Does desflurane modify circulatory responses to stimulation in humans?

The assessment of dermatomal level of surgical anesthesia after spinal tetracaine

Transcutaneous electrical stimulation (TES), a 60-mA, 50-Hz continuous square wave, has been considered equivalent to surgical incision. We examined whether TES at a smaller current (10 mA) can be used to predict surgical anesthesia and compare the results with sensory block to cold, pinprick, and touch after the administration of spinal tetracaine. Two groups of 40 consecutive patients, 17-69 yr old and 70 yr old or older received a subarachnoid injection of 0. 5% tetracaine in 10% glucose or saline according to the type of surgery. Patients undergoing abdominal surgery received glucose solution, and those scheduled for lower extremities surgery received saline solution, and thus, the resultant four groups of patients were studied. Neural block was assessed by the loss of sensation to cold, pinprick, touch, and TES at 10 mA (T10s), and tolerance (i.e., the loss of pain or discomfort) to TES at 10 (T10p) and 60 (T60) mA. Dermatomal levels of sensory block to cold, pinprick, and touch that were cephalad to T60 varied widely. In contrast, dermatomal levels of T10s and T10p cephalad to T60 were less variable, and the difference between T10s and T60 was the smallest among all the differences in any groups. Our results demonstrate that, regardless of patient age and baricity of a local anesthetic solution, T10s is a good predictor of T60 equivalent to the dermatomal level of surgical anesthesia.

IMPLICATIONS

Our results show that the loss of sensation to transcutaneous electrical stimulation at 10 mA, but not cold, pinprick, or touch, is a good predictor of the dermatomal level of block to transcutaneous electrical stimulation at 60 mA, which is considered equivalent to the dermatomal level of surgical anesthesia after the administration of spinal anesthesia.

A method for overcoming the ceiling effect of bounded pain scales

OBJECTIVE

The Verbal Numerical Scale (VNS) for rating pain is bounded between 0 (= no pain) and 10 (= worst pain imaginable). We hypothesized that the limitations inherent to this boundary when rating extremely painful stimuli may be identified by integrating the VNS with an unbounded score such as magnitude estimation of relative change.

METHODS

Volunteers received stimuli of increasing current via cutaneous electrodes until they rated >5 on the VNS scale. This stimulus, termed S, was arbitrarily assigned a magnitude estimate of 100%. Then, stimuli of varying currents were delivered; two were 10 mA and 20 mA higher than S (S(+10) and S(+20)), two were 1/2 of the current for the S stimulus (S(1/2)), and one was at the original current (Srepeat). The pain elicited by each stimulus was scored in proportion to the S stimulus. The extrapolated VNS score (VNSext) was determined by multiplying this magnitude estimate (%) by the VNS score for S.

MAIN RESULTS

Seventy percent of the stimuli with higher intensity than S generated a VNSext score above 10. The mean magnitude estimations for S(+10) and S(+20) were 186% and 242%: they generated mean (median) VNSext values of 12.4 and 16.2, respectively (p = 0.019 for the difference between them by Wilcoxon signed rank test).

CONCLUSIONS

The combined use of VNS and magnitude estimation confirmed that the ceiling of the bounded pain scale may significantly limit a patient's ability to describe a new pain stimulus. VNSext may provide a means of overcoming this limitation.

Dissociation between haemodynamics and sympathetic activation during anaesthetic induction with desfluranes

PURPOSE

To compare the simultaneous haemodynamic effects, sympathetic activation and cardiac risks associated with desflurane used in a balanced technique, with those of isoflurane anaesthesia.

METHODS

A prospective, randomized, open label study was conducted at a University medical centre. Forty patients undergoing major non-cardiac surgery were randomized to receive either desflurane or isoflurane as the primary anaesthetic agent. After premedication, fentanyl and thiopentone were administered i.v.. Anaesthesia was increased up to 1.0 MACET in O2 via controlled mask ventilation and maintained at 1.0 MAC before tracheal intubation. Maintenance consisted of N2O, O2 and desflurane or isoflurane for 10 min. During the study, HR and arterial BP were continuously measured, as were ECG ST-segments and ventricular dysrhythmias using a 3-channel Holter ECG recorder. Left ventricular global and regional function were measured using precordial echocardiography. Serial plasma catecholamine concentrations were measured.

RESULTS

For both groups, HR was maintained without increases over baseline values while systolic BP showed a progressive decrease during induction. Use of beta blockade during induction was higher in the desflurane (7/20 = 35%) than in the isoflurane group (1/20 = 5%), P = 0.04. The plasma norepinephrine concentrations progressively increased in the desflurane group but not in the isoflurane group. Four patients in the desflurane and three in the isoflurane group developed transient worsening of regional function but no change in mean left ventricular ejection fraction area and no ECG ischaemia occurred during anaesthetic induction.

CONCLUSIONS

Desflurane differs from isoflurane in that sympathetic stimulation persisted despite blunting of potential hyperdynamic haemodynamic responses by narcotic and beta blockade. However, this sympathetic activation did not appear to increase cardiac risks.

Haemodynamic comparison of sevoflurane and isoflurane anaesthesia in surgical patients

PURPOSE

To compare the haemodynamic responses to surgical incision during sevoflurane and isoflurane anaesthesia and to compare the haemodynamic effects of each anaesthetic alone with those obtained using an equipotent mixture of each anaesthetic plus N2O during steady-state surgical stimulation.

METHODS

Twenty-four patients undergoing gastrectomy were randomized to receive sevoflurane (n = 12) or isoflurane (n = 12). At 1.5 MAC, haemodynamic measurements were performed before and after surgical incision. During intestinal anastomosis, patients in each group were given (in random order) either 1.5 MAC of the designated anaesthetic or 0.85 MAC of the volatile plus 0.65 MAC N2O. Haemodynamic measurements were repeated under each condition.

RESULTS

One patient in the sevoflurane group and two in the isoflurane group were excluded from the incision study because of hypotension. In both groups, incision increased the heart rate (HR), mean arterial pressure, mean pulmonary arterial pressure (MPAP), pulmonary capillary wedge pressure (PCWP), cardiac index, and systemic vascular resistance index (SVRI). There were no intergroup differences in the effects of incision. Inclusion of N2O resulted in an increase of MPAP (P < 0.05) in both groups, an increase of central venous pressure and PCWP in the sevoflurane group (P < 0.005), and a decrease of HR (P < 0.005) and an increase of SVRI (P < 0.05) in the isoflurane group. There were no intergroup differences in the effects of N2O.

CONCLUSIONS

At 1.5 MAC, sevoflurane and isoflurane do not prevent the haemodynamic response to incision. The haemodynamic effects of each volatile anaesthetic with N2O are minimal compared with those of equi-MAC volatile alone.

Desflurane attenuates the somatosympathetic reflex in rats

Arterial blood pressure and heart rate changes after afferent somatic sensory nerve stimulation are termed the "somatosympathetic reflex" (SSR). Inhibition of the SSR may partially represent an antinociceptive action. This investigation examined the actions of the volatile anesthetic, desflurane, on the SSR evoked by peripheral nerve stimulation. Rats anesthetized with alpha-chloralose (50 mg/kg) and urethane (500 mg/kg) were mechanically ventilated and cannulated with arterial and venous catheters for monitoring arterial pressure and for fluid administration, respectively. The sciatic (n = 7) or tibial (n = 6) nerves were isolated and stimulated at one, two, and four times the voltage threshold required to elicit a change in systemic hemodynamics. These cardiovascular responses were recorded before, during, and after varying concentrations of desflurane, 1.8% (0.25 minimum alveolar anesthetic concentration [MAC]), 3.6% (0.5 MAC), 7.2% (1.0 MAC), and 10.8% (1.5 MAC). Desflurane decreased arterial pressure at 1.0 and 1.5 MAC and heart rate (at more than 0.5 MAC) compared to baseline levels. Tibial nerve stimulation decreased mean arterial pressure (MAP) with no consistent changes in heart rate. Desflurane significantly attenuated this depressor response to tibial nerve stimulation (MAP decrease: control; -20 +/- 2 mm Hg versus 1.0 MAC desflurane; -6 +/- 4 mm Hg). The increases in MAP after sciatic nerve stimulation were also significantly inhibited by increasing concentrations of desflurane. At more than 0.5 MAC desflurane, the pressor response to sciatic nerve stimulation was significantly converted to a depressor response in four of seven rats (MAP: control; increase 24 +/- 2 mm Hg versus 1.0 MAC desflurane; decrease -2 +/- 4 mm Hg). Sciatic nerve stimulation also elicited increases in heart rate which were significantly attenuated by desflurane (control; 37 +/- 6 bpm versus 1.5 MAC desflurane; 0 +/- 2 bpm). These findings demonstrate that desflurane produces dose-dependent cardiovascular depression in rats and, despite previous reports of sympathoexcitation, desflurane significantly attenuated both excitatory and inhibitory types of SSR. The results of this study also support a potential antinociceptive action for this anesthetic.

Cardiopulmonary effects of desflurane in the dog during spontaneous and artificial ventilation

The cardiopulmonary effects of desflurane at end tidal concentrations of 10.3, 12.9 and 15.5 per cent during either spontaneous or artificial ventilation were studied in five beagle dogs. Desflurane anaesthesia resulted in tachycardia and a decrease in arterial blood pressure which were not significantly related to the end tidal desflurane concentrations or the mode of ventilation. At an end tidal desflurane concentration of 15.5 per cent there was a significant increase in central venous and pulmonary arterial wedge pressures and, with artificial ventilation, a reduction in cardiac output and stroke volume when compared with similar measurements at an end tidal desflurane concentration of 10.3 per cent. When allowed to breathe spontaneously, the dogs panted at times when they were lightly anaesthetised, but their respiration was depressed to a varying extent at the highest end tidal desflurane concentration. The induction of anaesthesia with desflurane was smooth, and the quality of anaesthesia during maintenance was excellent. There was one episode of a transient tachyarrhythmia associated with the measurement of cardiac output, but no other side effects were observed.

Controlling the hemodynamic response to laryngoscopy and endotracheal intubation

The hemodynamic response to the stress of laryngoscopy and endotracheal intubation does not present a problem for most patients. However, patients with cardiovascular or cerebral disease may be at increased risk of morbidity and mortality from the tachycardia and hypertension resulting from this stress. These hemodynamic effects gained notice after the introduction and use of muscle relaxants, such as curare and succinylcholine, for endotracheal intubation at the time of anesthesia induction. A variety of anesthetic techniques and drugs are available to control the hemodynamic response to laryngoscopy and intubation. The method or drug of choice depends on many factors, including the urgency and length of surgery, choice of anesthetic technique, route of administration, medical condition of the patient, and individual preference. The possible solutions number as many as the medications and techniques available and depend on the individual patient and anesthesia care provider. This paper reviews these medications and techniques to guide the clinician in choosing the best methods.

Desflurane. A review of its pharmacodynamic and pharmacokinetic properties and its efficacy in general anaesthesia

Desflurane is a halogenated ether inhalation general anaesthetic agent with low solubility in blood and body tissues, and approximately one-fifth the potency of isoflurane. The pharmacodynamic properties of desflurane generally resemble those of isoflurane; thus, it produces dose-dependent depression of the central nervous and cardiorespiratory systems, and tetanic fade at the neuromuscular junction. The alveolar equilibration of desflurane is rapid (90% complete at 30 minutes compared with 73% for isoflurane). Both desflurane and isoflurane are distributed to various tissues to a similar extent. Desflurane is resistant to chemical degradation and undergoes negligible metabolism (approximately equal to 10% of that seen with isoflurane). Desflurane 'wash-out' is approximately equal to 2 to 2.5 times faster than that of isoflurane in the first 2 hours after discontinuation of anaesthesia. The low solubility of desflurane facilitates a rapid induction of anaesthesia and precise control of the depth of anaesthesia (during maintenance). Results from a few clinical studies indicate that emergence from desflurane is significantly earlier (by approximately equal to 2 to 6 minutes) than that from propofol anaesthesia, whereas other studies do not concur. In comparison with isoflurane, emergence from desflurane anaesthesia is significantly earlier (by 5 minutes) after ambulatory and approximately equal to 50% earlier (also significant) after nonambulatory surgical procedures. Limited comparative studies with halothane or sevoflurane also suggest an earlier time of emergence from desflurane anaesthesia. Comparative studies of desflurane and propofol, and other inhalation agents, indicate that the times to toleration of oral fluids, sitting and discharge from recovery room are similar, regardless of the general anaesthetic agent administered. However, some limited data in elderly patients (aged > 65 years) suggest that this patient group spends a significantly shorter time in the postanaesthesia care unit after desflurane than after isoflurane anaesthesia. Differences, if any, in the recovery of cognitive and psychomotor functions after desflurane or propofol anaesthesia remain unclear. However, in comparison with isoflurane anaesthesia, recovery of these functions (up to 45 minutes post-operatively) occurs earlier after desflurane. Significantly fewer patients are subjectively impaired (i.e. drowsy, clumsy, fatigued or confused) upon recovery from desflurane than from isoflurane anaesthesia. Likewise, significantly fewer adult patients are delirious when recovering from desflurane than from isoflurane anaesthesia, though in paediatric patients delirium is more likely when recovering from desflurane than from halothane anaesthesia. Haemodynamic stability during coronary artery surgery is as well maintained with desflurane as with isoflurane, and the drug does not worsen the adverse postoperative outcomes.(ABSTRACT TRUNCATED AT 400 WORDS)

A new method to evaluate cardiovascular response in anesthetized rats. Hypertension after variable intensity, brief electrical stimuli

To establish and standardize a nociceptive response in anesthetized rats, the hypertensive responses to defined electrical and mechanical stimuli were studied. Rats (n = 7) were given etomidate, 3.8 mg/kg/hr intravenously (i.v.) 2 hr following carotid artery and jugular vein cannulation. At 15 min after beginning the infusion, four types of noxious stimuli were administered sequentially at 1-min intervals (14 stimuli total): Type 1: Square electrical waves, 125 cps, 1.6 msec, 2-sec train duration, varying current from 0.4 to 12 mA (11 stimuli); Type 2: A single 10-mA electrical stimulus, 5-sec train duration; Type 3: Tail clamping; and, Type 4: Skin incision. After each stimulus, maximum change in systolic blood pressure (delta SBP) was measured. delta SBP after the most intense stimuli was as follows: Type 1 (12 mA, 2 sec), 32.1 +/- 2.14 mmHg; Type 2 (10 mA 5 sec), 42.9 +/- 2.4 mmHg; Type 3 (tail-clamping), 34.3 +/- 3.3 mmHg; Type 4 (skin incision), 14.2 +/- 2.8 mmHg. For the multiple Type-2 stimuli, a relationship between current and delta SBP was present. The authors believe that characterized graded electrical stimulation will allow a more quantitative evaluation of the hypertensive response to noxious stimuli in etomidate anesthetized rats, as compared to observing a single response to a single stimulus. The characterization of the electrical stimulation by amplitude, frequency, and wave form makes research work on nociception under anesthesia easily reproducible.