Author's reply re: Microcirculation in women with severe pre-eclampsia and HELLP syndrome: a case control study.

Abstract

Sir, In their letter the authors describe a case of placental abruption with fetal demise in a women with severe pre-eclampsia and HELLP syndrome. Despite delivery and supportive treatment, she deteriorated over the following days with occurrence of kidney failure, eclamptic seizures and cardiac arrest, for which CPR was started. Spontaneous circulation was recovered but remained unstable, for which ECMO and hypothermia were initiated with short delays. While experience with extracorporeal cardiopulmonary resuscitation (E-CPR) in pregnancy is limited, evidence in the general population suggests its superiority over conventional CPR. It is probably the prompt action of the team with rapid initiation of ECMO that contributed to the good maternal recovery. As timing is crucial in these circumstances and obstetricians are often first involved, knowledge about these evolutions in E-CPR will probably help in reducing ECMO initiation time, thereby improving outcome. We also agree with the authors that this case strongly suggests microvascular dysfunction. It can occur independently from the apparent macrocirculatory hemodynamic instability. Yet, it is on this capillary level that the main goal of circulation, the exchange of O2, nutrients and fluids, for CO2, and waste products between blood and tissue cells takes place. We and others have previously demonstrated microcirculatory perfusion problems in women with HELLP. While more research is needed on the subject, microvascular assessment has the potential to assist in predicting prognosis and in guiding treatment. In this case, the clinical condition deteriorated despite delivery and adequate supportive treatment. It highlights that in severe pre-eclampsia, our current management is in essence limited to damage control until the maternal condition spontaneously recovers after delivery. Hypertension control within the safe zone merely prevents cerebrovascular incidents and magnesium sulphate is mainly for seizure prophylaxis. None of these actions substantially improves the pre-eclamptic condition. While intravascular volume depletion is prominent, fluid management remains a controversial issue, given the capillary leak and risk of iatrogenic pulmonary oedema. In the future, assessment of functional microcirculatory haemodynamics with small handheld cameras, might assist in optimising fluid therapy. The main two mechanisms behind oxygen delivery from red blood cells (RBC) to tissues are convection and diffusion. The former depends on RBC velocity, O2 saturation and O2 carrying capacity. The latter is mainly dependent on the O2 gradient and is inversely proportional to the distance between tissues and RBC. Although crystalloids have little inherent capacities to improve O2 delivery, administration can increase RBC velocity, thereby improving convection and, by opening previously closed capillaries, reducing distance and improving passive diffusion. However, if too much is given, interstitial oedema again increases the distance. Microvascular imaging could assist in achieving optimal convection and diffusion by measuring parameters of RBC velocity and perfused capillary density. While this concept seems promising, it remains experimental at this moment. Extensive research is still needed before its clinical value and benefice can be truly be evaluated in women with severe pre-eclampsia.