ISOFLURANE IN NITROUS-OXIDE AND OXYGEN INCREASES PLASMA-CONCENTRATIONS OF NORADRENALINE BUT ATTENUATES THE PRESSOR-RESPONSE TO INTUBATION

The haemodynamic response to laryngoscopy and intubation was evaluated in 52 ASA I patients anaesthetized with thiopentone 4-6 mg.kg-1. Vecuronium 0.1 mg.kg-1, followed by 3 min mask ventilation with nitrous oxide in oxygen with (isoflurane group) or without (control group) 3% inspired isoflurane preceded tracheal intubation. In 21 of 52 patients, concentrations of noradrenaline (NA), adrenaline and 3,4-dihydroxyphenylethyleneglycol (DHPG) were measured from central venous plasma. During the 3-min ventilation, in the isoflurane group, heart rate increased by 22% but remained stable in the control group. A marked pressor response to laryngoscopy and intubation was seen in the control but not in the isoflurane group. During the 3-min ventilation, the plasma concentration of NA was doubled in the isoflurane group and increased by 49% in the control group (P < 0.05). The concentration of DHPG also increased in the isoflurane group. Peripheral skin temperature increased similarly after 3 min ventilation in both groups. After intubation, it was significantly higher in the isoflurane than in the control group (P < 0.05). In conclusion, compared to nitrous oxide in oxygen, ventilation with isoflurane in nitrous oxide in oxygen causes a sympathetic activation combined with an increase in heart rate and peripheral temperature while the pressor response to laryngoscopy and intubation is attenuated.