Effects of fentanyl on sympathetic activation associated with the administration of desflurane

Cardiorespiratory Effects and Desflurane Requirement in Dogs Undergoing Ovariectomy after Administration Maropitant or Methadone

General anesthesia for ovariectomy in dogs is based on a balanced anesthesia protocol such as using analgesics along with an inhalant agent. While opioids such as fentanyl and methadone are commonly used for their analgesic potency, other drugs can also have analgesic effects. Maropitant, an antiemetic for dogs and cats, has also been shown to exert analgesic effects, especially on visceral pain. The aim of this study was to compare the cardiorespiratory effects and analgesic properties of maropitant and methadone combined with desflurane in dogs undergoing ovariectomy. Two groups of 20 healthy mixed-breeds bitches undergoing elective ovariectomy received intravenous either maropitant at antiemetic dose of 1 mg kg^-1 or methadone at the dose of 0.3 mg kg^-1. Cardiorespiratory variables were collected before premedication, 10 min after sedation and during surgery. Recovery quality and postoperative pain were evaluated 15, 30, 60, 120, 240 and 360 min postoperatively. Results showed that maropitant produced analgesia and reduced the requirement of desflurane in amounts similar to those determined by methadone (5.39 ± 0.20% and 4.91 ± 0.26%, respectively) without significant difference, while maintaining heart rate, arterial blood pressure, respiratory rate and carbon dioxide end-tidal partial pressure even at a more satisfactory level. Therefore, maropitant may be recommended as an analgesic drug for abdominal surgery not only in healthy dogs but also in those with reduced cardiorespiratory compensatory capacities or at risk of hypotension, especially when combined with a sedative such as dexmedetomidine.

Low-dose fentanyl reduces pain perception, muscle sympathetic nerve activity responses, and blood pressure responses during the cold pressor test

Our knowledge about how low-dose (analgesic) fentanyl affects autonomic cardiovascular regulation is primarily limited to animal experiments. Notably, it is unknown if low-dose fentanyl influences human autonomic cardiovascular responses during painful stimuli in humans. Therefore, we tested the hypothesis that low-dose fentanyl reduces perceived pain and subsequent sympathetic and cardiovascular responses in humans during an experimental noxious stimulus. Twenty-three adults (10 females/13 males; 27 ± 7 yr; 26 ± 3 kg·m^-2, means ± SD) completed this randomized, crossover, placebo-controlled trial during two laboratory visits. During each visit, participants completed a cold pressor test (CPT; hand in ∼0.4°C ice bath for 2 min) before and 5 min after drug/placebo administration (75 μg fentanyl or saline). We compared pain perception (100-mm visual analog scale), muscle sympathetic nerve activity (MSNA; microneurography, 11 paired recordings), and beat-to-beat blood pressure (BP; photoplethysmography) between trials (at both pre- and postdrug/placebo timepoints) using paired, two-tailed t tests. Before drug/placebo administration, perceived pain (P = 0.8287), ΔMSNA burst frequency (P = 0.7587), and Δmean BP (P = 0.8649) during the CPT were not different between trials. After the drug/placebo administration, fentanyl attenuated perceived pain (36 vs. 66 mm, P < 0.0001), ΔMSNA burst frequency (9 vs. 17 bursts/min, P = 0.0054), and Δmean BP (7 vs. 13 mmHg, P = 0.0174) during the CPT compared with placebo. Fentanyl-induced reductions in pain perception and Δmean BP were moderately related (r = 0.40, P = 0.0641). These data provide valuable information regarding how low-dose fentanyl reduces autonomic cardiovascular responses during an experimental painful stimulus.

Effects of anesthetic and sedative agents on sympathetic nerve activity

BACKGROUND

The effects of sedative and anesthetic agents on sympathetic nerve activity (SNA) are poorly understood.

OBJECTIVE

The purpose of this study was to determine the effects of commonly used sedative and anesthetic agents on SNA in ambulatory dogs and humans.

METHODS

We implanted radiotransmitters in 6 dogs to record stellate ganglion nerve activity (SGNA), subcutaneous nerve activity (ScNA), and blood pressure (BP). After recovery, we injected dexmedetomidine (3 μg/kg), morphine (0.1 mg/kg), hydromorphone (0.05 mg/kg), and midazolam (0.1 mg/kg) on different days. We also studied 12 human patients (10 male; age 68.0 ± 9.1 years old) undergoing cardioversion for atrial fibrillation with propofol (0.77 ± 0.18 mg/kg) or methohexital (0.65 mg/kg) anesthesia. Skin sympathetic nerve activity (SKNA) and electrocardiogram were recorded during the study.

RESULTS

SGNA and ScNA were significantly suppressed immediately after administration of dexmedetomidine (P = .000 and P = .000, respectively), morphine (P = .011 and P = .014, respectively), and hydromorphone (P = .000 and P = .012, respectively), along with decreased BP and heart rate (HR) (P <.001 for each). Midazolam had no significant effect on SGNA and ScNA (P = .248 and P = .149, respectively) but increased HR (P = .015) and decreased BP (P = .004) in ambulatory dogs. In patients undergoing cardioversion, bolus propofol administration significantly suppressed SKNA (from 1.11 ± 0.25 μV to 0.77 ± 0.15 μV; P = .001), and the effects lasted for at least 10 minutes after the final cardioversion shock. Methohexital decreased chest SKNA from 1.59 ± 0.45 μV to 1.22 ± 0.58 μV (P = .000) and arm SKNA from 0.76 ± 0.43 μV to 0.55 ± 0.07 μV (P = .001). The effects lasted for at least 10 minutes after the cardioversion shock.

CONCLUSION

Propofol, methohexital, dexmedetomidine, morphine, and hydromorphone suppressed, but midazolam had no significant effects on, SNA.

Cardiopulmonary and acid–Base effects of desflurane and sevoflurane in spontaneously breathing cats

The cardiopulmonary effects of desflurane and sevoflurane anesthesia were compared in cats breathing spontaneously. Heart (HR) and respiratory (RR) rates; systolic (SAP), diastolic (DAP) and mean arterial (MAP) pressures; partial pressure of end tidal carbon dioxide (PETCO2), arterial blood pH (pH), arterial partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2); base deficit (BD), arterial oxygen saturation (SaO2) and bicarbonate ion concentration (HCO3) were measured. Anesthesia was induced with propofol (8±2.3 mg/kg IV) and maintained with desflurane (GD) or sevoflurane (GS), both at 1.3 MAC. Data were analyzed by analysis of variance (ANOVA), followed by the Tukey test ( P<0.05). Both anesthetics showed similar effects. HR and RR decreased when compared to the basal values, but remained constant during inhalant anesthesia and PETCO2 increased with time. Both anesthetics caused acidemia and hypercapnia, but BD stayed within normal limits. Therefore, despite reducing HR and SAP (GD) when compared to the basal values, desflurane and sevoflurane provide good stability of the cardiovascular parameters during a short period of inhalant anesthesia (T20–T60). However, both volatile anesthetics cause acute respiratory acidosis in cats breathing spontaneously.

Desflurane: a clinical update of a third-generation inhaled anaesthetic

Available volatile anaesthetics are safe and efficacious; however, their varying pharmacology provides small but potentially clinically important differences. Desflurane is one of the third-generation inhaled anaesthetics. It is the halogenated inhaled anaesthetic with the lowest blood and tissue solubilities, which promotes its rapid equilibration and its rapid elimination following cessation of administration at the end of anaesthesia. The low fat solubility of desflurane provides pharmacological benefits, especially in overweight patients and in longer procedures by reducing slow compartment accumulation. A decade of clinical use has provided evidence for desflurane's safe and efficacious use as a general anaesthetic. Its benefits include rapid and predictable emergence, and early recovery. In addition, the use of desflurane promotes early and predictable extubation, and the ability to rapidly transfer patients from the operating theatre to the recovery area, which has a positive impact on patient turnover. Desflurane also increases the likelihood of patients, including obese patients, recovering their protective airway reflexes and awakening to a degree sufficient to minimise the stay in the high dependency recovery area. The potential impact of the rapid early recovery from desflurane anaesthesia on intermediate and late recovery and resumption of activities of daily living requires further study.

Desflurane - revisited

The search for an ideal inhalational general anesthetic agent continues. Desflurane, which was recently introduced in the Indian market, possesses favorable pharmacokinetic and pharmacodynamic properties and is closer to the definition of an ideal agent. It offers the advantage of precise control over depth of anesthesia along with a rapid, predictable, and clear-headed recovery with minimal postoperative sequelae, making it a valuable anesthetic agent for maintenance in adults and pediatric patients in surgeries of all durations. The agent has advantages when used in extremes of age and in the obese. Its use may increase the direct costs of providing anesthetic care. Methods or techniques, such as low-flow anesthesia, to reduce the overall cost and along with minimal environmental implications must be followed.

Optimal effect-site concentration of remifentanil for preventing development of hypertension during tracheal intubation with inhaled desflurane induction

BACKGROUND

The aim of the present study was to determine the effect-site concentration of remifentanil needed to prevent haemodynamic instability during tracheal intubation with inhaled desflurane induction.

METHODS

One hundred American Society of Anesthesiologists I and II female patients were randomized to receive an effect-site concentration of remifentanil of 0, 1, 2, 3, or 4 ng/ml. Induction of anaesthesia was started with intravenous injection of propofol 2 mg/kg. Ninety seconds after the completion of propofol injection, rocuronium (0.8 mg/kg) and remifentanil were administered simultaneously with 3% desflurane inhalation. Tracheal intubation was attempted 150 sec after the commencement of remifentanil administration.

RESULTS

A probit model of remifentanil concentration was predictive of successful intubation without development of hypertension (P for goodness-of-fit = 0.419). The effect-site concentration of remifentanil needed to achieve successful intubation without development of hypertension in 95% of the patients was 3.3 ng/ml (95% confidence interval, 2.6-4.8 ng/ml).

CONCLUSIONS

The effect-site concentration of remifentanil of 3.3 ng/ml is effective in blunting the haemodynamic response in 95% of the patients when 2.0 mg/kg of propofol induction was followed by 3% desflurane inhalation.

The effects of lidocaine and fentanyl on airway irritability during inhalation induction with desflurane

BACKGROUND

Inhalation induction with desflurane can cause airway irritability and sympathetic stimulation. The aim of this study was to investigate whether lidocaine and fentanyl could reduce these unwanted reactions.

METHODS

Seventy-five patients who had premedication with midazolam were randomly allocated to one of three groups to receive intravenous saline (S group), lidocaine 1.5 mg/kg (L group), fentanyl 1 microgram/kg (F group), respectively, before tidal volume induction with desflurane in oxygen and nitrous oxide. We recorded airway irritability such as cough, apnea, laryngospasm and excitatory movement and hemodynamic changes.

RESULTS

Airway irritability was not significantly different between the groups. In F group, mean blood pressure at LOC ver and LOC BIS and heart rate at LOC ver, LOC BIS and just before intubation were lower than those of S group (P < 0.05). Other results were not significantly different.

CONCLUSIONS

The results of the study showed that intravenous fentanyl and lidocaine had no beneficial effects to reduce airway irritability, but intravenous fentanyl could significantly reduce hemodynamic stimulation during inhalation induction with desflurane in the patients who were premedicated with midazolam.

Efeitos cardiovasculares e neuroendócrinos do butorfanol e da buprenorfina em cães anestesiados pelo desfluorano

Avaliaram-se os efeitos do butorfanol e da buprenorfina sobre variáveis cardiovasculares e neuroendócrinas em cães anestesiados com desfluorano, utilizando-se 30 cães adultos, machos e fêmeas, distribuídos em três grupos denominados grupo butorfanol (GBT), grupo buprenorfina (GBP) e grupo-controle (GCO). A anestesia foi induzida com propofol (8mg/kgIV) e nos animais intubados administrou-se desfluorano (1,5CAM). Após 30 minutos, nos cães do GBT, aplicou-se butorfanol (0,4mg/kgIM); nos do GBP, buprenorfina (0,02mg/kgIM); e nos do GCO, solução de NaCl a 0,9% (0,05ml/kgIM). Avaliaram-se: freqüência cardíaca; pressões arteriais sistólica, diastólica e média; débito cardíaco; pressão venosa central; cortisol; hormônio adrenocorticotrópico; noradrenalina; e glicose. As colheitas dos dados foram feitas aos 30 minutos após o início da administração do desfluorano (M0), 15 minutos após a administração do opióide ou placebo (M15), e a cada 15 minutos após M15 (M30, M45, M60 e M75). Para a avaliação neuroendócrina utilizaram-se os momentos M-30 (antes da administração dos fármacos), M0, M15 e M45. Na freqüência cardíaca houve diferença entre M0 e M15 (129 e 111bat/min) em GBT, e entre M0 e M30 (131 e 112bat/min) em GBP. Na pressão arterial média, a diferença foi entre M0 (86mmHg) e todos os momentos que se seguiram (todos os valores foram menores que 72mmHg), em GBT. A pressão arterial diastólica foi menor em todos os momentos (<53mmHg) quando comparada com a do M0 (67mmHg), em GBT. Na pressão arterial sistólica, a diferença foi entre M0 e M15 e M30 (112 versus 93 e 94mmHg, respectivamente) em GBT. A inclusão dos opióides determinou discreta redução nos parâmetros cardiovasculares, enquanto o desfluorano interferiu na função neuroendócrina elevando os níveis plasmáticos de glicose.

Accuracy of a third (Dolphin Voyager) versus first generation pulse oximeter (Nellcor N-180) in predicting arterial oxygen saturation and pulse rate in the anesthetized dog

OBJECTIVE

To compare the accuracy of a 3rd (Dolphin Voyager) versus 1st generation pulse oximeter (Nellcor N-180).

STUDY DESIGN

Prospective laboratory investigation.

ANIMALS

Eight adult dogs.

METHODS

In anesthetized dogs, arterial oxygen saturation (SpO(2)) was recorded simultaneously with each pulse oximeter. The oxygen fraction in inspired gas (FiO(2)) was successively reduced from 1.00 to 0.09, with re-saturation (FiO(2) 0.40) after each breathe-down step. After each 3-minute FiO(2) plateau, SpO(2) and pulse rate (PR) were compared with the fractional arterial saturation (SaO(2)) and PR determined by co-oximetry and invasive blood pressure monitoring, respectively. Data analysis included Bland-Altman (B-A) plots, Lin's concordance correlation factor (rho(c)), and linear regression models.

RESULTS

Over a SaO(2) range of 33-99%, the overall bias (mean SpO(2) - SaO(2)), precision (SD of bias), and accuracy (A(rms)) for the Dolphin Voyager and Nellcor N-180 were 4.3%, 4.4%, and 6.1%, and 3.2%, 3.0%, and 4.3%, respectively. Bias increased at SaO(2) < 90%, more so with the Dolphin Voyager (from 1.6% to 8.6%) than Nellcor N-180 (from 3.2% to 4.5%). The SpO(2) readings correlated significantly with SaO(2) for both the Dolphin Voyager (rho(c) = 0.94) and Nellcor N-180 (rho(c) = 0.97) (p < 0.001). Regarding PR, bias, precision, and accuracy (A(rms)) for the Dolphin Voyager and Nellcor N-180 were -0.5, 4.6, and 4.6 and 1.38, 4.3, and 4.5 beats minute(-1), respectively. Significant correlation existed between pulse oximeter and directly measured PR (Dolphin Voyager: rho(c) = 0.98; Nellcor N-180: rho(c) = 0.99) (p < 0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

In anesthetized dogs with adequate hemodynamic function, both instruments record SaO(2) relatively accurately over a wide range of normal saturation values. However, there is an increasing overestimation at SaO(2) < 90%, particularly with the Dolphin Voyager, indicating that 3rd generation pulse oximeters may not perform better than older instruments. The 5.4-fold increase in bias with the Dolphin Voyager at SaO(2) < 90% stresses the importance of a 93-94% SpO(2) threshold to ensure an arterial saturation of >or=90%. In contrast, PR monitoring with both devices is very reliable.

Acute response to intracisternal bupivacaine in patients with refractory pain of the head and neck

Continuous intracisternal infusion of bupivacaine for the management of intractable pain of the head and neck is effective in controlling pain in this patient group. With the catheter tip being located at the height of the C1 vertebral body, autonomic regulatory information may also be influenced by the infusion of bupivacaine. By combining direct sampling of cerebrospinal fluid (CSF), via a percutaneously placed catheter in the cisterna magna, with a noradrenaline and adrenaline isotope dilution method for examining sympathetic and adrenal medullary activity, we were able to quantify the release of brain neurotransmitters and examine efferent sympathetic nervous outflow in patients following intracisternal administration of bupivacaine. Despite severe pain, sympathetic and adrenal medullary activities were well within normal range (4.2 +/- 0.6 and 0.7 +/- 0.2 nmol min(-1), respectively, mean +/-S.E.M.). Intracisternal bupivacaine administration caused an almost instantaneous elevation in mean arterial blood pressure, increasing by 17 +/- 7 mmHg after 10 min (P < 0.01). Heart rate increased in parallel (17 +/- 5 beats min(-1)), and these changes coincided with an increase in sympathetic nervous activity, peaking with an approximately 50% increase over resting level 10 min after injection (P < 0.01). CSF levels of GABA were reduced following bupivacaine (P < 0.05). CSF catecholamines and serotonin, and EEG, remained unaffected. These results show that acutely administered bupivacaine in the cisterna magna of chronic pain sufferers leads to an activation of the sympathetic nervous system. The results suggest that the haemodynamic consequences occur as a result of interference with the neuronal circuitry in the brainstem. Although these effects are transient, they warrant caution at the induction of intracisternal local anaesthesia.

Optimization of desflurane administration in morbidly obese patients: a comparison with sevoflurane using an ‘inhalation bolus’ technique

BACKGROUND

The concept of an 'inhalation bolus' can be used to optimize inhaled drug administration. We investigated the depth of anaesthesia, haemodynamic stability, and recovery time in morbidly obese patients resulting from bispectral index (BIS)-guided sevoflurane or desflurane administration and BIS-triggered inhalation boluses of sevoflurane or desflurane combined with titration of remifentanil.

METHODS

Fifty morbidly obese patients undergoing laparoscopic gastroplasty received either BIS-guided sevoflurane or desflurane anaesthesia in combination with a remifentanil target-controlled infusion. Intraoperative haemodynamic stability and BIS control were measured. Immediate recovery was recorded.

RESULTS

Intraoperatively, the BIS was between 40 and 60 for a greater percentage of time in the sevoflurane (78 (13)% of case time) than in the desflurane patients (64 (14)% of case time), owing to too profound anaesthesia in the desflurane patients at the start of the procedure. However, fewer episodes of hypotension were found in the desflurane group, without the occurrence of more hypertensive episodes. During immediate recovery, eye opening, extubation, airway maintenance, and orientation occurred sooner in the desflurane group.

CONCLUSIONS

Immediate recovery was significantly faster in the desflurane group. Overall hypnotic controllability measured by BIS was less accurate with desflurane. Overall haemodynamic controllability was better when using desflurane. Fewer episodes of hypotension were found in the desflurane group. The use of the inhalation bolus was found to be appropriate in both groups without causing severe haemodynamic side effects. Minimal BIS values were significantly lower after a desflurane bolus.

Effects of desflurane, sevoflurane and isoflurane on pulmonary shunt in dogs during spontaneous ventilation

The aim of this study was to compare the effects of desflurane, sevoflurane and isoflurane on pulmonary shunt in dogs during spontaneous ventilation. General anesthesia was induced in 30 healthy, adult, mongrel dogs by intravenous administration of propofol. The animals were separated into three groups of 10 dogs each and submitted to general inhalation anesthesia with 1.5 MAC of desflurane (G1), sevoflurane (G2) and isoflurane (G3). Arterial blood was collected by puncture of the right femoral artery, and mixed blood was collected by introducing a Swan-Ganz catheter into the pulmonary artery. These samples were used to determine the parameters employed for calculation of the intrapulmonary shunt. Measurements began at 20min after orotracheal intubation and were repeated every 20min, totaling six measurements. Means were compared by the Student t-test (P<FONT FACE=Symbol>£</FONT> 0.05). Desflurane led to a higher shunt than sevoflurane and isoflurane at 40 and 60min. At 80min, the mean values obtained for desflurane were higher than those obtained for isoflurane, while at 100min the values observed for dogs anesthetized with desflurane were higher than those obtained with sevoflurane. Desflurane caused respiratory depression by reducing PaO2, and a higher percentage of intrapulmonary shunt than isoflurane and sevoflurane.

Effects of desflurane and isoflurane on intestinal tissue oxygen pressure during colorectal surgery

Volatile anaesthetics differ in the effects they have on splanchnic haemodynamics and oxygenation. The aim of this study was to evaluate the effects of desflurane and isoflurane as part of a balanced anaesthetic technique on intestinal tissue oxygenation during colorectal surgery. Data were analysed from 44 patients randomly assigned to receive either desflurane (desflurane group, n = 20), or isoflurane (isoflurane group, n = 24) for inhalational anaesthesia. Tissue oxygen pressure (P(tiss)O2) was measured on the serosal side of the large intestine prior to colonic resection (T1) and following the completion of the bowel anastomosis (T2). In addition, haemodynamic and oxygenation parameters were assessed. No difference in mean P(tiss)O2 was observed between the groups at T1 [desflurane group: 8.1 (2.9) kPa vs. isoflurane group: 7.7 (2.7) kPa]. Following completion of the anastomosis (T2) mean P(tiss)O2 was higher in the isoflurane group [9.6 (2.9) kPa] than the desflurane group [7.7 (2.4) kPa, p = 0.025]. During surgery no difference between the groups could be observed with regard to haemodynamics and global oxygenation parameters. The lack of a difference between the groups in P(tiss)O2 before resection of the colon suggests that, under normal conditions, desflurane and isoflurane have comparable effects on intestinal blood flow and oxygenation. However, following local ischaemia, the reactive hyperaemia seems to be better preserved during isoflurane anaesthesia indicated by a local increase in P(tiss)O2blank(p = 0.013) following completion of the bowel anastomosis.

Chronic mu-opioid receptor stimulation in humans decreases muscle sympathetic nerve activity

BACKGROUND

Opioid-addicted patients undergoing detoxification provide a unique opportunity to assess the effects of chronic opioid receptor stimulation on the sympathetic nervous system. We tested the hypothesis that chronic oral methadone intake decreases resting efferent sympathetic nerve activity to muscle (MSA). Furthermore, we assessed whether this effect is reversed by mu-opioid receptor blockade during antagonist-supported detoxification under general anesthesia.

METHODS AND RESULTS

Fifteen young patients (30+/-1 years old, mean+/-SEM) with a long history of mono-opioid addiction and under oral methadone substitution therapy (65+/-10 mg/d for 21+/-6 months) were selected. Peroneal MSA (microneurography) and catecholamine plasma concentrations (high-performance liquid chromatography) were assessed in the awake state and compared with those of age-matched healthy control subjects. The effects of mu-opioid receptor blockade by naloxone (12.4 mg IV) were determined during propofol anesthesia. Compared with healthy volunteers, resting MSA (4+/-2 versus 22+/-2 bursts/min, P<0.0001) and antecubital venous norepinephrine plasma concentration (100+/-64 versus 256+/-48 pg/mL, P=0.01) were markedly decreased in addicted patients despite similar arterial blood pressure and heart rate. Opioid receptor blockade markedly increased MSA (5+/-2 to 24+/-3 bursts/min) and norepinephrine (49+/-12 to 305+/-48 pg/mL) and epinephrine (13+/-2 to 482+/-67 pg/mL) arterial plasma concentrations as well as mean arterial pressure (82+/-4 to 108+/-3 mm Hg) and heart rate (70+/-3 to 86+/-4 beats/min).

CONCLUSIONS

Chronic mu-opioid receptor stimulation by methadone decreases resting MSA in humans.

High concentrations of isoflurane do not block the sympathetic nervous system activation from desflurane

PURPOSE

The volatile anesthetic desflurane has been associated with neurocirculatory responses that have been relatively refractory to adjuvant treatment. We have employed desflurane to evaluate the integrity of the sympathetic nerve recording after establishment of the anesthetized state with another anesthetic agent. This retrospective evaluation of data from volunteers determined if higher concentrations of isoflurane that were sufficient to block the neurocirculatory response to laryngeal and tracheal stimulation would abolish the neurocirculatory response to desflurane.

METHODS

Data from eight, healthy, young volunteers met our criteria for inclusion. They had been anesthetized with propofol or thiopental and intubated after neuromuscular blockade. Each subject was monitored with radial artery blood pressure (BP), heart rate (HR)(ECG), and sympathetic microneurography. Isoflurane had been administered to achieve a steady state concentration of 1.5 MAC (minimum alveolar concentration) while oxygenation and carbon dioxide were monitored with pulse oximetry and infrared spectrometry, respectively. A deep level of anesthesia was confirmed when laryngoscopy and endotracheal tube movement failed to elicit a neurocirculatory response. A brief exposure to 11% desflurane in the inspired gas was then provided.

RESULTS

The responses to desflurane included significant increases in HR, range 32-84 b/min, and BP, range 15-72 mm Hg (P < 0.05). Sympathetic nerve activity increased substantially in the three volunteers with functional nerve recordings.

CONCLUSION

In healthy volunteers receiving 1.5 MAC isoflurane, which was sufficient to block the neurocirculatory response to laryngoscopy and tracheal stimulation, there were striking increases in sympathetic outflow, HR and BP when 11% desflurane was substituted for isoflurane.

Effects of epidural anesthesia on the cardiovascular response to a rapid increase in isoflurane concentration

STUDY OBJECTIVE

To compare circulatory variables to an abrupt increase in isoflurance concentration via mask in patients who received either upper thoracic or lumbar epidural anesthesia, or neither.

DESIGN

Prospective study.

SETTING

Operating room at a university hospital.

PATIENTS

45 ASA physical status I female patients scheduled for elective surgeries with general anesthesia.

INTERVENTIONS

Patients received thoracic (TEA group) or lumbar (LEA group) epidural anesthesia, or neither (control group) (n = 15 per group). An epidural catheter was inserted through the T1-T2 intervertebral space in the TEA group or L2-L3 in the LEA group, and 10 mL of 2% lidocaine without epinephrine was injected. Two minutes after induction of anesthesia with thiamylal, the inspired isoflurane concentration was rapidly increased from 0.5% to 5% and maintained for 5 minutes.

MEASUREMENTS AND MAIN RESULTS

Heart rate and mean arterial pressure (MAP) were measured every minute. Mean analgesic levels obtained by epidural block were C4-T6 and T10-S1 in the TEA and LEA groups, respectively. Heart rate increased after the increase in isoflurane concentration in all groups, but increased significantly less in the TEA group than in the control or LEA groups (p < 0.05). Isoflurane also increased MAP in the control group throughout the 5-minute period, but only at the first minute of inhalation in the TEA and LEA groups. The increases in MAP in the TEA and LEA groups were significantly less than that in the control group (p < 0.05).

CONCLUSION

Epidural anesthesia can blunt circulatory responses to a sudden increase in isoflurane concentration.

Propofol, but not etomidate, reduces desflurane-mediated sympathetic activation in humans

PURPOSE

The administration of desflurane to humans can lead to substantial activation of the neurohumoral axis. Propofol can inhibit the sympathetic response to stress. This study compared the neurocirculatory effects of induction of anesthesia with propofol with those of etomidate on desflurane-mediated sympathetic activation.

METHODS

After informed consent, awake baseline recordings of heart rate (HR), mean arterial blood pressure (MAP), and efferent sympathetic nerve activity (SNA, peroneal nerve) were obtained from healthy volunteers randomly assigned to receive either 2.5 mg x kg(-1) propofol (n=8) or 0.3 mg x kg(-1) etomidate (n=7). Two minutes after i.v. induction, desflurane 3.6% was added to the inspired gas, and increased in consecutive minutes to 7% and 10.9%. Ventilation via mask was continued for an additional seven minutes. Normocarbia was maintained while neurocirculatory parameters were continuously recorded.

RESULTS

There were no differences between groups at baseline. The administration of desflurane via mask after etomidate led to increases in HR, MAP and SNA. Propofol significantly reduced the MAP response and delayed and attenuated the sympatho-excitation.

CONCLUSION

Propofol induction reduced the sympathetic activation and hypertension associated with desflurane.

Effects of desflurane and isoflurane on systemic vascular resistance during hypothermic cardiopulmonary bypass

OBJECTIVE

The objective of this study was to examine the dose-related effects of desflurane and isoflurane on systemic vascular resistance during hypothermic cardiopulmonary bypass.

DESIGN

Randomized, prospective trial.

SETTING

University hospital.

PARTICIPANTS

Sixty consenting patients, 65 years of age or older, scheduled for elective coronary artery surgery.

INTERVENTIONS

Patients were randomly allocated to one of five groups to receive 0.5 or 1.0 minimum alveolar concentration (MAC) (exhaust gas concentration) desflurane or 0.5 or 1.0 MAC isoflurane during hypothermic (32 degrees to 33 degrees C) nonpulsatile cardiopulmonary bypass or to a control group that did not receive any anesthetic agent. Systemic vascular resistance index was recorded at baseline, every 2 minutes for the first 10 minutes during initial administration and every 5 minutes for another 15 minutes during maintenance of anesthesia.

MEASUREMENTS AND MAIN RESULTS

In patients receiving 0.5 MAC desflurane and isoflurane, there were significant differences in systemic vascular resistance index only at 20 and 25 minutes compared with control values. In the desflurane 1.0 MAC group, significant decreases were observed at 15, 20, and 25 minutes compared with controls. In the 1 MAC isoflurane group, the 10-, 15-, 20-, and 25-minute value differed significantly from the control. There were significant decreases in systemic vascular resistance index in the 1.0 MAC groups at 20 and 25 minutes compared with 0.5 MAC values, as well.

CONCLUSIONS

Equi-MAC concentrations of desflurane and isoflurane had similar effects on systemic vascular resistance; 0.5 MAC maintained systemic vascular resistance; 1.0 MAC decreased systemic vascular resistance during hypothermic cardiopulmonary bypass.

Alfentanil modifies the neurocirculatory responses to desflurane

Activation of the sympathetic nervous system occurs in response to desflurane, causing tachycardia and hypertension. Fentanyl partially blunts the hemodynamic effects of desflurane but fails to attenuate the sympathetic response. This study determined the clinical effectiveness and dose response of alfentanil on the neurocirculatory responses to desflurane. Twenty-five healthy, male volunteers were randomized into one of three groups to receive either placebo (n = 9), 10 micrograms/kg intravenous (IV) bolus alfentanil (n = 9), or 20 micrograms/kg IV bolus alfentanil (n = 7) in conjunction with anesthetic induction by propofol, 2.5 mg/kg. Mean arterial pressure (MAP, radial artery), heart rate (HR), and efferent muscle sympathetic nerve activity (SNA, peroneal nerve) were recorded. After conscious baseline measurements, anesthesia was induced by propofol and alfentanil/placebo. One minute later, the desflurane vaporizer was activated at 11%. Neurocirculatory measurements were recorded for 11 min. There were no differences between the groups at conscious baseline. Induction of anesthesia was associated with significantly decreased MAP in the placebo and the 10 micrograms/kg alfentanil groups and increased HR in all groups with little change in SNA. In placebo subjects, desflurane administration increased HR and MAP above baseline. In both alfentanil groups, during desflurane administration HR and MAP never increased significantly above baseline. However, SNA was significantly increased in both groups. Alfentanil effectively blunts the hemodynamic changes but not the sympathetic responses associated with rapid increases in the inspired concentration of desflurane.

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)