Effect of increased blood-oxygen affinity on oxygen transport in hemorrhagic shock

Abstract

Effect of increased blood-O2 affinity on tolerance of hemorrhagic shock was studied in pentobarbital-anesthetized rats. Rats were 1st exchanged transfused with blood whose P50 [O2 partial pressure at which Hb is half-saturated with O2] was reduced by various methods by 4-21 torr. Hypotension (BP [blood pressure] = 30 torr) was induced and maintained at this level by controlled hemorrhage; it was terminated when reinfusion of shed blood became necessary to sustain this blood pressure. Initial rate of bleeding during shock was inversely proportional to P50, varying from 0.52 ml .cntdot. min-1 .cntdot. kg-1 in controls to 1.5 ml .cntdot. min-1 .cntdot. kg-1 in the group with the lowest P50, a reaction probably indicating increased sympathetic output in the latter group. Duration of shock tolerance varied from 50 .+-. 16 min in controls to 28 .+-. 11 min (SD, P < 0.001) in the group with the lowest P50. Central venous SO2 [O2 saturation] (SCVO2) and PO2 [O2 partial pressure] (PCVO2) were significantly higher and lower, respectively, in low-P50 animals than in controls, probably because of limited O2 extraction due to increased blood O2 affinity. .ovrhdot.VO2 [O2 consumption] and cardiac output were significantly lower, and mortality was significantly greater, in low-P50 animals. A left shift of the O2 dissociation curve may limit O2 delivery during hemorrhagic shock.