Patterns and Problems of Adult Total Parenteral Nutrition Use in US Academic Medical Centers

Paul R. Schloerb, MD; Jeanne F. Henning, RN. Arch Surg. 1998;133:7-12

Objective: To determine the pattern of total parenteral nutrition (TPN) use in US academic medical centers because TPN in adults may be associated with complications related to excessive glucose (dextrose) administration and a respiratory quotient greater than 1.0.

Design: Two surveys of the University HealthSystems Consortium (n=106, 74 members and 32 network partners using TPN) to determine TPN formulas and amounts of TPN nutrients given to 2 hypothetical abdominal trauma patients (1 man and 1 woman), each of whom weighed 70kg.

Main Outcome Measures: Amounts of dextrose, amino acids, and fat and rates of administration of TPN.

Results: In the first survey, 80% (59/74) of members and 41% (13/32) of network partners of the University HealthSystems Consortium reported using TPN formulas with more than 20% dextrose; half used 25% dextrose. In the second survey, the mean (±SD) TPN dextrose concentrations were 190±43 and 170±45 g/L (902±204 and 807±214 mmol/L), with amino acid concentrations at 40 to 50 g/L, in the male and female patients, respectively. The amounts of amino acids and glucose given, when referred to body cell mass in the male and female patients, were equivalent. In 26% (22/86) of the institutions surveyed, the amounts of glucose given in TPN were high enough (>4.48 mg/kg per minute) to produce a respiratory quotient greater than 1.0. A standard TPN formula was derived as 4.25% amino acids, 15% dextrose, and 20% fat emulsion, at a rate to provide required calories.

Conclusion: Excessive TPN glucose administration, found in at least one fourth of US academic medical centers, suggests use of a TPN formula with no more than 15% dextrose, administered at a rate to provide no more than 4 mg/kg of glucose per minute.


Problems of Total Parenteral Nutrition

Jorge E. Albina, MD Providence, RI (Arch Surg. 1998; 133:679)

The recent article by Schloerb and Henning[1] raises concerns about the understanding and formulation of total parenteral nutrition (TPN). Beyond the dismay caused to this reader by the fact that members of the nutritional support service from a major university hospital struggled to define a difference between glucose and dextrose (there is none) and considered the natural target for a survey on TPN prescriptions to be pharmacy directors and not physicians, the authors' apparent conclusion that the glucose concentration of TPN solutions determines the rate of glucose delivery to the patient is remarkably wrong. Glucose delivery is a function of glucose concentration and rate of infusion. The authors regrettably fail to understand this concept, stating, ...the glucose concentration should be limited to less than 4 mg/kg per minute. A concentration is not a rate of delivery.

The point the authors try to make, that excessive glucose administration during TPN should be avoided, is sound even when they provide no evidence that the prescriptions obtained through their survey would necessarily have resulted in a respiratory quotient of greater than 1 in their hypothetical patients. To make this point based on glucose concentrations in TPN is incorrect.

The authors propose a glucose concentration of 15% in TPN solutions, based on the assumption that all of the patients' fluid requirements are provided by TPN. This is rarely the case. Patients, mostly those critically ill, require other intravenous products (such as blood products, antibiotics, and analgesics) or even fluid restriction, thus reducing the volume available for TPN. The use of concentrated solutions is the result of adjusting to this reality.

While the search for evidence-based indications for nutritional support in general and TPN in particular continues, articles like this contribute little but confusion to the debate.


References

1. Schloerb PR, Henning JF. Patterns and problems of adult total parenteral nutrition use in US academic medical centers. Arch Surg. 1998; 133:7-12.