Caloric intake and the fat-to-carbohydrate ratio in hypercapnic acute respiratory failure: Post-hoc analysis of the PermiT trial

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The effect of moderate caloric enteral intake in critically ill patients with hypercapnic acute respiratory failure (HCARF) is unclear. We studied the impact of permissive underfeeding (PUF) compared with standard feeding (SF) on various HCARF outcomes. The PermiT trial randomized 894 patients to either PUF (40-60% caloric requirement) or SF (70-100% requirement) with similar protein intake and found no difference in mortality, mechanical ventilation (MV) duration and ventilator-free days. In this post-hoc study, we restricted analysis to mechanically-ventilated patients with HCARF (PaCO2 >45mmHg on the first two study days) and assessed the impact of trial interventions and fat-to-carbohydrate ratio on outcomes. One-hundred-twenty patients had HCARF (59 PUF and 61 SF, age 53.7±17.8 years, body mass index 31.1±11.2kg/m2, Acute Physiology and Chronic Health Evaluation II score 21.7±7.1 and day-1 PaCO2 61±16mmHg). Caloric intake was 815±270kcal/day in PUF group and 1289±407kcal/day in SF group. The two groups had similar PaCO2 levels during ICU stay. The 90-day mortality (33.9% versus 35.6%, p=0.85), MV duration (10.7±6.8 versus 11.1±8.1 days, p=0.56) and ventilator-free days (52.9±38.6 versus 51.2±38.0 days, p=0.80) were also similar in PUF and SF groups, respectively. Ventilator-free days and 90-day mortality were similar when the fat-to-carbohydrate ratio was <or≥the median value (0.73) in all patients and in PUF and SF groups. In patients with HCARF, SF and PUF were associated with similar PaCO2, MV duration, ventilator-free days and mortality. Fat-to-carbohydrate ratio was not associated with mortality or ventilator-free days. ISRCTN Registry: ISRCTN68144998.