Emergence from isoflurane/N2O or isoflurane anaesthesia

Background: The first goal of anaesthetic recovery is return of the patient's ability to independently maintain respiratory and circulatory functions. Nitrous oxide remains popular due to minor effects on the cardiovascular and respiratory systems. However, diffusion hypoxaemia can occur during recovery and there is a potential advantage of providing the patient with only a potent vaporised agent. Results :Patients anaesthetised with isoflurane/N₂O resumed their spontaneous breathing 16 min earlier and were extubated 22 min earlier than those anaesthetised with only isoflurane. At extubation, total MAC and end–tidal CO₂ were similar in both groups, 0.22–0.26 and 5.5–5.9 vol%, respectively. The isoflurane/N₂O group had greater minute ventilation and CO₂ excretion rates than the isoflurane group throughout the emergence period. There were no significant differences between the groups in blood gas variables or in heart rate, mean arterial blood pressure or cardiac index. Cardiac index was between 3.4 and 3.9 1 m^-2 min^-1 throughout the emergence period in both groups. Conclusion :Patients anaesthetised with only isoflurane had a longer delay until resumption of spontaneous breathing and extubation in the emergence period. Minute ventilation and carbon dioxide elimination were also significantly more suppressed throughout emergence after anaesthesia with isoflurane as compared with isoflurane/N₂O. Methods: This randomised study of 20 gynaecological patients evaluated respiratory and circulatory variables during emergence after anaesthesia with equipotent mixtures of isoflurane/ nitrous oxide or isoflurane. Inspired, end–tidal and mixed expired gas concentrations, expired minute volume, pulse oximetry saturation and arterial blood gases were registered. Monitoring of cardiac output was performed by transthoracic bioimpedance.     

Comparison of the haemodynamic actions of desflurane/N2O and isoflurane/N2O anaesthesia in vascular surgical patients

Background: The purpose of this study was to compare heart rate and arterial blood pressure response to desflurane/N₂O vs isoflurane/N₂O anaesthesia in a randomised clinical trial performed in patients before vascular surgery.
Methods: To evaluate associated changes in the autonomic nervous system with maintenance of anaesthesia, we used power spectral analysis (PSA) of heart rate and blood pressure and measured plasma catecholamine concentrations. Twenty-five patients whose trachea had been intubated after propofol induction were given either desflurane or isoflurane at 1 and 1.5 MAC in N₂O (60%) in a random manner.
Results: At an anaesthetic depth of up to 1.5 MAC, arterial blood pressure, indices of sympathetic activity derived from PSA, decreased with both anaesthetics, while heart rate and plasma catecholamine concentrations did not significantly change. Plasma renin activity significantly increased at 1.5 MAC anaesthesia in both groups.
Conclusions: We conclude that sympathetic hyperactivity previously reported during desflurane anaesthesia in healthy volunteers is not frequent in clinical practice in elderly vascular surgical patients under desflurane/N₂O anaesthesia, since it occurs at an anaesthetic depth which cannot be reached in these patients because of the lowering arterial blood pressure effects of desflurane, which are similar to those of isoflurane.     

No inhibition of gastro-intestinal propulsion after propofol-or propofol/ketamine-N2O/O2 anaesthesia: A comparison of gastro-caecal transit after isoflurane anaesthesia

Background: Gastrointestinal motility may be considerably reduced by anaesthesia and or surgery resulting in postoperative ileus. Inhibition of propulsive gut motility is especially marked after an opioid-based technique. Little, however, is known of the gastrointestinal effects of the hypnotic propofol when given continuously over a longer period of time, which is the case in total intravenous anaesthesia (TIVA) and in intensive care sedation. We therefore set out to study the effects of a propofol-based nitrous oxide/oxygen anaesthesia (group PO) on gastro-caecal transit time. The results were compared with a propofol-ketamine technique (group PK) and an isoflurane-based anaesthesia (group I; each group n=20).
Methods: Gastro-caecal transit was determined by measurement of endexpiratory hydrogen concentration (ppm). Following gastral installation of lactulose at the end of the operation, the disacchharide was degraded by bacteria in the caecum, resulting in the liberation of hydrogen which was expired. A 100% increase in endexpiratory hydrogen concentration compared to the preinduction period was considered the end-point of gastrocaecal transit.
Results: There was no significant difference with regard to gastro-caecal transit in the three groups of patients. In the propofol group mean gastro-caecal transit was 119 (±50.6 SD) min, in the propofol-ketamine group it was 147 (±57.4 SD) min, and in the isoflurane group transit time was 122 (±48.6 SD) min.
Conclusion: The data suggest that propofol, even when given as a continuous infusion, does not alter gastrointestinal tract motility more than a standard isoflurane anaesthesia. The data may be particularity relevant to patients who are likely to develop postoperative ileus. They also suggest that in an ICU setting propofol does not alter gut motility more than a sedation technique with the analgesic ketamine.     

O2 and N2O analysis with a single intravascular catheter electrode

The simultaneous measurement of O2 and N2O in liquid, using a single polarographic catheter electrode, is described. It is shown that commercial PO2 intravascular electrodes, with silver cathodes, produce separate and distinct polarograms for O2 and N2O, and that these electrodes can be used for the measurement of both PO2 and PN2O.     

Respiratory Depressant Action of Tilidine during N2O+O2, Anaesthesia

The respiratory depressant actions of pethidine and tilidine during anaesthesia were compared in 18 surgical patients anaesthetized with N₂O + O₂ after thiopental induction. Five minutes after thiopental, 0.5 mg/kg pethidine or 1.5 mg/kg tilidine were each given intravenously to six patients, the remaining six patients serving as controls.
Minute ventilation, respiratory rate, end-tidal CO₂ and Pco₂ from arterialized venous blood were measured up to 30 min. Pethidine caused the following maximal changes: 0–0.98±0.24 (s.e. mean) 1/min, rate -.5.5 ± 0.7/min, C0_2ET+0.7±0.1 vol % and Pco₂ + 5.7±1.1 mm Hg. These changes occurred within 10 xnin of the injection.
In terms of the above parameters, tilidine caused at least as pronounced a respiratory depression as pethidine. The peak effect of tilidine, however, could not be measured with certainty, since the respiratory depression first became apparent 15 min after the injection, and then increased throughout the study period. The long onset time of tilidine explains our previous failure to demonstrate tilidine-induced respiratory depression.     

Concurrent recording of AEP, SSEP and EEG parameters during anaesthesia: a factor analysis

Background. Spontaneous EEG, mid-latency auditory evoked potentials(AEP) and somatosensory evoked potentials (SSEP) have been usedto monitor anaesthesia. This poses the question as to whetheror not EEG, AEP and SSEP vary in parallel with varying conditionsduring surgical anaesthesia. Methods. A total of 81 variables (31 EEG, 22 SSEP, 28 AEP) weresimultaneously recorded in 48 surgical patients during anaesthesia.A total of 307 cases of the 81 variables in stable anaestheticstates were recorded. A factor analysis was performed for thisdata set. Results. Sixteen variables were excluded because of multicollinearity.We extracted 13 factors with eigenvalues >1, representing78.3% of the total variance, from the remaining 65 x 307 matrix.The first three factors represented 12%, 11% and 10% of thetotal variance. Factor 1 had only significant loadings fromEEG variables, factor 2 only significant loadings from AEP variablesand factor 3 only significant loadings from SSEP variables. Conclusion. EEG, AEP and SSEP measure different aspects of neuralprocessing during anaesthesia. This gives rise to the hypothesisthat simultaneous monitoring of these quantities may give additionalinformation compared with the monitoring of each quantity alone.      

The effect of clonidine on sevoflurane requirements for anaesthesia and hypnosis

We evaluated the effects of clonidine given orally on sevoflurane requirements for anaesthesia and hypnosis. Patients received either clonidine (5 μg.kg⁻¹) by mouth ( n  =21) 90 min before surgery or no premedication ( n  =21) by random allocation. MAC was calculated using repeated tetanic nerve stimulation with end-tidal sevoflurane concentration increased or decreased by 0.3 vol.% depending on the previous response. MAC awake was calculated according to the response to verbal command. The mean (SD) MAC in the clonidine-treated patients was 1.53 (0.20)% compared with 1.83 (0.15)% in the control group (p <0.001). Similarly, MAC awake was reduced in the clonidine group (0.50 (0.08)% compared with 0.60 (0.07)% in the control group) (p <0.001). We conclude that clonidine 5 μg.kg⁻¹ orally administered pre-operatively reduces sevoflurane requirements for anaesthesia and hypnosis.     

Antagonism of Fentanyl with Naloxone during N2O+O2+ Halothane Anaesthesia

To investigate the antagonistic effect of naloxone on fentanyl-induced respiratory depression, 55 patients (randomly divided into various study and control groups were studied during nitrous-oxide-oxygen-halothane anaesthesia. Respiratory depression after 0.1 mg of fentanyl was totally reversed by 10 microgram/kg of naloxone, measured as 100% restoration of spontaneous respiration, normal minute volume and end-tidal CO2, while 15 microgram/kg of naloxone was needed to antagonize 0.2 mg of fentanyl. The respective control groups remained apnoeic. If no fentanyl had previously been administered, there was no difference in the respiratory behaviour of naloxone-treated and control patients, which indicates that no unspecific analeptic effect of naloxone could be demonstrated. The circulatory changes after fentanyl were nearly reversed by naloxone, as has been found earlier with other narcotics. Recovery from anaesthesia was scored from 0 to 10 (using a modification of Apgar scores for newborns), and somewhat higher mean scores were obtained with the naloxone-treated patients than with their controls. However, higher postoperative pain scores were recorded in these patients as well as a higher incidence of nausea and vomiting. The study demonstrates the dose-relationships of fetanyl and naloxone for estimation of total antagonism; however, the use of naloxone for partial antagonism at the termination of anaesthesia cannot be based on these findings.     

Changes in CMRO2, EEG and concentration of etomidate in serum and brain tissue during craniotomy with continuous etomidate supplemented with N2O and fentanyl

Fourteen patients with supratentorial cerebral tumours were anaesthetized with continuous etomidate infusion (30 or 60 μg kg^-1 min^-1) supplemented with N₂O 67% and fentanyl. Peroperatively cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMR_O2) were measured twice by the Kety and Schmidt method. Simultaneously with the CBF measurements, blood for serum etomidate was sampled and EEG was recorded in 2-min periods in 12 patients. In 10 patients a brain biopsy for etomidate was taken peroperatively and correlated with the other data. The results indicate a dose-dependant increase in scrum etomidate and brain tissue etomidate, a decrease in CMR_o2 and suppression of EEG activity. In individual studies an increase in serum etomidate or a decrease in CMR_o2 correlated to a suppression of the EEG activity, and vice versa . However, the wide variations in these relationships within and between patients make any conclusion regarding CMR_o2 impossible from the EEG recording, infusion rate of etomidate or scrum concentration of etomidate.     

Respiration during emergence from anaesthesia with desflurane/N2O vs. desflurane/air for gynaecological laparoscopy

Background: The complications related to anaesthesia usually occur in the early postoperative period. Hypercapnia and hypoxaemia may result from any persistent depression of the respiratory drive relative to the metabolic demand. The purpose of this study was to compare the respiratory effects of desflurane anaesthesia with or without nitrous oxide during the period of emergence. Methods: Twenty patients scheduled for a standardised surgical procedure, laparoscopic hysterectomy, were randomly allocated to anaesthesia with 1.3 MAC of desflurane/N₂O (Group 1) or desflurane alone (Group 2), with 10 patients in each group. Times of resumption of spontaneous breathing and extubation were recorded and elimination rates of carbon dioxide, end-tidal concentrations of desflurane and N₂O, and blood gases were measured. Results: Spontaneous breathing was resumed in both groups when pH had decreased by about 0.07 and PaCO₂ increased by about 1.4 kPa compared with the values at the end of 1.3 MAC anaesthesia with controlled normoventilation. There were no significant differences between the groups with regards to extubation time, 6 vs. 13 min, or total MAC value at extubation, 0.20 vs. 0.19 in Group 1 and 2, respectively. Neither did the groups differ in minute ventilation, end-tidal carbon dioxide, oxygen concentrations, or blood gases. CO₂ elimination decreased in both groups from about 220 ml 70 kg^?1 min^?1 at the end of anaesthesia to a lowest value of about 160 ml 70 kg^?1 min^?1. Conclusion: The respiratory profiles during recovery from gynaecological laparoscopy with either desflurane/N₂O or desflurane anaesthesia were similar with fast resumption of spontaneous breathing, short time to extubation, and no signs of CO₂ retention.     

Clinical relevance of the B12/N2O interaction A report of a seminar

The interaction of nitrous oxide and vitamin B₁₂ and its implications are not the exclusive territory of any one discipline. The initial discovery was by a chemist but it is of obvious relevance to anaesthetists and intensivists; some complications are neurological others haematological. The interaction provides an extremely important research tool as the first easily available B₁₂-deficient animal model. Finally there are implications for exposure to contaminated atmospheres in hospitals and in industry.     

Respiratory Effects of Premedication during Enflurane N2O Anaesthesia in Children

The influence of premedication on induction characteristics and respiration was studied in 40 children breathing spontaneously during enflurane-nitrous oxide anaesthesia. Two different premedications were used. Twenty children (Group DA) received a rectal solution containing diazepam 0.25 mg kg-1 and atropine 0.015 mg kg-1 and 20 (Group DMS) received a rectal solution of diazepam 0.5 mg kg-1, morphine 0.15 mg kg-1 and scopolamine 0.01 mg kg-1. The children in Group DMS had a significantly higher preoperative sedative score (P less than 0.01), faster induction of anaesthesia (P less than 0.01), lower occurrence of airway problems during induction and a smoother intubation (P less than 0.05) than the children in Group DA. However, the end-tidal carbon dioxide tensions were higher and the occurrence of apnoea was more common in Group DMS than in Group DA. Thus it was concluded that if the more sedative premedication (DMS) is to be used for enflurane anaesthesia in children, controlled ventilation would be preferable.     

CBF and CMRO2 during Continuous Etomidate Infusion Supplemented with N2O and Fentanyl in Patients with Supratentorial Cerebral Tumour. A Dose-Response Study

In 14 patients with supratentorial cerebral tumours with midline shift below 10 mm, CBF and CMRO2 were measured (Kety & Schmidt) during craniotomy. The anaesthesia was continuous etomidate infusion supplemented with nitrous oxide and fentanyl. The patients were divided into two groups. In Group 1 etomidate infusion of 30 micrograms kg-1 min-1 was used throughout the anaesthesia, and CBF and CMRO2 were measured twice. In this group CMRO2 (means +/- s.d.) averaged 2.31 +/- 0.43 ml O2 100 g-1 min-1 70 min after induction and 2.21 +/- 0.38 ml O2 100 g-1 min-1 130 min after induction. In Group 2 the etomidate infusion was increased from 30 to 60 micrograms kg-1 min-1 after the first study and a significant fall in CMRO2 from 2.52 +/- 0.56 to 1.76 +/- 0.40 ml O2 100 g-1 min-1 was found. Simultaneously, a significant fall in CBF was observed. The CO2 reactivity was preserved during anaesthesia.     

A New Perfusion Circuit for the Newborn with Lung Immaturity: Extracorporeal CO2 Removal via an Umbilical Arteriovenous Shunt During Apneic O2 Diffusion

In spite of improved prophylaxis and therapy, the respiratory distress syndrome is still a major cause of morbidity and mortality in premature babies. Owing to the fact that a number of patients are unresponsive to other methods of neonatal care, an increasing number of perinatal centers have started to treat this group of patients with extracorporeal membrane oxygenation successfully. To make the extracorporeal gas exchange more practicable for the neonate directly after birth, a modification of this method using an umbilical arteriovenous shunt for CO2 removal in apneic premature lambs as an animal model was evaluated. A miniaturized low-resistance extracorporeal circuit that is totally incorporated in a regular intensive care baby incubator was developed. The benefit of using extracorporeal CO2 removal in very low birth weight newborns could be a conditioning of the premature lung during a short period of bypass, after which ventilation at nontraumatic pressures and nontoxic O2 concentrations would become possible.