EFFECTS OF ANTIVENOM SEROTHERAPY ON HEMODYNAMIC PATHOPHYSIOLOGY IN DOGS INJECTED WITH L-QUINQUESTRIATUS SCORPION-VENOM

In dogs, scorpion venom causes an immediate increase in cardiac output that declines below baseline Values within one hour. We tested the hy potheses that antivenom given before venom injection may prevent chang es in cardiac output, while antivenom given after the inotropic stage of envenomation cannot reverse cardiac output decline. Twenty-five ane sthetized, mechanically Ventilated dogs were given 0.1 mg/kg IV venom of the scorpion Leiurus quinquestriatus. The dogs were randomized into 4 groups: 5 dogs were given venom alone (control group) and 6 dogs we re given 6 mi of antivenom one minute before venom injection while 8 a nd 6 dogs were given 6 mi of antivenom 20 and 60 min after venom injec tion, respectively. Parameters reflecting respiratory and circulatory functions were measured for 180 min after venom injection. Scorpion ve nom caused a gradual decrease in heart rate, an initial elevation of s ystemic and pulmonary blood pressure and cardiac output followed by a decline in these parameters. PO2, pH and HCO3- gradually decreased, wh ile PCO2 gradually increased from baseline. Antivenom given before ven om injection prevented all the effects induced by the venom. Antivenom given at 20 and 60 min after Venom injection had no effect on cardiac output and HCO3- decline, but caused an increase in heart rate, PO2 a nd pH and a decrease in PCO2. We assume that antivenom clears free tox ins from the circulation and since cardiac output and HCO3- did not im prove after this clearance, we conclude that following intravenous ven om injection, heart and circulation are rapidly affected by the toxins or by other substances released by the venom which do not respond to antivenom. Improvements in respiration and heart rate with antivenom g iven after venom injection may be secondary to reversion of cholinergi c effects of the venom. Improvement in respiration may be also explain ed by reversion of the toxic effects on Ca2+ activated K+ channels of branchial smooth muscle. All these effects may be secondary to clearan ce of toxins by the antivenom. (C) 1998 Elsevier Science Ltd. All righ ts reserved.