Lipid Emulsions and Unbound Bilirubin in Preterm Infants

Happy birthday Stan!

In previous work, it had been shown that free bilirubin (Bf) and unbound free fatty acids (FFAu) were increased in extremely low birth weight infants who received intralipid (soybean) at 3 g/kg/d.  A recent study (T Hegyi et al. J Pediatr 2017; 184: 45-50) showed that Bf and FFAu are increased with increasing intralipid dosage (1 to 3 g/kg/d) in all gestational ages (23-34 weeks).

The concern with Bf and FFAu is that elevated concentrations could have adverse neurologic effects; intralipids may act to displace bilirubin from binding to albumin. For most infants in this study, the levels “would not be expected to pose a neurotoxic risk” (per editorial pg 6-7).  Factors that enhance the generation of FFAu include infection, steroids, carnitine deficiency, and low albumin conditions. Phototherapy, in this study, reduced total serum bilirubin but not Bf in those receiving 2-3 g/kg/d of intralipid.

My take: This study does not provide any information regarding neurotoxicity.  It shows that potentially toxic levels of Bf & FFAu can occur in infants born <28 weeks who receive 2 g/k/day or more of intralipid.  While this is a concern, we also know that poor growth is associated with worsened neurocognitive outcomes (Nutrition Week: Downside of Lipid Reduction)

Foil PNALD with FOLE?

As noted on previous blog entries (see below), there has been significant enthusiasm for fish oil based lipid emulsion (FOLE) despite a lack of data showing superiority compared with standard soy-based lipid emulsions at similar dosing.  More data for FOLE helping infants with cholestasis are available (J Pediatr 2013; 162: 793-8).

Design: Single center, prospective observational study of 57 infants with parenteral nutrition-associated liver disease (PNALD) which  took place between 2007-2011.  All infants were between 2 weeks and 6 months of age at enrollment.  At enrollment, FOLE (Omegaven) at a dose of 1 g/kg/d was infused over 24 hrs.  FOLE which is not FDA-approved is available on a compassionate use protocol.

Infant characteristics: Median gestational age: 28 weeks. 47 of 57 were long-term survivors.  The median time at initiation of FOLE was 39.3 weeks post-menstrual age.

Results:

  • Median conjugated bilirubin at initiation of FOLE therapy was 7.5 mg/dL.
  • Resolution of cholestasis occurred at a median of 35 days (range 7-129) after starting FOLE.  Longer times for resolution were noted in those with higher initial bilirubin.
  • Time to resolution was inversely proportional to gestational age at birth (p=0.02) and directly to time to receive 100% calories enterally (p=0.03)

The authors note that none of the infants who died had liver failure; most deaths were due to multi-organ failure and sepsis.

In the discussion, the authors state “the most significant finding from this study is the effectiveness of FOLE in resolving cholestasis irrespective of the initial serum bilirubin values.”  I take issue with this statement primarily because the design of the study does not allow such attribution.  Without a randomized trial comparing FOLE to standard intralipids, this statement overstates any conclusion that can be drawn from this study.  Given the fact that resolution was correlated with advancement of enteral feedings, it is plausible that a similar result would occur with standard intralipids.

The authors make a number of other speculations about the potential superiority of FOLE over standard soy-based lipid emulsions, but concede that “our study was not adequately equipped to address” the association of reduced intralipid with improvement in cholestasis.  Despite this concession, the authors boldly proclaim in the concluding paragraph: “while awaiting the more general availability of FOLE, infants at high risk should be identified early and referred to centers that provide the option of FOLE…in which families are fully informed of both the potential benefits and limited current data.”

A recent media report also promotes the effectiveness of FOLE: http://nbcnews.to/11vbL2E 

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