Biomedical subjects
B L Partridge
Publications and source records attributed to B L Partridge.
Dexmedetomidine does not modify the neuromuscular blocking action of vecuronium in the anaesthetized rat.
Dexmedetomidine is a new alpha 2 adrenergic agonist anaesthetic adjuvant. In animal studies, dexmedetomidine produced muscle flaccidity and prevented opioid-induced muscle rigidity, apparently via a central mechanism. The effect of dexmedetomidine on the neuromuscular junction or on non-depolarizing neuromuscular block during anaesthesia has not been reported. We have studied in the anaesthesized rat, the effects of dexmedetomidine on vecuronium-induced twitch depression. Wistar rats (n = 35) were anaesthetized and their lungs ventilated to maintain normocapnia. An infusion of vecuronium of 2.3 (SEM 0.1) micrograms kg-1 min-1 produced a stable twitch height (T1) depression of the tibial nerve of 53 (2)% of control in all groups. Rats were allocated randomly to receive either saline or dexmedetomidine 10, 30 or 100 micrograms kg-1 i.v. and T1 height was measured continuously for 60 min. Dexmedetomidine did not significantly affect T1 height during the first 30 min of infusion. At later times there were minor differences between groups. With cessation of the infusion of vecuronium, T1 height recovered rapidly to normal in all groups. These data suggest that the neuromuscular blocking properties of dexmedetomidine are unlikely to be produced by action at the neuromuscular junction.
Automated St-segment trending: what does it mean?
This article is the first segment of what we hope will become a regular feature in the Journal of Clinical Monitoring. The Monitoring Dilemmas series is designed for clinicians who are struggling with the information presented by new monitoring. The past decade has seen an explosion in the number and type of clinical monitors in daily use. Health-care providers are increasingly faced with a plethora of monitoring data, often without guidance on how to interpret it. Each Monitoring Dilemma consists of a case report that describes a clinical dilemma brought on by information from a monitor--a dilemma that would not even have been considered had the monitor not been in place or existence. The case reports are sent to experts in the particular fields concerned. To prevent "Monday morning quarterbacking," each reviewer is sent several envelopes, each containing information that progressively reveals more and more about the case. The case is presented as it actually evolved, and the experts comment as the case unfolds. Thus, the reader can share the dilemma with the reviewers, as well as with the original clinicians. We welcome your comments on this new section. We also welcome your own Monitoring Dilemmas. Please contact the Section Editor, Dr Partridge, for more details.
Intraoperative monitoring of tibialis anterior muscle motor evoked responses to transcranial electrical stimulation during partial neuromuscular blockade.
We studied the feasibility of recording motor evoked responses to transcranial electrical stimulation (tce-MERs) during partial neuromuscular blockade (NMB). In 11 patients, compound muscle action potentials were recorded from the tibialis anterior muscle in response to transcranial electrical stimulation during various levels of vecuronium-induced NMB. The level of NMB was assessed by accelerometry of the adductor pollicis muscle after train-of-four stimulation of the ulnar nerve. The compound muscle action potential was also recorded from the tibialis anterior muscle after direct stimulation of the peroneal nerve (M-response) as an alternative means of assessing the degree of NMB. In all patients, tce-MERs could be recorded reliably during anesthesia with N2O and a continuous infusion of sufentanil (0.5 micrograms.kg-1.h-1). An intact train-of-four was present in all patients, and the amplitude of the first twitch was recorded and designated as the control value. Before administration of vecuronium, the M-response amplitude was 9.6 +/- 3.6 (mean +/- SD) mV, and the tce-MER amplitude was 1.21 +/- 0.66 mV. Although administration of vecuronium (0.05 mg/kg) resulted in loss of the mechanical adductor pollicis response in 8 of the 11 patients, the M-response and the tce-MER remained recordable. Subsequently, during an infusion of vecuronium, adjusted to maintain one or two mechanical responses to train-of-four stimulation, the average M-response to peroneal nerve stimulation was 5.2 +/- 2.5 mV (53% of the control value), and tce-MER amplitude was 0.59 +/- 0.36 mV (59% of the control value).(ABSTRACT TRUNCATED AT 250 WORDS)
The effects of local anesthetics and epinephrine on rat sciatic nerve blood flow.
The effects of topical application of local anesthetics on peripheral nerve blood flow (NBF) were studied in the rat sciatic nerve. Sciatic NBF was measured by laser doppler in 45 adult female Sprague-Dawley rats (90 nerves) after topical application of 25 microliter lidocaine and epinephrine, alone and in combination (lidocaine plus epinephrine), as well as bupivacaine, tetracaine, and normal saline, and studied in a randomized, blinded experimental design. NBF changes produced by lidocaine were dose-dependent. Compared with that for saline, blood flow reduction for lidocaine 0.5% was not significant, but it was significant for lidocaine 1.0% at 2-5 min and for lidocaine 2.0% at all time periods after 1 min (P less than 0.05). Maximum reduction was seen at all concentrations by 5 min after application. Average blood flow reduction at 5 min was 7% for lidocaine 0.5%, 12% for lidocaine 1.0% and 18% for lidocaine 2.0%. Epinephrine also produced dose-dependent changes in NBF. Epinephrine 2.5 micrograms/ml produced a transient 20% increase in NBF lasting 2-3 min (P less than 0.05), followed by a return to baseline. Epinephrine 5.0 micrograms/ml and epinephrine 10.0 micrograms/ml produced reductions of 20% and 35%, respectively (P less than 0.05), which lasted throughout the study. The effects of each of the three concentrations were significantly different from the others. The combination of lidocaine plus epinephrine resulted in synergistic reduction of NBF for all drug concentrations (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Is the cardiovascular response to electroconvulsive therapy due to the electricity or the subsequent convulsion?
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Prevention of the cardiovascular and neuroendocrine response to electroconvulsive therapy: II. Effects of pretreatment regimens on catecholamines, ACTH, vasopressin, and cortisol.
The neuroendocrine response to electroconvulsive therapy (ECT) was assessed in four patients after pretreatment with esmolol (1.0 mg/kg), fentanyl (1.5 micrograms/kg), labetalol (0.3 mg/kg), and saline solution (control). Each patient received each drug pretreatment using a double-blind, randomized study block-design. During each of the five studies, blood samples were obtained from each patient before anesthetic induction, before ECT shock, and at 1, 5, 10, and 30 min after seizure. Samples were subsequently analyzed for epinephrine, norepinephrine, adrenocorticotrophic hormone (ACTH), arginine vasopressin (AVP), and cortisol. Electroconvulsive therapy after saline pretreatment resulted in a 3-fold and 15-fold increase in norepinephrine and epinephrine levels, respectively (P less than 0.05). The ACTH and cortisol levels gradually increased over 30 min, peaking at values that were two to three times the control values (P less than 0.05). The AVP levels increased significantly after induction of ECT (P less than 0.005) and remained higher than control levels at 5, 10, and 30 min. The effect of pretreatments varied. Pretreatment with esmolol and fentanyl resulted in significant attenuation of the norepinephrine peak after seizure (P less than 0.05). Only esmolol significantly attenuated ECT-induced epinephrine secretion, whereas fentanyl pretreatment significantly reduced release of ACTH after ECT. No pretreatment significantly affected the elevated AVP or cortisol levels seen on emergence or up to 30 min after treatment. The ability of esmolol pretreatment to attenuate serum catecholamine release after ECT is consistent with its ability to block the cardiovascular responses to ECT.
Prevention of the cardiovascular and neuroendocrine response to electroconvulsive therapy: I. Effectiveness of pretreatment regimens on hemodynamics.
Electroconvulsive therapy (ECT) under anesthesia is associated with hypertension and tachycardia. The cardiovascular effects of ECT were studied after pre-treatment of 10 patients with esmolol (1.0 mg/kg), fentanyl (1.5 micrograms/kg), labetalol (0.3 mg/kg), lidocaine (1.0 mg/kg), and saline solution (control), using a double-blind, randomized block-design. Each patient received all five pretreatment regimens over the course of five ECT sessions. During control studies, arterial blood pressure and heart rate increased significantly in all patients after ECT (P less than 0.05 and P less than 0.01, respectively). The rate-pressure product increased by an average of 336% +/- 14% (P less than 0.01). There were appreciable individual differences in the cardiovascular response to ECT, independent of pretreatment (P less than 0.01). Pretreatment with esmolol and labetalol significantly reduced the hemodynamic response to ECT, compared with fentanyl, lidocaine, or saline solution (P less than 0.05). Esmolol attenuated arterial blood pressure to a larger extent than did labetalol (P less than 0.05). Compared with saline solution (control), pretreatment with labetalol, fentanyl, or lidocaine significantly reduced seizure duration (P less than 0.05) and increased the frequency with which a second electrical stimulus was required. In contrast, esmolol pretreatment did not significantly affect seizure duration. Esmolol (1 mg/kg), administered 1 min before induction of anesthesia, produced significant amelioration of the cardiovascular response to ECT with minimal effect on seizure duration.
Prolonged neuromuscular blockade after long-term infusion of vecuronium bromide in the intensive care unit.
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The effects of incisional bupivacaine on postoperative narcotic requirements, oxygen saturation and length of stay in the post-anesthesia care unit.
We compared postoperative pain and narcotic requirements, oxygen saturation (SaO2) and length of stay in the post-anesthesia care unit (PACU) in patients who received 30 ml of either 0.25% bupivacaine (B) or saline placebo (S) infiltrated into the operative incision. Twenty ASA I-III patients undergoing abdominal surgery were studied in a double-blinded randomized prospective trial. Study and control groups were not different in patient age, procedure, intra-operative narcotics administered or preoperative SaO2. In the PACU, patients receiving B had significantly lower analog pain scores (6.0 vs 8.3, P = 0.02). They had lower respiratory rates (15.6 b/min vs 19.1, P = to 0.02), required significantly less narcotic (4.5 mg morphine sulphate vs 11.0, P = to 0.03) and were discharged from the PACU almost an hour sooner than patients receiving S (P = 0.02). Patients receiving B had significantly higher minimum SaO2 than those receiving S (93.3% vs 89.9, P = 0.04). Discharge pain scores, SaO2 and respiratory rates were not significantly different between B and S groups. Finally, mean requirements for narcotics for the first 24 h were reduced by approximately 30% (from 406.9 mg meperidine to 255.5 mg, P = 0.006). This study demonstrates that infiltration of a long-acting local anesthetic lowers initial pain scores and requirements for narcotics in the PACU. The effect can be seen for at least the first 24 h. A lower requirement for postoperative narcotics is accompanished by faster wake-up, more alert patients, and, most importantly, higher SaO2 and shorter PACU stay. This may have a significant effect on pulmonary morbidity following abdominal operations.
Preventing unauthorized access to narcotics in the operating room.
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Air entrainment through a multiport injection system.
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MAC of sevoflurane in humans and the New Zealand white rabbit.
The minimum alveolar concentration of sevoflurane necessary to prevent movement in 50 per cent of patients (MAC) was determined to be 2.05 per cent in 20 adult surgical patients. Because this value was higher than the only other experimentally determined human MAC value for sevoflurane (1.71 per cent), MAC was also determined in New Zealand white rabbits. Comparisons of the MAC ratios of sevoflurane to other volatile anaesthetics in both the human and the rabbit suggest that the human MAC value we obtained for sevoflurane is consistent with experimental determinations of MAC of other volatile anaesthetics in humans.
Nitrous oxide and endotracheal tube cuff leaks.
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Life-threatening effects of intravascular absorption of PGF2 alpha during therapeutic termination of pregnancy.
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Use of pulse oximetry as a noninvasive indicator of intravascular volume status.
The use of pulse oximetry as a noninvasive method to assess intravascular volume status is described. Pulse oximeters providing a continuous display of the pulse waveform offer a new method of estimating relative volume status during positive-pressure ventilation. Like intraarterial pressure tracings, the peaks of the pulse waveform demonstrate increased variation in response to positive-pressure ventilation when a patient becomes hypovolemic. Pulse oximeter waveform tracings were compared with central venous pressure and intraarterial pressure tracings in 12 patients undergoing major operative procedures. A significant correlation (r = 0.61) was seen between pulse waveform variation and systolic pressure variation, which has previously been shown to be a sensitive indicator of hypovolemia. When data from individual patients were analyzed separately, the correlation between pulse waveform variation and systolic pressure variation was as high as 0.88.
Functional anatomy of the brachial plexus sheath: implications for anesthesia.
Anatomical study of the brachial plexus of 18 cadavers was undertaken to confirm the presence and significance of "septa" dividing the brachial plexus or axillary sheath. Dissection demonstrated that the sheath consists of multiple layers of thin connective tissue surrounding the various elements of the neurovascular bundle. These septa are incomplete, however, forming small bubble-like pockets when solution is injected. Single injections of methylene blue and Latex solutions into the axillary sheath resulted in immediate dye staining of median, radial, and ulnar nerves, despite the presence of septa. These data demonstrate that there are connections between compartments within the sheath and, therefore, do not support the need for multiple injections when performing an axillary block.
Margin of safety in positioning modern double-lumen endotracheal tubes.
The authors have defined the margin of safety in positioning a double-lumen tube as the length of tracheobronchial tree over which it may be moved or positioned without obstructing a conducting airway. The purpose of this study was to measure the margin of safety in positioning three modern double-lumen tubes (Mallinkrodt [Broncho-Cath], Rusch [Endobronchial tubes], and Sheridan [Broncho-Trach]). The margin of safety in positioning a: 1) left-sided double-lumen tube (all manufacturers) is the length of the left mainstem bronchus minus the length from the proximal margin of the left cuff to left lumen tip; 2) Mallinkrodt right-sided double-lumen tube is the length of the right mainstem bronchus minus the length of the right cuff; and 3) Rusch right-sided double-lumen tube is the length of the right upper lobe ventilation slot minus the diameter of the right upper lobe. The length of the right and left mainstem bronchi were measured by in vivo fiberoptic bronchoscopy (n = 69), in fresh cadavers (n = 42), and in lung casts (n = 55), and the diameter of the right upper lobe bronchus was measured in lung casts (n = 55). The average +/- SD male left and right mainstem bronchial lengths were 49 +/- 8 and 19 +/- 6 mm, respectively, the average +/- SD female left and right mainstem bronchial lengths were 44 +/- 7 and 15 +/- 5 mm, respectively, the average right upper lobe bronchial diameter was 11 mm, the proximal left cuff to left lumen tip distance was 30 mm, the length of the Mallinkrodt right cuff was 10 mm, and the length of the Rusch right upper lobe ventilation slot was 15 mm. The average margin of safety in positioning left-sided double-lumen tubes ranged 16-19 mm for the different manufacturers. The average margin of safety in positioning Mallinkrodt right-sided double-lumen tubes was 8 mm, and the margin of safety in positioning Rusch right-sided double-lumen tubes ranged 1-4 mm, depending on French size. The authors concluded that left-sided double-lumen tubes are much preferable to right-sided double-lumen tubes because they have a much greater positioning margin of safety, and that proper confirmation of proper position of either a left- or right-sided double-lumen tube should be aided by fiberoptic bronchoscopy, because the absolute distances that constitute the margin of safety are extremely small.