Negative pressure in the middle ear in children after nitrous oxide anaesthesia

Middle Ear Pressure Changes During Anesthesia With or Without Nitrous Oxide are Similar Among Airway Devices

We tested the hypothesis that middle ear pressure (MEP) is influenced by the choice of airway device during anesthesia with or without nitrous oxide (N2O) in the gas mixture. Eighty consecutive anesthetized, paralyzed ventilated patients (ASA physical status I-II, 18-65 yr) were randomly allocated for airway management with the orally inserted tracheal tube, classic laryngeal mask airway, ProSeal laryngeal mask airway, or laryngeal tube suction with or without N2O 66% in the gas mixture. MEP was measured from both ears in random order by a blinded observer before induction of anesthesia and every 10 min for 70 min. In the N2O groups, N2O was changed to air after 40 min. There were no differences in MEP among the airway devices in the N2O or air groups. MEP was unchanged in the air groups but increased in the N2O groups with N2O (P < 0.0001) and decreased with air (P < 0.02). Baseline values for MEP were similar, but MEP was always higher for the N2O groups (P < 0.001). We conclude that the choice of airway device does not influence MEP among orally inserted tracheal tube, classic laryngeal mask airway, ProSeal laryngeal mask airway, and laryngeal tube suction during anesthesia with or without N2O in the gas mixture.

Middle Ear Pressure Changes after Nitrous Oxide Anesthesia and Its Effect on Postoperative Nausea and Vomiting

OBJECTIVES/HYPOTHESIS

This study was designed to explore the relationship between changes in middle ear pressure associated with inhalational anesthesia and the incidence of postoperative nausea and vomiting (PONV).

STUDY DESIGN

Prospective, randomized.

METHODS

Middle ear compartment pressures were measured by tympanometry in 27 randomly assigned knee arthroscopy patients throughout the surgical procedure as well as into recovery.

RESULTS

A positive correlation between the maximum positive pressure (MPP) and maximum negative pressure (MNP) gradient and PONV was demonstrated (P <.05). The incidence of PONV in the nitrous oxide (N2O) treatment group was 6 of 16 patients, whereas only 2 of 11 patients in the control group developed nausea, vomiting, and vertigo symptoms. Those patients that did not experience PONV demonstrated a median MPP of 155 with a median MNP of -52. The patients that experienced PONV exhibited a median MPP of 179 with a median MNP of -164. This demonstrates a significant increase in the incidence of PONV in the N2O treatment group.

CONCLUSIONS

Barometric changes in the middle ear contribute to the incidence of PONV induced by N2O.

Regeneration of mastoid air cells: clinical applications

The objective of this study was to establish a method for regenerating mastoid air cells and their functions for clinical use in incurable otitis media. For this clinical study three patients (one male, two female) were randomly selected from patients with severe cholesteatoma about to undergo staged operations. Hydroxy-apatite in three-dimensional, honeycomb-like structures (3D-HA) were used as artificial pneumatic bones. This 3D-HA is made of calcium phosphate and has a high percentage of micropores (90%). Its surface is coated with collagen. At the first stage of tympanoplasty, collagen-coated 3D-HA was put into the opened mastoid cavity and fixed by fibrin glue. Recovery of mastoid aeration and regeneration of the pneumatic air cells of the mastoid cavity were estimated on CT scan images after the first operation. Aeration was recovered in all cases. The mastoid air cells were regenerated in two cases. In the failed case, subcutaneous connective tissues and granulations invaded into the spaces of the 3D-HA. This study demonstrated that mucosa would grow on the surface of a 3D-HA implant and could provide gas exchange functions in the newly opened mastoid cavity. This tissue engineering method may be a possible treatment for intractable otitis media.

Recovery characteristics of propofol anaesthesia, with and without nitrous oxide: a comparison with halothane/nitrous oxide anaesthesia in children

Few studies have examined whether nitrous oxide influences the recovery characteristics of propofol anaesthesia. The present study examined the effect of nitrous oxide on the recovery characteristics of propofol anaesthesia, and compared these data with those for halothane/nitrous oxide anaesthesia. Sixty children aged 3-12 years were assigned at random to receive one of three maintenance regimens: propofol with or without nitrous oxide (70%) or halothane/nitrous oxide (70%). During propofol/N2O anaesthesia, the infusion rate of propofol (180 +/- 39 micrograms.kg-1.min-1) required to maintain the mean arterial pressure and heart rate within 20% of the baseline values was significantly less than that during propofol/O2 (220 +/- 37 micrograms.kg-1.min-1; P < 0.005). The time from discontinuation of anaesthesia to eye-opening (11 +/- 6 min), to response to commands (12 +/- 6 min), and to return of full wakefulness (21 +/- 10 min) after propofol/N2O were similar to those after propofol/O2, but significantly less (by approximately 30%) than those after halothane (P < 0.05). The overall incidence of emesis after propofol/N2O (53%) was greater than that after propofol/O2 (17%, P < 0.05) and comparable to that after halothane/N2O (58%). These data suggest that N2O has little effect on the rate of recovery after propofol, but significantly increases the incidence of postoperative emesis, thereby attenuating one of the main attributes of propofol anaesthesia.

Middle-ear pressure variations during total intravenous anesthesia with propofol, fentanyl, and ketamine

PURPOSE

As the middle-ear cavity is one of the noncompliant gas-filled cavities, an increase in middle-ear pressure (MEP) instead of volume expansion is observed with inhalation of nitrous oxide (N₂O). Changes in MEP cause many complications, such as ear pain, temporary hearing impairment, and postoperative emesis. Therefore, we investigated changes in MEP during total intravenous anesthesia (TIVA) with propofol, fentanyl, and ketamine (PFK) and inhalation of N₂O.

METHODS

Twelve patients were anesthetized with PFK until 60 min after the induction of anesthesia, and then N₂O (60%) inhalation was started. MEP was measured by impedance audiometry (ranging from -300 daPa to +200 daPa) at 10-min intervals during PFK, and at 2-min intervals after the inhalation of N₂O.

RESULTS

MEP gradually but significantly increased from the preanesthetic value of 16±8 to 34±12 (SEM) daPa 50 min after the induction of PFK. However, MEP did not exceed the normal limit. The values of MEP in all patients were more than 200 daPa within 36 min after the start of inhalation of N₂O in oxygen.

CONCLUSION

PFK had a minimal effect on MEP, whereas addition of N₂O to PFK increased MEP dramatically. Therefore, TIVA, or at least PFK, would be a better choice for patients with middle-ear or upper-airway diseases.

The mobility of the malleus and incus with varying middle ear pressures

The mobility of the malleus and incus was studied in two fresh human temporal bones. Various pressure gradients were applied across the intact tympanic membrane and the movement of the ossicles examined, firstly with the incus in situ and secondly, with the incus removed. The displacement of the long process of the incus was less than 100 microns at the extremes of pressure gradient. However, this mobility increased by over twofold when the posterior incudal ligament was divided. With removal of the incus, the mobility of the umbo with pressure changes was further increased and can be as much as half a millimetre. In all cases the maximal rate of ossicular excursion was noted with pressure gradients of less than 100 daPa (mmH2O) across the tympanic membrane.

Vomiting after outpatient tonsillectomy and adenoidectomy in children: the role of nitrous oxide

The role of nitrous oxide anesthesia in causing postoperative vomiting (POV) was studied in 60 children undergoing outpatient tonsillectomy and adenoidectomy. In this controlled, randomized, double-blind investigation, anesthesia was induced by inhalation of a volatile anesthetic in both groups. The nonnitrous oxide group received no nitrous oxide, even during induction of anesthesia. Designated nurses in the postanesthesia care unit (PACU) who were blinded to the anesthetic technique evaluated the incidence and the severity of the patient's emetic symptoms, both in the PACU as well as after discharge. Pharmacologic intervention was administered on the basis of evaluation by the nurses. Although a high incidence of POV was noted in both groups, there was no difference in either the incidence or the severity of POV between the group receiving nitrous oxide and the group receiving no nitrous oxide.

Assessment of the gas exchange function of the middle ear using nitrous oxide. A preliminary study

A method for assessing the gas exchange through the middle ear (ME) mucosa using nitrous oxide is introduced. Increases in the ME pressure was determined by a tympanogram or a micropressure sensor inserted into the mastoid cavity during ear surgery under general anesthesia using 67% nitrous oxide, 33% oxygen, and sevoflurane on 30 normal ears, 12 ears with otitis media with effusion (OME), and 3 postoperative ears with chronic adhesive otitis media or cholesteatoma. All the 30 normal ears except one showed varying pressure increase, and an inverse correlation was observed between pressure increase and area of mastoid on radiographs. Pressure increase was observed in 6 (50%) ears with OME, and this finding correlated well with the presence or absence of air space in the ME on computed tomography images examined preoperatively, on ears which had ear surgery, the presence or absence of pressure increase correlated with the degree of previous surgical intervention on the mastoid. The rationale and possibility of clinical application of this method is discussed.

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.

Adverse effects of nitrous oxide

Although once considered completely devoid of complications, it is now recognised that the misuse or inappropriate use of nitrous oxide (N2O) often results in adverse side effects. Hypoxia, particularly the entity 'diffusion hypoxia', can occur with the administration of inadequate amounts of oxygen during or immediately after a N2O anaesthetic. N2O will diffuse into air-containing cavities within the body faster than nitrogen diffuses out. This results in a temporary increase in either the pressure and/or volume of the cavity depending upon the distensibility of its walls. The magnitude of the effect is proportional to the blood supply of the cavity, the concentration of N2O inhaled and the length of time the patient is exposed to N2O. Significant morbidity or even death can result from this phenomenon. A property unique to N2O is its ability to oxidise and inactivate the vitamin B12 components of certain enzymes in both animals and man. One such enzyme, methionine synthetase is essential for normal DNA production. Animal and human studies have demonstrated that the haematological, immune, neurological and reproductive systems are each affected. These adverse effects of N2O can occur after both acute (surgical) or long term (occupational) exposure to the gas. Because of its effects on the pressure and volume characteristics of air-containing spaces, N2O should not be used for patients with bowel obstruction, pneumothorax, middle ear and sinus disease, and following cerebral air-contrast studies. Many anaesthesiologists feel that use of N2O should be restricted during the first two trimesters of pregnancy because of its effects on DNA production and the experimental and epidemiological evidence that N2O causes undesirable reproductive outcomes. Since N2O affects white blood cell production and function, it has been recommended that N2O not be administered to immunosuppressed patients or to patients requiring multiple general anaesthetics. Many anaesthesiologists believe that the potential dangers of N2O are so great that it should no longer be used at all for routine clinical anaesthesia. However, the continued use of N2O remains a controversial topic since, at present, a suitable substitute gas is not available.