May 2012 e-journal club

Greetings,

 

The month of May has been a bit more routine here than the preceding months.  We did not host a training program in May, but we have been preparing new presentations and planning future “On the Road” Weekend Warrior programs.  Luckily our downtime will be short-lived since we have an “On the Road” Weekend Warrior in North Carolina planned for the first weekend in June.  Our journal club article this month addressed an important topic – the effects of Omega-6 rich lipid emulsions in PN.

May Citation:

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]

Summary: 

This was a double-blind study that investigated clinical outcomes and metabolic response of 100 medical and surgical ICU patients randomized to receive either PN with standard soybean-based lipid emulsion or olive oil-based lipid emulsion.  The primary outcome was the rate of new infections; defined as culture-proven wound, drain, bloodstream, respiratory, and urinary tract infections.  Secondary outcomes were ICU and hospital length of stay, glycemic control, specific neutrophil and monocyte functions, inflammatory and oxidative stress markers, respiratory failure, need for mechanical ventilation, cardiac complications, acute renal failure, and ICU and hospital mortality.

The olive oil emulsion used in this study contained 80% olive oil and 20% soybean oil.  Nutrition goals were determined by the Harris Benedict equation X 1.3 for total kcals, and 1.5gm/kg for protein using actual or adjusted weight (in obese patients).

Inclusion and Exclusion Criteria were:

Inclusion criteria:

Medical surgical ICU patients aged 18-80, who were expected to require PN for longer than 5 days.

Exclusion criteria:

Patients who had received PN within 48 hours prior to study entry, those with septic shock, h/o organ transplantation, active malignancy, cirrhosis, serum total bilirubin ≥10 mg/dL, AIDS, chronic renal failure, pregnant, breastfeeding, terminal illness and life expectancy <7 days, and baseline serum triglyceride >400 mg/dL.

Major Results reported by authors:

Results were based on the 100 patients randomized, with 49 patients receiving soybean oil–based and 51 olive oil–based lipid emulsion.  PN was started an average of 12.6 ± 13.9 days after hospital admission and was administered for a mean duration of 12.9 ± 8.3 days.  ICU length of stay (LOS) was 16.1 ± 16 days and hospital LOS was 43.6 ± 42 days.  The mean actual amount of PN received by the patients provided 22 ± 6 kcal/kg/day, 1.19 ± 0.27 g protein/kg/day, and 0.59 ± 0.2 g total fat/kg/day with no significant difference in nutrition provided between groups.

There were no significant differences in any of the primary or secondary outcomes between the two groups.  In the primary outcome of nosocomial infections, the difference between the olive oil-based lipids compared to the soybean oil-based lipids was 43% vs. 57% (p = 0.16), respectively.  The overall hospital mortality during the entire hospital stay, including the period following discontinuation of PN, was 16.3% with soybean oil–based and 9.8% with olive oil–based PN (p = 0.38).

The overall mean BG concentration during PN was 129 ± 14 mg/dL with no differences in BG concentration between lipid groups.

Author’s Conclusions:

“…. the administration of PN containing soybean oil–based and olive oil–based lipid emulsions results in similar overall rates of infectious and noninfectious complications, mortality, and ICU length of stay and no significant differences in metabolic, inflammatory, or immune markers in critically ill adult patients.”

Evaluation:

This was a well designed study, with patients randomized to their respective groups, and analyzed with all patients that were randomized.  It is also notable that the investigators recorded the amount of PN that was actually received by the patient, rather than just assuming that patients received every drop that was prescribed.  All too often the amount of nutrition that is actually infused is a neglected aspect of nutrition support studies, and the results here illustrate that actual amounts of nutrients infused needs to be reported for parenteral as well as enteral studies--I can’t help but point out that it also illustrates why it is pointless to worry about how precisely accurate your initial calorie-need calculation is.

The authors point out several limitations of this study in the discussion section, including the modest number of subjects, and the fact that 89% of the patients were surgical ICU patients.  The study was adequately powered to detect differences in infections and there was no significant differences in infections or inflammatory mediators between the groups.

The investigators also discuss another factor that may have influenced the results of this study – the fact that PN was started relatively late (12 days) after admission.  Starting PN later may mean that the severe stress stage of illness (with altered prostaglandin production from omega-6 fatty acids) may have already resolved by the time PN was initiated.  It is possible that these study results may not apply to patients that receive PN early in the admission.  However, the results of this study may reflect the typical patient that I see, because we usually reserve PN for those patients that have failed enteral nutrition or are more stable.

Another factor that we noted was the modest amount of total calories and lipids that were received by the patients.  The amount of fat provided was under a gram/kg (0.59 ± 0.2 g/kg), and based on the mean would give a 68kg reference patient only 40 gm of fat – which means that the amount of omega-6 fatty acids provided was actually very modest.  It is possible that modest amounts of lipid infusion (within the limits of normal intake for a mixed diet) do not cause inflammation or immunosuppression, therefore no difference could be realized with alternate lipids.

Our Take Home Message (s)

·           Olive oil-based lipid emulsions do not appear to offer significant clinical advantages compared to soybean-based lipid emulsions when adult surgical patients receive PN after 12 days +/- of their admission, with modest amounts of fat and calories.

·           Patients do not receive the same amount of nutrition that is prescribed, which may make precise estimations of calorie expenditure moot.

 

Other News on the UVAHS GI Nutrition Website: (www.ginutrition.virginia.edu):

Upcoming Webinars for Spring 2012:

--Tuesday, June 12--Effectively Communicating with Physicians--Kate Willcutts, MS, RD, CNSC

Upcoming Fall topics include Hydration / Oral Rehydration, Pediatrics, Nutritional Anabolics and Nutrition Support Cases

Check out What’s New:

-- “Nutrition Support Blog”  

--“ Resources for the Nutrition Support Clinician

Latest Practical Gastroenterology article:

--Shah N.  High Risk PEGs.  Practical Gastroenterology 2012;XXXVI(5):28. 

 

Joe Krenitsky MS, RD

Carol Rees Parrish MS, RD

 

PS – Please feel free to forward on to friends and colleagues.