It is generally recognized that energy needs rise with the increased demands for wound healing (18). Although energy needs increase, this increase may not be at a level as significant as initially thought. Studies have shown that energy needs are variable and are not necessarily related to burn wound size, although nitrogen balance is related to the size of the open burn wound (19,20). Hart demonstrated that body surface area (BSA) burned increased catabolism until 40% BSA was reached and then did not increase significantly after that (21). Hart also demonstrated that ventilatory status is associated with energy expenditure in patients with burns, as has been shown previously; however, this data also showed a correlation between energy expenditure and burn size (22). In the critical care literature, various equations are used to predict energy expenditure. For burnpatients alone, there are more than seven equations that can be used (5,20,23).
In the critically ill or injured patient, energy expenditure can be measured using indirect calorimetry (24). Indirect calorimetry is the measurement of oxygen consumption and carbon dioxide production during respiratory gas exchange to determine energy expenditure (15). It is based on the principle that the energy released by oxidative processes and by anaerobic glycolysis is ultimately transformed into heat or external work. Indirect calorimetric measurements are usually done using portable machines called metabolic measurement carts that allow portability of the measurement equipment inside the hospital. Energy expenditures of ventilator-dependent and spontaneously breathing patients can be measured by indirect calorimetry. Smaller, handheld versions of the indirect calorimeter are available; however, these are only useful in measuring the energy expenditures of spontaneously breathing patients (25). Measuring a patient's energy expenditure allows the clinician to tailor the nutrition support regimen to the individual patient's needs. In addition, because critically ill patients have many variables that affect their energy expenditure during recovery, measurement of energy expenditure during recovery is preferable to the use of a static energy expenditure equation.
However, when indirect calorimetry is not available, an equation must be used to estimate energy expenditure. It is important to avoid both underfeeding and overfeeding in the critically injured patient. Hart recommended an energy intake of 1.2 times measured resting metabolic rate (22). The resting metabolic rate in critically ill patients is higher than that of a healthy individual, even one with a wound. Therefore, energy needs of the critically ill should be separated from those of the healthy individual. Examples of equations that can be used to predict the energy expenditures of critically ill patients are found in Table 2.1 (26-28).
Patients who are not critically ill make up a large number of patients who will have wounds. It is important to be as accurate as possible in estimating the energy needs of these individuals as well. These patients may have comorbidities, such as diabetes, renal disease, or obesity, that further complicate the wound healing process as well as the decision of the calorie provision. Energy expenditure studies have not focused on the ambulatory care patient with a wound. In a study conducted in a tertiary care setting of acute and intensive care patients of various diagnoses, the presence of a burn did not make a difference in the energy expenditures of patients who were spontaneously breathing; however, in those who were ventilator dependent, it did (26). While the need for adequate and effective nutrient and energy intake is extremely important in the patient with a wound, there may only be a small effect on overall energy expenditure. For the non-ICU and ambulatory care patient, there are two equations that are
Energy Expenditure Equations for Critically Ill or Injured Individuals
IJEE(v) = 1784 - 11(A) + 5(W) + 244(G) + 239(T) + 804(B)
IJEE = kcal/day
T = trauma
No additional factor is added for activity or injury.
25 kcal/kg using usual or current body weight
H = height (cm) W = actual weight (kg) A = age (years)
Use with stress factors: Mild: RMR x 1 Moderate: RMR x 1.2 - 1.3 Moderate: RMR x 1.2 - 1.3 Severe: RMR x 1.4 - 1.5
aFrom Ireton-Jones C, Jones J. Improved equations for estimating energy expenditure in patients: the
Ireton-Jones equations. Nutr. in Clin. Prac., 17 (4), 236-239, 2002. With permission.
bFrom McCowen KC, Friel C, Sternberg J, Chan S, Forse RA, Burke PA, Bistrian BR. Hypocaloric total parenteral nutrition: effectiveness in prevention of hyperglycemia and infectious complications —
a randomized clinical trial. Crit. Care Med., 28 (11), 3606-3611, 2000. With permission.
cFrom Mifflin MD, St. Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am. J. Clin. Nutr., 51, 241-247, 1990. With permission.
recommended for consideration, and these are listed in Table 2.2. It is important to note that for obese patients, the actual body weight is used in these energy equations. For morbidly obese patients, there are many challenges to the care of the patient, including mobility. Maximization of nutrients with a concomitant decrease in energy (calories) may be useful to meet health goals. A qualified dietitian should always be involved in the management of a patient with wounds, especially those who are obese.
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