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Biomedical subjects

W M Weightman

Publications and source records attributed to W M Weightman.

17 recordsLinked to original sources
PubMed2005

The relationship between oxygenator exhaust P(CO2) and arterial P(CO2) during hypothermic cardiopulmonary bypass.

During cardiopulmonary bypass the partial pressure of carbon dioxide in oxygenator arterial blood (P(a)CO2) can be estimated from the partial pressure of gas exhausting from the oxygenator (P(E)CO2). Our hypothesis is that P(E)CO2 may be used to estimate P(a)CO2 with limits of agreement within 7 mmHg above and below the bias. (This is the reported relationship between arterial and end-tidal carbon dioxide during positive pressure ventilation in supine patients.) During hypothermic (28-32 degrees C) cardiopulmonary bypass using a Terumo Capiox SX membrane oxygenator, 80 oxygenator arterial blood samples were collected from 32 patients during cooling, stable hypothermia, and rewarming as per our usual clinical care. The P(a)CO2 of oxygenator arterial blood at actual patient blood temperature was estimated by temperature correction of the oxygenator arterial blood sample measured in the laboratory at 37 degrees C. P(E)CO2 was measured by connecting a capnograph end-to-side to the oxygenator exhaust outlet. We used an alpha-stat approach to cardiopulmonary bypass management. The mean difference between P(E)CO2 and P(a)CO2 was 0.6 mmHg, with limits of agreement (+/-2 SD) between -5 to +6 mmHg. P(E)CO2 tended to underestimate P(a)CO2 at low arterial temperatures, and overestimate at high arterial temperatures. We have demonstrated that P(E)CO2 can be used to estimate P(a)CO2 during hypothermic cardiopulmonary bypass using a Terumo Capiox SX oxygenator with a degree of accuracy similar to that associated with the use of end-tidal carbon dioxide measurement during positive pressure ventilation in anaesthetized, supine patients.

Blood Gas Analysis↗
PubMed2001

Low serum S100beta protein levels following coronary artery surgery with or without cardiopulmonary bypass.

BACKGROUND: S100beta protein has been used as a serum marker of brain injury during cardiac surgery. Previous studies may have been confounded by the re-transfusion of shed mediastinal blood, which has a high concentration of S100beta. AIM: To examine serum S100beta levels in coronary artery surgery patients in whom re-transfusion of shed mediastinal blood was avoided, and to compare levels with and without cardiopulmonary bypass (CPB). METHODS: Serum S100beta levels were measured preoperatively, pre-heparin, post-protamine and 24 h postoperatively in 31 patients undergoing elective coronary artery surgery with (n = 14) or without (n = 17) CPB. The postoperative values were compared to their preoperative controls using two-tailed paired t-tests. RESULTS: There was a minor increase in serum S100beta post-protamine in the CPB group only (0.41 ng/mL; P < 0.01). All other levels in both groups were within normal limits. CONCLUSIONS: Coronary artery surgery without CPB is not associated with an increase in serum S100beta. The observed increase in the CPB group was four- to ninefold lower than levels previously reported. A possible explanation for the lower level was the avoidance of retransfusing shed mediastinal blood. If elevated S100beta levels are thought to represent a cerebral insult caused by CPB, the magnitude of the insult might be less than previously assumed.

Journal Article↗
PubMed2001

The effects of recent aspirin ingestion on platelet function in cardiac surgical patients.

OBJECTIVE: To examine the effects of the preoperative aspirin-free interval on platelet function in cardiac surgical patients. DESIGN: Prospective clinical investigation. SETTING: University-affiliated teaching hospital. PARTICIPANTS: Patients undergoing elective coronary artery bypass graft surgery (n = 100). INTERVENTIONS: The patients were divided into 3 groups based on the number of days since they last ingested aspirin: < or =2 days, 3 to 7 days, and >7 days. Preoperative platelet function was assessed in all patients using platelet aggregation responses to arachidonic acid, 5 microg/mL, and Platelet Function Analyser (PFA100) collagen/epinephrine closure times. MEASUREMENTS AND MAIN RESULTS: Patients who ceased aspirin < or =2 days preoperatively had weaker platelet aggregation responses (18.5% +/- 7% maximum aggregation, mean +/- SD, n = 36) than patients who ceased aspirin 3 to 7 days preoperatively (68.8% +/- 29%, n = 48, p < 0.001) or >7 days preoperatively (68.3% +/- 28%, n = 16, p < 0.001). Similarly, patients who ceased aspirin < or =2 days preoperatively had longer PFA100 closure times (168 +/- 52 sec) than patients who ceased aspirin 3 to 7 days preoperatively (122 +/- 43 sec, p < 0.001) or >7 days preoperatively (128 +/- 42 sec, p < 0.01). The percentage of abnormal responses was also greatest in the aspirin < or =2 days group. CONCLUSION: Cardiac surgical patients who ingest aspirin < or =2 days preoperatively have greater impairment of platelet function than patients who have a longer preoperative aspirin-free interval.

Aged↗
PubMed1999

Drug therapy before coronary artery surgery: nitrates are independent predictors of mortality and beta-adrenergic blockers predict survival.

UNLABELLED: We conducted this study to evaluate whether there is an association between preoperative drug therapy and in-hospital mortality in patients undergoing coronary artery graft surgery. We collected data on 1593 consecutive patients undergoing coronary artery surgery. The relative risk of in-hospital mortality was determined by logistic regression with in-hospital mortality as the dependent variable, and independent variables that included known risk factors and preoperative cardioactive or antithrombotic drug treatment, i.e., age; left ventricular function; left main coronary artery disease; urgent priority; gender; previous cardiac surgery; concurrent cardiovascular surgery; chronic lung disease; creatinine concentration; hemoglobin concentration; diabetes; hypertension; cerebrovascular disease; recent myocardial infarction; prior vascular surgery; number of arteries bypassed; and regular daily treatment with beta-blockers, aspirin within 5 days, calcium antagonists, angiotensin converting enzyme (ACE) inhibitors, digoxin, or warfarin. In-hospital mortality was 3.3%. The relative risk of in-hospital mortality (with 95% confidence intervals of the relative risk) associated with the following drug treatments was: nitrates 3.8 (1.5-9.6), beta-blockers 0.4 (0.2-0.8), aspirin within 5 days 1.0 (0.5-1.9), calcium antagonists 1.1 (0.6-2.1), ACE inhibitors 0.8 (0.4-1.5), digoxin 0.7 (0.2-1.8), and warfarin 0.3 (0.1-1.6). We conclude that in-hospital mortality is positively associated with preoperative nitrate therapy and negatively associated with beta-adrenergic blocker therapy. A significant association between in-hospital mortality and the preoperative use of calcium antagonists, ACE inhibitors, aspirin, digoxin, and warfarin was not confirmed. IMPLICATIONS: We examined the association between common drug treatments for ischemic heart disease and short-term survival after cardiac surgery using a statistical method to adjust for patients' preoperative medical condition. Death after surgery was more likely after nitrate therapy and less likely after beta-blocker therapy.

Adrenergic beta-Antagonists↗
PubMed1998

Evaluation of the TAS coagulation analyzer for monitoring heparin effect in cardiac surgical patients.

OBJECTIVE: To assess the relationship between the Thrombolytic Assessment System (TAS); (Cardiovascular Diagnostics, Inc, Raleigh, NC) measurements and heparin levels in cardiac surgical patients. DESIGN: Equipment evaluation in vitro and in vivo. SETTING: A university teaching hospital. PARTICIPANTS: Sixty adult patients undergoing elective cardiac surgery requiring cardiopulmonary bypass (CPB). INTERVENTIONS: Part 1: Simultaneous heparin management tests (HMTs) and activated coagulation times (ACTs) were measured in 20 patients pre-CPB, during CPB, and post-CPB. In the same patients, the effect of heparin, 1 to 5 IU/mL, on the HMT was assessed in vitro. The effect of aprotinin, 50 to 200 KIU/mL, on the HMT, was assessed in vitro in a further 10 patients. Part II: Simultaneous TAS and laboratory (LAB) activated partial thromboplastin times (APTTs) were measured pre-CPB and post-CPB in 20 patients. In the same patients, the effect of heparin, 0.1 to 0.5 IU/mL, on the TAS APTT was assessed in vitro. The effect of aprotinin on the TAS APTT was assessed in vitro in a further 10 patients. MAIN RESULTS: Part I: Heparin, 0, 1, 2, and 5 IU/mL in vitro resulted in HMTs of 164 +/- 12, 281 +/- 19, 338 +/- 16, and 436 +/- 33 seconds (mean +/- standard deviation [SD]), respectively. The HMT had less variability than the ACT in vivo. Part II: Heparin, 0, 0.1, 0.2, and 0.5 IU/mL in vitro, resulted in TAS APTTs of 34.9 +/- 4.7, 61.2 +/- 2.5, 97.4 +/- 34.7, and 197.1 +/- 64.3 seconds, respectively. The correlation (r) between the TAS and LAB APTT was 0.726 pre-CPB and 0.794 post-CPB. Aprotinin increased both the HMT and TAS APTT in a dose-related manner. CONCLUSION: The TAS may be a useful monitor of heparin effect in cardiac surgical patients.

Adult↗
PubMed1997

Risk prediction in coronary artery surgery: a comparison of four risk scores.

OBJECTIVE: To determine which of four proposed risk scores best predicts immediate outcome of cardiac surgery. DESIGN: Observational cohort study. SETTING: Sir Charles Gairdner Hospital (a university teaching hospital), Perth, Western Australia, 18 March 1993 to 5 March 1996. SUBJECTS: 927 consecutive patients undergoing surgery for coronary artery disease. OUTCOME MEASURES: Patient risk scores (by methods of Parsonnet et al., Higgins et al., Tremblay et al. and Tu et al.); in-hospital mortality; postoperative hospital stay > 14 days; receiver operating characteristic (ROC) curves comparing sensitivity and specificity in predicting adverse outcomes for each risk score. RESULTS: In-hospital mortality rate was 3.5% and mean postoperative hospital stay was 10.7 days. The four scores had similar predictive abilities, with mean areas under the ROC curves (95% confidence intervals) for mortality and postoperative stay > 14 days, respectively: 0.70 (0.62-0.78) and 0.70 (0.65-0.75) for the Parsonnet score; 0.68 (0.59-0.77) and 0.70 (0.64-0.75) for the Higgins score; 0.68 (0.59-0.77) and 0.67 (0.62-0.73) for the Tremblay score; and 0.68 (0.60-0.76) and 0.69 (0.64-0.75) for the Tu score. CONCLUSION: Any of the scores may be used to estimate perioperative risk and to compare outcome between coronary surgery units, but none has sufficient specificity and sensitivity to identify specific individuals who will experience an adverse outcome. Further development of risk assessment is needed before adverse outcome can be accurately predicted in cardiac surgical patients.

Aged↗
PubMed1996

Sensitivity and specificity of the Hemochron, Hemotec and APTT for the detection of low concentrations of heparin.

This study compared two bedside methods recommended for the detection of low concentrations of heparin and the activated partial thromboplastin time (APTT), with reference to a laboratory measure of heparin concentration. Patients undergoing cardiopulmonary bypass had blood drawn at four stages when low levels of heparin could be expected. At each stage four tests were performed: whole blood clotting time using a Hemochron analyser with a Saline-Rinsed test cartridge, whole blood clotting time using a Hemotec analyser with a High Range Heparinase test cartridge, APTT, and heparin concentration by polybrene neutralization. Thirty patients were studied. The sensitivity of the Saline-Rinsed Hemochron, Hemotec High Range Heparinase, and APTT in detecting concentrations of heparin less than 1 U/ml was 38%, 40% and 97%, respectively, while specificities were 87%, 90%, and 30%, respectively. Neither the Saline Rinsed Hemochron, nor the Hemotec Heparinase cartridge reliably detected concentrations of heparin less than 1 U/ml.

Anticoagulants↗
PubMed1992

Functionally crossed pipelines. An intermittent condition by a faulty ventilator.

Unexpectedly high blood oxygen tension in intensive care patients occurring over a 5-year period were found to have been caused by an apparently normally functioning ventilator which was intermittently acting as a conduit between the oxygen and air pipelines. Responses to a circular letter sent to Quality Control Pharmacists in England and Wales suggest that similar faults may have occurred at least five times in the past 10 years. Recommendations are given for the prevention of this problem, including monitoring of gas pipeline composition.

Accident Prevention↗
PubMed1987

Comparison of propofol and thiopentone anaesthesia (with special reference to recovery characteristics).

Thiopentone and propofol were used for the induction and maintenance of anaesthesia in unpremedicated patients undergoing minor gynaecological procedures. There were no significant differences in the induction and maintenance characteristics except for a high incidence of pain on injection and a greater fall in the mean systolic blood pressure associated with propofol in comparison with thiopentone. Propofol was associated with a quicker early recovery as well as a faster psychomotor recovery, as tested by a peg-board. However, complete psychomotor recovery was not achieved for up to three hours in some patients receiving propofol and so caution is advised regarding the early street fitness of patients receiving repeated doses of the drug for day case surgery.

Adolescent↗