Serial measurements of energy expenditure in critically ill children: optimizing nutritional therapy?

Objectives

First, to determine the variation of total daily energy expenditure (TDEE) and respiratory quotient (RQ) in serial measurements of mechanically ventilated critically ill children. Second, to relate TDEE and RQ with daily and cumulative energy intake.

Methods

Patients requiring mechanical ventilation for more than 24 hours were enrolled if; FiO₂ < 0.60, tubeleakage < 10%, ventilated with Servo 300 (Siemens) and haemodynamically stable. Daily measurements to determine TDEE and RQ were performed (Deltatrac^™ II MBM-200, Datex), until the 7th day of admission. TDEE and RQ values were compared with daily and cumulative energy intake.

Results

The study consisted of 17 patients (11 male, 6 female), with different clinical diagnoses (8 meningococcal septic shock, 5 post-surgical, 4 other). Median (range) for; age 14 months (1/4–53), admission period 7 days (3–15), length of ventilatory support 5 days (2–12), PRISM 20 (4–27) and temperature 37.4°C (36.1–38.5). All patients were sedated, 4 received muscle paralysis and 11 inotropic therapy. A total of 66 measurements were performed (4/patient). There was no significant difference in TDEE between the first and last day of measurement (Table). The mean coefficient of variation (CV) among daily measurements of TDEE was in 14 out of 17 patients (82%) < 10%, in the other 3 patients the CV was 10, 11 and 14%. Including all measurements there was a strong positive correlation between the ratio energy intake/TDEE and RQ (r_s = 0.65, P < 0.01). There was a significant difference in RQ between patients with a ratio energy intake/TDEE < 1 or ≥ 1 (resp. 0.82 and 0.90, P < 0.01). At the last day of measurement, nine patients with a positive cumulative energy balance (PCEB) (89 kcal/kg, range: 3–446) had a significant higher RQ than eight patients with a negative cumulative energy balance (NCEB) (-21 kcal/kg range: –53 to –4), (resp. 0.89 vs 0.83, P < 0.01), whereas there was no significant difference in RQ between these groups at the first day of measurement.

Table

Conclusion

During mechanical ventilation of critically ill children, TDEE can be predicted in 82% of the patients by performing only one measurement, despite individual differences. RQ is strongly influenced by the ratio energy intake/TDEE and by the cumulative energy balance. We advocate to feed critically ill mechanically ventilated children according to or in excess of their TDEE as soon as possible during admission, in order to optimize nutritional therapy.