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Biomedical subjects

I R Thomson

Publications and source records attributed to I R Thomson.

At least 37 records · Page 2Linked to original sources
PubMed1995

Haemodynamic instability and myocardial ischaemia during carotid endarterectomy: a comparison of propofol and isoflurane.

The purpose of this study was to compare two anaesthetic protocols for haemodynamic instability (heart rate (HR) or mean arterial pressure (MAP) < 80 or > 120% of ward baseline values) measured at one-minute intervals during carotid endarterectomy (CEA). One group received propofol/alfentanil (Group Prop; n = 14) and the other isoflurane/alfentanil (Group Iso; n = 13). Periods of haemodynamic instability were correlated to episodes of myocardial ischaemia as assessed by Holter monitoring (begun the evening before surgery and ceasing the morning of the first postoperative day). In Group Prop, anaesthesia was induced with alfentanil 30 micrograms.kg-1 i.v., propofol up to 1.5 mg.kg-1 and vecuronium 0.15 mg.kg-1, and maintained with infusions of propofol at 3-12 mg.kg-1.hr-1 and alfentanil at 30 micrograms.kg-1.hr-1. In Group Iso, anaesthesia was induced with alfentanil and vecuronium as above, thiopentone up to 4 mg.kg-1 and maintained with isoflurane and alfentanil infusion. Phenylephrine was infused to support MAP at 110 +/- 10% of ward values during cross-clamp of the internal carotid artery (ICA) in both groups. Emergence hypertension and/or tachycardia was treated with labetalol, diazoxide or propranolol. Myocardial ischaemia was defined as ST-segment depression of > or = 1 mm (60 msec past the J-point) persisting for > or = one minute. For the entire anaesthetic course (induction to post-emergence), there was no difference between groups for either duration or magnitude outside the < 80 or > 120% range for HR or MAP. However, when the period of emergence from anaesthesia (reversal of neuromuscular blockade to post-extubation) was assessed, more patients were hypertensive (P = 0.004) and required vasodilator therapy in Group Iso (10/13 vs 5/14; P = 0.038 Fisher's Exact Test). The mean dose of labetalol was greater in Group Iso (P = 0.035). No patient demonstrated myocardial ischaemia during ICA cross-clamp. On emergence, 6/13 patients in Group Iso demonstrated myocardial ischaemia compared with 1/14 in Group Prop (P = 0.029). Therefore, supporting the blood pressure with phenylephrine, during the period of ICA cross-clamping, appears to be safe as we did not observe any myocardial ischaemia at this time. During emergence from anaesthesia, haemodynamic instability was associated with myocardial ischaemia. Under these specific experimental conditions, with emergence, hypertension and myocardial ischaemia were more prevalent with more frequent pharmacological interventions in patients receiving isoflurane.

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PubMed1995

Improved cardiac risk stratification in major vascular surgery with dobutamine-atropine stress echocardiography.

OBJECTIVES: This study sought to optimize preoperative cardiac risk stratification in a large group of consecutive candidates for vascular surgery by combining clinical risk assessment and semiquantitative dobutamine-atropine stress echocardiography. BACKGROUND: Dobutamine-atropine stress echocardiography has been used for the prediction of perioperative cardiac risk in a small group of patients scheduled for elective major vascular surgery on the basis of the presence or absence of stress-induced regional left ventricular wall motion abnormalities. METHODS: Clinical risk assessment and dobutamine-atropine stress echocardiography were performed in 302 consecutive patients presenting for major vascular surgery. The extent and severity of stress wall motion abnormalities and the heart rate at which they occurred, in addition to the presence of wall motion abnormalities at rest, were assessed. RESULTS: The absence of clinical risk factors (angina, diabetes, Q waves on the electrocardiogram, symptomatic ventricular tachyarrhythmias, age > 70 years) identified a low risk group of 100 patients with a 1% cardiac event rate (unstable angina). Dobutamine-atropine stress echocardiographic findings were positive in 72 patients. Twenty-seven patients had a perioperative cardiac event (cardiac death in 5, nonfatal infarction in 12, unstable angina pectoris in 10); all 27 patients had positive stress test results (positive predictive value 38%, negative predictive value 100%). The semiquantitative assessment of the extent and severity of ischemia did not provide additional prognostic information in patients with positive test results. In contrast, the heart rate at which ischemia occurred defined a high risk group with a low ischemic threshold (38 patients with 20 events [53%]) and an intermediate risk group with a high ischemic threshold (34 patients with 7 events [21%]). All 5 patients with a fatal outcome and 8 of 12 with a nonfatal myocardial infarction were in the high risk group with a low ischemic threshold. CONCLUSIONS: Clinical variables identify 33% of patients at very low risk for perioperative complications of vascular surgery in whom further testing is redundant. In all other candidates, dobutamine-atropine stress echocardiography is a powerful tool that identifies those patients at intermediate risk and a small group at very high risk. Risk stratification with a combination of clinical assessment and pharmacologic stress echocardiography has the potential to facilitate clinical decision making and conserve resources.

Adult↗
PubMed1994

Con: intraoperative myocardial ischemia is not benign.

The principal importance of intraoperative ischemia is its consistent association with adverse outcome. In coronary artery surgery the finding of prebypass ischemia is an important predictor, and postbypass ischemia is a critical predictor of adverse outcome. One in three patients with postbypass ischemia will suffer an adverse outcome in CABG. Furthermore, prevention of postbypass ischemia may improve outcome in CABG. Clearly, intraoperative ischemia in CABG surgery is an ominous sign that should be regarded with the utmost concern by anesthesiologists. In noncardiac surgery, intraoperative ischemia also indicates about a one in three chance of adverse outcome. Although it is less sensitive than postoperative ischemia, it may have superior positive predictive power and specificity. Most importantly, intraoperative monitoring for ischemia is currently available to most patients, whereas extended postoperative monitoring is not. The finding of intraoperative ischemia defines a high-risk group of patients who may merit special monitoring and treatment. To regard intraoperative ischemia as benign would be inconsistent with available information.

Cardiopulmonary Bypass↗
PubMed1994

Cerebral pressure-flow relationship during cardiopulmonary bypass in the dog at normothermia and moderate hypothermia.

We studied cerebral autoregulation by analyzing cerebral pressure-flow curves during cardiopulmonary bypass (CPB) with alpha-stat (alpha-stat) acid-base management at 28 (n = 9) and 37 degrees C (n = 9) in two groups of dogs. Cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRO2) were determined multiple times in each animal over an extensive range of cerebral perfusion pressure (CPP). The CPP was altered by changing perfusion flow rate. The dependence of CBF on CPP during normothermic and moderate hypothermic CPB was assessed using a block design analysis of covariance with CPP as the covariate. We anticipated maximal statistical power with this analysis to define if cerebral autoregulation was intact. This method of statistical analysis was compared with the conventional interpretation by linear regression analysis. Animals were administered sodium thiopental until an isoelectric electroencephalogram was obtained to assure stable depth of anesthesia independently of temperature effects. The animals were randomly assigned to either temperature group. The CBF was determined by injection of radioactive microspheres at each of five target CPPs randomly allocated (50, 60, 70, 80, and 90 mm Hg). The brain oxygen content difference was defined as arterial minus superior sagittal sinus (SSS) oxygen content. No difference in CPP, hemoglobin, arterial carbon dioxide tension, or pH was seen between groups at any time period. In both groups, total CBF (tCBF) increased significantly with increasing CPP (p = 0.012 and 0.017 for normothermic and hypothermic CPB, respectively; CPP as covariate). The between-group difference in slopes (CPP x temperature effect) approached statistical significance (p = 0.059).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1993

Dobutamine stress echocardiography for assessment of perioperative cardiac risk in patients undergoing major vascular surgery.

BACKGROUND: The purpose of this study was to determine the predictive value of dobutamine stress echocardiography for perioperative cardiac events in patients scheduled for elective major noncardiac vascular surgery. METHODS AND RESULTS: Patients (n = 136; mean age, 68 years) unable to exercise underwent a dobutamine stress test before surgery (incremental dobutamine infusion [10-40 micrograms.kg-1.min-1] continued with atropine [0.25-1 mg i.v.] if necessary to achieve 85% of the age-predicted maximal heart rate without symptoms or signs of ischemia). The clinical risk profile was evaluated by Detsky's modification of Goldman's risk factor analysis. Echocardiographic images were evaluated by two observers blinded to the clinical data of the patients, and results of the test were not used for clinical decision making. Technically adequate images were obtained in 134 of 136 patients, one major complication occurred (ventricular fibrillation), and three tests were discontinued prematurely because of side effects. Finally, data from 131 patients were analyzed with univariate and multivariate methods. The dobutamine stress test was positive (new or worsened wall motion abnormality) in 35 of 131 patients. In the postoperative period, five patients died of myocardial infarction, nine patients had unstable angina, and one patient developed pulmonary edema. All patients with cardiac complications (15 patients) had a positive dobutamine stress test. No cardiac events occurred in patients with negative tests. Five patients with a technically inadequate or prematurely stopped test were operated on without complications. By multivariate analysis (logistic regression), only age > 70 years and new wall motion abnormalities during the dobutamine test were significant predictors of perioperative cardiac events. CONCLUSIONS: Dobutamine stress echocardiography is a feasible, safe, and useful method for identifying patients at high or low risk of perioperative cardiac events. The test yields additional information, beyond that provided by clinical variables, in patients who are scheduled for major noncardiac vascular surgery.

Adult↗
PubMed1993

Paraplegia following thoracic aortic cross-clamping in dogs. No difference in neurological outcome with a barbiturate versus isoflurane.

BACKGROUND AND PURPOSE: We compared the incidence and severity of paraplegia following thoracic aortic cross-clamping in dogs for two anesthetic regimens. Animals were randomly assigned to receive methohexital (group M; n = 9) or isoflurane (group I; n = 9). We expected a better neurological outcome in animals administered methohexital because of superior neuronal protection and greater spinal cord perfusion pressure (mean arterial pressure below the cross-clamp site minus mean cerebrospinal fluid pressure). METHODS: After surgical preparation and a 30-minute stabilization period, dogs in group M received 14 +/- 6 mg.kg-1 i.v. methohexital to induce an isoelectric electroencephalogram followed by a continuous infusion of methohexital at 20 mg.kg-1 x h-1. Dogs in group I received 1.4 +/- 0.2% end-tidal isoflurane (1 minimum alveolar concentration). The thoracic aorta was then occluded 2.5 cm distal to the left subclavian artery for 30 minutes and then released. Hemodynamics and cerebrospinal fluid pressure were measured at (1) baseline, (2) 2 minutes after aortic cross-clamping, (3) 20 minutes after aortic cross-clamping, (4) 5 minutes after aortic unclamping, and (5) 30 minutes after resuscitation. At 24 hours a neurological assessment was performed. After the clinical assessment the dogs were killed and the spinal cord removed immediately for histopathologic study. RESULTS: There were no differences in nasopharyngeal temperature, PaCO2, pH, or hemoglobin at any time between groups. With cross-clamping, the spinal cord perfusion pressure decreased precipitously. However, there was no difference in spinal cord perfusion pressure between groups at any time (P = .5555). The neurological outcome, assessed at 24 hours after thoracic aortic cross-clamping by a veterinarian unaware of the anesthetic protocol, was not different between groups (P > .5, two-tailed Mann-Whitney rank-sums test). When anesthetized with methohexital 5 of 9 dogs were paraplegic; with isoflurane 7 of 9 dogs were paraplegic. By Spearman's rank test, a strong inverse correlation between the Tarlov score and the ratio of dead to total lumbar anterior spinal cord neurons was seen (Spearman's correlation coefficient = -.8358; P = .0001). CONCLUSIONS: We conclude that no advantage was offered by the choice of anesthesia to neurological outcome after 30 minutes of thoracic aortic cross-clamping in this canine model.

Analysis of Variance↗
PubMed1992

Drug interactions with sufentanil. Hemodynamic effects of premedication and muscle relaxants.

Induction of anesthesia with synthetic opioids is occasionally accompanied by undesirable hemodynamic changes such as tachycardia and hypertension, or bradycardia and hypotension. We hypothesized that drug interactions cause many of these adverse responses. Therefore, we conducted a randomized double-blind study to investigate the interactive effect of premedication and muscle relaxants on the hemodynamic response to induction with intravenous (iv) sufentanil 10 micrograms.kg-1. Eighty patients with left ventricular ejection fraction greater than or equal to 0.40, undergoing elective coronary artery surgery, were premedicated with either morphine 0.1 mg.kg-1 and scopolamine 6 micrograms.kg-1 intramuscularly, or lorazepam 60 micrograms.kg-1 orally, and paralyzed with either pancuronium 0.1 mg.kg-1 or vecuronium 0.1 mg.kg-1 iv. The four treatment groups were SP (morphine-scopolamine + pancuronium), LP (lorazepam + pancuronium), SV (morphine-scopolamine + vecuronium), and LV (lorazepam + vecuronium). Hemodynamics were recorded at three time periods: 1) control, 2) induction, and 3) intubation. Premedication-relaxant interactions significantly affected hemodynamics. In group SP, mean heart rate (HR) increased significantly on induction (56 +/- 11 to 69 +/- 13 beats.min-1), while mean arterial pressure (MAP) and cardiac index (CI) were unchanged. HR, MAP, and CI were significantly higher after induction in group SP compared to the other three groups. In group LP, mean HR increased less than in group SP (56 +/- 8 to 62 +/- 14 beats.min-1), whereas MAP and CI declined significantly. In group SV, HR and CI were unchanged, but MAP declined significantly. In group LV, HR was stable, whereas both MAP and CI declined significantly. The incidence of pharmacologic interventions during the study period also differed significantly among groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Treatment of proximal aortic hypertension after thoracic aortic cross-clamping in dogs. Phlebotomy versus sodium nitroprusside/isoflurane.

Thoracic aortic cross-clamping causes proximal aortic hypertension. Theoretically, the method used to treat hypertension can influence spinal cord perfusion pressure and neurologic outcome. Phlebotomy was compared to sodium nitroprusside/isoflurane in terms of ability to treat increased proximal mean aortic pressure (MAPp) after thoracic aortic cross-clamping in dogs. Dogs were assigned randomly to one of three groups depending on the method used to treat hypertension after cross clamping: 1) phlebotomy (n = 10); 2) sodium nitroprusside/isoflurane (n = 11); and 3) control (no treatment) (n = 8). In each dog, anesthesia was maintained with isoflurane in oxygen, 1.4% end-tidal. The thoracic aorta was occluded 2.5 cm distal to the left subclavian artery for 50 min and then was released. Hemodynamics, cerebrospinal fluid pressure (CSFP), and regional blood flows by the radioactive microsphere technique, were measured at 1) baseline; 2) 2 min after aortic cross-clamping; 3) after treatment of proximal aortic hypertension; 4) 5 min after aortic unclamping; and 5) 30 min after resuscitation. At 24 h, a neurologic assessment was performed. Thoracic aortic cross-clamping increased MAPp, decreased distal MAP (MAPd), and reduced lumbar spinal cord perfusion pressure (SCPPl), [SCPPl = MAPd - CSFP], in all three groups. Control of increased MAPp necessitated removal of 36 +/- 9 ml/kg of blood in the phlebotomy group. In the sodium nitroprusside/isoflurane group, sodium nitroprusside (16 micrograms.kg-1.min-1) was infused and end-tidal isoflurane concentration increased to 2.5 +/- 0.7%, restoring MAPp to baseline level.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Hemodynamic and temperature changes after aortocoronary bypass grafting.

Perioperative hemodynamic and temperature changes were reviewed in 58 patients who underwent aortocoronary bypass grafting. Core temperature showed an immediate decline postoperatively, secondary to core temperature cooling during bypass. Subsequent rewarming occurred over the next 8 to 12 hours, with the temperature often increasing above normal. The reason for this pyrexial response is discussed. The cardiac index was depressed immediately postoperatively, again with substantial recovery within 8 hours. This improvement over time occurred not only because of recovery of intrinsic function but also because of reduction in myocardial work due to falling systemic vascular resistance. The latter was high immediately postoperatively and then consistently fell during the rewarming phase. During the first 8 hours postoperatively there were significant changes in temperature and cardiac and systemic vascular resistance indices. The hemodynamic data correlated strongly with changes in temperature. Falling systemic vascular resistance required the institution of alpha-agonist therapy in 25% of patients.

Aged↗
PubMed1991

Alfentanil pharmacokinetics in patients undergoing abdominal aortic surgery.

The pharmacokinetics of alfentanil, 300 micrograms.kg-1 IV, were determined in patients undergoing elective abdominal aortic reconstruction. The mean age (+/- SD) of the patients was 64.3 +/- 7.4 yr; their mean weight was 74.7 +/- 13.8 kg. Five patients underwent aneurysm repair and six had aortobifemoral grafting. Serum alfentanil concentrations were measured by gas-liquid chromatography in samples drawn at increasing intervals over a 24-hr period. A three-compartment model was fitted to the concentration versus time data. The volume of the central compartment and the volume of distribution at steady state (Vdss) were 0.44 +/- 0.022 and 0.63 +/- 0.32 L.kg-1, respectively. Total drug clearance was 6.4 = 1.9 ml.min-1.kg-1. The elimination half-time was 3.7 +/- 2.6 hr. Patient age was positively correlated with both Vdss and elimination half-time. There were no significant correlations between the pharmacokinetic variables and the duration of aortic cross-clamping, the duration of surgery, or the rate or total volume of IV fluids infused intraoperatively. In general surgical patients, the elimination half-time of alfentanil has been reported to be 1.2-2.0 hr. Although the elimination half-time of alfentanil was longer in patients undergoing abdominal aortic surgery, alfentanil was eliminated much faster than either fentanyl or sufentanil in this patient population.

Age Factors↗
PubMed1991

Phlebotomy reverses the hemodynamic consequences of thoracic aortic cross-clamping: relationships between central venous pressure and cerebrospinal fluid pressure.

In dogs (n = 11) anesthetized with sodium pentobarbital (to an isoelectric EEG), the authors investigated the influence of thoracic aortic cross-clamping (AXC) on systemic hemodynamics and cerebrospinal fluid pressure (CSFP) with concurrent measurement of total brain flow (tCBF) and regional (cervical, thoracic, and lumbar) spinal cord blood flow (SCBF). The effect of phlebotomy (to control the hemodynamic consequences of AXC) on tCBF and SCBF was assessed. Radioactive microspheres were injected at four time periods in each animal: 1) at baseline; 2) with application of the AXC; 3) after phlebotomy, to reduce the proximal mean arterial pressure (MAPp) to baseline values; and 4) 2 min after removal of the AXC (mean AXC time 68 +/- 6 min). With application of the AXC, the MAPp, central venous pressure (CVP), and CSFP significantly increased (104 +/- 6 to 156 +/- 6 mmHg, 3.4 +/- 0.4 to 5.2 +/- 0.7 mmHg, and 3.3 +/- 0.7 to 5.2 +/- 0.8 mmHg, respectively), while distal mean aortic pressure (MAPd) significantly decreased (98 +/- 6 to 14 +/- 1 1 mmHg). Phlebotomy (24 +/- 3 ml.kg-1) significantly decreased MAPp (to 106 +/- 6 mmHg), CVP (to 1.6 +/- 0.6 mmHg), and CSFP (to 1.2 +/- 1.1 mmHg). The CSFP changed in parallel with the changes in CVP, a result suggesting that the alterations in CSFP depended on cardiac preload. The spinal cord perfusion pressure (SCPP; SCPP = MAPd - CSFP) was unchanged after phlebotomy, since both MAPd and CSFP decreased. The tCBF and cervical SCBF were unchanged when MAPp increased by 50% with application of the AXC; this indicated that autoregulation was intact.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

A comparison of desflurane and isoflurane in patients undergoing coronary artery surgery.

Animal studies indicate that desflurane and isoflurane have similar hemodynamic effects when administered in equipotent anesthetic concentrations. The authors compared desflurane and isoflurane, used as primary anesthetics for patients undergoing elective coronary artery bypass surgery whose left ventricular ejection fractions were greater than 0.34. After induction of anesthesia with thiopental (dose 180 +/- 45 mg [mean +/- standard deviation]) and fentanyl, 10 micrograms.kg-1, either desflurane or isoflurane was administered to maintain systolic blood pressure within 70-120% of, and heart rates less than 120% of, the patients' average preoperative values. If adjusting the end-tidal anesthetic concentration within the range of 0-2.0 MAC could not maintain these predefined hemodynamic limits, additional fentanyl or vasoactive drugs were used. Induction and maintenance of anesthesia was accompanied by a significant decrease in mean arterial pressure in both groups (desflurane 97 +/- 12 mmHg at control, decreasing to 71 +/- 5 mmHg during skin preparation; isoflurane 95 +/- 9 mmHg at control, 74 +/- 9 mmHg during skin preparation). One minute after sternotomy, mean arterial pressure in the isoflurane group had returned to control, 97 +/- 9 mmHg, which was significantly greater than in the desflurane group, 87 +/- 12 mmHg. Systolic arterial pressure was also significantly greater in the isoflurane group 1 min after intubation, during skin preparation, and 1 min after sternotomy. Otherwise, the hemodynamic effects of these volatile agents were similar. There were no differences between groups in the incidence of ECG changes indicative of myocardial ischemia prior to cardiopulmonary bypass, perioperative myocardial infarction, or perioperative mortality.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Pharmacokinetics of sufentanil in patients undergoing abdominal aortic surgery.

The authors determined the pharmacokinetics of sufentanil, 12.5 micrograms.kg-1 iv in patients undergoing elective abdominal aortic surgery. The mean age (+/- SD) of the ten patients was 68.4 +/- 7.9 yr; their mean weight was 74.4 +/- 19.1 kg. Six patients underwent aortobifemoral grafting and four had abdominal aortic aneurysm repair. Serum sufentanil concentrations were determined in samples drawn at increasing intervals over a 24-h period. A three-compartment pharmacokinetic model was fit to the concentration versus time data. Total drug clearance was 15.0 +/- 3.2 ml.min-1.kg-1. The volume of distribution at steady-state (Vdss) was 8.7 +/- 4.5 l.kg-1. The elimination half-time were positively correlated with patient age. There were no significant correlations between the pharmacokinetic variables and the duration of aortic cross-clamping, the duration of surgery, or the rate or total volume of iv fluids given intraoperatively. In general surgical patients, the mean elimination half-time of sufentanil has been reported to be 2.7 h. When sufentanil is used in large doses as the primary anesthetic agent for patients undergoing abdominal aortic surgery, the long elimination half-time observed implies that recovery will take much longer than would have been anticipated from previously published pharmacokinetic data.

Aged↗