James M. Moore

Lumbosacral Cerebrospinal Fluid Volume Is the Primary Determinant of Sensory Block Extent and Duration during Spinal Anesthesia

Background Injection of local anesthetic into cerebrospinal fluid (CSF) produces anesthesia of unpredictable extent and duration. Although many factors have been identified that affect the extent of spinal anesthesia, correlations are relatively poor and the extent of spread remains unpredictable. This study was designed to determine whether variability in the volume of lumbosacral CSF among individuals is a contributing factor in the variability of spinal anesthesia. Methods Spinal anesthesia was administered to 10 healthy volunteers with 50 mg lidocaine in 7.5% dextrose. The technique was standardized to minimize variability in factors known to affect the distribution of spinal anesthesia. The extent of sensory anesthesia was assessed by pin‐prick and by transcutaneous electrical stimulation. Motor blockade was assessed in the quadriceps and gastrocnemius muscles by force dynamometry. Duration of anesthesia was assessed by pin‐prick, transcutaneous electrical stimulation, and duration of motor blockade. Lumbosacral CSF volumes were calculated from low thoracic, lumbar, and sacral axial magnetic resonance images obtained at 8‐mm increments. Volumes of CSF were correlated with measures of extent and duration of spinal anesthesia using the Kendall rank correlation test. Results Lumbosacral CSF volumes ranged from 42.7 to 81.1 ml. Volumes of CSF correlated with pin‐prick assessments of peak sensory block height (P = 0.02) and duration of surgical anesthesia (as assessed by the duration of tolerance to transcutaneous electrical stimulation at the ankle (P < 0.05). Conclusions Variability in lumbosacral CSF volume is the most important factor identified to date that contributes to the variability in the spread of spinal sensory anesthesia.

Quantitative analysis of respiratory, motor, and sensory function after supraclavicular block

The incidence and clinical significance of hemidiaphragmatic paresis after supraclavicular block of the brachial plexus is unknown.Eight healthy volunteers received a supraclavicular block with a standard technique using 30 mL of 1.5% lidocaine. Respiratory function was assessed with ultrasound of the diaphragm, respiratory inductive plethysmography (RIP), and pulmonary function tests (PFT) every 20 min. Sensory block was assessed with pinprick and motor block with isometric force dynamometry every 20 min. Four of eight subjects demonstrated hemidiaphragmatic paresis on both ultrasound and RIP. No subject experienced changes in PFT values or subjective symptoms of respiratory difficulty. Motor and sensory blockade outlasted hemidiaphragmatic paresis. These results are contrasted to the often symptomatic, 100% incidence of hemidiaphragmatic paresis seen after interscalene block. In this study of healthy volunteers, supraclavicular block was associated with a 50% incidence (95% confidence interval 14-86) of hemidiaphragmatic paresis that was not accompanied by clinical evidence of respiratory compromise. Implications: Interscalene block is always associated with diaphragmatic paralysis and respiratory compromise. The significance of these side effects after supraclavicular block is unknown. Using sensitive measures of respiratory function, we determined that diaphragmatic paralysis occurs less often with the supraclavicular approach and is not associated with respiratory difficulties in healthy subjects. (Anesth Analg 1998;86:1239-44)

Comparison of Three Solutions of Ropivacaine/Fentanyl for Postoperative Patient-controlled Epidural Analgesia

BACKGROUND Ropivacaine, 0.2%, is a new local anesthetic approved for epidural analgesia. The addition of 4 microg/ml fentanyl improves analgesia from epidural ropivacaine. Use of a lower concentration of ropivacaine-fentanyl may further improve analgesia or decrease side effects. METHODS Thirty patients undergoing lower abdominal surgery were randomized in a double-blinded manner to receive one of three solutions: 0.2% ropivacaine-4 microg fentanyl 0.1% ropivacaine-2 microg fentanyl, or 0.05% ropivacaine-1 microg fentanyl for patient-controlled epidural analgesia after standardized combined epidural and general anesthesia. Patient-controlled epidural analgesia settings and adjustments for the three solutions were standardized to deliver equivalent drug doses. Pain scores (rest, cough, and ambulation), side effects (nausea, pruritus, sedation, motor block, hypotension, and orthostasis), and patient-controlled epidural analgesia consumption were measured for 48 h. RESULTS All three solutions produced equivalent analgesia. Motor block was significantly more common (30 vs. 0%) and more intense with the 0.2% ropivacaine-4 microg fentanyl solution. Other side effects were equivalent between solutions and mild in severity. A significantly smaller volume of 0.2% ropivacaine-4 microg fentanyl solution was used, whereas the 0.1% ropivacaine-2 microg fentanyl group used a significantly greater amount of ropivacaine and fentanyl. CONCLUSIONS Lesser concentrations of ropivacaine and fentanyl provide comparable analgesia with less motor block despite the use of similar amounts of ropivacaine and fentanyl. This finding suggests that concentration of local anesthetic solution at low doses is a primary determinant of motor block with patient-controlled epidural analgesia after lower abdominal surgery.

Dose-response effects of spinal neostigmine added to bupivacaine spinal anesthesia in volunteers.

BACKGROUND Intrathecal adjuncts often are used to enhance small-dose spinal bupivacaine for ambulatory anesthesia. Neostigmine is a novel spinal analgesic that could be a useful adjunct, but no data exist to assess the effects of neostigmine on small-dose bupivacaine spinal anesthesia. METHODS Eighteen volunteers received two bupivacaine spinal anesthetics (7.5 mg) in a randomized, double-blinded, crossover design. Dextrose, 5% (1 ml), was added to one spinal infusion and 6.25, 12.5, or 50 microg neostigmine in dextrose, 5%, was added to the other spinal. Sensory block was assessed with pinprick; by the duration of tolerance to electric stimulation equivalent to surgical incision at the pubis, knee, and ankle; and by the duration of tolerance to thigh tourniquet. Motor block at the quadriceps was assessed with surface electromyography. Side effects (nausea, vomiting, pruritus, and sedation) were noted. Hemodynamic and respiratory parameters were recorded every 5 min. Dose-response relations were assessed with analysis of variance, paired t tests, or Spearman rank correlation. RESULTS The addition of 50 microg neostigmine significantly increased the duration of sensory and motor block and the time until discharge criteria were achieved. The addition of neostigmine produced dose-dependent nausea (33-67%) and vomiting (17-50%). Neostigmine at these doses had no effect on hemodynamic or respiratory parameters. CONCLUSIONS The addition of 50 microg neostigmine prolonged the duration of sensory and motor block. However, high incidences of side effects and delayed recovery from anesthesia with the addition of 6.25 to 50 microg neostigmine may limit the clinical use of these doses for outpatient spinal anesthesia.

Vasopressor therapy for hypotension during epidural anesthesia for cesarean section: effects on maternal and fetal flow velocity ratios.

The purpose of this study was to identify the influence of hypotension as a result of epidural anesthesia and of its treatment with either ephedrine or methoxamine on uteroplacental and umbilical flow velocity ratios and fetal acid-base status. Fifty healthy women with an uncomplicated full-term pregnancy were studied during elective cesarean section under epidural anesthesia. A method of continuously recording flow velocity waveforms was used that allowed the identification of simultaneous values of maternal and fetal Doppler indices related to events during the induction of anesthesia. In 15 patients in whom arterial blood pressure did not decrease, the uteroplacental pulsatility index (UtPI) did not change, but the umbilical pulsatility index (UmPI) decreased from a mean (95% confidence interval) of 0.98 (0.88-1.09) to 0.91 (0.82-0.99) (P less than 0.05). In 32 patients who experienced hypotension of at least 15%, the UtPI increased from 0.82 (0.76-0.89) to 1.04 (0.92-1.17) (P less than 0.01). Treatment with ephedrine had no influence on either the UtPI or UmPI, but treatment with methoxamine resulted in brief increases in the UtPI of 0.47 (0.24-0.69) during the first 5 min after its administration; the increases were brief and resolved within 2 min. The choice of vasopressor drug had no influence on the UtPI recorded just before surgery commenced (final UtPI), but those patients who experienced hypotension had significantly larger final UtPIs (1.02 (0.91-1.10)) than those who never became hypotensive (0.86 (0.72-0.99)), and this was associated with significantly increased placental hydrogen ion gradients. The choice of vasopressor drug appears to be of minor importance compared with the avoidance of hypotension.

How acute pain management affects outcome

Many factors can contribute to patient outcome after surgery. The method of acute pain relief may be an important factor in postoperative outcome. This article discusses the pathophysiology of pain and highlights the effects of different modes of analgesia on patient outcome variables. Epidural anesthesia and analgesia can decrease the risk of vaso-occlusive complications after lower extremity vascular surgery. Currently, there is inconclusive evidence that mode of acute pain relief affects clinical outcome after thoracic surgery. After abdominal operations, both epidural analgesia and intravenous patient-controlled analgesia may reduce the incidence of pulmonary complications in selected patients, and epidural analgesia can hasten the return of gastrointestinal motility and potentially shorten the hospital stay. For patients undergoing hip or knee replacement, spinal and epidural techniques can improve clinical outcome by preventing the development of thromboembolic complications.