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Biomedical subjects

J W Sear

Publications and source records attributed to J W Sear.

At least 55 records · Page 3Linked to original sources
PubMed1997

Eltanolone for induction of anaesthesia in the surgical patient. A comparison of dose requirements in young and elderly patients.

BACKGROUND: The relative potency of the steroid anaesthetic agent eltanolone has been compared with respect to induction of anaesthesia in ASA I and II young (18-40 years) and elderly (> 65 years) patients. METHOD: 113 temazepam premedicated patients (60 elderly) were evaluated in an open randomised study. They were allocated to receive doses between 0.05 and 0.75 mg/kg given i.v. over 30 s. The first 33 patients formed a pilot phase; the formal study comprised 80 patients. The primary efficacy variable was loss of verbal contact within 120 s and an effect lasting more than 4 min. All patients breathed 100% oxygen throughout the study period. Safety data (heart rate, blood pressure, respiratory apnoea, involuntary movements, hypertonus and other adverse effects) were noted. RESULTS: Anaesthesia was adequately induced in 12/40 elderly and 7/40 young patients. The lowest effective induction dose was 0.2 mg/kg in elderly and 0.3 mg/kg in young patients. This gave a relative potency of 0.28 (95% CI 0.12-0.52; P = 0.0039). The cardiovascular effects associated with induction were small; other side-effects included involuntary movement and hypertonus, and respiratory upsets (apnoea, hiccups and coughing). CONCLUSION: The effective induction dose of eltanolone was significantly lower in the elderly patients; but the drug safety profile was similar in both age groups of patients.

Adjuvants, Anesthesia↗
PubMed1996

Kinetics of methaemoglobin and serum nitrogen oxide production during inhalation of nitric oxide in volunteers.

Inhaled nitric oxide is used increasingly to treat pulmonary hypertension and ventilation/perfusion mismatching in seriously ill patients, but little is known of the pharmacokinetics of its two principal metabolites, methaemoglobin and nitrogen oxides (nitrates and nitrites). We have studied the changes in these metabolites in six healthy volunteers during and after 3 h inhalation of 100 volumes per million of nitric oxide. Mean nitric oxide uptake was 0.49 (SD 0.08) ml min-1 at standard temperature and pressure, corresponding to 74% of the inhaled dose. During inhalation, methaemoglobin increased monoexponentially with a time constant of 45.6 (11.1) min by 1.77 (0.47)% of total haemoglobin. Serum nitrogen oxides increased from 36.7 (7.6) to 124 (17) mumol litre-1, with a time constant of 172 (91.4) min and a volume of distribution of 331 (104) ml kg-1. The volume of distribution for methaemoglobin calculated from nitric oxide uptake and the increase in methaemoglobin, was, on average, 14.3% less than predicted blood volume, suggesting that most of the absorbed nitric oxide initially forms methaemoglobin. Serum nitrogen oxides declined initially after inhalation ceased but then increased to a second peak between 45 and 180 min later. The cause of the second peak was not determined.

Administration, Inhalation↗
PubMed1996

Peri-operative management of diabetic patients. Any changes for the better since 1985?

Two hundred and seven anaesthetists in the Oxford region were sent a questionnaire asking about their peri-operative management of patients with diabetes mellitus. One hundred and seventy two valid returns were received. The results of this survey were compared with those of a similar survey conducted in 1985. A greater proportion of anaesthetists in 1993 would maintain their diabetic patients with a peri-operative blood glucose concentration of less than 10 mmol.l-1. Anaesthetists are more likely to be interventional in their management of diabetic patients than in 1985 and the methods used have changed in relative popularity. In 1993 diabetic patients undergoing major surgery were most commonly managed with separate infusions of insulin and glucose, while in 1985 the combined infusion of glucose, insulin and potassium was the most popular technique. The use of protocols in hospitals may increase the degree of uniformity of practice between anaesthetists.

Anesthesia↗
PubMed1996

Silent myocardial ischaemia in patients undergoing transurethral prostatectomy. A study to evaluate risk scoring and anaesthetic technique with outcome.

Ninety four patients undergoing transurethral resection of the prostate underwent Holter electrocardiographic monitoring pre- and postoperatively. There was no difference in silent myocardial ischaemia incidence or load between the spinal (n = 60) and the general anaesthesia (n = 34) groups. Ischaemic heart disease and a higher Detsky score both significantly increased the incidence of silent myocardial ischaemia but not the ischaemic load of those patients that actually demonstrated ischaemia. In this specific surgical population, not undergoing cardiac or vascular surgery, both ischaemic heart disease and cardiac risk scores are poor predictors of ischaemic load. Merely the presence of short duration silent myocardial ischaemia probably has little predictive value for postoperative adverse outcome.

Aged↗
PubMed1996

Hypertension, admission blood pressure and perioperative cardiovascular risk.

We performed a retrospective case-control study to investigate hypertension and admission blood pressure as risk factors for postoperative cardiovascular death. We identified records of 76 patients who had died of a cardiovascular cause within 30 days of anaesthesia and elective surgery and 76 matched controls. From the records of each patient (case and control) we recorded the admission blood pressure and details of any history of hypertension. A pre-operative history of hypertension was strongly associated with perioperative cardiovascular death (p < 0.001 with one degree of freedom: odds ratio 4.14, 95% confidence intervals 1.63-11.69). There was no association between systolic or diastolic pressure at admission for operation and perioperative cardiovascular death. The mean admission systolic pressure of the cases was 145.5 mmHg (range 90-250 mmHg) and that of the controls was 146.5 mmHg (range 100-200 mmHg). The mean admission diastolic pressure of the cases was 83.2 mmHg (range 60-130 mmHg), and that of the controls was 84.5 mmHg (range 60-110 mmHg).

Aged↗
PubMed1996

Physiologic effects of anesthesia induced and maintained by intravenous administration of a climazolam-ketamine combination in ponies premedicated with acepromazine and xylazine.

OBJECTIVE: To examine the physiologic and pharmacokinetic effects of a technique of total intravenous anesthesia in ponies. ANIMALS: 6 healthy ponies. PROCEDURE: Ponies were premedicated with acepromazine (0.03 mg/kg of body weight, IV) and xylazine (1.0 mg/kg, IV). Two minutes later, anesthesia was induced with ketamine (2.0 mg/kg, IV) followed by climazolam (0.2 mg/kg, IV). Anesthesia was maintained for 120 minutes by an infusion of climazolam (0.4 mg/kg/h) and ketamine (6.0 mg/kg/h). Oxygen (5 L/min) was supplemented. 20 minutes after the infusion was stopped sarmazenil (0.04 mg/kg, IV) was administered. Cardiovascular and respiratory function measurements were taken before and after premedication, and during anesthesia. Plasma cortsol, ACTH, and catecholamine concentrations were used to assess adrenal and pituitary gland function Ketamine and climazolam kinetics were calculated, on the basis of plasma drug concentrations. RESULTS: There were no significant changes from pre-xylazine values in heart rate, respiratory rate, arterial blood pressure, cardiac index, systemic vascular resistance, or arterial PO2, PCO2, and pH. Plasma cortisol concentration decreased during anesthesia, but plasma ACTH and catecholamine concentrations did not change. Recovery was fairly smooth, but some excitement and ataxia were noted in 2 ponies. CONCLUSION: Ketamine-climazolan infusion appeared suitable for maintenance of anesthesia in ponies, although recovery was not ideal in 2 of 6 ponies.

Acepromazine↗
PubMed1995

Total intravenous anaesthesia in ponies using detomidine, ketamine and guaiphenesin: pharmacokinetics, cardiopulmonary and endocrine effects.

Pharmacokinetics and some pharmacological effects of anaesthesia induced by a combination of detomidine, ketamine and guaiphenesin were investigated in eight ponies. Cardiopulmonary function was studied and plasma met-enkephalin, dynorphin, beta-endorphin, arginine vasopressin, adrenocorticotrophin, cortisol, 11-deoxycortisol and catecholamine concentrations were measured. The combination produced slight cardiorespiratory depression, hyperglycaemia and a reduction in haematocrit. There were no changes in plasma opioids, pituitary peptides or catecholamines. Plasma cortisol concentration decreased and plasma 11-deoxycortisol increased indicating a suppression of steroidogenesis. Steady state ketamine and guaiphenesin concentrations were attained during the infusion period, and ketamine concentrations likely to provide adequate analgesia for surgical operations were achieved (more than 2.2 micrograms ml-1). Steady state detomidine concentration was not attained. The ponies took on average 68 minutes to recover to standing and the recovery was uneventful.

Anesthesia, Intravenous↗
PubMed1995

Hemodynamic effects during induction, laryngoscopy, and intubation with eltanolone (5 beta-pregnanolone) or propofol. A study in ASA I and II patients.

STUDY OBJECTIVE: To evaluate the cardiovascular changes following induction of anesthesia, laryngoscopy, and intubation in patients receiving a bolus dose of either eltanolone or propofol. DESIGN: Randomized, controlled, blind, prospective clinical study. SETTING: General operating theaters of a university hospital. PATIENTS: 40 ASA status I and II patients scheduled for elective surgery. INTERVENTIONS: Patients were premedicated with oral temazepam 20 mg. Anesthesia was induced with either eltanolone 0.58 mg/kg or propofol 1.7 mg/kg, neuromuscular blockade was achieved with vecuronium 0.1 mg/kg, and anesthesia was maintained with enflurane 0.5% to 1.0% in nitrous oxide (67%). MEASUREMENTS AND MAIN RESULTS: Blood pressure was measured using an automatic oscillometric technique, heart rate (HR) was derived from the ECG, oxygen saturation was measured by pulse oximetry, and cardiac output (Q) was measured by a thoracic bioimpedance technique. Induction of anesthesia with either drug, eltanolone or propofol, decreased arterial systolic (SAP) and diastolic (DAP) blood pressure, Q, and stroke volume (SV). HR increased. Systemic vascular resistance (SVR) was unaltered. After laryngoscopy and intubation, SAP and DAP increased secondary to an increase in SVR. HR also increased; SV decreased in patients receiving eltanolone. Side effects (e.g., apnea occurring for more than 30 seconds, involuntary movements, limb hypertonus) occurred at a similar incidence with both treatments, but pain following injection was greater with propofol (59% vs. 9%). CONCLUSIONS: Patients receiving either eltanolone or propofol showed similar cardiovascular changes to induction of anesthesia, although there were greater increases in arterial pressure and HR in those patients receiving eltanolone.

Anesthesia↗
PubMed1995

Effects of propofol and thiopentone, and benzodiazepine premedication on heart rate variability measured by spectral analysis.

We studied the effects of temazepam premedication and induction of anaesthesia with thiopentone or propofol on the heart rate power spectrum in 47 patients undergoing elective minor surgery. Eighteen patients received temazepam 20 mg orally as premedication. There was a significant reduction in high frequency power and total power, and an increase in the ratio of low to high frequency power after induction of anaesthesia with either propofol or thiopentone. Patients who had received temazepam premedication had significantly greater low frequency, high frequency and total power than those who were not premedicated. There was no significant difference between premedicated and unpremedicated patients in the ratio of low to ventilatory frequency power.

Adult↗
PubMed1995

Propofol administered by a manual infusion regimen.

We have evaluated the clinical utility and blood propofol concentrations produced with two different infusion regimens for propofol, given to supplement 67% nitrous oxide-morphine anaesthesia. Patients received a standardized three-step infusion of propofol based either on body weight (weight-corrected group) or on a mean body weight of 70 kg (standard dose group). Both groups showed similar cardiovascular stability and recovery times. In the 48 patients studied, isoflurane was used as a supplement in nine (two in the weight-corrected group). Apparent steady state blood propofol concentrations were 3.41 (SD 0.69) micrograms ml-1 in the weight-corrected group and 3.46 (0.79) microgram ml-1 in the standard dose group. These results suggest that for patients weighing 60-90 kg body weight, a standard dose infusion regimen may be a suitable starting point. In routine clinical practice, the need for isoflurane supplementation may be avoided by subsequent titration of the infusion rate according to clinical response. Computer simulation of the actual infusion rates used in each patient has allowed retrospective comparison of the predictive performance of different pharmacokinetic descriptors for propofol. The variables described by Tackley and colleagues provided a more accurate prediction of the measured blood propofol concentration than did the variable set reported by Gepts and colleagues.

Adolescent↗
PubMed1995

Effect of ketorolac, bupivacaine and low-dose heparin on thrombelastographic variables in vitro.

We have studied the effects of ketorolac, bupivacaine and low-dose heparin on three thrombelastographic (TEG) variables (r, alpha, MA) in vitro. Blood samples were obtained from 12 healthy volunteers and 88 ASA I-II elective surgical patients. Clinically relevant concentrations of ketorolac (4.1 micrograms ml-1) and bupivacaine (2.7 micrograms ml-1) had little or no effect on the TEG variables. However, low concentrations of heparin (0.07-0.28 u. ml-1) had marked effects on all three TEG variables. Thus the interpretation of TEG abnormalities during anaesthesia and surgery may be confounded by the presence of heparin, but not by clinical concentrations of ketorolac or bupivacaine.

Adult↗
PubMed1995

SCOTI--a new device for identification of tracheal intubation.

A new lightweight device for the detection of placement of a tracheal tube in the trachea or oesophagus is described. The device utilises a sonic technique detecting resonating frequencies in an open (trachea) or closed (oesophagus) structure. Evaluation of the device in a clinical environment is described and it has been shown to be capable of verifying the correct placement of the tracheal tube in the trachea in 98% of patients studied. Further evaluation of this intubating aid appears justified.

Adolescent↗
PubMed1994

Continuous infusions of propofol administered to dogs: effects on ICG and propofol disposition.

We have studied the effects of stepwise increasing infusion rates of propofol 200-500 micrograms kg-1 min-1 on blood concentrations of propofol and the disposition and clearance of a bolus dose of indocyanine green (ICG) 0.5 mg kg-1 in 10 acutely instrumented dogs. Drug concentrations and ICG clearance were measured 30 min after each change of infusion rate and after reverting for 60 min to the basal propofol infusion rate. Increasing infusion rates resulted in significant prolongation of the elimination half-life of ICG and decrease in ICG clearance at the largest infusion rate (500 micrograms kg-1 min-1) compared with the basal rate. Similarly, there were greater than predicted blood concentrations of propofol at the largest infusion rate. When the infusion rate reverted to 200 micrograms kg-1 min-1, and continued for 60 min, there was a significant difference between the initial blood concentration of propofol at this basal infusion rate and this latter value (P < 0.01). These changes reflect the persistent myocardial depression observed during the recovery phase.

Animals↗
PubMed1994

Does the choice of antihypertensive therapy influence haemodynamic responses to induction, laryngoscopy and intubation?

We have measured haemodynamic responses to induction of anaesthesia, laryngoscopy and intubation in 103 mild-moderate hypertensive patients (83 patients (diastolic pressures < or = 110 mm Hg) currently receiving one of four monotherapies (ACE inhibitors, group A; beta adrenoceptor blocking drugs, group B; calcium channel antagonists, group C; diuretics, group D) and 24 were untreated hypertensive patients). Anaesthesia was induced with fentanyl 1.5-2.0 micrograms kg-1 and thiopentone 3-5 mg kg-1. Tracheal intubation was facilitated by vecuronium 0.1 mg kg-1 and anaesthesia maintained with enflurane and nitrous oxide in oxygen. Systolic and diastolic pressures (SAP, DAP) were measured at 1-min intervals by a non-invasive oscillometric method and cardiac output (CO) and stroke volume (SV) by thoracic bioimpedance. Induction of anaesthesia was associated with a decrease in SAP, DAP and CO in groups A-D (P < 0.05). Heart rate (HR) decreased in groups A and D (P < 0.01) and systemic vascular resistance (SVR) decreased in groups A and B (P < 0.05). SAP and HR increased in all groups after laryngoscopy and intubation (P < 0.01) as did SVR in groups A, B and D (P < 0.02). CO was unaltered. Similar changes occurred in the untreated hypertensive patients, although nine of 24 patients exhibited HR > or = 100 beat min-1 after laryngoscopy and intubation. Comparison of the changes in SAP, DAP, CO and SVR with time showed no differences in the five treatment groups; changes in HR were significantly less in group B compared with the other groups (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1994

Resistant hypertension and preoperative silent myocardial ischaemia in surgical patients.

We studied 325 patients undergoing elective noncardiac surgery who had preoperative ambulatory ECG monitoring performed for a duration of 5130 h (range 8-24 h; mean 15.8 h). Sixty-four subjects (20%) had one or more episodes of ST segment depression consistent with myocardial ischaemia. Of all preoperative cardiovascular variables measured, the presence of elevated arterial pressure, despite patients being maintained on long term antihypertensive therapy, was the only factor associated significantly with the presence of preoperative silent myocardial ischaemia (P < 0.002). This correlation was confirmed when arterial hypertension was defined in four separate ways. The incidence of silent ischaemia in these patients was 33-55%. We suggest that admission arterial pressure may therefore be a useful screening test to identify patients at risk of preoperative myocardial ischaemia.

Adult↗