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Biomedical subjects

S J Brull

Publications and source records attributed to S J Brull.

At least 55 records · Page 3Linked to original sources
PubMed1995

Pulse width, stimulus intensity, electrode placement, and polarity during assessment of neuromuscular block.

BACKGROUND: Although the intensity of neurostimulation (i.e., charge) is a product of current intensity and pulse duration, the effects of the latter on the amplitude of evoked response and subjective discomfort are unknown. Therefore, the authors investigated the effects of current intensity and pulse width, and their interaction with electrode placement and polarity, on force translation (FTR), accelerography (ACG), and electromyography (EMG) at the adductor pollics muscle. METHODS: Ulnar stimulating electrodes were applied in one of two configurations: over the distal forearm and olecranon groove ("A") or 5 cm apart on the distal forearm ("B"). Stimuli for FTR and EMG with current intensities of 20, 40, 60, and 70 mA and pulse widths of 0.05, 0.1, 0.2, and 0.4 msec resulted in 16 different charges. These combinations were delivered in each of four orientations: "A-" ("A" configuration with negative electrode distal); "A+", "B-", and "B+" (n = 64 stimuli). Eight stimulus combinations (n = 32 stimuli) were used for ACG. For each monitoring technique, the effects of current intensity, pulse width, electrode polarity, and placement were analyzed with repeated measures ANOVA. Pain responses were scored on a 0-100-mm verbal analog scale and analyzed with ANOVA and Fisher's exact test. RESULTS: The evoked response amplitude varied directly with current intensity and pulse width. In both electrode placement configurations, the response was greater when the negative electrode was distal. The electrode positioning ("A" vs. "B") had less of an impact on evoked responses than did polarity, regardless of monitoring technique. The evoked pain varied directly with the amplitude of evoked neuromuscular response in all electrode position-polarity combinations. CONCLUSIONS: The total current charge required for evoking a supramaximal neuromuscular response is much higher than previously appreciated, and electrode polarity is important in attaining a supramaximal plateau. Failure to attain (and maintain) a supramaximal stimulus allows changes in the effectiveness of neurostimulation, thus influencing the magnitude of the evoked neuromuscular response and confounding measurements of neuromuscular block.

Electrodes↗
PubMed1994

Neuroleptic malignant syndrome and mivacurium: a safe alternative to succinylcholine?

Neuroleptic malignant syndrome (NMS) and malignant hyperthermia (MH) may have a common pathogenic mechanism; therefore, it has been suggested that known triggering agents for MH (such as succinylcholine) should be avoided in patients with NMS. Electroconvulsive therapy (ECT) continues to play a major therapeutic role in contemporary psychiatry, and succinylcholine has been the muscle relaxant of choice in attenuating violent muscle contractions induced by ECT. Mivacurium is a non-depolarizing muscle relaxant with a relatively rapid onset and a short duration of action, and to date it has been proved safe in MH-susceptible patients. In this case report, following succinylcholine use during ECT, a patient with NMS developed an increase in temperature and serum creatine kinase (CK) level, possibly due to an MH reaction. Since the patient's mental status necessitated further ECT, mivacurium was administered during subsequent treatment and resulted in effective attenuation of muscle contractions without elevation of patient temperature or CK levels. In addition, there was no marked prolongation of the anaesthetic. Mivacurium is a suitable agent for patients with NMS undergoing ECT, as it has not been associated with precipitation of an MH response.

Adult↗
PubMed1994

Facilitation of fiberoptic orotracheal intubation with a flexible tracheal tube.

Advancement of a tracheal tube (TT) over a flexible fiberoptic bronchoscope (FOB) is often impeded by obstruction at the arytenoid cartilage or epiglottis. We tested the hypothesis that the use of a flexible, spiral-wound TT, rather than the standard, preformed TT would facilitate tube passage into the trachea over the FOB. Forty patients scheduled to undergo general anesthesia with tracheal intubation were randomized to two groups. Then the trachea was intubated with a FOB, followed by passage of either a standard, preformed TT or a flexible, spiral-wound TT over the FOB. Ease of TT advancement over the FOB into the trachea was graded on a 1 (easy) to 3 (difficult) scale, and differences between the two groups were compared with chi 2 analysis. The overall scores were compared with Wilcoxon's ranked sum test. Statistical significance was defined as P < 0.05. In patients randomized to the regular TT, only 35% (7/20) of first attempts to advance the TT over the FOB were successful. In the patients randomized to the spiral-wound TT, 95% (19/20) of first attempts were successful (P < 0.0001). Of the 13 regular TTs that were not successfully advanced on the first attempt, seven could not be passed after the second or third attempt (necessitating the use of the cross-over spiral-wound TT). In the only instance in which a spiral-wound tube was not successfully passed into the trachea on the first attempt, passage also was not achieved after the second or third attempt.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Liquid crystal skin thermometry: an accurate reflection of core temperature?

Oesophageal, rectal, bladder, tympanic and pulmonary artery sites are used intraoperatively to measure body temperature. However, the temperatures measured at each site have different physiological and practical importance. The present two-part study sought to compare liquid crystal (CR) skin temperature with other temperature monitors which are used routinely during surgery. The first part compared CR with oesophageal (OS) temperature during general inhalational anaesthesia. The second part compared CR with OS, pulmonary artery (PA), and bladder (BL) temperatures during the periods of rapid temperature change associated with cardiopulmonary bypass (CPB). During the first part, the mean difference between OS and CR was -0.14 +/- 0.85 degrees C; this difference remained consistent over time (P < 0.05 by repeated measures analysis of variance). During the second part, the difference in temperature readings between CR and each of the other monitors remained consistent except for CR vs PA and CR vs OS during the cooling period of CPB, when the iced cardioplegia slush directly affected the PA and OS temperatures. This study suggests that CR, an inexpensive and noninvasive means of temperature monitoring, reflects trends in temperature changes in the clinical setting.

Anesthesia, Endotracheal↗
PubMed1993

Assessment of double-burst monitoring at 10 mA above threshold current.

We compared fade measurements in response to double-burst stimulation (DBS) at 10 mA above the threshold for the second response (D2) to that for DBS at 60 mA in order to determine the utility of low-current DBS testing. In 20 healthy adults undergoing general endotracheal anesthesia with isoflurane 0.5-1% end-tidal, a vecuronium infusion (0.25-1.5 micrograms.kg-1 x min-1) was delivered until a stable train-of-four (TOF) response to ulnar nerve stimulation was documented with an adductor pollicis force transducer. Then DBS responses were recorded, and the D2/D1 ratios were determined at 60 mA and at 10 mA above the D2 threshold current (TS + 10 mA). The mean difference (bias) between D2/D1 /TS+10 mA and D2/D1 / 60 mA was -0.02 (P < 0.05); the 95% limits of agreement were from -0.12 to +0.08. The bias and limits of agreement were similar to those for T4/T1 of train-of-four. A strong correlation was noted between the degrees of fade determined at the low and high currents (r = 0.95). We conclude that, although stimulation at 10 mA above the D2 threshold is associated with a slight negative bias, it is virtually interchangeable with testing at higher current in the clinical setting. This technique thus may be used effectively to monitor neuromuscular fade in settings where neurostimulation with low current is deemed desirable.

Adult↗
PubMed1993

Laparoscopic cholecystectomy: anesthetic implications.

Laparoscopic cholecystectomy is a relatively new surgical procedure, enjoying ever-increasing popularity and presenting new anesthetic challenges. The advantages of shorter hospital stay and more rapid return to normal activities are combined with less pain associated with the small limited incisions and less postoperative ileus compared with the traditional open cholecystectomy. Complications are mostly due to traumatic injuries sustained during blind trocar insertion, and physiologic changes associated with patient positioning and pneumoperitoneum creation. The choice of anesthetic technique for laparoscopic cholecystectomy is limited most frequently to general anesthesia. Controlled ventilation avoids hypercarbia, and an anesthetic technique incorporating antiemetics and nonsteroidal antiinflammatory agents has reduced postoperative nausea and vomiting. The use of nitrous oxide and narcotics during laparoscopic cholecystectomy is controversial. Laparoscopic cholecystectomy is a major advance in the management of patients with symptomatic gallbladder disease. However, in the present era of cost containment, older and sicker patients may present for this procedure on the day of surgery without adequate preoperative evaluation. Anesthesiologists thus should be prepared to recommend conversion to an open procedure if hemodynamic, oxygenation, or ventilation difficulties occur during the procedure.

Anesthesia↗
PubMed1993

Visual and tactile assessment of neuromuscular fade.

The accuracy of visual and tactile assessment of the neuromuscular fade in response to train-of-four (TOF) and double-burst stimulation (DBS) were compared to assess their relative utility in the clinical setting. For each of 74 data sets with a mechanographic TOF ratio less than 0.70, an observer (blinded to the presence or degree of fade) performed visual and tactile assessments of fade in response to TOF, DBS3,3, and DBS3,2 stimuli at low current (20 and 30 mA) and high current (50 and 60 mA). For the range of mechanographic TOF ratios between 0.41 and 0.70, visual assessment failed to identify TOF, DBS3,3, and DBS3,2 fade in 46%, 18%, and 14% of cases at high current and in 23%, 5%, and 0% of cases at low current, respectively. Tactile assessments failed to identify fade in 55%, 23%, and 14% of cases at high current and in 23%, 14%, and 14% of cases at low current. Overall, the ability to detect fade was comparable for visual and tactile assessments regardless of the method of neurostimulation (P = NS with paired t-test). However, the degree of overestimation of the fade ratio (i.e., quantitative assessment) tended to be less when using tactile means; the difference achieved significance for TOF at low current and DBS3,3 at both low and high currents. We conclude that the differences between the visual and tactile means of assessment are relatively small compared to the differences among the TOF and DBS patterns of neurostimulation. Both subjective techniques are often inadequate in settings in which assurance of full recovery of neuromuscular function is critical.

Adolescent↗
PubMed1993

The effect of a tetanic stimulus on the response to subsequent tetanic stimulation.

We evaluated the effect of tetanic stimulation (5 s, 50 Hz, 60 mA) on the response to tetanic stimulation delivered 2 min (TET@2) and 5 min (TET@5) later in 22 anesthetized patients receiving a vecuronium infusion. Once a consistent mechanomyographic train-of-four ratio was obtained at the adductor pollicis muscle, the first (baseline) tetanic stimulus was delivered. Tetanic sequences were repeated randomly after 2- and 5-min intervals. Tetanic fade was consistent among the study periods: the tetanic fade ratio for the first second of tetanus was 0.35 during baseline tetanic stimulation, 0.32 during TET@2 (P = NS by paired t-test), and 0.33 during TET@5 (P = NS). The respective fade ratios for the entire 5-s period were 0.15, 0.15 (P = NS), and 0.14 (P = NS). In contrast, the peak tetanic height increased from 10.8 mm at baseline to 11.3 mm at TET@2 (P < 0.05), and 11.3 mm at TET@5 (P < 0.05). We conclude that, in light of the consistency exhibited by tetanic fade, the small change in twitch height is clinically insignificant.

Anesthesia, Endotracheal↗
PubMed1993

Depth of block after divided doses of mivacurium spaced 60 seconds apart.

We compared the depth of block attained after divided- and single-dose administration of mivacurium to evaluate our clinical impression that the former regimen resulted in a lesser depth of block. In 30 patients anesthetized with midazolam, fentanyl, thiopental, and nitrous oxide, adductor pollicis contraction was measured in response to train-of-four stimulation at 12-s intervals. Patients then received (by random assignment) mivacurium as a single 0.15 mg/kg bolus (Group I) or two 0.075 mg/kg (Group II) boluses separated by 60 s. All 15 Group I patients developed > or = 95% twitch (T1) depression, and 10/15 attained 100% depression; the maximum depression (mean +/- SD) was 99.1% +/- 1.4%. Only 8/15 Group II patients achieved > or = 95% T1 depression (P < 0.05 for the interregimen comparison with chi 2 analysis), and only 4/15 achieved 100% depression (P = 0.07); the maximum depression was 92.2% +/- 12.9% (P < 0.05 by unpaired t-test). Thus, administration of mivacurium in divided doses spaced 60 s apart does not provide the depth of neuromuscular block that is attained when a single bolus of the same total dose is administered.

Drug Administration Schedule↗
PubMed1992

Accelographic train-of-four at near-threshold currents.

The authors evaluated train-of-four (TOF) fade, as quantified by accelography, in response to neurostimulation at currents ranging from 10 to 60 mA. This was done to determine the range of currents over which measurements of fade remain consistent. In 31 patients (ASA Physical Status 1,2, and 3), anesthesia was induced with fentanyl, midazolam, and thiopental and was maintained with isoflurane and 66% nitrous oxide in oxygen. Surface stimulating electrodes were placed over the ulnar nerve, and an acceleration transducer was placed on the thumb. Succinylcholine was administered to facilitate tracheal intubation; after neuromuscular recovery, a bolus of vecuronium (0.01-0.05 mg.kg-1) and an infusion (0.25-1.5 micrograms.kg-1.min-1) were administered. After documentation of a stable TOF ratio, accelographic TOF responses were quantified in response to 200-microseconds stimulation at 10, 15, 20, 30, 40, 50, and 60 mA, in random order. A total of 95 data sets were collected at different depths of blockade. The TOF ratios maintained intercurrent consistency (P = not significant by nonparametric repeated measures analysis of variance), except at currents near the fourth-twitch (T4) threshold current. This inconsistency was eliminated by testing at greater than or equal to 10 mA above threshold. TOF ratios obtained at 10 mA above T4 threshold correlated highly with those at 60 mA (Spearman r value = 0.94). The authors conclude that the TOF ratio is consistent over a wide range of stimulating currents and that testing with submaximal currents can be performed reliably at greater than or equal to 10 mA above the T4 threshold.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Tetanus-induced changes in apparent recovery after bolus doses of atracurium or vecuronium.

The current study evaluated the duration and magnitude of post-tetanic effects in 56 patients recovering from a bolus dose of nondepolarizing relaxant to assess the impact of tetanus on monitoring in a common clinical setting. After induction of general anesthesia (thiopental, fentanyl, oxygen, nitrous oxide, and isoflurane), a baseline response to train-of-four (TOF) stimulation was recorded using an adductor pollicis force transducer, and the ratio of the fourth response (T4) to the first (T1) was calculated. Patients then received a bolus dose of either atracurium 0.50 mg.kg-1 (n = 28) or vecuronium 0.10 mg.kg-1 (n = 28). TOF was recorded at 12-s intervals between 25% and 75% recovery of T1 (time25-75%, first data set); then, block was reestablished with the same agent (atracurium 0.10 or vecuronium 0.02 mg.kg-1), and monitoring of time25-75% was repeated (second data set). Subjects were randomized such that none, one, or both sets had TOF monitoring interrupted by a 5-s, 50-Hz tetanic stimulus at 50% recovery (TET). For each drug, 7 patients were assigned to each of the four possible sequences: no tetanus (NOTET) set followed by NOTET set; NOTET-TET; TET-NOTET; and TET-TET. After either drug, the TET data sets demonstrated significant acceleration of recovery of T1 from 50% to 75% (time50-75%) of its baseline height (P less than 0.05 by paired t test). After atracurium, time50-75% was shortened by the tetanic stimulation from a control of 6.3 +/- 1.1 to 5.0 +/- 1.3 min (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Assessment of residual curarization using low-current stimulation.

The present study employed train-of-four (TOF) stimulation at a current of 20 mA to assess the incidence and degree of residual neuromuscular blockade in 64 randomly selected Post Anesthesia Care Unit (PACU) patients. Group C (Control, n = 10) had received anaesthesia without nondepolarizing muscle relaxant; Group V (n = 25) had received vecuronium; and Group P (n = 29) had received pancuronium. At the end of surgery, each patient had been considered by his anaesthetist to have adequate neuromuscular function on the basis of clinical signs and tactile or visual evaluation of responses to TOF stimulation. However, upon testing in the PACU 15 min later, 45% (13 of 29) of Group P patients and 8% (2 of 25) of Group V patients had a TOF ration less than 0.70. This study indicates that residual curarization may be commonly encountered following long-acting relaxants despite qualitative intraoperative TOF monitoring. The present incidence, detected at a current of 20 mA, is consistent with previous reports which employed supramaximal TOF stimulation. We conclude that despite intraoperative monitoring, residual curarization following long-acting nondepolarizing agents is common and that it may be detected with TOF at a low stimulating current (20 mA).

Adult↗
PubMed1991

Zones of differential sensory block during extradural anaesthesia.

We have measured spinal segmental levels of anaesthesia to light touch (LT), pinprick (PP) and cold temperature discrimination (TE) during 2% lignocaine extradural anaesthesia in 22 patients, to determine if zones of differential sensory block develop during extradural anaesthesia and, if so, the extent to which TE extends beyond PP or LT levels and how age affects differential block. The median thoracic dermatomal levels were 4.5 for LT, 2.0 for PP and 2.0 for TE. Zones of differential sensory block developed within 5 min of extradural injection of local anaesthetic, and persisted for the next 55 min. In all instances, PP extended more cephalad than LT, and TE extended above PP levels. There were no differences in the extent of zones between the two groups of patients with mean ages of 28 and 48 yr. Thus, during extradural anaesthesia, sympathetic denervation extended one to two spinal segments above the sensory levels of LT and PP anaesthesia, age (28 vs 48 yr) affected neither the cephalad extent nor the width of zones of differential block, and PP levels of anaesthesia were closer to presumed levels of sympathetic block than were LT levels.

Adult↗