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Biomedical subjects

R L Royster

Publications and source records attributed to R L Royster.

At least 55 records · Page 3Linked to original sources
PubMed1990

Baseline activated coagulation time should be measured after surgical incision.

The activated coagulation time (ACT) is widely used to guide heparin and protamine dosing during cardiac surgery. A common protocol involves establishing a baseline ACT before administering heparin, then using this ACT as a target value for assessing the adequacy of heparin neutralization after cardiopulmonary bypass. Results vary in previous comparisons of baseline ACT to postprotamine ACT, with some showing postprotamine ACT significantly below baseline values. The present study examined ACTs at three possible baseline intervals in 68 patients at two institutions: (a) before anesthetic induction; (b) after anesthetic induction; and (c) after sternotomy. Baseline ACT decreased significantly with anesthesia and surgery. The poststernotomy baseline ACT best matched the postprotamine ACT. It appears likely that surgery induces a thromboplastic response that decreases ACT. Establishing baseline ACT before anesthetic induction would predispose to false diagnoses of adequate protamine neutralization after cardiopulmonary bypass, because ACT is relatively insensitive to low concentrations of unneutralized heparin. Baseline ACTs should therefore be measured after surgical incision.

Aged↗
PubMed1989

Sufentanil is preferable to etomidate during rapid-sequence anesthesia induction for aortocoronary bypass surgery.

To evaluate rapid-sequence anesthetic induction techniques for aortocoronary bypass grafting, 20 patients scheduled for elective surgery were randomly assigned to receive bolus injections of either etomidate, 0.4 mg/kg, intravenously (IV), or sufentanil, 5 micrograms/kg, IV, with succinylcholine, 1 mg/kg, IV. Patients in the two groups had similar demographic characteristics and baseline (preinduction) hemodynamic values. Following induction and intubation, 8 of 9 etomidate patients required a pharmacologic intervention to treat hypertension and tachycardia, whereas only 1 of 11 sufentanil patients required additional treatment (P less than 0.001). Three of 9 etomidate patients had ST segment changes of new myocardial ischemia following induction and intubation; two other etomidate patients developed Q waves on their postoperative electrocardiograms, indicative of a perioperative myocardial infarction. No sufentanil patient demonstrated either ischemia or infarction. It is concluded that sufentanil-succinylcholine provides more stable hemodynamics and fewer ischemic myocardial events than etomidate-succinylcholine in patients undergoing myocardial revascularization surgery.

Anesthesia, Intravenous↗
PubMed1989

Premedication determines the circulatory responses to rapid sequence induction with sufentanil for cardiac surgery.

Thirty-three patients undergoing elective aortocoronary bypass were allocated randomly to receive morphine 0.1 mg kg-1 i.m. and either lorazepam 50 micrograms kg-1 by mouth or hyoscine 6 micrograms kg-1 i.m. before rapid sequence induction of anaesthesia with sufentanil 5 micrograms kg-1 i.v.and suxamethonium 1 mg kg-1 i.v. Following induction and tracheal intubation, patients premedicated with hyoscine had a significantly higher mean heart rate, mean arterial pressure, cardiac index and left ventricular stroke-work index than patients premedicated with lorazepam. The incidence of new myocardial ischaemia was low in both groups.

Anesthesia, Intravenous↗
PubMed1989

Efficacy of noninvasive transcutaneous cardiac pacing patients undergoing cardiac surgery.

Noninvasive transcutaneous cardiac pacing (NTP) is a rapid, safe, and easily utilized form of emergency cardiac pacing, with hemodynamics similar to right ventricular endocardial pacing. Although the technique has proven effective for hemodynamically significant bradycardias and early use during cardiopulmonary resuscitation, NTP under anesthetic conditions has been poorly characterized. In particular, it is unknown to what degree the multiple physiologic perturbations of cardiac surgery and cardiopulmonary bypass (CPB) affect myocardial thresholds and the efficacy of the unit itself. Patients undergoing procedures utilizing CPB (n = 23) were studied in an effort to address these issues. All patients were able to be paced at all points throughout the 24-h study interval, although four patients developed hemodynamic instability during this period causing their exclusion from additional investigation. Only one patient requested discontinuation from the study due to discomfort. A statistically significant increase in mean current requirements for capture was demonstrated over time (P less than 0.0001), with baseline thresholds being significantly less than other study points (P less than or equal to 0.05). Thresholds following chest wall closure were significantly greater than all other study points (P less than or equal to 0.05), possibly due to accumulation of pericardial and mediastinal air. Multiple measured variables changed significantly during the study, but only increases in cardiac output and core temperature were related to statistically significant increases in current thresholds (P less than or equal to 0.05). Increasing age and pump time were of borderline importance. NTP represents an effective pacing alternative in cardiac surgical patients.

Adult↗
PubMed1988

Cardiac conduction interactions of propranolol and verapamil with halothane in pentobarbitone-anaesthetized dogs.

We have studied the effects of propranolol 0.25 mg kg-1 and verapamil 0.075 mg kg-1 on cardiac conduction and refractoriness in 21 dogs anaesthetized with pentobarbitone 30 mg kg-1 using His bundle electrocardiography and programmed stimulation. After baseline studies under pentobarbitone and halothane (1.3 MAC) anaesthesia, the dogs were allocated randomly to two groups: group 1 received verapamil followed by propranolol; group 2 received propranolol followed by verapamil; the drugs were given in a continuous infusion over 10 min. The atrial-His (AH) interval, the atrioventricular node effective (AVERP), and functional (AVFRP) refractory periods, were prolonged by verapamil in both groups, but not the His-ventricle (HV) interval or the ventricular effective refractory period (VERP). AVFRP and VERP were prolonged by propranolol in both groups. Corrected sinus node recovery times were normal after each drug. Heart rate and the rate required to produce Wenckebach were decreased by each drug. The combination of verapamil and propranolol during halothane anaesthesia in dogs has significant cardiac conduction effects; however, no spontaneous AV block occurred during the study.

Anesthesia, Inhalation↗
PubMed1988

Cardiac electrophysiologic effects of fentanyl and combinations of fentanyl and neuromuscular relaxants in pentobarbital-anesthetized dogs.

The effects of fentanyl, both alone and in combination with pancuronium bromide or succinylcholine, on atrioventricular (AV) node and ventricular conduction times and refractory periods were studied. Twenty-four pentobarbital-anesthetized dogs were instrumented both with an intraaortic catheter to measure cardiac conduction times and, through a thoracotomy, with atrial and ventricular epicardial pacing electrodes to provide premature stimulation that would allow measurement of atrial and ventricular refractoriness. Fentanyl prolonged the RR interval in both low- (100 micrograms/kg) and high-dose (400 micrograms/kg) groups by 26 and 45%, respectively, and prolonged AV node conduction time by 28 and 25%, respectively. During atrial pacing at a rate sufficient to capture the atria, AV node conduction time lengthened in the low- and high-dose groups by 27 and 25%, respectively. Fentanyl also significantly lengthened AV node effective and functional refractory periods and ventricular effective refractory periods in both groups. Pancuronium (0.1 mg/kg) administered after fentanyl shortened RR intervals in the low- and high-dose groups by 14 and 22%, respectively, and shortened AV conduction times by 18 and 20%, respectively, but did not restore all values to baseline. Pancuronium significantly shortened AV node refractory periods in the low-dose but not the high-dose group. When administered after fentanyl, succinylcholine (2 mg/kg) significantly shortened the RR interval in the low- and high-dose groups by 14 and 12%, respectively. Succinylcholine shortened AV node conduction slightly but without significance and had no effect on cardiac refractoriness. His-Purkinje conduction remained unaffected by any drug intervention. These data demonstrate that fentanyl depresses cardiac conduction; subsequent administration of pancuronium and succinylcholine partially reverses this effect.

Animals↗
PubMed1987

Pulmonary artery wedge pressure measurement during experimental pulmonary hypertension: comparison of techniques in relation to catheter-induced hemorrhage.

Two methods of wedging a pulmonary artery catheter were studied in dogs with experimental pulmonary hypertension secondary to left atrial balloon inflation. In Group 1 (N = 8), the catheter tips were located in a branch of the pulmonary artery so that wedge pressures were obtained with balloon inflation. In Group 2 (N = 8), the catheter tips were positioned 1 to 2 cm beyond the pulmonic valve and readvanced into a branch of the pulmonary artery for each wedge pressure determination. In both groups, wedge pressures were obtained using a balloon inflation volume of 0.8 mL. With left atrial hypertension, the pressure gradient across the inflated balloon (calculated as mean pulmonary artery pressure minus pulmonary artery wedge pressure) was lower than baseline (P < .05). Wedge pressures were determined every five minutes. After two hours, the lungs were removed and studied grossly for hemorrhage. The incidence of pulmonary hemorrhage was 50% in Group 1 dogs, but 0% in Group 2 dogs (P < .03). It is concluded that locating the catheter tip in the proximal pulmonary artery and readvancing it for each wedge pressure determination significantly reduces the risk of catheter-induced pulmonary hemorrhage in this model.

Animals↗
PubMed1987

Predicting the pharmacodynamics of heparin: a clinical evaluation of the Hepcon System 4.

The magnitude of the anticoagulation response to heparin (heparin responsiveness) varies substantially from patient to patient. Identifying extremes of sensitivity and resistance prior to intravenous administration of heparin would facilitate anticoagulation for cardiopulmonary bypass (CPB). The performance of the Hepcon System 4 (HemoTec, Inc, Englewood, CO), an instrument designed for that purpose, was tested. Using nonheparinized blood samples from 157 patients scheduled for surgery requiring CPB, this device performed activated coagulation times (ACT) with three different concentrations of in vitro heparin. After determining each patient's in vitro heparin response, the heparin dose predicted to produce ACT values of 480 seconds (group 1, N = 77) or 600 seconds (group 2, N = 80) was administered. Five minutes later each patient's ACT was determined with the Hemochron method (International Technidyne, Inc, Edison, NJ). Simultaneously, several other variables that might predict heparin responsiveness were investigated. When compared with the observed ACT, the Hepcon System 4 inadequately predicted the response. There was considerable scatter in this comparison, but most frequently the in vitro method substantially underestimated the in vivo heparin dose requirement. Heparin responsiveness decreased significantly with high platelet counts and advanced age, but was unaffected by the initial hematocrit, ACT, partial thromboplastin time, or preoperative heparin therapy. Previous investigations have not identified a relationship between advanced age and reduced heparin responsiveness. Combining the Hepcon heparin dose-response in vitro method with the other parameters evaluated, stepwise regression could only account for 39% of the observed variability in heparin responsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1985

Pulmonary artery wedge pressure may fail to reflect left ventricular end-diastolic pressure in dogs with oleic acid-induced pulmonary edema.

We investigated the accuracy with which pulmonary artery wedge pressure (WP) reflected left ventricular end-diastolic pressure (LVEDP) in dogs with oleic acid-induced pulmonary edema. We compared hemodynamic variables before and during edema, as measured from a pulmonary artery catheter placed before oleic acid (PA-1) and from a second catheter (PA-2) placed 2 h after oleic acid infusion. Oleic acid decreased arterial oxygen saturation and cardiac output and increased pulmonary vascular resistance and phasic pulmonary artery pressure. LVEDP did not change after oleic acid, although WP measured by both catheters was increased. In addition, WP measured by PA-2 (7.1 +/- 0.7 mm Hg) was greater than that measured by PA-1 (5.6 +/- 0.5 mm Hg) (p less than or equal to 0.037). Using PA-1, we found that WP increased in a linear manner with LVEDP both before and after pulmonary injury (r2 = 0.91, 0.68, respectively). There was no relationship between LVEDP and WP using PA-2 (r2 = 0.07). We conclude that oleic acid-induced pulmonary edema lessens the accuracy with which WP reflects LVEDP, and that WP from a catheter placed after edema less accurately reflects LVEDP than does WP from a catheter placed before edema.

Animals↗
PubMed1985

Cardiopulmonary effects of hypertonic saline in canine oleic acid-induced pulmonary edema.

Vasoactive drugs may increase intrapulmonary shunt in patients with permeability edema. Because 7.5% hypertonic saline solution has cardiotonic properties, we studied its hemodynamic and pulmonary effects in a canine model of oleic acid-induced lung injury. Immediately after saline infusion, there were increases in cardiac output (2.0 +/- 0.1 to 3.4 +/- 0.2 L/min; p less than .001) and intrapulmonary shunt (50.3 +/- 4.4 to 57.3 +/- 3.2%; p less than .01) without alteration in arterial or mixed venous oxygen tension. Although arterial oxygen content decreased from 16.4 +/- 1.1 to 14.4 +/- 0.9 ml/dl (p less than .001), paralleling the change in hemoglobin concentration, oxygen delivery to the tissues increased from 327 +/- 23 to 486 +/- 36 ml/min (p less than .001). These effects were transient, inasmuch as all values returned to preinfusion levels within 30 min. Tissue oxygen consumption increased proportionately with cardiac output, and the directional change in arterial oxygenation was similar to the change in mixed venous oxygen tension. We conclude that tissue oxygen delivery improves after hypertonic saline infusion despite changes in intrapulmonary shunt and oxygen consumption. However, any benefit appears to be transient.

Animals↗
PubMed1985

Coronary revascularization in patients with bilateral internal carotid occlusions.

Coronary revascularization that is neurologically uneventful in patients with bilateral totally occluded internal carotid arteries has not been previously reported. We performed saphenous vein coronary artery bypass grafting on three such patients and observed them for 6 to 23 months. Preoperatively two of our patients had chronic stable symptoms of cerebrovascular insufficiency, and one had received cerebral revascularization via a superficial temporal-to-middle cerebral artery bypass. Controversy exists regarding proper cerebral protective maneuvers during coronary revascularization for patients with advanced cerebrovascular disease. Cerebral protection for our patients during cardiopulmonary bypass included hypothermia and high perfusion flows and pressures. Two patients also received prophylactic sodium thiopental. None of these three patients had a stroke perioperatively or during the follow-up period. We believe that these case histories strongly suggest that the functional state of the cerebral collateral circulation, as judged by preoperative neurological symptoms, predicts neurological outcome after coronary revascularization better than the specific occlusive anatomy of the extracranial carotid arteries.

Arterial Occlusive Diseases↗