We read with interest the paper by Dempsey and colleagues regarding permissive hypotension in low birth weight infants. We are unsure that the data as presented fully supports some of the conclusions drawn.

Those infants in whom hypotension was treated were deemed to be unwell by the clinicians looking after them. This appears to have been a sicker group at outset in terms of clinical and crib assessment. These infants had a significantly lower blood pressure at all stages than the other groups. This suggests that those infants were still in shock and the adverse outcome may possibly be due to achieving inadequate therapeutic goals, for whatever reason. We believe another conclusion for this study may possibly be that inadequate resuscitation from shock is associated with an adverse outcome and that this should be mentioned to give balance to the discussion.

Since the case has not been made that hypotension, as defined in this study, in sick infants is safe and in view of the very non-specific signs of ill health in the neonate, we feel that this study does not suggest that clinical equipoise exists with respect to trial of permissive hypotension.

Yours faithfully

Conflict of Interest:

None declared

These findings have a rational metabolic amplified in a succession of earlier rapid responses to this and other BMJ publications. Permissive hypotension was the norm in adalts following, for example, abdominal aortic surgery until the advent of "haemodynamic management", that is optimizing filling pressures and maintaining a blood pressure high enough to ensure glomerular filtration and a good urine output.

With the former practice of permissive hypotension in adults peripheral circulation and urine output seemed to return as the postoperative temperature returned to normality despite the practice at that time of "keeping patients dry" by restricting fluid input in the first 24 hours after surgery in accordance with Frannie Moore's metabolic teachings at Harvard. Permissive hypotension is considered suboptimal in adults today because of the reduced incidence of renal failure, seen in combat casualties during the Korean war, following the introduction of aggressive resuscitation with crystaloids pioneered by Zuidema and Shires. This change in practice, which has since become an entrenched surgical meme, was accompanied by the appearance of pulmonary problems, Da Nang lung as it was dubbed in the Vietnam war. It has, however, never been clearly established whether the one complication is better than the other.

The success of renal transplantation has established that oliguria and even anuria are compatible with the return of normal renal function. In the absence of any good evidence-base to support the practice of keeping the blood pressure high enough to ensure glomerular filtration might the addition of permissive oliguria and even anuria to permissive hypotension be accompanied by an even greater improvement in outcome? Should "renal failure" then develop it could be managed expectantly just as it is after renal transplanatation today. Management of renal failure has improved greatly since the Korean war between 1950 and 1953. Even peritoneal dialysis was unavailable at that time (1). It was not much more advanced in the Vietnam war, 1961-1975.

1. THOMSON WB, BUCHANAN AA, DOAK PB, PEART WS. PERITONEAL DIALYSIS. Br Med J. 1964 Apr 11;1(5388):932-5