N2O In O2 Research Articles

ROCURONIUM VERSUS CISATRACURIUM: INTUBATING CONDITIONS, EFFICACY, AND SAFETY.

Background: Neuromuscular blockers (NMB) are very important adjuvant to general anesthesia,Rocuronium bromide (aminosteroidal NMB) and cisatracurium besylate (benzylisoquinoline NMB) are recently introduced non-depolarizing muscle relaxants.In a prospective randomized study,we had compared both the drugs as regard to the onset of action, intubating conditions,clinical duration,hemodynamic changes,and adverse effects. Method: 80 female patients ASA I&II,18-60 year old underwent elective abdominal surgery under general anesthesia (GA) were randomly assigned into 2 equal groups.ROC group,where 0.9mg/kg rocuronium was given and CIS group, where 0.15mg/kg cisatracurium was given. Standardized GA was given to all patients as follows, fentanyl 1mcg/kg, propofol 2mg/kg,intubation was tried by the same anesthetist who was blind to the given NMB after 60 sec of injection, intubation was done if the intubating condition was acceptable (excellent or good),and it was re-attempted every 30 sec if it was poor or inadequate.Anesthesia was maintained by 60% N2O in O2 and isoflurane to a total MAC 1.5,controlled ventilation was adjusted to normocapnia.Mean arterial blood pressure (MAP),heart rate,and intubating conditions were recorded. Results: Clinically acceptable intubating conditions were achieved after 60 sec more frequently with rocuronium (80%) than with cisatracurium(0%).Rocuronium had advantage of rapid onset of action with good intubating conditions as compared to Cisatracurium and both were found to be potent and safe with excellent cardiovascular stability and also without any apparent histamine release. Conclusion: Rocuronium has a rapid onset of action with good intubating conditions in comparison to cisatracurium both are potent and safe with excellent cardiovascular stability and do not cause apparent histamine release

The fraction of nitrous oxide in oxygen for facilitating lung collapse during one-lung ventilation with double lumen tube

BackgroundThe ideal fraction of nitrous oxide (N2O) in oxygen (O2) for rapid lung collapse remains unclear. Accordingly, this prospective trial aimed to determine the 50% effective concentration (EC50) and 95% effective concentration (EC95) of N2O in O2 for rapid lung collapse.MethodsThis study included 38 consecutive patients undergoing video-assisted thoracoscopic surgery (VATS). The lung collapse score (LCS) of each patient during one-lung ventilation was evaluated by the same surgeon. The first patient received 30% N2O in O2, and the subsequent N2O fraction in O2 was determined by the LCS of the previous patient using the Dixon up-and-down method. The testing interval was set at 10%, and the lowest concentration was 10% (10, 20, 30, 40%, or 50%). The EC50 and EC95 of N2O in O2 for rapid lung collapse were analyzed using a probit test.ResultsAccording to the up-and-down method, the N2O fraction in O2 at which all patients exhibited successful lung collapse was 50%. The EC50 and EC95 of N2O in O2 for rapid lung collapse were 27.7% (95% confidence interval 19.9–35.7%) and 48.7% (95% confidence interval 39.0–96.3%), respectively.ConclusionsIn patients undergoing VATS, the EC50 and EC95 of N2O in O2 for rapid lung collapse were 27.7 and 48.7%, respectively.Trial registrationhttp://www.chictr.org/cn/ Identifier ChiCTR19 00021474, registered on 22 February 2019.

Minimal flow anesthesia can be initiated early with the use of higher fresh gas flow to facilitate desflurane "Wash-in".

Background and Aims:More than 80% of delivered anesthetic gases get wasted at high fresh gas flows as they are vented out unused. Use of minimal flow anesthesia is associated with less waste anesthetic gas emission and environmental pollution. There is no approved or validated technique to initiate minimal flow anesthesia and simultaneously achieve denitrogenation of the breathing circuit. We studied the wash-in characteristics of desflurane, when delivered with 50% nitrous oxide, to reach a target end-tidal concentration at two different gas flow rates.Material and Methods:Patients were allocated randomly to two groups of 25 adults each. In Group A, with the vaporizer dial fixed at 4 vol %, after an initial fresh gas flow of 4 L/min was administered to wash-in of desflurane using the closed-circuit, with 50% N2O in O2, and in group B, 6 L/min was used. Minimal flow anesthesia, with 0.5 L/min, was initiated in both groups on attaining a target end-tidal desflurane concentration of 3.5 vol %. After initiation of desflurane delivery, the inspired/expired gas concentrations were noted every minute for 15 min.Results:In Group A, the target desflurane end-tidal concentration was reached in 499.2 ± 68.6 s±, and in the Group B (P < 0.001), it was reached significantly faster in 314.4 ± 69.89 s. Denitrogenation of the circuit was adequate in both groups.Conclusion:Minimal flow anesthesia can be initiated, without any gas-volume deficit, in about 5 min with an initial fresh gas flow rate of 6 L/min and the vaporizer set at 4 vol%.

Comparison of Neuromuscular Blockade with Rocuronium in Young and Elderly Patients with or without Renal Failure

ABSTRACT Context The duration of neuromuscular block with rocuronium is affected by old age as well as renal impairment. It would be helpful for anesthetists to know the variation in the block in elderly patients with renal failure and the significance of neuromuscular monitoring in this group. Aim The aim of our study is to investigate the neuromuscular effects of 0.6 mg/kg rocuronium under general anesthesia in young adults and elderly patients with or without renal failure. Study design Prospective randomized controlled study. Materials and methods Young and elderly 100 patients were divided into 4 groups of 25 each, with or without renal failure. General anesthesia with propofol 2 mg kg intravenous (iv), fentanyl 2 μg kg iv, and 60% N2O in O2 were given. Neuromuscular monitoring was started immediately after the induction of anesthesia and before the administration of muscle relaxant. After the stabilization of control responses, 0.6 mg kg rocuronium was injected intravenously. The onset time, time to achieve maximum block, and the recovery times were noted. Statistical analysis used The statistical analysis of the data from the study was performed with the Statistical Package for the Social Sciences (SPSS) software for Window Release 14.0. One-way analysis of variance, Bonferroni's, and chi-square test were used to compare patients’ characteristics. Results The duration of block as well as the recovery indices were significantly prolonged in the elderly compared to the young patients. Maximum prolongation was observed in the elderly group with renal failure. This underlines the importance of neuromuscular monitoring in these patients. How to cite this article Gvalani SK, Pradeep L. Comparison of Neuromuscular Blockade with Rocuronium in Young and Elderly Patients with or without Renal Failure. Res Inno in Anesth 2016;1(2):45-51.

Effect of ketamine and midazolam on oculocardiac reflex in pediatric strabismus surgery

BackgroundThe oculocardiac reflex (OCR) can be elicited during manipulation of the orbital structures in the strabismus correction surgery. A sinus bradycardia is the most common manifestation of OCR; and cardiac dysrhythmia and asystole may also occur. Various efforts to reduce OCR have been attempted, but without coherent outcome results.MethodsSixty one children, undergoing elective strabismus surgery, were randomly allocated into 2 groups: Group K received ketamine 1.0 mg/kg; and Group M received midazolam 0.15 mg/kg for induction of anesthesia. Anesthesia was maintained with 1-1.3 MAC of sevoflurane with 50% N2O in O2. Heart rate and blood pressure were measured 30 seconds before extraocular muscle (EOM) traction and immediately after traction. The OCR was defined as a decrease in heart rate more than 20% of the baseline heart rate, following manipulating EOM. Postoperative nausea and vomiting (PONV) and emergence agitation (EA) were assessed in postanesthetic care unit (PACU).ResultsBlood pressure before tightening EOM in Group K was higher than that in Group M (P < 0.05). However Δ HR (2.7 ± 15% vs. - 0.9 ± 16%) and incidence of OCR (10.0% vs. 19.4%) after traction an EOM were not different between the two groups. The occurrence of PONV (6.7 vs. 9.7%) and EA (30.0% vs. 22.6%) were similar.ConclusionsKetamine does not reduce the incidence of OCR compared with midazolam in pediatric strabismus surgery. In addition, ketamine does not increase the incidence of PONV and EA. In conclusion, it is reliable to use ketamine in pediatric strabismus surgery.

Perioperative respiratory complications in cleft lip and palate repairs: An audit of 1000 cases under ′Smile Train Project′

Background and Aim:Anaesthesia for cleft surgery in children is associated with a variety of airway related problems. This study aims to review the frequency of associated anomalies and other conditions as well as perioperative respiratory complications during the cleft lip/palate repair surgeries.Methods:An audit of 1000 cleft surgeries in children enrolled under “Smile Train” is presented. Following informed consent, general anaesthesia was induced with endotracheal (ET) intubation using halothane in O2 and/or intravenous thiopentone 5 mg/kg or propofol 1.5 mg/kg, suxamethonium 1.5 mg/kg or rocuronium 0.8 mg/kg and maintained with halothane/isoflurane 0.4-1% in 50% N2O in O2 with rocuronium. The observational data regarding the occurrence of perioperative complications in 1000 cleft surgeries are mentioned as mean (standard deviation), number and percentage as appropriate. ‘Two sample t-test between percentage’ is applied for significance.Results:The frequency of isolated cleft lip was 263 (36.4%), cleft palate 183 (25.3%) and combined defect 277 (38.3%) of the operated cases. Other congenital anomalies were present in 21 (2.8%) of the children. The intraoperative airway complications occurred in 13 (2.4%) of cleft lip and 40 (8.7%) of cleft palate repairs (P < 0.05). Post-operative respiratory complications were observed in 9 (1.7%) and 34 (7.4%) patients of cleft lip and palate repairs respectively (P < 0.05). Mortality occurred post-operatively in 2 (0.2%) of cleft repairs (n = 1000).Conclusion:Cleft deformities in children when associated with other congenital anomalies or respiratory problems pre-dispose them to difficult airway and pulmonary complications. Frequency of perioperative respiratory complications were significantly higher with cleft palate repair than with cleft lip repair. Anaesthetic expertise, optimum monitoring facility and specialised post-operative care is necessary to decrease the morbidity.

A prospective randomized multicenter comparative study of BLM-240 (desflurane) versus sevoflurane in Japanese patients

The present study was conducted to evaluate the efficacy and safety of BLM-240 (desflurane) in comparison to sevoflurane in Japanese patients. A total of 216 patients were enrolled in this randomized comparative study at 15 medical institutions. The patients received either BLM-240 with 50-70% N2O in O2 (n=111), BLM-240 with 30% O2 in air (n=55), or sevoflurane with 50-70% N2O in O2 (n=50). Efficacy was evaluated by an efficacy rate based on an efficacy evaluation criteria and recovery time to extubation from the discontinuation of the anesthetics. Safety was evaluated by incidence of adverse drug reactions (ADR) and other clinical indicators. The efficacy rate of BLM-240 was 98.8% (164/166 patients), indicating that BLM-240 is effective as an anesthetic. Time from discontinuation of anesthetic delivery to extubation was 9.7±0.6min in the BLM-240/N2O group and 14.3±0.9min in the sevoflurane/N2O group, meeting the pre-defined non-inferiority criteria of BLM-240 to sevoflurane. There was no statistically significant difference in the incidence of total ADR between the BLM-240 group (62.0%) and sevoflurane group (48.0%). The results indicate that BLM-240 is an effective and safe inhalation anesthetic in Japanese patients.

Effects of chronic stress on nitrous oxide (N2O)‐induced antinociceptive and anxiolytic effects in mice

Subanesthetic concentrations of N2O are routinely used in clinical dentistry to produce conscious sedation. The aim of this study was to assess the influence of chronic stress on the antinociceptive and anxiolytic effects of N2O. To induce chronic stress, male NIH Swiss mice (20–25 g) were subjected to a modified forced‐swim test four times over 48 min. Thirty min later, they were exposed to 30%, 50% or 70% N2O in O2, and antinociceptive or anxiolytic responsiveness was assessed using the hot plate test or the light/dark exploration box. Non‐stressed control mice responded to N2O with a dose‐dependent antinociceptive effect, but chronically‐stressed, N2O‐exposed mice showed a marked hyperalgesic response. Exposure of non‐stressed control mice to N2O increased both the time spent in the light compartment and the number of intercompartmental transitions in a generally dose‐dependent manner. Chronic stress did not influence either parameter, but chronically‐stressed, N2O‐exposed mice showed increases in the number of transitions but not in time spent in the light compartment. These findings may be of clinical significance in the use of N2O in patients with chronic stress. Further investigation in the influence of stress on the antinociceptive and anxiolytic actions of N2O is warranted. (Supported in part by NIH Grant GM‐77153 and the Allen I. White Distinguished Professorship.)

Effect of Gabapentin on Morphine Consumption and Pain after Surgical Debridement of Burn Wounds: A Double-Blind Randomized Clinical Trial Study

Background:Burn pain is recognized as being maximal during therapeutic procedures, and wound debridement can be more painful than the burn injury itself. Uncontrolled acute burn pain increases the stress response and the incidence of chronic pain and associated depression. Although opiates are excellent analgesics, they do not effectively prevent central sensitization to pain. The anticonvulsant gabapentin has been proven effective for treating neuropathic pain in large placebo-controlled clinical trials. Experimental and clinical studies have demonstrated antihyperalgesic effects in models with central neuronal sensitization. It has been suggested that central neuronal sensitization may play an important role in postoperative pain.Objectives:The aim of this study was to investigate the effect of gabapentin on morphine consumption and postoperative pain in burn patients undergoing resection of burn wounds.Patients and Methods:In a randomized, double-blind, placebo-controlled study, 50 burn patients received a single oral dose of gabapentin (1200mg) or placebo 2h before surgery. Anesthesia was induced with propofol and fentanyl and maintained by infusingpropofol, remifentanil, and 50% N2O in O2. All patients received patient-controlled analgesia with morphine at doses of 2.5 mg bolus and a lock-out time of 10 min for 24h before the operation. Pain was assessed on a visual analog scale (VAS) at rest and during movement at 1,4,8,12,16,20, and 24 h before the operation. Heart rate, oxygen saturation, mean arterial blood pressure, respiratory rate, sedation score, and morphine consumption were studied.Results:All the enrolled patients were able to complete the study; therefore, data from 50 patients wereanalyzed. The VAS scores at rest andduring movement at 1,4,8,12,16,20, and 24 h after the operation were significantly lower in the gabapentin group than in the placebo group (P < 0.05). Morphine consumption was significantly lessr in the gabapentin group than in the placebo group (P < 0.05). Sedation scores were similar in the 2 groups at all measured times. There were no differences in adverse effects between the groups.Conclusions:A single oral dose of 1200mg gabapentin resulted in a substantial reduction in postoperative morphine consumption and pain scores after surgical debridement in burn patients.

Nasotracheal intubation with the McGrath videolaryngoscope in patients with difficult airway

Nasotracheal intubation (NTI) is frequently indicated for maxillofacial surgery and the patients usually have difficult airway1. NTI may be complicated by trauma, failure, haemorrhage, sinusitis and glottic palsy. Fibreoptic laryngoscopy is useful, but expensive, bulky and requires experience. The McGrath videolaryngoscope (Aircraft Medical, Edinburgh, UK) is a portable, indirect laryngoscope designed to improve glottic view and orotracheal intubation in patients with difficult airways 2. There is no previous report of McGrath videolaryngoscopy to facilitate NTI. This report is a prospective evaluation of the McGrath for NTI in a cohort of maxillofacial surgery patients with difficult airways. Following the initial successful use of the McGrath for NTI in a patient with previous difficult laryngoscopic and fibreoptic intubation, we conducted a clinical evaluation of this device for NTI. Twenty-five adults, who underwent maxillofacial surgery under general anaesthesia and NTI, were studied. Preoperative airway assessment included Mallampati score, mandibular protrusion, thyromental distance and neck mobility. The study was approved in January 2010, by the research department and audit committee of Central Manchester University Hospital, Manchester, UK. The study was a prospective observational clinical evaluation in adult patients. All the patients gave informed consent to general anaesthesia, laryngoscopy and NTI. Perioperative patient monitoring included electrocardiography, pulse oximetry, blood pressure and respiratory gas measurement. Patients’ nostrils were sprayed with 5% lidocaine and phenylephrine. After preoxygenation, anaesthesia was induced with remifentanil 0.2 mcg/kg/min, propofol 2–3 mg/kg and atracurium 0.5 mg/kg. A lubricated 6 mm cuffed nasotracheal tube was inserted through a nostril into the pharynx. Initial Macintosh laryngoscopy was performed and the Cormack–Lehane grade of laryngoscopic view was noted. Final laryngoscopy was promptly performed with the McGrath, and the grade of glottic view was noted before NTI. Magill forceps were not required for NTI. After intubation, anaesthesia was maintained with 2% sevoflurane and 50% N2O in O2. An observer measured time to intubation, as time from first insertion of the McGrath into patients’ mouth, until first ventilation via nasotracheal tube. Other measurements included number of intubation attempts (withdrawal of laryngoscope and reinsertion), ease of NTI (measured as 1 = easy, 2 = difficult), anaesthetists’ satisfaction with McGrath videolaryngoscopy (measured as 1 = satisfied, 2 = dissatisfied) and complications. Twenty-five patients underwent general anaesthesia and NTI for maxillofacial surgery. Mean age was 45 years, mean BMI was 27 kg m−2, male : female ratio was 1 : 1 and 84% were American Society of Anesthesiologists class 1 or 2. About 80% of patients had known preoperative risk factors for difficult intubation. The frequency distribution of Mallampati airway assessment showed that 24% were grade 1, 36% were grade 2, 28% were grade 3 and 12% were grade 4. The frequency distribution of Macintosh laryngoscopic views showed that 28% were Cormack–Lehane grade 1, 32% were grade 2, 24% were grade 3 and 16% were grade 4. Compared with the mostly difficult Macintosh laryngoscopic views in the majority of patients; the McGrath provided grade 1 laryngoscopic views in all patients and NTI was accomplished at first attempt in 96% of cases. The mean time to NTI was 18 (±8) s. There were no complications. In 96% of cases, NTI was rated as easy; and 100% of anaesthetists were satisfied with McGrath videolaryngoscopy. The prediction of difficult airways, using the measures in our study, is reliable 3,4. However, our study showed no association between predictors of difficult airways and NTI using McGrath videolaryngoscopy. Previous studies showed the benefit of the GlideScope (Verathon, Bothell, Washington, USA) for NTI,5,6. Our study is the first to show the benefit of the McGrath for NTI and also suggests shorter intubation time relative to the Macintosh or GlideScope. McGrath videolaryngoscopy avoids the use of Magill forceps for NTI, thereby reducing intubation time and complications, as shown in our study. In conclusion, the McGrath videolaryngoscope is useful for NTI, especially in patients with a difficult airway. Further evaluation for NTI, in randomised comparison with other videolaryngoscopes, would be useful.

Effects of patient's tolerance to laryngeal mask airway and tracheal tube on the appropriate level of sevoflurane anesthesia

Objective To compare the effects of patient's tolerance to laryngeal mask airway (LMA) and tracheal tube (TT) on the appropriate level of sevoflurane anesthesia.Methods Eighty ASA Ⅰ or Ⅱ patients aged 30-60 yr weighing 50-70 kg undergoing elective thyroid or breast surgery were randomly divided into 2 groups (n=40 each):LMA group and TT group.Anesthesia wag induced with propofol 1.6mg/kg,fentanyl 3μg/kg and recuronium 0.6mg/kg.LMA or tracheal tube was inserted,and the patients were mechanically ventilated.Anesthesia was maintained with inhalation of 1.5%-3.0% sevoflurane and 50% N2O in O2 in group LMA,and with 2.5%-5.0% sevoflurane and 50% N2O in O2 in group TT.The flow of O2 and N2O was 0.7-1.0L/min,and the concentration of sevofluranee was adjusted to maintain AAI at 15-25.ECG,HR,MAP,SpO2,PETCO2,AEP and end-tidal sevoflurane concentration were continuonsly monitored.The end-tidal sevoflurane concentration was recorded at 1,5 and 10 min after LMA/TT was placed (T1-3),at 1h after skin incision (T4) and at the end of operation before removal of LMA or extubation (T5).The recovery time of consciousness,adverse cardiovascular events and adverse reactions were recorded.Results The end-tidal sevoflurane concentration was significantly lower,the recovery time of consciousness and removal of LMA or extubation time were shorter,and the incidence of adverse cardiovascular events and adverse reactions was lower in LMA group than in TT group.Conclusion At the same depth of anesthesia (AAI 15-25),sevoflurane concentration is significantly lower in LMA group than in TT group,with fewer complications and smaller cardiovascular reaction. Key words: Laryngeal masks; Intubation,intratracheal; Sevoflurane

The use of emergency medical cooling system pads in the treatment of malignant hyperthermia

Editor, Malignant hyperthermia is an inherited and potentially lethal hypermetabolic syndrome triggered by halogenated volatile inhalational agents and/or depolarizing muscle relaxants. Because malignant hyperthermia is always associated with general anaesthesia, the syndrome is theoretically well known among anaesthesiologists. However, due to its rarity, clinical experience is limited. Early diagnosis and prompt but appropriate intervention are essential to reduce morbidity and mortality.

Effect of remifentanil on oculocardiac reflex in paediatric strabismus surgery

Rapidly acting narcotics enhance the degree of bradycardia due to the oculocardiac reflex (OCR) elicited by extraocular muscle (EOM) tension during strabismus surgery. We evaluated and compared the effects of remifentanil and sevoflurane on OCR during paediatric strabismus surgery. One hundred and twenty children, 1-9 years old, undergoing elective strabismus surgery, were randomly assigned to receive sevoflurane or remifentanil. No anticholinergic prophylaxis was administered. Anaesthesia was induced using ketamine 1.0 mg/kg or midazolam 0.15 mg/kg with 66% N(2)O in O(2). Laryngeal mask airways were placed with rocuronium 0.5 mg/kg. Anaesthesia was maintained with sevoflurane 2.0-3.0 vol% with 66% N(2)O in O(2) or remifentanil 0.75 mug/kg over 1 min and followed by the continuous infusion of remifentanil 0.5 mug/kg/min with 66% N(2)O in O(2). Heart rate (HR) and blood pressure (BP) were measured and compared. OCR was defined as a reduction in HR of >20% induced by traction of an EOM. During anaesthesia, HR and BP were maintained at a lower level in the remifentanil group than in the sevoflurane group (each, P<0.05). The mean percent change in HR (-23.3+/-17.0% vs. -11.2+/-13.0%; P<0.05) and the incidence of OCR (58.3% vs. 28.3%; P<0.05) following traction of an EOM were higher in the remifentanil group than in the sevoflurane group. Remifentanil enhanced the degree of bradycardia due to OCR as compared with sevoflurane during paediatric strabismus surgery.

Nitrous Oxide Sedation and Bispectral Index

To determine whether bispectral analysis (BIS) changes during nitrous oxide (N(2)O) sedation in anxious children undergoing extraction of primary teeth. In this prospective study 45, ASA physical status I children, aged between 7 to 12 years and scheduled for primary teeth extraction under N(2)O/O(2) sedation are included. At baseline (T0) and during the sedation procedure (T1-6); BIS levels, Ramsay Sedation Scores (RSS), oxygen saturation (Sp0(2)), and heart rate (HR) were recorded at one-minute intervals. Forty percent N(2)O in O(2) was given by a nasal hood, and N(2)O concentration was enhanced to 60% in a two-minute period. Paired measurements of BIS levels with Observer's Assessment of Alertness and Sedation (OAA/S) scores were obtained during sedation procedure. Since 5 patients refused application of the nasal hood, a total 40 of the original 45 subjects completed the study. Mean age and weight of the children were 9.5 +/- 1.4 years and 23.7 +/- 9.7 kg, respectively. Nitrous oxide inhalation produced no changes in BIS levels despite a sedation level in OAA/S scores were observed at 40-60% N(2)O concentrations. BIS values do not change during N(2)O/O(2) sedation and the BIS monitor is not appropriate to evaluate the depth of sedation provided by N(2)O/O(2) during primary teeth extraction in children.

A case of Churg–Strauss syndrome undergoing radical mastectomy under general anaesthesia and thoracic epidural analgesia

A case of Churg–Strauss syndrome undergoing radical mastectomy under general anaesthesia and thoracic epidural analgesia

Development of tolerance to nitrous oxide (N2O)‐induced anxiolysis and cross‐tolerance to chlordiazepoxide (CP) in mice

Our laboratory has long studied the pharmacology of the anesthetic gas N2O, and we have implicated brain benzodiazepine receptors in N2O-induced anxiolytic effects (Li and Quock, Pharmacol. Biochem. Behav. 68:789-796, 2001). This study was conducted to determine the extent to which tolerance develops to the anxiolytic effect of N2O and whether there is cross-tolerance to the anxiolytic effects of the benzodiazepine CP. Male NIH Swiss mice, 18–30 g, were exposed to 70% N2O in oxygen (O2) for 1½ to 24 hr, removed to 100% O2 (to reduce diffusion hypoxia) and placed in a room air environment to complete the washout of N2O. Thirty minutes following removal from N2O, mice were individually tested in the light/dark exploration test to determine behavioral responsiveness to 70% N2O in O2. Results show that it required a continuous exposure of 9 hr or longer of 70% N2O to induce tolerance to the anxiolytic-like effects of a subsequent exposure to 70% N2O in the light/dark box paradigm. Preliminary results suggest that N2O-tolerant mice also exhibited reduced responsiveness to the anxiolytic-like effects of some doses of CP when compared to control mice that were exposed for an equal period of time to compressed air. These results provide evidence for development of tolerance of mice to the anxiolytic effects of N2O and possible cross-tolerance to the effects of benzodiazepines. (Supported in part by NIH Grant DA-10343.)

Nitrous oxide diffusion into tracheal tube cuffs – efficacy of a new prototype cuff pressure release valve

The aim of this study was to evaluate the performance of a new cuff pressure release valve (CPRV), in which the release pressure can be adjusted from 10 to 25 cmH2O, particularly intended to control pressure in paediatric cuffed tracheal tubes and to avoid cuff hyperinflation caused by N2O diffusion. In vitro: the PRV was set to 10, 15, 20 or 25 cmH2O release pressure and connected to a cuffed tube placed into a box flushed with 66% N2O in O2. The cuff pressure was monitored with and without CPRV for 60 min. Experiments were performed four times using two different CPRVs. In vivo: with Institutional Review Board approval, CPRV was studied in 50 children undergoing general anaesthesia with tracheal intubation and standardized anaesthesia technique (including 66% N2O in O2) and ventilator settings. Patients were randomized into two groups (with and without CPRV). The cuff pressure baseline was 20 cmH2O and CPRV was set to 25 cmH2O. If the cuff pressure exceeded 25 cmH2O, it was manually released to 20 cmH2O. The numbers of deflations in both groups were noted and compared by Mann-Whitney U-test (P<0.05). In vitro: the cuff pressure exceeded 50 cmH2O after 60 min without CPRV, but did not exceed the settings with CPRV. In vivo: there was no need to manually deflate the cuff in the CPRV group but, in every patient in the control group, three (two to seven) deflating manoeuvres were required within the first hour of anaesthesia (P<0.0001). The CPRV allows reliable cuff pressure release at various pressure levels and reliably prevents cuff pressure increases caused by N2O.

The addition of clonidine 2 μg·kg−1 does not enhance the postoperative analgesia of a caudal block using 0.125% bupivacaine and epinephrine 1 : 200 000 in children: a prospective, double‐blind, randomized study1

In this prospective, randomized, double-blind study, we compared the efficacy of 0.125% bupivacaine and epinephrine 1:200,000 with and without clonidine 2 microg.kg-1 for 'single shot' pediatric caudal analgesia. Thirty ASA I and II children, ages 2-8 years, undergoing outpatient surgical procedures below the umbilicus received 1 ml.kg-1 0.125% bupivacaine with fresh epinephrine 1:200,000 and clonidine 2 microg.kg-1 (group-C) or 1 ml.kg-1 0.125 % bupivacaine with epinephrine 1:200 000 (group-NC). All patients received a standardized general anesthetic (induction with 67% N2O in O2 and sevoflurane followed by isoflurane maintenance). Primary outcome measures were time to first rescue analgesic and number of patients requiring rescue analgesic at 4, 6, 8, 12, and 24 h after caudal placement. Secondary outcome measures included: extubation times, Objective Pain Scale (OPS) scores, sedation scores, time in postanesthesia care unit (PACU), discharge time, number of analgesic doses given in 24 h following caudal blockade, and adverse effects (vomiting, hypotension, and bradycardia). There were no differences in demographics, investigated parameters, or adverse effects between groups. We found that the addition of clonidine 2 microg.kg-1 to 0.125% bupivacaine with fresh epinephrine 1:200,000 for caudal analgesia did not significantly delay the time to first rescue analgesic or decrease the overall need for rescue analgesics in children 2-8 years undergoing surgical procedures below the umbilicus.

Anaesthetic management in a case of Kabuki syndrome

Anaesthetic management in a case of Kabuki syndrome

Comparison of the work of breathing imposed by three anaesthetic breathing systems in children

Introduction There is concern that the resistance of the valves in circle systems may impose an unacceptable respiratory load in children (1). In this study we compared the work of breathing imposed by the Bain, Jackson Rees and the circle systems in anaesthetised spontaneously breathing children.Methods Following local ethics committee approval and the written informed consent of a parent, 12 children, aged 2–6 years, ASA grades I–II scheduled for routine genital surgery (e.g. circumcision) were recruited [Weight 14.4 ± 2.9 kg and age 3.02 ± 1.3 years (meant SD)]. Patients were premedicated with midazolam 0.5 mg·kg−1. Anaesthesia was induced by inhalation of 66% N2O in O2 and sevoflurane 8%, and the trachea was intubated. Caudal analgesia was provided using bupivacaine 0.25% in a dose of 0.5 mg·kg−1. Anaesthesia with spontaneous ventilation was maintained with 66% N2O in O2, and sevoflurane 2–4%. Routine monitoring consisted of ECG, pulse oximetry, capnography and non‐invasive blood pressure.When anaesthesia had been stable for at least 15 min, the patients were attached to three different breathing systems in random succession for 10 min: 1, a Circle (Draeger Julian); 2, a Bain; 3, a Jackson Rees system. At the end of these 10 min periods, work of breathing was measured using a computerised, portable respiratory monitor (CP‐100 Pulmonary Monitor, Bear Medical). Work of breathing (W) was calculated by measuring the area enclosed in the oesophageal pressure‐volume loop (2). Oesophageal pressure was measured using a disposable balloon catheter (Smartcath, Bear Medical) and flow was measured using a disposable flow transducer (Varflex, Bear Medical). All equipment was calibrated in accordance with the manufacturers instructions prior to use.The total work of breathing (W) was expressed as Joules per litre of ventilation (J·l−1). This was compared between breathing systems using anova. P &lt; 0.05 was considered statistically significant.Results The results are presented in Table 1. Direct measurements and calculated variables (mean ± SD) Circle Bain Jackson – Rees Work of breathing (J·l−1) 0.34 ± 0.1 0.36 ± 0.07 0.34 ± 0.09 Peak inspiratory flow rate (l·s−1) 0.19 ± 0.03 0.20 ± 0.04 0.20 ± 0.04 Peak expiratory flow rate (l·s−1) 0.16 ± 0.03 0.14 ± 0.03 0.16 ± 0.03 Δ Poes(cmH2O) 5.5 ± 2.71 6.3 ± 1.49 5.9 ± 1.83 Minute ventilation (l·min−1) 2.9 ± 0.6 2.8 ± 0.7 2.9 ± 0.6 End‐tidal CO2 (kPa) 7.8 ± 0.9 7.7 ± 0.9 7.0 ± 2.4 Δ Poes = difference between end‐expiratory oesophageal pressure and lowest oesophageal pressure. Conclusions Our results indicate that there was no difference in the total work of breathing in children attached to a circle system compared to a Bain or Jackson Rees systems.Acknowledgements This work was supported by a grant from Draeger UK Ltd.