Analgesia and ventilatory response to carbon dioxide after intramuscular and epidural alfentanil

Pain Management in Trauma Patients

Trauma is a major cause of mortality throughout the world. In recent years, major advances have been made in the management of trauma, the end result of which has been reduced mortality and enhanced function. One of these areas is pain control. Improved pain management has not only led to increased comfort in trauma patients, but has also been shown to reduce morbidity and improve long-term outcomes. This review focuses on the treatment of pain in the setting of acute injury and on pain management in trauma patients who go on to develop chronic pain. Emphasis is placed on pharmacologic interventions, invasive and noninvasive pain management techniques, analgesia in challenging patients, and pain control in commonly encountered trauma conditions.

Elimination of alfentanil delivered by infusion is not altered by the chronic administration of atorvastatin

BACKGROUND AND OBJECTIVE

Statins are prescribed for patients with hypercholesterolemia. Atorvastatin is metabolized by cytochrome P4503A4 and inhibits P4503A4 activity in vitro. Alfentanil is a potent opioid used in clinical anaesthetic practice and is also metabolized by P4503A4. This study tested the hypothesis that chronic atorvastatin administration inhibits the metabolism of alfentanil.

METHODS

Sixteen patients undergoing elective surgery were studied as matched pairs. One member of each pair was maintained on standard doses of atorvastatin for at least 4 months. Each patient received an alfentanil bolus (80 microg kg(-1)) intravenously (i.v.), followed by an alfentanil infusion (0.67 microg kg(-1) min(-1)) for 90 min. Serial plasma alfentanil concentrations were measured using gas chromatography-nitrogen phosphorous detection. Pharmacokinetic parameters were calculated using two-compartment linear modelling.

RESULTS

One patient and the corresponding match were excluded from the analysis. The elimination half-life of alfentanil was similar in the control and atorvastatin groups (98.8 +/- 12.4 versus 98.3 +/- 11.3 min, respectively). The clearance (Cl), volume of distribution at steady-state (Vdss) and area under the curve (AUC) were similar in the two groups (Cl = 0.20 (+/- 0.06) and 0.22 (+/- 0.04) L min(-1), Vdss = 0.38 (+/- 0.07) and 0.39 (+/- 0.07) L kg(-1), AUC = 0.05 (+/- 0.02) and 0.04 (+/- 0.01) mg min mL(-1)).

CONCLUSIONS

Concurrent atorvastatin administration does not alter the pharmacokinetics of alfentanil in patients undergoing elective surgery.

A pharmacokinetic approach to resolving spinal and systemic contributions to epidural alfentanil analgesia and side-effects

A pilot study was conducted in 7 normal volunteers to demonstrate the feasibility of employing pharmacokinetic tailoring to achieve matching plasma opioid concentration-time curves after epidural (e.p.) and intravenous (i.v.) alfentanil administration. Each subject participated in 1 pretest and 2 test sessions. Our pain model was cutaneous electrical stimulation of the finger and toe, adjusted to produce a baseline pain report of 5 (strong pain on a 0-5 scale). On test day 1, subjects received e.p. alfentanil (750 micrograms) and an i.v. saline infusion. Serial measurements of analgesia, end tidal CO2, pupil size, subjective side effects, and plasma alfentanil concentrations were conducted before and at various time intervals over a 4-h period after alfentanil administration. On test day 2, subjects received e.p. saline and a pharmacokinetically tailored i.v. infusion (using individual pharmacokinetics determined on the pretest day) designed to achieve a plasma concentration-time profile identical to that observed on the epidural day. The same battery of effect measurements was administered as on the 1st test day. Plasma alfentanil was measured to verify the accuracy of the tailored infusion. Plasma alfentanil concentration profiles were nearly identical on both test days. Peak plasma alfentanil concentrations were near the reported minimum effective analgesic concentration (MEAC). Overall, analgesia was slightly greater with e.p. administration. Onset of pain relief was rapid, and duration was approximately 1.5 h with e.p. and 1 h with i.v. alfentanil. There were no differences in pupil size, ETCO2, or subjective side effects between e.p. versus i.v. administration. We conclude that systemic redistribution from the epidural space appears to account for most, but not all, of the analgesia.

Postoperative pain treatment after cholecystectomy with epidural sufentanil at lumbar or thoracic level

The difference in analgesic activity following lumbar (group I) or thoracic (group II) epidural administration of 50 micrograms sufentanil was studied after cholecystectomy. Fifteen patients in each group were evaluated for pain relief using a linear analog scale (LAS), heart rate (HR), mean arterial pressure (MAP), respiratory rate (RR), peak expiratory flow (PEF), forced vital capacity (FVC), forced expiratory volume (FEV1) and arterial CO2 tension (PaCO2). In five additional patients in each group 75 micrograms sufentanil was injected for determination of serum levels. Pain scores were lower than three in both groups after 10 min, while mean pain scores remained below one from 20 min until 2 h following injection in both groups. Satisfactory pain relief lasted for 4 h. RR was significantly decreased from two until 360 min. in the lumbar group and from five until 120 min in the thoracic group. PaCO2 was raised in both groups only during the first hour. PEF and FVC were significantly improved compared to control 1, 2 and 4 h following injection. Serum sufentanil levels reached a maximum of 0.299 +/- 0.052 ng.ml-1 in the lumbar group and 0.377 +/- 0.076 ng.ml-1 in the thoracic group after 5 min. There were no significant differences between the two groups in the variables studied.

Premedication for outpatient cataract surgery: a comparative study of intramuscular alfentanil, midazolam and placebo

The effects of i.m. alfentanil and midazolam on anxiety, sedation, hemodynamics, oxygen saturation and intraocular pressure were studied in 90 patients scheduled for outpatient cataract surgery with regional anesthesia. The study was randomized, double-blind, placebo-controlled, and performed on outpatients with ASA physical status I-III and mean age 67.7 +/- 11.7 years. Alfentanil (12.5 micrograms/kg) administered into the deltoid muscle had a marked anxiolytic and short sedative effect, and was associated with stable hemodynamics. Midazolam (20 micrograms/kg) administered similarly had a more prolonged anxiolytic and sedative effect, which impaired co-operation in some patients during surgery. The regional blockade was associated with a significant reduction of oxygen saturation (SpO2), regardless of the premedication used (P less than 0.05). A slight reduction of intraocular pressure (IOP) was found after premedication, but the change was not statistically significant. We conclude that i.m. alfentanil is well tolerated, and its anxiolytic and short sedative effects make it especially suitable as premedication for day-case cataract surgery.

Steady-state infusions of opioids in human. II. Concentration-effect relationships and therapeutic margins

We used computer-controlled individually tailored infusions to study relationships between plasma drug concentration and opioid effects, and to evaluate the therapeutic margins of alfentanil, fentanyl and morphine in human subjects. In order to compare the 3 drugs, we infused each opioid to 3 different steady-state target plasma concentrations during separate 8 h test periods so that concentration-effect curves could be defined for each opioid and subject. Dental electrical stimulation produced a consistent degree of baseline experimental pain, and we measured the influence of increasing plasma opioid concentrations on pain intensity and the magnitude of pain-related evoked potentials. We also quantified ventilatory function and subjective side-effects during baseline (no drug), at the 3 target plasma concentrations with each drug. Finally, we measured actual plasma opioid concentrations during each phase of the infusion period. This procedure allowed us to calculate for each opioid the plasma concentration required to produce a 50% decrease in reported pain intensity and evoked potential amplitude (IC50). Subsequent calculation of side-effect magnitudes at the analgesic IC50s permitted direct comparisons of therapeutic margins between alfentanil, fentanyl and morphine. We found a robust relationship between plasma drug concentration and analgesic, ventilatory, and subjective-effect magnitudes for each opioid in this study. We conclude that the magnitudes of individual side-effects associated with equianalgesic, steady-state plasma concentrations of these 3 mu receptor-selective opioids do not differ across drugs.

[Use of morphinomimetics in regional anesthesia]

Pain relief is one of medicine's most important challenges and the first aim of anaesthesia. The most common technique of postoperative analgesia remains intramuscular or subcutaneous opiates. There has been a better understanding of the mechanisms of action of opiates over the last decade, and new techniques and methods of administration have been developed especially their regional application. In 1979, two reports acted as catalysts to promote further studies. Wang et al. reported on the efficacy of intrathecal morphine to relieve unbearable malignant pain in 8 patients whereas Behar et al reported on the efficacy of morphine by epidural route. More recently, several studies pointed out the usefulness of the peripheral perineural route for opiates. However, this remains controversial, as some discrepancies persist in the results. The classification of opiate receptors and their relationship to opiate analgesia, as well as the mechanisms of action of regionally administered opiates are analyzed. The dual pre- and postsynaptic actions of spinal opiates are then considered. The parts played by the different neurotransmitters and pathways are set out. The evidence for opiate receptors at peripheral nerve sites and the different hypotheses suggested to explain the effect of opiates given by the perineural route are discussed. The pharmacokinetics and pharmacodynamics of opiates given by the subarachnoid and epidural routes are considered, in particular with respect to the comparative pharmacology of the commonly used opiates. The adverse effects of spinal opiates are reviewed, with their potential risks, and their clinical and therapeutic implications. Opiates and local anaesthetics given by the spinal route are compared. The clinical applications of intrathecal and epidural opiates are discussed, especially in the fields of postoperative analgesia, treatment of chest trauma, and cancer pain. Lastly, the few controlled studies concerning the use of opiates in peripheral nerve blocks, especially brachial plexus blocks, and the prospects of this new technique of giving opiates regionally are discussed.