I realize that many of my gentle readers may not have access to the Cochrane reviews in full text as soon as they are published. The NICHD do provide free access to the neonatal reviews, (together with a useful introduction to the value, limitations and methodology of the Cochrane reviews) but it seems to take a couple of months for them to catch up with a new review arriving. Even OVID, one of the ways of accessing some of the Wiley content, which is how I access the reviews from my university, hasn’t updated the Cochrane Library to include the fluid restriction review yet. Which means I can’t even access the full text on-line myself yet!
I will re-post about the 3 latest reviews that we have published as soon as full text is available from the NICHD web-site.
I thought therefore I would re-post this, about the fluid restriction SR, and add a slightly edited version of the Summary of Findings table, with the secondary outcomes of the systematic review that we included. You will note that I could not calculate the confidence intervals for the duration of oxygen therapy, the standard deviations weren’t included in the original article (rather they included the ranges). Nevertheless the means are so similar that the confidence intervals are likely to be wide, and certainly to be ‘not significant’.
I have never been convinced that fluid restriction is a good thing for kids with BPD. I think the common practice came about because of the short-term improvements in lung function that sometimes follow if you start diuretics. The idea being that if diuretics improve lung function, then giving less fluid will also.
But this is a false equivalency, diuretics cause sodium depletion, and therefore decrease total body water, and probably lung water content also. Fluid restriction in contrast leads to a reduction in urine output, and, within clinically reasonable limits, will not have an impact on total body water, and there is no reason to believe that they will reduce lung water content either.
Diuretics may have other direct effects on pulmonary function, that will not occur with fluid restriction. Inhaled furosemide, for example, improves pulmonary mechanics in BPD, presumably by acting on the same sort of ion pump that loop diuretics block in the kidney.
Even in adults with fluid overload (those with oedematous congestive heart failure) RCTs of fluid restriction show no effect, unless sodium intake is also severely restricted. Sodium restriction alone works as well, so the fluid restriction adds nothing.
Despite this, there are recommendations from usually reliable people that babies with BPD should have their fluid intake restricted, such recommendations are often accompanied by a reference, usually a reference to another recommendation or to a narrative-type review article.
I have been planning for years to do a systematic review for the Cochrane library, of fluid restriction as treatment for early or established BPD. We have finally finished the review and it has just appeared. (Barrington KJ, Fortin-Pellerin E, Pennaforte T. Fluid restriction for treatment of preterm infants with chronic lung disease. Cochrane Database of Systematic Reviews. 2017(2).)
Using the usual search procedures we could only find one relevant trial. In fact the initial search didn’t find the article (Fewtrell MS, et al. Randomized trial of high nutrient density formula versus standard formula in chronic lung disease. Acta Paediatrica. 1997;86(6):577-82.) even though I knew it existed; the Pubmed key words did not mention fluid volumes or restriction, so we tweaked the search to ensure that we found the article, and to make sure that we would find any others that exist.
So the only RCT evidence addressing fluid restriction is a study of 60 preterm babies with early chronic lung disease (needing oxygen at 28 days of age) who were randomized to either get 180 mL/kg/day of a regular formula, or 145 mL/kg/d of a concentrated formula. Unfortunately they didn’t report on one of our outcomes, oxygen requirement at 36 weeks, as it wasn’t, at that time, the standard outcome that it has since become.
That study showed no benefit of fluid restriction on any outcome. The fluid restricted group had more apneas, a finding unlikely to be due to chance, and also had more babies who needed more than 30% oxygen during the trial, a difference which may have been due to chance.
Fluid restriction risks nutritional restriction also; even though the idea may be to reduce the free water intake, babies often get fewer calories and less protein when fluid restricted, while babies with BPD actually need more calories. They will also produce more concentrated urine, which might increase the risk of nephrocalcinosis as well.
The final message is that there is no evidence to support the practice of fluid restriction of babies with early or established BPD. There is no physiologic rationale either. There are potential risks to the practice.
We should stop doing it.