A comparison of target-controlled therapy with patient-controlled administration of propofol combined with midazolam for sedation during dental surgery.

Forty anxious day case patients undergoing extraction of third molar teeth under local anaesthesia with sedation, were studied in a randomised double-blind controlled trial. A target-controlled infusion of propofol was compared with patient-controlled propofol for sedation, combined with a small dose of midazolam to improve amnesia. The objectives of the study were to measure the total dose of propofol used by the two groups and assess recovery and patient satisfaction. The mean dose of propofol used in the patient-controlled sedation group was significantly less than the target-controlled group (p < 0.00007). Five patients became over-sedated in the target-controlled group compared with none in the patient-controlled group. Only one of the three tests of performance showed that the target-controlled patients were more sedated. Patient satisfaction was high in both groups despite a greater recollection of events in the patient-controlled group.

Pharmacokinetic and clinical study of ropivacaine and bupivacaine in women receiving extradural analgesia in labour.

We have compared, in a randomized, double-blind study, the pharmacokinetics of ropivacaine and bupivacaine during labour. Total and free plasma concentrations of ropivacaine and bupivacaine were measured after the first of two extradural doses. The main dose was 20 mg (test dose) and 30 mg, with a top-up dose of 25 mg when requested. After the main dose, Cpmax (total) of ropivacaine (0.50 mg litre-1) was similar to that of bupivacaine (0.48 mg litre-1). At 20 min, Cpmax (free) of ropivacaine (0.04 mg litre-1) was higher than that of bupivacaine (0.02 mg litre-1) (P = 0.0025). The clinical effectiveness of the block was similar in both groups.

An in vitro comparison of fluid leakage after dural puncture with Atraucan, Sprotte, Whitacre, and Quincke needles.

BACKGROUND AND OBJECTIVES: The study was designed to evaluate the influence of needle size and design on the rate of leakage following dural puncture. METHODS: An in vitro model and fresh human lumbar dura were used to examine the rate of fluid leakage after puncture with Sprotte (24-gauge and 26-gauge), Atraucan (24-gauge and 26-gauge), Quincke (26-gauge and 29-gauge), and Whitacre (22-gauge and 25-gauge) needles. RESULTS: The study confirmed that finer-gauge needles tend to produce less leakage and that traditional Quincke pattern bevels result in greater leakage than pencil-point designs of the same diameter. CONCLUSIONS: The comparably low leakage rate produced by the Atraucan, a new needle with a terminal opening, suggests that this needle is worthy of further clinical evaluation.

Comparison of ropivacaine and bupivacaine in extradural analgesia for the relief of pain in labour.

Forty women having requested extradural analgesia for labour were allocated randomly to receive 0.5% ropivacaine or bupivacaine 10 ml as the main dose. When a top-up was requested, 0.25% ropivacaine or bupivacaine 10 ml was given (the same drug as the main dose). The study ended when a second top-up was requested or delivery of the baby occurred. Pain from two contractions was assessed before extradural block by visual analogue scoring and thereafter with every contraction. Sensory block and motor block were assessed at intervals. The only significant difference between the groups was a shorter onset of pain relief after the main dose of bupivacaine; there were no other significant differences in duration, onset of pain relief after top-up, quality of analgesia, spread of sensory block and motor block between the groups. Cardiovascular changes and neonatal outcome were similar in the two groups.

Halothane sensitivity in replicate mouse lines selected for diazepam sensitivity or resistance.

We have previously shown that mice selected for sensitivity to diazepam are also more sensitive to halothane, and that halothane augments the gamma-aminobutyric acid (GABA)-mediated chloride flux response in brain tissue from diazepam-sensitive (DS) mice to a greater degree than in diazepam-resistant (DR) mice. These findings suggest that the GABAA receptor is an important site of halothane action. To confirm this correlation, halothane requirement was determined in two independently developed replicate lines of DS and DR mice. Association of the traits of diazepam and halothane sensitivity in replicate lines of DS mice diminishes the probability that the original finding was due to a false-positive correlation, and instead suggests that it results from the common action of genes controlling diazepam sensitivity. Halothane median effective concentration (EC50) was determined by using the end-point of loss of righting reflex in two replicate lines of mice selected for diazepam sensitivity (resistant mice = diazepam high performance-1 and -2 [DHP-1 and DHP-2], sensitive mice = diazepam low performance-1 and -2 [DLP-1 and DLP-2]). DLP-1 and DLP-2 mice were sensitive to halothane, whereas DHP-1 and DHP-2 mice were resistant to halothane. Halothane EC50 in the DLP-1 and DHP-1 mice was 0.86 +/- 0.01 (SE) and 1.10 +/- 0.04 atm%, respectively (P < 0.0001), and that in the DLP-2 and DHP-2 mice was 0.88 +/- 0.01 and 0.97 +/- 0.02 atm%, respectively (P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous spinal anaesthesia--evolution of a technique.

Continuous spinal anaesthesia is an established technique in which renewed interest has been generated by the availability of small bore catheters suitable for use in the subarachnoid space. Problems include technical difficulty, post dural puncture headache and maldistribution of local anaesthetic, the latter being implicated in the development of caudal equina lesions. Maldistribution of local anaesthetic may possibly be reduced by attempting to place the tip of the catheter at the apex of the lumbo-sacral curve and the use of local anaesthetic solution that is only marginally hyperbaric. This article is in the form of a short review together with an account of the authors' own studies of continuous spinal anaesthesia, conducted to assess the technique for peripheral vascular surgery.

Prevention and treatment of hypotension during central neural block.

Hypotension during central neural block may occur by three main mechanisms: decrease in venous return (in turn influenced by posture, bleeding and inferior vena cava compression), vasodilatation and decreased cardiac output. It is also important to recognize that, occasionally, other factors play a part. Bladder distension during central nerve block has been shown to produce hypotension inappropriate to the level of block [48, 62] and vagal overactivity may contribute in the unsedated patient. Preventive measures to reduce the likelihood of hypotension include correction of hypovolaemia, restriction of the upper level of block, use of a slight head-down tilt to maintain venous return and judicious use of sedation, especially in anxious patients. In the obstetric patient, the single most important factor in eliminating hypotension is the use of full left-lateral tilt. Mechanical methods to improve venous return by compressing the legs are not particularly helpful. Volume loading does not guarantee maintenance of arterial pressure and excessive fluid may be harmful in patients with bladder neck obstruction or at risk of pulmonary oedema. The administration of up to 1 litre before surgery may be particularly advisable if significant blood loss is expected (no matter what the anaesthetic technique), but colloid solutions do not have clear proven benefit over crystalloid. The prevention or treatment of hypotension induced by central block by administration of large volumes of fluid is a more contentious subject, although the practice is widespread. Review of the literature has shown that many studies have been poorly designed and the results have often been contradictory, even in such basic principles as the incidence of hypotension in control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Volatile anesthetic requirements differ in mice selectively bred for sensitivity or resistance to diazepam: implications for the site of anesthesia.

One approach to elucidating the general anesthetic target has used genetic selection procedures, wherein animals are bred for sensitivity or resistance to general anesthetics and correlations are sought with a specific neuronal structural or functional defect. For example, murine strains have been developed that are either sensitive or resistant to the obtunding effects of diazepam, as assessed by their ability to maintain balance on a rotating rod. The present study explored whether diazepam-sensitive (DS) and diazepam-resistant (DR) mice might also be similarly divergent in the obtunding response to general anesthetics, by testing the requirements for halothane and enflurane in these strains. Using a carousel enclosed in a chamber, the end-point of loss-of-righting reflex was defined. For both anesthetics, the DS groups had a lower median effective dose (ED50, %atm) than did the DR group, and the reductions paralleled diazepam susceptibility. For example, with halothane, the ED50 for the DS group was 0.72 +/- 0.022 (SE); the ED50 for the DR group was 0.87 +/- 0.030 (P < 0.0001). Similar results were obtained with enflurane. Such findings associate an inbred difference in response to diazepam with altered volatile anesthetic requirement, suggesting that these two phenotypes are mediated by a common underlying mechanism.

Repeated unilateral epidural blockade.

Unilateral epidural analgesia occurring in a parturient three times in successive pregnancies is reported. Possible causes are reviewed, and clinical and radiological evidence in support of the most likely explanation are presented.