Subjective, psychomotor, cognitive, and analgesic effects of subanesthetic concentrations of sevoflurane and nitrous oxide

BACKGROUND: Sevoflurane is a volatile general anesthetic that differs in chemical nature from the gaseous anesthetic nitrous oxide. In a controlled laboratory setting, the authors characterized the subjective, psychomotor, and analgesic effects of sevoflurane and nitrous oxide at two equal minimum alveolar subanesthetic concentrations. METHODS: A crossover design was used to test the effects of two end-tidal concentrations of sevoflurane (0.3% and 0.60%), two end-tidal concentrations of nitrous oxide (15% and 30%) that were equal in minimum alveolar concentration to that of sevoflurane, and placebo (100% oxygen) in 12 healthy volunteers. The volunteers inhaled one of these concentrations of sevoflurane, nitrous oxide, or placebo for 35 min. Dependent measures included subjective, psychomotor, and physiologic effects, and pain ratings measured during a cold-water test. RESULTS: Sevoflurane produced a greater degree of amnesia, psychomotor impairment, and drowsiness than did equal minimum alveolar concentrations of nitrous oxide. Recovery from sevoflurane and nitrous oxide effects was rapid. Nitrous oxide but not sevoflurane had analgesic effects. CONCLUSIONS: Sevoflurane and nitrous oxide produced different profiles of subjective, behavioral, and cognitive effects, with sevoflurane, in general, producing an overall greater magnitude of effect. The differences in effects between sevoflurane and nitrous oxide are consistent with the differences in their chemical nature and putative mechanisms of action.     

Renal medullary carcinoma

Hyperhomocysteinemia is an independent risk factor for coronary artery and cerebrovascular disease, but its significance in the perioperative period is unknown. Nitrous oxide inhibits methionine synthase, which aids in the conversion of homocysteine to methionine. In this prospective, controlled, randomized study, we determined the effect of intraoperative nitrous oxide exposure on postoperative plasma homocysteine concentrations. Twenty ASA physical status I-III patients, aged >18 yr, presenting for elective craniotomy, were randomized to receive general anesthesia with or without nitrous oxide (inspired nitrous oxide >50%). Plasma was sampled before the induction of anesthesia, on arrival in the postanesthesia care unit (PACU) after discontinuation of nitrous oxide, and 24 h after induction. There was a significant increase (22.6+/-11.4 vs 13.0+/-4.7 micromol/L; P = 0.0038 for postoperative versus preinduction values) in plasma homocysteine concentrations in the nitrous oxide group on arrival in the PACU and for 24 h. In the nonnitrous oxide group, mean plasma homocysteine concentrations did not change (9.5+/-1.9 vs 9.8+/-1.6 micromol/L; P = 0.86 for postoperative versus preinduction values). The change in plasma homocysteine concentrations in the nitrous oxide group was significantly different from that in the nonnitrous group (P = 0.0031). We conclude that the use of intraoperative nitrous oxide leads to significant increases in perioperative plasma homocysteine concentrations. IMPLICATIONS: Short-term exposure to nitrous oxide led to significant increases in plasma homocysteine. Further investigations are required to determine the clinical significance of this change.     

Effects of halothane and sevoflurane on the electroretinogram of dogs

OBJECTIVE: To study the effects of halothane and sevoflurane on the electroretinogram of dogs. ANIMALS: 6 clinically normal Beagles. PROCEDURE: Beagles were paralyzed by continuous IV administration of muscle relaxant and were artificially ventilated with a gas mixture of nitrous oxide and oxygen during experiments. Corneal electroretinograms were recorded, using full-field stimuli under several recording conditions before and during 1% halothane or 2% sevoflurane inhalation. RESULTS: The amplitude of the scotopic threshold response (STR) and b-wave was significantly decreased by halothane or sevoflurane inhalation, but the degree of decrease in the STR was much greater. In contrast, the amplitudes of oscillatory potentials were increased. The peak latencies of the 3 components tended to be prolonged by inhalation of the anesthetic. There seemed to be no difference between the effects of halothane and sevoflurane. CONCLUSIONS: Halothane and sevoflurane strongly depressed the STR in Beagles while moderately depressing the b-wave and increasing oscillatory potential amplitudes. Thus, neither is an appropriate anesthetic for use in recording of the STR in dogs.     

Bilateral transvaginal sacrospinous colpopexy: preliminary experience

OBJECTIVE: Our goal was to determine how often a transvaginal sacrospinous colpopexy procedure can be done bilaterally. STUDY DESIGN: Between August 1993 and July 1996, 66 patients were prospectively evaluated for uterine prolapse (19 patients) and posthysterectomy vaginal vault prolapse (47 patients). Twenty-six patients (25 with posthysterectomy vaginal vault prolapse) underwent an abdominal sacral colpopexy. The remaining 40 patients (18 with uterine prolapse, 22 with posthysterectomy vaginal vault prolapse) were preoperatively and intraoperatively assessed for a bilateral sacrospinous colpopexy. All patients with uterine prolapse underwent hysterectomy. RESULTS: In 10 of the 18 (56%) patients with uterine prolapse and in 16 of the 22 (73%) patients with posthysterectomy vaginal vault prolapse, bilateral suspension to the sacrospinous ligament was carried out. Follow-up has ranged from 6 to 40 months, and no recurrent vaginal cuff prolapses have been detected in any patients. In 3 patients, however, all in the bilateral fixation categories, distention cystoceles have developed; one patient has undergone a successful anterior colporrhaphy. CONCLUSIONS: The bilateral suspension is different from the unilateral suspension in that the former requires significant intraoperative judgment in its feasibility and in maintaining the width of the vaginal cuff to allow a bilateral suspension without tension. A bilateral fixation appears more attainable in a patient with posthysterectomy vaginal vault prolapse than in one with uterine prolapse.     

Does nitrous oxide antagonize isoflurane-induced suppression of learning?

BACKGROUND: A greater MAC fraction of nitrous oxide than isoflurane is required to prevent response to verbal commands and suppress the capacity to learn. Speculating that this difference between these agents may be caused by nitrous oxide's capacity to increase sympathetic activity, we tested the hypothesis that nitrous oxide may antagonize the suppression of learning found with isoflurane. METHODS: We administered a combination of isoflurane and nitrous oxide at three subanesthetic test concentrations (0.43, 0.56, and 0.68 MAC) to 24 healthy male volunteers. Assuming additivity of the anesthetics, the first test concentration was selected to suppress learning of new information by 50% (ED50 for suppression of learning); the second concentration, to suppress the ability to respond appropriately to verbal command by 50% (MAC-awake); and the third, to provide 1.4 times MAC-awake. Three tests of learning were applied. At each test concentration, we provided 7 answers to "trivial pursuit"-type questions, resulting in a set of 21 answered questions for each volunteer; an additional 7 unanswered questions served as controls. At the highest test concentration, each volunteer also heard two examples from each of two categories (4 words) repeated 30 times (the category-example task), and a message instructing them to touch either their nose or their ear during a specified interval in the postanesthetic interview (the behavior task). RESULTS: The MAC-awake value for the combination of isoflurane and nitrous oxide was 118 +/- 4% of the expected value (i.e., the two anesthetics were antagonistic for this effect). Consistent with antagonism, the anesthetic concentration predicted to suppress learning by 50% permitted significantly more learning, and the ED50 was 105 +/- 2% of that predicted. Neither the category task nor the behavior task demonstrated evidence of learning at 1.4 times MAC-awake. CONCLUSIONS: Our results are consistent with an antagonism between nitrous oxide and isoflurane; however, the degree of antagonism is small.     

Effect of nitrous oxide on spinal dorsal horn WDR neuronal activity in cats

The effects of nitrous oxide (75%) on the spinal dorsal born wide dynamic range (WDR) neuronal activity were studied in either spinal cord intact or spinal cord-transected cats. Extracellular activity was recorded in the dorsal horn from single WDR neurons responding to noxious and non-noxious stimuli applied to the cutaneous receptive fields on the left bind foot pads of intact or decerebrate, spinal cord-transected (L 1-2) cats. The experiment was divided into four sections as follows: (1) When 10 micrograms of bradykinin (BK) was injected into the femoral artery ipsilateral to the recording site as the noxious test stimulus in the spinal cord-transected cat, all of 6 WDR neurons gave excitatory responses which were not depressed by 75% nitrous oxide. (2) When the injection of 10 micrograms of BK into the femoral artery ipsilateral to the recording site was used in the spinal cord-intact cat, 6 of 15 WDR neurons (40%) gave excitatory responses, which were significantly depressed by 75% nitrous oxide, and 9 of 15 WDR neurons (60%) gave inhibitory responses, which were not affected by 75% nitrous oxide. (3) When 10 micrograms of bradykinin (BK) was injected into the femoral artery contralateral to the recording site as the noxious test stimulus in the spinal cord transected cat, 6 of 12 WDR neurons gave excitatory reasons, which were not depressed by 75% nitrous oxide. (4) When the injection of 10 micrograms of BK into the femoral artery contralateral to the recording site was used in the spinal cord-intact cat, 6 of 6 WDR neurons (100%) gave responses, which were affected by 75% nitrous oxide. We have observed that nitrous oxide reduces the excitation and inhibition of dorsal born WDR neuronal activities induced by BK injection in spinal cord-intact cats, but does not reduce the excitation of those in spinal cord-transected cats. This finding confirmed that the antinociceptive effect of nitrous oxide might be modulated by supraspinal descending inhibitory control systems. In addition our result showed that the supraspinal effect of nitrous oxide was mediated not only by an increase but also a decrease in a supraspinal descending inhibition.     

Snowboard traumatology: an epidemiological study

OBJECTIVE: To estimate the frequency of perioperative morbidities in patients who underwent anesthesia and a surgical procedure with no preoperative laboratory testing. MATERIAL AND METHODS: We conducted an electronic database search of medical records of 56,119 patients who underwent surgical or diagnostic procedures and anesthesia at Mayo Clinic Rochester in 1994 and found 5,120 who had no laboratory tests done within 90 days before the procedure. From this group, we randomly selected 1,044 patients (87 from each month) to document the absence of preoperative tests, the presence of preexisting disease (by organ system), the type of anesthetic agent, and the outcomes and tests intraoperatively and postoperatively. RESULTS: The 1,044 patients ranged in age from 0 to 95 years (median age, 21). No deaths or major perioperative morbidities occurred (0.0%; exact 95% confidence interval, 0.00 to 0.35%). Although 10 patients underwent blood typing and screening for antibodies immediately preoperatively, no blood transfusions were necessary. Intraoperatively, 17 laboratory tests and 1 electrocardiogram were obtained, and 3 results were abnormal. Postoperatively, 42 blood tests and 2 electrocardiographic procedures were performed. Five of the 42 blood tests showed abnormal results (hemoglobin levels in 3, serum sodium in 1, and arterial blood gases in 1). One electrocardiogram showed normal findings, and the other revealed normal results except for premature ventricular contractions. No laboratory test done intraoperatively or postoperatively was found to change surgical or medical management substantially. One patient who had unanticipated blood loss during an outpatient procedure was admitted to the hospital for observation. CONCLUSION: All 1,044 patients, 97% of whom were relatively healthy, with no recent laboratory testing safely underwent anesthesia and an operation. We conclude that patients who have been assessed by history and physical examination and determined to have no preoperative indication for laboratory tests can safely undergo anesthesia and operation with tests obtained only as indicated intraoperatively and post-operatively. Current anesthetic and medical practices rapidly identify perioperative indications for laboratory evaluation as they arise.     

Anesthetic management of Seckel syndrome: a case report

Seckel syndrome is a rare syndrome of chromosome aberration, in which bird-headed dwarfism, microcephalus and other minor deformities are recognized. A 24-year-old male patient with Seckel syndrome underwent both abdominal and orthopaedic surgeries in 1 year under general anesthesia. The first operation was an emergent operation under preshock state and enterostomy was performed. The second was arthrodesis of the hip joint. Before the second operation, laryngeal CT, tomography and fiberscopy revealed stenosis just below his vocal cord. During the second operation, the anesthesia was unsatisfactory with inhalation of nitrous oxide and sevoflurane and intravenous vecuronium, because of intraoperative abnormal hypertension. But the recovery from the anesthesia was prompt. Although we experienced no difficulty in intubation except for intraoperative abnormal hypertension, preoperative laryngeal and renal examinations are necessary in the anesthetic management of this syndrome.     

A serological survey for bovine immunodeficiency-like virus in Ontario dairy cattle and associations between test results, production records and management practices

The release of waste anesthetic gases (WAG) in hospital operating rooms (ORs) was evaluated to determine if staff exposure to nitrous oxide exceeded the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) and investigate possible correlations between symptoms and nitrous oxide exposure. The monitoring strategy consisted of nitrous oxide measurements by personal monitoring of the anesthetists and scrub nurses, and area monitoring at the exhaust grills. In addition, room ventilation rates and carbon dioxide concentrations were measured. Self-administered questionnaires were given to both the operating room personnel and staff on control wards. Nitrous oxide levels exceeded the current TLV of 50 ppm in 4 of 12 ORs. Anesthetists typically received the highest nitrous oxide exposure. There was a strong correlation (r2 = 0.90) for nitrous oxide dosimetry results between anesthetists and scrub nurses, and a fair correlation (r2 = 0.35) between area monitoring results and the anesthetists' personal exposures. Carbon dioxide levels commonly exceeded 1000 ppm on control wards. A correlation between reported symptoms and nitrous oxide exposure was not demonstrated. Reported symptoms more closely correlated with carbon dioxide levels. Nitrous oxide dosimetry of the anesthetists appears to be the only accurate strategy for monitoring human exposure to WAG in an operating room.     

Localization of NADPH diaphorase in the thoracolumbar and sacrococcygeal spinal cord of the dog

The distribution of NADPH-d activity and NOS-immunoreactivity in the spinal cord of the dog was studied to evaluate the role of nitric oxide in lumbosacral afferent and spinal autonomic pathways. At all levels of the spinal cord examined, NADPH-d staining and NOS-immunoreactivity were present in neurons and fibers in the superficial dorsal horn, dorsal commissure and in neurons around the central canal. Sympathetic preganglionic neurons in the rostral lumbar segments identified by choline acetyl transferase (ChAT) immunoreactivity exhibited prominent NADPH-d and and NOS-immunoreactive staining; whereas the ChAT-immunoreactive parasympathetic preganglionic neurons in the sacral segments were not stained. The most prominent NADPH-d activity in the sacral segments occurred in fibers extending form Lissauer's tract through lamina I along the lateral edge of the dorsal horn to the region of the sacral parasympathetic nucleus. These fibers were prominent in the S1-S3 segments but not in adjacent segments (L5-L7 and Cx1 or in thoracolumbar segments. The NADPH-d fibers were not NOS-immunoreactive, but did overlap with a prominent fiber bundle containing vasoactive intestinal polypeptide immunoreactivity in the sacral spinal cord. These results indicate that nitric oxide may function as a transmitter in thoracolumbar sympathetic preganglionic neurons, but not in sacral parasympathetic preganglionic neurons. The functional significance of the NADPH-d positive, NOS-negative fiber bundle on the lateral edge of the sacral dorsal horn remains to be determined. However, based on anatomical studies in other species it seems reasonable to speculate that the fiber tract represents, in part, visceral afferent projections to the sacral parasympathetic nucleus.     

Anaesthetic management of an adult patient with X-linked adrenoleukodystrophy

PURPOSE: Adrenoleukodystrophy (ALD) is a rare genetic disorder. Findings include various central nervous system problems in addition to adrenal insufficiency. We present a case of an adult man with X-linked ALD undergoing surgery. CLINICAL FEATURES: A 40-yr-old man with X-linked ALD presented with an intertrochanteric femoral fracture. Past medical history included recurrent lung atelectasis, urinary incontinence, mental retardation, seizure disorder, and adrenal insufficiency. No sedative pre-medications were ordered, but perioperative steroid coverage with 100 mg hydrocortisone was initiated. In the operating room, the patient would not allow placement of all monitors. Therefore, 1 mg midazolam then 275 mg thiopentone followed immediately by 40 mg rocuronium were used to induce anesthesia with the application of cricoid pressure and the remaining monitors. Fentanyl 50 micrograms i.v. was given soon after induction, and anaesthesia was maintained with nitrous oxide and isoflurane. No further muscle relaxant or opioid was administered and anaesthesia was uneventful. The trachea was extubated with the patient awake and he was taken to the recovery area in stable condition. CONCLUSION: Patients with X-linked ALD are rarely seen in a clinical setting because the condition is so uncommon. Adrenal insufficiency, mental retardation, and osteoporosis are major considerations for these patients. In addition, these patients are at risk for reflux, seizures, and major post-operative complications.     

Anesthesia in a patient with epidermolysis bullosa

A 6-year-old-boy with epidermolysis bullosa underwent plastic surgeries for the scar contraction of hands. Anesthesia was induced with inhalation of sevoflurane in combination with nitrous oxide and oxygen. The tracheal was not intubated. Anesthesia was maintained with sevoflurane, nitrous oxide and oxygen with continuous intravenous infusion of ketamine. The courses of anesthesia and the operations were uneventful. The most important point in the anesthetic management of the patient with this disease is to avoid mechanical stimulation to skin and mucous membrane.     

Methods for reduction of homologous blood transfusions in operative medicine

For ethical and socio-economical reasons (cost-explosion in transfusion-medicine, patient's individual destiny), development and consistent application of allogeneic transfusion sparing techniques in surgery is a challenge to anesthesiologists, surgeons and blood-bankers. The combination of different techniques, i.e. autologous predonation, hemodilution, choice of anesthetic regimen, deliberate hypotension, application of antifibrinolytic agents and autotransfusion of intraoperatively saved blood allow for avoidance of allogeneic blood transfusion even in patients presenting important intraoperative hemorrhage. The present article summarizes (1) risks associated with transfusion of allogeneic blood, (2) actually applied pre- and intraoperative techniques to reduce transfusion of allogeneic blood and (3) new concepts (administration of erythropoietin, hyperoxic ventilation and administration of artificial oxygen carries) to further increase the efficacy of autologous predonation and preoperative normovolemic hemodilution.     

Dependence of dopamine calibration factors on media Ca2+ and Mg2+ at carbon-fiber microelectrodes used with fast-scan cyclic voltammetry

We give a brief history and development of the use of analgesic nitrous oxide in various clinical situations, emphasizing the very important difference between analgesic and anesthetic concentrations of the gas. We give evidence for the opioid nature of analgesic nitrous oxide and the probable role that these opioid properties play in its clinical effects. Its uniqueness among the opioids arises from its ability to safely stimulate both mu and kappa opioid receptors thereby modulating these systems, which are at times antagonistic to each other. These opposing systems appear to be particularly important during addictive withdrawal. We also discuss the possible relationship existing between nitric and nitrous oxide.     

Mediastinal parathyroid adenoma detected by 99mTc-methoxyisobutylisonitrile: report of a case

In a randomized controlled clinical trial, 14 patients requiring resection of tumors were divided in two groups: one group was anesthetized with nitrous oxide [67% N2O-33% O2 (vol/vol)] and the other with propofol. Two other groups of subjects were studied: a group of patients that was undergoing orthopedic procedures and was anesthetized with nitrous oxide [67% N2O-33% O2 (vol/vol)] and a control group (fasted for 10 hrs and no anesthesia). In patients requiring resection of tumors, the blood L-methionine concentration was significantly lower and the blood amino acid pattern was significantly affected after the administration of nitrous oxide (120-310 mins) compared with values after the induction of anesthesia and before surgery. The administration of propofol (120-240 mins) did not produce any of these changes. No patients required blood transfusion during surgery, and the patients had not previously been treated with cancer chemotherapeutic agents. The administration of nitrous oxide (60-150 mins) to patients undergoing orthopedic procedures did not affect blood L-methionine. It is concluded that the administration of nitrous oxide to cancer-bearing patients, but not to those undergoing orthopedic surgery, produced major changes in amino acid metabolism; therefore, consideration should be given to the avoidance of exposure of cancer patients to nitrous oxide.     

The effects of idazoxan combined with 30% nitrous oxide on the jaw-opening reflex in the rat

In rats, the jaw-opening reflex is elicited by activation of a nociceptive receptor by the electric stimulation of the tooth pulp. This study was undertaken to assess the effects of 30% nitrous oxide and 30% nitrous oxide with idazoxan, an alpha 2-adrenergic antagonist, on this reflex. Each rat received electric stimulation for the jaw-opening reflex at 3, 5, 7, 10, 15, and 20 min after both the start of inhalation and the withdrawal of 100% oxygen or 30% nitrous oxide in oxygen. Idazoxan, 400 micrograms/ kg, was administered intravenously at the start of the inhalation period. Amplitudes significantly decreased during inhalation of nitrous oxide, but they returned gradually to control levels after cessation of nitrous oxide inhalation. In the cases of 100% oxygen, 100% oxygen with idazoxan, and 30% nitrous oxide in oxygen with idazoxan, amplitudes did not change from controls during and after 30% nitrous oxide inhalation. The latency remained unchanged irrespective of the treatment. Since in rats the degree of inhibition by 30% nitrous oxide in oxygen is partially diminished by administration of idazoxan, we conclude that nitrous oxide affects an alpha 2-adrenergic receptor in the central nervous system.     

Anesthetic management of two patients with mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS)

MELAS is a type of the mitochondrial myopathy characterized by elevation of pyruvate and lactate levels in both the blood and cerebrospinal fluid. This syndrome frequently accompanies cerebral infarction like symptoms. Recently, we experienced two patients for anesthesia with MELAS (both 11-year-old girls). V-P shunt construction and IVH reservoir implantation were conducted, respectively. Anesthesia was induced with fentanyl and midazolam, and vecuronium was used to facilitate tracheal intubation. Volatile anesthetic was avoided, and anesthesia was maintained with fentanyl, midazolam, and nitrous oxide. Arterial blood gases and pH were frequently checked, and acetated electrolyte solution was infused mainly during surgery. No complications occurred during anesthesia in both patients. In the anesthetic management for MELAS, measures to prevent malignant hyperthermia must also be considered.     

Effects of inhalational anesthetics on biochemical events in growing neuronal tips

BACKGROUND: The influence of general anesthetics on developing organs has been a source of concern for many years. The central nervous system, which is developing rapidly at the time of birth, is of special interest in this regard. In this study, the biochemical characteristics of developing neural tips (growth cones) were examined after exposure to anesthetics to elucidate the molecular mechanism by which long-lasting alterations in the nervous system, including neuroteratogenicity, as previously described, were evoked. METHODS: Neonatal rats were exposed to an atmosphere containing inhalational anesthetics (1% halothane or 75% nitrous oxide) or a control atmosphere (25% O2 and 75% N2) for 6 h at postnatal day 1. After this exposure, growth cone particles were isolated from the forebrain using a recently devised cell fractionation method at postnatal days 2, 3, 4, and 5. Protein composition, phosphoprotein patterns, and protein kinase C (PKC) activities of the isolated growth cones were compared between each group exposed to anesthetics and the control group. The dose-response relationship of the action of anesthetics on PKC activity was also examined (at 0.5 and 0.75% halothane and 25 and 50% N2O). RESULTS: The increase in body weight and brain wet weight were not significantly affected by exposure to either anesthetic. No apparent influence on protein composition was observed by sodiumdodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE). However, calcium-dependent protein phosphorylation of the 46 kDa protein and of the 80 kDa protein, which is reported to be mediated by PKC, were significantly reduced after exposure to the anesthetics. A direct assay of PKC activity in growth cone particles indicated that PKC activity in the growth cone was 70.6 +/- 9.6% of the control value at 24 h after exposure to 1% halothane, and 63.2 +/- 4.9% after exposure to 75% nitrous oxide. Exposure to 0.75% halothane or 50% nitrous oxide had a similar, but lesser, effect on this parameter. In contrast, exposure to 0.5% halothane or 25% nitrous oxide evoked no apparent effect. Thus the PKC activity in growth cone particles, which is thought to play an important role in signal transduction in the developing brain, was shown to be affected by exposure to inhalational anesthetics over a range of concentrations. CONCLUSIONS: Considering the crucial role of growth cones in the establishment of the neuronal network, the interruption of signal transduction in the growth cone at a time that is critical in directing the neurite extension may evoke a long-lasting alteration in the neural network. Therefore, the effect of inhalational anesthetics on the growth cone enzyme observed in this study may have a major role in the mechanism that induces morphologic or behavioral neuroabnormalities in later life.     

Tumour cell killing using chemically engineered antibody constructs specific for tumour cells and the complement inhibitor CD59

BACKGROUND: Although beta blockers have been used primarily to decrease unwanted perioperative hemodynamic responses, the sedative properties of these compounds might decrease anesthetic requirements. This study was designed to determine whether esmolol, a short-acting beta 1-receptor antagonist, could reduce the propofol concentration required to prevent movement at skin incision. METHODS: Sixty consenting patients were premedicated with morphine, and then propofol was delivered by computer-assisted continuous infusion along with 60% nitrous oxide. Patients were randomly divided into three groups, propofol alone, propofol plus low-dose esmolol (bolus of 0.5 mg/kg, then 50 micrograms.kg-1.min-1), and propofol plus high-dose esmolol (bolus of 1 mg/kg, then 250 micrograms.kg-1.min-1). Two venous blood samples were drawn at equilibrium. The serum propofol concentration that prevented movement to incision in 50% of patients (Cp50) was calculated by logistic regression. RESULTS: The propofol Cp50 with nitrous oxide was 3.85 micrograms/ ml. High-dose esmolol infusion was associated with a significant reduction in the Cp50 to 2.80 micrograms/ml (P < 0.04). Propofol computer-assisted continuous infusion produced stable serum concentrations with a slight positive blas. Esmolol did not alter the serum propofol concentration. No intergroup differences in heart rate or blood pressure response to intubation or incision were found. CONCLUSIONS: Esmolol significantly decreased the anesthetic requirement for skin incision. The components and mechanism of this interaction remain unclear. A simple pharmacokinetic interaction between esmolol and propofol does not explain the Cp50 reduction. These results demonstrate an anesthetic-sparing effect of a beta-adrenergic antagonist in humans under clinically relevant conditions.     

Evoked potential testing

Electrophysiologic tests of the sacral neuromuscular system and its suprasegmental control may be divided into EMG and methods involving stimulation (i.e., evoked potential and sacral reflex testing). The latter group of methods tests the function of defined parts of the motor or sensory nervous system, or reflex arcs. There already is ample experience with testing the somatic sensory pathways (pudendal SEP) and the (somatic) sacral reflex arc, whereas other methods (testing the motor system and tests involving visceral afferents and sympathetic efferents) need further study to establish their proper place in everyday clinical diagnostics. The application of these methods in research has led to important advances in our understanding of nervous system involvement in different pathologic conditions leading to neurogenic sacral dysfunctions. If applied in individual patients, these methods should however, be used and interpreted with restraint; they should be considered in patients with probable or proved nervous system lesions, those in whom additional clarification regarding proof of, localization of, and the nature (i.e., axonal versus demyelinative) of the lesion is relevant for diagnosis and prognosis. If applied in patients with central nervous system involvement, evoked potential studies may be used on their own; but, in the author's opinion, in patients with putative peripheral nervous system involvement these tests should be considered, as a rule, only as an extension of a needle EMG exploration. It is expected that further experience will clarify the sensitivity and specificity of the available methods. The already available methods certainly will gain a place in the operating room helping the surgeon in selected procedures involving the pelvis and particularly conus and cauda equina better to identify neuromuscular structures and to monitor their function throughout the operation in order to prevent subsequent development of lesions.