End-tidal N2O Research Articles

Long‐Term Effects of and Physiological Responses to Nitrous Oxide Gas Treatment During Alcohol Withdrawal: A Double‐Blind, Placebo‐Controlled Trial

Background Nitrous oxide gas (N2O) has been proposed to be effective in the treatment of the alcohol withdrawal syndrome (AWS). This has not been proved, however, in studies performed according to good clinical practice guidelines. Moreover, previous studies have not measured end tidal N2O concentrations or physiologic responses during N2O treatment. We have recently reported that in a double‐blind, randomized, controlled setting, N2O was not superior to placebo in relieving AWS symptoms. In this previous study, we did not find significant differences between the treatments either in the Clinical Institute Withdrawal Assessment of Alcohol scores or in the total use of benzodiazepines (diazepam and temazepam). The aim of the present study was to characterize other effects and side effects of the N2O treatment using several objective measures and to study the possible long‐term efficacy of the treatment.Methods A total of 105 inpatients who had AWS and were admitted to the A‐Clinic detoxification center were included in the study. The subjects were randomly assigned to one of the following three treatments: (1) N2O/oxygen (from 30 to 70% in oxygen), (2) air/oxygen (30%/70%), and (3) medical (normal) air. During the single 45‐min treatment period, end‐tidal N2O, carbon dioxide, and oxygen concentrations were measured. The physiologic responses were studied by measuring heart rate, blood pressure, pulse oximetric saturation, frontal muscle electromyographic activity, and plethysmographic pulse amplitude. Long‐term effects were studied by measuring craving with the Obsessive‐Compulsive Drinking Scale; severity of dependency with Severity of Alcohol Dependence Data; and liver enzymes with aspartate aminotransferase, alanine aminotransferase, and γ‐glutamyltransferase 3 and 6 months after the treatment.Results Patients in the N2O group demonstrated significantly higher facial muscle electromyographic activity and higher pulse amplitude than the air‐treated subjects. Self‐reported side effects between the gas treatments, however, did not differ between the groups. Regarding long‐term effects of the treatments, there were no differences between the groups.Conclusions Contrary to previously published data, N2O treatment did not decrease craving or liver enzymes during the 6‐month follow‐up. At the concentration used, N2O treatment produced signs of arousal instead of strong sedation.

The Effects of Different Oxygen Flow on End-Tidal N2O after Nitrous Oxide/Oxygen Anesthesia

Nitrous oxide is the most commonly used inhaled anesthetic in the part of anesthesia and used up to 75% of concentrations. Diffusion hypoxia among the disadvantages or harmful damages due to nitrous oxide exposure must be prevented by moderate flow (4-6 liters/minute) of oxygen for a few minutes. This study was investigated the effect of the amount of oxygen flow on the speed of removal of exposed nitrous oxide followed by oxygen flow rate of 2, 4, and 6 liters/minute when halted the administration of nitrous oxide. These variables were taken in 57 patients of 16 to 60 years old, who were performed the elective surgery. All patients were anesthetized with the 0.5-1.5 MAC of enflurane or isoflurane combined with nitrous oxide(2 liters/minute) and oxygen(2 liters/minute), and paralyzed with IV route pancuronium 0.07-0.08 mg/kg. Ventilation was controlled with Ohmeda 7000 ventilator (BOC Health Care Inc, Madison, USA), using a constant tidal volume of 10 ml/Kg of ideal body weight. Ventilatory rate was adjusted 12 times/minute to maintain the end-tidal CO2 of 20-35 mmHg. After 60 to 90 minutes of anesthesia, the nitrous oxide/oxygen mixture was changed to 100% oxygen, but ventilation being held constant. The results were as follows; 1) After the first 30 seconds, the end-tidal nitrous oxide concentration was 39.6±+3.7% in 2 liters/minute of oxygen flow, 28.2±5% in 4 liters/minute and 23.4±6.3% in 6 liters/minute. 2) After the 2 minutes, the end-tidal nitrous oxide concentration was 29.1±3.6% in 2 liters/minute of oxygen flow, 14.4±3.2% in 4 liters/minute and 10.13±2% in 6 liters/minute. 3) After the 5 minutes and 30 seconds, the end-tidal nitrous oxide concentration was 16.4±3.3% in 2 liters/minute of oxygen flow, 5.5±1.9% in 4 liters/minute and 4.0±1.7% in 6 liters/minute. 4) After 15 minutes, the end tidal nitrous oxide was 7.5±2.1% in 2 liters/minute of oxygen flow, 2.3±0.7% in 4 liters/minute and 2.0±0.8% in 6 liters/minute. In conclusion, the larger size of oxygen flow, the more rapid elimination of nitrous oxide. The removal rate of nitrous oxide was greatest at first 30 seconds after halting the nitrous oxide administration in all cases.

Fentanyl-induced ventilatory depression: effects of age.

To determine whether infants are more sensitive than older patients to the ventilatory-depressant effects of fentanyl, patients were anesthetized with fentanyl and nitrous oxide (N2O) and ventilatory depression was assessed following elimination of N2O and in the immediate postoperative period. Three groups of patients were studied: infants (1-12 mo old, n = 14), children (1-5 yr old, n = 14), and adults (23-38 yr old, n = 13). Skin-surface PCO2 was measured to determine the peak PCO2 occurring at the end of anesthesia when end-tidal N2O concentration was less than 6%. Naloxone was administered if PCO2 exceeded 70 mmHg. During recovery from anesthesia, ventilatory pattern was recorded using impedance pneumography to determine the longest breath-to-breath interval and the number of episodes of central apnea (defined as breath-to-breath intervals greater than or equal to 10 s in infants and children and greater than or equal to 20 s in adults). Elevation of PCO2 correlated with increasing plasma fentanyl concentrations but did not differ between groups. Four patients (two infants, one child, and one adult) required naloxone. The only subject who had a low plasma fentanyl concentration but required naloxone was a 6-wk-old infant; this was the only subject younger than 3 mo. For each range of fentanyl concentrations, the incidence of apnea increased with age, as did the number of episodes of apnea per subject. Fentanyl-induced ventilatory depression, as assessed by elevation of resting PCO2 during emergence from anesthesia and disruption of ventilatory pattern during recovery from anesthesia, is not greater in infants older than 3 mo than in children and adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrous oxide exposure in the operating room.

One-hundred and eight-five pairs of gas samples were collected from inspired gas (10 cm behind the head at nose level) and end-tidal gas of persons administering anesthesia in 3 operating rooms during daily routine anesthesia. Mean operating-room N2O concentrations from 22 to 144 ppm (volume/volume [V/V]) were measured by gas chromatography, and large moment-to-moment variations (temporal gradients) were seen in individual operating rooms. Mean end-tidal N2O concentrations from 51 to 114 ppm (V/V) were observed. There were low correlations between inspired and end-tidal N2O concentrations (r values as low as r = 0.35). This poor relationship is presumably due to spatial and temporal gradients of N2O in the operating rooms. We conclude that the temporal and spatial gradients in N2O concentrations within active operating rooms are sufficiently large to invalidate estimation of exposure of anesthetic personnel to N2O from "spot" or "grab" samples collected in the breathing area.

Entonox analgesia--a method of reducing the delay between demand and supply.

Mothers in labour using a self-administered 50% N2O and 50% O2 (Entonox) demand system, experience a time lag between making a demand at the onset of a contraction and pain relief. A practical method is described of reducing this time lag by supplementing the intermittent supply from the demand valve system with a continuous nasal flow of N2O and O2. Consequently a basal arterial N2O tension is maintained and when a demand is made, a higher level of N2O is attained in any time interval compared with that using the demand system alone. In six trained volunteers under laboratory conditions, the N2O levels measured at the mouth on a breath-by-breath basis using a mass spectrometer, showed a substantial and statistically significant reduction in the time taken to attain end-tidal N2O concentrations in the range 10-25%. This method seems worthy of a clinical trial.