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Serum membrane osmotic pressure is lower in patients with shock associated with systemic inflammation
  1. Gareth Clegg


Introduction Shock syndromes are a common feature of critically ill patients presenting to the Emergency Department. We suggest that the lack of consensus around the optimum strategy for fluid resuscitation exists because previous work has not taken into account the pathophysiological state of the microcirculation in shocked patients. Aetiologies characterised by marked systemic inflammation – such as sepsis or anaphylaxis – are likely to have greater initial capillary leak than those caused by haemorrhage or sudden cardiac pump failure. Membrane osmotic pressure (MOP) is a marker of capillary leak, with acute changes reflecting the loss of large circulating molecules from the intravascular space. We hypothesise that in patients with shock syndromes osmolality could provide a tool for guiding initial resuscitation.

Methods In this prospective observational study we enrolled 55 non-pregnant patients over 16 years of age with a mean arterial pressure of 2.9 mmol/l, or shock index (heart rate/systolic blood pressure) >0.9 presenting to our Emergency Department between 2 February, 2010 and 9 September, 2010. MOP, and serum levels of the pro-inflammatory cytokine interleukin-8 were measured 24 h after presentation.

Results We compared the MOP in those patients with levels of IL-8 consistent with significant systemic inflammation (>100 pg/ml) to those with lower levels. MOP was significantly lower in patients with greater systemic inflammation (18.58 (CI 17.03 to 20.12) CF 21.24 (CI 20.03 to 22.44) p=0.016).

Discussion Our results are consistent with the hypothesis that patients whose shock is associated with marked systemic inflammation have a greater degree of capillary leak leading to an acute drop in serum osmotic pressure.

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