End-tidal Nitrous Oxide Research Articles

Support-vector classification of low-dose nitrous oxide administration with multi-channel EEG power spectra

Support-vector machines (SVMs) can potentially improve patient monitoring during nitrous oxide anaesthesia. By elucidating the effects of low-dose nitrous oxide on the power spectra of multi-channel EEG recordings, we quantified the degree to which these effects generalise across participants. In this single-blind, cross-over study, 32-channel EEG was recorded from 12 healthy participants exposed to 0, 20, 30 and 40% end-tidal nitrous oxide. Features of the delta-, theta-, alpha- and beta-band power were used within a 12-fold, participant-wise cross-validation framework to train and test two SVMs: (1) binary SVM classifying EEG during 0 or 40% exposure (chance = 50%); (2) multi-class SVM classifying EEG during 0, 20, 30 or 40% exposure (chance = 25%). Both the binary (accuracy 92%) and the multi-class (accuracy 52%) SVMs classified EEG recordings at rates significantly better than chance (p < 0.001 and p = 0.01, respectively). To determine the relative importance of frequency band features for classification accuracy, we systematically removed features before re-training and re-testing the SVMs. This showed the relative importance of decreased delta power and the frontal region. SVM classification identified that the most important effects of nitrous oxide were found in the delta band in the frontal electrodes that was consistent between participants. Furthermore, support-vector classification of nitrous oxide dosage is a promising method that might be used to improve patient monitoring during nitrous oxide anaesthesia.

An Electroencephalogram Metric of Temporal Complexity Tracks Psychometric Impairment Caused by Low-dose Nitrous Oxide.

Nitrous oxide produces non-γ-aminobutyric acid sedation and psychometric impairment and can be used as scientific model for understanding mechanisms of progressive cognitive disturbances. Temporal complexity of the electroencephalogram may be a sensitive indicator of these effects. This study measured psychometric performance and the temporal complexity of the electroencephalogram in participants breathing low-dose nitrous oxide. In random order, 20, 30, and 40% end-tidal nitrous oxide was administered to 12 participants while recording 32-channel electroencephalogram and psychometric function. A novel metric quantifying the spatial distribution of temporal electroencephalogram complexity, comprised of (1) absolute cross-correlation calculated between consecutive 0.25-s time samples; 2) binarizing these cross-correlation matrices using the median of all channels as threshold; (3) using quantitative recurrence analysis, the complexity in temporal changes calculated by the Shannon entropy of the probability distribution of the diagonal line lengths; and (4) overall spatial extent and intensity of brain complexity, was quantified by calculating median temporal complexity of channels whose complexities were above 1 at baseline. This region approximately overlay the brain's default mode network, so this summary statistic was termed "default-mode-network complexity." Nitrous oxide concentration correlated with psychometric impairment (r = 0.50, P < 0.001). Baseline regional electroencephalogram complexity at midline was greater than in lateral temporal channels (1.33 ± 0.14 bits vs. 0.81 ± 0.12 bits, P < 0.001). A dose of 40% N2O decreased midline (mean difference [95% CI], 0.20 bits [0.09 to 0.31], P = 0.002) and prefrontal electroencephalogram complexity (mean difference [95% CI], 0.17 bits [0.08 to 0.27], P = 0.002). The lateral temporal region did not change significantly (mean difference [95% CI], 0.14 bits [-0.03 to 0.30], P = 0.100). Default-mode-network complexity correlated with N2O concentration (r = -0.55, P < 0.001). A default-mode-network complexity mixed-effects model correlated with psychometric impairment (r2 = 0.67; receiver operating characteristic area [95% CI], 0.72 [0.59 to 0.85], P < 0.001). Temporal complexity decreased most markedly in medial cortical regions during low-dose nitrous oxide exposures, and this change tracked psychometric impairment.

Direct measurement of nitrous oxide kinetics

Using conscious subjects, measurement of the effects of low concentrations of anaesthetic agents can allow the dynamics of onset and offset of the agent to be measured and kinetic values estimated. However, the tests have to be rapid and preferably assess cerebral function. We used a short version of the digit symbol substitution test (DSST) that allowed frequent measurement of the impairment caused by nitrous oxide. We compared 10 min of onset and offset of breathing 5% and 30% nitrous oxide in 30% oxygen, compared with 30% oxygen only. End-tidal nitrous oxide concentrations were used to predict the concentration in a central compartment, according to a range of T(1/2) values chosen to be consistent with possible cerebral blood flow values. We studied 19 volunteers and estimated a mean response. Only 30% nitrous oxide decreased the DSST. When DSST scores were related to the values in the predicted central compartment, the best dose-effect relationship was found when the T(1/2) was 37 s, consistent with a regional blood flow of about 120 ml 100 g(-1) min(-1). The onset of nitrous oxide effect on DSST is rapid, consistent with the perfusion of metabolically active cerebral cortical tissues. The rate of onset is greater than previous measures based on a motor test which involved the function of subcortical structures in the central nervous system.

The Effects of Subanesthetic Concentrations of Sevoflurane and Nitrous Oxide, Alone and in Combination, on Analgesia, Mood, and Psychomotor Performance in Healthy Volunteers

We studied the effects of subanesthetic concentrations of sevoflurane and nitrous oxide, alone and in combination, on analgesia, mood, and psychomotor performance in human volunteers. We hypothesized that nitrous oxide and sevoflurane would produce both opposing and potentiating effects within the same study. Over the course of three sessions, 20 subjects inhaled 0%, 0.2%, or 0.4% end-tidal sevoflurane for a 68-min period that was divided into four 17-min blocks. During either the second or fourth block, 30% end-tidal nitrous oxide was added to the concentration of sevoflurane being inhaled. Pain response, psychomotor performance, and mood were evaluated during the second and fourth blocks. Pain ratings were higher when sevoflurane and nitrous oxide were administered together than when nitrous oxide was administered alone, which indicates that sevoflurane attenuated the analgesic effects of nitrous oxide. Sevoflurane increased self-reported ratings of sleepiness, and the addition of nitrous oxide decreased these ratings. Nitrous oxide potentiated psychomotor impairment that was induced by sevoflurane. The combination of sevoflurane and nitrous oxide produced both opposing and potentiating effects within the same study. The results suggest that nitrous oxide and sevoflurane may act through different neurochemical mechanisms on some end points, such as analgesia and sleepiness. Healthy volunteers inhaled subanesthetic concentrations of sevoflurane and nitrous oxide. Sevoflurane made nitrous oxide less effective as an analgesic, and nitrous oxide made sevoflurane less effective as a sedative. The two drugs may work at cross purposes on different end points of anesthesia.

Gas kinetics during nitrous oxide analgesia for labour

Hypoxaemia may occur after hyperventilation with nitrous oxide during labour. The purpose of this study was to assess whether diffusion hypoxia is a contributory factor. Twenty-four parturients were randomly allocated to receive 50 or 70% nitrous oxide in oxygen. The median nitrous oxide inhalation time per contraction was 58 s and 33 s, respectively. The end-tidal carbon dioxide and the minute ventilation remained unchanged. The end-tidal oxygen concentration was lowest at 120 s, reaching 15.4% in both groups. The oxygen saturation did not differ between the groups with a lowest median value of 96% before the start of nitrous oxide inhalation. Two parturients had episodes of desaturation. Both had low end-tidal oxygen concentrations in association with the desaturation but, as the end-tidal nitrous oxide concentrations were low, the desaturations could not be attributed to diffusion hypoxia.

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.

Duration of apnea in anesthetized infants and children required for desaturation of hemoglobin to 95%. The influence of upper respiratory infection.

Sixty-one patients ASA physical status 1-2 aged 1 month to 12 years undergoing elective surgery were included in the study. Anesthesia was induced via a mask with sevoflurane up to 5% and 66% nitrous oxide in oxygen. After paralysis with vecuronium (0.12 mg/kg iv), the trachea was intubated and the lungs were ventilated manually with 3% sevoflurane in oxygen until the end-tidal nitrous oxide decreased to less than 5%. Apnea was started by disconnecting the breathing circuit from the endotracheal tube. The time from the start of apnea to Spo2 of 95% was measured. Manual ventilation was reinstituted when Spo2 decreased to 95% and another set of vital signs was recorded. Twenty of 61 patients had symptoms of upper respiratory infection. The time to Spo2 of 95% correlated well with height, age, and body weight both by linear and non-linear regression analyses. The patients with symptomatic upper respiratory infection required less time for Spo2 to decrease to 95% compared to the asymptomatic children. We conclude that younger children require less time for Spo2 to decrease to 95%. The presence of upper respiratory infection is an additional factor increasing the susceptibility of small children to hypoxemia.

Treatment of Stress Response during Balanced Anesthesia Comparative Effects of Isoflurane, Alfentanil, and Trimethaphan

Acute hypertensive responses during nitrous oxide-opioid-relaxant anesthesia are a common clinical problem. In adult men undergoing radical prostatectomy procedures and anesthetized with a standardized technique, we evaluated the effectiveness of alfentanil, isoflurane, and trimethaphan in treating acute hemodynamic and stress hormone responses to surgical stimulation. Stress hormone concentrations were measured 1 min before skin incision, after the onset of an acute hypertensive response, and after returning the mean arterial pressure to within 10% of the preincision values with one of the three treatment modalities. Pretreatment plasma alfentanil concentrations (151 +/- 47 to 156 +/- 47 ng.ml-1) and end-tidal nitrous oxide concentrations (66 +/- 2 to 68 +/- 2%) were similar in all three groups. Acute hypertensive events were associated with significantly increased concentrations of catecholamines and vasopressin (antidiuretic hormone [ADH]). Whereas intravenous alfentanil returned all hormone concentrations to preincision values, norepinephrine and glucose concentrations were significantly increased after adjunctive isoflurane administration. Although trimethaphan decreased the norepinephrine concentration, the epinephrine, beta-endorphin, cortisol, ADH, and glucose concentrations were significantly increased compared to preincision values. However, the persistent elevation in the posttreatment ADH concentration in the trimethaphan group was the only significant difference between the three groups. Mean (+/- standard deviation) times to awakening (2.8 +/- 3.3 to 3.8 +/- 4.2 min), extubation (8.1 +/- 4.8 to 10.3 +/- 8.5 min), and orientation (19.6 +/- 20.4 to 24.6 +/- 19.1 min) were similar in all three groups. Naloxone was required more frequently in patients in the alfentanil (35%) and isoflurane (24%) groups than in the trimethaphan group (4%).(ABSTRACT TRUNCATED AT 250 WORDS)

EFFECTS OF NITROUS OXIDE ON AUDITORY CORTICAL EVOKED POTENTIALS AND SUBJECTIVE THRESHOLDS

This study has examined the effects of inhaled nitrous oxide on the N1 and P2 components of the cortical auditory evoked potentials (AEP) in the latency interval 80-300 ms after the stimulus. The amplitudes, latencies and thresholds of the AEP were measured at a range of end-tidal nitrous oxide concentrations (0%, 10%, 20%, 40%) in 10 subjects with normal hearing. Systematic decreases in amplitude and latency were observed with an increase in threshold. A study of the effect of stimulus intensity on AEP amplitude showed that the amplitude change with nitrous oxide was accounted for largely by systematic increase in evoked potential threshold. Subjective pure tone thresholds were not affected by the concentrations of nitrous oxide used, indicating that the AEP changes were independent of subjective hearing level.

Supraglottic jet ventilation for laser surgery of the larynx in children.

To investigate the efficacy and safety of supraglottic jet ventilation for laser surgery on the larynx, ten studies were performed in seven children scheduled for laser excision of juvenile laryngeal papillomata. The children were anesthetized using halothane, nitrous oxide, fentanyl 3 micrograms/kg, and a succinylcholine infusion. After the Leonard-Jako laryngoscope was in place, jet ventilation with 70% nitrous oxide in oxygen was begun through a 12-gauge Medicut intravenous cannula inserted in the right-hand light channel of the laryngoscope. Tracheal, inspired, and end-tidal oxygen, nitrous oxide, nitrogen, and carbon dioxide were determined by mass spectrometry simultaneously with arterial blood gases. Oxygen and carbon dioxide levels were always within normal limits, the end-tidal to arterial differences averaging 50 +/- 9 and 2 +/- 1 (SEM) mm Hg, respectively. Room air entrainment averaged 32 +/- 2%. The end-tidal nitrous oxide averaged 39 +/- 2%. The advantages of this technique are that it leaves the larynx completely free for the surgeon and it eliminates the possibility of endotracheal tube ignition. Supraglottic jet ventilation for this surgical procedure was determined to be effective and relatively safe.