Large volume N2O uptake alone does not explain the second gas effect of N2O on sevoflurane during constant inspired ventilation

Background. The second gas effect (SGE) is considered to besignificant only during periods of large volume N₂O uptake (VN₂O);however, the SGE of small VN₂O has not been studied. We hypothesizedthat the SGE of N₂O on sevoflurane would become less pronouncedwhen sevoflurane administration is started 60 min after thestart of N₂O administration when VN₂O has decreased to     

Correlation of oxygen uptake and cardiovascular dynamics during N2O-fentanyl and N2O-thiopental anesthesia in the dog

The relationship between changes in wholebody O2 consumption (VO2) and cardiovascular dynamics during changing levels of N2O-fentanyl and N2O-thiopental anesthesia was determined in 24 dogs. Dose-dependent reductions in VO2, mean blood pressure, and cardiac output occurred with infusion of fentanyl and thiopental. Painful stimuli increased VO2 during light anesthesia but not during deeper levels of anesthesia. Deep levels of N2O-fentanyl and N2O-thiopental anesthesia may protect the patient with limited cardiac reserve by reducing VO2 and preventing increases in VO2 caused by painful stimuli.     

Measurement of gas concentrations (O2, CO2, N2O and volatile agents)

Analysis of respiratory gases is part of standard monitoring, and is used in operating theatres, intensive care units, and for patient transfer.Common methods for oxygen analysis include: galvanic (fuel) cell, Clark (polarographic) electrode, and paramagnetic analyser. Common methods for carbon dioxide measurement include: infrared absorption spectroscopy and Severinghaus electrode. Other methods utilize mass spectroscopy, Raman scattering, and the piezoelectric effect.     

Persisting concentrating and second gas effects on oxygenation during N2O anaesthesia

Theoretical modelling predicts that the concentrating effect of nitrous oxide (N2O) uptake on alveolar oxygenation is a persisting phenomenon at typical levels of ventilation - perfusion (V/Q) inhomogeneity under anaesthesia. We sought clinical confirmation of this in 20 anaesthetised patients. Arterial oxygen pressure (P(aO2)) was measured after a minimum of 30 min of relaxant general anaesthesia with an inspired oxygen (F(I O2)) of 30%. Patients were randomly allocated to two groups. The intervention group had N2O introduced following baseline blood gas measurements, and the control group continued breathing an identical F(I O2) in nitrogen (N2). The primary outcome variable was change in P(aO2). Mean (SD) in P(aO2) was increased by 1.80 (1.80) kPa after receiving a mean of 47.5 min of N2O compared with baseline conditions breathing O2/N2 (p = 0.01). This change was significantly greater (p = 0.03) than that in the control group: + 0.09 (1.37) kPa, p = 0.83 and confirms the presence of significant persisting concentrating and second gas effects.     

Bispectral index and regional cerebral oxygen saturation during propofol/N2O anesthesia

PURPOSE: A study was undertaken to compare the influence of midazolam, isoflurane, and aminophylline (which may antagonize anesthetic action) on bispectral index (BIS) and regional cerebral oxygen saturation (rSO(2)) during propofol/N(2)O anesthesia, and to test the hypothesis that the drug-induced changes in BIS values are accompanied by a change in rSO(2). METHODS: General anesthesia was administered to 36 patients with a continuous infusion of propofol to maintain a BIS value of 40 +/- 5. After baseline recordings, patients were randomly assigned to receive either midazolam, isoflurane, or aminophylline. Bispectral index values, rSO(2) using near-infrared spectroscopy, and hemodynamic parameters were recorded for 60 min. RESULTS: Midazolam (0.05 mg x kg(-1)) significantly decreased the BIS from 47.8 +/- 5.4 to 35.0 +/- 4.5 at five minutes after injection (P < 0.001 vs control) during propofol anesthesia, whereas the rSO(2) was unchanged. Similarly, isoflurane (1.1% end-tidal) decreased the BIS from 42.5 +/- 7.5 to 27.8 +/- 6.9 (P < 0.001) without affecting rSO(2). In contrast, aminophylline (3 mg.kg(-1)) was associated with an increase in BIS from 41.6 +/- 2.1 to 48.3 +/- 9.2 at five minutes after injection (P < 0.05) without affecting rSO(2). CONCLUSIONS: Midazolam or isoflurane-induced decreases in the BIS during propofol anesthesia were not accompanied by a decrease in rSO(2). Aminophylline significantly increased the BIS score during propofol anesthesia, suggesting that aminophylline can antagonize, at least in part, the sedative actions of propofol.     

N2O volumes absorbed and excreted during N2O anesthesia in children.

Exhaled volumes were measured in 8 children during uptake and elimination of 3 percent and 75 percent N2O, using a volume-controlled ventilator. Absorption of 75 percent N2O during induction reduced the exhaled minute volume, which fell a mean of 16 percent in the 1st or 2nd minute and returned to normal by 15 to 20 minutes. Elimination was the mirror image of uptake; the mean increase in the exhaled minute volume was 13 percent. The concentration effect during uptake was measured (3 percent versus 75 percent N2O) and the data were used to calculate a fall in alveolar volume of at least 8 percent by the 2nd minute of uptake. The type of ventilation (volume-limited, pressure-limited, or spontaneous) was seen to have a modifying role on the respiratory pattern caused by the absorbed and excreted volume of N2O.     

Double blind comparison of alfentanil N2O and fentanyl N2O for outpatient surgical procedures

Alfentanil - nitrous oxide and fentanyl - nitrous oxide techniques were compared in outpatients undergoing therapeutic abortion or dilatation and curettage. Thirty patients were studied in each group. Time to awakening was similar in both groups but patients who received alfentanil responded to verbal commands one minute sooner and were alert 1.5 minutes before those who received fentanyl. At ten minutes post anaesthesia the recovery scores were the same for both groups. Patients who received alfentanil were not street-worthy earlier than those who received fentanyl. During the procedure approximately two thirds of the patients moved. This movement was vigorous in 23 per cent of the patients who received alfentanil and in 30 per cent of those given fentanyl. We conclude that: (1) a more flexible dosage schedule is required in order to prevent disturbing movement of the patient during the procedure and (2) patients who received alfentanil were not street-worthy earlier than those who were given fentanyl.     

Comparative study of etomidate-alfentanil anesthesia with N2O/O2 or with air/O2

Systolic, diastolic blood pressures, heart rate, glycaemia, blood gases and clinical status were studied preinduction, 10' after anesthesia induction and intubation, 3', 30', 60' and 90' after surgical incision, when awake on the operating table and 60' after awakening in 20 hysterectomy patients. Etomidate (0.3 mg/kg + continuous infusion), alfentanil (75 micrograms/kg + increments of 15 micrograms/kg) anesthesia was used with a N2O/O2 mixture (10 pt) or with air/O2 (10 pt), both at a FIO2 = 0.33. This technique gave a smooth induction and recovery. Cardiovascular changes were moderate. The additional dose of alfentanil was 5.25 +/- 0.65 mg in the N2O/O2 group and 6.45 +/- 0.85 mg in the air/O2 group. The incidence of vomiting was 15%. Statistical analysis of both groups indicated no major difference between the two types of anesthesia, for the cardiovascular, acid base data and glycaemia. This technique is a simple and effective way of anesthetising patients, but from a clinical point of view the etomidate/alfentanil anesthesia combined with N2O/O2 gives better results than when combined with air/O2.     

The effect of 30% N2O on the general hemodynamics of patients with heart valve lesions

The effect of 50% N2O on the general haemodynamics of patients with heart valve lesions was evaluated. The addition of N2O to oxygen before cardiopulmonary bypass was associated with a decrease in the cardiac output from 3.60 +/- 0.23 to 3.04 +/- 0.17 l.min-1/m2 (P less than 0.001) although the filling pressure of the left ventricle remained constant and right ventricle preload was increased from 8.18 +/- 0.99 to 9.85 +/- 1.14 mmHg (P less than 0.05). Because the systemic blood pressure fell after N2O was added, the decrease in cardiac output is interpreted as representing a decrease in myocardial contractility. The changes in the inverse relationship between arterial blood pressure and stroke volume also support the concept that N2O suppresses myocardial contractility.     

Cerebrospinal fluid pressure during O2 encephalography and N2O inhalation.

Cerebrospinal fluid (CSF) pressure was studied in 8 patients and 5 dogs during pneumoencephalography (PEG) or ventriculography in which either O2 or N2O was used as the contrast gas prior to and during N2O inhalation. In 7 patients, the use of O2 as the contrast gas increased CSF pressure 8.7 torr (range 4 to 12 torr) following N2O inhalation. In 1 patient, when N2O was used as the contrast gas, CSF pressure did not change after N2O inhalation. These findings were confirmed in anesthetized animals ventilated at a constant PaCO2. The authors conclude that if N2O inhalation is required during PEG, maximum patient safety can be achieved if the contrast gas is also N2O.     

三种麻醉方法在维持期间血流动力学的变化

目的：观察异丙酚／阿芬太尼、七氟醚／笑气以及安氟醚／笑气等三种麻醉维持期间血流动力学指标的变化。方法：４５例病人随机分为三组，每组１５例，麻醉快速诱导后经气管插入特殊的ＴＴＤ导管，麻醉维持分别采用０．１ｍｇ·ｋｇ－１·ｍｉｎ－１异丙酚和１μｇ·ｋｇ－１·ｍｉｎ－１阿芬太尼静脉泵入（Ｐ／Ａ组），１％七氟醚－６６％笑气（Ｓ／Ｎ组）或１％安氟醚－６６％笑气吸入（Ｅ／Ｎ组）。于麻醉诱导后３０分钟、手术开始后３０分钟、４５分钟、６０分钟以及术毕测定ＭＡＰ、ＣＶＰ、ＣＯ、ＣＩ和ＳＶＲ等血流动力学指标的变化。结果：在ＡＳＡⅠ～Ⅱ级的病人，临床麻醉剂量的异丙酚／阿芬太尼、七氟醚／笑气和安氟醚／笑气麻醉对血流动力学指标的影响轻微。结论：三种麻醉方法对心血管功能的影响程度相似。