Cardiovascular effects of neuromuscular blockade during induced hypothermia

Young lambs were used to study the effects of progressive cooling and rewarming on cardiovascular function during neuromuscular blockade induced by gallamine. Initially, it was shown that gallamine exerted no immediate, direct haemodynamic effect in normothermic or hypothermic lambs (cooled by 10 degrees C). By comparison with hypothermic controls, neuromuscular blockade was associated with increases in left ventricular (LV) max dP/dt (153%; P less than 0.02) as cooling progressed, and even greater increases (232%; P less than 0.001) during rewarming. It was concluded that these changes seem likely to represent enhanced myocardial contractility since preload did not closely follow LV max dP/dt (heart rate and mean aortic pressure fell gradually during cooling but values were restored in the rewarming phase). LV max dP/dt in lambs given gallamine only after cooling also showed a similar response during rewarming. Results of this study may have clinical relevance relating to the mechanical recovery of the hypothermic heart in patients receiving neuromuscular blockade during cardiac surgery, and they argue against using gallamine as such an agent.