Articles: opioid-analgesics.
-
Current use of opioids in anaesthesia is reviewed with particular emphasis on the use of opioids in anaesthetic doses, techniques that recently have become popular in cardiovascular anaesthesia. A major benefit of opioid anaesthesia (particularly fentanyl) is the cardiovascular stability which obtains during induction and throughout operation, even in patients with severely impaired cardiac function. Anaesthetic doses of morphine are associated with a higher incidence of cardiovascular disturbances and other problems. ⋯ High doses of opioids can reduce or prevent hormonal and metabolic responses to the stress of surgery. Even very large doses of fentanyl or its new analogues do not prevent marked increases in plasma catecholamine concentrations in response to cardiopulmonary bypass. The reduction in hormonal and metabolic stress response does not appear to continue postoperatively.
-
Relief of pain after surgery remains poor for the majority of patients. The pain is unpleasant, and is associated with arterial hypoxaemia, venous thrombosis, myocardial ischaemia and a more florid hormonal response to surgery. Regional analgesia, systemic, subarachnoid or extradural opioids and antiprostaglandin drugs are all used to treat pain after surgery. ⋯ Intravenous administration avoids both problems and excellent results have been obtained using Patient Controlled Analgesia devices, but these machines are expensive. A simple regimen suitable for application to large numbers of surgical patients is required. Continuous infusion of fentanyl 100 micrograms h-1 IV begun two hours before surgery and supplemented by a single bolus dose of fentanyl 100 micrograms IV provided an effective background of analgesia.
-
Small doses of epidural and intrathecal opioids produce effective and prolonged analgesia postoperatively, although the quality of analgesia does not differ from when conventional routes are used. The different opioids differ only in the speed of onset and duration of action, and in the incidence of side-effects. 'Minor' complications such as nausea, vomiting, pruritus and retention of urine are relatively common. ⋯ It is commoner after morphine and after intrathecal administration, and is also associated with advanced age, concomitant use of other central depressant drugs, respiratory disease and large doses. Because of the potentially lethal nature of this complication, it is recommended that the epidural and intrathecal routes of administration are used only when patients can be closely and constantly observed postoperatively.
-
Opioids were available in clinical practice since before the birth of modern anaesthesia--Setürner isolated morphine in 1806. They have a record of safety which is reflected in their high therapeutic ratios, especially the synthetic opioids introduced recently (table III). The most serious immediate adverse effect, respiratory depression, is a predictable effect related closely to analgesia. It is fortunate for anaesthetists who use opioids regularly, that recognition and treatment of respiratory problems are an integral part of their craft and that opioid antagonists are effective in reversing respiratory depression.
-
During a period of one year, 119 patients with chronic pain received injections of opioids via a catheter inserted in the lumbar epidural space. Twenty-three patients (19%) showed evidence of tolerance and were given droperidol 1.25-5.0 mg epidurally. ⋯ One patient given an accidental overdose of droperidol developed reversible Parkinsonism. It is concluded that epidural administration of the dopamine antagonist droperidol may be beneficial as supplementary medication to epidural opioids when tolerance develops.