Bradycardia and cardiac arrest during tracheal suction--mechanisms in tetraplegic patients.

The cardiovascular responses to tracheal suction were observed in 4 consecutive recently-injured tetraplegics with physiologically complete cervical spinal cord transections (C3-5) who were in spinal shock and needed artificial ventilation. In all 4 patients tracheal suction induced bradycardia and in 2 patients even cardiac arrest. The bradycardia occurred when the patients were hypoxic, and was prevented by the addition of oxygen to inspired air, or, if this was inadequate, by the administration of atropine. Two of the patients were agains studied several months later, after return of isolated spinal cord activity and spontaneous breathing. In both patients tracheal suction then caused tachycardia and increased respiratory effort. It is concluded that: 1. Tetraplegics with high cervical spinal cord transections who are in spinal shock and unable to breathe spontaneously are prone to bradycardia and cardiac arrest during tracheal suction. This is more likely to occur when they are hypoxic. 2. The bradycardia appears to be due to a vago-vagal reflex for both afferent and efferent limbs of the arc are in the vagus nerve. A number of factors play a part, including (I) absent sympathetic activity; (II) airway receptor stimulation; (III) hypoxia and (IV) the inability to breathe spontaneously (The pulmonary (inflation) vagal reflex which would normally oppose the cardio-inhibition caused by (II) and (III) is absent). 3. The bradycardia in response to tracheal suction can be prevented by adequate oxygenation, or if this cannot be achieved, by repeated atropine.