The effect of nitrous oxide on middle-ear effusions

Pre-operative prediction of 'dry taps'

OBJECTIVES

The treatment of children with 'glue ear' often presents surgeons with the question of whether or not to insert a grommet when myringotomy reveals no fluid in the middle ear. We present a study designed to assess which factors contribute to the presence of a 'dry tap'.

DESIGN

We prospectively gathered data from a cohort of 280 children (504 myringotomies). The cohort included two subgroups, one received halothane and nitrous oxide anaesthesia, and the other received enflurane anaesthesia.

SETTING

The ENT department of a district general hospital.

PARTICIPANTS

Children (aged less than 17 years) requiring myringotomy.

MAIN OUTCOME MEASURES

The presence of a 'glue' or dry tap at myringotomy was documented. We also recorded data on the following: pre- and post-induction tympanometry; age; season; anaesthetic type; and the delay from listing to actual operation.

RESULTS

A non type B pre-induction tympanogram and delay to operation were strong indications of finding a dry tap at surgery.

CONCLUSIONS

In our study population, the proportion of dry taps at myringotomy was 18 per cent. The presence of a dry tap was rarely due to the induction of anaesthesia. Multivariate analysis revealed that the combination of factors most likely to predict a dry tap were non type B tympanogram and delay to operation.

Effects of desflurane on middle ear pressure

OBJECTIVE

To evaluate the effects of desflurane on middle ear pressure.

STUDY DESIGN

A prospective clinical study.

METHODS

In this study, 38 ears of 19 male children that were scheduled for circumcision were included. Baseline tympanometry reading was performed on each ear just before anesthesia. After induction anesthesia with propofol a laryngeal mask was applied and desflurane administration was started. The next tympanometry reading was taken at 5th, 10th and 15th minute after administration and at the 10th minute after the cessation of desflurane. Data were analysed using Wilcoxon test.

RESULTS

Mean MEP values before anesthesia in 38 ears of 19 boys were -10.32+/-33.14. After starting the administration of desflurane 5th minute mean value was 71.15+/-60.42, at the 10 th minute 111.56+/-59.03 and at the 15th minute it increased to 120.50+/-54.14, and these measurements were significantly higher than the starting value (p<0.001). After cessation of desflurane mean MEP value dropped to 57.56+/-79.06, but compared with the starting value this was also significantly higher (p<0.001).

CONCLUSION

Desflurane may increase the middle ear pressure and it may be unsuitable for certain middle ear surgeries.

Effects of sevoflurane and TIVA with propofol on middle ear pressure

OBJECTIVE

To evaluate the effects of sevoflurane and TIVA with propofol on middle ear pressure and to show the importance of anesthesia without using any inhalational agents during middle ear surgery.

STUDY DESIGN

A prospective, randomized controlled clinical study.

METHODS

In this study, 25 male children that were scheduled for circumcision were randomised into two groups. Group I (n=13) received TIVA with propofol and group II (n=12) received sevoflurane. Baseline tympanometry reading was performed on each ear just before anesthesia. The next tympanometry reading was taken 10min after applying the laryngeal mask. Data were analysed by Mann-Whitney U (between groups) and Wilcoxon tests (within groups).

RESULTS

Mean MEP values in 26 ears of 13 boys in group I did not show any significant difference before and after the anesthesia with propofol (p>0.05). In group II mean MEP values in 24 ears of 12 boys showed a significant increase after the anesthesia with sevoflurane (p<0.001). No significant difference was found between the MEP values of the two groups before the anesthesia (p>0.05), and MEP values measured during the anesthesia were significantly higher in group II (p=0.007).

CONCLUSION

Sevoflurane may increase the middle ear pressure and TIVA with propofol may be used in middle ear operations more safely than sevoflurane.

Effects of inhalant anesthesia: tympanometry validation (R98/217)

OBJECTIVES

The purpose of this study was to determine the best time to assess middle ear status with tympanometry for tympanometric instrument validation. The research question addressed three logical times for tympanometric reading prior to myringotomy.

METHODS

Fifty-one children, ranging in age from nine months to 10 years, were recruited for this investigation. Participants underwent inhalant anesthesia for myringotomy and grommet placement with or without adenoidectomy and/or tonsillectomy. Tympanometry data was analyzed across three time periods.

RESULTS

Findings indicated that tympanometric readings prior to anesthesia produced the most accurate results.

CONCLUSIONS

Implicated in findings, in order to ensure that tympanometric instruments are reliable, typanometric measurements should be taken prior to the administration of any anesthesia.

Remifentanil-based anesthesia versus a propofol technique for otologic surgical procedures

Otologic procedures require a still surgical field and are associated with a 50% incidence of emetic symptoms. Propofol reduces nausea and vomiting but not intraoperative movement. This study compares a remifentanil/propofol anesthetic to a propofol/fentanyl combination to determine which provides the best perioperative conditions for otologic microsurgery. Eighty healthy patients were randomly assigned to receive one of the anesthetic combinations. Demographic data, hemodynamic variables, movement, and bispectral index monitoring values in addition to anesthetic emergence, nausea, vomiting, pain, and other recovery variables were compared between groups with appropriate statistical methods. Both groups were similar. Times to eye opening (7.7 +/- 0.7 vs 12.4 +/- 1.2 minutes) and extubation (9.8 +/- 0.9 vs 12.4 +/- 1.0 minutes) were shorter with remifentanil. This group also had lower hemodynamic variables and movement (23% vs 65%) under anesthesia. Postoperative pain was mild in both groups, but remifentanil patients had more than the propofol group. All other postoperative parameters were similar. Remifentanil-based anesthesia produces better hemodynamic stability, less movement, and faster emergence after otologic surgery, with propofol's antiemetic effect, for the same cost.

Diagnostic value of tympanometry in infants in clinical practice

One hundred and twenty-one visits of 58 infants (2-11 months of age) were evaluated in the Finnish Otitis Media Vaccine Trial. Infants were examined with tympanometry (Grason-Stadler GSI 38 Autotymp) and pneumatic otoscopy by one study doctor. Diagnosis of otitis media was verified by myringotomy in 74% of cases. Tympanometry was technically successful in 94% of ears. The success rate was statistically significantly higher (P < 0.05) among infants less than 7 months of age than those above 7 months. The sensitivity of tympanometry (type B) to detect ears with middle ear fluid was 0.70 and the specificity 0.98 with a positive predictive value of 0.93 and negative predictive value of 0.94. The sensitivity was somewhat lower in the younger age group (0.61); specificity and positive and negative predictive values were good in both age groups. The high success rate and high negative and positive predictive values of tympanometry make it a useful aid for assuring the correct diagnosis of otitis media in infants in routine clinical practice.

Middle ear pressure variation: effect of nitrous oxide

Previous studies examining middle ear pressure changes due to inhalant anesthesia, including nitrous oxide, have cited equivocal results. An investigation was performed to closely monitor changes in middle ear pressure during middle ear surgery. Baseline tympanometry was performed before anesthesia, and middle ear pressure was then documented in 1-min time intervals. A total of 97 subjects were studied; 51 received nitrous oxide and halothane, and 46 received halothane alone. Results indicate that nitrous oxide causes significantly greater pressure fluctuations than halothane alone. There were no effects for time of surgery, type of fluid, or baseline. Pressure fluctuation was attributed to eustachian tube function. Case studies are presented to demonstrate subject variability, and suggestions for validation study procedures are presented.

The effect of anaesthesia on tympanograms of children undergoing grommet insertion

A prospective study was designed to assess the effect of anaesthesia, including nitrous oxide, on tympanometric results of children undergoing myringotomy and possible grommet insertion. 155 patients (310 ears) were examined with a pneumatic otoscope and had tympanograms performed within 1 hour of operation. The patients were then anaesthetized by a combination of intravenous and gaseous anaesthetic. Immediately before myringotomy, a tympanogram was repeated. In 13% of patients predicted to have fluid at admission, there was a change in their tympanogram after induction of anaesthesia, suggesting clearance of fluid. At myringotomy, these ears were dry. We surmise that there was displacement of fluid from the middle ear by nitrous oxide during the early stages of anaesthesia. Thus we feel that, if an otologist confidently expects to find an effusion at myringotomy, the presence of a dry tap should not change his management plan.

Nitrous oxide analgesia in a pediatric emergency department

Nitrous oxide (N2O) has been shown to be an effective analgesic in adult medical outpatients, yet no prospective studies of its use in the pediatric medical outpatient exist. Thirty-four children requiring laceration repair were randomly assigned to one of two treatment groups: 30% N2O/70% O2 or a placebo, 100% O2. Pain behavior, using the observer-scored Children's Hospital of Eastern Ontario Pain Scale, was assessed by double-blind techniques, before and during the laceration repair. Less pain behavior was seen in children less than 8 years old who received the N2O mixture than in those receiving the placebo. In patients 8 or more years old who received N2O, there was a significant improvement in the second evaluation as compared with those receiving only O2 during the procedure (P less than .05). There also was a smaller increase in pain behavior, from the first to the second evaluation, in those receiving N2O (P less than .05). No side effects were encountered. The authors conclude that continuous N2O inhalation is an effective and painless analgesic in children for outpatient procedures. More effective analgesia will likely occur with 40% to 50% N2O, although these concentrations remain to be studied in pediatric outpatients.

Adenoid histamine and its possible relationship to secretory otitis media

We have shown that adenoid tissue contains large amounts of the inflammatory mediator histamine. Children with fluid present in both ears at operation were found to have increased amounts of histamine in their adenoid tissue compared to a group with no signs or symptoms of SOM. Also mouth breathing and nasal obstruction were associated with adenoid histamine content whereas other signs and symptoms were not. No significant differences in adenoid weight were seen between SOM and non SOM patients. Histamine, both free and cell-associated, was found in nasopharyngeal secretions and middle-ear fluid although the source and mechanism of release has not yet been identified. We suggest that the benefits of adenoidectomy in children with SOM may possibly come from removing a potential source of inflammatory mediators in the vicinity of the Eustachian tube.