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The Installation, patient connections, and additional features of nitrous oxide-oxygen sedation machines and devices are reviewed. Desirable features include standardized equipment to provide ready resuscltative devices.

The effect of long-term exposure to an analgesic concentration of nitrous oxide-oxygen on the cerebral cortex of rats was determined in this experimental study. Observable effects on the cerebral cortex of rats after prolonged exposure to nitrous oxide-oxygen in an analgesic concentration were determined. Sixteen rats in two experimental groups were housed in airtight cages through which 40% nitrous oxide in oxygen was passed for eight hours a day. Four rats composed the control group. The animals in the first experimental group were killed after seven days’ exposure and rats in the second group after 14 days’ exposure. Rats in the control group were killed at the same intervals. Blocks of tissue from the frontal, parietal, and occipital portions of the brain were removed from the animals, and a cortical cell count was completed. Observable signs of damage to cortical cells, especially those in the occipital region, were found. Differences in some aspects of cellular response seem to be sex related.

Using changes in nasal temperature to reflect changes in nasal blood flow, an assessment has been made of the efficacy of various nasal vasoconstrictive drugs. The drugs tested were 10 per cent and 5 per cent cocaine, 1 1,000 epinephrine, and naphazoline hydrochloride 0.05 per cent (Privine), with normal saline solution as a control. The drugs were found to be effective in producing nasal vasoconstriction if applied following induction of anesthesia rather than prior to induction, as usually recommended. Epinephrine 1 1,000 and 10 per cent cocaine were found to be the most efficacious drugs in producing vasoconstriction of nasal mucous membrane. Naphazoline hydrochloride 0.05 per cent was comparable to 5 per cent cocaine in producing vasoconstriction of the nasal mucosa.

Cardiorespiratory and analgesic effects of intravenous analgesia with pentobarbital, meperidine, and scopolamine were investigated in healthy volunteers not undergoing operation. Relief of anxiety and tension attendant on the dental experience were achieved with minimal physiologic upset. The lack of analgesia to tooth stimulation indicated the need for local anesthesia in conjunction with this technique.

SUMMARY Respiratory changes following transurethral resection of the prostate were studied in 26 men. Right-to-left pulmonary shunt determinations were made in ten patients, and total lung volume and weight determinations were made in the remainder. Nine of ten showed postoperative decrease in pulmonary shunt. The tenth showed no change. Total lung volume, functional residual capacity, inspiratory capacity, and body weight measurements showed no consistent change after transurethral resection. The significance of a large right-to-left shunt preoperatively, and its apparent decrease after surgery are discussed.

High peridural blocks with 2 per cent lidocaine were studied in 20 normal volunteers 21 to 43 years of age. Epinephrine 1:200,000 was incorporated into the local anesthetic solution used to produce blocks in ten of the subjects. The following control measurements were made: mean arterial pressure, central venous pressure, cardiac rate, output and stroke volume, total peripheral resistance, pH Paco2 Paco2 glomerular filtration rate {GFR) and effective renal plasma flow (ERPF). These measurements were repeated at 15-minute intervals until cutaneous analgesia disappeared. With lidocaine alone, there were BO significant systemic cardiovascular changes, although maximum decreases of 9 per cent in GFR and 15 per cent in ERPF were seen. Epinephrine caused highly significant cardiovascular changes attributable to beta-receptor stimulation. The maximum changes were: mean arterial pressure –21 per cent, cardiac rate +26 per cent, cardiac output +68 per cent, stroke volume +34 per cent, total peripheral resistance –49 per cent, CFR –11 per cent, and ERPF –26 per cent. The differences between GFR values in the two groups were not significant, but the greater decrease in ERPF when epinephrine was added was significant and was due primarily to decrease in mean arterial pressure.

Continuous-flow and demand-flow anesthetic machines are compared as to economy, air dilution, gas flow, and influence of positive pressure.

The Jorgensen technique and nitrous oxide-oxygen sedation were evaluated for the risk of aspiration. Volunteers and patients were studied in the supine, semisupine, and Trendelenburg positions. Aspiration occurred in a single patient under the Jorgensen technique and could be related to the presence of a narcotic in the mixture. The incidence of tracheal soiling was lower than that with other intravenous techniques and could be attributed to the use of the semisupine position or the baseline concept of narcotic dosage in the Jorgensen technique. In the nitrous oxide-oxygen sedation technique, aspiration was not noted. The study suggests that use of a narcotic in an intravenous sedative technique increases the hazard of aspiration.

Blood cortisol levels of oral surgery patients were analyzed to objectively determine the effect of intravenous sedation on surgical stress. Results showed a measure of sedation but did not adequately reflect the stress of oral surgery or the changes produced by intravenous sedation.

To evaluate the hypothesis that inhalation of low levels of nitrous oxide-oxygen produces an altered state of consciousness similar to hypnosis, 20 subjects were given three suggestions (analgesia, compulsive behavior, and amnesia) during double-blind administration of either nitrous oxide-oxygen or oxygen. Results suggest that administration of nitrous oxide-oxygen may be of increased clinical usefulness if it is combined with careful use of suggestion.

Halothane has proved its value as an adjuvant to nitrous oxide-oxygen for dental outpatient anesthesia. Rapid induction and recovery, smooth maintenance, and low incidence of nausea and vomiting have been factors in its wide acceptance by oral surgeons and anesthetists. There is a more stable cardiovascular response during anesthesia with halothane-nitrous oxide-oxygen than with halothane-oxygen alone or with thiopental induction. Premedication is usually unnecessary, indeed, it may actually cause serious cardiac arrhythmias, mask signs of halothane overdosage, or delay recovery time. A demand-flow, nonrebreathing system is most suitable for outpatient anesthesia. The advisability of frequent recalibration of gas machines and halothane vaporizers is stressed. Use of the nasal mask or nasopharyngeal tube provides an equally satisfactory airway, but the nasopharyngeal tube may create iatrogenic complications during its placement. Endotracheal intubation in outpatients is avoided except where positively indicated. Although the relationship of halothane to massive hepatic necrosis has received inordinate scrutiny, present evidence indicates that halothane presents no greater hazard than other anesthetic agents. The use of catecholamines on outpatients anesthetized with halothane cannot be recommended, as the risk of serious cardiac arrhythmias outweighs any possible advantages. Extensive experience with halothane in the general operating theater, followed by its supervised administration to outpatients, should be prerequisites to its use in private dental or oral surgery practice.

Four halothane vaporizers produced for continuous-flow methods and two specifically designed for use with demand-flow machines were investigated with regard to their efficacy in vaporization with demand flow. None of the vaporizers investigated was accurate, but, apart from the Goldman vaporizer, none could be said to deliver excess increments of halothane with regular changes of the vaporizer setting.

A study was made to evaluate the cardiorespiratory and analgesic effects of nitrous oxide-oxygen analgesia in ten healthy volunteers who were not undergoing operation. Correlation of findings with those from oxygen inhalation alone showed that physiologic changes during nitrous oxide-oxygen analgesia parallel those of inhalation of 100% oxygen. The safety of nitrous oxide-oxygen inhalation anesthesia, when used for relief of anxiety and tension, was demonstrated.

Continuous auscultatory monitoring of heart sounds has proved to be the most direct and foolproof method of evaluating alterations in cardiovascular dynamics during surgery.

Through controlled studies of cardiovascular and respiratory response and correlation of analgesia levels with the physiological status of the patient as required, efforts were made to establish intravenous analgesia on a sound physiologic basis. Cardiorespiratory and analgesic effects of intravenous analgesia in conjunction with regional block anesthesia were investigated in nine healthy men not undergoing dental operation. Significant decreases in cardiac output, cardiac rate, and minute work were found, and indicate the need for careful postoperative evaluation before the patient is discharged.

T he problems of posture relative to maintenance of a natural relationship between the head and body during dental operations were emphasized as long ago as 189&l The upright sitting posture was accepted until 195’7, when it was suggested that the common fainting attack could occur unrecognized under outpatient anesthesia and result in permanent brain damage or, indeed, death.2 Studies of the problems relative to cardiorespiratory effects of posture are inconc1usive.3-6 Therefore, we attempted to determine and establish control measurements of cardiorespiratory and peripheral blood flow responses exhibited by (1) the unpremeditated, unanesthetized patient positioned in the five postures shown in Fig. 1 and (2) two comparable groups of six persons, each selected at random, stressed with sleep doses of intravenous methohexital in the 45 degree upright sitting position (Position 4) and in the Trendelenburg position (Position 5). If dental operations are performed on patients in the supine position, then to ensure maintenance of a patent airway and prevention of laryngeal soiling by stomach contents, endotracheal intubation becomes mandatory. The assumption in clinical practice is that Positions 4 and 5 avoid these problems (Appendix).

A clinical investigation was conducted to assess the value of utilizing the special sensory functions of vision and/or hearing in determining complete recovery from anesthesia. Eighty patients were divided equally between assessments of auditory and visual acuity to preoperative levels as end points. Auditory perception was determined on the basis of verbal response evoked by a human voice. Visual acuity and cerebral activity were assessed by flicker-fusion thresholds. Ten patients in each phase of the project were given either (A) halothane-oxygen, (B) halothane-nitrous oxide-oxygen, (C) thiopental for induction followed by halothane-nitrous oxide-oxygen, or (D) premedication and thiopental for induction followed by halothane-nitrous oxide-oxygen. The mean duration of anesthesia for the entire project was 31.8 minutes. In none of the cases did recovery from anesthesia exceed 90 minutes, as assessed by either visual or auditory acuity. Within 20 minutes of the termination of anesthesia, 92.5 per cent of the patients were fully recovered when auditory acuity was used as the criterion, whereas only 20 per cent were determined to be awake when CFF was used to measure recovery. No significant correlations were found between mode or duration of anesthesia and recovery time. The data suggest that recovery is most rapid following halothane-nitrous oxide-oxygen anesthesia, whereas halothane-oxygen produces the longest recovery period. There was a 12 per cent incidence of postoperative nausea and vomiting when the patients were rapidly ambulated in Phase II; this was directly related to orthostatic hypotension. It can be concluded that a visual test is a more appropriate measurement of recovery from anesthesia than a test of hearing.