence of different ventilator modes on carbon dioxide elimination (Vco(2)) and oxygen uptake (Vo(2)) using a new compact modular metabolic monitor (E-COVX) and its impact on calculated respiratory quotient (RQ) and resting energy expenditure (REE) in critically ill children.

METHODS

Sequential 30-min ventilation by pressure-regulated volume controlled ventilation (PRVC), synchronized intermittent mandatory ventilation (SIMV), and biphasic intermittent positive airway pressure/airway pressure release ventilation (BiVent) in mechanically ventilated critically-ill children was assessed. To determine within- or between-day variations, 30-min Vo(2) and Vco(2) measurements were repeated at four separate occasions.

RESULTS

A total of 3960pulmonary 1-min gas exchange measurements were recorded in the 44 sessions for the three ventilator modes. Vo(2), Vco(2), and REE did not differ significantly among the PRVC, SIMV, and BiVent sequence of measurements. RQ (0.86+/-0.1) in the SIMV and Vco(2) (113+/-55mL/min) in the BiVent mode had a higher trend compared with PRVC (0.82+/-0.01, P<0.05, and 103+/-49mL/min, P<0.2, respectively). All three modes displayed good agreement and there were no significant differences between the first and second same-day or between the first- and second-day measurements or sequentially changed ventilator modes. Bland-Altman plots comparing the means of sequential REE, Vo(2), Vco(2), and RQ during the PRVC, SIMV, and BiVent modes of ventilation indicated that the average paired differences were <-5.5%.

CONCLUSION

The influence of different ventilator modes on Vo(2) and Vco(2) measurements in adequately sedated critically ill children is not significant. The E-COVX metabolic module is suitable for repeated measurements in well-sedated mechanically ventilated children with stable respiratory patterns using the PRVC, SIMV, or BiVent modes of ventilation.