]N NON-ANAESTHETIZED PATEENTS who are ,mbjected to a lethal level of hypothermm, the cause of death xs beheved to b~ I, related to autonomm reflexes wbach might reduce ventncular fibnllatmn It has been shown that surgma] sympathectomy, 2 sympathohsls with drugs, a and deep general anaesthesm 4 decreased the occurrence of hypothermm ventncular fibrlllatmn In this laboratory we demonstrated that wath total epldural anaesthesia, annnals can be cooled to lower temperatures before their hearts fibrillate 4-6The purpose of th~s mvestxgatlon was tel, ascertaan the relatmns|up between the observed protectmn of sympathetm block and ventncular excltablhty dunng hypothermm
METHODTwenty mongrel dogs were used m thl~serres of experiments 'Thlopentone 2(} m g / k g was administered mtravenousl~ fol reduction After endotrachea] mtubatlon, the ammals were ventilated artdi,~lally wath 100 per cent oxygen using a Bird respirator (Mark 8) Succlnylchohne 10 nag was administered intravenously every 20-30 rmnutes Hypotherrma was obtained by extracorporeal blood coohng using a techmque describe d an detail elsewhere 6 In brief, the femoral artery and veto were cannulated, Iblood was taken from the femoral artery (10 c c/kg/minute), cooled to 200-25 ~ C, and returned to the femoral veto Thas shunt was sustamecl until the oesophageal temperatlare reached 270-30 ~ C At this temperature, the &rectmni of the shunt was reversed, the blood flow was increased to 20 to 30 c c/kg/minute, and maintained until an oesophageal temperature of 10 ~ C was achieved The extracorporeal system was prtraed wath blood obtained from donor do~s Oxygen 100 per cent was used an the oxygenator Artlficaa] respiration was ~scontmued below 25 ~ C of oesophageal temperature Lead 2 of the E C G, t/ae fronto-occlpltal lead ot the E E G, the oesophageal temperature, the arterml blood pressure, and the venous blood pressure were recorded w~th a Sanborn 150 polygraph Statham transducers were used for pressure determmatmns Five mflhh~res cff arterial blood wer~" withdrawn at normal temperature, and at 35 ~ and 5 ~ intervals thereafter for pH and pCO2 determmatmns The experament was &scontmued when ventnculal fibnllatmn occurred or the oesophageal temperature reached 10 ~ C