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Biomedical subjects

P S Withington

Publications and source records attributed to P S Withington.

At least 19 recordsLinked to original sources
PubMed2001

Comparison of the hemodynamic effects of milrinone with dobutamine in patients after cardiac surgery.

OBJECTIVE: To compare the hemodynamic effects, efficacy, and safety of intravenous milrinone (M), 50 microg/kg during 10 minutes followed by 0.5 microg/kg/min, with intravenous dobutamine (D), 10 to 20 microg/kg/min, in patients with low cardiac output after cardiac surgery. DESIGN: Randomized, open-label, multicenter study. SETTING: Cardiothoracic surgery departments, operating rooms, and intensive care units in 6 university hospitals. PARTICIPANTS: Patients (n = 120; 60 per group) after elective cardiac surgery. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Analysis compared the hemodynamics at baseline and the percentage change from baseline during 4 hours of the drug infusion. The incidence of adverse events was recorded. Both groups had low mean (+/- SEM) cardiac indices (M, 1.6 ([0.03] L/min/m(2); D, 1.7 [0.03] L/min/m(2)) in association with adequate mean pulmonary capillary wedge pressures (M, 13.7 [1.3] mmHg; D, 12.7 [1.9] mmHg) at baseline. Group M had significantly higher systemic arterial pressures and systemic vascular resistances compared with group D; otherwise, the hemodynamics in both groups were comparable. During the study, hemodynamic responses included the following: group D had greater increases in cardiac index (at 1 hour, D = 55%, M = 36%; p < 0.01), heart rate (at 1 hour, D = 35%, M = 10%; p < 0.001), arterial pressures (mean arterial pressure at 1 hour, D = 31%, M = 7%; p < 0.001), and left ventricular stroke work index (at 1 hour, D = 75%, M = 45%; p < 0.05). Group M had greater decreases in mean pulmonary capillary wedge pressure (at 1 hour, D = -3%, M = -14%; p < 0.05). Comparisons of adverse events showed that dobutamine was associated with a higher incidence of hypertension (D = 40%, M = 13%; p < 0.02) and change of rhythm from sinus to atrial fibrillation (D = 18%, M = 5%; p < 0.04). Milrinone was associated with a higher incidence of sinus bradycardia (D = 2%, M = 13%; p < 0.03). CONCLUSIONS: Milrinone and dobutamine are appropriate and comparable for the pharmacologic treatment of the low- output syndrome after cardiopulmonary bypass.

Adrenergic beta-Agonists↗
PubMed1998

Thoracic electrical bioimpedance: a non-invasive measure of cardiac output for porcine research.

A comparison of two techniques for measuring cardiac output, thermodilution (TD) and thoracic electrical bioimpedance (TEB), was undertaken in a porcine model. Eight anaesthetized large white pigs were studied. A total of 436 paired measurements were performed over a range of cardiac outputs from 1.7 to 15.1 l/min as measured by thermodilution. The Pearson product moment correlation coefficient was r = 0.963 with P < 0.001. Analysis by Bland and Altman statistics revealed a mean difference (bias) of -0.02 l/min and the limits of agreement were +/- 1.6 l/min, similar to figures found in human comparative studies. These results confirm that thoracic electrical bioimpedance is a valid method of measuring cardiac output in pigs. It has significant advantages compared to thermodilution, in particular it is cheap, simple to use, non-invasive and provides continuous data.

Animals↗
PubMed1997

A model of gastric emptying using paracetamol absorption in intensive care patients.

OBJECTIVES: To describe the range and factors which may affect gastric emptying in the ICU patient. DESIGN: Validation sample. SETTING: The adult Intensive Care Unit (ICU) of a teaching hospital. PATIENTS: Twenty-seven ICU patients, aged 18-65 years were studied within 3 days of their ICU admission. All patients had normal hepatic and renal chemistry and had no contraindications to enteral feeding. MEASUREMENTS AND MAIN RESULTS: The area under the concentration curve from 0-60 min (AUC60) of a paracetamol absorption test was used as the measure of gastric emptying. The variables of the presence or absence of bowel sounds, volume of gastric aspirate ( > 50 ml or < 50 ml), an estimated risk of death (ROD), an APACHE II score calculated 24 h before the study, a pHi measurement, the use of dopamine (2.5-5 microg/kg, yes or no) and of opioids were included in a multiple regression analysis. Using Pearson correlation, AUC60 was positively correlated with the estimated ROD (r = 0.50, p < 0.05). There was a statistically significant difference in the mean AUC60 between those patients who did, and those who did not, receive dopamine (t = 3.06, p < 0.005). On multiple regression analysis the only variable which was significantly associated with AUC60 was estimated ROD, which accounted for 25% of the variance in AUC60. CONCLUSION: The results suggest that there is a wide range in gastric emptying in critically ill patients. The results may be due to the case mix of the patients. The use of dopamine may adversely affect gastric emptying and requires further investigation in the ICU patient. Prediction of gastric emptying is difficult in these patients and further investigation is necessary in order to improve our understanding of this process.

APACHE↗
PubMed1997

Validation of thoracic electrical bioimpedance as a porcine research tool.

We have compared the accuracy of two methods of measuring cardiac output, thoracic electrical bioimpedance (TEB) and thermodilution (TD), in pigs. We studied four anaesthetized pigs, producing 145 paired cardiac output values over a range of TD cardiac outputs of 2.6-12.6 litre min-1. TEB cardiac output was less than that measured by TD, by a constant factor throughout the observed range of values, because of differences in porcine thoracic shape. The Pearson product moment correlation coefficient suggested a good correlation (r = 0.984, P < 0.001). More importantly, analysis by the Bland and Altman statistical method suggested a high level of agreement, with 95% confidence intervals of +/- 1.0 litre min-1. These results suggest that TEB can be used as a satisfactory method to measure cardiac output in porcine models.

Animals↗
PubMed1997

Double-blind, randomized study of the effect of cisapride on gastric emptying in critically ill patients.

OBJECTIVES: To investigate the absorption of the gastrokinetic drug, cisapride, and effect of cisapride on gastric emptying in critically ill patients; and to assess the usefulness of clinical signs of gastric emptying. DESIGN: Prospective, randomized, controlled study. SETTING: Medical/surgical/trauma intensive care unit (ICU) in a university hospital. PATIENTS: Twenty-seven consecutively enrolled patients, aged 18 to 65 yrs, with normal hepatic and renal biochemistry who were not receiving enteral nutrition and who had no contraindications to enteral nutrition. These patients were expected to stay in the ICU for at least 4 days. INTERVENTIONS: Patients were randomized to receive either placebo or rectal cisapride, 60 mg initially followed by two doses of 30 mg at 8-hr intervals. MEASUREMENTS AND MAIN RESULTS: Gastric emptying was estimated, using acetaminophen absorption on day 1 of the study. Placebo or cisapride was administered and a second acetaminophen absorption test for gastric emptying was carried out on day 2,24 hrs after the first test. Four patients were excluded because of incomplete data. Statistical analysis was performed, using the area under the acetaminophen absorption curve from 0 to 60 mins as the primary measure of gastric emptying. There was no significant change in the area under the acetaminophen absorption curve from 0 to 60 mins from day 1 to day 2 in patients who received placebo or cisapride. Using the combination of the time to maximum acetaminophen concentration (< or = 30 mins) with a maximum concentration (> 12 mg/L) to define "normal" emptying, on day 1, four of the 11 placebo patients had the "normal" gastric emptying, and by day 2, five patients fulfilled this criterion. Before administration of cisapride, four of the 12 patients fulfilled this criterion, whereas nine fulfilled the criterion after receiving cisapride. There was a large variation in gastric emptying from day 1 to day 2; a power calculation suggests that approximately 150 patients would have to be studied to determine the effect of cisapride. There was no correlation between gastric emptying and the volume of gastric aspirate or the presence of bowel sounds. Plasma cisapride concentrations 4 hrs after the third dose, during the second acetaminophen absorption test, averaged 53 ng/mL (range 20 to 111). CONCLUSIONS: Rectal cisapride in the dose given achieved average plasma concentrations similar to those concentrations achieved in healthy subjects after 30 mg of cisapride rectally. There is a large variation in gastric emptying from one day to the next and large numbers of patients are required to determine if cisapride administration improves early gastric emptying in critically ill patients. The volume of gastric aspirate and the presence of bowel sounds do not correlate with gastric emptying.

Administration, Rectal↗
PubMed1996

The effect of casemix adjustment on mortality as predicted by APACHE II.

OBJECTIVE: To describe the effect of casemix on mortality as predicted by APACHE II scoring. DESIGN: Retrospective analysis of an ICU database. PATIENTS AND PARTICIPANTS: All patients admitted to 19 ICU between 1 January 1992 and 31 May 1994 on whom data had been entered into a database. Excluded from the analysis were those readmitted to ICU, those aged under 16 years, those admitted after cardiac surgery or with burns, those for whom physiological data was incomplete and those for whom hospital outcome was unknown. Data on the remaining 6258 patients are reported. MEASUREMENTS AND RESULTS: APACHE II scores were calculated from the worst values within 24 h of ICU admission. Hospital mortality was predicted with the published equation and coefficients. Mortality ratios (observed hospital deaths divided by predicted hospital deaths) were calculated for various groups. Mortality ratios varied widely by subgroup, and observed hospital deaths were greater than predicted, particularly for the following patient groups: those with predicted mortality of less than 70%, those with APACHE II scores in the range of 5-19, those older than 55 years, those with a Glasgow Coma Score of 15 or in the range 9-14, those not having emergency surgery, those with either 0 or 4 chronic health points and those in non-operative respiratory or neurological categories. The mortality ratio was markedly less than 1.0 only among non-operative cardiovascular patients. CONCLUSIONS: APACHE II did not accurately adjust for casemix in our data. Unless account is taken of differences in casemix, using mortality ratios to compare ICU is likely to be inaccurate and misleading.

APACHE↗
PubMed1996

Mortality predicted by APACHE II. The effect of changes in physiological values and post-ICU hospital mortality.

The contribution of physiological values to the APACHE II score was determined by retrospective analysis of 11348 patients undergoing intensive care. Eleven physiological variables contributed a mean of 8.9 points, 54% of the total APACHE II score. The mortality ratio (observed hospital mortality/hospital mortality predicted by APACHE II) was 1.13. We altered the APACHE II scores and post-intensive care hospital mortality in order to examine the effect on the mortality ratio of these changes. Increasing scores by two or four points decreased mortality ratios to 1.00 and 0.89 respectively: decreasing scores by two or four points to a minimum of zero increased mortality ratios to 1.27 and 1.44 respectively. A 25% increase or decrease in post-intensive care hospital mortality changed mortality ratios to 1.21 and 1.05 respectively. Physiological values vary with the timing of collection and accuracy of recording. Small consistent differences in scores cause potentially important changes in the mortality ratio. Unless data collection and the effect of management before and after intensive care are standardised, using mortality ratios to compare intensive care units is likely to be inaccurate and misleading.

APACHE↗
PubMed1995

Right ventricular failure in patients requiring left ventricular assistance.

Right ventricular failure may complicate isolated left ventricular assistance. In a series of 8 patients undergoing left ventricular assistance in postcardiotomy cardiogenic shock, right ventricular failure developed in 5, directly contributing to death in all cases despite initially satisfactory support. Difficulty in grafting a dominant right coronary artery was a common factor in all cases. Early consideration should be given to biventricular support under these circumstances.

Aged↗
PubMed1995

The cerebral function monitor (CFM) is a useful addition to a bilateral carotid artery, vein graft model.

Following human coronary artery bypass surgery, vein graft occlusion is a major cause of morbidity and mortality. An agent is required which will reduce the incidence of early graft thrombosis without causing systemic bleeding. To assess the efficacy of such agents a suitable experimental vein-graft model is required. A porcine, unilateral saphenous vein-carotid artery bypass graft model has been described previously, although to assess the effect of locally applied anticoagulant drugs, insertion of grafts bilaterally would be advantageous, allowing treated and control grafts to be implanted in the same animal which would then act as its own control. Pigs are reported as having an excellent collateral cerebral circulation and hence in theory, would be suitable animals to use as a bilateral carotid vein-graft model. This paper describes the occurrence of serious neurological complications during the development of such a model and suggests that by using a cerebral function monitor, detection of critical reductions in cerebral perfusion can be made early and remedial action take.

Animals↗
PubMed1993

The measurement of right ventricular ejection fraction by thermodilution. A comparison of values obtained using differing injectate ports.

Thermodilution measurements of cardiac output and right ventricular ejection fraction were obtained using a rapid response pulmonary artery catheter. Values were compared when injectate was administered via either a cannula within the right internal jugular vein or the dedicated right atrial port of the pulmonary artery catheter. Mean (SD) bias for cardiac output and right ventricular ejection fraction measurements were 0.08 (0.32) l.min-1 and 2.6 (6.6)% respectively. We therefore conclude that both injectate techniques will provide similar values for cardiac output but dissimilar values for right ventricular ejection fraction measurement.

Cardiac Output↗
PubMed1992

Initial evaluation of an intracorporeal oxygenation device.

We describe a recently developed intracorporeal gas transfer device, its potential applications and hazards. To date, patients with potentially reversible respiratory failure have been treated with controlled oxygen therapy and positive pressure ventilation, but this treatment may itself contribute to lung parenchymal damage from barotrauma and oxygen toxicity. Total or partial extracorporeal gas exchange can be used to reduce these risks, but this treatment is complex and has significant morbidity and mortality. This gas exchange device has been designed to provide partial gas transfer with simplicity of insertion and use. The oxygenator lies in the vena cava to provide prepulmonary gas exchange. In preliminary studies with three calves we have shown that the device increases both mean mixed venous and arterial oxygen content and reduces mean arterial carbon dioxide tension.

Adult↗
PubMed1991

Support when gas exchange fails--ECMO, ECCO2R and IVOX.

The principles and problems of extracorporeal respiratory support (extracorporeal membrane oxygenation and extracorporeal carbon dioxide removal) are reviewed. The recent development of intravenous oxygenation (IVOX) is noted and compared with existing forms of extracorporeal support.

Age Factors↗
PubMed1990

The use of an implantable left ventricular assist device following irreversible ventricular fibrillation secondary to massive myocardial infarction.

A TCI1 rough surface left ventricular assist device (LVAD) was implanted in a 47-year-old man who had sustained a recent massive myocardial infarction complicated by ventricular failure which remained unresponsive to intra-aortic balloon pump therapy and which was further complicated by irreversible ventricular fibrillation. Following implantation of the device and while awaiting a suitable donor organ for transplantation, further extension of the previous infarct resulted in left ventricular rupture and massive haemorrhage which led to his death. We report the successful use of the device in providing haemodynamic support, but caution against inordinate delay in bridging to transplantation patients who are at risk of extension of infarction.

Heart-Assist Devices↗
PubMed1989

Glycopyrronium requirements for antagonism of the muscarinic side effects of edrophonium.

We have compared, in 60 adult patients, the cardiovascular effects of glycopyrronium 5 micrograms kg-1 and 10 micrograms kg-1 given either simultaneously or 1 min before edrophonium 1 mg kg-1. Significant differences between the four groups were detected (P less than 0.001). Both groups receiving 10 micrograms kg-1 showed increases in heart rate of up to 30 beat min-1 (95% confidence limits 28-32 beat min-1). Use of glycopyrronium 5 micrograms kg-1 provided greater cardiovascular stability and, given 1 min before the edrophonium, was sufficient to minimize early, edrophonium-induced bradycardias. This low dose of glycopyrronium provided good control of oropharyngeal secretions.

Adult↗