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Biomedical subjects

B A MacLeod

Publications and source records attributed to B A MacLeod.

At least 19 recordsLinked to original sources
PubMed2001

Combined pre- and post-surgical bupivacaine wound infiltrations decrease opioid requirements after knee ligament reconstruction.

PURPOSE: To test the efficacy of a combination of selective pre- and post-surgical local anesthetic infiltrations of the knee, compared with standard intra-articular injection at the end of surgery alone, to reduce postoperative opioid requirements following arthroscopic cruciate ligament reconstruction (ACLR). METHODS: In a double-blind, randomized, controlled trial, we studied 23 patients (ASA I or II) scheduled for elective ACLR under general anesthesia. The treatment group (n = 12) received infiltrations with bupivacaine 0.25% with epinephrine 1:200,000 presurgically (10 ml into the portals, 10 ml at the medial tibial incision site, 10 ml at the lateral femoral incision site, and 10 ml intra-articularly) and postsurgically (5 ml at the medial tibial incision and 10 ml at the lateral femoral incision). The control group (n = 11) received infiltrations with saline 0.9% in the same manner. All patients received a standard intra-articular local anesthetic instillation of the knee (25 ml of bupivacaine 0.25% with epinephrine 1:200,000) at the completion of surgery. RESULTS: Postoperative opioid requirements were lower in the treatment group (5.8 +/- 2.9 mg morphine equivalent) than in the control group ( 13.7 +/- 5.8 mg; P = 0.008). Treatment patients were ready for discharge approximately 30 min earlier than control patients (P = 0.046). There were no adverse events in the treatment group. In the control group, 2/11 patients vomited and a third experienced transient postoperative diaphoresis, dizziness and pallor. CONCLUSION: We conclude that a combination of selective pre- and post-surgical wound infiltration with bupivacaine 0.25% provides superior analgesia compared with a standard post-surgical intra-articular injection alone.

Adult↗
PubMed2000

RSD1019 suppresses ischaemia-induced monophasic action potential shortening and arrhythmias in anaesthetized rabbits.

The electrophysiological actions of lidocaine, tedisamil and RSD1019 were assessed on normal and ischaemic cardiac tissue using monophasic action potentials (MAPs) recorded from the epicardium of anaesthetized rabbits. Drug effects on ischaemia-induced arrhythmias were assessed simultaneously in the same rabbits. Lidocaine, infused at 2.5, 5 and 10 micromol kg(-1) min(-1) i.v., accelerated and worsened the electrophysiological derangement caused by ischaemia, had profibrillatory actions and reduced the time to the occurrence of ventricular fibrillation (VF) relative to controls. Tedisamil, infused at 0.063, 0.125 and 0.25 micromol kg(-1) min(-1) i.v., prolonged MAP duration at 90% repolarization (MAPD(90%)) before induction of ischaemia in a dose-related manner; however, this effect was not maintained 5 min after induction of ischaemia. Tedisamil had no significant antiarrhythmic actions over the dose-range tested. RSD1019, infused at 2, 4 and 8 micromol kg(-1) min(-1) i.v., produced a small increase in MAPD(90%) before induction of ischaemia and only at the highest dose tested. In contrast to tedisamil, RSD1019 suppressed ischaemia-induced MAP shortening assessed 5 min after induction of ischaemia. This effect was dose-related. RSD1019 completely prevented ischaemia-induced tachyarrhythmias at the mid and highest infusion levels tested. The results of this study illustrate a pathologically targeted approach for preventing ischaemia-induced arrhythmias. Suppression of ischaemia-induced MAP shortening, demonstrated herein for RSD1019, represents a novel antifibrillatory approach.

Action Potentials↗
PubMed2000

Effect of an administrative intervention on rates of screening for domestic violence in an urban emergency department.

OBJECTIVES: This study measured the effects of an administrative intervention on health care provider compliance with universal domestic violence screening protocols. METHODS: We used a simple, interrupted-time-series design in a stratified random sample of female emergency department patients 18 years or older (n = 1638 preintervention, n = 1617 postintervention). The intervention was a 4-tiered hospital-approved disciplinary action, and the primary outcome was screening compliance. RESULTS: Preintervention and postintervention screening rates were 29.5% and 72.8%, respectively. Before the intervention, screening was worse on the night shift (odds ratio [OR] = 0.46, 95% confidence interval [CI] = 0.31, 0.68) and with psychiatric patients (OR = 0.34, 95% CI = 0.14, 0.85); after the intervention, no previous screening barriers remained significant. CONCLUSIONS: An administrative intervention significantly enhanced compliance with universal domestic violence screening.

Adult↗
PubMed1999

Cost comparison of sevoflurane with isoflurane anesthesia in arthroscopic menisectomy surgery.

PURPOSE: To determine the "real world" cost of sevoflurane compared with isoflurane in balanced general anesthesia for daycare arthroscopic menisectomy, we prospectively investigated perioperative drug requirement and expense as well as recovery time. METHODS: Following intravenous induction, 40 consenting adult patients randomly received either sevoflurane- or isoflurane-based anesthesia with a standardized gas inflow rate of 3 l x min. Recovery was assessed in the postanesthetic recovery room (PARR) in a double-blind manner at 15 min intervals using the Aldrete scoring system until patients met discharge criteria. RESULTS: Patient demographics, anesthetic duration, volatile potency and adjunct drug requirements were similar in the two groups. Total perioperative drug cost per patient was CAN$38.10+/-10.13 (mean +/- SD) for the sevoflurane group and $23.87+/-6.59 for the isoflurane group (P<0.01). Although the nonvolatile drug cost was comparable between the two groups, the volatile drug cost per patient was $19.40+/-8.80 for sevoflurane and $4.50+/-1.90 for isoflurane (P<0.01). This four-fold sevoflurane-to-isoflurane cost difference was the product of two ratios, both based on the volume of liquid anesthetic: the ratio of consumption, 2.1; and the ratio of institutional price, 2.1. Intraoperative hemodynamic response, time until discharge from the PARR and incidences of postoperative nausea and vomiting did not significantly differ between the two groups. CONCLUSIONS: When used to maintain equipotent balanced general anesthesia for daycare arthroscopic menisectomy, volatile consumption and cost were greater for sevoflurane compared with isoflurane. Nonvolatile perioperative drug cost and recovery times were similar, however, in the two groups.

Adult↗
PubMed1999

Addition of femoral 3-in-1 blockade to intra-articular ropivacaine 0.2% does not reduce analgesic requirements following arthroscopic knee surgery.

PURPOSE: To test the hypothesis that the addition of a preincisional femoral 3-in-1 block to intra-articular instillation with ropivacaine 0.2% at the end of surgery improves postoperative pain control in patients undergoing arthroscopic anterior cruciate ligament reconstruction (ACLR) under general anesthesia. METHODS: In a prospective, randomized, placebo-controlled, double-blind trial, we studied 44 patients scheduled for inpatient ACLR. Prior to incision, the treatment group (n = 22) received a femoral 3-in-1 block with 40 ml ropivacaine 0.2%, augmented by infiltrations of the lateral and anteromedial incisions with 20 ml ropivacaine 0.2% at the end of the procedure. The control group (n = 22) received saline 0.9% instead of ropivacaine. All patients received an intra-articular instillation with 30 ml ropivacaine 0.2% at the end of surgery. The primary efficacy variable was 24 hr morphine consumption postoperatively standardized by weight, administered intravenously via a patient-controlled analgesia (PCA) pump. RESULTS: There was no difference between both groups in 24 hr PCA morphine consumption postoperatively (control, 0.45 +/- 0.44 [mean +/- SD] mg x kg(-1); treatment, 0.37 +/- 0.50 mg x kg(-1); p = 0.55). No difference was found in postoperative visual analog scale pain scores, adverse events, or vital signs. In the treatment group, R = 10/22 patients did not require postoperative morphine compared with R = 6/22 in the control group (P = 0.35). CONCLUSION: We found no effect of a femoral 3-in-1 block with ropivacaine 0.2% on postoperative analgesic consumption, compared to intra-articular instillation with ropivacaine 0.2% alone, in patients undergoing ACLR under general anesthesia.

Adult↗
PubMed1999

Universal screening for intimate partner violence in the emergency department: importance of patient and provider factors.

STUDY OBJECTIVE: Screening for intimate partner violence has been widely advocated in the health care setting, but efforts to assess effectiveness and ensure adequacy of universal screening are largely untested. We sought to identify barriers to screening of female emergency department patients for intimate partner violence during the first year of implementation of a screening protocol. METHODS: A retrospective, structured medical chart review of 1,638 randomly identified visits included demographic factors of age, race, marital status, employment status, insurance status, arrival mode, mechanism of presenting complaint, severity of condition, presentation time, and nurse gender. The study was conducted an an inner-city Level I trauma center with 43,000 annual ED visits and universal procedures for screening for intimate partner violence in place since February 1994. The participants were a cohort of 1,509 female patients, 18 years of age or older, who were discharged from the ED between July 1994 and June 1995. The main outcome measure was the odds of being screened as a function of patient and provider variables. Statistical analyses involved univariate and multivariate logistic regression on screening rates (Yes/No) as derived from universal screening instrument variables. RESULTS: Of 1,638 records reviewed, 483 patients (29.5%) were screened for intimate partner violence. Univariate analyses revealed that women presenting with nonpsychiatric, less acute complaints and those who presented during daylight hours were more likely to be screened than women who presented with psychiatric or more acute complaints, or during the night shift. Male and female nurse providers were equally likely to screen for intimate partner violence. Step-down multivariate analyses agreed with these findings. CONCLUSION: In this random sample of female patients, screening rates varied by severity of the patient's condition, type of presenting complaint, and presentation time.

Adolescent↗
PubMed1998

Correlation between triage nurse and physician ordering of ED tests.

Triage nurse ordering of tests can reduce patient time in the emergency department. This benefit must be balanced with the extra expense and potential morbidity of unnecessary tests. This study examined whether triage nurse ordering of lab tests and X-rays correlated with physician ordering. In Phase I, a prospective study, triage nurses completed an order form for each patient triaged during randomly selected 2-hour blocks over a 3-week period. In Phase II, Phase I was repeated with test ordering guidelines derived from Phase I results. Correlations of nurse and physician orders were analyzed by kappa statistics and paired t tests. In Phase I, 176 patients were enrolled of a possible 204 (82%). In Phase II, 350 patients were enrolled of a possible 418 (84%). The percentage of nurse overordering of tests in Phase I was 35%; In Phase II, it was 34% (P NS). Kappa values were determined for blood testing (Phase I, 0.48; Phase II, 0.54 [P = .048]), for X-ray (Phase I, 0.68; Phase II, 0.65 [P = .523]), for urinalysis (Phase I, 0.76; Phase II, 0.67 [P = .338]), and for electrocardiogram (Phase I, 0.78; Phase II, 0.77 [P = .438]). The improved lab correlation in Phase II resulted from the nurses ordering fewer tests (P = .046). Nurses deviated from the test ordering guidelines in 37% of patients. Triage nurse ordering of X-rays, electrocardiogram, and urinalysis has moderate to substantial correlation with physician ordering. Correlation of triage nurse and physician ordering of tests can be improved with the use of test ordering guidelines.

Diagnostic Tests, Routine↗
PubMed1997

A model of myocardial ischemia for the simultaneous assessment of electrophysiological changes and arrhythmias in intact rabbits.

A method of recording epicardial monophasic action potentials (MAPs) and ischemia-induced arrhythmias following coronary artery ligation in intact rabbits is described. It is expected that this model will have utility in analyzing drug effects and mechanisms of ischemic arrhythmogenesis. Rabbits were found to have two arrhythmic phases following coronary artery occlusion which correspond to phase Ia and Ib arrhythmias in other species. Epicardial MAPs recorded from ischemic tissue allowed electrophysiological effects to be correlated with these phases. Phase Ia arrhythmias occurred within the first 2 min of coronary artery occlusion and were associated with a reduction in the maximum upstroke velocity of MAPs and changes in MAP duration, including the occurrence of alternans in duration. Phase Ib arrhythmias occurred between 8 and 15 min after coronary artery occlusion. These arrhythmias were associated with a decrease in MAP duration and amplitude, alternans in MAP duration as well as conduction block. Coronary artery occlusion reliably induced arrhythmias in rabbits if the left branch of the coronary artery and the left anterior descending artery were occluded. There was a 95% incidence of premature ventricular contractions, 38% of ventricular tachycardia, and 48% of ventricular fibrillation (n = 21). The results of this study show that epicardial MAPs can be used to aid in the characterization of the electrophysiological mechanisms of ischemia-induced arrhythmias in vivo.

Action Potentials↗
PubMed1996

Liposomal bupivacaine. Extended duration nerve blockade using large unilamellar vesicles that exhibit a proton gradient.

BACKGROUND: There is a clinical requirement for longer-acting local anesthetics, particularly for the management of post-operative and chronic pain. In this regard, liposomes have been suggested to represent a potentially useful vehicle for sustained drug release after local administration. In the current study, the authors used a transmembrane pH gradient to efficiently encapsulate bupivacaine within large unilamellar vesicles. They report on the kinetics of drug uptake and release and the duration of nerve blockade. METHODS: The rate and extent of bupivacaine uptake into large unilamellar vesicles that exhibit a pH gradient (interior acidic) were determined and compared to drug association with control liposomes that did not exhibit a proton gradient. In subsequent studies, researchers examined the kinetics of bupivacaine release from these liposome systems in vitro. Using the guinea pig cutaneous wheal model, the rate of clearance of the liposome carrier was monitored after intradermal administration, using a radiolabelled lipid marker, and the duration of nerve blockade produced by free and liposomal bupivacaine was compared. RESULTS: Bupivacaine was rapidly and efficiently accumulated within liposomes that exhibited a pH gradient (interior acidic) with trapping efficiencies of 64-82% of total drug, depending on the initial bupivacaine:phospholipid ratio. Little uptake was seen, however, for control vesicles that did not exhibit a transmembrane proton gradient. Using an in vitro model of drug clearance, liposomally encapsulated bupivacaine was found to be slowly released for a longer period of time compared with either the free drug or bupivacaine associated with control (no pH gradient liposomes). In the guinea pig cutaneous wheal model, more than 85% of the liposomal carrier was found to remain at the site of administration for 2 days. The sustained drug release afforded by liposomes that exhibited a pH gradient resulted in an increase in the duration of nerve blockade of as much as threefold compared with either the free drug or bupivacaine in the presence of control (no pH gradient) liposomes. Recovery of half maximal response (R2.5) after administration of 0.75% free bupivacaine, for example, was approximately 2 h, whereas the same dose of bupivacaine in pH gradient liposomes exhibited a R2.5 of approximately 6.5 h. CONCLUSIONS: Large unilamellar vesicles that exhibit a pH gradient can efficiently encapsulate bupivacaine and subsequently provide a sustained-release system that greatly increases the duration of neural blockade.

Anesthetics, Local↗
PubMed1995

Anaesthesia by intravenous emulsified isoflurane in mice.

An emulsion of isoflurane in Intralipid for intravenous (iv) injection was formulated and its anaesthetic properties determined in mice. The major advantage of iv delivery of volatile agents is to accelerate the induction of anaesthesia by circumventing the anesthetic circuitry and the lung's functional residual capacity. Isoflurane was added to Intralipid in varying concentrations. The ED50 (n = 34) and LD50 (n = 20) were determined by a single iv bolus injection. Anaesthesia was also induced and maintained for 30 min (n = 5) by continuous infusion and the time to emergence was measured. The ED50 and LD50 were 0.7 +/- 0.2 microliter and 2.4 +/- 0.2 microliter of isoflurane equivalent respectively. An average infusion rate of 1.6 +/- 0.4 microliters.min-1 of isoflurane equivalent was required for maintenance following which the average emergence time was 193 +/- 35 secs. The only negative effect was local skin ulceration with an inadvertent interstitial injection. We conclude that iv induction and maintenance with emulsified isoflurane in Intralipid can be carried out with safety and reproducibility in the mouse. Further larger animal studies are warranted assessing the haemodynamic, toxicological, physiochemical and pharmacokinetic characteristics of these and other similar preparations.

Anesthesia Recovery Period↗
PubMed1994

Pregnancy in the emergency department: risk factors and prevalence among all women.

STUDY OBJECTIVE: To determine the prevalence of unrecognized pregnancy in the emergency department and to ascertain if patient history can effectively detect unrecognized pregnancies. DESIGN: Prospective study. SETTING: Urban ED with annual census of 40,000. PARTICIPANTS: One hundred ninety-one consecutive women meeting inclusion criteria. INTERVENTIONS: All participants completed a menstrual/sexual history questionnaire and had a urine pregnancy test. RESULTS: Overall, we found a 6.3% prevalence of unrecognized pregnancy. Women with abdominal/pelvic complaints had a 13% prevalence; those with other complaints had a 2.5% prevalence. Two historical risk factors, the patient's suspicion that she might be pregnant and an abnormal last menstrual period, had a statistically significant correlation with unrecognized pregnancy. A third risk factor, the presence of abdominal/pelvic complaints, nearly achieved statistical significance. These risk factors detected all unrecognized pregnancies with a sensitivity of 100% and a specificity of 54%. CONCLUSION: The prevalence of unrecognized pregnancy in our ED was 6.3%. Historical risk factors detected all of them.

Adult↗
PubMed1993

Improved peribulbar anaesthesia with alkalinization and hyaluronidase.

A prospective double-blind randomized study was carried out to determine the effect of pH and the addition of hyaluronidase to a mixture of lidocaine and bupivacaine on the efficacy of peribulbar anaesthesia. One hundred patients were assigned to one of five groups. All groups received a solution of two parts bupivacaine (0.75%) and one part lidocaine (2%) (with 1:100,000 adrenaline) as the base components of their anaesthesia. Group 1 received only the bupivacaine-lidocaine mixture, pH 3.9. Group 2 received a solution supplemented with hyaluronidase (ten units.ml-1), pH of 5.1. Group 3 received the bupivacaine-lidocaine mixture alkalinized with sodium bicarbonate to a pH of 5.1, the same as solution 2. Group 4 received the mixture with hyaluronidase alkalinized to pH of 6.7. Group 5 received the bupivacaine-lidocaine mixture alkalinized to a pH of 6.7. Efficacy of each block was graded according to the degree of residual movement 30 min following injection, as described by House et al. The solution containing hyaluronidase and pH adjusted to 6.7 was found to be the most effective (P < 0.025). The presence of hyaluronidase without alkalinization did not improve the efficacy of the mixture; and similarly, alkalinization in the absence of hyaluronidase was ineffective. These results reflected the pH- and temperature-dependent thermodynamic properties of local anaesthetics, and the pH-dependent activity of hyaluronidase.

Aged↗
PubMed1992

Quinacainol, a new antiarrhythmic with class I antiarrhythmic actions in the rat.

The antiarrhythmic and electrophysiological actions of quinacainol, a new Class I antiarrhythmic, were assessed in rats. Electrophysiological actions of quinacainol were assessed in vivo in terms of drug-induced changes in ECG, responses to left ventricular electrical stimulation, and changes in epicardial intracellular potentials to precisely characterize the electrophysiological effects of this putative subclass Ic antiarrhythmic compound. Antiarrhythmic actions were assessed in conscious rats subjected to occlusion of the LAD coronary artery. Antiarrhythmic actions occurred with 2.0 and 4.0 mg/kg, whereas 8.0 mg/kg was pro-arrhythmic. At doses of 0.5 mg/kg and above quinacainol increased threshold currents for capture and for ventricular fibrillation. Doses of 2.0 mg/kg and above increased ventricular refractoriness. From 1.0 to 8.0 mg/kg, quinacainol reduced dV/dtmax of phase 0 of epicardial action potentials but only 8.0 mg/kg increased action potential duration. The Q-T interval was also increased with the highest dose. Quinacainol dose-relatedly increased P-R interval whereas QRS did not change. Thus the Class I electrophysiological properties of quinacainol over the dose range tested did not fit accurately into a single subclass of the various subclasses of Class I. However, the Class Ic actions seen with 2.0 and 4.0 mg/kg were associated with antiarrhythmic actions.

Action Potentials↗
PubMed1992

Ischemic but not reperfusion arrhythmias depend upon serum potassium concentration.

The effects of variations in serum concentrations of potassium on the occurrence and severity of ischemia- and reperfusion-induced arrhythmias have been studied in conscious rats. Serum potassium concentrations were modified by maintaining rats on diets which varied in potassium concentration, by treatment with hydrochlorothiazide, amiloride, spironolactone or infusions of potassium chloride. An inverse linear relationship was demonstrated between ischemia-induced arrhythmias and log(e) serum potassium concentration such that a 50% reduction in arrhythmias occur with a 3.8-fold increase in serum potassium concentration. On the other hand, the incidence of reperfusion-induced arrhythmias after 7 min of regional ischemia prior to reperfusion in previously untreated rats were not influenced by elevation of serum potassium concentrations prior to and after reperfusion. Effects on ischemia-induced arrhythmias could not be explained by changes in blood pressure or heart rate. It is speculated that modification of potassium concentration in non-ischemic or border zone ventricular tissue may directly modify arrhythmogenesis due to ischemia but not that due to reperfusion.

Animals↗
PubMed1991

Verification of endotracheal tube placement with colorimetric end-tidal CO2 detection.

STUDY OBJECTIVE: To determine the ability of a disposable colorimetric CO2 detector to accurately confirm or refute endotracheal tube placement. DESIGN: Two hundred fifty prospective emergency intubations. SETTING: Emergency intubations performed in the emergency department, helicopter, and prehospital ground environment. TYPE OF PARTICIPANTS: Intubations were performed by emergency medicine residents, paramedics, and flight nurses. INTERVENTIONS: The FEF CO2 detector was applied after 250 emergency intubations. Notation of color change indicating intratracheal placement was recorded in each case. Confirmation of refutation of the detector's results was determined subsequently through traditional methods. RESULTS: The sensitivity for confirmation of endotracheal intubation in the 137 patients with a palpable pulse was 100%. However, only 76 of 103 patients (sensitivity, 72%) in cardiac arrest had endotracheal intubation confirmed by color change. The device was uniformly specific for tracheal intubation in 73 arrested patients in whom a color change was noted (100%). There was one instance (of a total of seven misintubations) in which a positive color change was noted, but the tube was not intratracheal (specificity, 86%). Overall sensitivity for tracheal intubation was 88% (95% confidence limits; range, 0.83 to 0.92), and specificity for tracheal intubation was 92% (95% confidence limits; range, 0.62 to 0.99). CONCLUSION: The FEF colorimetric detector reliably detects intratracheal placement in the nonarrested patient. Its use in prolonged cardiac arrest merits further study.

Breath Tests↗
PubMed1991

Antiarrhythmic properties of tedisamil (KC8857), a putative transient outward K+ current blocker.

1. Rats were used to evaluate the antiarrhythmic properties of tedisamil, a novel agent with the electrophysiological properties of a Class III antiarrhythmic drug. Tedisamil was tested against coronary artery occlusion-induced arrhythmias in conscious animals. 2. The actions of tedisamil on the ECG, as well as responses to electrical stimulation, were compared with those on the configuration of epicardial intracellular action potentials recorded in vivo. 3. Tedisamil (1-4 mg kg-1, i.v.) caused bradycardia, elevated blood pressure and dose-dependently reduced ventricular fibrillation (VF) induced by occlusion of the left anterior descending coronary artery. Other ischaemia-associated arrhythmias were not so well suppressed. Antiarrhythmic activity was greatest when the tedisamil-induced bradycardia was prevented by electrically-pacing the left ventricle. 4. Tedisamil dose-dependently lengthened the effective refractory period and prevented electrically-induced VF. In vivo, tedisamil (0.5-4 mg kg-1, i.v.) prolonged the duration of epicardial intracellular action potentials by up to 400%. 5. Results showed that tedisamil possessed antifibrillatory actions in rats that were related to Class III electrophysiological actions as revealed by electrical stimulation and electrophysiological analyses.

Action Potentials↗