cogitation objective: To evaluate an equation that estimates resting power expenditure from two easily obtained measurements--expired carbon dioxide and minute ventilation.

cogitation objective: To evaluate an equation that estimates resting power expenditure from two easily obtained measurements--expired carbon dioxide and minute ventilation, and compare the be deriveds of this equation with standard modes of estimating and measuring caloric expenditure in mechanically ventilated patients.

Design: Prospective evaluation in a consecutive, unselect cohort.

Setting: Medical, surgical, and coronary intensive care units in a university hospital.

Patients: Twenty-five patients (16 to 79 years of age) receiving mechanical ventilation.

Intervention: Indirect calorimetry (IC), minute ventilation (VE) and partial hurry of expired carbon dioxide ([PECOsub2]) were obtained upon all patients. Harris-Benedict equations were calculated and corrected for known stres factors (HBc) Calculated activity expenditure (CEE) was determined using the following equation:

CEE = 927 x VE x [PECOsub2] CEE was then compared with IC and HBc

Measurements and results: The IC was interpretable in 22 of 25 patients, and CEE was significantly better at estimating caloric requirements than HBc The mean absolute difference between CEE and IC was significantly les than between HBc and IC (118 [+ or -] 96 v 302 [+ or -] 269 p [les than] 003) CEE estimated caloric requirements to within 200 kcal of IC in 16 of 22 (72 percent); HBc estimated within 200 kcal of IC in 9 of 22 (41 percent)

Conclusions: Minute ventilation and expired carbon dioxide measurements are easily and inexpensively obtainable. zeal expenditures calculated from these measurements (CEE) compare favorably with values obtained from a metabolic cart and are significantly more accurate than HBc

Multiple physiologic stresse in critically ill patients can complicate prescriptions for nutritional support. granting calculations are available to estimate these metabolic demands, it has been shown previously that equations used for predicting resting force expenditure (REE) do not accurately assess the caloric requirements of critically ill patients.[1-4] Inaccurate nutritional assessment may lead to adverse general intents from either underfeeding or overfeeding. Malnutrition, for example, delays harm healing, decreases resistance to infection, and may increase postsurgical complications.[5] reciprocally overfeeding can cause hyperventilation, hepatic steatosis, and dysfunction, as well as elevated plasma triglyceride and cholesterol levels[6]

Although the principles of indirect calorimetry have been well established for many years, the calculation of caloric requirements was facilitated by dint of Weir,[7] who described a convenient equation that related caloric exigencys to oxygen consumption ([VO.sub.2]) and carbon dioxide production ([VCOsub2]) latter advances in technology have l to completely automated metabolic carts that can indirectly measure life expenditure expeditiously. However, the costliness of a metabolic cart is high and the availability is consequently limited. Furthermore, the use of a metabolic cart requires technical personnel familiar with its operation as well as significant technician time to perform the measure The use of indirect calorimetry is thus limited to those hospitals willing to pay for the equipment and technical time.

Because these expenditures may be prohibitive in many center a formula was derived from united of Weir's original equations to estimate a calculated resting life expenditure (CEE) from two easily obtainable measurements -- expired partial urgency of carbon dioxide ([PECO.sub.2]) and expired minute ventilation (VE) The sense of this study was to papal court whether this new, simple rule of calculating energy expenditure from expired gas sampling approximated actual caloric requirements better than using the standard anthropometric calculations of Harris and Benedict.

METHOD

Derivation of Equations

Weir's equation relating caloric consumption to gas exchange states that

(1) K = 39 + 11R where K is the caloric value of 1 L of oxygen in kg cal and R is the respiratory quotient. Weir multiplied the pair sides of this equation by dint of liters of oxygen consumed to obtain the familiar equation

(2) [VOsub2] x K = (39 x [VOsub2]) + (11 x [VCOsub2]) or

(3) EE = (39 x [VOsub2]) + (11 x [VCOsub2]) where EE is might expenditure in kilocalories per day, and [VOsub2] and [VCOsub2] are consumption and production of gas in liters by means of day, and the patient is in steady state.[7]

If, instead, we assume an R of 083 in equation 1 reflecting mixed substrate utilization,[8] then

(4) K = 39 + (11 x 083) = 4813 kg cal through liter oxygen consumed Since R = [VCOsub2]/[VOsub2]

(5) K/R = kg cal by liter of carbon dioxide produced

(6) 4813/83 = 5799 kg cal by means of liter of carbon dioxide produc therefore

(7) CEE = 5799 x [VCOsub2] where CEE is "calculated" mechanical value expenditure in kilocalories per day and [VCOsub2] is carbon dioxide produc in liters by day.

We can approximate [VCOsub2] on measuring minute production of carbon dioxide ([VCOsub2]) and extrapolate above 24 h.

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