Minimum volume of local anaesthetic required to surround each of the constituent nerves of the axillary brachial plexus, using ultrasound guidance: a pilot study.

BACKGROUND: The minimum effective volume of local anaesthetic needed to provide effective analgesia of the four main branches of the axillary brachial plexus is unknown. This study was performed to determine the minimum volume of local anaesthetic required to surround the nerves of the axillary brachial plexus and document onset and duration of sensory and motor effects. METHODS: We enrolled 19 ASA I-II patients undergoing hand or forearm surgery. The four nerves of the axillary plexus were identified with ultrasound guidance. Lidocaine 1.5% with epinephrine 1:200 000 was loaded into a syringe driver. A 22 G needle was inserted in the long axis to each nerve and injection commenced using the bolus function (600 ml h(-1)). The needle was repositioned until the nerve was completely surrounded. The bolus dose in millilitres displayed on the syringe driver was recorded. This was repeated for each nerve. The degree of sensory and motor block was recorded as secondary outcomes. RESULTS: The mean (95% CI) volume to surround each nerve was: radial 3.42 (2.84-3.99) ml, median 2.75 (2.31-3.19) ml, ulnar 2.58 (2.14-3.03) ml, and musculocutaneous 2.30 (1.96-2.64) ml. The mean (95% CI) onset time for complete sensory block was: radial 22.5 (13.5-31.5) min, median 26.8 (18.5-35.0) min, ulnar 26.6 (17.8-35.4) min, and musculocutaneous 15.8 (7.45-24.2) min. The mean (95% CI) last recorded time with complete block was: radial 137.1 (105.6-168.7) min, median 144.7 (123.4-166.0) min, ulnar 183.2 (158.1-208.2) min, and musculocutaneous 158.3 (131.8-184.9) min. Seven patients required additional local anaesthetic infiltration and two required i.v. analgesia. No patient required conversion to general anaesthesia for surgery. CONCLUSIONS: We found that it is possible to surround each nerve of the axillary brachial plexus with 2-4 ml of local anaesthetic. We speculate that increasing this volume would produce blocks of quicker onset and longer duration while still using smaller volumes than previously thought.

Sciatica: a review of history, epidemiology, pathogenesis, and the role of epidural steroid injection in management.

Radicular pain in the distribution of the sciatic nerve, resulting from herniation of one or more lumbar intervertebral discs, is a frequent and often debilitating event. The lifetime incidence of this condition is estimated to be between 13% and 40%. Fortunately, the majority of cases resolve spontaneously with simple analgesia and physiotherapy. However, the condition has the potential to become chronic and intractable, with major socio-economic implications. This review discusses the history, epidemiology, pathophysiology, and natural history of sciatica. A Medline search was performed to obtain the published literature on the sciatica, between 1966 and 2006. Hand searches of relevant journals were also performed. Epidemiological factors found to influence incidence of sciatica included increasing height, age, genetic predisposition, walking, jogging (if a previous history of sciatica), and particular physical occupations, including driving. The influence of herniated nucleus pulposus and the probable cytokine-mediated inflammatory response in lumbar and sacral nerve roots is discussed. An abnormal immune response and possible mechanical factors are also proposed as factors that may mediate pain. The ongoing issue of the role of epidural steroid injection in the treatment of this condition is also discussed, as well as potential hazards of this procedure and the direction that future research should take.

Modeling plasma virus concentration during primary HIV infection.

During primary HIV infection the viral load in plasma increases, reaches a peak, and then declines. Phillips has suggested that the decline is due to a limitation in the number of cells susceptible to HIV infection, while other authors have suggested that the decline in viremia is due to an immune response. Here we address this issue by developing models of primary HIV-1 infection, and by comparing predictions from these models with data from ten anti-retroviral, drug-naive, infected patients. Applying nonlinear least-squares estimation, we find that relatively small variations in parameters are capable of mimicking the highly diverse patterns found in patient viral load data. This approach yields an estimate of 2.5 days for the average lifespan of productively infected cells during primary infection, a value that is consistent with results obtained by drug perturbation experiments. We find that the data from all ten patients are consistent with a target-cell-limited model from the time of initial infection until shortly after the peak in viremia. However, the kinetics of the subsequent fall and recovery in virus concentration in some patients are not consistent with the predictions of the target-cell-limited model. We illustrate that two possible immune response mechanisms, cytotoxic T lymphocyte destruction of infected target cells and cytokine suppression of viral replication, could account for declines in viral load data not predicted by the original target-cell-limited model. We conclude that some additional process, perhaps mediated by CD8+ T cells, is important in at least some patients.

An intervention to increase physicians' use of adherence-enhancing strategies in managing hypercholesterolemic patients.

PURPOSE: Patients' lack of adherence to medical regimens frustrates many practicing physicians. This study was conducted to determine the effectiveness of a combined continuing medical education intervention in increasing physicians' adherence-enhancing skills and improving hypercholesterolemic patients' health. METHOD: A prospective, randomized, controlled trial was designed using a nested cohort of 28 community physicians throughout Alabama and 222 of their hypercholesterolemic outpatients. The intervention, carried out in 1998, consisted of three interactive case audio-conferences plus chart reminders. Physicians' learning was measured by unannounced standardized patients, and patients' health by serum cholesterol levels, weight, knowledge of hypercholesterolemia, self-reported dietary habits, and health status. RESULTS: No significant difference was found in the numbers of physician adherence-enhancing strategies, although the number did increase within the treatment group. There were significant differences in the intervention group's patients' knowledge of cholesterol management (p = .008) and significant reductions in their self-reported consumption of dietary fats (p = .002). A significant difference was found in the serum cholesterol level of men in the intervention group nine months after the intervention (p = .02). CONCLUSION: Combining a series of interactive case audio-conferences with chart reminders shows promise in increasing physicians' adherence-enhancing strategies. In chronic disease management, the problem of enhancing adherence remains complex.

Pharmacokinetics and pharmacodynamics of cisatracurium in young and elderly adult patients.

BACKGROUND: The effects of a muscle relaxant may differ in elderly compared with young adult patients for a variety of reasons. The authors compared the effects of a new muscle relaxant (cisatracurium) in young and elderly adults and used pharmacokinetic/pharmacodynamic modeling to identify factors explaining differences in time course of effect. METHODS: Thirty-one young (18-50 yr) and 33 elderly ( > 65 yr) patients anesthetized with nitrous oxide, isoflurane, and fetanyl were studied. Cisatracurium (0.1 mg/kg) was given after induction of anesthesia and later additional boluses of 0.025 mg/kg or an infusion of cisatracurium was given. Neuromuscular transmission was measured using the first twitch of the train-of-four response at the adductor pollicis after supramaximal stimulation of the ulnar nerve at 2 Hz every 15 s. Five venous blood samples were obtained for plasma drug concentration at intervals ranging from 2 to 120 min from every patient. Three additional samples were obtained from those who received an infusion. A population pharmacokinetic/pharmacodynamic model was fitted to the plasma concentration and effect data. The parameters of the model were permitted to vary with age to identify where differences existed between young and elderly adults. RESULTS: Onset of block was delayed in the elderly; values being mean 3.0 (95% confidence interval 1.75-11.4) min and 4.0 (2.4-6.5) min in the young and elderly, respectively (P < 0.01). Duration of action was similar in the two groups. Plasma clearance was 319 (293-345) ml/min in the study population and did not differ between young and elderly patients. Apparent volume of distribution was 13.28 (9.9-16.7) 1 and 9.6 (7.6-11.7) 1 in the elderly and young adults, respectively (P < 0.05). There also were differences in pharmacodynamic parameters between the young and elderly; the predominant change being a slower rate of biophase equilibration (ke0) in the elderly (0.060 [0.052-0.068])/min compared with the young (0.071 [0.065-0.077]/min; P < 0.05). CONCLUSIONS: The pharmacokinetics of cisatracurium differ only marginally between young and elderly adults. Onset is delayed in the elderly because of slower biophase equilibration.

Repetitive elastance measurement as a means of recording pharmacological responses in vascular smooth muscles.

We describe a method of recording pharmacological responses in isolated arterial segments, based on the direct measurement of vascular wall elastance. The segment outflow is intermittently occluded, and the elastance determined from the subsequent pressure-flow relationship. Since the measurement cycle can be repeated 12 times per minute, rapid pharmacological responses can be studied. The method is capable of demonstrating a sigmoid dose-response relationship to noradrenaline added to the perfusate.

Measurement of arterial blood pressure during anaesthesia.

Regular measurement and recording of blood pressure, with pulse monitoring and ECG, are the 'minimal monitoring' without which no anaesthetic should take place. This is because blood pressure is an index of some of the most fundamental physiological processes.

Incremental propofol for short procedures.

Propofol was used to induce and maintain anaesthesia in patients undergoing minor gynaecological procedures. Quality of anaesthesia, the rate of recovery and the influence of different methods of premedication were assessed. Unpremedicated patients required a higher induction dose than those premedicated with either lorazepam or papaveretum and hyoscine, but maintenance dose requirements were comparable. Regardless of premedication, there were similar decreases in mean arterial pressure, although respiratory function recovered more rapidly in patients premedicated with lorazepam. No significant changes in heart rate were noted in any group. The overall incidence of pain on injection was 3.7% (lignocaine 0.5 mg added to each 9.5 mg of propofol) and a skin rash occurred in 6% of patients. All patients recovered rapidly and uneventfully.