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Biomedical subjects

R C Cork

Publications and source records attributed to R C Cork.

At least 19 recordsLinked to original sources
PubMed1999

The incidence of fetal heart rate changes after intrathecal fentanyl labor analgesia.

UNLABELLED: We performed a retrospective review to compare the incidence of new fetal heart rate abnormalities after institution of either intrathecal fentanyl or conventional epidural labor analgesia. In chronological order, the first 100 parturients in active labor who had received epidural analgesia and had recorded fetal heart rate (FHR) traces for 30 min before and after injection were identified, as were the first 100 parturients who had received intrathecal fentanyl analgesia. A perinatologist blinded to the anesthetic technique evaluated each recording and identified any changes in the FHR between the before and after tracings. The incidence of new "negative" (implying worsened fetal status) changes was 6% in the epidural group and 12% in the intrathecal group (P > 0.05, not significant). There were no differences in incidence or degree of blood pressure change, need for cesarean delivery, neonatal outcome, parity, or oxytocin use. No parturient required urgent or emergent cesarean delivery, and all changes resolved within the 30-min observation period. A much larger study would be required to determine whether this six percentage point difference represents a true difference between groups, and its clinical significance. IMPLICATIONS: We compared the incidence of fetal heart rate changes after two techniques of labor analgesia. Both techniques were associated with a low (6%-12%) incidence of changes, but a much larger series would be required to determine whether this represents a true difference. No difference in neonatal outcome was found.

Adult↗
PubMed1998

Effects of severe hypoxemia on mesenteric blood flow in neonatal piglets.

BACKGROUND: The purpose of this work was to determine the effects of hypoxemia on systemic hemodynamic variables and regional conduit arterial blood flows in neonatal piglets. MATERIALS AND METHODS: Using transit time blood flow probes, cardiac output and cranial mesenteric artery blood flow were monitored in groups of prematurely delivered (90% of term gestational age) and 2-week-old piglets prior to, during, and after exposure to a 30-min hypoxic (FIO2 = 0.12) challenge. RESULTS: The documented alterations in systemic mean arterial pressure and cardiac output pressure during hypoxia and reoxygenation were consistent with the maturational age of the animals. In response to hypoxia, all animals demonstrated significant reductions in mesenteric blood flow, with returns to baseline levels during the 30-min reoxygenation phase. In still other prematurely delivered piglets, nutrient mesenteric arterial blood flows were measured using in vivo videomicroscopy. The marked hypoxemia-induced decline in mucosal blood flow was reversed by reoxygenation. CONCLUSIONS: The physiologic mechanisms responsible for neonatal mesenteric vasoactive responsiveness are present in conduit and in nutrient vessels well prior to birth and can be activated by a significant perturbation. These observations are germane insofar as they provide a stable, age-matched acute animal model to study neonatal intestinal ischemic diseases, including necrotizing enterocolitis.

Animals↗
PubMed1998

The dose-response relation of intrathecal fentanyl for labor analgesia.

BACKGROUND: This study determined the dose-response relation of intrathecal fentanyl for labor analgesia and described the onset, duration, and quality of analgesia when used as the sole analgesic. METHODS: Eighty-four parturients in active labor who requested analgesia were randomized to one of seven treatment groups. They received 5-45 microg intrathecal fentanyl as part of a combined spinal-epidural technique. Visual analog pain scores were recorded before and at intervals after injection patients requested additional analgesia. The occurrence and severity of pruritus, nausea, and vomiting were also recorded. Maternal blood pressure was recorded before injection and at intervals after injection. Fetal heart rate was recorded before and 30 min after injection. RESULTS: By 5 min after injection, pain scores were significantly different among groups (P < 0.001). Mean duration of analgesia increased to 89 min as the dose increased to 25 microg. Maternal diastolic blood pressure was significantly lower 10 and 30 min after injection. There was no difference among groups in the incidence of pruritus; nausea and vomiting were uncommon. Fetal heart rates did not change after injection. A dose-response curve indicates that the median effective dose of intrathecal fentanyl for labor analgesia is 14 microg (95% confidence interval, 13-15 microg). CONCLUSIONS: Intrathecal fentanyl produces rapid, profound labor analgesia with minimal side effects. These data indicate that there is little benefit to increasing the dose beyond 25 microg when it is used as the sole agent for intrathecal labor analgesia.

Adult↗
PubMed1996

Characterization of alpha-adrenoceptor activity in the preterm piglet mesentery.

To characterize neonatal mesenteric alpha-adrenoceptor populations, an extracorporeal perfusion circuit was established to control intestinal blood flow in prematurely delivered (by cesarean section at 90% of gestational age) piglets. Activation of alpha 1-adrenoceptors was documented by observing dose-dependent increases in mesenteric perfusion pressure after intramesenteric arterial injection of methoxamine; alpha 2-adrenoceptor activity was confirmed by finding similar increases in mesenteric perfusion pressure after intramesenteric arterial injections of BHT 933. Peripheral intravenous injections of WB 4101 (a competitive alpha 1A-adrenoceptor antagonist), but not clorethylclonidine (CEC, an alpha 1B-adrenoceptor antagonist), significantly blunted (P < .05, ANOVA) the mesenteric vasoconstrictor responses to methoxamine. The mesenteric vasoconstrictor response to BHT 933 (an alpha 2-adrenoceptor agonist) also was blunted by WB 4101, but not by CEC. These data suggest that alpha 1A- and alpha 2-adrenoceptors can be activated in the small intestinal mesentery of piglets well before they reach full-term maturation, although receptor specificity has not been fully established.

Adrenergic alpha-Agonists↗
PubMed1996

Is there implicit memory after propofol sedation?

Recent evidence indicates that implicit memory may be preserved during general anaesthesia. We tested for the presence of explicit and implicit memory in patients undergoing surgical procedures with local or regional anaesthesia and sedation with propofol. Initial i.v. boluses of propofol 0.5 mg kg-1 and fentanyl 1 microgram kg-1 were administered, followed by an infusion of propofol 50 micrograms kg-1 min-1. Administration of one or more doses of propofol 30 mg i.v. during operation was controlled either by the patient or the anaesthetist. At the start of the last skin stitch, patients were presented with a list of 15 stimulus words and the most frequently associated response. The infusion was then discontinued. After 1 h in the recovery area, all patients were tested for free recall, free association, cued recall and recognition on the list presented during surgery (critical list) and a matched list not presented (neutral list). Data of all patients without free recall (explicit memory) were analysed with repeated-measures analysis of variance. Of 36 patients, five demonstrated free recall. For the remaining 31 patients, cued recall and recognition showed no evidence of explicit memory. However, the free association tests demonstrated significant priming. The mean number of critical free associations was 6.6 (SEM 0.4) compared with 5.5 (0.4) neutral free association (P < 0.05). In the absence of explicit memory, implicit memory persists after intraoperative sedation with propofol.

Adult↗
PubMed1995

Asymptomatic undetected mediastinal mass: a death during ambulatory anesthesia.

T-cell lymphoma is the fastest growing non-Hodgkin's lymphoma occurring in children. Its clinical presentation is frequently abrupt, and total tumor mass can double every few days. At the same time, the number of ambulatory anesthesia procedures for children is increasing at a rapid rate. Anesthesiologists are constantly faced with decisions regarding the adequacy of available preoperative information. What information do we need, and how recent should it be? This case shows that recent diagnostic imaging studies not showing the presence of a mediastinal lymphoma can be misleading. It provides a strong warning to all anesthesiogists involved in ambulatory anesthesia.

Ambulatory Surgical Procedures↗
PubMed1995

The effect of esmolol given during cardiopulmonary bypass.

beta-Adrenergic antagonism decreases the size of myocardial infarction and provides myocardial protection during hypothermic arrest for cardiac surgery. However, concern regarding the negative inotropic and chronotropic effects of beta-adrenergic antagonism persisting after cardiopulmonary bypass (CPB) has impeded the use of esmolol for this purpose during cardiac surgery. This is a randomized, double-blind prospective study of the effects of esmolol infused during CPB and the effects of hypothermic CPB on esmolol. Patients scheduled for CPB were randomized to receive intravenous esmolol (300.micrograms.kg-1.min-1 during CPB after a bolus of 2 mg/kg prior to CPB) or placebo. Infusion was stopped at 10 min after release of aortic cross-clamp. Hemodynamics were measured, as well as serum esmolol, catecholamines, lactate, and potassium. Postoperative variables measured included electrocardiographic changes, creatine kinase (CK)-MB fractions, post-CPB dysrhythmias and drugs, hospitalization time and cost, and mortality. Esmolol was administered to 16 patients and placebo to 14. Esmolol levels reached a high of 10.5 +/- 0.9 micrograms/mL during CPB, but decreased to 0.1 +/- 0.02 microgram/mL within 30 min after stopping infusion. Cardiac indices (cardiac index, stroke volume index, left cardiac work index, left ventricular stroke work index, right cardiac work index, and right ventricular stroke work index) were higher in the esmolol group for the first hour post-CPB (P < 0.05). Systemic arterial lactate and coronary sinus lactate were lower in the esmolol group after CPB (P < 0.05), but myocardial lactate extraction was not significantly different between groups. After CPB, hemoglobin was lower in the esmolol group (P < 0.05) due to longer CPB and aortic cross-clamp time (P < 0.05), but oxygen consumption was less than in the control group (P < 0.05). Post-CPB serum potassium was higher in the esmolol group (P < 0.05). Results are confounded by more chronically beta-adrenergically blocked patients randomized to the esmolol group (P < 0.05). Esmolol infused during CPB in this series of patients was associated with high concentrations during CPB but did not result in any adverse clinical effects after CPB.

Adrenergic beta-Antagonists↗
PubMed1995

Effect of esmolol given during cardiopulmonary bypass on fractional area of contraction from transesophageal echocardiography.

The infusion of esmolol during hypothermic cardiopulmonary bypass (CPB) has no negative myocardial effects after CPB, despite increased esmolol levels during CPB due to hypothermia. The purpose of this randomized, double-blind, prospective study was to measure the effects of esmolol infused during CPB on cardiac function as measured by calculated indices of cardiac work and by transesophageal echocardiography (TEE). Patients scheduled for CPB were randomized to receive intravenous esmolol (300 micrograms.kg-1.min-1 during CPB after bolus of 2 mg/kg prior to CPB) or placebo. Infusion was stopped at 10 min after release of aortic cross-clamp. Hemodynamics and TEE were recorded during the procedure. Fractional area of contraction (FAC), an approximation of left ventricular ejection fraction, was calculated from end-diastolic and end-systolic areas. Esmolol was administered to 15 patients and placebo to 14. Heart rates in the esmolol group were lower during infusion and prior to CPB (P < 0.05). Stroke volume index and left ventricular stroke work index were higher in the esmolol group at 15 min post-CPB (P < 0.05). FAC was higher in the esmolol group at 15 and 30 min post-CPB (P < 0.05), but no difference was observed between groups at 1 h post-CPB. Esmolol infused during CPB in this series of patients was associated with better left ventricular function during the first 0.5 h post-CPB.

Adrenergic beta-Antagonists↗
PubMed1995

Prospective survey of continuous versus single-injection spinal anesthesia in obstetrics.

Prior to the removal of spinal microcatheters from the market in 1992, these catheters were used extensively in the Obstetric Anesthesia Service at the Medical Center of Louisiana. We report on a prospective survey of the clinical application of single-injection versus continuous-catheter spinal anesthesia. Two hundred sixteen patients had single-injection anesthesia, and 218 had continuous-catheter anesthesia. No neurologic complications other than postdural puncture headache (PDPH) were encountered in either group. Five patients had PDPH after single-injection technique, and 8 patients had PDPH from continuous spinal anesthesia. Patients with diabetes were at higher risk for PDPH, and blacks were at lower risk (relative risks 4.35 and 0.31, respectively). Additionally, PDPH was associated with lower intraoperative urine output. No increased risk of complications was found after continuous spinal anesthesia with microcatheters.

Adult↗
PubMed1994

Treatment of the cutaneous pain of acute herpes zoster with 9% lidocaine (base) in petrolatum/paraffin ointment.

BACKGROUND: Treatment of the pain of acute herpes zoster by local anesthetic injections has drawbacks. Topical percutaneous local anesthesia (TPLA) may offer another strategy of providing regional analgesia in affected patients. OBJECTIVE: We evaluate the analgesic efficacy and safety of 9% (wt/vol) lidocaine (base) in petrolatum/paraffin ointment in patients with acute herpes zoster. METHODS: Ointment was applied to the affected skin of 22 patients. Pain, tenderness, sensitivity to pinprick and cold, and blood lidocaine concentration were measured repeatedly during a 20-hour interval and intermittently thereafter. RESULTS: Mean pain, tenderness, and cutaneous sensation scores were reduced at measurements taken from 4 to 20 hours after ointment application (p < 0.05), but not every patient obtained relief. No patient had local skin irritation or systemic toxic effects related to the local anesthetic. CONCLUSIONS: TPLA is a promising therapy for control of cutaneous pain of acute herpes zoster. Controlled studies should be performed to prove efficacy, determine optimal TPLA formulation, and define dosage limits.

Acute Disease↗
PubMed1994

Prospective comparison of use of the laryngeal mask and endotracheal tube for ambulatory surgery.

We examined the response to the laryngeal mask (LM) compared to the endotracheal tube (ETT) in patients undergoing ambulatory anesthesia. The differences in management by the anesthesiologists for these two airways were also examined. Peripheral orthopedic procedures were studied in 44 outpatients randomized to receive a LM or ETT, and either spontaneous or controlled ventilation. Anesthesia was induced with propofol and succinylcholine intravenously (i.v.) and maintained with N2O and isoflurane. Anesthesiologists were allowed to determine ventilatory variables and anesthetic concentration. Hemodynamic and ventilatory measurements were made during the anesthesia. Barium sulfate was poured into the oropharynx after the airway was secure. Fiberoptic examination through the LM was performed at the beginning and at the end of the administration of each anesthetic. Radiographs were taken at the end of the anesthetic administration before LM or ETT removal to look for barium in the trachea. After airway removal, presence of blood on the airway, sore throat, coughing, nausea, vomiting, shivering, and amount of morphine demanded during recovery were noted. No barium in the trachea or bronchial tree was seen in any of the radiographs. The ETT was associated with greater hemodynamic response not only to airway placement (P < 0.05), but also to surgical incision (P < 0.05) and airway removal (P < 0.05). Spontaneous or controlled ventilation favored neither airway, although the ETT was associated with increased work of inspiration with controlled ventilation (P < 0.05). Anesthesiologists tended to elect smaller tidal volumes, faster ventilation rates, and lower anesthetic concentrations for patients with the LM (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Comparative myocardial depressive effects of propofol and thiopental.

To compare the direct myocardial effects of thiopental and propofol, concentration-contractility curves were determined by using an isolated guinea pig left atrial preparation. Contractility was measured as peak twitch tension, maximum rate of contraction (dT/dt), and maximum rate of relaxation (-dT/dt). Drug concentrations ranged from 56 microM (10 micrograms/mL) to 2800 microM (500 micrograms/mL) propofol and 3.8 microM (1 microgram/mL) to 190 microM (50 micrograms/mL) thiopental. Data were fitted to a sigmoidal inhibitory pharmacodynamic model in which an increasing incremental drug concentration is needed to cause a consistent incremental effect. Comparisons were then made of the drug concentrations at which a 50% inhibition in contractility was noted (IC50). To compare drugs on an equi-anesthetic basis, comparisons also were made between IC50 values normalized to anesthetic concentrations needed to produce anesthesia (67.8 microM and 28.1 microM for thiopental and propofol, respectively). Data from seven atrial preparations for thiopental and seven atrial preparations for propofol were analyzed. The IC50 (microM) for peak twitch tension were 20.9 +/- 6.3 and 96.6 +/- 10.1 (P < 0.05), for dT/dt were 21.1 +/- 5.9 and 86.9 +/- 8.3 (P < 0.05), and for -dT/dt were 21.0 +/- 6.1 and 84.3 +/- 9.2 (P < 0.05) for thiopental and propofol, respectively. When the normalized IC50 were compared, the differences between anesthetics became greater. For guinea pig left atria in vitro, thiopental is a more potent myocardial depressant than propofol, especially when compared relative to anesthetic potencies; neither anesthetic preferentially affects peak twitch tension, maximum rate of contraction, or maximum rate of relaxation.

Animals↗
PubMed1992

Absence of explicit or implicit memory in patients anesthetized with sufentanil/nitrous oxide.

Verbal paired associates were presented to 25 surgical patients from initial incision to closure of the incision during general anesthesia. Sufentanil with nitrous oxide and oxygen was administered; intravenous morphine (0.05 mg/kg) was administered when the skin suturing was completed; no volatile anesthetic agents or benzodiazepines were administered. When ready for discharge from the postanesthesia care unit, and again 2 weeks later by telephone, patients were tested for free recall, cued recall, recognition, and free association. No evidence of explicit memory for the word list was demonstrated by patients on tests of free recall, cued recall, or recognition, nor did a free-association test of implicit memory demonstrate a significant priming effect, in contrast to previous results obtained with isoflurane. The precise conditions under which surgical events can be processed, and retained in the form of implicit memory outside of conscious awareness, remain to be determined.

Adult↗
PubMed1991

A noninvasive method of estimating mean pulmonary artery pressure in the pneumatic total artificial heart.

Accurate hemodynamic monitoring is essential for the clinical management of the recipient of a total artificial heart (TAH). The high incidence of pulmonary congestive disorders in this population complicates this already formidable task. Lack of diagnostic pulmonary artery pressure (PAP) information is recognized as a fundamental source of these problems. Because conventional methods of obtaining hemodynamic information are difficult to implement in TAH recipients, improvement of TAH case management depends on the development of innovative monitoring strategies. Noninvasive monitoring techniques have been developed for three (right atrial pressure, left atrial pressure, and aortic pressure) of the four auxiliary circulatory pressures used to quantify hemodynamic performance. Development of the fourth, for PAP, was the subject of this work. We developed a noninvasive, in vitro method of estimating mean PAP in the Jarvik-7 TAH (Symbion, Inc, Salt Lake City, UT) recipient. This information was obtained by analyzing the relationship between the pneumatic right drive pressure (RDP) and PAP waveforms produced by a Jarvik-7 (70 ml) connected to a Donovan mock circulation and driven by a Utahdrive System IIIe Controller (Symbion, Inc, Salt Lake City, UT). Total artificial heart driver parameters (i.e., heart rate, percent systole, and vacuum) were manipulated to produce a range of ventricular filling volumes (FV), from 40 to 60 ml, for three distinct states of the pulmonary vasculature: hypotensive, normal, and hypertensive. A unique multiple-linear regression equation was derived for each FV from the RDP-PAP relationship exhibited under these conditions. Comparison of computed estimates of PAP with actual measurements showed overall average correlations of greater than 0.92, with a standard error of the estimate of less than 1.9 mm Hg. The mean difference between actual and computed PAP measurements was -0.03 +/- 2.0 Hg. Estimations were accurate within 8.5% of true PAP values. Additional experimentation revealed that while the RDP-PAP relationships are dependent on FV, they are independent of the manner in which FV was obtained. Estimates proved useful over the clinical operating range of the pneumatic heart driver, as well as over the normal physiologic range of PAP in the human. This method is readily applicable to a computer-based monitoring implementation, although its effectiveness needs to be demonstrated in vivo.

Aorta↗
PubMed1989

Automated measurements of isolated heart muscle contractions: effects of halothane, calcium, and magnesium on guinea pig left atrial muscle.

An in vitro method for automatically measuring muscle contraction force has been demonstrated in a study of the effects of the inhalation anesthetic halothane followed by calcium chloride or magnesium sulfate on isolated guinea pig left atrial muscle. An automated computer-controlled system was used to collect muscle contraction force waveforms and to analyze contraction waveforms for comparison of variables before and after drug administration. Two concentrations of halothane (0.5 and 1.5%) were administered to the atrial preparation for 30 minutes and followed by calcium chloride or magnesium sulfate. Six variables (latency, time to peak tension, peak tension, maximum rate of change of pressure, force time integral, and relaxation time) were automatically determined from averaged stimulus-response curves. Results were normalized and compared with controls administered only calcium and magnesium and with controls administered no drugs. The automated system greatly simplified data collection and accumulation and statistical analysis of multiple responses. The system made possible averaging and analysis of more data with less variability than is normally obtained with manual systems. The results confirm several known actions of these agents. Halothane prolongs latency (9 and 21% for 0.5 and 1.5% halothane, respectively) and shortens time to peak tension (6 and 17% for 0.5 and 1.5% halothane, respectively) and relaxation time (17 and 39% for 0.5 and 1.5% halothane, respectively). At high halothane concentrations (1.5%) calcium chloride shortens latency (10%) and prolongs time to peak tension (11%); magnesium sulfate prolongs latency (14%) and shortens time to peak tension (10%).

Animals↗
PubMed1988

Comparison of effects of atracurium and vecuronium in cardiac surgical patients.

To compare the cardiovascular effects of intubating doses of atracurium besylate and vecuronium bromide in cardiac surgical patients while utilizing fentanyl anesthesia, 20 patients scheduled for elective coronary artery bypass surgery were randomly assigned to two equal groups in a double-blind fashion. Two minutes after induction of anesthesia, baseline hemodynamic measurements were obtained and either atracurium 0.5 mg/kg (group 1) or vecuronium 0.12 mg/kg (group 2) was administered as an intravenous bolus. Hemodynamic measurements were then repeated 2, 5, and 10 minutes after injection. Atracurium produced a statistically significant decrease in blood pressure at 2 minutes and a statistically significant increase in cardiac output and decrease in systemic vascular resistance at 2, 5, and 10 minutes. Vecuronium produced no statistically significant changes in any hemodynamic variable measured other than a decrease in pulmonary capillary wedge pressure 10 minutes after the drug was administered. The hemodynamic changes seen with atracurium were closely related to changes in serum histamine levels, whereas histamine level did not change after vecuronium. There were no statistically significant differences between the two groups, even though after atracurium statistically significant changes were observed while there were no statistically significant changes associated with vecuronium. It is concluded that when utilizing the above clinical dose range, use of vecuronium may be advantageous over use of atracurium when hemodynamic stability is crucial in the anesthetic management of cardiac surgical patients.

Atracurium↗