Meperidine infusion for postoperative analgesia in grossly obese patients

[Application procedures and dosage recommendations for postoperative analgesia.]

Systemic application of analgesics is still the most frequently used method of postoperative relief of pain. However, neither intermittent intramuscular nor intermittent intravenous application can provide the patient with a continuous level of analgesia. Lipid-soluble analgesics or those with polar binding that are rapidly metabolized demonstrate an rapid effectiveness. If the analgesia must be administered over a long period, it is due to a low level of lipid solubility, high receptor affinity and low elimination rates. Oral as well as sublingual buccal and rectal applications are characterized by uncertain absorption conditions. There are few investigations on the subcutaneous application of analgesics. After intramuscular administration analgesic levels are achieved within 15 to 60 min, but various conditions may alter the absorption criteria. Intradeltoidal application is preferable to intragluteal injection. Analgesics may be administered intravenously as a bolus, as continuous infusion, or as patient-controlled analgesia. The bolus injection is characterized by a short period of action and the necessity to administer several bolus injections by repeated administration. The continuous infusion of analgesics should begin with the administration of an initial bolus injection. Infusion analgesia should be performed under careful monitoring conditions. The most promising method of pain relief is patient-controlled analgesia (PCA). After an initial bolus injection, the continuous infusion of an analgesic is guaranteed and may be completed by the patient with several bolus injections. PCA requires careful monitoring. We suggest that a special analgesia team to take care of the patient in special analgesia units might be appropriate in the future.

Postoperative pain management of the obese patient

In the obese patient, the goal of postoperative pain management is provision of comfort, early mobilisation and improved respiratory function without causing inadequate sedation and respiratory compromise. The pathophysiology of obesity, typical co-morbidities and the high prevalence of obstructive sleep apnoea (OSA) amongst obese patients make safe analgesic management difficult. In particular, pain control after bariatric surgery is a major challenge. Although several reviews covering anaesthesia and analgesia for obese patients are published, there is mainly expert opinion and a paucity of evidence-based recommendations. Advice on general management includes multimodal analgesic therapy, preference for regional techniques, avoidance of sedatives, non-invasive ventilation with supplemental oxygen, early mobilisation and elevation of the head of bed to 30 degrees. Finally, with regard to monitoring, sedation scoring is most relevant, but there should be a low threshold for continuous pulse oxymetry, arterial blood pressure measurement and placement in a high-dependency area for the postoperative period.

Influence of opioid agonists on cardiac human ether-a-go-go-related gene K(+) currents

We have evaluated the ability of various opioid agonists, including methadone, L-alpha-acetylmethadol (LAAM), fentanyl, meperidine, codeine, morphine, and buprenorphine, to block the cardiac human ether-a-go-go-related gene (HERG) K(+) current (I(HERG)) in human cells stably transfected with the HERG potassium channel gene. Our results show that LAAM, methadone, fentanyl, and buprenorphine were effective inhibitors of I(HERG), with IC(50) values in the 1 to 10 microM range. The other drugs tested were far less potent with respect to I(HERG) inhibition. Compared with the reported maximal plasma concentration (C(max)) after administration of therapeutic doses of these drugs, the ratio of IC(50)/C(max) was highest for codeine and morphine (>455 and >400, respectively), thereby indicating that these drugs have the widest margin of safety (of the compounds tested) with respect to blockade of I(HERG). In contrast, the lowest ratios of IC(50)/C(max) were observed for LAAM and methadone (2.2 and 2.7, respectively). Further investigation showed that methadone block of I(HERG) was rapid, with steady-state inhibition achieved within 1 s when applied at its IC(50) concentration (10 microM) for I(HERG) block. Results from "envelope of tails" tests suggest that the majority of block occurred when the channels were in the open and/or inactivated states, although approximately 10% of the available HERG K(+) channels were apparently blocked in a closed state. Similar results were obtained for LAAM. These results demonstrate that LAAM and methadone can block I(HERG) in transfected cells at clinically relevant concentrations, thereby providing a plausible mechanism for the adverse cardiac effects observed in some patients receiving LAAM or methadone.

Nalbuphine versus meperidine for post-operative analgesia: a double-blind comparison using the patient controlled analgesic technique

A double-blind study was undertaken to compare nalbuphine, a synthetic partial agonist opiate, with meperidine in providing analgesia in patients following abdominal surgery, using the patient controlled analgesic technique. Both drugs showed a wide variation in demand requirements, but they were equally effective in relieving pain as assessed by the linear analogue technique. Neither drug caused a reduction of respiratory rate. The patient-controlled analgesic technique gave analgesia of good quality and it aided the comparison of the two drugs. However, some of the patients found the technique difficult to manage, and it is expensive and time-consuming. Until further experience is gained with this device its use should be confined to a constant care unit.