Allen I. Hyman

Nutrition for the patient with respiratory failure: glucose vs. fat.

High glucose intakes given during administration of total parenteral nutrition (TPN) have been demonstrated to increase CO2 production. The workload imposed by the high CO2 production may precipitate respiratory distress in patients with compromised pulmonary function.Changes in CO2 production and O2 consumption induced by TPN using either glucose as the entire source of non-protein calories, or fat emulsions as 50 percent of the non-protein calories, have been analyzed either in patients with chronic nutritional depletion or in acutely ill patients secondary to injury and infection. In patients with chronic nutritional depletion, shifting from the lipid to the glucose system caused a 20 per cent (P < 0.025) increase in CO2 production which resulted in a 26 per cent increase in minute ventilation (P < 0.01). In the acutely ill patients receiving the glucose system, CO2 production was significantly higher than in those receiving the lipid system (179 vs. 147 ml·min−1 · m−2; P < 0.01).Fat emulsions can serve as a source of non-protein colories and are associated with lesser degrees of CO2 production than isocaloric amounts of glucose.

Nutrition and the respiratory system

SUMMARYMalnutrition and weight loss are among the signs of a poor prognosis in the natural history of patients with COLD.123, 124 Patients whose only source of daily nutrition is 2–31 of 5% dextrose suffer malnutrition and weight loss. This has been documented to be detrimental.Currently, there are insufficient data to propose the optimum form and amount of nutritional intake. Thus, it is appropriate to suggest moderation in nutritional support of patients with compromised pulmonary reserve. Glucose infusions may be expected to replenish tissue glycogen and, hence, be associated with improved work performance; however, CO2 production is significantly increased. However, an increased RQ may provide a more favorable alveolar Po2 which could be important in patients with COLD during room air breathing. Fat emulsions are commercially available, can minimize CO2 production, and have been shown to be N sparing. However, serum hyperlipemia may compromise pulmonary diffusing capacity. Increasing nitrogen intake can increase ventilatory drive, but this may lead to a feeling of dyspnea and be detrimental in patients unable to increase minute ventilation.Parenteral nutrition should be guided by whether the goal is to: (a) preserve lean body mass in patients who are in satisfactory nutritional condition but whose return to oral intake is not imminent, or (b) restore lean body mass in patients who have lost greater than 10% of normal body weight. In patients where the intent is maintenance of lean body mass, nutritional support should be designed to attain calorie and nitrogen equilibrium. Practically speaking, this means: (1) energy intake of 1–1.2 χ energy expenditure; (2) nitrogen intake of 200–300 mg/kg. At this institution, 50% of the nonprotein calories are given as fat emulsions. In patients where the goal is restoration of lean body tissue, the nutritional regimen should be designed to achieve a distinctively positive calorie and nitrogen balance. Energy intake is set at 1.4–1.6 χ energy expenditure. Nitrogen intake is between 250–400 mg/kg body weight. One-half of the nonprotein calories are given as lipid.These recommendations are based upon limited data and indirect evidence. Further studies of nutrition and respiration are needed to construct more definitive guidelines in this important area of clinical care.

Effects of hypercaloric glucose infusion on lipid metabolism in injury and sepsis.

UNLABELLED Lipolysis was studied by measuring glycerol turnover (GTO) in injured and infected patients. GTO was elevated two to three times the normal values in five injured and four infected patients during D5W infusion. No correlation was found between GTO and plasma glycerol concentration in the two patient groups. GTO showed similar levels when measured during TPN in five injured and three infected patients. During TPN, plasma FFA levels remained unchanged in injured but decreased by 48% in septic patients. B-OH butyrate concentrations were high during D5W and dropped in both groups during TPN. Norepinephrine urinary output was high in both groups during D5W and TPN. CONCLUSIONS 1) GTO was elevated two to three times the normal range in injury and infection; plasma glycerol concentration was not related to GTO. 2) In face of high catecholamine output, the insulin response to TPN did not inhibit TG breakdown but did decrease plasma ketone body concentrations.

A systematic method for validation of gas exchange measurements.

The measurement of gas exchange is useful, but thus far, has not been practical during the mechanical ventilation of critically ill patients. To validate two new commercial instruments, (Siemens-Elema Servo Ventilator 900B, Beckman Metabolic Cart), the authors constructed a lung model into which they delivered CO2 and N2 at precise rates to simulate Co2 production (Vco2) and O2 consumption (Vos). The model consists of 13.5-1 gas jar with an attached one liter anesthesia bag. The lung model was ventilated at present tidal volumes and frequencies. The authors also compared the measured respiratory quotient (RQ) with the known RQ of burning methanol (RQ = 0.67) in the jar. When the model was ventilated with levels of tidal volume and gas exchange applicable to adults, both instruments measured V02 within 5 to 13% of predicted values. Varying the FI02 did not significantly affect this accuracy. At tidal volumes below 350 ml, the difference increased between predicted VCO2 and measured VCO2. The difference between measured vs. the actual RQ of methanol was 5 and 1.5% in the Siemens-Elema and Beckman Systems, respectively.

Cardiovascular changes during transport of critically ill and postoperative patients

We examined cardiovascular changes in 37 patients transported to an ICU after major general or vascular surgery (n = 14), open heart surgery (n = 13), or carotid endarterectomy (n = 10). Cardiovascular variables were also measured in a control group of 11 patients transported from an ICU for diagnostic or therapeutic procedures. All patients were followed for 30 min before transport until approximately 30 min after they arrived at their destinations. During this period, systolic BP and heart rate significantly increased only in patients recovering from major general/vascular surgery or carotid endarterectomy. These changes were apparently related to acute emergence from inhalational anesthesia (isoflurane plus nitrous oxide), since the other surgical patients were anesthetized with narcotic anesthesia, and the control group did not receive any anesthesia.

Amino Acids and Respiration

Parenteral nutrition containing glucose and amino acids may stimulate respiration. To ascertain the effects of these solutions on respiration, eight normal subjects received an infusion of 5% dextrose (100 mL/h) for 7 days followed by an infusion of 3.5% amino acids (125 mL/h) for 24 hours. Minute ventilation (VE), tidal volume, mean inspiratory flow (VT/VI), oxygen consumption, and carbon dioxide production were significantly depressed after 7 days of 5% dextrose infusion. Ventilation and metabolic rate increased within 4 hours after initiation of the amino acid infusion and returned to normal 24 hours after the infusion. The effects of the amino acids on (VE) was secondary to an increase in (VT/VI), which is an indicator of neuromuscular ventilatory drive. Thus, within 4 hours amino acids will restore depressed metabolic rate, minute ventilation, and ventilatory drive after prolonged infusion of 5% dextrose.

Caloric requirements and supply in critically ill surgical patients.

ObjectiveTo compare the caloric intake with the caloric requirements in postoperative patients being fed enterally via nasoenteric tubes, parenterally, or by both enteral and parenteral methods. DesignDescriptive study. SettingSurgical ICU in a university teaching hospital. PatientsSample of 22 mechanically ventilated postoperative patients, mean age 62 ± 17 yrs, selected from among those patients routinely scheduled to receive enteral or parenteral nutrition or both, for ≥4 days. The patients were studied for a total of 144 study days. InterventionEight patients received total parenteral nutrition, eight patients received enteral nutrition, and six patients received both parenteral and enteral nutrition. MeasurementsResting energy expenditure was measured by using indirect calorimetry, and daily nutritional intake was quantitated. ResultsThe patients who received parenteral, or enteral plus parenteral nutrition received an average of 80% of their caloric requirements, while those patients who received only enteral nutrition received only 68% of their caloric requirements. There was more day-to-day variation in nutrient intake in the enteral group (40% ± 56%) than in the parenteral group (12.2% ± 24%, p <.001). ConclusionsEnteral nutrition delivered via nasoenteric tubes as the sole delivery method in postoperative critically ill patients resulted in an inadequate and inconsistent nutrient supply. The use of parenteral or parenteral plus enteral nutrition resulted in more stable and adequate feeding than feeding byenteral nutrition alone.

Variation in the Resting Metabolic Rate of Mechanically Ventilated Critically Ill Patients

There has been increasing interest in the nutritional support of the critically ill patient. The day-to-day variation in resting energy expenditure (REE) was studied over a 35-day period in 17 postoperative mechanically ventilated critically ill patients to gain insight as to how often caloric intake should be reassessed, whether changes observed over 3–5 days are of sufficient magnitude to make frequent adjustments in caloric intake, and what factors are associated with large alterations in metabolic rate. REE was measured daily for 3–5 days, and the percent variation in REE [(highest REE - lowest daily REE)/(lowest daily REE) × 100] calculated. The variation ranged from 4 to 56%, and on further analysis two distinct groups were identified, one with a mean variation of 12 ± 4% (sD) (range 4–18%) and the other with a mean variation of 46 ± 8% (range 37–56%). The former group was clinically stable, whereas the latter was not. Clinically stable patients need less frequent measurements than those who are more ill, but when designing a nutritional regimen for them, at least 20–25% should be added to the REE, 15% to account for day-to-day variation and 5–10% for activity.

Temporary Unilateral Pulmonary Artery Occlusion: A Method for Controlling Swan-Ganz Catheter–Induced Hemoptysis

A patient undergoing mitral and aortic valve replacement suffered catheter-induced pulmonary artery trauma and massive hemoptysis during weaning from cardiopulmonary bypass. Hemorrhage ceased when the ipsilateral pulmonary artery was occluded. Forty-eight hours later the temporary band was removed, and the patient did well without further bleeding.

Effects of the mask and mouthpiece plus noseclip on spontaneous breathing pattern.

Studies of breathing patterns that use a mask (M) or mouthpiece plus noseclip (MP + NC) may contain artifacts due to the stimuli of the apparatus used. A canopy-spirometry-computer system was used to analyze respiratory patterns in a noninvasive manner. Changes in respiration induced by the application of M or MP + NC were analyzed. Twenty-two normal subjects and five critically ill patients were studied in (1) canopy alone, (2) canopy with M and (3) canopy with a MP + NC (in normal subjects only). An algorithm quantified each breath and determined tidal volume (VT), frequency (f), minute ventilation (V), O2 consumption (VO2), CO2 production (Vco2), sigh frequency (SF), ventilatory equivalent (VEco2 defined as V/Vco2), and tidal volume distribution (VTD) VTD that reflects the tendency to breathe in a relatively narrow range of tidal volumes and is quantified as VTD10, VTD20 (% breaths within ± 10% and ± 20% of mean VT). The M increased VT, V, VEco2 (presumbly secondary to its increased dead space) VTD10 and VTD20. MP + NC increased VT, V and decreased VTD10 and VTD20. Neither device affected SF. The M produced similar changes in the resting ventilation of both the patients and normal subjects. Our previous studies have shown that ill patients breathe at relatively fixed VT, i.e., high VTD10 and VTD20. Use of a M or MP + NC obscured this phenomenon and altered VT, V, and VEco2