Can we/ should we estimate energy requirements in the

critically ill?

Clare Soulsby

Arguments for the proposition

• Can we estimate energy requirements in the critically ill?

• Should we estimate requirements in the critically ill?

• Aim of feeding critically ill patients: should we feed to measured energy expenditure?

Estimating energy requirements in critically ill patients

PENG guidelines:• BMR (Schofield) +

combined activity/ DIT + stress

ASPEN guidelines:• BMR (Harris

Benedict) + 30%

Disease specific:• Ireton Jones Energy

equations• 20-35kcal/kg

BMR: Harris Benedict vs Schofield

• Data collected 1909 and 1917 Study population: – 136♂ (27± 9 yrs BMI

21± 3– 103♀(31±14 yrs BMI

22±4• Tends to

overestimate in healthy (Daly 1985, Owen 1986, Owen 1987)

• Developed from a meta analysis of 100 studies 3500 ♂1200 ♀

• includes HB data• 2200 (46%) of

subjects were military Italian adults

• SE 153-164kcal/d ♀ 108-119kcal/d ♂

Disease specific (IJEE)

Methodology and generalisability:

• 3 x 1 minute measurements 200 patients

• unclear whether measurements took place during feed infusion/ after treatment etc

• 52% burns, 31% trauma

Clinical manipulation:

• energy prescription “arrived at”

Accuracy of measured vs estimated energy requirements

Accuracy of weight -20% to +20%

Standard error of Schofield equation

-15% to +15%

Combined activity DIT (15%) 0 to 15%

Stress factor (20-60%) 20 to 60%

Total -15% to +110%

ICU stress factor

• Evidence is only as good as the studies on which they were based:

• Measurement error:– during feed infusion– immediately post injury– historical studies

“When estimating energy requirements, we recommend that you initially use the lower end of the range for the specific clinical condition and then monitor, and amend upwards if necessary”

Can we estimate energy requirements in the critically ill?

• Possibly but not accurately

• Potential for error (-15% to 100%)

Should we estimate energy expenditure?

• ICU patients are a heterogeneous population

• Energy expenditure varies widely and is affected by patient’s condition

• Measured energy expenditure in UK ICU populations:– 34kcal/kg/d (26-58kcal/kg/d) (Green 1995)– 26kcal/kg/d (20-38kcal/kg/d) (Reid 2001)

Should we feed to estimated energy expenditure?

• Aim of nutritional support (historical):to meet have fed to energy requirements

• What is the evidence for this?

Consequences of overfeeding

• Cannot achieve:– +ve N balance in visceral protein

• even when energy requirements are met (Streat 1987, Green 1995, Hart 2002, Reid 2004)

• Overfeeding can lead to fat gain (Streat 1987) and increased ventilator dependence (Hart 2002)

Consequences of underfeeding: nitrogen balance

• Energy balance– influences the utilisation of

dietary protein– is an important factor in

determining nitrogen balance

• Both energy and protein requirements are related to active tissue mass (Waterlow 1978)

• Negative nitrogen balance can exacerbate muscle loss

MOF, BMI and survival in the ICU (Galanos 1997)

Benefits of feeding

• In MOF:– Survival is improved by raising BMI

above 15th towards the 85th percentile. Outcome worsens as BMI falls (Galanos 1997)

Benefits of feeding

• Re-nutrition has an immediate and short term effects on muscle function before increase in muscle mass is observed (Hill 1992, Jeejeebhoy 1988)

• Improved limb muscle function can improve rehab in fractured neck of femur (Bastow 1983)

• Respiratory muscles also suffer wasting (Lewis 1986, Lewis 1990)

• Correlation between muscle strength and peak flow in surgical patients (Hillman 2001, Hill 1992)

Benefits of feeding

• Providing early nutrition in critically ill patients (even parenterally) reduces mortality (Simpson 2005)

• Energy intake of 35kcal/kg/d have been associated with improved outcomes in critically ill patients (Van den Berghe 2001)

• Maybe adverse effects of overfeeding in critically ill patients are indirect (poor blood glucose control) rather than the effect of the nutrition per se.

Can we/ should we estimate requirements

• Large range in energy expenditure in a very heterogeneous group

• Clinical experience and a good understanding of the evidence will facilitate more accurate estimation

Should we aim to meet energy expenditure

• Low BMI associated with low survival rate in MOF patients

• In the short term nutritional support can improve muscle function

• Respiratory muscles become wasted which correlates with peak flow

• Reduced mortality has been seen with intakes of 35kcal/kg/d and tight blood sugar control

Beware of fashion

• Aim of nutritional support in the critically ill:– minimise loss of lean

body mass

• If we underfeed, how low do we go?

Support the proposition!

• We can and we should estimate requirements in the critically ill

• Aim to provide sufficient energy to minimise losses of lean body mass metabolically controlled patients

References

• Bastow MD Rawlings J et al (1983) BMJ 287: 1589-1592• Galanos AN, Peiper CF et al (1997) Critical Care

Medicine 25:1962-1968• Green CL, Campbell IT et al (1995) Nutrition 11:739-746• Hart DW, Wolf SE et al (2002) Annals of Surgery 235:

151-161• Hill GL (1992) JPEN 16:197-218• Jeejeebhoy KN (1988) JPEN 12:539-549• Hillman TE, Hornby ST (2001) Clinical Nutrition 20: 37

(suppl)

References

• Lewis MI Sieck GC (1986) J Appl Physiol 60: 596-603• Lewis MI Sieck GC (1990) J Appl Physiol 68: 1938-1944• Reid C & Campbell I (2001) Clinical Nutrition 20: A87

(suppl)• Reid C & Campbell I et al (2004) Clinical Nutrition 23:

273-280• Simpson F & Doig GS (2005) Intensive Care Medicine

31: 12-23• Streat SJ, Beddoe AH et al (1987) Journal of Trauma

27:262-266• Van den Berghe G, Wouters P et al (2001) N England J

of Med 19: 1359-1367