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Biomedical subjects

P Viars

Publications and source records attributed to P Viars.

At least 163 records · Page 9Linked to original sources
PubMed1986

[Prevention of hypertensive attacks after carotid surgery. The value of nifedipine and diltiazem].

A randomized study was carried out to determine whether postoperative administration of either intranasal nifedipine or intravenous diltiazem was effective in preventing hypertensive episodes after carotid endarterectomy. Sixty-three consecutive patients undergoing this surgery were randomly assigned to three groups (n = 21): control (C), nifedipine (N) and diltiazem (D). Anaesthesia was induced with flunitrazepam (0.02 mg X kg-1), fentanyl 6 micrograms X kg-1 and pancuronium (0.1 mg X kg-1), and maintained by N2O/O2 (50%), additional fentanyl and halothane or enflurane when warranted. Postoperatively, patients were warned whilst under mechanical ventilation in a recovery room. Upon arrival in the recovery room, intranasal nifedipine (10 mg) was given to patients included in group N, while patients from group D received an intravenous dose of 0.3 mg X kg-1 of diltiazem, followed by a continuous infusion of 3 micrograms X kg-1 X min-1 until 15 min after extubation. No preventive treatment was given to patients in group C. If postoperative systolic blood pressure rose to more than 180 mmHg, 10 mg of nifedipine were administered intranasally. During the postoperative period, 13 patients from group C, 5 from group N and 4 from group D exhibited hypertensive episodes (systolic blood pressure greater than 180 mmHg or diastolic blood pressure greater than 100 mmHg). Intranasal administration of 10 mg nifedipine led to the normalization of blood pressure in 20 out of these 22 patients. This study confirmed the high incidence of hypertensive attacks after carotid endarterectomy, and showed that prophylactic administration of nifedipine or intravenous diltiazem was highly effective in preventing such hypertensive episodes.

Aged↗
PubMed1986

High frequency jet ventilation in acute respiratory failure: which ventilator settings?

Seven hypoxaemic patients with acute respiratory failure were ventilated with HFJV (Ventilator VS 600). Arterial oxygenation was improved in each patient by the increases induced in mean airway pressure (PAW) (to 20 cm H2O) using three different ventilatory settings applied in a random order: technique A: I:E ratio 0.43, driving pressure 2.9 bar, no PEEP; technique B: I:E ratio 1.0, driving pressure 1.9 bar, no PEEP; technique C: I:E ratio 0.43, driving pressure 1.8 bar, PEEP 11 cm H2O. Respiratory frequency was maintained at 250 b.p.m. throughout the study. There were no significant differences in PaO2 (FlO2 = 1) or Qs/Qt between the three techniques. In contrast, carbon dioxide elimination was markedly affected by the method used to increase PAW:PaCO2 was significantly higher during technique C (8.5 +/- 3.6 kPa) and technique B (6.6 +/- 2.1 kPa) than during technique A (4.8 +/- 0.9 kPa). Significant increases in cardiac index, heartrate, mean pulmonary arterial pressure and a decrease in the arterio-venous oxygen content difference were observed when PaCO2 increased. We conclude that, to obtain the PAW necessary to improve pulmonary oxygen exchange, more effective carbon dioxide elimination is achieved by increasing the driving pressure, rather than by increasing the I:E ratio, or using a PEEP valve.

Acute Disease↗
PubMed1986

Effect of halothane on diaphragmatic muscle function in pentobarbital-anesthetized dogs.

The mechanism underlying the decrease in minute ventilation (VE) observed under halothane anesthesia was investigated in nine spontaneously breathing dogs. Anesthesia was induced with pentobarbital sodium and was maintained with halothane. Inspired fraction of halothane (FIhal) was increased every 30 min, from 0.005 to 0.02. VE decreased from 8.1 +/- 0.9 to 4.8 +/- 0.4 l . min-1 (P less than 0.001), as FIhal increased from 0 to 0.02. This resulted from a decrease in both mean inspiratory flow (VT/TI) and the duty ratio (TI/TTOT). Transdiaphragmatic pressure (Pdi) and the integrated electrical activity of both hemidiaphragms (Edi) were measured during normal breathing, and during breathing against closed airways (P0di, E0di), in order to obtain an index of the inspiratory neuromuscular output of the diaphragm. With increasing FIhal, there was a significant decrease in Pdi, P0di, Edi, and E0di. The authors measured Pdi and Edi generated during supramaximal stimulation of the two phrenic nerves (PSdi, Esdi) at frequencies of 10, 20, 50, and 100 Hz, in order to eliminate in this decrease the role played by a decrease in the neural drive to breathing. PSdi and ESdi decreased significantly with increasing FIhal, and had not returned to the control values 30 min after discontinuation of halothane administration. The authors conclude that, in pentobarbital-anesthetized dogs, halothane is responsible for a diaphragmatic dysfunction, which may be located either at the neuromuscular junction, on the contractile processes of the muscle, or on both, and for a decrease in the activation time of the inspiratory muscles. Both of these effects contribute to the decrease in VE observed under halothane anesthesia.

Anesthesia↗
PubMed1986

Hemodynamic effects of high-frequency jet ventilation in patients with and without circulatory shock.

Nineteen critically ill patients with acute respiratory failure were studied to compare the hemodynamic effects of continuous positive-pressure ventilation (CPPV) and high-frequency jet ventilation (HFJV) at comparable levels of alveolar ventilation. Patients were divided into three groups: Group 1 included seven patients without circulatory shock in whom mean airway pressure (Paw) was slightly higher during CPPV than during HFJV (17.3 +/- 3.0 vs. 13.0 +/- 2.9 mmHg); Group 2 included six patients without circulatory shock in whom HFJV and CPPV were compared at the same level of Paw (19.2 +/- 5.0 mmHg); Group 3 included seven patients with circulatory shock in whom HFJV and CPPV were compared at the same level of Paw (16.0 +/- 3.9 mmHg). The following respiratory frequencies were used in HFJV: Group 1, 200 +/- 76 beats/min; Group 2, 238 +/- 103 beats/min; Group 3, 286 +/- 149 beats/min. In all patients comparable levels of PaCO2 were obtained with CPPV and HFJV. In Group 1 patients, mean arterial pressure, cardiac index, and stroke index were significantly higher during HFJV. In Group 2 patients, no significant difference was found between HFJV and CPPV. In Group 3 patients, the following hemodynamic variables were significantly higher during HFJV: mean arterial pressure (71 +/- 24 vs. 84 +/- 23 mmHg), cardiac index (3.6 +/- 1 vs. 4.1 +/- 1.41 X min-1 X m-2), and oxygen delivery (403 +/- 93 vs. 471 +/- 124 ml X min-1 X m-2).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1986

Ventilatory pattern and chest wall mechanics during ketamine anesthesia in humans.

The effects of anesthetic doses of ketamine (iv bolus of 3 mg X kg-1 followed by a continuous infusion of 20 micrograms X kg-1 X min-1) on functional residual capacity (FRC) measured by the helium dilution method and on the breathing pattern recorded by a noninvasive method (NIM) based on chest wall circumference changes were studied in 14 ASA P.S. I patients. Ketamine anesthesia was associated with: 1) the maintenance of FRC, minute ventilation, and tidal volume; 2) an increase in rib cage contribution to tidal breathing; and 3) an alteration of volume-motion relationships of the chest wall compartments. It is concluded that: 1) in contrast to volatile anesthetic agents, ketamine anesthesia has a sparing effect on intercostal muscle activity, which may explain the maintenance of FRC; and 2) changes in chest wall geometry and compliance induced by anesthetic agents must be taken into account for NIM to be valid.

Adult↗
PubMed1986

The influence of hepatic plasma flow on alfentanil plasma concentration plateaus achieved with an infusion model in humans: measurement of alfentanil hepatic extraction coefficient.

In a group of seven patients undergoing intracranial surgery under neurolept anesthesia, an alfentanil infusion was initiated with a loading dose of 235 micrograms/kg over 5 min, followed by a maintenance infusion rate of 1.8 microgram X kg-1 X min-1 in order to obtain a steady state plasma concentration (Css) of 400 ng/ml-1 according to an infusion model. The mean values of Css (446 +/- 209 ng/ml) were close to the predicted ones. Nevertheless, an important intersubject variability in Css values was observed. A positive linear correlation existed between alfentanil steady state clearance and indocyanine green clearance (r = 0.88) and between alfentanil steady state clearance and cardiac index (r = 0.93). In three patients, a catheter was inserted into an hepatic vein to determine the alfentanil hepatic extraction coefficient. Alfentanil plasma clearance did not differ from alfentanil hepatic clearance and alfentanil hepatic extraction coefficient values ranged from 0.32-0.53. We conclude that alfentanil is a drug with an intermediate hepatic extraction coefficient and that alfentanil plasma clearance depends on hepatic plasma flow, which is thus one of the factors accounting for individual variability in plasma concentration plateaus achieved with an infusion model.

Adult↗
PubMed1986

Pharmacology of vecuronium in patients with end-stage renal failure.

Vecuronium was administered as an intravenous bolus (50 micrograms kg-1) to 10 normal and 10 anephric patients. The elimination half-life was 50.7 +/- 20.3 min in normal patients and 67.826.3 min in anephric patients. The plasma clearance was 3.6 +/- 1.5 ml min-1 for normal patients and 4.5 +/- 2.6 ml min-1 kg-1 for anephric patients. Only the volume of the second compartment was statistically increased (+90%, P less than 0.05) in anephric patients. The duration of action in normal patients (25.3 +/- 9.8 min) was comparable to the duration of action in patients with renal failure (32.8 +/- 10.7 min), but the recovery index was prolonged (+45%, P less than 0.05) in anephric patients.

Adult↗
PubMed1986

Response of left ventricular ejection fraction to recovery from general anesthesia: measurement by gated radionuclide angiography.

To test the hypothesis that, after anesthesia for noncardiac surgical procedures, the increased cardiac work during recovery induces wall motion and ejection fraction (EF) abnormalities in patients with mild angina pectoris, gated radionuclide angiography was performed in patients undergoing simple cholecystectomy under narcotic-relaxant general anesthesia. The ejection fraction was determined during anesthesia at the end of surgery, and then determined 3 min and 3 hr after extubation. A new angiography was performed 24 hr later, and a myocardial scintigraphy (Thallium 201) was performed during infusion of the coronary vasodilator, dipyridamole. In the first part of the investigation, eight patients without coronary artery disease (CAD) (group 1) and 20 patients with mild angina (group 2) were studied. In the second part of the study, seven patients (group 3) with mild angina pectoris received an intravenous infusion of 0.4 microgram X kg-1 X min-1 of nitroglycerin started before surgery and gradually decreased 4 hr after extubation. In group 1, EF remained unchanged at recovery. In contrast in group 2, EF responded abnormally to recovery: EF decreased from 55% during anesthesia to 45% 3 min after extubation (P less than 0.001). Patients in group 3, who received intravenous nitroglycerin, showed no change of EF at recovery. This study demonstrates that recovery from general anesthesia causes abnormalities in left ventricular function in patients suffering from CAD. These abnormalities are prevented by prophylactic intravenous nitroglycerin.

Aged↗
PubMed1986

Roles of fentanyl and nitroglycerin in prevention of myocardial ischemia associated with laryngoscopy and tracheal intubation in patients undergoing operations of short duration.

The purpose of this study was to evaluate intravenous nitroglycerin given during induction of anesthesia as a means for prevention of myocardial ischemia and hemodynamic changes associated with induction, laryngoscopy, and intubation, in patients with stable angina scheduled for vascular operations of moderate duration. Forty-six patients were randomly assigned to receive either fentanyl, 3 micrograms/kg (group 1, n = 6), fentanyl, 8 micrograms/kg (group 2, n = 20), or fentanyl 3 micrograms/kg plus a continuous intravenous nitroglycerin infusion, 0.9 microgram X kg-1 X min-1 (group 3, n = 20), in addition to thiopental-pancuronium anesthetic induction, prior to laryngoscopy and intubation. The criteria for recognizing myocardial ischemia were the following: horizontal or downsloping ST segment depression equal to or greater than 1 mV, and/or ventricular arrhythmia, on CM5 recording. In group 1, myocardial ischemia occurred during laryngoscopy and intubation in four patients, and mean blood pressure (MBP), heart rate, and mean pulmonary wedge pressure (PCWP) increased significantly (P less than 0.05). Despite greater stability in MBP and heart rate in group 2, myocardial ischemia still occurred in four patients (not significantly different from group 1). Nitroglycerin added to low-dose fentanyl (group 3) produced significant reduction in myocardial ischemia (1/20) when compared with group 1 (P less than 0.01), and significantly greater stability in PCWP during laryngoscopy and intubation in comparison to groups 1 and 2. In patients with stable angina undergoing operations of short duration, the use of nitroglycerin infusion and low-dose fentanyl significantly decreases the incidence of myocardial ischemia associated with induction of anesthesia and tracheal intubation.

Aged↗
PubMed1986

Intermittent positive pressure ventilation with either positive end-expiratory pressure or high frequency jet ventilation (HFJV), or HFJV alone in human acute respiratory failure.

Continuous Positive Pressure Ventilation (CPPV), High-Frequency Jet Ventilation (HFJV), and a combination of HFJV with Intermittent Positive Pressure Ventilation (CV) were randomly compared in 13 critically ill patients with severe acute respiratory failure. Ventilatory settings were chosen in order to apply the same mean airway pressure (Paw) during the three modes. Respiratory frequencies were adjusted during CPPV (16 +/- 2 breaths/min) and HFJV (235 +/- 32 breaths/min) to achieve the same level of PaCO2 and were then combined during CV. All patients were heavily sedated during the study and had had peripheral and balloon-tipped pulmonary arterial catheters previously inserted. After a steady state at FIO2 1 in each mode of ventilation, hemodynamic and respiratory parameters were measured. A Paw of 13.8 +/- 2.9 mm Hg was applied to each patient by using a PEEP of 7.4 mm Hg during CPPV; a driving pressure of 2.9 +/- 0.2 bars and an I/E ratio of 0.43 during HFJV; and by combining HFJV, using a driving pressure of 1.2 +/- 0.3 bars with intermittent positive pressure ventilation during CV. There were no significant differences in any of the hemodynamic or respiratory parameters measured, except for a significant decrease in PaCO2 during CV when compared to CPPV or HFJV. We concluded that 1) arterial oxygenation and cardiac output depend mainly on Paw independent of the method used to increase Paw and 2) CV can improve CO2 elimination without increasing Paw.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1985

[Determination of the dose-response curve for atracurium dibesylate in the anesthetized adult].

The mechanical response of the adductor pollicis to a 0.15 Hz stimulation of the ulnar nerve was studied in 35 unpremedicated adult patients (mean age 38 yr) under general anaesthesia using thiopentone, fentanyl and a N2O/O2 mixture under mechanical ventilation. PaCO2, pH, K, Ca, Mg plasma levels and temperature were in the normal range. Each patient received a single bolus of atracurium dibesylate: 0.10 mg . kg-1 (n = 11), 0.15 mg . kg-1 (n = 10), 0.20 mg . kg-1 (n = 11) or 0.30 mg . kg-1 (n = 4). The dose-response curve was constructed using the log-probit method for 0.10, 0.15, 0.20 mg . kg-1 doses, giving neuromuscular blocks greater than 0% and less than 0.20 mg . kg-1. The 0.20 mg . kg-1 dose had an onset time of 6.1 +/- 0.6 min, duration 0-90% of 34.3 +/- 3.2 min and a recovery index 25-75% of 10.9 +/- 1.0 min. The 0.3 mg . kg-1 dose resulted in onset time of 4.7 +/- 1.3 min, duration of 39.9 +/- 3.7 min and a recovery index of 10.7 +/- 1.8 min. Thus atracurium dibesylate seemed to be an agent of intermediate potency. Onset time was approximately the same as that for other non-depolarizing neuromuscular blocking drugs, but duration of action and recovery index were quite shorter, except for vecuronium bromide.

Adult↗
PubMed1985

[Hemodynamic effects of atracurium in man].

Haemodynamic effects of atracurium at three doses (0.2, 0.6 and 1.2 mg . kg-1) were studied in thirty patients, anaesthetized with thiopentone (5 mg . kg-1) and fentanyl (0.2 microgram . kg-1 . min-1). No cardiovascular side-effects were observed with doses of 0.2 and 0.6 mg . kg-1. However, a 1.2 mg . kg-1 dose induced a transient but significant decrease in mean arterial pressure (-10%; p less than 0.001), maximal in the second minute, associated with an increase in heart rate (+10%; p less than 0.001) and cardiac index (+9%), and a decrease in systemic vascular resistance (-16%; p less than 0.001). The decrease in arterial pressure was constant in every patient and associated with a generalized flush in one of them. Histamine-release induced by atracurium may be one of the possible mechanisms involved in this hypotension.

Atracurium↗
PubMed1985

[Modeling and BASIC program for the kinetics of inhalation anesthetic agents].

The pharmacokinetics of inhaled anaesthetics has been well described by Eger's model using a monoalveolar lung with continuous alveolar ventilation and four extrapulmonary compartments defined by their blood supply and anaesthetic solubility. The model is presented with its equations. A Basic microcomputer programme is proposed for this model: expected concentrations of anaesthetic in various conditions of administration, ventilation or cardiac output are shown, such as the uptake and distribution of nitrous oxide during anaesthesia. Different inhaled anaesthetics were compared for induction and recovery times in standardized conditions of administration.

Anesthesia, Inhalation↗
PubMed1985

Use of nitroglycerine to produce controlled decreases in mean arterial pressure to less than 50 mm Hg.

The cardiovascular effects of nitroglycerine (TNG) were studied in 30 patients requiring controlled hypotension for intracranial aneurysm surgery. In patients "resistant" to TNG (n = 9), sodium nitroprusside (SNP) was used to supplement the TNG. With TNG alone at a total dose of 31 mg and a mean hypotension duration of 28 min, mean arterial pressure (MAP) decreased by 43%, from 78.3 to 44.4 mm Hg as a result of decreases in cardiac index (Cl) (18%) and systemic vascular resistances (SVR) (21%). Simultaneously, a moderate increase in (Cao2 - Cvo2) (21%), and a significant increase in plasma renin activity (90%) were observed. In patients "sensitive" to TNG, the MAP decreased by 54%, Cl by 27% and SVR by 35%; HR remained stable. In patients "resistant" to TNG, the decreases in Cl and SVR were less marked: 2% and 22% respectively; the observed increase in HR was 12%. When non-toxic doses of SNP were used (less than 2 micrograms kg-1 min-1), hypotension was caused by decreased SVR (31%) and increased Cl (8%). TNG alone can be used to produce controlled decreases in MAP to around 50 mm Hg, and in patients "resistant" to TNG, SNP can be added to increase the hypotensive effect.

Adult↗
PubMed1985

Effect of postoperative extradural morphine on ADH secretion.

The effect of extradural morphine on antidiuretic hormone (ADH) secretion was assessed for the first 6 h after surgery in three groups of patients. Surgery was conducted under extradural bupivacaine: thereafter patients in group I (n = 6) received further injections of bupivacaine, patients in group II (n = 6) received an extradural injection of morphine and in patients in group III (n = 5) both bupivacaine and morphine, were administered extradurally. In group I, plasma ADH values remained unchanged throughout the study. In contrast, in the two groups of patients receiving extradural morphine a delayed and stepwise increase in plasma ADH concentration was documented. These results indicate that extradural morphine induces ADH secretion and suggest that this effect is the consequence of the migration of morphine to the brainstem.

Adult↗
PubMed1985

Clinical assessment and plasma pharmacokinetics associated with intramuscular or extradural alfentanil.

Patients with postoperative pain received alfentanil in doses of 15 micrograms kg-1 (n = 6) or 30 micrograms kg-1 (n = 6) via the extradural route or 15 micrograms kg-1 (n = 6) i.m. Effective analgesia was obtained in all patients in the extradural groups and in none in the i.m. group. Maximum pain relief developed within 10-15 min and the average duration of adequate analgesia was 78 min with the lower dose and 45 min with the higher dose, but this difference was not statistically significant. The 15-micrograms kg-1 extradural and i.m. groups showed the same pharmacokinetic pattern. Plasma concentrations were greater in the 30-micrograms kg-1 extradural group and this was associated with unwanted systemic effects. We conclude that the extradural administration of alfentanil can produce effective spinal analgesia. Its lipophilic property reduces the onset time, but does not modify its duration of action or impair absorption.

Adult↗