Resting energy expenditure and substrate oxidation rates correlate to temperature and outcome after cardiac arrest - a prospective observational cohort study

Associations of systemic oxygen consumption with age and body temperature under general anesthesia: retrospective cohort study

BACKGROUND

Body temperature (BT) is thought to have associations with oxygen consumption (VO2). However, there have been few studies in which the association between systemic VO2 and BT in humans was investigated in a wide range of BTs. The aims of this study were 1) to determine the association between VO2 and age and 2) to determine the association between VO2 and BT.

METHODS

This study was a retrospective study of patients who underwent surgery under general anesthesia at a tertiary teaching hospital. VO2 was measured by the Dräger Perseus A500 anesthesia workstation (Dräger Medical, Lubeck, Germany). The associations of VO2 with age and BT were examined using spline regression and multivariable regression analysis with a random effect.

RESULTS

A total of 7,567 cases were included in this study. A linear spline with one knot shows that VO2 was reduced by 2.1 ml/kg/min with one year of age (p < 0.001) among patients less than 18 years of age and that there was no significant change in VO2 among patients 18 years of age or older (estimate: 0.014 ml/kg/min, p = 0.08). VO2 in all bands of BT < 36.0 °C was not significantly different from VO2 in BT >  = 36 °C and < 36.5 °C. Multivariable linear regression analysis showed that compared with VO2 in BT >  = 36 °C and < 36.5 °C as a reference, VO2 levels were significantly higher by 0.57 ml/kg/min in BT >  = 36.5 °C and < 37 °C (p < 0.001), by 1.8 ml/kg/min in BT >  = 37 °C and < 37.5 °C (p < 0.001), by 3.6 ml/kg/min in BT >  = 37.5 °C and < 38 °C (p < 0.001), by 4.9 ml/kg/min in BT >  = 38 °C and < 38.5 °C (p < 0.001), and by 5.7 ml/kg/min in BT >  = 38.5 °C (p < 0.001). The associations between VO2 and BT were significantly different among categorized age groups (p = 0.03).

CONCLUSIONS

VO2 increases in parallel with increase in body temperature in a hyperthermic state but remains constant in a hypothermic state. Neonates and infants, who have high VO2, may have a large systemic organ response in VO2 to change in BT.

Methods for Estimating Energy Expenditure in Critically Ill Adults

Energy expenditure (EE) is the sum of metabolic activity within the body at a given time and comprises basal EE, diet-induced thermogenesis, and physical activity. In the intensive care unit, EE is most often assessed to determine a patient's caloric requirements. Energy expenditure also may be useful to understand disease states and the metabolic impact of interventions. Several methods for estimating EE are relevant for clinical use, including indirect calorimetry, predictive equations, exhaled carbon dioxide volume, and the Fick method. Indirect calorimetry is the preferred method for evaluating EE and is considered the gold standard for estimating EE in hospitalized patients. However, use of indirect calorimetry is not always practical or possible. Therefore, other methods of estimating EE must be considered. In this review, methods of evaluating EE in critically ill adults are examined and the benefits and limitations of each method are discussed, with practical considerations for use.

Measured energy expenditure in mildly hypothermic critically ill patients with traumatic brain injury: A sub-study of a randomized controlled trial

BACKGROUND & AIMS

Prophylactic hypothermia, often used in critically ill patients with traumatic brain injury, reduces energy expenditure and may affect energy delivered by nutrition therapy. The primary objective of this study was to measure energy expenditure in hypothermic patients over the first 3 days after traumatic brain injury (TBI). Secondary objectives included comparison of measured energy expenditure and nutrition delivery to day 7.

METHODS

A prospective sub-study of a randomized controlled trial conducted in patients with severe TBI, investigating prophylactic hypothermia (33-35 °C) as a neuroprotective therapy. In two centers, indirect calorimetry was initiated within 24 h of randomization and repeated up to twice daily to day 7. Data are presented as n (%), mean (standard deviation (SD)), median [interquartile range (IQR)], and mean difference (95% confidence interval (CI)).

RESULTS

Forty patients were included (20 in each group), with 17 patients in the hypothermic and 16 in the normothermic group having an indirect calorimetry measurement in the first 3 days. Over the first 3 days, the mean temperature in the hypothermic and normothermic groups was 33.5 (0.6) ºC (n = 17) and 37 (0.5) ºC (n = 16), p < 0.0001, and the mean measured energy expenditure, was 21 (5) and 27 (4) kcal/kg, p = 0.002, representing a mean difference of 5 (95% CI: 2-8) kcal/kg. Energy expenditure was 20% (95% CI: 9.5-29%) less in hypothermia patients compared to normothermia patients. Hypothermia patients also had higher gastric residual volumes across the 7 day study period (438 (237) mls vs 184 (103) mls, p < 0.0001) and higher use of metoclopramide and erythromycin as prokinetics. Despite enteral nutrition intolerance, hypothermia patients received 93% of measured energy expenditure over 7 days.

CONCLUSION

In TBI patients, energy expenditure was 20% less when receiving prophylactic hypothermia compared to normothermia. Greater gastric residual volumes, use of prokinetics and energy delivery that approximated measured energy expenditure was also observed in hypothermia patients.

TRIAL REGISTRY NUMBER

POLAR-RCT: clinicaltrials.gov Identifier: NCT00987688; Anzctr.org.au Identifier: ACTRN12609000764235. This sub-study was not registered separately.

Energy Expenditure and Shivering Severity During Targeted Temperature Management at 36°C After Cardiac Arrest: A Case Series

Patients undergoing targeted temperature management (TTM) after cardiac arrest are at risk for shivering, which increases energy expenditure (EE) and may attenuate TTM benefits. This article reports patterns of EE for patients with and without shivering who received TTM at 36°C after cardiac arrest. Based on 96 case assessments, there were 14 occasions when more than one 15-minute interval period was required to appropriately modify the Bedside Shivering Assessment Scale (BSAS) score. Investigators noted that although higher EE was related to higher BSAS scores, there may be opportunities for earlier detection of shivering.

The effect of cisatracurium infusion on the energy expenditure of critically ill patients: an observational cohort study

Background

Both overfeeding and underfeeding of intensive care unit (ICU) patients are associated with worse outcomes. A reliable estimation of the energy expenditure (EE) of ICU patients may help to avoid these phenomena. Several factors that influence EE have been studied previously. However, the effect of neuromuscular blocking agents on EE, which conceptually would lower EE, has not been extensively investigated.

Methods

We studied a cohort of adult critically ill patients requiring invasive mechanical ventilation and treatment with continuous infusion of cisatracurium for at least 12 h. The study aimed to quantify the effect of cisatracurium infusion on EE (primary endpoint). EE was estimated based on ventilator-derived VCO₂ (EE in kcal/day = VCO₂ × 8.19). A subgroup analysis of septic and non-septic patients was performed. Furthermore, the effects of body temperature and sepsis on EE were evaluated. A secondary endpoint was hypercaloric feeding (> 110% of EE) after cisatracurium infusion.

Results

In total, 122 patients were included. Mean EE before cisatracurium infusion was 1974 kcal/day and 1888 kcal/day after cisatracurium infusion. Multivariable analysis showed a significantly lower EE after cisatracurium infusion (MD − 132.0 kcal (95% CI − 212.0 to − 52.0; p = 0.001) in all patients. This difference was statistically significant in both sepsis and non-sepsis patients (p = 0.036 and p = 0.011). Non-sepsis patients had lower EE than sepsis patients (MD − 120.6 kcal; 95% CI − 200.5 to − 40.8, p = 0.003). Body temperature and EE were positively correlated (Spearman’s rho = 0.486, p < 0.001). Hypercaloric feeding was observed in 7 patients.

Conclusions

Our data suggest that continuous infusion of cisatracurium in mechanically ventilated ICU patients is associated with a significant reduction in EE, although the magnitude of the effect is small. Sepsis and higher body temperature are associated with increased EE. Cisatracurium infusion is associated with overfeeding in only a minority of patients and therefore, in most patients, no reductions in caloric prescription are necessary.

Systematic review of factors associated with energy expenditure in the critically ill

BACKGROUND AND AIMS

Indirect calorimetry is the reference standard for energy expenditure measurement. Predictive formulae that replace it are inaccurate. Our aim was to review the patient and clinical factors associated with energy expenditure in critically ill patients.

METHODS

We conducted a systematic review of the literature. Eligible studies were those reporting an evaluation of factors and energy expenditure. Energy expenditure and factor associations with p-values were extracted from each study, and each factor was classified as either significantly, indeterminantly, or not associated with energy expenditure. Regression coefficients were summarized as measures of central tendency and spread. Metanalysis was performed on correlations.

RESULTS

The search strategy yielded 8521 unique articles, 307 underwent full text review, and 103 articles were included. Most studies were in adults. There were 95 factors with 352 evaluations. Minute volume, weight, age, % body surface area burn, sedation, post burn day, and caloric intake were significantly associated with energy expenditure. Heart rate, fraction of inspired oxygen, respiratory rate, respiratory disease diagnosis, positive end expiratory pressure, intensive care unit days, C- reactive protein, and size were not associated with energy expenditure. Multiple factors (n = 37) were identified with an unclear relationship with energy expenditure and require further evaluation.

CONCLUSIONS

An important interval step in the development of accurate formulae for energy expenditure estimation is a better understanding of relationships between patient and clinical factors and energy expenditure. The review highlights the limitations of currently available data, and identifies important factors that are not included in current prediction formulae of the critically ill.

Energy Balance in Critically Ill Children With Severe Sepsis Using Indirect Calorimetry: A Prospective Cohort Study

OBJECTIVES

Energy needs in critically ill children are dynamic and variable. Data on energy balance in children with severe sepsis using indirect calorimetry (IC) is lacking. Thus, we planned to study the energy needs and balance of this cohort.

METHODS

Prospective observational study conducted in ventilated children aged 5 to 12 years, admitted in pediatric intensive care unit with severe sepsis from May 2016 to June 2017. Measured resting energy expenditure (mREE) was measured with IC (Quark RMR, COSMED) till 7 days or pediatric intensive care unit discharge. Predicted energy expenditure (pREE) was estimated using Schofield, Harris and Benedict, and FAO/WHO/UNU equations. Primary outcome was to study the daily energy balance. Secondary outcome was to determine nitrogen balance and agreement of mREE with pREE.

RESULTS

Forty children (24 boys) with median age of 7 (5.2, 10) years were enrolled. All received enteral nutrition; 35 (87.5%) received inotropic support. Median ventilation-free days were 19 days and 4 children died (10%). A total of 176 IC measurements were obtained with an average of 4 per patient. The mean mREE was 51 ± 17 kcal/kg and mean respiratory quotient was 0.77 ± 0.07. There was persistent negative energy balance from days 1 to 7 and negative nitrogen balance from days 1 to 5. There was poor agreement of pREE with mREE using Bland Altman plots. None of severity of illness scores (PRISM III, daily Sequential Organ Function Assessment, daily Vasoactive Inotropic Score) showed correlation with mREE.

CONCLUSIONS

Persistent negative energy and nitrogen balance exist during acute phase of severe sepsis. Predictive equations are inaccurate compared with IC as the criterion standard.

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.

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.