Cardiac transplantation: a prospective comparison of ketamine and sufentanil for anesthetic induction

The hemodynamic effects of ketamine, 1.5 mg/kg, or sufentanil, 3.4 +/- 0.3 micrograms/kg, were studied prospectively for the anesthetic induction of 20 patients with cardiomyopathies undergoing cardiac transplantation. Plasma epinephrine (EPI), norepinephrine (NE), and sufentanil levels were also obtained. Measurements were taken at various times before induction and following intubation. Following ketamine, progressive increases (P less than 0.05) in mean arterial pressure (28%, MAP), mean pulmonary artery pressure (56%, PAP), central venous pressure (109%, CVP), and pulmonary capillary wedge pressure (84%, PCWP) occurred over time, whereas the cardiac index (CI), stroke volume index (SVI), and stroke work index (SWI) remained unchanged or decreased. The use of sufentanil was associated with no significant changes in MAP, PAP, CVP, PCWP, CI, SVI, or SWI. The heart rate (HR) did not significantly change in either group. Plasma NE significantly increased (31%) in the ketamine group, peaking at 10 minutes; whereas EPI levels did not significantly change in either group. Plasma sufentanil did not reflect the microgram/kg or microgram/BSA administered dose, suggesting individualized distribution kinetics. Since perioperative morbidity and mortality did not differ between groups, both ketamine and sufentanil are acceptable drugs for the anesthetic induction for cardiac transplantation. However, the dissimilar hemodynamic effects caused by ketamine and sufentanil suggest that this conclusion may not be applicable to the patient with a cardiomyopathy undergoing noncardiac surgery.

Propofol-fentanyl anaesthesia for coronary artery surgery and cardiopulmonary bypass

A two-stage propofol infusion combined with fentanyl was used to maintain anaesthesia during coronary artery surgery in patients with good ventricular function. Whole blood propofol concentrations were measured at frequent intervals; plasma protein binding was measured before, during and after cardiopulmonary bypass. An initial infusion rate of 10 mg/kg/hour provided good protection from the pressor response to sternotomy. A predictable steady state concentration was achieved in the prebypass period with a maintenance infusion rate of 3 mg/kg/hour. The onset of bypass resulted in a small decrease in propofol concentration as a result of haemodilution. Induced hypothermia resulted in an increase in propofol concentration which returned rapidly to the prebypass steady state value during rewarming. The free propofol fraction increased during cardiopulmonary bypass. No patient had any recall of operative events or required inotropic support during weaning from bypass.

Pharmacokinetics of sufentanil in patients undergoing abdominal aortic surgery

The authors determined the pharmacokinetics of sufentanil, 12.5 micrograms.kg-1 iv in patients undergoing elective abdominal aortic surgery. The mean age (+/- SD) of the ten patients was 68.4 +/- 7.9 yr; their mean weight was 74.4 +/- 19.1 kg. Six patients underwent aortobifemoral grafting and four had abdominal aortic aneurysm repair. Serum sufentanil concentrations were determined in samples drawn at increasing intervals over a 24-h period. A three-compartment pharmacokinetic model was fit to the concentration versus time data. Total drug clearance was 15.0 +/- 3.2 ml.min-1.kg-1. The volume of distribution at steady-state (Vdss) was 8.7 +/- 4.5 l.kg-1. The elimination half-time were positively correlated with patient age. There were no significant correlations between the pharmacokinetic variables and the duration of aortic cross-clamping, the duration of surgery, or the rate or total volume of iv fluids given intraoperatively. In general surgical patients, the mean elimination half-time of sufentanil has been reported to be 2.7 h. When sufentanil is used in large doses as the primary anesthetic agent for patients undergoing abdominal aortic surgery, the long elimination half-time observed implies that recovery will take much longer than would have been anticipated from previously published pharmacokinetic data.

[The pharmacokinetics of propofol used in cesarean section; a preliminary study in the newborn infant]

A prospective study was carried out: 1) To compare the pharmacokinetics of propofol in two groups of patients: group 1 (eight pregnant women undergoing a prophylactic caesarean section at term), group 2 (control group: eight non pregnant women anaesthetized for short gynaecological procedures). 2) To study the kinetics of this agent in five newborns. Both groups were similar for weight, age, ASA I, oral premedication, anaesthetic method and duration. Dosages were performed using HPLC and results were statistically compared by Student's t-test. The haemodynamic parameters did not show large variations during induction. Propofol plasma levels were high (4,600 +/- 2,200 ng/ml-1) at intubation time; however, at extraction time (group 1) or 25 minutes after induction (group 2), plasma levels were close to anaesthetic threshold. The decreasing slopes were similar in the two groups. The quality of recovery in both groups was satisfactory. The first measured level in umbilical cord blood after birth was low, close to half of the maternal level, without any constant correlation. During the first hour of life, the drug catabolism is lesser in the newborn than in its mother, then plasmatic concentrations decrease similarly. Apgar scores were excellent in four of the five studied newborns; one child had a mean score notwithstanding a low propofol level (171 ng/ml-1), but recovery was perfect after a short oxygenation. There was no significant difference between pregnant women and control group with the propofol dose of 4 mg/kg-1 used for anaesthesia. Thus propofol appears to be convenient for prophylactic caesarean section without damage for the newborn.

Pharmacokinetics of alfentanil in newborn premature infants and older children

Because developmental pharmacokinetics appear to be closely associated with anatomic and physiologic changes that occur with growth, we were interested in determining the disposition and elimination of alfentanil in premature infants and older children. The pharmacokinetic profile of alfentanil was determined in 6 premature infants requiring sedation for medical management or analgesia for stressful intensive-care procedures. These pharmacokinetic profiles were compared with pharmacokinetic profiles determined in 9 older infants and children undergoing operative procedures that required invasive monitoring. In both groups the plasma decay curves best fit a 2-compartment model. Compared with older children, premature infants demonstrated a significantly larger apparent volume of distribution (1.0 +/- 0.39 vs. 0.48 +/- 0.19 l/kg), a smaller clearance (2.2 +/- 2.4 vs. 5.6 +/- 2.4 ml/kg/min) and a markedly prolonged elimination half-life (525 +/- 305 vs. 60 +/- 11 min).

Simultaneous determination of fentanyl and alfentanil in rat tissues by capillary column gas chromatography

Fentanyl and alfentanil were determined in blood and in thirteen tissues from rats by gas chromatography, with splitless injections on a fused-silica capillary column and nitrogen-selective detection. Sufentanil was used as the internal standard for both drugs and the acetyl analogue of sufentanil was used as an external standard to quantitate extraction recoveries. The extraction solvent was isopentanol-pentane (1:49) and a back-extraction into 0.1 M hydrochloric acid was used for sample clean-up. The extraction recoveries from tissue homogenates averaged 88% for fentanyl, 72% for alfentanil and 87% for sufentanil. The standard curves were linear over a range of 0.5-800 ng per sample for both drugs and the coefficients of variation for eight determinations of the drugs in tissue homogenates were 2-9% at 0.8-32 ng per sample. Assays of tissues from rats treated with simultaneous intravenous infusions of fentanyl and alfentanil confirmed the high precision and sensitivity of the method, which should therefore prove feasible for studies of the tissue distribution of these opioids.

Pharmacokinetics and protein binding of propofol in patients with cirrhosis

The pharmacokinetics and protein binding of propofol were studied in ten patients with cirrhosis and in ten control patients undergoing elective surgery. All patients received 2.5 mg.kg-1 propofol as an intravenous bolus injection for the induction of anesthesia. Whole blood propofol concentrations were measured at intervals up to 12 h, using a high-performance liquid chromatography (HPLC) technique. Propofol protein binding was estimated by equilibrium dialysis 10 min after injection of propofol. Individual propofol profiles for all patients were best described by a three-compartment open mammillary model. Rapid and slow propofol distribution half-times were observed, followed by an elimination phase with a half-time of 4-5 h. Propofol total body clearance was reduced (1.99 +/- 0.68 l.min-1) in the patients with cirrhosis but did not differ significantly from that in the control patients (2.30 +/- 0.61 l.min-1). The apparent volume of distribution at steady state (Vdss) was similar in the two groups. No significant difference in elimination half-life was observed between the two groups. Propofol was extensively bound (mean: 97-98%) to the plasma protein of both cirrhotic and control groups. This study shows that propofol pharmacokinetics and protein binding of propofol following a single intravenous bolus dose were not markedly affected by uncomplicated cirrhosis of the liver.

[Blood reflux into cartridge in dental anesthesia. Detection of total protein and human hemoglobin in residual anesthetic solution]

The present study was designed to elucidate the blood reflux into cartridge under infiltration anesthesia. When imitation examination was carried out using pontamine blue dye solution in 7 kinds of syringes for the use of cartridge, dye reflux was observed in all of them. Compared 4 kinds of cartridges on the market, dye reflux was observed in all except one. The amounts of protein in residual anesthetic solution of cartridges after infiltration anesthesia were quantitatively measured by dye binding method. Human hemoglobin was also measured by enzyme immunoassay (EIA). The detection rates of protein and human hemoglobin were 26.2% (85/324) and 24.2% (24/99), respectively. From these facts that blood reflux cannot be avoided in the cartridge system, it is necessary to prohibit the reuse of residual anesthetic solution of cartridge as quickly as possible to avert the risk of cross infection of HB and AIDS virus.

In vitro anesthetic washin and washout via bubble oxygenators: influence of anesthetic solubility and rates of carrier gas inflow and pump blood flow

The uptake and elimination of volatile anesthetic agents administered to patients under conditions of hemodilution and hypothermia during cardiopulmonary bypass have not been determined. To define the limitations imposed by oxygenators, we defined washin and washout curves for volatile anesthetic agents administered to bubble oxygenators primed with diluted blood (without connection to a patient). There was rapid equilibration of anesthetic partial pressure between delivered gas and blood (85-90% within 16 minutes). Increasing the gas inflow to the oxygenator from 3 to 12 L/min hastened washin and washout slightly, while increasing the pump blood flow from 3 to 5 L/min had no effect. Rates of washin and washout of anesthetics differed as a function of their blood/gas solubilities: enflurane greater than isoflurane greater than halothane during washin; isoflurane greater than enflurane greater than halothane during washout. However, these differences were small. Oxygenator exhaust partial pressures of anesthetic correlated with simultaneously obtained blood partial pressures, suggesting that monitoring exhaust gas may be useful clinically.

Alfentanil plasma concentration v. effect relationships in cardiac surgical patients

Effects of alfentanil, preceded by lorazepam, on suppression of haemodynamic and somatic responses to noxious stimuli was studied in patients undergoing CABG. Plasma concentration of alfentanil, somatic and haemodynamic responses were measured at loss of consciousness, tracheal intubation, sternotomy and during multiple application of electrocoagulation. Additional alfentanil was administered i.v. to control unwanted responses. Study 1 (six patients): lorazepam 0.08 mg kg-1 by mouth 1-2 h before operation, alfentanil priming infusion (60 micrograms kg-1 min-1 for 10 min) followed by maintenance infusion (4.5 micrograms kg-1 min-1). With mean plasma alfentanil 1178 (SEM 54) ng ml-1, two patients required supplementary alfentanil to suppress somatic motor responses; one patients required nitroglycerin to control an increase in arterial pressure which was unresponsive to additional alfentanil following sternotomy. Study 2 (13 patients): lorazepam 0.04 mg kg-1 by mouth as premedication; one of three maintenance infusion rates of alfentanil: 5.4 (n = 4), 6.6 (n = 5), or 7.8 (n = 4) micrograms kg-1 min-1, each preceded by a proportional priming infusion. With plasma alfentanil 2181 (62) ng ml-1, somatic motor responses requiring additional alfentanil occurred in nine patients; haemodynamic responses in four of seven patients tested could not be controlled by alfentanil. The highest plasma concentration of alfentanil to prevent response to a stimulus other than tracheal intubation was different between the two studies (P less than 0.05). We conclude that alfentanil alone is insufficient to suppress haemodynamic and somatic motor responses to noxious stimulation during CABG and that the role of premedication is significant.

Extended blood collection period required to define distribution and elimination kinetics of propofol

The pharmacokinetics of propofol were investigated following bolus intravenous administration of 2-3 mg kg-1 of drug to eight surgical patients. Apparent elimination half-life, volume of distribution and systemic blood clearance of propofol correlated strongly with the sampling period, which ranged from 8 to 52 h, depending on the time taken for the propofol concentration to reach the detection limit of the assay. In the three patients in whom the sampling period exceeded 42 h, apparent elimination half-life (55.6 h) and apparent volume of distribution (1370 l) greatly exceeded previously published estimates and systemic blood clearance (1020 ml min-1) was much less than previous estimates. This suggests that previous estimates were biased by the relatively short duration of blood collection in those studies (8 to 12 h).

[The course of blood concentrations of propofol administered at a constant rate, combined with fentanyl]

The blood concentration of propofol was studied in 14 ASA 1 informed patients, who were to undergo orthopaedic or plastic surgery lasting at least 90 min. Anaesthesia was induced with a 2 mg.kg-1 bolus of propofol together with 0.86 microgram.kg-1 fentanyl. This was followed by a constant rate infusion of propofol and fentanyl, 5 mg.kg-1.h-1 and 3 micrograms.kg-1.h-1 respectively. The mean duration of propofol infusion was 153 +/- 63 min, with extremes of 90 and 315 min. Propofol concentration was measured using gas phase chromatography on total arterial blood; the lower limit of detection was 0.05 mg.l-1. During the infusion, blood concentrations were found between 2 and 4 mg.l-1. It was 2.25 mg.l-1 at the fifth min; this was 80% of the concentration found at the 120th min. There was in fact no statistically significant difference between the values found at the 90th, 120th and 150th min. On stopping the infusion, the concentrations fell rapidly during the first 5 min, and then more slowly. By the 30th min, it had reached a value 4.5 times less than that at the end of the infusion. However, individual variations were found, which could explain delayed recovery. The calculated pharmacokinetic parameters were: elimination half-life = 41.7 +/- 20 min, clearance = 2.14 +/- 0.55 l.min-1 and equilibrium distribution volume = 43.4 +/- 15.2 l. These results are discussed. It is therefore possible to give propofol continuously at a constant rate without having any accumulative effect.

Sufentanil disposition during cardiopulmonary bypass

In order to investigate the ability of a computer-assisted continuous infusion (CACI) system to maintain constant plasma levels of sufentanil during cardiopulmonary bypass (CPB) using pharmacokinetic data derived from healthy surgical patients to determine the infusion rate, ten patients were anaesthetized with diazepam, enflurane and oxygen until ten minutes prior to the expected time of initiation of CPB. At that point, an infusion of sufentanil, aimed to reach a central compartment concentration of 5 ng.ml-1, was started via CACI. Plasma concentrations of sufentanil, haematocrit, total protein and albumin concentrations, and nasopharyngeal and CPB inflow temperatures were obtained at predetermined intervals before and up to 90 min after the initiation of CPB. Plasma concentrations of sufentanil reached 3.8 +/- 0.4 ng.ml-1 before CPB and approached the 5.0 ng.ml-1 set point (4.7 +/- 0.4 ng.ml-1) over the 90 min of CPB. In conclusion, our results show that it is possible to obtain stable plasma levels of sufentanil on CPB using a pharmacokinetically driven infusion scheme; however, our data suggest that use of such a system may lead to accumulation of drug during CPB.

[Pharmacokinetics of propofol as an induction agents in adults]

The disposition kinetics of Propofol have been determined in 7 patients (3 men, 4 women) receiving 2.5 mg/kg for induction of anaesthesia. Peripheral venous samples were collected up to 12 hours after injection of the drug. Data analysis indicates a 3 compartment model with a terminal half-life of 480 +/- 141 min, clearance of 0.0352 +/- 0.0014 l/min/kg and volume of distribution of 24.2 +/- 6.2 l/kg.

Partition coefficients for sevoflurane in human blood, saline, and olive oil

The purpose of this study was to determine partition coefficients for a new, rapid-acting inhaled anesthetic, sevoflurane. Blood samples were taken from 19 ASA physical status I-III patients ranging in age from 21 to 77 yr who were scheduled for elective surgery. At 37 degrees C, we found a blood/gas partition coefficient of 0.686 +/- 0.047 (mean +/- SD), a saline/gas partition coefficient of 0.370 +/- 0.016; and an oil/gas partition coefficient of 47.2 +/- 2.7. These values are consistent with the clinical observation that sevoflurane is a potent inhaled anesthetic that produces a rapid induction of and recovery from anesthesia.

The role of pharmacokinetics in anaesthesia: application to intravenous infusions

Pharmacokinetic concepts describe the relationship between drug dose and resulting plasma concentration. A drug's pharmacokinetic profile can be described by distribution and elimination half-lives, initial volume of distribution, steady-state distribution volume, and metabolic and distributional clearance. After initiating a fixed rate of drug infusion, four to five terminal elimination half-lives are required to reach a steady state of constant plasma concentration. If a loading dose is given, a steady state can be achieved more rapidly. The most rapid method of achieving a constant plasma concentration involves using a variable rate of drug infusion that adjusts for the metabolic clearance and distribution of the drug. Computer-driven infusion pumps can be used to rapidly achieve, then maintain, constant plasma concentrations of a drug.

[Passage of propofol in the colostrum. Preliminary data]

So as to ascertain whether propofol passed into human milk, a study was carried out in five women who had undergone general anaesthesia with propofol in the puerperium. Concentrations of propofol were measured both in plasma and colostrum. The results showed clearly the excretion of propofol in the colostrum, and the similar time-courses of propofol levels in the blood and colostrum; the ratio of concentrations blood:colostrum was close to 1.

Effects of anaesthesia and surgery on the solubility of volatile anaesthetics in blood

To determine the effects of anaesthesia and surgery on the solubility of volatile anaesthetics in blood, we measured the blood/gas partition coefficients of enflurane, halothane, isoflurane, and methoxyflurane in vitro in blood obtained from six healthy unpremedicated adults at three different times during isoflurane anaesthesia: awake; 20 minutes after induction of anaesthesia, but before surgical incision; and, 90 minutes after surgical incision. The blood/gas partition coefficients of the four volatile anaesthetics decreased significantly after induction of anaesthesia and after surgical incision (p less than 0.05). Values for haematocrit and the serum concentrations of albumin, globulin, and cholesterol decreased parallel to the decrease in blood/gas partition coefficients.