26 DISCUSSION

o 1 . 2 e,- I - z 0

(a 1 . 0 - - l,li 0

° l ~ 0 . 8

N2OorSevo. "" ] 0 .3 MAC

I 0 .2 MAC 0 , 1 M A C 1 0 0 % 0 2 . T I M E

FIGURE 4. Mean heart rate during and after inhalation of N20 (dotted line) and sevofturane (solid line).

dental surgery. The advantages of such a reg imen are its min imal effects on respira tory and card iovascular function, protect ive reflexes, and pat ient cooperat ion; the min imal requirement for monitor ing; and the rapid recovery to street fitness. In pract ice, a low concentra- t ion of N20 with oxygen is widely accepted by dental patients to re l ieve anxiety and tension. However , be- cause N20 is the least potent of the anesthetic gases, there are indiv idual differences in its sedat ive effect among objects. In v iew of this, some invest igators have suggested that isoflurane could be an acceptable alter- nat ive to N20. 3-5 However , the odor of isoflurane may be too pungent, as stated by M c L e o d et al, 4 who re- por ted that all patients not iced the smell of isoflurane at a concentrat ion of 0.75% and one patient found this concentrat ion unacceptable . To successful ly use inhalat ion sedation, the odor o f the gas is a very im- por tant factor because the subject is conscious through- out the procedure. No one in this study found breathing sevoflurane unpleasant , and no one had a negat ive reac- t ion to the exper ience (ie, anxious or uncomfor table feel ings) whi le breathing sevoflurane. Fur thermore , all subjects who inhaled sevofturane indicated that they would be wil l ing to submit to the same procedure again.

At the concentrat ion o f sevoflurane used in this

1 . 1 _1 o ¢ 1 . 0 i-- z o 0 . 9 ~ (J

u. o

1 . 1 o

P I . 0 gc

0 . 9

I4J l s , .

N,O o, Sevo.

1 0 . 2 MAC [0.3 MAC ] 0 . 1 M A C ~ 1 0 0 % O ,

D.B.P.

T I M E

FIGURE 5. Mean systolic and diastolic blood pressure during and after inhalation of N20 (dotted line) and sevoflurane (solid line) (P < .05) Abbreviations: sBp, systolic blood pressure; DBP, diastolic blood pressure; *Significant differences between N20 group and sevoflurane group in DBP.

study, the respiratory and card iovascular functions changed insignificantly, and the mean recovery t ime was s imilar to that with N20. Thus, sevoflurane seems to be an acceptable al ternative to N20. However , the specific sedat ive and analgesic effects of subanesthetic concentrat ions require further study.

R e f e r e n c e s

1. Wallin RF, Regan BM, Napoli MD, et al: Sevoflurane: A new inhalational anesthetic agent. Anesth Analg 54:758, 1975

2. Holady DA, Smith FR: Clinical characteristics and biotransfor- marion of sevoflurane in healthy human volunteers. Anesthe- siology 54:100, 1981

3. McMenemin IM, Parbrook GD: Comparison of the effects of subanaesthetic concentrations of isoflurane or nitrous oxide in volunteers. Br J Anaesth 60:56, 1988

4. McLeod DD, Ramayya GP, Tunstall ME: Self-administered isoflurane in labour. A comparative study with Entonox. An- aesthesia 40:424, 1985

5. Parbrook GD, James J, Braid DP: Inhalational sedation with isoflurance: An alternative to nitrous oxide sedation in den- tistry. Br Dent J 163:88, 1987

d Oral Maxillofac Surg 53:26-27, 1995

Discussion

I n h a l a t i o n S e d a t i o n W i t h S e r o f l u r a n e : A C o m p a r a t i v e S t u d y W i t h N i t r o u s O x i d e

Joel Weaver, DDS, PhD The Ohio State University, Columbus

The administration of low concentrations of potent volatile anesthetics for conscious sedation and analgesia was com- mon during the first half of this century. Trichlorethylene and methoxyflurane were even self-administered by patients

for acute episodes of trigeminal neuralgia and during labor and delivery. Although these antiquated drugs were highly lipid soluble, which provided a rather slow but relatively safe onset and slow elimination, they were often preferred in place of the more rapid onset but impotent gas, nitrous oxide.

The development of a multiplicity of intravenous sedative, anxiolytic, amnestic, and analgesic medications in the last 20 years has all but eliminated the use of the volatile anesthe- tic agents for these nongeneral anesthesia purposes. A1-

JOEL WEAVER 27

though enflurane and isoflurane were developed and had much less lipid solubility, their pungent odor discouraged their use for other than maintenance of general anesthesia. Only nitrous oxide has survived as a conscious sedative and analgesic, and in many respects it is quite satisfactory. Ni- trous oxide has a slightly sweet odor and is only minimally metabolized. Its low blood: gas solubility coefficient of 0.47 provides for a rapid onset and recovery. It is the only sedative that permits the patient to leave the office unescorted. Unfor- tunately nitrous oxide has a minimum alveolar concentration (MAC) of greater than 100%. Deep sedation and enhanced analgesia require the delivery of high concentrations, with excitement, hallucinations, and hypoxemia common at these levels (> 80% nitrous oxide). Two new potent volatile anes- thetics, desflurane and sevoflurane, have physical properties similar to nitrous oxide. Desflurane, currently available in the United States, has a blood: gas solubility coefficient of 0.42.1 It is an extremely stable compound and is the least metabolized of all the modem volatile agents (0 .02%). 2 Un- fortunately its pungent odor prevents its use as an induction agent in children and probably would make it intolerable for conscious or deep sedation and analgesia.

Sevoflurane, currently available in Japan but not in the United States, also has a very low blood:gas solubility coef- ficient of 0.69 and a MAC of approximately 2%, depending on the population studiedfl Its MAC-awake, the end-tidal concentration permitting voluntary response to a command in 50% of patients, is about one third MAC. 4 Sevoflurane is therefore anticipated to be a potent amnestic drug. It is metabolized to a much greater extent then desflurane and slightly more than the 2.4% for enflurane. 2 Nevertheless, sevoflurane has been used for several hundred thousand an- esthetics in Japan without reports of hepatic or renal toxicity. It provides such a pleasant induction for children that it

has replaced halothane in pediatric anesthesiology in some Japanese hospitals.

This article compares the respiratory and cardiovascular effects, as well as the subjective evaluations of volunteer patients, when breathing several equipotent concentrations of nitrous oxide or sevoflurane. Both drugs produced favorable subjective evaluations and minimal physiologic changes. However, it would have been more valuable to have used patients actually undergoing dental procedures rather than volunteer subjects, and to have evaluated amnesia, analgesia, and psychomotor recovery. Nevertheless, this paper provides a basis for further research in revitalizing the use of potent inhalation agents for deep sedation and analgesia. Sevoflu- rane could provide a rapid, pleasant, easily controllable, two- way titratable inhalation conscious or deep sedation with potent analgesia and amnesia. Recovery may be so rapid that an escort may not be necessary. For dentists proficient in the administration of inhalation general anesthesia, sev- oflurane or some similar agent could eventually replace the intravenous benzodiazepines and narcotics that are currently considered "state of the art" drugs for ambulatory sedation. The importance of continuing research is paramount.

References

1. Eger El: Partition coefficients for 1-653 in human blood, saline, and olive oil. Anesth Analg 66:971, 1987

2. Eger EI: New inhalation agents-desflurane and sevoflurane. Can J Anaesth 40:R3, 1993

3. Wallin RF, Regan BM, Napoli MD, et al: Sevoflurane: A new inhalational anesthetic agent. Anesth Analg 54:758, 1975

4. Katoh T, Suguro Y, Nakajima R, et al: Blood concentration of sevoflurane and isoflurane on recovery from anesthesia. Br J Anaesth 69:259, 1990