Clinical validation of the Deltatrac monitoring system in mechanically ventilated patients

Design of a randomised controlled trial: does indirect calorimetry energy information influence weight loss in obesity?

INTRODUCTION

Respiratory quotient (RQ) provides an indication of the relative balance of carbohydrate and fat oxidation. RQ could serve as an early biomarker of negative energy balance during weight loss. Restriction of energy intake relative to total daily energy requirements produces a negative energy balance which can lead to a fall in RQ, accompanied by a decrease in resting energy expenditure (REE). However, the net change in body weight does not usually match predicted weight change due to intraindividual metabolic adaptations. Our aim is to determine the effectiveness of utilising EE information from indirect calorimetry during weight loss intervention.

METHODS AND ANALYSIS

We will undertake an assessor-blinded, parallel-group randomised controlled trial of 105 adults with obesity randomised in 1:1 ratio to receive either standard weight management care (SC) or EE information plus SC (INT) during a 24-week multicomponent weight management programme. The primary outcome is difference in weight loss between INT and SC group at 24 weeks. Secondary outcomes include: change in RQ, REE, glycaemic variability, and appetite-relating gut hormones (glucagon-like peptide 1, gastric inhibitory polypeptide, peptide YY). Generalised linear mixed models (intention to treat) will assess outcomes for treatment (INT vs SC), time (baseline, 24 weeks) and the treatment-by-time interaction. This will be the first study to evaluate impact of utilising measured REE and RQ on the lifestyle-based intensive intervention programme.

ETHICS AND DISSEMINATION

Ethics approval was obtained from the Health Research Authority and the North West Research Ethics Committee (18/NW/0645). Results from this trial will be disseminated through publication in peer-reviewed journals, national and international presentations.

TRIAL REGISTRATION NUMBERS

NCT03638895; UoL001379.

In vitro validation of indirect calorimetry device developed for the ICALIC project against mass spectrometry

RATIONALE

Accurate evaluation of the energy needs is required to optimize nutrition support of critically ill patients. Recent evaluations of indirect calorimeters revealed significant differences among the devices available on the market. A new indirect calorimeter (Q-NRG^®, Cosmed, Roma, Italy) has been developed by a group of investigators supporting the international calorimetry study initiative (ICALIC) to achieve ultimate accuracy for measuring energy expenditure while being easy to use, and affordable. This study aims to validate the precision and the accuracy of the Q-NRG^® in the in-vitro setting, within the clinically relevant range for adults on mechanical ventilation in the ICU. Mass spectrometry is the reference method for the gas composition analysis to evaluate the analytic performances of the Q-NRG^®.

METHODS

The accuracy and precision of the O₂ and CO₂ measurements by the Q-NRG were evaluated by comparing the measurements of known O₂ and CO₂ gas mixtures with the measurements by the mass spectrometer (Extrel, USA). The accuracy and precision of the Q-NRG^® for measurements of VO₂ (oxygen consumption) and VCO₂ (CO₂ production) at clinically relevant ranges (150, 250 and 400 ml/min STPD) were evaluated by measuring simulated gas exchange under mechanically ventilated setting at different FiO₂ settings (21-80%), in comparison to the reference measurements by the mass spectrometer-based mixing chamber system.

RESULTS

The measurements of gas mixtures of predefined O₂ and CO₂ concentrations by the Q-NRG^® were within 2% accuracy versus the mass spectrometer measurements in Passing Bablok regression analysis. In a mechanically ventilated setting of FiO₂ from 21 up to 70%, the Q-NRG^® measurements of simulated VO₂ and VCO₂ were within 5% difference of the reference mass spectrometer measurements.

CONCLUSION

In vitro evaluation confirms that the accuracy of the Q-NRG^® indirect calorimeter is within 5% at oxygen enrichment to 70%; i.e. maximum expected for clinical use. Further recommendations for the clinical use of the Q-NRG^® by will be released once the ongoing multi-center study is completed.

Carbon dioxide absorption during retroperitoneoscopic adrenalectomy: comparison between monolateral and synchronous bilateral approaches

Synchronous posterior retroperitoneoscopic bilateral adrenalectomy (PR-BilA) is a novel technique proposed for the definitive cure of hypercortisolism when a surgical approach is indicated. The aim of the present prospective cohort study was to compare the carbon dioxide (CO₂) absorption in patients undergoing PR-BilA with those undergoing single posterior retroperitoneoscopic adrenalectomy (PRA). Twenty-nine patients undergoing PR-BilA or PRA were consecutively enrolled. Anaesthesia was standardised. In both groups, CO₂ elimination (VCO₂), CO₂ dissolved in arterial blood (PaCO₂), end-tidal CO₂ (EtCO₂), and volume per minute (VM) were measured at the following time points: after anaesthesia induction and before CO₂ insufflation (T1), 5 min after CO₂ insufflation (T2), at the time of maximum VCO₂ (T3), and at desufflation (T4). VCO₂ was continuously measured using a metabolic monitor. ANOVA for repeated measures was used for statistical analysis. With respect to VCO₂, a significant group × time interaction was found (p = 0.03). Post hoc analysis revealed that VCO₂ was significantly increased at T4 compared with T1 in both groups (p = 0.02 and p = 0.0001 in the PRA and PR-BilA groups, respectively). Regarding PaCO₂, ANOVA analysis showed a significant group effect (p = 0.01), with higher values in the PR-BilA group. EtCO₂ and VM did not differ between the two groups. We found that the CO₂ absorption was increased in both groups at the end of surgery, in the presence of a higher trend in PaCO₂ values during PR-BilA. Therefore, PR-BilA may be considered a safe surgical approach with respect to CO₂ absorption, when a mild degree of hypercapnia may be accepted.

Determining the Accuracy and Reliability of Indirect Calorimeters Utilizing the Methanol Combustion Technique

BACKGROUND

Several indirect calorimetry (IC) instruments are commercially available, but comparative validity and reliability data are lacking. Existing data are limited by inconsistencies in protocols, subject characteristics, or single-instrument validation comparisons. The aim of this study was to compare accuracy and reliability of metabolic carts using methanol combustion as the cross-laboratory criterion.

METHODS

Eight 20-minute methanol burn trials were completed on 12 metabolic carts. Respiratory exchange ratio (RER) and percent O₂ and CO₂ recovery were calculated.

RESULTS

For accuracy, 1 Omnical, Cosmed Quark CPET (Cosmed), and both Parvos (Parvo Medics trueOne 2400) measured all 3 variables within 2% of the true value; both DeltaTracs and the Vmax Encore System (Vmax) showed similar accuracy in measuring 1 or 2, but not all, variables. For reliability, 8 instruments were shown to be reliable, with the 2 Omnicals ranking best (coefficient of variation [CV] < 1.26%). Both Cosmeds, Parvos, DeltaTracs, 1 Jaeger Oxycon Pro (Oxycon), Max-II Metabolic Systems (Max-II), and Vmax were reliable for at least 1 variable (CV ≤ 3%). For multiple regression, humidity and amount of combusted methanol were significant predictors of RER (R² = 0.33, P < .001). Temperature and amount of burned methanol were significant predictors of O₂ recovery (R² = 0.18, P < .001); only humidity was a predictor for CO₂ recovery (R² = 0.15, P < .001).

CONCLUSIONS

Omnical, Parvo, Cosmed, and DeltaTrac had greater accuracy and reliability. The small number of instruments tested and expected differences in gas calibration variability limits the generalizability of conclusions. Finally, humidity and temperature could be modified in the laboratory to optimize IC conditions.

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.

Measurement of Oxygen Consumption Variations in Critically Ill Burns Patients: Are the Fick Method and Indirect Calorimetry Interchangeable?

OBJECTIVES

To evaluate the interchangeability of oxygen consumption variations measured with the Fick equation (ΔVO2Fick) and indirect calorimetry (ΔVO2Haldane) in critically ill burns patients.

METHODS

Prospective observational single-center study conducted in a university hospital. Twenty-two consecutive burns patients with circulatory insufficiency and hyperlactatemia (>2 mmol/L) who required a fluid challenge (FC) were included. All patients had cardiac output monitoring (transpulmonary thermodilution technique) and were ventilated and sedated. Simultaneous measurements of VO2Fick and VO2Haldane were performed before and immediately after the FC, at rest, and in hemodynamic conditions stabilized for at least 1 h. VO2Fick and VO2Haldane were measured, respectively, with the standard formulae (using arterial and central venous saturation measured with a blood gas analyzer) and with a metabolic monitor.

RESULTS

Forty-four paired measurements of VO2 were obtained. At each timepoint, the median (interquartile range, 25-75) VO2Haldane values were significantly higher than the median VO2Fick values (126 (103-192) vs. 90 (66-149) mL O2/min/m (P = 0.004) before FC and 129 (105-189) vs. 80 (54-119) mL O2/min/m (P = 0.001) after FC). Correlation between the ΔVO2Fick and the ΔVO2Haldane (%) measurements was poor, with an r = 0.06, (P = 0.77). The mean bias was 8.6% [limits of agreement (LOA): -75.7%, 92.9%].

CONCLUSIONS

Analysis of agreement showed poor concordance for the ΔVO2Haldane and the ΔVO2Fick (%) with a low mean bias but large and clinically unacceptable LOA. ΔVO2Haldane and ΔVO2Fick (%) are not interchangeable in these conditions.

Indirect Calorimetry: History, Technology, and Application

Measurement of energy expenditure is important in order to determine basal metabolic rate and inform energy prescription provided. Indirect calorimetry is the reference standard and clinically recommended means to measure energy expenditure. This article reviews the historical development, technical, and logistic challenges of indirect calorimetry measurement, and provides case examples for practicing clinicians. Formulae to estimate energy expenditure are highly inaccurate and reinforce the role of the indirect calorimetry and the importance of understanding the strength and limitation of the method and its application.

Performance of Predictive Equations Specifically Developed to Estimate Resting Energy Expenditure in Ventilated Critically Ill Children

OBJECTIVE

To determine, based on indirect calorimetry measurements, the biases of predictive equations specifically developed recently for estimating resting energy expenditure (REE) in ventilated critically ill children, or developed for healthy populations but used in critically ill children.

STUDY DESIGN

A secondary analysis study was performed using our data on REE measured in a previous prospective study on protein and energy needs in pediatric intensive care unit. We included 75 ventilated critically ill children (median age, 21 months) in whom 407 indirect calorimetry measurements were performed. Fifteen predictive equations were used to estimate REE: the equations of White, Meyer, Mehta, Schofield, Henry, the World Health Organization, Fleisch, and Harris-Benedict and the tables of Talbot. Their differential and proportional biases (with 95% CIs) were computed and the bias plotted in graphs. The Bland-Altman method was also used.

RESULTS

Most equations underestimated and overestimated REE between 200 and 1000 kcal/day. The equations of Mehta, Schofield, and Henry and the tables of Talbot had a bias ≤10%, but the 95% CI was large and contained values by far beyond ±10% for low REE values. Other specific equations for critically ill children had even wider biases.

CONCLUSIONS

In ventilated critically ill children, none of the predictive equations tested met the performance criteria for the entire range of REE between 200 and 1000 kcal/day. Even the equations with the smallest bias may entail a risk of underfeeding or overfeeding, especially in the youngest children. Indirect calorimetry measurement must be preferred.

The Measurement of Energy Expenditure

Proper nutrition support depends upon the clinician's ability to estimate the patient's energy expenditure. The accuracy of estimation is inversely proportional to the severity of the patient's illness. This fact has spurred academic and industry groups to pursue the measurement of energy expenditure. Harris and Benedict used indirect calorimetry to develop their now-famous equation nearly 100 years ago. The concept of indirect calorimetry is simple; if you know the concentration of inspired gases and expired gases, along with the flow, you can determine the amount of a gas consumed or produced. The complexity and expense of indirect calorimeters suggest that this simple concept is technically challenging. Because we desire to know the energy expenditure of the most critically ill patients, indirect calorimetry is further confounded by the presence of oxygen and mechanical ventilation. This paper will discuss the myriad of variables and obstacles that complicate the measurement of energy expenditure and will suggest methods to avoid or overcome them.

Predicting Energy Expenditure in Extremely Obese Women

BACKGROUND

The most common clinical method for resting energy expenditure (REE) assessment is prediction equations. The purpose of this study was to elucidate which prediction equation is most accurate for REE assessment in extremely obese women.

METHODS

Fourteen extremely obese women (mean +/- SD body mass index: 49.8 +/- 6.2 kg/m(2); age: 49 +/- 10 years) were measured for height and weight and REE via indirect calorimetry (IC) by a metabolic cart system. Predicted REE was evaluated by several equations, including Harris-Benedict with actual body weight, Harris-Benedict with several adjustments to body weight, Cunningham, Mifflin-St Jeor, Owen, World Health Organization (WHO), and Bernstein equations. Accuracy was determined by mean difference data (IC REE - equation REE; Student's paired t-test), correlation coefficients, and agreement between methods by Bland-Altman plots. Accuracy was also evaluated on an individual basis, defined by the percentage of individuals within +/-10% of IC REE.

RESULTS

The Mifflin-St Jeor, Harris-Benedict with actual body weight, and the WHO equations were the most accurate in terms of mean predicted REE. The mean predicted REE values by all other equations were different from the IC REE values (p < .1). According to the individual data, the Mifflin-St Jeor was most accurate (14% outside +/-10% IC REE). The Harris-Benedict with actual body weight and WHO equations were less accurate on individual terms, with 29% and 42% of the predicted REE values, respectively, falling outside +/-10% of IC REE.

CONCLUSIONS

The Mifflin-St Jeor equation was most accurate method for REE assessment in extremely obese women.

Indirect calorimetry in nutritional therapy. A position paper by the ICALIC study group

BACKGROUND & AIMS

This review aims to clarify the use of indirect calorimetry (IC) in nutritional therapy for critically ill and other patient populations. It features a comprehensive overview of the technical concepts, the practical application and current developments of IC.

METHODS

Pubmed-referenced publications were analyzed to generate an overview about the basic knowledge of IC, to describe advantages and disadvantages of the current technology, to clarify technical issues and provide pragmatic solutions for clinical practice and metabolic research. The International Multicentric Study Group for Indirect Calorimetry (ICALIC) has generated this position paper.

RESULTS

IC can be performed in in- and out-patients, including those in the intensive care unit, to measure energy expenditure (EE). Optimal nutritional therapy, defined as energy prescription based on measured EE by IC has been associated with better clinical outcome. Equations based on simple anthropometric measurements to predict EE are inaccurate when applied to individual patients. An ongoing international academic initiative to develop a new indirect calorimeter aims at providing innovative and affordable technical solutions for many of the current limitations of IC.

CONCLUSION

Indirect calorimetry is a tool of paramount importance, necessary to optimize the nutrition therapy of patients with various pathologies and conditions. Recent technical developments allow broader use of IC for in- and out-patients.

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.

Approximation of Resting Energy Expenditure in Intensive Care Unit Patients Using the SenseWear Bracelet: A Comparison With Indirect Calorimetry

BACKGROUND AND AIMS

Indirect calorimetry (IC) is the gold standard for determining energy expenditure in patients requiring mechanical ventilation. Metabolic armbands using data derived from dermal measurements have been proposed as an alternative to IC in healthy subjects, but their utility during critical illness is unclear. The aim of this study was to determine the level of agreement between the SenseWear armband and the Deltatrac Metabolic Monitor in mechanically ventilated intensive care unit (ICU) patients.

METHODS

Adult ICU patients requiring invasive ventilator therapy were eligible for inclusion. Simultaneous measurements were performed with the SenseWear Armband and Deltatrac under stable conditions. Resting energy expenditure (REE) values were registered for both instruments and compared with Bland-Altman plots.

RESULTS

Forty-two measurements were performed in 30 patients. The SenseWear Armband measured significantly higher REE values as compared with IC (mean bias, 85 kcal/24 h; P = .027). Less variability was noted between individual SenseWear measurements and REE as predicted by the Harris-Benedict equation (2 SD, ±327 kcal/24 h) than when IC was compared with SenseWear and Harris-Benedict (2 SD, ±473 and ±543 kcal/24 h, respectively).

CONCLUSIONS

The systematic bias and large variability of the SenseWear armband when compared with gas exchange measurements confer limited benefits over the Harris Benedict equation in determining caloric requirements of ICU patients.

Measuring energy expenditure in the intensive care unit: a comparison of indirect calorimetry by E-sCOVX and Quark RMR with Deltatrac II in mechanically ventilated critically ill patients

Background

Indirect calorimetry allows the determination of energy expenditure in critically ill patients by measuring oxygen consumption (VO₂) and carbon dioxide production (VCO₂). Recent studies have demonstrated variable performance of “breath-by-breath” instruments compared to mixing chamber technology. The aim of this study was to validate two modern devices (E-sCOVX and Quark RMR) against a reference method (Deltatrac II).

Method

Measurements of VO₂/VCO₂ with the test and reference devices were performed simultaneously over a 20-min period in mechanically ventilated adult intensive care unit patients. Accuracy and precision of instruments were analyzed using Bland-Altman plots.

Results

Forty-eight measurements in 22 patients were included for analysis. Both E-sCOVX and Quark RMR overestimated VO₂ and VCO₂ compared to Deltatrac II, corresponding to a 10 % higher mean resting energy expenditure. Limits of agreement of resting energy expenditure within ±2 standard deviations were ±461 kcal/24 h (±21 % expressed as percentage error) for ΔE-sCOVX–Deltatrac II and ±465 kcal/24 h (±22 %) for ΔQuark RMR–Deltatrac II.

Conclusion

Both test devices overestimate VO₂ and VCO₂ compared to Deltatrac II. The observed limits of agreement are comparable to those commonly accepted in evaluations of circulatory monitoring, and significantly less than results from predictive equations. We hypothesize that the discrepancy between methods is due to patient/ventilator-related factors that affect the synchronization of gas and spirometry waveforms.

Trial registration

Australian New Zealand Clinical Trials Registry, Trial ID ACTRN12615000205538. Date registered 3 March 2015.

Validation of an indirect calorimeter using n-of-1 methodology

BACKGROUND

Validation data for currently available indirect calorimeters is limited. The purpose of this investigation was to validate a newer indirect calorimeter system (Vmax Encore) against a criterion device (Deltatrac Metabolic Monitor) in spontaneously breathing mode.

MATERIALS AND METHODS

An n-of-1 methodology was used in which both indirect calorimeters were employed in the same subject repeatedly until 15 measurement pairs were generated for oxygen consumption (VO2), carbon dioxide production (VCO2), resting metabolic rate (RMR), and respiratory quotient (RQ). Bias was defined as a 95% confidence interval of differences between devices that excluded zero. A set of intradevice measurement pairs was also obtained to analyze the precision of the Vmax and Deltatrac (precision defined as not more than 5% of measurements being ≥5% different).

RESULTS

Both Vmax and Deltatrac precisely measured VO2 and RMR. The largest intradevice difference for RMR in the Deltatrac was 4.7% (one of 20 pairs) and in the Vmax 4.8%. On the other hand, VCO2 and RQ were not measured precisely by either device, with 10% or more of the measurement pairs differing by ≥ 5%. The Vmax was biased toward low measurement of VO2 and RMR relative to the Deltatrac. Oxygen consumption was on average 4.5 ± 2.4% lower for the Vmax device compared to Deltatrac while RMR was lower by an average of 4.1 ± 2.2%.

CONCLUSIONS

The Vmax Encore indirect calorimeter is a precise instrument for measuring VO2 and RMR in spontaneously breathing individuals, but it is biased toward lower values compared to the Deltatrac.

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.

The impact of high-intensity intermittent exercise on resting metabolic rate in healthy males

INTRODUCTION

High-intensity intermittent exercise training (HIT) may favourably alter body composition despite low training volumes and predicted energy expenditure (EE).

PURPOSE

To characterise the acute impact of two common HIT protocols on EE and post-exercise oxygen consumption (11 h EPOC).

METHODS

Oxygen consumption (l min(-1)), respiratory exchange ratio (RER) and EE were measured in nine healthy, lean males over 12 h under three conditions: control (CON), HIT1 (10 × 1 min high-intensity cycling bouts followed by 1 min rest) and HIT2 (10 × 4 min high-intensity cycling bouts followed by 2 min rest).

RESULTS

Total exercise period EE during HIT1 (1,151 ± 205 kJ) (mean ± SD) was significantly lower than HIT2 (2,788 ± 322 kJ; p < 0.001). EE within the 60 min after exercise was significantly albeit marginally higher after HIT1 (388 ± 44 kJ; p = 0.02) and HIT2 (389 ± 39 kJ; p = 0.01) compared with CON (329 ± 39 kJ), with no difference between exercise conditions (p = 0.778). RER during this period was significantly lower in HIT1 (0.78 ± 0.06; p = 0.011) and HIT2 (0.76 ± 0.04; p = 0.004) compared with CON (0.87 ± 0.06). During the 'slow phase' of EPOC (1.25-9.75 h), there were no significant differences in EE (p = 0.07) or RER (p = 0.173) between trials.

CONCLUSIONS

Single HIT sessions notably increases EE during exertion; however, the influence on metabolic rate post-exercise is transient and relatively minor.

Comparison of three indirect calorimetry devices and three methods of gas collection: a prospective observational study

BACKGROUND & AIMS

Indirect calorimetry was performed for a long time with the DeltatracII(®) device (Datex, Finland), considered as a reference but no longer produced. This study aims at comparing the energy expenditure (EE), the volume of oxygen (VO2) and carbon dioxide (VCO2) measured by two new available indirect calorimeters, the QuarkRMR(®) (Cosmed, Italy) and the CCMexpress(®) (MedGraphic,USA), using three different methods of gas collection, with the DeltatracII(®) in healthy subjects.

METHODS

Twenty-four healthy subjects (15 women and 9 men, age 53 ± 15 yrs, mean BMI 25.5 ± 7.1 kg/m(2)) underwent measurements of EE with DeltatracII(®) using canopy, QuarkRMR(®) using canopy and CCMexpress(®) using canopy, face tent and facemask. All measurements were performed for 10 min in random order. Results are presented as mean ± SD and compared by linear regression, repeated measure one-way ANOVA with Bonferroni's post hoc test and Bland & Altman test.

RESULTS

EE was 1630 ± 340 kcal for DeltatracII(®) and 1607 ± 307 kcal, 1741 ± 360 kcal, 1666 ± 315 and 1626 ± 336 kcal for QuarkRMR(®) and CCMexpress(®) with canopy, face tent and facemask, respectively (p = 0.001). Compared to DeltatracII(®), Bland & Altman test showed a mean EE difference (2SD) of 24(220)kcal for QuarkRMR(®), and -111(260) kcal, -36(304) kcal, 5(402) kcal for CCMexpress(®) with canopy, face tent and facemask, respectively. There was no systematic over- or underestimation with any device or gas collection method.

CONCLUSION

Mean EE was similar between QuarkRMR(®) and DeltatracII(®) but not between CCMexpress(®), in any mode of gas collection, and DeltatracII(®). Bland & Altman test shows a large variability in EE differences with both devices compared to DeltatracII(®), highlighting the need for refining their accuracy.

The challenge of developing a new predictive formula to estimate energy requirements in ventilated critically ill children

BACKGROUND

Traditionally, energy requirements have been calculated using predictive equations. These methods have failed to calculate energy expenditure accurately. Routine indirect calorimetry has been suggested, but this method is technically demanding and costly. This study aimed to develop a new predictive equation to estimate energy requirements for critically ill children.

METHODS

This prospective, observational study on ventilated children included patients with an endotracheal tube leak of < 10% and fractional inspired oxygen of < 60%. An indirect calorimetry energy expenditure measurement was performed and polynomial regression analysis was used to develop new predictive equations. The new formulas were then compared with existing prediction equations.

RESULTS

Data from 369 measurements were included in the formula design. Only weight and diagnosis influenced energy expenditure significantly. Three formulas (A, B, C) with an R² > 0.8 were developed. When we compared the new formulas with commonly used equations (Schofield, Food and Agriculture Organization/World Health Organization/United Nations University, and White equation), all formulas performed very similar, but the Schofield equation seemed to have the lowest SD.

CONCLUSIONS

All 3 new pediatric intensive care unit equations have R² values of > 0.8; however, the Schofield equation still performed better than other predictive methods in predicting energy expenditure in these patients. Still, none of the predictive equations, including the new equations, predicted energy expenditure within a clinically accepted range, and further research is required, particularly for patients outside the technical scope of indirect calorimetry.

The effect of altering skin-surface cooling speeds on vasoconstriction and shivering thresholds

BACKGROUND

Both core and skin temperatures contribute to steady-state thermoregulatory control. Dynamic thermoregulatory responses trigger aggressive defenses against rapid thermal perturbations. These responses potentially complicate interpretation of thermoregulatory studies and could slow induction of therapeutic hypothermia. We thus tested the hypothesis that rapid external skin-cooling triggers vasoconstriction and shivering at higher mean skin temperatures than slow or moderate rates of skin cooling.

METHODS

Eleven healthy volunteers were cooled at 3 skin-cooling rates using forced air or/and conductive cooling in random order. One day volunteers received slow (≈2°C/h) skin cooling, and on another day, they received both medium (≈4°C/h) and fast (≈6°C/h) skin cooling. An endovascular heat-exchanging catheter maintained core temperature. Fingertip blood flow ≤0.25 mL/min defined onset of vasoconstriction; sustained ≥25% increase in oxygen consumption defined onset of shivering. Results were evaluated with repeated-measures analysis of variance, with P < 0.05 representing statistical significance.

RESULTS

Volunteers were 25 ± 5 years of age (mean ± SD), 175 ± 7 cm tall, and weighed 63 ± 10 kg. Core temperature remained constant (≈37°C) throughout each study day. At vasoconstriction, mean skin temperatures were 33.2°C (95% confidence interval [CI]: 32.0°C, 34.4°C), 33.5°C (95% CI: 32.3°C, 34.7°C), and 33.0°C (95% CI: 31.4°C, 34.6°C) at slow, medium, and fast skin-cooling rates, respectively. Mean skin temperatures at shivering were also comparable: 31.4°C (95% CI: 30.3°C, 32.5°C), 31.5°C (95% CI: 30.2°C, 32.8°C), and 30.7°C (95% CI: 28.9°C, 32.5°C), respectively.

CONCLUSIONS

Onset of vasoconstriction and shivering occurred at similar mean skin temperatures with all 3 cooling rates. Aggressive surface cooling can thus be used in thermoregulatory studies and for induction of therapeutic hypothermia without provoking dynamic thermoregulatory defenses.

Energy imbalance and the risk of overfeeding in critically ill children

OBJECTIVE

To examine the role of targeted indirect calorimetry in detecting the adequacy of energy intake and the risk of cumulative energy imbalance in a subgroup of critically ill children suspected to have alterations in resting energy expenditure. We examined the accuracy of standard equations used for estimating resting energy expenditure in relation to measured resting energy expenditure in relation to measured resting energy expenditure and cumulative energy balance over 1 week in this cohort.

DESIGN

A prospective cohort study.

SETTING

Pediatric intensive care unit in a tertiary academic center.

INTERVENTIONS

A subgroup of critically ill children in the pediatric intensive care unit was selected using a set of criteria for targeted indirect calorimetry.

MEASUREMENTS

Measured resting energy expenditure from indirect calorimetry and estimated resting energy expenditure from standard equations were obtained. The metabolic state of each patient was assigned as hypermetabolic (measured resting energy expenditure/estimated resting energy expenditure >110%), hypometabolic (measured resting energy expenditure/estimated resting energy expenditure <90%), or normal (measured resting energy expenditure/estimated resting energy expenditure = 90-110%). Clinical variables associated with metabolic state and factors influencing the adequacy of energy intake were examined.

MAIN RESULTS

Children identified by criteria for targeted indirect calorimetry, had a median length of stay of 44 days, a high incidence (72%) of metabolic instability and alterations in resting energy expenditure with a predominance of hypometabolism in those admitted to the medical service. Physicians failed to accurately predict the true metabolic state in a majority (62%) of patients. Standard equations overestimated the energy expenditure and a high incidence of overfeeding (83%) with cumulative energy excess of up to 8000 kcal/week was observed, especially in children <1 yr of age. We did not find a correlation between energy balance and respiratory quotient (RQ) in our study.

CONCLUSIONS

We detected a high incidence of overfeeding in a subgroup of critically ill children using targeted indirect calorimetry The predominance of hypometabolism, failure of physicians to correctly predict metabolic state, use of stress factors, and inaccuracy of standard equations all contributed to overfeeding in this cohort. Critically ill children, especially those with a longer stay in the PICU, are at a risk of unintended overfeeding with cumulative energy excess.

Resting energy expenditure in young adults born preterm--the Helsinki study of very low birth weight adults

Background

Adults born preterm with very low birth weight (VLBW; <1500g) have higher levels of cardiovascular and metabolic risk factors than their counterparts born at term. Resting energy expenditure (REE) could be one factor contributing to, or protecting from, these risks. We studied the effects of premature birth with VLBW on REE.

Methodology/Principal Findings

We used indirect calorimetry to measure REE and dual x-ray absorptiometry (DXA) to measure lean body mass (LBM) in 116 VLBW and in 118 term-born control individuals (mean age: 22.5 years, SD 2.2) participating in a cohort study. Compared with controls VLBW adults had 6.3% lower REE (95% CI 3.2, 9.3) adjusted for age and sex, but 6.1% higher REE/LBM ratio (95% CI 3.4, 8.6). These differences remained similar when further adjusted for parental education, daily smoking, body fat percentage and self-reported leisure time exercise intensity, duration and frequency.

Conclusions/Significance

Adults born prematurely with very low birth weight have higher resting energy expenditure per unit lean body mass than their peers born at term. This is not explained by differences in childhood socio-economic status, current fat percentage, smoking or leisure time physical activity. Presence of metabolically more active tissue could protect people with very low birth weight from obesity and subsequent risk of chronic disease.

Measuring energy expenditure in community-dwelling older adults: are portable methods valid and acceptable?

The objective of this study was to assess the validity and acceptability of a handheld indirect calorimeter for measurement of resting energy expenditure in a sample of community-dwelling older adults. It was a measurement study involving 48 healthy community-dwelling older adults. Assessment of resting energy expenditure was performed in 48 healthy older adults under fasting conditions using the Europa Gas Exchange Monitor (GEM; ventilated hood indirect calorimeter, NutrEn Technology Ltd, Cheshire, UK) and the MedGem (handheld indirect calorimeter, HealtheTech Inc, Golden, CO). An eight-item self-administered survey was used to determine the acceptability of the two measurement devices. Bias and limits of agreement were calculated to determine the level of agreement between the two measurements. The Wilcoxon signed-ranks test was used to test for significant differences across items of the self-administered survey. Participants mean age was 80 years and mean body mass index (calculated as kg/m(2)) was 23. Mean (95% confidence interval) resting energy expenditure was 1,149 kcal/day (1,086, 1,194) and 1,489 kcal/day (1,386, 1,592) for the traditional and handheld indirect calorimeter, respectively; paired t test P<0.001. Mean bias and limits of agreement were 349 kcal (-270, 969) or 5 kcal/kg/day (-3.6, 13.2) with least products regression resulting in a slope of b(1)=1.9 (95% confidence interval 1.2, 2.7, P<0.05). The handheld indirect calorimeter was less acceptable to participants than the ventilated hood indirect calorimeter. Measurement of resting energy expenditure from the handheld indirect calorimeter used in this study is not acceptable for use in healthy older adults given the magnitude of the overestimate, the wide limits of agreement, the significant slope of the bias, and the discomfort experienced by the participants.

Novel portable device measures preoperative patient metabolic gas exchange

BACKGROUND

Indirect calorimetry (IC), the measurement of airway CO2 elimination (VCO2), O2 [corrected] uptake (VO2) [corrected], and respiratory exchange ratio (RER = VCO2/VO2), is a noninvasive modality for the assessment of body metabolism. In anesthesia, IC can signal critical events and onset of acute metabolic derangements. We have previously demonstrated the accuracy and precision of a new IC measurement system designed for mechanically ventilated patients, comprised of a new clinical bymixer, fast response humidity and temperature sensor, and a flowmeter. However, measurement of IC during spontaneous breathing is challenging because of unstable tidal volume, frequency, and functional residual capacity (FRC).

METHODS

A new device for IC measurements, designed specifically for spontaneous breathing, was validated against a metabolic lung simulator bench setup. In a second study, the same device was used to conduct preoperative measurements of VCO2 and VO2 in 15 patients.

RESULTS

Our measurements showed excellent correlation and agreement with metabolic lung simulator values: The average (+/-SD) percent error for airway VCO2 was -4.7% +/- 3.31%; the average (+/-SD) percent error for airway VO2 was -0.30% +/- 5.25%. Average values of VCO2 and VO2 in the patient study (3.01 +/- 0.56 and 3.44 +/- 0.69 mL x kg(-1) x min(-1), respectively) were in agreement with previously reported values.

CONCLUSION

We have shown that the new, portable bymixer-flow device, using a bymixer and a fast response humidity sensor, provided accurate and convenient bedside measurement of VCO2 and VO2. We believe that it can contribute in the future to preoperative assessment and baseline reference value for perioperative management.

Day-to-day variance in measurement of resting metabolic rate using ventilated-hood and mouthpiece & nose-clip indirect calorimetry systems

BACKGROUND

To know if the magnitude of change in resting metabolic rate (RMR) observed during an intervention is meaningful, it is imperative to first identify the variability that occurs within individuals from day to day under normal conditions. The 2 most common systems used to measure RMR involve a ventilated hood or a mouthpiece & nose clip to collect expired gases. The variation in measurement using these 2 approaches has not been systematically compared.

METHODS

RMR was measured in 10 healthy adults during 5 separate testing sessions within a 2-week period where usual diet and physical activity were maintained. Each testing session consisted of one measurement of RMR using a ventilated hood system, followed by another using a mouthpiece & nose-clip system.

RESULTS

No significant difference in RMR was evident between measurement sessions using either indirect calorimeter. Oxygen consumption and RMR were significantly higher using the mouthpiece & nose-clip system. Average within-individual coefficient of variation for RMR was significantly lower for the ventilated-hood system. RMR measures were consistently lower using the ventilated-hood system by an average of 94.5 +/- 63.3 kcal. Day-to-day variance was between 2% and 4% for both systems.

CONCLUSIONS

The use of either system is appropriate for assessing RMR in clinical and research settings, but alternating between systems should be undertaken with caution. A change in RMR must be greater than approximately 6% (96 kcal/d; 1.2 kcal/kg/d) or approximately 8% (135 kcal/d; 1.7 kcal/kg/d) when using a ventilated-hood system or a mouthpiece & nose-clip system, respectively, to observe any meaningful intervention-related differences within individuals.

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.

Validation of the VO2000 calorimeter for measuring resting metabolic rate

BACKGROUND & AIMS

Metabolic carts used in laboratory settings for the measurement of resting metabolism are cumbersome limiting their use in the field. The validity of a newly developed portable calorimeter (Medical Graphics VO2000) under resting conditions was assessed in comparison to a well-established reference system, the DELTATRAC.

METHODS

Gas exchange and energy expenditure were measured for 25 min consecutively using the two devices. Values of the last 20 min were averaged and used in the analysis. The order of device for the first subject was randomly chosen and the calorimeters were alternated thereafter.

RESULTS

Among 33 subjects, acceptable measures of resting metabolism were obtained in 25 (11 men) aged 20-78 years because eight subjects (three men) either hyperventilated or did not adapt well enough to the facemask. VO(2), VCO(2), and RQ were not significantly different between devices. Small (2.8%) non-clinically relevant mean differences (-0.145+/-0.341 MJ day(-1)) were found. Results of the two devices were highly correlated (r=0.95) yielding a more accurate estimate than predictive equations.

CONCLUSIONS

The VO2000 calorimeter is a valid system to measure resting metabolism but the facemask may not be suitable for some people.

Bi-level positive airway pressure ventilation maintains adequate ventilation in post-polio patients with respiratory failure

BACKGROUND

Patients suffering from post-polio syndrome still contribute significantly to the number of patients with chronic respiratory failure requiring home mechanical ventilation (HMV). Many of these patients are treated either with invasive (tracheostomy) or non-invasive (nasal mask) controlled mechanical ventilation i.e. volume-controlled ventilation (VCV). In this group of patients, we have previously shown that bi-level pressure support ventilation (bi-level PSV) decreases the oxygen cost of breathing. The aim of this study was to compare the effect of bi-level PSV, with special regard to the adequacy of ventilation and the oxygen cost of breathing, during the patients' ordinary VCV and spontaneous breathing.

METHODS

Eight post-polio patients on nocturnal VCV were investigated. Five of them were tracheostomized and three of them used a nasal mask. Work of breathing was analysed by assessing differences in oxygen consumption (VO2) using indirect calorimetry. Blood gases were obtained regularly to assess adequacy of ventilation.

RESULTS

Bi-level PSV decreases the oxygen cost of breathing in post-polio patients with respiratory failure without decreasing ventilation efficiency. Furthermore, PaCO2 decreased significantly using this mode of ventilation (P < 0.05).

CONCLUSION

In this study, it was shown that bi-level PSV reduces the oxygen cost of breathing and gave a significant decrease in PaCO2 in PPS patients. These data suggest that bi-level PSV ventilation maintains adequate ventilation in patients who suffer from post-polio syndrome with respiratory failure.

Comparison between Medgem and Deltatrac resting metabolic rate measurements

OBJECTIVE

The primary aims of this trial were to evaluate the reproducibility of a portable handheld calorimeter (Medgem) in a clinical population, and to compare its measures with a calorimeter in typical use with these patients.

DESIGN

Cross-sectional clinical validation study.

SETTING

Outpatient Clinical Research Center.

SUBJECTS

A total of 24 stable home nutrition support patients.

INTERVENTIONS

In random order three measures of resting metabolic rate (RMR) were taken after a 4-h fast, 15 min rest and 2-h abstention from exercise. Two measures were taken with the same Medgem (MG) and one with the traditional calorimeter (Deltatrac). Reproducibility of MG measures and their comparability to a Deltatrac measure were assessed by Bland-Altman analysis, with >+/-250 kcal/day established a priori as a clinically unacceptable error. In addition, disagreement between the two types of measures was defined as greater than 10% difference.

RESULTS

The mean difference between two MG measures was -6.8 kcal/day, with limits of agreement between 233 and -247 kcal/day and clinically acceptable. The mean difference between the Deltatrac and mean of two MG measures was -162 kcal/day, with limits of agreement between 577 and -253 kcal/day and clinically unacceptable. In all, 80% of the repeated MG RMR measures agreed within 10%, and the mean MG reading agreed with the Deltatrac in 60% of cases.

CONCLUSIONS

RMR obtained using the MG calorimeter has an acceptable degree of reproducibility, and is acceptable to patients. The MG measures, however, are frequently lower than traditional measures and require further validation prior to application to practice in this vulnerable patient group.

The agreement between the MedGem indirect calorimeter and a standard indirect calorimeter in anorexia nervosa

OBJECTIVES

Measurement of the basal metabolic rate (BMR) can be used to estimate the calories required for weight gain during refeeding in anorexia nervosa (AN). The reference method for measuring the BMR is indirect calorimetry. MedGem has developed a new indirect calorimeter that calculates the metabolic rate much more quickly than standard indirect calorimeters. This study compared the BMR measured by the MedGem and standard indirect calorimetry in an AN population.

METHODS

We measured the BMR using the Deltatrac metabolic cart followed immediately by the MedGem indirect calorimeter in 27 subjects (12 patients and 15 controls).

RESULTS

Bland-Altman plots show that there is poor agreement between the BMR reported by the MedGem compared to the Deltatrac.

DISCUSSION

Until better agreement with standard indirect calorimetry can be shown the MedGem should not be used for calorimetry in AN. Possible factors that may limit the MedGem's reliability include patient discomfort with the mouthpiece, use of a fixed RQ, and the short sampling period.

Assumed oxygen consumption frequently results in large errors in the determination of cardiac output

OBJECTIVE

We sought to investigate the differences in assumed and measured oxygen consumption values for the determination of cardiac output by using the Fick principle in a pediatric population with congenital heart disease.

METHODS

The patient population consisted of 143 patients with a mean age of 11.3 years (age range, 2 days to 23.8 years) undergoing cardiac catheterization during general anesthesia and with mechanical ventilation. Oxygen consumption was measured with a standard commercial analyzing system (Deltatrac II; Datex, Engström, Helsinki, Finland). Assumed oxygen consumption values were calculated according to the formulas of Krovetz and Goldbloom and LaFarge and Miettinen. Comparisons between measurements and assumptions were performed by Bland-Altman plots. Two-sided paired t tests were used to assess a difference of the assumed and measured values.

RESULTS

The range of measured oxygen consumption values was between 55.2 and 249 mL . min -1 . m -2 . The Krovetz-Goldbloom formula led to systematically larger values compared with the measured values (P = .0001; mean difference of -53.3 mL . min -1 . m -2 ; 95% confidence interval, -56.7 to -49.8 mL . min -1 . m -2 ). The use of the LaFarge-Miettinen formula tends to overestimate oxygen consumption (P = .0037; mean difference of -15.9 mL . min -1 . m -2 ; 95% confidence interval, -26.5 to -5.4 mL . min -1 . m -2 ). A similarly poor agreement was found when analyzing a subgroup of 25 patients with Fontan-type circulation.

CONCLUSION

The use of assumed instead of measured oxygen consumption values introduces large errors in the determination of cardiac output.

Simple and accurate assessment of energy expenditure in ventilated paediatric intensive care patients

AIMS

To assess validity and reliability of energy expenditure measurements with a short Douglas bag protocol compared to the standard metabolic monitor in a paediatric intensive care setting.

METHODS

51 paired measurements were performed in 14 ventilated patients (age 0-18 years) with sepsis, trauma or following major surgery. Measured data were compared mutually and compared to Schofield equations using Bland-Altman analysis.

RESULTS

Comparing Douglas bag (3.21 +/- 1.43 MJ/day) and metabolic monitor (3.15 +/- 1.49 MJ/day) we found bias in energy expenditure of -0.06 (equal to -2%, NS) with limits of agreement of -0.5 to 0.4 MJ/day (equal to -16% to +13%). Intra-measurement variability (coefficient of variation) was within 10% for both methods. Both the metabolic monitor and Douglas bag showed significant bias compared to Schofield equations (3.39 +/-1.64 MJ/day) of -7% (P < 0.01) and -5% (P < 0.05), respectively, with wide limits of agreement: metabolic monitor vs. Schofield: -37% to +22%, Douglas bag vs. Schofield: -37% to +26%.

CONCLUSIONS

The Douglas bag method compared favourably to the metabolic monitor where Schofield equations failed to predict individual energy expenditure. Considering its low cost, this renders the short and simple Douglas bag method a robust measure and a routinely applicable instrument for tailored nutritional assessment in critically ill children.

Validity and reproducibility of resting metabolic rate measurements in rural Bangladeshi women: comparison of measurements obtained by Medgem™ and by Deltatrac™ device

OBJECTIVE

To assess reproducibility and validity of resting metabolic rate (RMR) of Bangladeshi women as measured with the MedGem device and using the Deltatrac metabolic monitor as a reference; and (2) to evaluate the FAO/WHO/UNU basal metabolic rate (BMR)-prediction equations.

DESIGN

In each of two sessions, resting oxygen consumption was measured in triplicate by MedGem and in triplicate by Deltatrac device.

SETTING

Matlab area, the rural field research area of the Centre for Health and Population Research, Bangladesh (ICDDR,B).

SUBJECTS

A total of 37 nonpregnant, nonlactating women, aged 27.6 +/- 4.5 y, BMI 20.8 +/- 3.1 kg/m(2) participated.

RESULTS

The difference in oxygen consumption by MedGem and Deltatrac device was significantly level dependent. Within-subject within-session variations (expressed as CV) were 9.0 and 3.0% (P < 0.01) and within-subject between-session variations were 8.2 and 4.5% (P < 0.01) for MedGem and Deltatrac, respectively. Mean RMR measured by Deltatrac (5.17 +/- 0.51 MJ/day) was not significantly different from the BMR predicted by the FAO/WHO/UNU equations (5.16 +/- 0.42 MJ/day) in the second session and only 0.19 MJ/day higher than predicted in the first session (P < 0.05).

CONCLUSION

Reproducibility and validity of the MedGem device was poor compared to the Deltatrac reference method. The FAO/WHO/UNU BMR-prediction equations give a good estimation of the BMR of rural, nonpregnant, nonlactating Bangladeshi women of 18-35 y.

SPONSORSHIP

Wageningen University (The Netherlands) and ICDDR,B (Bangladesh).

Bi-level positive airway pressure ventilation reduces the oxygen cost of breathing in long-standing post-polio patients on invasive home mechanical ventilation

BACKGROUND

Today, patients with chronic respiratory failure are commonly treated with non-invasive bi-level positive airway pressure ventilation, supporting spontaneous breathing. However, in conformity with previous clinical routine, many post-polio patients with chronic respiratory failure are still treated with invasive (i.e. via a tracheostomy) controlled mechanical ventilation (CMV). The aim of the study was to investigate the effect of invasive bi-level positive airway pressure ventilation on the work of breathing compared with that during the patients' ordinary CMV and spontaneous breathing without mechanical support.

METHODS

Nine post-polio patients on invasive (tracheostomy) nocturnal CMV were investigated. Work of breathing was analysed by assessing differences in oxygen consumption (VO2) using indirect calorimetry. Hereby, the oxygen cost of breathing during the various ventilatory modes could be estimated and related to one another. Data on energy expenditure were also obtained.

RESULTS

The oxygen cost of breathing decreased by approximately 15% during bi-level positive airway pressure ventilation compared with CMV and spontaneous breathing. There was no difference between predicted (Harris-Benedict equation) and measured energy expenditure.

CONCLUSION

Invasive bi-level positive airway pressure ventilation reduces the oxygen cost of breathing in long-standing tracheostomized post-polio patients, compared with CMV. Furthermore, the Harris-Benedict equation provides a reasonable prediction of energy expenditure in this group of patients.

Novel method of quantifying pulmonary vascular resistance by use of simultaneous invasive pressure monitoring and phase-contrast magnetic resonance flow

BACKGROUND

Pulmonary vascular resistance (PVR) quantification is important in the treatment of children with pulmonary hypertension. The Fick principle, used to quantify pulmonary artery flow, may be a flawed technique. We describe a novel method of PVR quantification by the use of magnetic resonance (MR) flow data and invasive pressure measurements.

METHODS AND RESULTS

In 24 patients with either suspected pulmonary hypertension or congenital heart disease requiring preoperative assessment, PVR was calculated by the use of simultaneously acquired MR flow and invasive pressure measurements (condition 1). In 19 of the 24 patients, PVR was also calculated at 20 ppm nitric oxide +30% (condition 2) and at 20 ppm nitric oxide +100% oxygen (condition 3), with the use of the MR method. This method proved safe and feasible in all patients. In 15 of 19 patients, PVR calculated by Fick flow was compared with the MR method. At condition 1, Bland-Altman analysis revealed a bias of 2.3% (MR > Fick) and limits of agreement of 50.2% to -45.5%. At condition 2, there was poorer agreement (bias was 28%, and the limits of agreement were 151.3% to 95.2%). At condition 3, there was very poor agreement (bias was 54.2%, and the limits of agreement were 174.4% to -66.0%).

CONCLUSIONS

We have demonstrated the feasibility of using simultaneous invasive pressure measurements and MR flow data to measure PVR in humans.

Insulin-like growth factor 1 improves the relationship between systemic oxygen consumption and delivery in piglets after cardiopulmonary bypass

OBJECTIVE

We sought to assess the effects of insulin-like growth factor 1 on the balance between systemic oxygen consumption and oxygen delivery after cardiopulmonary bypass in piglets.

METHODS

Twelve piglets weighing 4.5 to 8.3 kg undergoing hypothermic (28 degrees C) cardiopulmonary bypass for 70 to 120 minutes with 40 minutes of aortic crossclamping were studied before and during the first 6 hours after cardiopulmonary bypass. Oxygen consumption was continuously measured by an indirect calorimeter, Deltatrac II MBM-200 Metabolic Monitor (Datex Division Instrumentarium, Helsinki, Finland). Oxygen delivery and cardiac output were calculated from oxygen consumption and the arterial and mixed venous oxygen contents sampled before and every 30 minutes after cardiopulmonary bypass. Oxygen extraction ratio was derived by the ratio of oxygen consumption to oxygen delivery. Arterial blood lactate was measured before and every 30 minutes after cardiopulmonary bypass. Six animals were randomly assigned to receive an intravenous infusion of insulinlike growth factor 1 at 1.2 mg/h from 1 to 6 hours after cardiopulmonary bypass; the remaining 6 served as a control group.

RESULTS

Relative to the control group, intravenous infusion of insulin-like growth factor 1 significantly reduced oxygen consumption (P =.02) and increased cardiac output (P =.016) and oxygen delivery (P =.049) during the first 6 hours after surgery with hypothermic cardiopulmonary bypass. As a result, oxygen extraction was significantly decreased (P =.012).

CONCLUSIONS

Intravenous infusion of insulin-like growth factor 1 improved oxygen transport by reducing oxygen consumption as well as increasing cardiac output and oxygen delivery during the first 6 hours after cardiopulmonary bypass in piglets. This may have important clinical implications for the care of critically ill children after surgery with cardiopulmonary bypass.

Dantrolene Reduces the Threshold and Gain for Shivering

Dantrolene is used for treatment of life-threatening hyperthermia, yet its thermoregulatory effects are unknown. We tested the hypothesis that dantrolene reduces the threshold (triggering core temperature) and gain (incremental increase) of shivering. Healthy volunteers were evaluated on 2 random days: control and dantrolene (approximately 2.5 mg/kg plus a continuous infusion). In Study 1, 9 men were warmed until sweating was provoked and then cooled until arteriovenous shunt constriction and shivering occurred. Sweating was quantified on the chest using a ventilated capsule. Absolute right middle fingertip blood flow was quantified using venous-occlusion volume plethysmography. A sustained increase in oxygen consumption identified the shivering threshold. In Study 2, 9 men were given cold lactated Ringer's solution i.v. to reduce core temperature approximately 2 degrees C/h. Cooling was stopped when shivering intensity no longer increased with further core cooling. The gain of shivering was the slope of oxygen consumption versus core temperature regression. In Study 1, sweating and vasoconstriction thresholds were similar on both days. In contrast, shivering threshold decreased 0.3 +/- 0.3 degrees C, P = 0.004, on the dantrolene day. In Study 2, dantrolene decreased the shivering threshold from 36.7 +/- 0.2 to 36.3 +/- 0.3 degrees C, P = 0.01 and systemic gain from 353 +/- 144 to 211 +/- 93 mL.min(-1).degrees C(-1), P = 0.02. Thus, dantrolene substantially decreased the gain of shivering, but produced little central thermoregulatory inhibition.

IMPLICATIONS

Dantrolene substantially decreases the gain of shivering but produces relatively little central thermoregulatory inhibition. It thus seems unlikely to prove more effective than conventional muscle relaxants for treatment of life-threatening hyperthermia.

The effects of standard and branched chain amino acid enriched solutions on thermogenesis and energy expenditure in unconscious intensive care patients

BACKGROUND & AIMS

This study aims to compare the effects of standard and branched chain amino acid enriched solutions on thermogenesis and energy expenditure in unconscious and mechanically ventilated intensive care patients.

DESIGNS

The study was carried out at multidisciplinary intensive care unit. Twenty unconscious and mechanically ventilated patients (18-65 years of age) were included in the study. Patients were hemodynamically stable and all received continuous enteral nutrition. Energy expenditure was calculated using the Harris-Benedict Equation for all of the patients. Patients were randomly assigned to receive a 4h infusion of 0.4 g/kg protein as amino acid solution. Group I (n = 10) received standard amino acid solution and group II (n = 10) received branched chain amino acid enriched solution. Energy expenditure, oxygen consumption and carbon dioxide production were measured by indirect calorimetric method every 30 min during the 4h infusion period and 3h thereafter. Rectal temperature was recorded concomitantly with the metabolic measurements throughout the study.

RESULTS

There was a statistically significant increase in body temperature during the infusion of amino acid solution between 30 and 210 min in group I and between 30 and 120 min in group II (P <0.05). We observed a significant increase in energy expenditure at 30, 150, 180 and 210 min in group I and at 30-240 min in group II (P <0.05). There were no differences between the two groups in terms of thermogenesis or energy expenditure values during the study (P >0.05).

CONCLUSION

Thermogenesis and energy expenditure values were increased during the parenteral infusion of both standard amino acid and branched chain amino acid enriched solutions in unconscious intensive care patients without any significance in between.