No abstract

The effect of a partial neuromuscular block on the ventilatory response to hypercarbia and to hypoxaemia was studied in 11 non-anaesthetized male subjects. Respiratory frequency, tidal volume, minute volume, respiratory timing and drive were measured during air breathing and during stimulation by hypercarbia and hypoxaemia. The ventilatory response was defined as the ratio between, respectively, tidal volume and minute volume during ventilation stimulated by hypercarbia and hypoxaemia compared to measurements during air breathing. The ventilatory measurements were repeated on three separate occasions: before neuromuscular block was established, during an infusion of vecuronium aiming at a mechanical adductor pollicis train-of-four (TOF) ratio of 0.70, and after the infusion had been stopped and the neuromuscular block had spontaneously recovered to a TOF ratio of > 0.90. Resting ventilation during air breathing remained with minor variations throughout the experiment. The ventilatory response to hypercarbia was not affected at a TOF ratio of 0.70 as compared to measurements before vecuronium and at a TOF ratio of > 0.90. In contrast, the ventilatory response to hypoxaemia was markedly reduced at a TOF ratio of 0.70. We conclude that a mechanical TOF ratio of 0.70 following vecuronium may be associated with an inadequate ventilatory response to hypoxaemia.

No abstract

It is concluded that vecuronium depresses carotid body chemoreceptor function to a varying extent during hypoxia and that the depression recovers spontaneously.

We investigated the effects of a close carotid injection of vecuronium on changes in phrenic nerve activity during different states of oxygenation. Experiments were performed on normothermic and mechanically ventilated adult New Zealand White rabbits with a tracheostomy under continuous thiopental infusion. Carotid arteries and carotid bodies were identified bilaterally followed by glomectomy on the contralateral side and positioning of a lingual artery catheter with its tip located in the carotid bifurcation on the ipsilateral side. From the dissected ipsilateral C-4 nerve root, changes in integrated phrenic nerve activity (IPA) were recorded after isocapnic step reductions from hyperoxia to normoxia (fraction of inspired oxygen [FIO2] 0.21, normoxic challenge) and from hyperoxia to moderate hypoxia (FIO2 0.15, hypoxic challenge) immediately after a close carotid bolus injection of either normal saline or 1 or 10 microgram of vecuronium. Arterial blood gases were analyzed during each ventilatory state. Phrenic nerve response to hypoxia expressed as chemosensitivity (Sch) was computed as the relative change in phrenic nerve activity per unit decrease in arterial oxygen saturation (Sao2), that is: Sch = (IPA challenge/IPA hyperoxia) - 1/Sao2 hyperoxia - Sao2 challenge. Hypoxic challenges were associated with reduced phrenic nerve response (Sch) after injection of 1 and 10 micrograms of vecuronium compared with normal saline. During normoxic challenges, no change occurred after 1 microgram, but reduced chemosensitivity was seen after 10 micrograms of vecuronium. We conclude that vecuronium depresses phrenic nerve activity during hypoxia.

No abstract

No abstract