Haemodynamic changes during high spinal anaesthesia in children having open heart surgery.

BACKGROUND: This prospective series examined the haemodynamic effects of high spinal anaesthesia in combination with light general anaesthesia in infants and children undergoing open heart surgery who were candidates for immediate or early postoperative extubation. METHODS: After midazolam premedication and sevoflurane inhalation induction, 30 patients, aged 7 months to 13 years, who were undergoing open heart surgery, received spinal anaesthetics with 0.5% tetracaine D10 mixed with morphine. The spinal blocks were placed at the L2,3 or L3,4 interspace with cephalad spread being promoted by positioning the patient in 30 degrees of Trendelenburg for a minimum of 10 min. Maintenance of anaesthesia was with isoflurane 0.2-0.5% in 70% nitrous oxide to maintain heart rate and blood pressure within 20% of postinduction baseline values. Haemodynamic values were recorded at predetermined timed intervals and intraoperative events up to and including aortic cannulation. For analysis of the data, patients were divided into four age groups (< 1 years, 1-3 years, 4-6 years and > 7 years). RESULTS: Haemodynamic stability was demonstrated in all four age groups. Statistically significant slowing of the heart rate did occur in the groups older than 1 year at 25 min, although clinically significant bradycardia requiring treatment never occurred. Hypotension did occur during specific surgical manipulations but recovered spontaneously. Atropine, fluid boluses and vasopressors were never used. At the conclusion of surgery, all patients met extubation criteria and could move all four extremities. CONCLUSIONS: High spinal anaesthesia with hyperbaric tetracaine and morphine in combination with light general anaesthesia is well tolerated haemodynamically by the paediatric population studied.

The effect of baricity of intrathecal morphine in children receiving tetracaine spinal anaesthesia for cardiac surgery: a preliminary report.

BACKGROUND: This prospective, randomized study examined the effect of baricity of intrathecal preservative-free morphine on the duration of postoperative analgesia and incidence of side-effects in infants and children receiving high spinal anaesthesia with hyperbaric tetracaine in combination with a light general anaesthetic. METHODS: Fourteen infants and children, aged 7-91 months, undergoing repair of either uncomplicated atrial or ventricular septal defects, were randomized to receive either 10 microg x kg(-1) of intrathecal morphine in combination with 0.5% tetracaine D10 (hyperbaric morphine group) or intrathecal morphine mixed with saline and injected sequentially after the administration of 0.5% tetracaine D10 (hypobaric morphine group). After spinal injection, patients were positioned in 30 degrees of Trendelenburg for a minimum of 10 min. Postoperatively, patients were monitored for a minimum of 12 h. Pain scores and the incidence and severity of side-effects were recorded every 1 h. RESULTS: All patients were extubated at the conclusion of surgery without any incidence of respiratory depression. There was a decreased incidence of vomiting in the hypobaric morphine group and no significant difference in the duration of analgesia. CONCLUSIONS: When intrathecal morphine is administered in conjunction with a hyperbaric tetracaine spinal to paediatric cardiac patients in the head down position, sequential administration of the hypobaric solution may mitigate side-effects.

Effects of naloxone on nitrous oxide actions in healthy volunteers.

A number of studies have examined the effects of naloxone on nitrous oxide-induced analgesia with conflicting results. In the present study the effects of a relatively high dose of naloxone was examined to determine its effects on nitrous oxide-induced analgesia, as well as on the subjective and psychomotor effects of nitrous oxide. Fourteen subjects participated in a four-session crossover trial in which they received intravenous injections of either saline or 30mg/70kg naloxone 10min into a 35min period in which they were inhaling either 100% oxygen or 30% nitrous oxide in oxygen. Ten minutes after the naloxone administration, subjects were tested on the cold pressor test. Mood and psychomotor performance were also assessed before, during and after the inhalation period. Subjects reported higher pain ratings after the naloxone injection than the saline injection, but there was no evidence of naloxone reversing the analgesic effects of nitrous oxide. Similarly while naloxone also affected mood and impaired psychomotor performance, there was no evidence of naloxone reversing the effect of nitrous oxide on these measures. The results of this study call into question the role of the opioidergic system in mediating various effects of nitrous oxide in humans.