MICROEMBOLISATION DURING SURGICAL SHOCK: EFFECT OF PROSTAGLANDIN E1

Embolisation of microaggregates following major surgery may be a cause of pulmonary arterio-venous shunt and postoperative respiratory failure (1). Prostaglandin E1 may prevent intravascular aggregation and we studied this possibility in a pig model of surgical shock.Following autologous platelet labelling with Indium, 16 pigs (20-30kg) were randomised to receive a perioperative infusion of PGE1 (100ng/kg/min) or placebo. Arterial and Swann Ganz catheters were inserted under anaesthesia prior to surgery consisting of midline laparotomy, exteriorisation of small bowel 1.5 hours of aortic clamping and 1 hour of hypotension. On induction, during shock and at 3 days in survivors platelet and leucocyte count, blood radioactivity, venous aggregates (SFP), lung platelet uptake (LPU), pulmonary vascular resistance (PVR) and alveolar-arterial p02 difference (A-ad02) were measured.All results mean ± sem *p <0.05 Mann Whitney U-testDuring surgical shock, the formation of venous aggregates, the fall in circulating radiolabelled platelets and their accumulation in lungs were reduced by PGE1 (p< 0.05). BP, CVP and PWP were all lower on PGE1 and at 3 days the improvement in A-ad02 in PGE1 pigs failed to reach significance.PGE1 reduced platelet aggregate formation and their subsequent pulmonary microembolisation despite worsening shock due to vasodilation.1. McCollum CN, Campbell IT. The value of measuring intravascular platelet aggregation in the prediction of postoperative pulmonary dysfunction. Br J Surg 1979: 66; 703-707

PULMONARY MICROEMBOLISATION IN SURGICAL SHOCK: THE EFFECT OF CYCLO-OXYGENASE INHIBITION

Thromboxane release from platelet microemboli during major arterial surgery may mediate depression of cardio-pulmonary function. The effect of cyclo-oxygenase inhibition by aspirin has been studied in a porcine model of aortic surgery.Following autologous platelet labelling with 111-lndium, 24 pigs (20-25kg) were randomised to low dose (LD) aspirin (0.5mg/kg), high dose (HD) aspirin (10mg/kg) or placebo.Arterial and Swann Ganz catheters were inserted prior to surgery consisting of midline laparotomy, small bowel extériorisation, 1.5 hours of aortic clamping and 1 hour shock before resuscitation. On induction, during shock and at 3 days, platelet and leucocyte counts, lung platelet uptake (LPU), venous aggregates by screen filtration (SFP), mean arterial pressure (BP), cardiac output (CO), pulmonary shunt (PS) and alveolar-arterial pO2 difference (A-adO2) were measured.During shock following aortic declamping aspirin preserved blood pressure by increasing vascular resistance rather than CO. Venous aggregates by SFP tended to be lower on aspirin with significantly reduced LPU, subsequent pulmonary shunting and A-adO2. The improvement in PS but not A-adO2 remained significant at 3 days (p<0.05).Cyclo-oxygenase inhibition improved pulmonary function during surgical shock either by inhibiting platelet microemboli or by a direct effect on pulmonary arteriovenous shunts.