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Objective: In mechanically ventilated patients, pulmonary gas exchange was investigated dur­ ing the administration of total parenteral nutri­ tion containing medium-chain triglycerides or long-chain triglycerides as fat emulsions. Design: Prospective, randomized, crossover trial (two lipid infusion periods of 8 hrs). Setting: Intensive care unit in a university hospital. Patients: Six mechanically ventilated pa­ tients, using the pressure-support mode. Interventions: Total caloric intake was adapted according to measured energy expen­ diture. Fat emulsion provided 50% ofthe energy expenditure. Patients were infused with 50% medium-chainl5O% long-chain triglycerides or 100% long-chain triglycerides in a ran«:!-om sequence. MeasurenumtsandMainResults: Oxygencon­ sumption, CO 2 production, and minute ventila­ tion were measured by indirect calorimetry. Pao 2 and Paco 2 were determined in blood samples. Medium-chain triglycerides increased oxygen consumption by 27.8% and minute ventilation by 14.3% at the end of the protocoL CO 2 produc­ tion, Pao 2 , and Paco 2 were not different between groups. Conclusions: Medium-chain triglycerides cause an increase in metabolic demand in me­ chanically ventilated patients when they are infused over a short period. Postoperative or intensive care unit patients with a low pulmo­ nary reserve should receive infusions of medium-chain triglycerides over a more prolonged period than long-chain triglycerides. (Crit Care Med 1994; 22:248-251)

A nitrogen-sparing effect of epidural anesthesia has been clearly demonstrated in gynecological and lower abdominal surgery. To determine if epidural anesthesia also has a protein-sparing effect during major upper or mid-abdominal surgery, postoperative nitrogen balance and 3-methylhistidine urinary excretion (an index of skeletal muscle protein catabolism) were measured for 6 days in 28 patients who had undergone colon resection for cancer with general anesthesia (N2O-O2-1% enflurane) either supplemented with low dose fentanyl plus intermittent systemic pentazocine for postoperative pain (n = 13), or the same general anesthetic plus epidural injection of either etidocaine 1% intraoperatively and bupivacaine 0.25% postoperatively (n = 8) or meperidine (n = 7) for 48 hr after skin incision. The cumulative 6-day nitrogen balance and the cumulative 3-methylhistidine urinary excretion were significantly less after epidural injection of etidocaine intraoperatively and bupivacaine postoperatively than in the two other groups. There was a significant correlation between the daily urinary excretion of 3-methylhistidine and the daily nitrogen balance in the three groups. This study suggests that in colon surgery, epidural analgesia with local anesthetics in the postoperative period improves nitrogen balance and this effect takes place partly in the muscle.