Circulatory reflexes in tetraplegics during artifical ventilation and general anaesthesia.

The arterial blood pressure, heart rate and electrocardiograph were recorded, and plasma electrolytes, arterial blood gases and pH, and plasma catecholamines were estimated in seven patients with physiologically complete cervical spinal cord transections who needed intermittent possitive pressure ventilation (I.P.P.V.) or were undergoing urological surgery under general anaesthesia. In the tetraplegics on I.P.P.V., bradycardia, and in two patients even cardiac arrest, occurred during tracheal suction, especially in the presence of hypoxia. In one tetraplegic being anaesthetised, cardiac arrest occurred during endotracheal intubation. This reflex bradycardia and cardiac arrest appeared to be due to a vago-vagal reflex, unopposed by sympathetic activity or by the pulmonary (inflation) vagal reflex. Atropine was effective in preventing this reflex. In the tetraplegics undergoing urological surgery, severe hypertension resulting from visceral stimulation was effectively reduced by halothane. In these patients, control of arterial blood pressure with lower concentrations of halothane may also be achieved with I.P.P.V.