British Journal of Anaesthesia, Vol 75, Issue 5 573-577, Copyright © 1995 by The Board of Management and Trustees of the British Journal of Anaesthesia
N. W. Goodman and N. Stratford
Local anaesthetics are ventilatory depressants, but previous investigators
have not commented on the effects on ventilatory timing. There is concern
about the possible ventilatory depression caused by systemic absorption of
local anaesthetics injected extradurally. We have studied ASA grade I
patients anaesthetized with a propofol infusion and breathing
spontaneously; they were given in random order lignocaine 1.5 mg kg-1 i.v.
and an equivalent volume of 0.9% saline. Breathing was analysed using
respiratory inductance plethysmography in 30-s periods for 4 min after
injection, each period scaled to the 30-s period preceding injection.
Lignocaine reduced minute ventilation. The greatest mean reduction in the 4
min was to 85%, occurring 2.5-3 min after injection; the greatest
individual reduction was to 60-65%, which occurred by 30-60 s. Lignocaine
decreased tidal volume and ventilatory rate by prolonging expiratory time.
Lignocaine had no effect on or promoted bimodality of expiratory time.
End-tidal carbon dioxide increased by a mean of 0.1%; the largest
individual change was 0.3%. This suggests that lignocaine may have reduced
the metabolic rate, affecting ventilation indirectly, but we conclude that
lignocaine in a normal extradural dose should not be an important
ventilatory depressant.
CLINICAL INVESTIGATIONS
Effect of i.v. lignocaine on the breathing of patients anaesthetized with propofol
University Department of Anaesthesia, Medical School Unit, Southmead Hospital, Bristol BS10 5NB
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