Effect of premedication on arterial blood gases prior to cardiac surgery

The effect of supplemental oxygen on the incidence of hypoxaemia after premedication in patients undergoing cardiac surgery

Opiate premedication may cause significant respiratory depression, particularly when other sedative agents such as scopolamine or benzodiazepines are added. This can cause hypoxaemia with potential for worsening myocardial ischaemia in cardiac surgery patients. The aim of this study was to investigate the incidence of hypoxaemia (SpO2 < 90%) in elective patients undergoing cardiac surgery and to assess the efficacy of supplemental oxygen in preventing it. One hundred elective patients without significant respiratory disease or cardiac failure, who received both an opiate and a sedative premedication, were prospectively randomized to receive either oxygen via a facemask at 4 l/min or no oxygen. Continuous arterial oxygen saturation was recorded using a pulse oximeter from the time of premedication until the patient arrived in theatre. An SpO2 < 90% was recorded as a significant event and oxygen was administered to the patients. Six patients were excluded because of equipment failure or protocol violations. The patient groups were comparable with respect to patient demographics, premedication type and dose or the duration of monitoring. In patients receiving oxygen (n = 48) there were no episodes of hypoxaemia (0%). In patients not receiving oxygen (n = 46) there were 14 episodes of hypoxaemia (30%, P < 0.0001). We conclude that there is a significantly high incidence of hypoxaemia in cardiac surgery patients following combined opiate and sedative premedication and that it can be reduced by the routine administration of supplemental oxygen.

A comparison of three induction agents in paediatric anaesthesia--cardiovascular effects and recovery

We studied 30 children undergoing circumcision randomly allocated to receive either thiopentone 4 mg.kg-1, propofol 2.5 mg.kg-1 or midazolam 0.5 mg.kg-1 (n = 10) IV over 30 seconds at induction of anaesthesia. Blood pressure and pulse rate during the first 15 minutes of induction were recorded by a Finapres 2300e and a Cardiocap CM-104, and changes from preinduction baseline compared between the three induction agents and the two recording instruments. Postoperatively, blood levels of the induction agents were measured and recovery from anaesthesia was assessed by clinical criteria, mood and sedation scores and psychomotor performance. The Cardiocap data revealed no statistically significant haemodynamic differences between the three induction agents. Finapres data demonstrated that propofol caused a greater decrease in mean arterial pressure when compared to thiopentone at one minute (P = 0.01) and the MAP remained significantly lower than midazolam at five minutes (P = 0.02), illustrating an advantage of continuous over intermittent non-invasive blood pressure monitoring. The midazolam group took longer to identify themselves compared to both the propofol (P = 0.005) and the thiopentone groups (P = 0.02), but there was no difference in the groups in time to eye-opening. Psychomotor performance on awakening was significantly worse in the midazolam group compared to the propofol (P < 0.03) and thiopentone groups (P < 0.02). Most children had recovered to 80% of their best, practised, unmedicated, preoperative performance four hours after awakening, irrespective of the induction agent administered. Drug blood levels correlated weakly with both methods of psychomotor assessment (r > or = 0.6). Of the three induction agents, thiopentone caused the least haemodynamic perturbation on induction, and anaesthesia induced with midazolam caused the greatest psychomotor impairment on awakening. Within one hour patients in all drug groups were equally awake, co-operative and co-ordinated.

Premedication with oral midazolam in children--an assessment of psychomotor function, anxiolysis, sedation and pharmacokinetics

We studied 30 children, aged 4 to 12 years, undergoing elective circumcision, premedicated with midazolam 0.5 mg.kg-1 and atropine 0.02 mg.kg-1 by mouth. A modified postbox test and the coding component of the Wechsler intelligence scale (WISC-R) was used to assess the preoperative effect of premedication on psychomotor function. Mood and sedation were also scored and related to serum midazolam concentrations. The children showed a significant decline in psychomotor performance 30 and 60 minutes after premedication when compared with their best unmedicated performance recorded the previous evening. This decline in psychomotor performance was only weakly associated with serum midazolam concentrations (r = 0.1). The postbox toy ratio is a suitable measurement of psychomotor performance in children because of its simplicity and ease of use in the clinical environment, although it may suffer the "test-retest" limitations of similar types of assessment. The sedative and anxiolytic effects of midazolam provide a quiet environment for a smooth induction of anaesthesia.