Mechanisms of reflex cardiac arrest in tetraplegic patients.

Four patients with physiologically complete high cervical spinal-cord lesions, sustained within the previous 6 weeks, were observed. All needed intermittent positive-pressure ventilation. In the stage of spinal shock, stimuli to the trachea induced bradycardia, and in two patients cardiac arrest resulted. The bradycardia occurred when the patients were hypoxic, and seemed to be due to a vaso-vagal reflex. Normally this reflex is opposed by sympathetic activity, and during hypoxia by increased pulmonary (inflation) vagal reflex activity due to increased breathing. In these patients, however, compensatory sympathetic activity was prevented by the cervical cord lesion, and increased pulmonary vagal reflex activity by the fact that the breathing was artificial and therefore did not increase with hypoxia. Treatment in emergency includes the administration of atropine. Adequate oxygenation and, if this cannot be achieved, maintenance atropin should prevent the bradycardia and cardiac arrest associated with stimulation of the trachea in artificially ventilated tetraplegic patients.