Development and current use of parenteral nutrition in critical care - an opinion paper

Abstract

Critically ill patients depend on artificial nutrition for the maintenance of their metabolic functions and lean body mass, as well as for limiting underfeeding-related complications. Current guidelines recommend enteral nutrition (EN), possibly within the first 48 hours, as the best way to provide the nutrients and prevent infections. EN may be difficult to realize or may be contraindicated in some patients, such as those presenting anatomic intestinal continuity problems or splanchnic ischemia. A series of contradictory trials regarding the best route and timing for feeding have left the medical community with great uncertainty regarding the place of parenteral nutrition (PN) in critically ill patients. Many of the deleterious effects attributed to PN result from inadequate indications, or from overfeeding. The latter is due firstly to the easier delivery of nutrients by PN compared with EN increasing the risk of overfeeding, and secondly to the use of approximate energy targets, generally based on predictive equations: these equations are static and inaccurate in about 70% of patients. Such high uncertainty about requirements compromises attempts at conducting nutrition trials without indirect calorimetry support because the results cannot be trusted; indeed, both underfeeding and overfeeding are equally deleterious. An individualized therapy is required. A pragmatic approach to feeding is proposed: at first to attempt EN whenever and as early as possible, then to use indirect calorimetry if available, and to monitor delivery and response to feeding, and finally to consider the option of combining EN with PN in case of insufficient EN from day 4 onwards.

Figures

Figure 1

Effect of nutrition support on total body protein in patients with an acute flare of ulcerative colitis. Conversely to patients with standard care (broken line; mean age 47.6 ± 12.1 years, mean weight 59.4 ± 12.5 kg), ulcerative colitis patients with total parenteral nutrition (TPN; solid black line; mean age 42.6 ± 10.2 years, mean weight 60.8 ± 10.6 kg) received TPN from hospital admission until day 14 after surgery. Patients without TPN showed a rapid body protein loss that fell under the critical threshold before hospital admission, and worsened during the perioperative period. On the contrary, TPN prevented the worsening of protein body loss during the perioperative period and was associated with an earlier restoration (18 weeks earlier) of normal protein stores (mean ± standard deviation). Reproduced with permission from [14].

Figure 2

Milestones in the development of artificial nutrition. Development steps in energy requirements and lipid emulsions (left) and amino acid and glucose steps (right). Adapted with permission from [20].

Figure 3

Relationship between two commonly used equations and the value of energy expenditure. Indirect calorimetry study on day 3 shows that both equations overestimated and underestimated energy expenditure in an unpredictable manner. (A) Pre-enrollment target 25 to 30 kcal/kg actual body weight (BW): arrows show the relation between the calculated energy target used for enrollment (25 or 30 kcal/kg/day) and the measured energy expenditure that became the target used from day 4. (B) Target of the supplemental parenteral nutrition patients recalculated using an equation based on a corrected ideal body weight, age and gender [39], which was used in the Early Parenteral Nutrition Completing Enteral Nutrition in Adult Critically Ill Patients (EPaNIC) trial [40] (corrected ideal body weight, age and gender [34] + absolute maximal target of 2,880 kcal).