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NUTRITION ISSUES IN GASTROENTEROLOGY, SERIES #131 NUTRITION ISSUES IN GASTROENTEROLOGY, SERIES #131
Carol Rees Parrish, M.S., R.D., Series Editor
The Calorie Requirement Conundrum
Joe Krenitsky
Severe overfeeding of critically ill patients results in increased complications without clinical
benefits. However, the optimal timing and amount of nutrition to feed critically ill adults has not
been established. There are multiple prediction equations for estimating calorie expenditure of
critically ill patients, but most studies comparing the accuracy of different prediction equations
are inadequate. There is a wide day to day variability of the energy expenditure of critically ill
patients, which means that a single indirect calorimetry study does not reflect average calorie
expenditure more accurately than prediction equations in the first weeks of critical illness.
Although guidelines often promote more complex means of estimating calorie expenditure,
critically ill patients receive variable and often incomplete amounts of nutrition that mitigates
any possible difference in the accuracy between the smorgasbord of calorie prediction equations.
INTRODUCTION
utrition recommendations for adult critically ill providing nutrition in excess of calorie expenditure
patients in the 1970’s and 1980’s encouraged in the early phase of illness or injury did not prevent
5,6
Nincreased calories to a range of 3000-5000 kcals/ catabolism and muscle breakdown. In view of the
day to reduce muscle breakdown or improve nutrition evidence that severe overfeeding of calories in the early
1
status. It was not uncommon for patients to receive 1.5 stage of critical illness caused negative consequences,
to more than 2X their actual calorie expenditure into the without apparent benefits, clinicians searched for a
2,3
mid 1980’s. However, case reports of hyperglycemia, means to guide the provision of nutrition support.
hepatic enzyme elevations, respiratory failure and
protracted ventilator weaning associated with purposeful Measurement Versus
overfeeding (hyperalimentation) were reported by Estimation of Calorie Expenditure
3,4
the early 1980’s. Research also demonstrated that Indirect calorimetry (IC) estimates 24-hour calorie
expenditure via measurement of oxygen consumption
Joe Krenitsky, MS, RD, Nutrition Support and carbon dioxide exhalation. Studies with indirect
Specialist, University of Virginia Health System, calorimetry have revealed that the calorie expenditure
Digestive Health Center, Charlottesville, VA of most critically ill adults were more modest than had
12 PRACTICAL GASTROENTEROLOGY • JULY 2014
The Calorie Requirement Conundrum
NUTRITION ISSUES IN GASTROENTEROLOGY, SERIES #131
9-14
Table 1: Commonly Used Calorie Prediction Equations
Formula Equation
ACCP13 25 kcal/kg body weight
10
Harris Benedict Men: 13.75(kg wt) + 5(cm ht) – 6.8(age) + 66
Women: 9.6(kg wt) + 1.8(ht) – 4.7(age) + 655
Swinamer Equation14 945(BSA) – 64(age) + 108(Tmax) + 24.2(RR) + 817(Vt) – 4349
Mifflin St. Jeor11 Men: 10(kg wt) + 6.25(ht) – 5(age) + 5
Women: 10(kg wt) + 6.25(ht) – 5(age) – 161
9
Ireton-Jones Version 1992: 1925 – 10(age) + 5(wt) + 281(male) + 292(trauma)
+ 851(burns)
Version 1997: 1784 + 5(wt) – 11(age) + 244(male) + 239(trauma)
+ 804(burns)
9,12
Penn State Version 1998: HBE(0.85) + Tmax(175) + Ve(33) – 6344
Version 2003: MSJ(0.96) + Tmax(167) + Ve(31) – 6212
Brandi15 0.96(HBE) + 7(HR) + 48(Ve) -702
16
Faisy 8(wt) + 14(ht) + 42(Ve) + 94(T) - 4834
wt, weight (kg); ht, height (cm) Tmax, maximum temperature in previous 24 hours (degrees C); Ve, expired
minute ventilation (L/min); MSJ, BSA, body surface area (m2); RR, respiratory rate (breath/min); Vt, tidal volume
(L/ breath); T, temperature at time of study (degrees C), HBE, Harris Benedict equation, MSJ, Mifflin-St.Jeor equation.
previously been thought; and early prediction equations these prediction equations with estimation of 24-hour
9
with activity and stress factors for estimation of calorie calorie expenditure via indirect calorimetry. Although
7,8
expenditure often led to overfeeding. there is a plethora of work regarding energy expenditure
IC is frequently not available at many facilities due and the accuracy of prediction equations, there is very
to the cost of the equipment and its maintenance, as well limited research about the amount of nutrition that will
as the training and time of experienced personnel. In optimize the outcome of critically ill people.
the absence of IC clinicians routinely use one or several
of the multitude of prediction equations to estimate a Calorie Requirements
patient’s calorie expenditure.9 -16 These equations are Versus Calorie Expenditure
based on physical attributes such as height, weight In order to understand the best way to estimate calorie
and age, and/or physiologic variables such as body needs, it is important to differentiate between the
temperature, respiratory rate, tidal volume, minute calorie expenditure of critically ill patients and the
ventilation, and/or severity of injury (See table 1). Over calorie provision that allows the best possible patient
the years, a number of “improved” equations have been outcome. To date, there are no large randomized
published and studies have compared the accuracy of trials demonstrating that meeting a critically ill adult
PRACTICAL GASTROENTEROLOGY • JULY 2014 13
The Calorie Requirement Conundrum
NUTRITION ISSUES IN GASTROENTEROLOGY, SERIES #131
patient’s full calorie expenditure results in improved needs and IC measurements, so neither study provides
outcomes. Obviously, providing minimal nutrition any meaningful data about indirect calorimetry. In one
for an extended period of time will eventually result unblinded single center pilot study, patients received
in serious malnutrition. However, it is possible that a bundle of increased calories and protein as well as
providing nutrition to critically ill adults that meets individualized attention from the study dietitian to
full calorie expenditure may actually have negative help ensure adequate nutrition delivery.24 Patients who
consequences, especially in the early, most acute phase received increased nutrition had significantly more
of critical illness. Patients may benefit from a period infectious complications, delayed ventilator weaning
of reduced, or even no nutrition during the early stage and increased time in the ICU. There was no significant
of illness, with increased nutrition at a later point. The difference in hospital mortality on intention to treat, but
ideal amount of nutrition support may be different in the smaller per protocol analysis (n=112), mortality
depending on the degree of malnutrition, age, severity was significantly decreased in the experimental group.24
of illness or injury, presence and severity of surgical The authors concluded that a much larger multi-center
wounds, trauma or burns, requirement for repeated trial would need to be conducted to understand the effect
surgical procedures and duration of recovery. The early of increased nutrition on mortality. 24 The other study
phase of critical illness is characterized by unavoidable did not result in any significant differences in infectious
catabolism that is not reversed by meeting full calorie complications over the entire study period, but did
5,6
expenditure. Additionally, increased insulin resistance report decreased adjusted probability of infections in
and decreased gastrointestinal motility in the early stage the group receiving increased calories and protein over
of critical illness or injury have the potential to increase a post-hoc selected time period between days 9-28
17 25
complications related to providing nutrition support. (after the parenteral nutrition was discontinued). In
Researchers have postulated that providing full nutrition contrast to these 2 studies of reduced calories with
needs in the early phase of critical illness may impair very limited protein, a modest sized study (n = 240) of
the normal activation of mechanisms that are needed reduced calories with supplemental protein (compared
to remove cellular damage.18 There is evidence that to full calories and protein) in medical-surgical ICU
in some critically ill adult populations, hypocaloric, patients reported significantly less mortality in the group
26
full protein feeding may actually improve patient receiving reduced calories.
19,20
outcomes. A much larger multi-center, randomized study of
A number of observational studies have described 1000 patients with acute lung injury (ALI) or ARDS
associations between the amount of nutrition provided found that attempting to provide full feedings did not
to critically ill patients and their outcomes.21-23 However, result in any outcome improvements compared to
observational studies cannot attribute cause and effect “trophic feeding” (approximately 25% of calculated
17
related to the amount of nutrition received because those needs). The group with planned full feedings received
patients with worse outcomes are more likely to receive an average of 80% of calculated needs, but had
less nutrition. It is not possible to statistically control significantly more minor gastrointestinal complaints
for all variables that affect outcome in observational such as elevated gastric residuals, regurgitation and
studies, and it is inappropriate to make practice episodes of emesis, as well as requiring increased
17
recommendations based on associations reported in prokinetic and anti-diarrheal medications. In this
observational studies. higher quality study, an average difference of 900
Two randomized studies have purported to describe kcals/day (56% of estimated needs) in well-nourished
improvements in selected outcomes in patients who patients with ALI/ARDS did not result in any significant
17
had calorie expenditure measured by IC followed by difference in patient outcomes.
24,25
increased nutrition delivery. However, the amount of
calories provided was not the only difference between Calorie Prediction Equations
the experimental groups in these studies. Both studies There are a large number of calorie prediction equations,
provided increased calories and significantly more and multiple studies have compared various prediction
protein to the experimental group, primarily by providing equations in assorted patient populations with indirect
increased parenteral nutrition. In both studies there was calorimetry.9-16 Although many prediction equations
only a trivial difference between the calculated nutrition (continued on page 16)
14 PRACTICAL GASTROENTEROLOGY • JULY 2014
The Calorie Requirement Conundrum
NUTRITION ISSUES IN GASTROENTEROLOGY, SERIES #131
(continued from page 14) accuracy (+/- 10%) used in most studies of prediction
have reasonable accuracy for groups of patients, equations. A study of daily calorie expenditure in
the potential error for most prediction equations in critically ill adults found that a single IC measurement
27
individual patients is +/- 500 calories. As stated above, extrapolated for 1 week has more cumulative error than
32
the clinical implications of this magnitude of error are several prediction equations. Although IC is frequently
unclear. referred to as the “gold standard,” it is clear that in
Early prediction equations such as the Harris- critically ill adults, a single IC study is not a more
Benedict equation used fixed variables such as weight, accurate predictor of average calorie expenditure than
height and age. Some recent prediction equations have most prediction equations. Due to the potential “error”
incorporated clinical variables such as body temperature, of a single IC measurement, compared to the average
respiratory rate, tidal volume, minute ventilation, and/ calorie expenditure, it is not appropriate to recommend
or severity of injury (See table 1 for a summary of one method of estimating calorie expenditure over any
several commonly used fixed and complex predictive other based on studies that used a single IC study.
equations). The American College of Chest Physicians In one study using daily indirect calorimetry,
recommended a simple weight-based method of one prediction equation that used maximum body
estimating initial calorie goals.28 More complex calorie temperature and expired minute ventilation as part of
estimation formulas generally require more time for the calculation estimated daily calorie expenditure with
collection of clinical variables and calculations that acceptable accuracy (compared to the daily indirect
32
can change throughout the day. calorimetry). However, temperature and minute
Several studies have suggested superior accuracy for ventilation used for the calculation in the study were
more complex prediction equations and some guidelines collected at the same time as IC was completed, so it
have favored one or another method for estimating is not surprising that the calculation was similar to the
9,27,28,29
calorie goals. Unfortunately, weaknesses of the indirect calorimetry. Temperature and minute ventilation
study methods in most of the research with prediction vary over the course of the day and there are no studies
equations severely limit any conclusions relevant to of prediction equations that use clinical variables where
clinical practice. The vast majority of studies with the calculations are done in a blinded fashion to the time
prediction equations used only a single IC study and results of the indirect calorimetry. Additionally,
per patient, measured at various points during the the investigators did not report the actual amount of
hospitalization for each patient. The largest validation nutrition received by the patients, nor discuss how the
study of predictive equations included 202 mechanically equation chosen to estimate calorie goals may affect
ventilated, critically ill patients and compared 17 the actual amount of nutrition provided to the patient.
29
different equations. Accuracy of the prediction A recent observational study demonstrated that patients
equations was arbitrarily defined as prediction within who were in the ICU > 4 days who had their calorie
10% of the IC measurement. However, there was only 1 goals determined with only weight-based equations
IC measurement per patient that was completed between had a significantly shorter time to discharge alive, than
day 2 and day 64 of the admission, between day 2 and patients who had calorie goals determined with more
27 of their ICU stay, and with a sepsis-related organ complex calculations.33 As stated above, no cause and
29
failure score between 1 and 18. effect conclusions can be made from observational
Studies of day to day variation in energy studies, but this association between complex
expenditure have established that in the early portion calculations and worse patient outcomes highlights the
of a patient’s admission the day to day variation in need for outcome data before any method of calculating
energy expenditure varies by as much as 46%, with a calorie goals can be recommended above another.
more recent study demonstrating that mean daily energy
30,31
expenditure varied by an average of 31.7 (+/-22.6)%. A Practical Issue: Calorie
Even in stable patients the daily variation measured Prediction Versus Calorie Delivery
30
by IC varies by an average of 12%. Translated, this Compounding the inaccuracy of predictive equations,
means that a single IC measure does not accurately and the daily variability of energy expenditure, is the
represent the average calorie expenditure of a critically issue of how much nutrition a critically ill patient
ill patient. A single IC does not mee the criteria of (continued on page 18)
16 PRACTICAL GASTROENTEROLOGY • JULY 2014
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