Effect of routine administration of analgesia on energy expenditure in critically ill patients.

Measurement of gas exchange using portable metabolic carts to indirectly determine energy expenditure (EE) has been a recent advance in the nutritional management of mechanically ventilated, critically ill patients. Although administration of large doses of morphine has been shown to significantly decrease EE, the influence on EE of morphine given in routine amounts to critically ill patients has not been studied previously. We examined the effect of morphine administration (given as bolus IV injections of 0.10 mg/kg every two hours and continuous IV infusion at 0.05 mg/kg/hr) on EE during rest and various ICU activities in seven mechanically ventilated patients. Morphine administration resulted in a significant reduction in resting EE and total EE of 6.0 and 8.6 percent, respectively. However, EE associated with activities (ie, chest x-ray examination and chest physiotherapy) were not significantly affected by morphine administration. Both bolus and continuous IV morphine infusion had similar effects on EE. Administration of routine doses of morphine significantly decreases total EE in critically ill patients. This should be considered an important factor influencing measurements of EE.

Energy expenditure associated with CPAP and T-piece spontaneous ventilatory trials. Changes following prolonged mechanical ventilation.

The use of portable metabolic carts to assess energy expenditure (EE) by measuring oxygen consumption (VO2) and carbon dioxide production (VCO2) has recently been applied to patients undergoing weaning from mechanical ventilation. The VO2 and EE can be used to estimate changes in the work of breathing (WOB) associated with different weaning strategies. The purpose of this study was to use VO2 and EE to assess changes in the WOB when assisted mechanical ventilation (AMV) was replaced with two spontaneous ventilatory trial (SVT) techniques: continuous positive airway pressure (CPAP) and T-piece. Nine difficult-to-wean patients were studied during the initial weaning period following 26 +/- 18 days (mean +/- SD) of mechanical ventilatory support. The VO2 and EE during all AMV were 296 +/- 75 ml/min and 2069 +/- 519 kcal/day, respectively. Compared to the baseline AMV levels, during CPAP overall VO2 and EE increased 14 percent and 13 percent, respectively, and during T-piece overall VO2 and EE increased 20 percent and 19 percent, respectively. Respiration rate (f) increased and tidal volume (VT) decreased during both SVTs compared to AMV although no significant change in minute ventilation was seen. The WOB, as judged from changes in VO2, was only 5 percent higher during T-piece compared to CPAP; however, patients tolerated an average of only 141 +/- 45 min on T-piece vs 165 +/- 29 minutes on CPAP. We conclude that during the initial weaning stages in patients who have received prolonged mechanical ventilatory support, the WOB associated with SVTs is increased compared to AMV but that the WOB associated with T-piece is not significantly greater than that for CPAP.

Nutritional support of the critically ill. Part I--Review.

Critically ill patients seen in an adult Intensive Care Unit often exhibit a hypermetabolic, hypercatabolic response to the stress of illness. The hypercatabolic response to trauma and sepsis is discussed in relation to macronutrient metabolism in this first of a two part article. The aim of nutrition therapy is provision of appropriate substrates to minimize the loss of lean body mass, without provoking additional metabolic stress. Selected topics in nutritional support are reviewed, with emphasis on current research and controversies in the care of the critically ill.

Nutritional support of the critically ill. Part II--Guidelines for clinical dietitians.

The second of a two part article, this section focuses on aspects of dietetic practice in a general adult Intensive Care Unit (ICU). Current recommendations for nutritional support are briefly outlined. Techniques of nutritional assessment and monitoring of nutritional support are reviewed, with a case study example taken from actual practice in the ICU at the University of Alberta Hospitals. The results of an audit of nutritional support in ICU patients at the University of Alberta Hospitals are presented. The audit provided documentation of the benefits of expanded dietitian involvement in the nutritional care of adult ICU patients.

Validation of a compact system for measuring gas exchange.

Measuring gas exchange in critically ill patients can provide valuable information on their nutritional status and energy expenditure. Several semiautomated machines are available for measuring oxygen consumption (VO2) and carbon dioxide production (VCO2). This study evaluated, under controlled laboratory conditions, a Gould 9000 IV prototype designed for use with mechanically ventilated patients. Various VO2 and VCO2 values were simulated at different combinations of frequency, tidal volume, minute ventilation, and inspired oxygen fraction (FIO2). Variations in frequency, tidal volume, and minute ventilation had no significant effect on the measured VO2 and VCO2, but FIO2 had a dramatic effect on the accuracy of VO2. Errors in measured VO2 were 2.6%, 3.5%, 5.9%, and 16.9% at FIO2 values of 0.22, 0.40, 0.60, and 0.80, respectively. Addition of a dead space to the spirometer dump port (to prevent room-air contamination) corrected a larger error initially found. The accuracy of VCO2 was +/- 2.6%.

Twenty-four hour energy expenditure in critically ill patients.

Resting energy expenditure (EE) is often used as the basis of nutritional support for critically ill patients but whether resting EE is representative of total daily EE is not known. EE was measured for 24 h in ten mechanically ventilated, critically ill patients (average Acute Physiology and Chronic Health Evaluation II score 23) to determine EE, resting EE, and the energy expended during various ICU activities. Although activities, such as weighing the patient on a sling-type bed scale, repositioning, and chest physiotherapy resulted in dramatic EE increases above resting levels (36%, 31%, and 20%, respectively), the actual contribution of these activities to total EE was small (1.1%, 2.1%, and 3.6%, respectively). The mean measured resting EE was 47.3 +/- 22.3% above mean predicted EE based on the Harris and Benedict equation, and the mean total 24-h EE was 6.9 +/- 2.6(SD)% above the mean measured resting EE. In this group of mechanically ventilated, critically ill patients, an activity factor of no greater than 10% above resting EE is appropriate.

Predictive equation for assessing energy expenditure in mechanically ventilated critically ill patients.

Traditional formulas, such as the Harris and Benedict equation (HBE), do not accurately predict energy expenditure (EE) in mechanically ventilated, critically ill patients (MVCIP). The purpose of this study was to develop a predictive EE equation to assess EE requirements in MVCIP. A portable metabolic cart was used to measure indirectly EE in 112 MVCIP. Patients were studied at rest and for 30 min on the first or second day of ICU admission. No nutrition was received during the study period. Variables investigated were: age, BSA, Acute Physiology and Chronic Health Evaluation (APACHE II) score, sepsis score, Injury Severity Score (ISS), respiratory rate (f), tidal volume (VT), minute ventilation, mean arterial pressure, heart rate, body temperature (Temp), and outcome. Patient age, APACHE II score, sepsis score, ISS, and BSA were 50 +/- 20 yr, 16 +/- 7, 11 +/- 6, 32 +/- 14, and 1.80 +/- 0.27 m2, respectively. Correlation and multiple regression analyses were used with EE as the dependent variable. A predictive equation (EE [kcal/day] = 945 BSA -6.4 age + 108 Temp + 24.2 f + 817 VT -4349) was determined from variables that contributed greater than 3% to the variance of EE: BSA (52%), age (10%), f (5%), VT (5%), and Temp (3%). The HBE underestimated measured EE by 34 +/- 19% and in 79 patients deviated greater than 15%. Using the new equation, only 15 patients' EE deviated greater than 15% from measured EE. The new predictive EE equation can accurately assess EE in MVCIP.

An evaluation of the effect of fasting on the exercise-induced changes in pH and Pi/PCr from skeletal muscle.

The changes in the response of skeletal muscle to maximal dynamic exercise were investigated in going from a fasted state to a refed state by means of 31P NMR spectroscopy. It was found that in the fasted state, exercise-induced changes in Pi/PCr and in pH were both inhibited, in comparison with those in the refed state.