Nitrous Oxide-oxygen Mixture Research Articles

Spontaneous tension pneumothorax following outpatient general anesthesia

A case is reported in which a spontaneous tension pneumothorax developed after outpatient general anesthesia with a nitrous oxide oxygen mixture. The patient was not intubated or ventilated with positive pressure on the airway. The pneumothorax could be attributed to either a postanesthetic coughing episode, the administration of nitrous oxide, which may have caused already present apical blebs to increase in size to the point of rupture, or both.

Effects of naloxone on prolactin, luteinizing hormone, and cortisol responses to surgical stress in humans.

To evaluate the possible involvement of endogenous opioid peptides in the responses of PRL, LH, and cortisol to surgical stress, we have studied the effect of naloxone on these hormones in otherwise normal subjects of both sexes undergoing cholecystectomy for gallstones. In 24 subjects (12 males and 12 females), premedication consisted of atropine sulfate (0.007 mg/kg BW); general anesthesia (30 min later) was induced by thiopental (7 mg/kg) and maintained constant by 1% ethrane in a 70%:30% nitrous oxide-oxygen mixture. In 6 males and 6 females, naloxone (0.4 mg) was injected iv before anesthesia induction. After skin incision, a clear PRL release was observed in all subjects; this was more evident in females than in males. PRL release was significantly lower in naloxone-pretreated subjects. LH release was observed only in males and was significantly higher in naloxone-pretreated subjects. Cortisol release occurred in both sexes in a similar way and was not significantly different in naloxone-pretreated subjects. Cortisol release occurred in both sexes in a similar way and was not significantly different in naloxone-pretreated subjects. These results indicate that endogenous opioid peptides are involved in stress-induced PRL and LH release in humans.

Pain Relief in Labor by Transcutaneous Electrical Nerve Stimulation

In this prospective randomized study of pain relief in labor, the effect of transcutaneous electrical nerve stimulation (TNS) performed over both the low-back and suprapubic region was evaluated and compared with a control group not receiving TNS. Both high frequency and pulse train TNS were used. The study included 24 induced labors. In the TNS group, conventional methods were added when needed, while in the control group only conventional methods were used. Assessment of low-back and suprapubic pain was performed by the parturient each hour during the first stage. In the TNS group most of the parturients reported minimal or moderate low-back pain throughout labor, while parturients in the control group reported an increased intensity of low-back pain as labor progressed. The effect of suprapubic pain was insignificant in both groups. Neither TNS nor nitrous oxide-oxygen mixture and pethidine could reduce this pain component. Course of labor, uterine activity and fetal heart patterns were similar in the two groups. The neonates were evaluated with Apgar score, assays of blood samples from the umbilical vein including blood lactate, plasma hypoxanthine and blood gas, and neurobehavioral assessment on two occasions. All newborn infants were in good condition and no significant differences between the two groups could be demonstrated.

Anxiolytic effects of low dosage nitrous oxide-oxygen mixtures administered continuously in apprehensive subjects.

We observed the effect of low doses of nitrous oxide on the cardiovascular and respiratory systems, the cortisol output in blood and saliva, and the degree of sedation and analgesia of 20 volunteers. A psychologic screening inventory was also performed. We found nitrous oxide, at low dosage, to be primarily an anxiolytic and not an analgesic or amnesic agent. The nasally inhaled concentrations necessary to induce an anxiolytic effect varied from subject to subject, ranging from 30% to 65% and averaging 35% to 40%. This finding justifies the use of the gas to relieve anxiety instead of nonvolatile parenterally administered psychosedatives and narcotics. Nitrous oxide is preferable because its action is established within several minutes, it is rapidly eliminated at the conclusion of a procedure, and the sensorium is clear after five or six minutes. The gas is simply and safely administered with fail-safe apparatus designed specifically for this purpose. The technic is admirably suited for use in ambulatory care units where minor surgical or dental procedures are performed.

Pain relief in labor by transcutaneous electrical nerve stimulation. A prospective matched study.

The study evaluated transcutaneous electrical nerve stimulation (TNS) for pain relief in labor, used in parallel with conventional methods. The investigation comprised 566 vaginally delivered women, 283 of whom were given TNS. Pain relief was evaluated with a questionnaire which the women answered shortly after delivery. With a statistical multivariate technique, it was concluded that TNS has a specific effect on pain localized to the back. Few women in either the TNS or the control group reported good relief of pain localized to the suprapubic region. Nitrous oxide-oxygen mixture was used less often in the TNS group than in the controls. Duration of labor and maternal blood loss were comparable in the two groups. The babies borne by primiparae in the TNS group tended to have better Apgar scores. Fewer babies of primiparae in the TNS group required observation for two days or more on the neonatal ward than was the case with the controls. However, the electrical stimulation could not be used optimally as it interfered with monitoring the fetal heart rate in half the cases. It is concluded that although TNS has a good effect on low-back pain and seems to have no negative effects on the mother or child, it is only a complement to conventional methods.

Does systemic morphine increase descending inhibitory controls of dorsal horn neurones involved in nociception?

The direct spinal depressive effect of morphine and related compounds has been demonstrated in numerous electrophysiological studies in spinal animals. Recently, research has focussed on those dorsal horn neurones activated by a large range of noxious inputs, the activities of which are strongly modulated by both segmental and supraspinal inhibitory mechanisms (see refs. in ref. 3). In the rat, for instance, the response of dorsal horn cells to C fibre is depressed in a naloxone-reversible and dosedependent fashion by morphine; in direct contrast, responses to Aa fibre stimulation is poorly affected 11. In addition to a direct spinal action of morphine, an indirect action with the strenthening of inhibitory controls from supraspinal origin has been proposed 16 and extensively reviewed3,6,1z, 13. The direct conclusion of both hypotheses is that the depressive effects of systemic morphine would be greater in intact than in spinal preparations. Considering the contradictory reports in this area 4,s,10,14, we have studied the action of systemic morphine on the activities of dorsal horn cells involved in the transmission of nociceptive messages in intact rats. A comparison of results in spinal 11 and intact animals could provide a basis for the discussion of the initial hypotheses. Forty-two male Sprague-Dawley rats weighing 250-300 g were used. Surgical preparation, monitoring and recording were performed as previously described 11. Recordings were carried out under volatile anaesthesia, i.e. 0.5 ~ halothane in a nitrous oxide-oxygen mixture (2/3-1/3), during which the EEG showed monomorphic waves (80-100 #V), often rhythmic, in the range of theta (4--5 c/sec) accompanied by few 12--14 c/sec spindles. The recording of dorsal horn cells began only when the anaesthetic state was stable, generally 45 min after the discontinuation of the deeper anaesthesia employed during the surgical procedure. Under these conditions, noxious, visual or auditory stimulation did not induce the arousal reaction or peripheral vasomotor modifications usually observed during suffering or stress reactions.

Does systemic morphine increase descending inhibitory controls of dorsal horn neurones involved in nociception?

The direct spinal depressive effect of morphine and related compounds has been demonstrated in numerous electrophysiological studies in spinal animals. Recently, research has focussed on those dorsal horn neurones activated by a large range of noxious inputs, the activities of which are strongly modulated by both segmental and supraspinal inhibitory mechanisms (see refs. in ref. 3). In the rat, for instance, the response of dorsal horn cells to C fibre is depressed in a naloxone-reversible and dosedependent fashion by morphine; in direct contrast, responses to Aa fibre stimulation is poorly affected 11. In addition to a direct spinal action of morphine, an indirect action with the strenthening of inhibitory controls from supraspinal origin has been proposed 16 and extensively reviewed3,6,1z, 13. The direct conclusion of both hypotheses is that the depressive effects of systemic morphine would be greater in intact than in spinal preparations. Considering the contradictory reports in this area 4,s,10,14, we have studied the action of systemic morphine on the activities of dorsal horn cells involved in the transmission of nociceptive messages in intact rats. A comparison of results in spinal 11 and intact animals could provide a basis for the discussion of the initial hypotheses. Forty-two male Sprague-Dawley rats weighing 250-300 g were used. Surgical preparation, monitoring and recording were performed as previously described 11. Recordings were carried out under volatile anaesthesia, i.e. 0.5 ~ halothane in a nitrous oxide-oxygen mixture (2/3-1/3), during which the EEG showed monomorphic waves (80-100 #V), often rhythmic, in the range of theta (4--5 c/sec) accompanied by few 12--14 c/sec spindles. The recording of dorsal horn cells began only when the anaesthetic state was stable, generally 45 min after the discontinuation of the deeper anaesthesia employed during the surgical procedure. Under these conditions, noxious, visual or auditory stimulation did not induce the arousal reaction or peripheral vasomotor modifications usually observed during suffering or stress reactions.

Middle ear gas composition during nitrous oxide-oxygen ventilation.

The middle ear gas composition during 180 minutes ventilation with nitrous oxide-oxygen mixture was determined in 12 mongrel dogs. The mean relative concentration of N2O in the middle ear (ME) rose to 12,26.4 and 29.3% after 60, 120 and 180 minutes respectively. During this period, the relative concentration of N2 dropped from a mean of 83.2% in the air-ventilated dogs to 54.8%, without an essential change in the concentrations of O2 or CO2. The elimination of N2O from the ME during 30 minutes of postanesthetic ventilation with O2 was incomplete, an average of 11.4% N2O remaining in the ME. At the same time, the mean relative concentration of O2 reached 19%, higher than the O2 relative concentration normally present in the ME. The results indicate that gas diffusion may occur across the ME mucosa for N2O as well as for O2, producing selective changes in the middle ear gas composition.

Increases in Cuff Volume and Pressure in Red Rubber Endotracheal Tubes during Anaesthesia

Increases in endotracheal tube cell volume and pressure during anaesthesia have been reported to be due to the diffusion of nitrous oxide into the cuff. This study compared cuff volume and pressure changes in anaesthetized intubated patients who were ventilated with those allowed to breath spontaneously. The cuffs of Magill red rubber endotracheal tubes were inflated with either air or a nitrous oxide-oxygen mixture. Serial pressure and volume recordings confirmed that both parameters increased when the cuff was inflated with air. The increase in cuff pressure was however, greater during intermittent positive pressure ventilation than for spontaneous respiration. There were no significant changes when the cuff was inflated with the nitrous oxide-oxygen mixture.

Pressure and volume changes in tracheal tube cuffs during anaesthesia.

Recently, it has been observed that, when a patient is breathing a nitrous oxide-oxygen mixture and the cuff of the tracheal tube is filled with air, nitrous oxide may diffuse into the cuff and thereby cause an increase in volume and pressure. In the present investigation, different gas mixtures were used to fill the cuff, and repeated measurements of pressure, and occasionally of volume, were made during anaesthesia. Both large-volume and small-volume cuffs were studied. A considerable increase in volume and pressure took place in both types of cuffs. The changes were directly proportional to time for the first few hours. If the cuff was inflated with nitrous oxide-oxygen, no pressure increase occurred, and this was also true for the air-filled cuff if halothane anaesthesia was given.

The haemodynamic effects of unsupplemented nitrous oxide-oxygen-relaxant anaesthesia in cardiac patients.

The effect on the systemic and pulmonary circulation of unsupplemented nitrous oxide in about 30% oxygen, with and without IPPV, was investigated in five cardiac patients and compared with control periods at rest with air breathing. The results of this investigation show that nitrous oxide in conventional oxygen concentration does not cause any great haemodynamic changes. During tracheal intubation, however, significant increases in both systemic and pulmonary blood pressures were registered. However, these pressures reverted to the control values immediately after the tracheal intubation. The results of this study support many earlier clinicaly good experiences obtained when using this conventional nitrous oxide-oxygen mixture in cardiac patients.

The effect of a nitrous oxid-oxygen mixture on the lateral heterophoria.

The distance and near lateral heterophorias were investigated in 10 subjects to determine the effect of a nitrous oxide (N2O)-oxygen (O2) mixture. The heterophorias were measured by the Maddox method before and after a 3-minute induction period of nitrous oxide. It was found that the distance lateral heterophoria for all 10 subjects changed toward more esophoria, whereas the changes in the near lateral heterophoria were inconsistent in their direction.

AN INSTRUMENT FOR THE ACCURATE AND CONTINUOUS MEASUREMENT OF HALOTHANE CONCENTRATIONS IN NITROUS OXIDE-OXYGEN MIXTURES

An instrument is described which measures continuously both the halothane concentration and the composition of the carrier gas when the vaporizer is situated outside the breathing circuit. The instrument is an adapted katharometer in which the out-of-balance voltage is used to measure the concentration of one compound in a three-component mixture, and the total voltage reduction across the constant-current-supplied bridge is used to indicate the proportions of the other two components. Halothane concentrations can be determined with an inaccuracy of 0.1% for concentrations up to 6%. Nitrous oxide (N2O) concentration in the nitrous oxide-oxygen mixture, serving as carrier gas, can be determined with an accuracy of 1% over the whole range up to 100% N2O. The 99% response time of the instrument is approximately 1 min.

THE EFFECT OF FLUROXENE ON INTRACRANIAL PRESSURE IN PATIENTS WITH INTRACRANIAL SPACE-OCCUPYING LESIONS

The intracranial pressure was studied in nine patients with space-occupying lesions before and after addition of 4% fluroxene to a nitrous oxide-oxygen mixture at normo-capnia and hypocapnia. At normocapnia (Paco2 38 mm Hg) fluroxene produced a 16 mm Hg (range 1–59 mm Hg) increase in intracranial pressure leading to a decrease in cerebral perfusion pressure, in three cases to critically low values. Hypocapnia (Pa co3 28 mm Hg) resulted in all cases in a rapid fall in intracranial pressure to near normal values and restoration of satisfactory cerebral perfusion pressure. It is concluded that fluroxene can be used in neuroanaesthesia, provided hyperventilation is applied and non-flammable concentrations are used.

Equilibria for mixtures of oxygen with nitrous oxide and carbon dioxide and their relevance to the storage of N2O/O2 cylinders for use in analgesia

The liquid-vapour equilibria for the systems nitrous oxide-oxygen and carbon dioxide-oxygen are presented in the form of isotherms on a pressure-composition graph, and isobars on a temperature graph, up to 200 atmospheres (20·7×106 N m−2). In the case of premixed cylinders of a 50/50 nitrous oxide-oxygen mixture used as an analgesic any liquid phase formed as a result of cooling the cylinder to not lower than −40°C can be dispersed by storing the cylinder horizontally for 24 hours at a temperature not less than 5°C.

Hidden Hazards of the McKesson Narmatic Anesthesia Machine

The McKesson Narmatic anesthesia machine was designed originally as a demand-flow device for nitrous oxide-oxygen mixtures. The machine functions adequately, although it is at times inaccurate and unstable. The addition of an optional bag and in-circuit vaporizer has provided other hazards in the use of the machine. Because of these dangers, strong recommendations are made that the machine not be used.

Hidden hazards of the McKesson narmatic anesthesia machine.

The McKesson Narmatic anesthesia machine was designed originally as a demand-flow device for nitrous oxide-oxygen mixtures. The machine functions adequately, although it is at times inaccurate and unstable. The addition of an optional bag and in-circuit vaporizer has provided other hazards in the use of the machine. Because of these dangers, strong recommendations are made that the machine not be used.

Apneic Oxygenation Following Respiration with Air or Nitrous Oxide-Oxygen Mixture

Apneic Oxygenation Following Respiration with Air or Nitrous Oxide-Oxygen Mixture

Effect of nitrous oxide on “spontaneous” salivation in dogs

Inhalation of nitrous oxide-oxygen mixtures containing not less than 40% of nitrous oxide causes “spontaneous” salivation and masticatory movements in dogs. The magnitude of the response varies with the concentration of nitrous oxide, with the sensitivity to stimulation of the alimentary center, and with the previous conditioning of the animals. The effect is due mainly to strengthening of the function of the subcortical alimentary center, resulting from removal of cortical inhibition. After numerous exposures of the animals to inhalation of nitrous oxide the effects may be elicited by passing the gas through the upper respiratory passages only. This effect is mediated by natural conditioned reflex, which is elaborated by repeated exposure to the gas, and which suffers extinction with further repetition.

An investigation of the oxygen saturation of arterial blood as determined by the modified millikan oximeter during anesthesia for oral surgical procedures

With the aid of a modified Millikan oximeter and a Beckman oxygen analyzer, a study was made of the effects of variable partial pressures of nitrous oxide and oxygen upon the arterial oxygen saturation in a random series of forty-eight patients undergoing oral surgical procedures. The results of this study were as follows: 1. 1. Patients who underwent anesthesia with thiopental (Pentothal) sodium supplemented with nitrous oxide and oxygen given through an intratracheal catheter had a mean arterial oxygen saturation of 95.5 per cent. 2. 2. Patients who received only thiopental and inspired room air had a mean arterial oxygen saturation of 94.5 per cent. 3. 3. Patients who received thiopental sodium supplemented with a nitrous oxide-oxygen mixture given through a nasal mask had a mean arterial oxygen saturation of 94 per cent. 4. 4. Patients who received only nitrous oxide-oxygen mixture inspired through a nasal mask had a mean arterial oxygen saturation of 61.5 per cent. In a control series, consisting of five groups totaling thirty patients who underwent anesthesia with nitrous oxide-oxygen mixtures, the partial pressure of oxygen was kept constant at a given level for each group; the mixtures were delivered at a rate of 8 liters per minute. In this series the degree of arterial oxygen saturation was observed to be correlated, roughly, with the partial pressure of oxygen in the inspired gas mixtures.