Clinical evaluation of a continuous oxygen consumption monitor in mechanically ventilated patients

OXYGEN CONSUMPTION AS AN EARLY WARNING SYSTEM IN THE CRITICALLY ILL

ABSTRACT

Introduction: In this study, we assessed whether changes in oxygen consumption (VO 2 ) and other metabolic parameters could be used as an early warning system for detecting clinical deterioration in mechanically ventilated patients. Methods: This was a prospective cohort study of adult patients requiring mechanical ventilation between February 2016 and March 2019. We looked for changes in VO 2 , carbon dioxide production (VCO 2 ), respiratory quotient (RQ), and end-tidal carbon dioxide (EtCO 2 ), occurring prior to clinical deterioration. Clinical deterioration was predefined as a requirement of vasopressor, an increase in serum lactate by 20% where at least one value was above 3 mmol/L, or a decrease in hemoglobin by 20% in the 4 hours prior to clinical deterioration. Results A total of 141 patients were included. There were no detectable changes in VO 2 , VCO 2 , and EtCO 2 within the 4 hours prior to any clinical deterioration. RQ increased significantly within the 4 hours prior to an increase in lactate as compared with no increase in lactate, but there were no detectable changes prior to other clinical deteriorations. Conclusions RQ has the potential to be an early marker of tissue hypoperfusion or mitochondrial dysfunction. However, future studies are necessary to evaluate the use of RQ as a bedside monitor in critical care settings.

Esmolol to Treat the Hemodynamic Effects of Septic Shock: A Randomized Controlled Trial

INTRODUCTION

Septic shock is often characterized by tachycardia and a hyperdynamic hemodynamic profile. Use of the beta antagonist esmolol has been proposed as a therapy to lower heart rate, thereby improving diastolic filling time and improving cardiac output, resulting in a reduction in vasopressor support.

METHODS

We conducted a two-center, open-label, randomized, Phase II trial comparing esmolol to placebo in septic shock patients with tachycardia. The primary endpoint was improvement in hemodynamics as measured by the difference in norepinephrine equivalent dose (NED) between groups at 6 hours after initiation of study drug. Secondary outcomes included assessing differences in inflammatory biomarkers and oxygen consumption (VO2).

RESULTS

A total of 1,122 patients were assessed for eligibility and met inclusion criteria; 42 underwent randomization, and 40 received study interventions (18 in the esmolol arm and 22 in the usual care arm). The mean NED at 6 h was 0.30 ± 0.17 mcg/kg/min in the esmolol arm compared to 0.21 ± 0.19 in the standard care arm (P = 0.15). There was no difference in number of shock free days between the esmolol (2, IQR 0, 5) and control groups (2.5, IQR 0, 6) (P = 0.32). There were lower levels of C-reactive protein at 12 and 24 h in the esmolol arm, as well as a statistically significant difference in trend over time between groups. There were no differences in terms of IL-4, IL-6, IL-10, and TNFα. Among a subset who underwent VO2 monitoring, there was decreased oxygen consumption in the esmolol patients; the mean difference between groups at 24 h was -2.07 mL/kg/min (95% CI -3.82, -0.31) (P = 0.02), with a significant difference for the trend over time (P < 0.01).

CONCLUSION

Among patients with septic shock, infusion of esmolol did not improve vasopressor requirements or time to shock reversal. Esmolol was associated with decreased levels of C-reactive protein over 24 h.

TRIAL REGISTRATION

www.clinicaltrials.gov. Registered February 24, 2015, https://clinicaltrials.gov/ct2/show/NCT02369900.

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.

Preliminary observations in systemic oxygen consumption during targeted temperature management after cardiac arrest

AIM

Limited data suggests low oxygen consumption (VO₂), driven by mitochondrial injury, is associated with mortality after cardiac arrest. Due to the challenges of measurement in the critically ill, post-arrest metabolism remains poorly characterized. We monitored VO₂, carbon dioxide production (VCO₂) and the respiratory quotient (RQ) in post-arrest patients and explored associations with outcome.

METHODS

Using a gas exchange monitor, we measured continuous VO₂ and VCO₂ in post- arrest patients treated with targeted temperature management. We used area under the curve and medians over time to evaluate the association between VO₂, VCO₂, RQ and the VO₂:lactate ratio with survival.

RESULTS

In 17 patients, VO₂ in the first 12 h after return of spontaneous circulation (ROSC) was associated with survival (median in survivors 3.35 mL/kg/min [2.98,3.88] vs. non-survivors 2.61 mL/kg/min [2.21,2.94], p = .039). This did not persist over 24 h. The VO₂:lactate ratio was associated with survival (median in survivors 1.4 [IQR: 1.1,1.7] vs. non-survivors 0.8 [IQR: 0.6,1.2] p < 0.001). Median RQ was 0.66 (IQR 0.63,0.70) and 71% of RQ measurements were <0.7. Patients with initial RQ < 0.7 had 17% survival versus 64% with initial RQ > 0.7 (p = .131). VCO₂ was not associated with survival.

CONCLUSIONS

There was a significant association between VO₂ and mortality in the first 12 h after ROSC, but not over 24 h. Lower VO_2: lactate ratio was associated with mortality. A large percentage of patients had RQs below physiologic norms. Further research is needed to explore whether these parameters could have true prognostic value or be a potential treatment target.

Evaluation of a method for isocapnic hyperventilation: a clinical pilot trial

BACKGROUND

Isocapnic hyperventilation (IHV) is a method that shortens time to extubation after inhalation anaesthesia using hyperventilation (HV) without lowering airway CO₂ . In a clinical trial on patients undergoing long-duration sevoflurane anaesthesia for major ear-nose-throat (ENT) surgery, we evaluated the utility of a technique for CO₂ delivery (DCO₂ ) to the inspiratory limb of a closed breathing circuit, during HV, to achieve isocapnia.

METHODS

Fifteen adult ASA 1-3 patients were included. After end of surgery, mechanical HV was started by doubling baseline minute ventilation. Simultaneously, CO₂ was delivered and dosed using a nomogram developed in a previous experimental study. Time to extubation and eye opening was recorded. Inspired (FICO₂ ) and expired (FETCO₂ ) CO₂ and arterial CO₂ levels were monitored during IHV. Cognition was tested pre-operatively and at 20, 40 and 60 min after surgery.

RESULTS

A DCO₂ of 285 ± 45 ml/min provided stable isocapnia during HV (13.5 ± 4.1 l/min). The corresponding FICO₂ level was 3.0 ± 0.3%. Time from turning off the vaporizer (1.3 ± 0.1 MACage) to extubation (0.2 ± 0.1 MACage) was 11.3 ± 1.8 min after 342 ± 131 min of anaesthesia. PaCO₂ and FETCO₂ remained at normal levels during and after IHV. In 85% of the patients, post-operative cognition returned to pre-operative values within 60 min.

CONCLUSIONS

In this cohort of patients, a DCO₂ nomogram for IHV was validated. The patients were safely extubated shortly after discontinuing long-term sevoflurane anaesthesia. Perioperatively, there were no adverse effects on arterial blood gases or post-operative cognition. This technique for IHV can potentially be used to decrease emergence time from inhalation anaesthesia.

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.

Isocapnic hyperventilation shortens washout time for sevoflurane - an experimental in vivo study

BACKGROUND

Isocapnic hyperventilation (IHV) is a method that fastens weaning from inhalation anaesthesia by increasing airway concentration of carbon dioxide (CO2 ) during hyperventilation (HV). In an animal model, we evaluated a technique of adding CO2 directly to the breathing circuit of a standard anaesthesia apparatus.

METHODS

Eight anaesthetised pigs weighing 28 ± 2 kg were intubated and mechanically ventilated. From a baseline ventilation of 5 l/min, HV was achieved by doubling minute volume and fresh gas flow. Respiratory rate was increased from 15 to 22/min. The CO2 absorber was disconnected and CO2 was delivered (DCO2 ) to the inspiratory limb of a standard breathing circuit via a mixing box. Time required to decrease end-tidal sevoflurane concentration from 2.7% to 0.2% was defined as washout time. Respiration and haemodynamics were monitored by blood gas analysis, spirometry, electric impedance tomography and pulse contour analysis.

RESULTS

A DCO2 of 261 ± 19 ml/min was necessary to achieve isocapnia during HV. The corresponding FICO2 -level remained stable at 3.1 ± 0.3%. During IHV, washout of sevoflurane was three times faster, 433 ± 135 s vs. 1387 ± 204 s (P < 0.001). Arterial CO2 tension and end-tidal CO2 , was 5.2 ± 0.4 kPa and 5.6 ± 0.4%, respectively, before IHV and 5.1 ± 0.3 kPa and 5.7 ± 0.3%, respectively, during IHV.

CONCLUSIONS

In this experimental in vivo model of isocapnic hyperventilation, the washout time of sevoflurane anaesthesia was one-third compared to normal ventilation. The method for isocapnic hyperventilation described can potentially be transferred to a clinical setting with the intention to decrease emergence time from inhalation anaesthesia.

Thiamine as an adjunctive therapy in cardiac surgery: a randomized, double-blind, placebo-controlled, phase II trial

Background

Thiamine is a vitamin that is essential for adequate aerobic metabolism. The objective of this study was to determine if thiamine administration prior to coronary artery bypass grafting would decrease post-operative lactate levels as a measure of increased aerobic metabolism.

Methods

We performed a randomized, double-blind, placebo-controlled trial of patients undergoing coronary artery bypass grafting. Patients were randomized to receive either intravenous thiamine (200 mg) or placebo both immediately before and again after the surgery. Our primary endpoint was post-operative lactate levels. Additional endpoints included pyruvate dehydrogenase activity, global and cellular oxygen consumption, post-operative complications, and hospital and intensive care unit length of stay.

Results

Sixty-four patients were included. Thiamine levels were significantly higher in the thiamine group as compared to the placebo group immediately after surgery (1200 [683, 1200] nmol/L vs. 9 [8, 13] nmol/L, p < 0.001). There was no difference between the groups in the primary endpoint of lactate levels immediately after the surgery (2.0 [1.5, 2.6] mmol/L vs. 2.0 [1.7, 2.4], p = 0.75). Relative pyruvate dehydrogenase activity was lower immediately after the surgery in the thiamine group as compared to the placebo group (15 % [11, 37] vs. 28 % [15, 84], p = 0.02). Patients receiving thiamine had higher post-operative global oxygen consumption 1 hour after the surgery (difference: 0.37 mL/min/kg [95 % CI: 0.03, 0.71], p = 0.03) as well as cellular oxygen consumption. We found no differences in clinical outcomes.

Conclusions

There were no differences in post-operative lactate levels or clinical outcomes between patients receiving thiamine or placebo. Post-operative oxygen consumption was significantly increased among patients receiving thiamine.

Trial registration

clinicaltrials.gov NCT02322892, December 14, 2014

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1245-1) contains supplementary material, which is available to authorized users.

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.

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.

Intravenous thiamine is associated with increased oxygen consumption in critically ill patients with preserved cardiac index

RATIONALE

Oxygen consumption may be impaired in critically ill patients.

OBJECTIVES

To evaluate the effect of intravenous thiamine on oxygen consumption ([Formula: see text]o2) in critically ill patients.

METHODS

This was a small, exploratory open-label pilot study conducted in the intensive care units at a tertiary care medical center. Critically ill adults requiring mechanical ventilation were screened for enrollment. Oxygen consumption ([Formula: see text]o2) and cardiac index (CI) were recorded continuously for 9 hours. After 3 hours of baseline data collection, 200 mg of intravenous thiamine was administered. The outcome was change in [Formula: see text]o2 after thiamine administration.

MEASUREMENTS AND MAIN RESULTS

Twenty patients were enrolled and 3 were excluded because of incomplete [Formula: see text]o2 data, leaving 17 patients for analysis. There was a trend toward increase in [Formula: see text]o2 after thiamine administration (16.3 ml/min, SE 8.5; P = 0.052). After preplanned adjustment for changes in CI in case of a delivery-dependent state in some patients (with exclusion of one additional patient because of missing CI data), this became statistically significant (16.9 ml/min, SE 8.6; P = 0.047). In patients with average CI greater than our cohort's mean value of 3 L/min/m(2), [Formula: see text]o2 increased by 70.9 ml/min (±16; P < 0.0001) after thiamine. Thiamine had no effect in patients with reduced CI (< 2.4 L/min/m(2)). There was no association between initial thiamine level and change in [Formula: see text]o2 after thiamine administration.

CONCLUSIONS

The administration of a single dose of thiamine was associated with a trend toward increase in [Formula: see text]o2 in critically ill patients. There was a significant increase in [Formula: see text]o2 in those patients with preserved or elevated CI. Further study is needed to better characterize the role of thiamine in oxygen extraction. Clinical trial registered with www.clinicaltrials.gov (NCT01462279).

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.

Comparison of metabolic monitors in critically ill, ventilated patients

OBJECTIVE

We compared the Deltatrac II, the M-COVX, and the Evita 4 metabolic monitoring devices under clinical conditions.

METHODS

A prospective simultaneous clinical comparison was performed in a general intensive care department of a tertiary university hospital in 43 ventilated, critically ill patients. The monitors were compared simultaneously. After 30 min of steady state, oxygen consumption per unit time, carbon dioxide consumption per unit time, resting energy expenditure, and respiratory quotient were recorded for the Deltatrac II; the same parameters in addition to end-tidal carbon dioxide and fraction of inspired oxygen were recorded for the M-COVX; and carbon dioxide consumption per unit time, end-tidal carbon dioxide, and fraction of inspired oxygen were recorded for the Evita 4. Pulmonary gas-exchange measurements from the Deltatrac II and resting energy expenditure and respiratory quotient from the M-COVX were obtained after 30 min. The other parameters were calculated from the last five measurements obtained at the end of the study period.

RESULTS

A good correlation was found between oxygen consumption per unit time and resting energy expenditure as obtained from the Deltatrac II and the M-COVX (r = 0.76 and 0.75, respectively; P < 0.001), but the correlation was lower between carbon dioxide consumption per unit time as obtained from the Deltatrac II and the M-COVX or Evita 4 (r = 0.67 and 0.48, respectively). Agreement between the different methods did not reach clinical acceptability, exceeding a 20% difference using the Bland-Altman statistical methods.

CONCLUSION

Poor agreement was found between the Deltatrac II and M-COVX or Evita 4 metabolic monitors, despite a good correlation between measurements, leading to the conclusion that the M-COVX and Evita 4 provide less accurate measurements of metabolic gas exchange in stable ventilated patients. These devices can be used for daily nutritional assessment and continuous monitoring, but the Deltatrac II remains the method of choice for metabolic measurement.

Indirect calorimetry: methodology, instruments and clinical application

PURPOSE OF REVIEW

This review aims to identify the basic methods for accurately measuring a patient's energy expenditure in clinical nutrition practice by indirect calorimetry, and the impact upon a disease state of applying the results obtained.

RECENT FINDINGS

The open-circuit method is the most widely used in the majority of classical instruments for measuring energy consumption. Advances in gas exchange measurement have made this technique readily and precisely available at the bedside. Nevertheless, it is important to understand its intricate primary methodology for safe and correct application. The stress and activity factors should be carefully and specifically applied, and the respiratory quotient abandoned, for tailoring a patient's daily nutrition regimens. Caloric expenditure measured by indirect calorimetry coupled with the doubly labeled water technique introduced the concept of physical activity energy expenditure, which added to resting energy expenditure results in total daily energy expenditure. Compact modular and handheld devices have been introduced into the market, together with similar technology for evaluating exercise energy expenditure, making utilization easier, safer and precise. In the critically ill population, which is exposed to medical and surgical interventions, indirect calorimetry has greatly changed the practice of caloric administration, significantly reducing the total daily amount.

SUMMARY

In conclusion, one has to be careful when choosing devices, and understanding and clinically applying the results obtained by indirect calorimetry, bearing in mind that measured resting energy expenditure should be the daily caloric goal in order to diminish clinical morbidity.