A reply

Abstract

Tanqueray and colleagues are correct in stating that a second suction and leucocyte depletion filters are commonly used techniques to diminish the risk of re-infusing fetal and amniotic fluid contaminants and that these were not mentioned in the recent Association of Anaesthetists of Great Britain and Ireland guidelines [1]. Since then an addendum has been sent out mentioning the use of leucocyte depletion filters in obstetrics and published in Anaesthesia News [2]. The use of leucocyte depletion filters to remove possible contaminants during cell salvage was highlighted in the previous paragraph on malignancy, but this was erroneously not repeated in the obstetric section. However, since the excellent review article by Allam et al. [3] was published in January 2008, there have been two developments in the field of cell salvage that are now relevant. Firstly, in August 2008 Sullivan et al. [4] published a small randomised controlled trial showing that amniotic fluid contamination (indicated by alphafetoprotein levels) is not significantly different whether one or two suckers are used, but that more red cells are retrieved with the single suction technique. Although the use of separate suction seems intuitively safer, there is in fact no evidence to support this. This study also confirmed earlier findings [5] that no further reduction in alphafetoprotein is achieved by filtration after washing. The significance of squamous cells in the maternal circulation remains unclear, and while some studies show total removal of these cells by leucocyte depletion filters [6], others suggest that squames persist in up to 7% of those studied but with no discernable clinical effect [4]. It is important to remember that all these clearance studies have been conducted in in-vitro work and whether leucocyte depletion filters make any difference clinically is currently not known. There is good evidence that amniotic fluid routinely enters the maternal circulation at caesarean section with no adverse effect [6]. In addition, before the introduction of the Pall RS Leucocyte Depletion Filter (Pall Medical, Portsmouth UK), several hundred obstetric patients received cell salvaged blood either with no filter or with earlier, less effective filters that have been shown to allow the passage of fetal material, again with no adverse effects [7]. A recent report in Vox Sanguinis described, in a prospective case series of 212 patients with ectopic pregnancies, the effective use of unwashed and unfiltered cell salvaged blood without apparent adverse outcome [8]. In individual maternity units in the United Kingdom, the use of leucocyte depletion filters varies; some units do not use them (personal communication, Dr S Catling; October 2009) and there has been no evidence of amniotic fluid embolus syndrome. In June 2009 the 12th Annual Serious Hazards of Transfusion Report (SHOT) [9] highlighted five cases in which unexpected hypotension occurred as cell-salvaged blood was administered via leucocyte depletion filters; one of these cases is obstetric where severe hypotension was witnessed during re-infusion of salvaged blood through a leucocyte depletion filter. While there is currently no convincing evidence that the leucocyte depletion filter was the cause of these reactions, this is currently under investigation by SHOT and the UK Cell Salvage Action Group. There is a theoretical mechanism by which this could occur, involving the release of vasoactive substances from white blood cells trapped on the negative filter surface [10, 11] This phenomenon was identified by the Food and Drug Administration in 1999 in a Public Health Notification and involved bedside filtration of allogeneic blood. Accordingly, it may be time to justify the routine use of leucocyte depletion filters: the evidence for the compulsory use of leucocyte depletion filters is not compelling, and for the first time there is a possible suggestion of harm. Like the authors, currently we continue to advocate their routine use, but would not hesitate to remove the filter if necessary, particularly when salvaged blood is required to be re-infused under pressure or if there is unexplained hypotension shortly following re-infusion of salvaged blood.