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H R Vinik

Publications and source records attributed to H R Vinik.

At least 19 recordsLinked to original sources
PubMed1999

Intraocular pressure changes during rapid sequence induction and intubation: a comparison of rocuronium, atracurium, and succinylcholine.

STUDY OBJECTIVE: To compare changes in intraocular pressure (IOP) during rapid sequence induction and intubation following rocuronium, succinylcholine, and atracurium. DESIGN: Open-label, prospective, randomized study. SETTING: Operating room at the Eye Foundation Hospital (University of Alabama at Birmingham) PATIENTS: 45 ASA physical status I, II, and III patients, aged 18 to 65 years, scheduled for elective eye surgery with general anesthesia. INTERVENTIONS: Anesthesia was rapidly induced in unpremedicated patients with a fixed combination of midazolam 0.025 mg/kg, alfentanil 0.025 mg/kg, and propofol 1.5 mg/kg. Intubation was performed, as clinically indicated, approximately 60 seconds following administration of rocuronium 0.6 mg/kg, atracurium 0.5 mg/kg, or succinylcholine 1 to 1.5 mg/kg. MEASUREMENTS AND MAIN RESULTS: Intraocular pressure was measured before induction of anesthesia (baseline), following anesthesia induction and administration of muscle relaxant (before intubation), and after intubation. The percent change in IOP from baseline was significantly decreased in the rocuronium group compared with the succinylcholine group (p = 0.046) before intubation. This trend continued after intubation, but the difference was no longer significant (p = 0.070). Intubation scores for rocuronium and succinylcholine groups were similar, and both scores were superior to that for the atracurium group (p = 0.002). CONCLUSION: Intraocular pressure can be controlled during emergency induction of anesthesia and intubation with adequate depth of anesthesia and muscle relaxation. Rocuronium, succinylcholine, and atracurium all provided sufficient muscle relaxation to achieve successful intubation and no increase in IOP. However, rocuronium 0.6 mg/kg provided significantly better intubating conditions compared with atracurium, and it resulted in a significantly greater decrease in IOP compared with baseline than succinylcholine.

Adolescent↗
PubMed1999

Isobolographic analysis of propofol-thiopental hypnotic interaction in surgical patients.

UNLABELLED: Drugs acting via the same mechanism interact additively, whereas a supraadditive effect can result from an interaction of drugs with different mechanisms of action. Hypnotic midazolam-propofol and midazolam-thiopental interactions are supraadditive. In contrast to midazolam, the mechanisms of actions of propofol and thiopental are quite similar. The aim of this study was to test the hypothesis that similarity in the mechanisms of action of propofol and thiopental results in the additive hypnotic interaction. We studied the hypnotic effects of thiopental, propofol, and their combinations in 150 unpremedicated patients in a randomized, double-blind fashion. The ability to open eyes on command was used as an end point. Dose-response curves for the drugs given separately and in combinations at three different dose ratios between the drugs were determined by using a probit procedure, and the 50% effective dose values were compared by using isobolographic and algebraic (fractional) analysis. The hypnotic propofol-thiopental combination was additive with all dose ratios between components of the combination. The absence of propofol-thiopental synergy, as demonstrated with midazolam-thiopental or propofol-midazolam combinations, suggests that the mechanisms underlying the hypnotic effects of propofol and thiopental, in contrast to the above combinations with midazolam, are very similar and could be identical. IMPLICATIONS: The propofol-thiopental hypnotic interaction is additive.

Adolescent↗
PubMed1998

Rapid development of tolerance to analgesia during remifentanil infusion in humans.

UNLABELLED: Studies in experimental animals have demonstrated a rapidly developing acute tolerance to the analgesic effect of opioids administered by continuous i.v. infusion. The aim of the present study was to determine whether acute tolerance plays an important role in the analgesic effect of remifentanil provided by i.v. infusion to humans. The analgesic effect of remifentanil, infused at a constant rate of 0.1 microg x kg(-1) x min(-1) for 4 h, was evaluated by measuring pain tolerance with thermal (2 degrees C water) and mechanical (pressure) noxious stimulations in 13 paid volunteers. The constant-rate infusion of remifentanil resulted in a threefold increase in pain tolerance with both tests. After reaching its maximum in 60-90 min, the analgesic effect of remifentanil began to decline despite the constant-rate infusion, and after 3 h of infusion, it was only one fourth of the peak value. A comparative rate in the development of acute tolerance measured in terms of time to 50% recovery during infusion was 129 +/- 27 min (mean +/- SD) with the cold water test and 138 +/- 39 min with the pressure test. We conclude that the development of tolerance should be included in the calculations for target-controlled infusions. IMPLICATIONS: Our study shows that tolerance to analgesia during remifentanil infusion is profound and develops very rapidly. The administration of opioids during anesthesia based on target-controlled infusions should include corrections for the development of tolerance.

Adult↗
PubMed1995

Intravenous anaesthetic drug interactions: practical applications.

The spectrum of effects that constitutes the state of general anaesthesia can be induced by the combined use of drugs. Each drug has a predominant action regarding one of the anaesthesia components, hypnosis, analgesia and amnesia. However, each agent, when used in combination, not only produces its own expected effect, but it can also modify the effect of another agent acting on a different component. For example, an opioid, in addition to its anti-nociceptive effect, can also potentiate the hypnotic effect of a benzodiazepine. Anaesthetists have long recognized these effects but did not quantify them until recently. Pharmacologists have provided us with techniques to measure drug interactions. We have utilized these techniques to demonstrate and quantify significant pharmacological interactions for hypnotic effect with commonly used intravenous agents. The clinical utility of these combinations can now be exploited precisely for the benefit of all our patients.

Anesthesia, Intravenous↗
PubMed1994

Triple anesthetic combination: propofol-midazolam-alfentanil.

The hypnotic effects of propofol, midazolam, alfentanil, and their binary and triple combinations, were studied in 130 unpremedicated patients in a randomized, double-blind fashion. The ability to open eyes on verbal command was used as an end-point. Dose-response curves for the three drugs given separately and in combination were determined with a probit procedure and the ED50 values were compared with an isobolographic analysis. The ratios of a single-drug fractional dose (ED50 = 1.0) to a combined fractional dose (in fractions of single-drug ED50 values) indicating the degree of superadditivity (synergism) were: 1.4 (P < 0.05) for propofol-alfentanil, 1.8 (P < 0.0005) for midazolam-propofol, 2.8 (P < 0.0001) for midazolam-alfentanil, and 2.6 (P < 0.0001) for propofol-midazolam-alfentanil. The results indicate that the propofol-midazolam-alfentanil interaction produces a profound hypnotic synergism which is not significantly different from that of the binary midazolam-alfentanil combination.

Adult↗
PubMed1991

Sedation in the ICU.

The effect of midazolam on the induction dose-response curve for alfentanil was studied in non-premedicated ASA physical status I or II patients. The response to the verbal command was used as an end point of anaesthesia. Dose-response curves for midazolam, alfentanil, and their combination were determined with a probit procedure, and compared with algebraic (fractional) analysis of drug interaction. Interaction between midazolam and alfentanil was found to be synergistic (supra-additive). The results suggest that the use of this combination is advantageous not only because it helps to achieve different anaesthetic goals with specific drugs (a benzodiazepine for unconsciousness and an opioid for blockade of the responses to noxious stimulation), but also because its components are complementary for unconsciousness.

Adolescent↗
PubMed1990

Alfentanil potentiates midazolam-induced unconsciousness in subanalgesic doses.

The effects of alfentanil on the midazolam dose-response curve for hypnosis was studied with response to the verbal command as an end point in 95 patients. The analgesic effect of alfentanil was studied by measuring the threshold for pain caused by pressure on the trapezius muscle with the use of a dolorimeter in 21 patients. The study was randomized, double-blind, and performed on the unpremedicated patients with ASA physical status I or II. Alfentanil was found to reduce the midazolam ED50 value for the induction of anesthesia in a dose-dependent fashion. The smallest dose of alfentanil (3 micrograms/kg) that caused a marked shift of the midazolam dose-response curve to the left along the dose axis (from the ED50 of 270 micrograms/kg to the ED50 of 142 micrograms/kg, P less than 0.0005) represents approximately 2% of the alfentanil ED50 for induction of unconsciousness (130 micrograms/kg). Alfentanil (10 micrograms/kg) caused only a tendency for increase in the pain threshold, whereas a dose of 15 micrograms/kg significantly increased the pain threshold by 37% (P less than 0.05). The results demonstrate that alfentanil potentiates the hypnotic effect of midazolam in very small doses. The high potency of alfentanil in this respect, as compared to its analgesic potency, suggests a very specific mechanism of alfentanil-midazolam hypnotic interaction, one that most likely is based on a functional relationship between the GABA receptor-benzodiazepine receptor system and the opioid receptor system in mediation of hypnosis.

Adult↗
PubMed1989

Midazolam-alfentanil synergism for anesthetic induction in patients.

The effect of midazolam on the induction dose-response curve for alfentanil was studied in nonpremedicated ASA physical status I or II patients. The response to the verbal command was used as an end point of anesthesia. Dose-response curves for midazolam, alfentanil, and their combination were determined with a probit procedure, and compared with algebraic (fractional) analysis of drug interaction. Interaction between midazolam and alfentanil was found to be synergistic (supraadditive). The results suggest that the use of this combination is advantageous not only because it helps to achieve different anesthetic goals with specific drugs (a benzodiazepine for unconsciousness and an opioid for blockade of the responses to noxious stimulation), but also because its components are complementary for unconsciousness.

Adolescent↗
PubMed1987

Barbiturates inhibit stress-induced analgesia.

The effect of pentobarbitone and thiopentone on stress-induced analgesia was studied in 40 male Sprague-Dawley rats. Antinociception was determined by measuring motor reaction threshold to the noxious pressure on the tail with the use of an "Analgesymeter." Stress was induced by placement of a clamp on the hind paw. The stress procedure was found to cause an increase in reaction threshold, which was partially suppressed by naloxone 0.5 mg X kg-1. Pentobarbitone in a subanaesthetic dose of 25 mg X kg-1, SC, almost completely abolished the stress-induced increase in the reaction threshold (an increase in reaction threshold from 329 +/- 33 g to 486 +/- 62 g in control group, and from 250 +/- 26 g to 273 +/- 35 g in pentobarbitone group, p less than 0.02 for the difference in the threshold changes). Thiopentone used in a dose of 25 mg X kg-1, IV, caused a loss of the righting reflex for 37 +/- 10 minutes; stress procedure applied ten minutes after regaining the righting reflex did not cause any increase in the reaction threshold (with an increase in the reaction threshold in control group from 355 +/- 50 g to 540 +/- 26 g, p less than 0.001 for the difference between the groups). The results suggest that the barbiturates in subanaesthetic doses inhibit stress-induced analgesia. Thiopentone used in an anaesthetic dose has the potential for inhibition of stress-induced analgesia in the period of recovery from anaesthesia.

Animals↗
PubMed1985

Midazolam: pharmacology and uses.

Midazolam is an imidazobenzodiazepine with unique properties when compared with other benzodiazepines. It is water soluble in its acid formulation but is highly lipid soluble in vivo. Midazolam also has a relatively rapid onset of action and high metabolic clearance when compared with other benzodiazepines. The drug produces reliable hypnosis, amnesia, and antianxiety effects when administered orally, intramuscularly, or intravenously. There are many uses for midazolam in the perioperative period including premedication, anesthesia induction and maintenance, and sedation for diagnostic and therapeutic procedures. Midazolam is preferable to diazepam in many clinical situations because of its rapid, nonpainful induction and lack of venous irritation. Compared with thiopental, midazolam is not as rapid acting nor predictable in hypnotic effect. It will not replace thiopental as an induction agent. Advantages of midazolam over thiopental are those of the more versatile pharmacologic properties of a benzodiazepine compared with a barbiturate such as amnestic and anxiolytic properties. Midazolam should be a useful addition to the formulary.

Adult↗
PubMed1985

Morphine--caffeine analgesic interaction in rats.

The ability of caffeine to modify the effect of morphine on motor response to noxious stimulation was studied in 195 rat experiments. Motor reaction responses to noxious stimuli were studied in three series of experiments with three different techniques of mechanical tail stimulation. In each series of experiments, dose-response curves for morphine (probit analysis) were determined with and without the addition of caffeine (30 mg X kg-1). It was found that caffeine decreased morphine ED50 values in all three series of experiments, from 1.1 to 0.6 mg X kg-1 (P less than 0.002), from 3.2 to 2.5 mg X kg-1 (P less than 0.01), and from 13.2 to 6.2 mg X kg-1 (P less than 0.002). When caffeine was used alone in a dose of 30 mg X kg-1, there were no significant changes in motor reaction responses with any of the three methods applied for the assessment of morphine-caffeine combinations. These data indicate that caffeine potentiates the inhibitory effect of morphine on motor response to noxious stimulation in rats. It has been suggested that the effect of morphine on the motor response to somatic noxious stimulation results primarily from activation of inhibitory control systems concerned with this response. Caffeine may modulate the antinociceptive effect of morphine by stimulating one of these systems.

Analgesics↗
PubMed1983

The pharmacokinetics of midazolam in chronic renal failure patients.

Fifteen patients with chronic renal failure (CRF) were given midazolam 0.2 mg/kg iv over 15 s. All but one lost consciousness in a time ranging from 22-100 s (mean +/- SD was 55 +/- 26 s) after drug administration. Patients regained consciousness from 6-105 min (mean 53 +/- 32) after drug administration. The calculated mean plasma level of midazolam at arousal was 81 +/- 47 ng/ml. Pharmacokinetics parameters were determined from midazolam plasma levels measured in 16 consecutive venous blood samples. The pharmacokinetic parameters in CRF patients were compared with those of healthy volunteers matched for age, sex, and body size with the CRF patients. Protein binding was determined by equilibrium dialysis. CRF patients had a significantly higher (P less than 0.005) plasma-free drug fraction (6.5% +/- 0.7) compared with the control patients (3.9% +/- 0.1). Total (bound plus unbound) kinetics differed in the two groups: volume of distribution 3.8 +/- .3 1/kg in CRF patients versus 2.2 +/- .2 1/kg in controls (P less than 0.001), and clearance 11.4 +/- 1.6 ml X min-1 X kg-1 in CRF patients versus 6.7 +/- 0.9 ml X min-1 X kg-1 in controls (P less than 0.02). When kinetic parameters were corrected for protein binding, CRF patients unbound volume of distribution (63.5 +/- 6.8 1/kg) and free drug clearance (189 +/- 29 ml X min-1 X kg-1) were not different from the control group's volume of distribution (55.6 +/- 5.7 1/kg) and free drug clearance (176 +/- 24 ml X min-1 X kg-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

Midazolam.

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Anesthetics↗
PubMed1982

Premedication with intramuscular midazolam: a prospective randomized double-blind controlled study.

One hundred A.S.A. physical status I and II surgical patients were randomized to receive midazolam, 0.07 mg/kg (group M, 31 patients), hydroxyzine, 1.0 mg/kg (group H, 34 patients), or midazolam diluent as a placebo (group P, 35 patients). Drugs were administered in the vastus lateralis muscle 60 to 90 minutes before anesthesia induction. Anesthesia was induced with thiopental, 3.0 mg/kg, followed by 1.0-mg/kg increments if required. An entry criterion was that patients score greater than or equal to 50% on a subjective Anxiety Visual Analog Test (AVAT). Anxiety was also objectively rated on a six-point scale by a trained observer. Patients and observer were unaware of type of premedication used. Midazolam and hydroxyzine produced significantly (p less than 0.05) greater reduction of anxiety than placebo on both the AVAT and objective anxiety evaluations. Peak onset appeared between 30 and 60 minutes after drug administration. Hemodynamic changes were similar in all groups, and no untoward reactions were encountered before anesthesia. The injection site 24 and 48 hours after administration showed evidence of mild tissue irritation in 68% of patients in group H, 26% of patients in group M, and none of the patients in group P. Midazolam is an efficacious, safe premedicant in relatively healthy patients. It has a prompt onset of action with only minimal tissue irritation.

Anxiety↗