High-dose buprenorphine: perioperative precautions and management strategies.

Buprenorphine has been in clinical use in anaesthesia for several decades. Recently, the high-dose sublingual formulation (Subutex, Reckitt Benckiser, Slough, U.K.) has been increasingly used as maintenance therapy in opioid dependence, as an alternative to methadone and other pharmacological therapies. Buprenorphine has unique pharmacological properties making it well suited for use as a maintenance therapy in opioid dependence. However, these same properties may cause difficulty in the perioperative management of pain. Buprenorphine is a partial opioid agonist, attenuating the effects of supplemental illicit or therapeutic opioid agonists. As a result of its high receptor affinity, supplemental opioids do not readily displace buprenorphine from the opioid receptor in standard doses. High-dose buprenorphine has an extended duration of action that prolongs both of these effects. The perioperative management of patients stabilized on high-dose buprenorphine and undergoing surgery requires consideration of the likely analgesic requirements. Where possible the buprenorphine should be continued. Pain management should focus on maximizing non-opioid analgesia, local anaesthesia and non-pharmacological techniques. Where pain may not be adequately relieved by these methods, the addition of a full opioid agonist such as fentanyl or morphine at appropriate doses should be considered, accompanied by close monitoring in a high dependency unit. In situations where this regimen is unlikely to be effective, preoperative conversion to morphine or methadone may be an option. Where available, liaison with a hospital-based alcohol and drug service should always be considered.

Awake fibreoptic intubation under remifentanil and propofol target-controlled infusion.

We present the first report of the use of remifentanil and propofol target-controlled infusion to sedate a patient with a difficult airway undergoing awake fibreoptic intubation. This regimen was rapidly titratable, aided suppression of airway reflexes, maintained patient comfort and cooperation and did not compromise spontaneous respiration. The literature regarding infusion rates and potential complications of this technique is reviewed.

Intrathecal diamorphine (heroin) for obstetric analgesia.

Intrathecal diamorphine (heroin, diacetyl morphine) 2.5 mg in isotonic saline 2.5 ml was given to 13 patients in labour through a 26 gauge Quincke needle. Three patients were given epidural bupivacaine at a mean of 295 min after injection of diamorphine and a further 2 used 50% nitrous oxide during the second stage of labour. Eight patients needed no additional analgesia for labour although 1 received a pudendal nerve block for forceps delivery. No neonatal complications attributable to diamorphine were observed. There was a high incidence of post partum headache (6/13 cases). The use of a Sprotte needle and a fine spinal catheter might overcome the limitations of spinal headache and limited duration of action respectively.

Acute carbon monoxide exposure and cerebral blood flow in rabbits.

Carbon monoxide (CO) 1% was administered to anaesthetised rabbits for 15 minutes. Despite a 28% +/- 5.8 (SEM) fall in mean arterial blood pressure during the CO exposure, cerebral blood flow increased by 236% +/- 36.5 in the left and 287% +/- 28.9 in the right cortex. Cerebrovascular resistance was reduced by 70.6% +/- 2.8 in the left and by 76.2% +/- 3 in the right cortex. These changes were accompanied by an increase in intracranial pressure, a drop in body temperature and ventilation requirement, and a metabolic acidosis. When the CO was withdrawn all these parameters returned to normal over three hours. Hence, these vascular effects are reversible and consistent with the natural history of CO intoxication in humans. Carboxyhaemoglobin levels correlated well with hemispheric cerebral blood flow (r = 0.90; r = 0.98) and cerebrovascular resistance (r = 0.87; r = 0.97).

Lumbar epidural diamorphine following thoracic surgery. A comparison of infusion and bolus administration.

Twenty-two patients received a single dose of diamorphine 5 mg through a lumbar epidural catheter before thoracic surgery. The patients were transferred after surgery to a high dependency unit where they were allocated randomly to receive either an infusion of epidural diamorphine at a rate of 1 mg/hour (group 1) or bolus doses of epidural diamorphine 5 mg on demand (group 2). There was no statistically significant difference between the groups in visual analogue pain scores in the first 18 postoperative hours. Arterial carbon dioxide tension was elevated in both groups and was consistently higher in group 1 than in group 2, with a statistically significant intergroup difference 12 hours after operation. Respiratory rate was not a useful index of respiratory depression. The commonest nonrespiratory side effect was urinary retention, but the incidences of this and other minor side effects were similar in the two groups.

The stability of atracurium in clinical practice.

Atracurium has an unusual intrinsic Hofmann elimination which is increased by an alkaline environment and increased temperature. Normally the relaxant is stored at pH 3.3 and kept at a temperature of 4 degrees C. However, it is convenient to have a reasonable quantity available within the operating theatre. This study examined the rate of degradation of atracurium in the operating theatre environment of 20 degrees C. Atracurium within one month of its expiry date was placed in the drawer for anaesthetic drugs in each of three operating theatres. At the end of each month, further drug was added to the stock. At the end of the study, atracurium which had been stored continuously at 4 degrees C, was at 102.9% of nominal strength, having started with 113.5% at manufacture. Atracurium which had been at room temperature for one, two and three months respectively retained 99%, 95% and 92% strength respectively. These results show that even three months' exposure to room temperature does not cause enough deterioration to be clinically significant.

Increasing doses of intracarotid air and cerebral blood flow in rabbits.

We studied the natural history of brain air embolism by observing bubbles in the pial vessels of rabbits and the effect of different doses of intracarotid air on brain function and blood flow. We identified and then studied two doses of air; 25 microliters in five rabbits caused rapid bubble transit, recovery, and then deterioration in brain function and blood flow and 400 microliters in five rabbits caused temporary bubble trapping and sustained deterioration in brain function. These dose responses correlate well with the natural history of divers with air embolism of the brain. All doses of air caused both arteriolar dilatation and reduced blood flow, which were independent of dose, whereas the detrimental effect of air embolism of brain function was dose dependent. Our results suggest that this is a good model of brain air embolism.

Peri-operative care in restrictive respiratory disease.

A total of 139 of 473 severely disabled, mainly ventilator-dependent patients required some form of surgery. Such patients require surgery more frequently than normal individuals, both because of their disability and because even minor unrelated disorders superimposed on permanent disability cause greater handicap. We report the peri-operative management and postoperative complications of 142 operations on 83 patients between 1982 and 1987. A simple inhalational anaesthetic technique was used; opioids and muscle relaxants were seldom given. Negative pressure ventilation was employed in the postoperative period when appropriate, and was combined with vigorous chest physiotherapy. There were three peri-operative deaths, but the overall death rate in the patients who underwent surgery was no greater throughout the study period than in those who did not require surgery. We believe that an aggressive surgical approach is appropriate in severely disabled, ventilator-dependent patients.