Oxide Anesthesia Research Articles

Anestesia com cetamina, midazolam e óxido nitroso em cães submetidos à esofagoplastia cervical

Este estudo foi realizado para avaliar a anestesia intravenosa com cetamina e midazolam (K-M) em cães ventilados mecanicamente com 66% de óxido nitroso e 33% de oxigênio ou 100% de oxigênio. Foram utilizados 16 cães sem raça definida, hígidos, com peso médio de 14,2 ± 3,78kg, submetidos a jejum sólido de 12 horas prévio ao procedimento. A anestesia foi induzida com a associação de cetamina (10mg.kg-1) e midazolam (0,5mg.kg-1) administrados na mesma seringa por via intravenosa (IV). Para manutenção anestésica, foi utilizada cetamina (5mg.kg-1) e midazolam (0,25mg.kg-1) administrados por via IV em intervalos de 10 minutos. Os animais foram distribuídos em dois grupos: N2O e O2. No grupo N2O, os cães foram ventilados mecanicamente com 66% de óxido nitroso e 33% de oxigênio. No grupo O2, somente o oxigênio foi utilizado para ventilação artificial. Em ambos os grupos, os animais foram submetidos à esofagoplastia cervical. As variáveis fisiológicas utilizadas para comparação entre os grupos foram: freqüência cardíaca, pressões arteriais sistólica, média e diastólica, saturação de oxigênio da hemoglobina e temperatura corporal. A necessidade ou não de doses adicionais da associação cetamina e midazolam também foi registrada para comparação. A análise estatística dos resultados não demonstrou diferenças significativas nas variáveis fisiológicas entre os grupos. No grupo O2, foram necessárias doses maiores da associação K-M para manutenção anestésica nos 30 minutos iniciais (p<0,05). Conclui-se que a anestesia injetável com K-M, nas doses utilizadas neste estudo, com ou sem inclusão de óxido nitroso, não deprime a função cardiovascular, não causa hipotermia, promove indução tranqüila e recuperação satisfatória com salivação e produz adequado grau de analgesia e relaxamento muscular para realização de cirurgias no esôfago cervical em cães. A inclusão do óxido nitroso permite a utilização de doses menores da associação cetamina-midazolam.

Fatal Combination: Nitrous Oxide Anesthesia and Methionine Pathway Defects

Selzer and colleagues provide a detailed case report of a previously healthy infant who died of severe CNS demyelination and respiratory collapse

Total intravenous anaesthesia with ketamine-midazolam versus halothane-nitrous oxide-oxygen anaesthesia for prolonged abdominal surgery

Background and objective: Total intravenous anaesthesia (TIVA) with ketamine-midazolam (KM) can be used for prolonged abdominal surgery. We compared this technique with halothane-nitrous oxide-oxygen anaesthesia using haemodynamic and endocrine stress responses as primary outcomes and adequacy of operating conditions and recovery profile as secondary outcomes. Methods: Fifty adult patients undergoing radical cystectomy and bladder substitution were randomly assigned to receive either TIVA with KM (n = 25) or halothane, nitrous oxide and oxygen anaesthesia (n = 25). Invasive haemodynamic and oxygenation variables were monitored along with plasma cortisol and growth hormone concentrations. Operative conditions and recovery profiles were registered. Results: Cardiac index and vascular resistance remained stable during and after surgery. Cortisol concentrations doubled during surgery and remained elevated in the recovery period. Growth hormone increased after induction, peaked during surgery and decreased during recovery. Neither the haemodynamic variables nor the plasma hormone concentrations differed significantly between the two groups. Intestinal loops were collapsed in the KM groups providing better operative conditions and a reduced need for postoperative analgesics. Conclusions: The stress responses during KM anaesthesia for prolonged abdominal surgery were comparable to those during halothane-nitrous oxide-oxygen anaesthesia. However, KM anaesthesia provided better surgical conditions and better recovery.

Recovery of elderly patients from two or more hours of desflurane or sevoflurane anaesthesia

The solubility of desflurane compared with sevoflurane suggests more rapid recovery from desflurane anaesthesia. This could be important after prolonged anaesthesia and fast recovery may be advantageous in the elderly where slow recovery of mental function is a concern. We compared emergence from desflurane vs sevoflurane in elderly patients undergoing two or more hours of anaesthesia. Fifty ASA physical status I, II, or III patients, 65 yr of age or older, undergoing anaesthesia expected to last two or more hours were randomly assigned to receive desflurane/nitrous oxide or sevoflurane/nitrous oxide anaesthesia. Patients were given 1-2 microg x kg(-1) fentanyl i.v. and anaesthesia was induced with propofol 1.5-2.5 mg x kg(-1) i.v. and maintained with either desflurane 2-6% or sevoflurane 0.6-1.75% with nitrous oxide 65% in oxygen. Inspired anaesthetic concentrations were adjusted to obtain adequate surgical anaesthesia and to maintain mean arterial pressure within 20% of baseline values. Early and intermediate recovery times were recorded. Digit-Symbol Substitution Test (DSST) scores and Visual Analog Scale (VAS) scores for pain and nausea were recorded before pre-medication and every 15 min in the Post Anaesthesia Care Unit (PACU) until patients were discharged. Early recovery times are given as median, quartiles. The times to extubation (5 (4-9); 9 (5-13) min), eye opening (5 (3-5); 11 (8-16) min), squeezing fingers on command (7 (4-9); 12 (8-17) min); and orientation (7 (5-9); 16 (10-21) min) were significantly less (P<0.05) for desflurane than for sevoflurane. Intermediate recovery, as measured by the DSST and time to ready for discharge from the PACU (56 (35-81); 71 (61-81) min) was similar in the two groups. Early but not intermediate recovery times of elderly patients undergoing a wide range of surgical procedures requiring two or more hours of anaesthesia is significantly (P<or=0.05) faster after desflurane.

Measurement of motor evoked potentials following repetitive magnetic motor cortex stimulation during isoflurane or propofol anaesthesia

Isoflurane and propofol reduce the recordability of compound muscle action potentials (CMAP) following single transcranial magnetic stimulation of the motor cortex (sTCMS). Repetition of the magnetic stimulus (repetitive transcranial magnetic stimulation, rTCMS) might allow the inhibition caused by anaesthesia with isoflurane or propofol to be overcome. We applied rTCMS (four stimuli; inter-stimulus intervals of 3, 4, 5 ms (333, 250, 200 Hz), output 2.5 Tesla) in 27 patients and recorded CMAP from the hypothenar and anterior tibial muscle. Anaesthesia was maintained with fentanyl 0.5-1 microg kg(-1) x h(-1) and either isoflurane 1.2% (10 patients) or propofol 5 mg kg(-1) x h(-1) with nitrous oxide 60% in oxygen (17 patients). No CMAP were detected during isoflurane anaesthesia. During propofol anaesthesia 333 Hz, four-pulse magnetic stimulation evoked CMAP in the hypothenar muscle in 75%, and in the anterior tibial muscle in 65% of the patients. Less response was obtained with 250 and 200 Hz stimulation. In most patients, rTCMS can overcome suppression of CMAP during propofol/nitrous oxide anaesthesia, but not during isoflurane anaesthesia. A train of four magnetic stimuli at a frequency of 333 Hz is most effective in evoking potentials from the upper and lower limb muscles. The authors conclude that rTCMS can be used for evaluation of the descending motor pathways during anaesthesia.

Evaluation of intense neuromuscular blockade caused by rocuronium using posttetanic count in male and female patients

Study objectiveTo establish the relationship between train-of-four (TOF) nerve stimulation and the number of posttetanic twitches (posttetanic count [PTC]) during neuromuscular blockade caused by rocuronium in males and females. DesignProspective, observational, clinical comparison. SettingOperating room of a university hospital. Patients60 ASA physical status I and II patients (30 women and 30 men), aged 18 to 60 years, who were scheduled for elective orthopedic surgery and ear, nose, throat surgery with a planned duration of 2 hours. InterventionsDuring fentanyl, propofol, and nitrous oxide (N2O) anesthesia, neuromuscular blockade was evaluated with accelerometry of the thumb using TOF and posttetanic twitch stimulation (PTTS) of the ulnar nerve in patients who received rocuronium 1 mg.kg–1. Measurements and main resultsThe first responses to PTTS were seen at mean times of 34.9 and 37.7 minutes after rocuronium injection in male and female patients, respectively (NS). The average interval between the appearance of a posttetanic response and the first response to TOF stimulation (T1) was not significantly different between male and female patients (15.4 ± 4.8 min (SD) vs. 15.9 ± 4.9 min, respectively). There was a significant negative correlation between PTC and the time to first response to TOF nerve stimulation (r = –0.83; p = 0.0001). Gender did not have a statistically significant effect on this relation (F = 0.9; p = 0.34). The intervals from administration of rocuronium to the first appearances of T1 and T2 were not significantly different between the two groups, but the intervals to the first appearances of T3 and T4 were significantly longer in female patients. ConclusionsEven though the times from initial administration of rocuronium 1 mg.kg–1 to the first appearances of T3 and T4 are significantly longer in female patients, the intervals to the first detectable responses to PTTS and TOF are not significantly different between females and males. Gender has no significant effect on the relation between PTC and the time to T1.

Pharmacologic and physiologic influences affecting sensory evoked potentials: implications for perioperative monitoring.

Pharmacologic and physiologic influences affecting sensory evoked potentials: implications for perioperative monitoring.

Quantitative characterization of visual response properties in the mouse dorsal lateral geniculate nucleus.

We present a quantitative analysis of the visual response properties of single neurons in the dorsal lateral geniculate nucleus (dLGN) of wild-type C57Bl/6J mice. Extracellular recordings were made from single dLGN cells in mice under halothane and nitrous oxide anesthesia. After mapping the receptive fields (RFs) of these cells using reverse correlation of responses to flashed square stimuli, we used sinusoidal gratings to describe their linearity of spatial summation, spatial frequency tuning, temporal frequency tuning, and contrast response characteristics. All cells in our sample had RFs dominated by a single, roughly circular "center" mechanism that responded to either increases (ON-center) or decreases (OFF-center) in stimulus luminance, and almost all cells passed a modified null test for linearity of spatial summation. A difference of Gaussians model was used to relate spatial frequency tuning to the spatial properties of cells' RFs, revealing that mouse dLGN cells have large RFs (center diameter approximately 11 degrees) and correspondingly poor spatial resolution (approximately 0.2c/degree). Temporally, most cells in the mouse dLGN respond best to stimuli of approximately 4 Hz. We looked for evidence of parallel processing in the mouse dLGN and found it only in a functional difference between ON- and OFF-center cells: ON-center cells were more sensitive to stimulus contrast than their OFF-center neighbors.

Topographic Plasticity in Primary Visual Cortex Is Mediated by Local Corticocortical Connections

The placement of monocular laser lesions in the adult cat retina produces a lesion projection zone (LPZ) in primary visual cortex (V1) in which the majority of neurons have a normally located receptive field (RF) for stimulation of the intact eye and an ectopically located RF (displaced to intact retina at the edge of the lesion) for stimulation of the lesioned eye. Animals that had such lesions for 14-85 d were studied under halothane and nitrous oxide anesthesia with conventional neurophysiological recording techniques and stimulation of moving light bars. Previous work suggested that a candidate source of input, which could account for the development of the ectopic RFs, was long-range horizontal connections within V1. The critical contribution of such input was examined by placing a pipette containing the neurotoxin kainic acid at a site in the normal V1 visual representation that overlapped with the ectopic RF recorded at a site within the LPZ. Continuation of well defined responses to stimulation of the intact eye served as a control against direct effects of the kainic acid at the LPZ recording site. In six of seven cases examined, kainic acid deactivation of neurons at the injection site blocked responsiveness to lesioned-eye stimulation at the ectopic RF for the LPZ recording site. We therefore conclude that long-range horizontal projections contribute to the dominant input underlying the capacity for retinal lesion-induced plasticity in V1.

Time required to achieve a stable cuff pressure by repeated aspiration of the cuff during anaesthesia with nitrous oxide

Background and objective: When the endotracheal tube cuff is repeatedly aspirated to avoid excessive cuff pressure during nitrous oxide anaesthesia, a stable cuff pressure is eventually achieved. We assessed the time required to achieve a stable cuff pressure after repeated cuff deflation. Methods: During 67% nitrous oxide and oxygen anaesthesia, air-filled cuffs of a standard tracheal tube (Mallinckrodt Hi-Contour®) were repeatedly deflated every 30 min for the first 3 or 4 h to inhibit excessive pressure (Groups Def-3 or Def-4, respectively, n = 10 for each); the cuff pressure was monitored for an additional 3 h. In some patients, the study was terminated at 1, 2, 3 and 4 h (n = 6 for each). Results: Cuff pressure in Group Def-3, but not in Group Def-4, >22 mmHg after stopping cuff aspiration. Intracuff nitrous oxide concentrations increased during repeated cuff deflation and increased further in Group Def-3 during an additional 3 h (from 39.8 ± 4.7% to 44.3 ± 3.8%; P < 0.05), whereas intracuff nitrous oxide concentrations at 4h were not different from those in Group Def-4 at the end of the study (43.7 ± 4.5% versus 42.3 ± 4.8%; P = 0.579). Conclusions: When the air-filled cuff of the standard endotracheal tube is repeatedly deflated every 30 min for 4 h, but not for only 3 h, during nitrous oxide anaesthesia, a stable cuff pressure can be achieved without further deflation of the cuff. Our data also suggest that achieving an equilibrating nitrous oxide concentration in the cuff provides a subsequent stable cuff pressure.

Endogenous opioids support the spinal inhibitory action of an α 2-adrenoceptor agonist in the decerebrated, spinalised rabbit

The present study examined the possible contribution of endogenous opioids to inhibition of spinal reflexes by an α 2-adrenoceptor agonist. In rabbits decerebrated and spinalised under halothane/nitrous oxide anaesthesia, the selective α 2-adrenoceptor agonist dexmedetomidine (3–30 μg intrathecal) induced significant decreases in short- and long-latency reflex responses evoked in medial gastrocnemius (MG) motoneurones by stimulation of the sural nerve. After recovery from dexmedetomidine, the μ-opioid receptor antagonist β-funaltrexamine (β-FNA; 100 μg intrathecal) significantly enhanced short-latency but not long-latency MG reflex responses. After β-FNA, inhibition of all reflexes by dexmedetomidine was significantly weaker than in the control state, whereas the cardiovascular actions of dexmedetomidine were unaffected. These data confirm that activation of spinal α 2-adrenoceptors depresses MG reflexes evoked by all groups of sural nerve afferent fibres, and shows that endogenous opioid tone supports the inhibitory action of α 2 agonists, possibly by a synergistic interaction in the spinal cord.

Toxicity of nitrous oxide

Nitrous oxide interacts with vitamin B12 resulting in selective inhibition of methionine synthase, a key enzyme in methionine and folate metabolism. Thus, nitrous oxide may alter one-carbon and methyl-group transfer most important for DNA, purine and thymidylate synthesis. Long-term exposure to high concentrations of nitrous oxide may cause megaloblastic bone-marrow depression and neurological symptoms. Exposure to higher doses for less than 6 hours, as in clinical anaesthesia, are considered harmless. Recent studies seem to suggest a correlation between nitrous oxide anaesthesia and hyperhomocysteinaemia which is accepted to be an independent risk factor for coronary artery disease. As for today, available data do not support the notion that exposure to trace amounts of nitrous oxide is associated with impaired fertility or an increased risk of developing cancer. Emission of nitrous oxide from medical use is estimated to contribute less than 0·05% to total annual greenhouse gas emission.

The Brandt™ Tube System Attenuates the Cuff Deflationary Phenomenon After Anesthesia with Nitrous Oxide

The Brandt™ tube system can limit excessive cuff pressure during nitrous oxide (N2O) anesthesia, but there is a lack of data assessing whether the Brandt™ tube system avoids cuff deflation after cessation of N2O administration. In this study, we recorded air-filled cuff pressures of the Mallinckrodt Brandt™ or Hi-Contour™ (control) tracheal tubes (Mallinckrodt, Athlone, Ireland) during 67% N2O anesthesia and the cuffs were aspirated if the cuff pressure exceeded 22 mm Hg; 180 min later, O2 was substituted for N2O. The cuff pressure of both groups significantly decreased after N2O anesthesia but the time required for the cuff pressure to return to the initial pressure was longer in the Brandt group than in the control group (76.5 ± 35.2 min and 36.5 ± 18.1 min, respectively;P = 0.03). The incidence of air leaks was more frequent in the control group than in the Brandt group (P = 0.015); changes in intracuff N2O were small in the Brandt group (6.6 ± 1.2% to 3.4 ± 0.9%) compared with those in the control group (46.2 ± 3.8% to 18.6 ± 5.6%). Therefore, the Brandt™ tube system attenuates the cuff deflationary phenomenon after N2O anesthesia, whereas repeated cuff deflation during N2O anesthesia causes cuff deflation after cessation of N2O, resulting in a possible risk of air leaks.

Propofol-Nitrous Oxide Anesthesia Enhances the Heart Rate Response to Intravenous Isoproterenol Infusion

Heart rate (HR) response to IV atropine is attenuated during propofol-nitrous oxide (N2O) anesthesia. We studied the effects of propofol-N2O anesthesia on isoproterenol-induced HR changes. The control group (n = 15) received no propofol and no N2O. Patients in the propofol-N2O group (n = 21) received IV propofol 2.5 mg/kg over 1 min followed by a continuous infusion of propofol 10 mg · kg−1 · h−1. After tracheal intubation, anesthesia was maintained with propofol 5 mg · kg−1 · h−1 and 67% N2O in oxygen. All patients in both groups received IV isoproterenol at incremental infusion rates (2.5, 5, 7.5, 10, 12.5, 15, and 17.5 ng · kg−1 · min−1 for 2 min at each dose) until HR increased more than 20 bpm from baseline values. At the end of each infusion period, hemodynamic data were collected. The HR response to isoproterenol 7.5 ng · kg−1 · min−1 was increased more in the propofol group than in the control group (20 ± 5 versus 14 ± 4 bpm;P < 0.05). During the isoproterenol infusion at 10 ng · kg−1 · min−1, HR increased by more than 20 bpm in all patients in the propofol group but in only 31% of patients in the control group (P < 0.0001). These results suggest that continuous isoproterenol infusion might be useful when a large dose of atropine is ineffective in restoring normal HR during propofol-N2O anesthesia.

Comparison of Neonatal Effects during General Anesthesia Using Sevoflurane and Spinal Anesthesia for Elective Cesarean Section

Background: The study was designed to compare neonatal outcome biochemically and clinically. We examined the administration of sevoflurane below 1.0% with 50% oxygen and 50% nitrous oxide and spinal anesthesia during elective cesarean section. Methods: The study examined 60 parturients, who were planned after 36 weeks gestation, ASA I-II, at term undergoing elective cesarean section, and who were allocated to receive 1.0% sevoflurane with 50% oxygen and 50% nitrous oxide (n = 30), and spinal anesthesia (n = 30). General anesthesia was induced with thiopental 5 mg/kg followed by succinylcholine 1.0 mg/kg to facilitate tracheal intubation. Parturients received sevoflurane given in a 50 : 50 oxygen and nitrous oxide mixture, using 0.5-1.0% progressive incremental dosing up to 1.5-2.0 MAC. Spinal anesthesia involving a spinal injection of 8 mg hyperbaric (plain) bupivacaine 0.5% with 20g fentanyl was added. A systolic blood pressure of less than 90 mmHg or a reduction in the systolic pressure of greater than 20% from baseline was considered as hypotension and treated with a bolus of 5 mg of intravenous ephedrine. We studied neonatal data including umbilical artery gas analysis results and Apgar scores at 1 and 5 min. Results: Comparing the general and the spinal anesthetic groups, no significant differences could be detected in neonatal outcome biochemically or clinically. Conclusions: Anesthesia type does not seem to influence the biochemical or clinical results of the neonates delivered by elective cesarean section. We believe that both general anesthesia with sevoflurane and spinal anesthesia could be performed in elective term cesarean sections without risk to neonates.

Perioperative Hearing Impairment

Perioperative Hearing Impairment

Loss of vision caused by expansion of intraocular perfluoropropane (C 3F 8) gas during nitrous oxide anesthesia

PURPOSE: To report visual loss associated with nitrous oxide anesthesia in patients with intraocular perfluoropropane (C 3F 8) gas. DESIGN: Observational case series. METHODS: Three patients are described who lost vision in the eye with intraocular gas after subsequent nitrous oxide general anesthesia. RESULTS: Three patients, aged 75, 80, and 73 years, with intraocular C 3F 8 gas in three eyes underwent nitrous oxide general anesthesia in three different medical centers for conditions unrelated to their ophthalmic surgery, ranging from 10 days to 1 month after their vitreoretinal procedure. All three patients suffered visual loss due to presumed central retinal artery occlusion caused by expansion of the intraocular gas by nitrous oxide during general anesthesia. In two patients, there was no recovery of light perception. In one patient, there was moderate recovery of vision. CONCLUSIONS: Identification of patients with intraocular gas is critical when planning nitrous oxide anesthesia. This may be achieved by the use of a simple intraocular gas identification bracelet issued to patients at the time of their vitreoretinal procedure.

The Legacy of Albert Faulconer Jr

The Legacy of Albert Faulconer Jr

Jugular Bulb Oxygen Saturation during Propofol and Sevoflurane/Nitrous Oxide Anesthesia during Deliberate Mild Hypothermia for Neurosurgical Procedures

Jugular Bulb Oxygen Saturation during Propofol and Sevoflurane/Nitrous Oxide Anesthesia during Deliberate Mild Hypothermia for Neurosurgical Procedures

Sustained Impairment of Novel Learning Following Isoflurane-Nitrous Oxide Anesthesia in Young and Aged Rats

Sustained Impairment of Novel Learning Following Isoflurane-Nitrous Oxide Anesthesia in Young and Aged Rats