The Detection and Importance of Intravascular Platelet Aggregation in Surgical Shock
Intravascular platelet aggregates (IPA) have as yet avoided detection in shocked patients hence their role in the aetiology of “shock lung” remains controversial. Screen filtration pressure (SFP) has only been shown to measure aggregates in vitro.A modified screen filtration technique was evaluated in 43 surgical patients. The characteristics (height,slope) of the pressure wave were compared with the number of aggregates seen to occlude filter pores on scanning electron microscopy (SEM). In 80 estimations on femoral vein blood the slope of the SFP curve was utilised improving SFP/ SEM correlation to r= .93. These aggregates arise in vivo as they were rarely detected in blood from the arm and IPA levels in femoral blood were not influenced by EDTA priming of the syringe. In 36 preoperative estimations mean SFP slope was identical to that in 14 patients after minor surgery (1.5 ± SD 1.6). After major surgery in 29 patients this value was elevated at 7.1 ± 6.1 (P<.001). Seventeen of these patients with SFP slope greater than 5 suffered a mean fall in arterial P2 at 5 days post operation of 1.85 KPa (13.9 mm Hg) which was significantly greater than that in the other major cases (0.85 KPa, 6.4 mm Hg)(P <.05). SFP also correlated closely with the fall in platelet count on day 1 post operation (r= .82, P< .001).Intravascular platelet aggregates arise in the veins of the lower limb immediately after major surgery. They can be measured by the screen filtration technique described and may be related to pulmonary dysfunction.