Tammisto O, Hamalainen L, Tarkkanen L. Halothane and methoxyflurane in ophthalmic anesthesia. Acta Anaesth Scand 9: 173–177, 1965.

Generic name: Nitrous oxide.

Proprietary name: None.

Primary use

This inhalation anesthetic and analgesic is used in dentistry, in the second stage of labor in pregnancy and during induction of general anesthesia.

Ocular side effects.

Systemic administration

Certain

1. Pupils – dependent on plane of anesthesia a. Mydriasis – reactive to light (initial)

b Miosis – reactive to light (deep level of anesthesia) c. Mydriasis – non-reactive to light (coma)

2. Intraocular pressure

a.Increased during anesthesia

b.Decreased immediately post anesthesia 3. Decreased vision

4. Decreased lacrimation

5. Abnormal ERG or VEP

6. Cortical blindness

Intravitreal injection of gas during vitrectomy

Certain

1. Nitrous oxide gas increases in volume up to 42 days (Fig. 7.4a)

2. Acute glaucoma

3. Central retinal artery occlusion

4. Optic atrophy

5. Pupillary block

Clinical significance

Pupillary changes due to nitrous oxide are common; however, other than aiding in determination of the anesthetic plane, they are seldom of importance. Nitrous oxide, as well as other anesthetics,­ produces the transitory effect of decreased basal tear production during general anesthesia. Although decreased vision or blindness after induction of general anesthesia is quite rare, this phenomenon is more frequent with nitrous oxide than with most other general anesthetics. Visual loss is probably secondary to asphyxic cerebral cortical damage.

Nitrogen from the bloodstream can enter an intraocular gas bubble from retinal surgery, causing it to expand. Nitrous oxide’s solubility is 34 times that of nitrogen, therefore long-lasting ­insoluble gases for retinal tamponades have expanded to cause central artery occlusion, pupillary block and acute glaucoma in a closed globe (Fig. 7.4a). While most gases will absorb within 10 days, Lee reports the onset of this complication at 3–7 days and Seaberg et al at 42 days post anesthesia. If these gases are used, therefore, nitirous oxide anesthesia is contraindicated and patients should be instructed to wear identifying bracelets (Fig. 7.4b) until the gas bubble is absorbed.

Fig. 7.4a  Vitreous cavity about 50% full of gas. Photo courtesy of Yang YF, et al. Nitrous oxide anaesthesia in the presence of intraocular gas can cause irreversible blindness. BMJ 325: 532–533, 2002.

Fig. 7.4b  Wristband worn by patient after retinal surgery using intraocular­ gas. Photo courtesy of Hart RH, et al. Loss of vision caused by expansion of intraocular perflurorpropan gas during nitrous oxide anesthesia. Am J Ophthalmol 134:761–763, 2002.

References and Further Reading

Boucher MC, Meyers E. Effects of nitrous oxide anesthesia on intraocular air volume. Can J Ophthalmol 18: 246, 1983.

Crandall DC, Leopold IN. The influence of systemic drugs on tear constituents. Ophthalmology 86: 115, 1979.

Fenwick PBC, et al. Changes in the pattern reversal visual evoked potential as a function of inspired nitrous oxide concentration. Electroencephalogr Clin Neurophysiol 57: 178, 1984.

Fu AR, McDonald HR, Eliott D, et al. Complications of general anesthesia using nitrous oxide in eyes with preexisting gas bubbles. Retina 22: 569–574, 2002.

Hart RH, Vote BJ, Borthwick JH, et al. Loss of vision caused by expansion of intraocular perfluoropropane (C3F8) gas during nitrous oxide anesthesia. Am J Ophthalmol 134: 761–763, 2002.

Lane GA, et al. Anesthetics as teratogens: Nitrous oxide is fetotoxic, xenon is not. Science 210: 899, 1980.

Lee EJK. Use of nitrous oxide causing severe visual loss 37 days after retinal surgery. Br J Anaesth 93: 464–466, 2004.

Mostafa SM, Wong SH, Snowdown SL, et al. Nitrous oxide and internal tamponade during vitrectomy. Br J Ophthalmol 75(12): 726–728, 1991.

Ratta C, et al. Changes in the electroretinogram and visual evoked potentials during general anaesthesia. Graefes Arch Clin Exp Ophthalmol 211: 139, 1979.

•anesthesia4 Sectionin used Agents