Nutrition Support Blog: Hold the Lipids?
May 24, 2012
The best available data tells us that parenteral nutrition (PN) causes more infectious complications than enteral nutrition (EN). The curious thing is that no one seems to know for sure exactly why PN results in increased infections. In the early days, the obvious thought was that PN infections were related to the central line or line care. While immaculate line care and dedicated lines reduce the incidence of infections, “careful” PN still has more infectious complications than EN. Also, in most studies of PN infections, line or bloodstream infections are not the most common infection. Pneumonia is frequently the most common infection in studies of patients receiving PN. In the early 1990’s translocation of bacterial through the GI tract was thought to be the primary source of infections from PN (and the source of the pneumonias). However, further research demonstrated that humans do not translocate bacteria as readily as mice or rat models. Furthermore, patients receiving PN have increased infections even when they receive EN that would preserve intestinal barrier function.1
When the early studies of tight glucose control were published, there was much buzz that perhaps the problems from PN could be eliminated with good glucose control. However, the most recent studies show that infectious complications of PN persist even in the setting of tight glycemic control (see our July 2011 e-journal club @ www.ginutrition.virginia.edu )
Another theory regarding PN and infections is that the Omega-6 rich lipid emulsions from soybean and/or safflower oil contribute to immunosuppression. However, a recent study in Critical Care Medicine reported no reduction in infectious complications when an olive oil-based lipid emulsion was substituted for standard soybean oil-based lipids.2 See our May 2012 e-journal club for more details on this study via the same website above.
On occasion we have been asked to withhold lipid emulsions from PN due to septic episodes or other infectious concerns. Several of our trainees have also reported that they have faced the same clinical conundrum.
However, there is no good data that withholding lipids improves patient outcomes. There are a number of limitations to the single small study of trauma patients that reported reduced infections when lipids were held from PN.3 It is unclear if the benefits of withholding lipids related to the reduction in calories, or to a negative effect of the lipid emulsion. It is important to remember that an excess of any fuel in PN can cause problems. A cohort study of lipid-free PN in ICU patients that did not reduce received total calories when lipids were held showed no reduction of infections.4
In the setting of this imperfect data, our clinical approach is to provide PN with mixed fuels (CHO, Pro, Fat) to prevent an excess of any substrate, keep total calories modest and give less than 1 gm of fat/kg from lipid emulsions to avoid excessive delivery of Omega-6 fatty acids. Obviously, this only applies to those patients that have a clear need for PN – because (of course), the very best way to avoid complications from PN is avoid it completely in those patients that can receive EN!
1. Singer P, Anbar R, Cohen J, et al. The tight calorie control study (TICACOS): a prospective, randomized, controlled pilot study of nutritional support in critically ill patients. Intensive Care Med 2011; 37(4):601-9.
2. Umpierrez GE, Spiegelman R, Zhao V, et al. A double-blind, randomized clinical trial comparing soybean oil-based versus olive oil-based lipid emulsions in adult medical-surgical intensive care unit patients requiring parenteral nutrition. Crit Care Med. 2012 Apr 6. [Epub ahead of print].
3. Battistella FD, Widergren JT, Anderson JT, Siepler JK, Weber JC, MacColl K. A prospective, randomized trial of intravenous fat emulsion administration in trauma victims requiring total parenteral nutrition. J Trauma. 1997 Jul;43(1):52-8
4. Gerlach AT, Thomas S, Murphy CV, Stawicki PS, Whitmill ML, Pourzanjani L, Steinberg SM, Cook CH. Does delaying early intravenous fat emulsion during parenteral nutrition reduce infections during critical illness? Surg Infect. 2011;12(1):43-47.
“Despite our imperfections, we are given opportunities to serve. Acceptance of those imperfections does not mean acquiescence, nor should it evoke guilt. It means understanding our human limitations.”