Metabolic requirement of septic shock patients before and after liberation from mechanical ventilation

Peggy Siu Pik Lee, Kar Lung Lee, Kin Ip Law, James Betts

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Negative energy balance can impair regeneration of the respiratory epithelium and limit the functionality of respiratory muscles, which can prolong mechanical ventilation. The present study sought to quantify and identify the difference in energy expenditure of patients with septic shock during and upon liberation from mechanical ventilation.

Patients admitted into intensive care with initial diagnosis of septic shock and mechanical ventilation-dependent were recruited. Their metabolic requirements before and after liberation from mechanical ventilation were measured by indirect calorimetry. A paired t-test was used to examine the variance between the two modes of breathing and a Spearman rho correlation coefficient to examine relationship of selected indicators.

Thirty-five patients, 20 males and 15 females mean age 69 ±10 years, body height of 1.58 ±0.08 meters, and ideal body mass 59.01 ±7.63 kg were recruited. Median APACHEII score was 22, length of stay in the intensive care was 45 ±65 days and duration on mechanical ventilation was 24 ±25 days. Measured energy expenditure during ventilation was 2090 ±489 kcal∙d-1 upon liberation from ventilation was 1910 ±579 kcal∙d-1 and actual caloric intake was 1148 ±495 kcal∙d-1. Measured energy expenditure (p=0.02), actual calories provision and energy expenditure with (p=0.00) and without (p=0.00) ventilator support were all significantly different. Mean carbohydrate oxidation was 0.17 ±0.09 g·min-1 when patients were on mechanical ventilation compared to 0.14 ±0.08 g·min-1 upon liberation, however, this difference was not statistically significant. Furthermore, mean lipid oxidation was 0.08 ±0.05 g·min-1 during mechanical ventilation and 0.09±0.07 g·min-1 upon liberation, which was also not statistically different. Comparison of carbohydrate utilization and lipid oxidation was not different during (0.7±0.36 vs 0.75±0.47 kcal·min-1) and upon liberation from mechanical ventilation (0.55±0.33 vs 0.78±0.59 kcal·min-1).

This study examined energy expenditure and substrate oxidation within a single cohort of patients with and without mechanical ventilation. Measured energy expenditure was found to be higher during mechanical ventilation. The possible explanations were positive pressure support from ventilation, the repeated cycle of “rest” and “work” during weaning from ventilators and the asynchronization between self-initiated breathing effort and the ventilatory support. The change energy expenditure with and without ventilatory support should be monitored so that mismatch could be aligned. Future studies are important to examine whether matching energy expenditure with energy intake would promote positive outcomes.
Original languageEnglish
Pages (from-to)993-999
JournalJournal of Parenteral and Enteral Nutrition
Issue number6
Early online date3 Oct 2016
Publication statusPublished - 1 Aug 2017


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