Cardiovascular effects of 50% nitrous oxide in older adult patients anaesthetized with isoflurane or halothane |
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Authors: | McKinney M S; Fee JPH |
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Institution: | Ards Hospital, Church Street, Newtownards, Co. Down, BT23 4AS; Department of Anaesthetics, Whitla Medical Building, 97 Lisburn Road, Belfast BT9 7BL |
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Abstract: | We have studied the cardiovascular effects of equipotent concentrations of
halothane or isoflurane, with or without 50% nitrous oxide in oxygen, in 80
patients, aged 60 yr or more, during 20 min of stable equipotent
anaesthesia. Non-invasive measurement techniques were used, with
suprasternal Doppler ultrasonography for estimating cardiac output. Both
isoflurane and halothane reduced heart rate and systemic arterial pressure.
With isoflurane, mean rate decreased from 72 (SD 9.7) to 67 (10.4) beat
min-1 and with halothane from 76 (10.1) to 65 (9.1) beat min-1 (P <
0.05). Mean diastolic arterial pressure decreased from 81 (11.3) to 58
(17.0) mm Hg with isoflurane and from 86 (14.7) to 70 (13.3) mm Hg with
halothane (P < 0.05). Cardiac index decreased from 3.1 (1.03) to 2.7
(0.71) litre min-1 m-2 with isoflurane and from 3.1 (0.98) to 2.5 (0.57)
litre min-1 m-2 with halothane (P < 0.05). Systemic vascular resistance
decreased significantly in all groups except those receiving halothane with
nitrous oxide. Nitrous oxide resulted in significantly less depression of
cardiac index when given with isoflurane than when given with halothane.
The mean percentage change in cardiac index during isoflurane anaesthesia
without nitrous oxide was 16.7%; with nitrous oxide there was a 0.5%
increase. Halothane, in combination with nitrous oxide, resulted in greater
depression of cardiac index than isoflurane with nitrous oxide. The mean
percentage change with halothane was 20.4% (22.2%); with isoflurane there
was a 0.5% (27.1%) increase (P < 0.05). Hypotension was more pronounced
in patients anaesthetized with isoflurane (n = 40) than those anaesthetized
with halothane (n = 40), irrespective of the presence of nitrous oxide. The
mean percentage decrease with isoflurane was 29.7% (21.10%) compared with
16.8% (16.78%) with halothane (P < 0.05).
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