Conceptual and technical insights into the basis of neuromuscular monitoring.

Unrecognised postoperative residual neuromuscular block remains a frequent occurrence in recovery rooms. Evidence indicates that current practice continues to perpetuate the status quo, in which 10-40% of patients experience postoperative residual weakness. A departure from the current practice requires small efforts on the clinicians' part. This review addresses several selected core questions regarding neuromuscular blockade monitoring and provides a framework to rationally discuss and develop basic guidelines for the use of neuromuscular blocking agents in patient care.

Combined spinal-epidural analgesia for labor in a patient with Marfan's syndrome.

We report the management of a patient with Marfan's syndrome for labor analgesia and vaginal delivery using a combined spinal-epidural technique. The rapid onset of analgesia for the first stage of labor provided by the intrathecal opioid, combined with the slow and controlled onset of sensory anesthesia and sympathetic block provided by the dilute epidural local anesthetic, may make this technique particularly useful for labor and delivery in patients with Marfan's syndrome.

The effect of desflurane on rocuronium onset, clinical duration and maintenance requirements.

Volatile anesthetics potentiate the effects of non-depolarizing agents. This study investigated the interaction between the inhalational anesthetic desflurane and rocuronium. Forty ASA I and II patients randomly received desflurane/N2O/fentanyl, or propofol/ N2O/fentanyl anesthesia, and rocuronium 0.6 mg/kg. Neuromuscular block was assessed at the adductor pollicis muscle. Block onset and clinical duration times were measured; a rocuronium infusion was started when the first twitch on train-of-four returned to 10% of control (T10%). Maintenance infusion requirements and recovery profiles (spontaneous and after reversal) were recorded until recovery of twitch to 90% of control (T90%). Rocuronium onset was prolonged by 67% (p = 0.034), clinical duration by 30% (p = NS), and infusion requirements were lower in the desflurane group (4.5 vs. 7.1 mg/kg/min, p = 0.003). Recovery times were not statistically different. Desflurane significantly delays the onset of neuromuscular block, potentiates rocuronium during maintenance infusion, but does not affect clinical duration or recovery.

The use of relational databases in the transition from quality assurance to continuous quality improvement: a clinical practice model.

The use of both clinical medical and administrative databases is discussed in the context of an academic anesthesiology's transition from the tenets of quality assurance to those of continuous quality improvements. A historical framework is presented. The basic and aggregate models are introduced, and examples are used to illustrate the composite system.

The cost of modern technology.

Continuous infusion of intravenous (i.v.) drugs is increasing in popularity, as technological advances in equipment (such as "smart" pumps) and pharmacologic improvements of drugs (such as ultra-short acting drugs) are introduced into clinical anesthesia practice. Such new technology, however, also introduces potential new complications. We report one such complication associated with the improper manufacturing of a proprietary i.v. tubing and cassette system.

The effect of solubility and hyperlipidemia on perioperative arterial blood gas tensions.

A case is presented to illustrate the need for technical care when handling blood gas samples. The physics of solubility are used to show hour samples changed their oxygen tension (pO2) during handling, while investigating a clinical case to show the effect of hyperlipidemia on blood gases. It appeared that inadvertent access to air allowed atmospheric oxygen to equilibrate with the sample. The physical laws predicting the effect of partial pressure and temperature on gas solubility in a liquid are illustrated by the pO2 levels measured in this case. Effects due to hyperlipidemia were not observed. The calculations are described in detail. Brief suggestions for sample handling to avoid misleading results from such cases are discussed.

Subcutaneous cysts: another cause of "failed" spinal anesthesia?

Spinal anesthesia continues to be one of the major techniques in the arsenal of the modern anesthesiologist. Inadequate anesthesia may follow a spinal anesthetic for a variety of reasons. We report a case in which entry of a spinal needle into a subcutaneous cyst mimicked the free flow of cerebrospinal fluid seen with dural puncture. This was confirmed by microscopic examination of the fluid, which was consistent with the contents of a subcutaneous cyst. This represents an unusual cause for failure of spinal anesthesia. Such a possibility should be borne in mind, especially when "clear fluid" return occurs through a spinal needle placed at a relatively superficial depth.

Use of single-dose epidural morphine in a patient undergoing an abdominal aortic aneurysm resection.

To avoid possible trauma to the epidural venous plexus in a 56-year-old male who presented for abdominal aortic aneurysm resection, the authors preoperatively injected a single dose of epidural morphine rather than inserting an indwelling epidural catheter. The patient's intraoperative anesthetic requirements appeared to have been decreased, he was extubated shortly after the end of the procedure, and he experienced good postoperative analgesia. No untoward neurologic sequelae occurred. The authors feel that a single dose of epidural morphine, compared to epidural catheter placement when systemic heparinization is planned, decreases intraoperative anesthetic requirements, provides good postoperative analgesia, and may have the benefit of decreasing the possibility of epidural hematoma formation.

Laparoscopic pelvic lymphadenectomy during epidural anesthesia.

This report describes the perioperative management of a 70-year-old man undergoing bilateral pelvic lymphadenectomy. Because of concerns regarding this patient's high risk for myocardial ischemia, the four-hour surgical procedure, which included the formation of pneumoperitoneum, was performed during epidural anesthesia with minimal sedation. The anesthetic implications of pneumoperitoneum during regional anesthesia are discussed.

Lidocaine plasma levels following two techniques of obturator nerve block.

STUDY OBJECTIVES: To assess plasma levels and the potential toxicity of lidocaine following two different approaches to the obtruator nerve. DESIGN: Prospective, randomized, clinical trial. SETTING: Operating rooms of a university hospital. PATIENTS: 45 ASA physical status I, II and III patients over 40 years of age, and undergoing transurethral resection of urinary bladder tumors. INTERVENTIONS: A prospective study compared lidocaine plasma levels following direct and indirect (3-in-1) obturator nerve block using lidocaine 1.5% plus 1:200,000 epinephrine. Patients with unilateral urinary bladder tumors were randomized to receive direct obturator nerve block with 15 ml of lidocaine (Group A, n = 20), while those with bilateral tumors received a bilateral direct obturator nerve block with 30 ml (2 x 15 ml) of lidocaine (Group B, n = 12). A third group of patients with unilateral bladder tumors received 3-in-1 indirect) obturator nerve block with 40 ml of lidocaine (Group C, n = 17). Plasma lidocaine concentration was determined every 5 minutes for 30 minutes, and at 45, 60, and 90 minutes after the block. MEASUREMENTS AND MAIN RESULTS: In Group A, mean (+/- SD) peak plasma lidocaine level of 1.35 +/- 0.5 micrograms/ml (range 0.61 to 2.41 micrograms/ml) occurred 45 minutes after injection. In Group B, a peak of 3.63 +/- 2.07 micrograms/ml (0.75 to 7.21 micrograms/ml) occurred 15 minutes after injection. Mean peak level in Group C of 2.08 +/- 0.77 micrograms/ml (0.84 to 3.21 micrograms/ml) occurred 60 minutes after injection Lidocaine concentrations were significantly higher in Groups B and C than in Group A, and they were higher in Group B than in Group C. No patient had any signs of symptoms of local anesthetic toxicity. CONCLUSIONS: Despite a lower total dose of lidocaine administered (450 mg), higher mean and peak plasma levels were reached sooner with bilateral direct obturator nerve block compared with the indirect obturator nerve block (600 mg), indicating a faster blood absorption of lidocaine following direct block. Both types of obturator nerve block prevented adductor muscle contraction in a large percentage of cases.

Temporal correlation of succinylcholine-induced fasciculations to loss of twitch response at different stimulating frequencies.

STUDY OBJECTIVE: The present study was undertaken to determine the time courses of succinylcholine-induced fasciculations and adductor pollicis single-twitch responses at two stimulating frequencies. DESIGN: A prospective, randomized study. SETTING: The main operating room of a university teaching hospital. PATIENTS: Forty-four patients undergoing general anesthesia and requiring tracheal intubation. INTERVENTIONS: In 22 patients, anesthesia was induced with thiopental sodium, fentanyl, and midazolam and maintained with 70% nitrous oxide in oxygen prior to the administration of succinylcholine 1 mg/kg. In another 22 patients, end-tidal isoflurane 0.75% to 1% was included in the induction regimen. Patients in each group were randomly assigned to receive ulnar nerve stimulation at either 0.1 Hz or 1.0 Hz. MEASUREMENTS AND MAIN RESULTS: The times at which fasciculations were first noticed and no longer visible and the times to 25%, 50%, 75%, 90%, and 100% twitch depression were recorded. These times were compared for the two rates of neurostimulation. With single-twitch nerve stimulation at 1.0 Hz, 100% twitch depression occurred 6 +/- 16 seconds following the end of fasciculations, while at a stimulating frequency of 0.1 Hz, it occurred 52 +/- 32 seconds later (p less than 0.05). At the end of fasciculations, single-twitch depression of 50% or more was noted in only 19% of patients in the 0.1 Hz groups and in all patients in the 1.0 Hz groups (p less than 0.05). In the 0.1 Hz groups, 50% twitch depression occurred 19 +/- 27 seconds after the end of fasciculations, with more than three-quarters of the patients having achieved 50% twitch depression 30 seconds following the disappearance of fasciculations. The addition of isoflurane did not significantly alter any of these times. CONCLUSIONS: The data reveal that cessation of fasciculations may be an inaccurate clinical sign of the readiness for intubation and confirm that standardized methods of neurostimulation are necessary in the pharmacodynamic evaluation of neuromuscular blocking drugs. In settings where profound neuromuscular relaxation is not required, waiting at least 30 seconds beyond the disappearance of fasciculations should provide good intubating conditions.

Electromyographic assessment of ulnar nerve motor block induced by lidocaine.

STUDY OBJECTIVE: To determine the differences in the onset time and duration of motor block produced by lidocaine 1% and lidocaine 2% via a quantitative and objective method, the measurement of compound muscle action potentials (CMAPs). STUDY DESIGN: Prospective study. SETTING: Main operating rooms of a university hospital. PATIENTS: 20 consecutive patients undergoing surgery not requiring intraoperative muscle relaxation. INTERVENTIONS: General anesthesia with unilateral ulnar nerve block was administered. In patients' nondominant (experimental) arms, an insulated block needle was placed adjacent to the ulnar nerve at the wrist while continuous nerve stimulation was delivered to ensure its proper placement. Through this needle, lidocaine 1% or lidocaine 2% was injected. The dominant (control) arm received no injection. MEASUREMENTS AND MAIN RESULTS: Monitoring of ulnar nerve-evoked CMAPs was performed simultaneously on both arms. Ulnar nerve function was assessed at baseline and then at 10-second intervals by automatically measuring the amplitude of the evoked CMAPs on a two-channel electromyogram. The mean (+/- SEM) baseline CMAP amplitude prior to injection of lidocaine 1% was 3.10 +/- 0.87 mV and 3.06 +/- 0.89 mV for the experimental and control ulnar nerves, respectively (p = NS); for lidocaine 2%, baseline CMAP amplitude was 3.58 +/- 1.39 mV and 3.70 +/- 1.46 mV, respectively (p = NS). Over the course of the study, the control CMAP amplitude varied by < 12%. At the experimental ulnar nerve, 90% CMAP decrease after injection of lidocaine 1% and lidocaine 2% occurred 7.5 +/- 2 minutes and 5 +/- 1.5 minutes, respectively (p = NS), whereas maximal blockade was achieved after 15 +/- 3 minutes and 11 +/- 5 minutes, respectively (p = NS). Recovery of CMAP to 90% of baseline occurred 184 +/- 31 minutes after injection of lidocaine 1% and 248 +/- 30 minutes following lidocaine 2% (p = NS). CONCLUSION: The present study describes a technique that can be used in vivo to objectively measure the speed of onset and duration of local anesthetic-induced motor blockade. Although statistically not different, lidocaine 2% demonstrated a faster onset and longer duration of ulnar nerve motor block than lidocaine 1%.

Variability of onset times within and among relaxant regimens.

STUDY OBJECTIVE: To evaluate the consistency of times to 95% twitch height depression (T95%) in groups of patients receiving identical induction and relaxant regimens. DESIGN: Prospective, noncontrolled, blinded study. SETTING: Ambulatory surgical unit at a university medical center. PATIENTS: Seventy-five ASA physical status I and II patients undergoing general endotracheal anesthesia. INTERVENTIONS: Patients received succinylcholine 1.5 mg/kg or a nondepolarizing regimen with doses ranging from approximately 1.5 to 6 times the ED95, with or without a priming dose. MEASUREMENTS AND MAIN RESULTS: For each of the eight relaxant regimens used in five or more patients, the intraregimen variability of T95% (at the adductor pollicis muscle upon ulnar stimulation at 0.1 Hz) was expressed as SD and range, and the individual data points were displayed. There was wide intraregimen variability. For each regimen, the slowest T95% was at least 73% longer than the fastest T95%. For the 16 patients receiving a priming dose plus an intubating dose 5 or more times the ED95, the median T95% was 95 seconds; however, T95% was beyond 120 seconds in 5 of the 16 cases. CONCLUSIONS: The wide variability in onset times among subjects receiving the same regimen indicates that monitoring of neuromuscular response, preferably to a relatively slow rate of neurostimulation, is essential if one elects to use moderate to high doses of atracurium and/or vecuronium for rapid-sequence induction in a patient in whom movement or coughing is unacceptable. Since onset times were not symmetrical about the mean, the magnitude and frequency of unacceptable onset times would not be fully appreciated unless the individual data points were displayed. Such information may be critical when reporting the suitability of a neuromuscular blocking drug for rapid intubation.

The efficacy of intramuscular ketorolac in combination with intravenous PCA morphine for postoperative pain relief.

STUDY OBJECTIVE: To examine the efficacy of intramuscular (IM) ketorolac used in combination with intravenous (IV) patient-controlled analgesia (PCA) morphine for postoperative pain relief following intra-abdominal gynecologic surgery. DESIGN: Randomized, double-blind, placebo-controlled study. SETTING: Patient care unit at a university medical center. PATIENTS: Thirty-five healthy women undergoing intra-abdominal gynecologic surgery who requested postoperative PCA. INTERVENTIONS: Postoperatively, all patients received IV PCA morphine, with the PCA device programmed to deliver a maximum of 1 mg every 6 minutes (maximum of 30 mg over 4 hours). In addition, patients received one of three regimens: (1) IM saline every 6 hours; (2) IM ketorolac 30 mg while in the postanesthesia care unit (PACU), followed by 15 mg every 6 hours; or (3) IM ketorolac 60 mg while in the PACU, followed by 30 mg every 6 hours. MEASUREMENTS AND MAIN RESULTS: Patients were assessed at regular intervals. Visual analog scale (VAS) scores were used to assess analgesia and patient satisfaction with therapy. Data on morphine usage were obtained from the PCA device, and the frequency and severity of adverse effects were assessed for the presence or absence of side effects. Cumulative morphine dosages were lower (p less than 0.05) in both ketorolac groups at 12, 18, and 24 hours. VAS scores and the frequency of side effects did not differ significantly among groups. CONCLUSIONS: IM ketorolac significantly decreased PCA morphine requirements. The analgesic effects of the two drugs appear to be additive.

Comparative recovery of 50-Hz and 100-Hz posttetanic twitch following profound neuromuscular block.

STUDY OBJECTIVE: To determine if posttetanic twitch following 100-Hz tetanic stimulation enables titration of a nondepolarizing relaxant infusion to a greater depth of block than that achieved with posttetanic twitch following 50 Hz. STUDY DESIGN: Prospective, observational study. SETTING: Operating rooms of a university tertiary care center. PATIENTS: 10 ASA physical status II and III patients free of known neuromuscular disease and undergoing general endotracheal anesthesia for routine elective surgery. INTERVENTIONS: Following induction of general anesthesia, neuromuscular block was maintained with a continuous intravenous vecuronium infusion. Depth of neuromuscular block was assessed by tactile evaluation of the evoked responses of the adductor pollicis muscle following supramaximal stimulation of the ulnar nerve via surface electrodes. The vecuronium infusion was titrated to loss of posttetanic twitch following 100-Hz tetanic stimulation, at which point the infusion was discontinued. MEASUREMENTS AND MAIN RESULTS: 100-Hz tetanic stimulation was repeated every two minutes until recovery of the first posttetanic twitch, at which point 50-Hz tetanic stimulation was repeated every two minutes until recovery of the first posttetanic twitch. The median time (interquartile range) from discontinuation of the vecuronium infusion to recovery of the first posttetanic twitch following 100-Hz tetanic stimulation was 27% faster than the corresponding time to recovery of the first posttetanic twitch following 50-Hz tetanic stimulation [19 (10 to 24) min and 26 (20 to 30) min respectively, p < 0.002]. CONCLUSIONS: Posttetanic twitch following 100-Hz tetanic stimulation enables titration of a vecuronium infusion to a greater depth of block than posttetanic twitch following 50-Hz tetanic stimulation. The present findings should enable more effective titration of this relaxant, thereby reducing the likelihood of unwanted patient movement or unduly prolonged recovery due to relaxant overdosing.

The effect of intravenous ketorolac given intraoperatively versus postoperatively on outcome from gynecologic abdominal surgery.

STUDY OBJECTIVES: To examine the effect of timing of an intravenous (i.v.) dose (intraoperative vs. postoperative) of ketorolac tromethamine on pain scores and overall outcome after total abdominal hysterectomy (TAH) and myomectomy. DESIGN: Prospective, randomized, placebo-controlled study. PATIENTS: 248 ASA physical status I and II adult female patients scheduled for elective hysterectomy or myomectomy. INTERVENTIONS: General anesthesia was administered that consisted of thiopental sodium for induction, enflurane or isoflurane in nitrous oxide-oxygen for maintenance, and small doses of fentanyl and midazolam. Patients were randomized into three groups to receive toradol/placebo on a dosing schedule of dose 1 given one-half hour prior to expected end of surgery, dose 2 given on awakening in the postanesthesia care unit, and doses 3, 4, and 5 given at 6, 12, and 18 hours, respectively, after dose 2; Group 1 patients received placebo (saline) for dose 1, ketorolac 60 mg i.v. for dose 2, and ketorolac 30 mg i.v. for doses 3, 4, and 5. Group 2 patients received ketorolac 60 mg i.v. for dose 1, placebo for dose 2, and ketorolac 30 mg i.v. for doses 3, 4, and 5. Group 3 patients received placebo for all doses. All patients were given i.v. morphine PCA postoperatively, and morphine usages, visual analog pain intensity (VAS) scores, as well as adverse events and median times to recovery milestones were recorded. MEASUREMENTS AND MAIN RESULTS: VAS scores (mean) before dose 2 were significantly lower in Group 2 than Group 1, as were at-rest evaluations at 15 minutes and one hour. Group 2 patients also had decreased morphine requirements as compared to placebo. Both ketorolac groups (Groups 1 and 2) had significantly higher values for patient and observer overall ratings, case of nursing care, and tolerability as compared to placebo (Group 3). There were no significant differences among groups in adverse events or median times to recovery milestones. CONCLUSIONS: Although it is possible to demonstrate an improvement in early postoperative pain scores with intraoperative ketorolac and better overall ratings of ketorolac both intraoperatively and postoperatively as compared with placebo, the lack of clinically significant differences in analgesic efficacy in the two active study groups indicates the need for a careful consideration by the clinician of the risks versus benefits involved in the administration of antiplatelet medication in the perioperative period.