Effects of general anaesthesia on the intraocular pressure in man. Trichloroethylene in nitrous oxide and oxygen

Comparison of effects of fentanyl and alfentanil on intra-ocular pressure. A double-blind controlled trial

The effects of fentanyl and alfentanil on intra-ocular pressure during anaesthesia were investigated in 50 consecutive patients in a double-blind controlled trial. Both drugs produced a significant reduction in intraocular pressure (p less than 0.01). Alfentanil produced significantly greater reduction (48.5 percent) than fentanyl (28.6 percent) (p less than 0.01). A small but statistically significant reduction in arterial pressure (15 percent approximately) and heart rate (18 percent approximately), were observed with both agents, but no significant differences between them were noted. It is suggested that alfentanil may be a suitable alternative to fentanyl in ophthalmic anaesthesia.

Intraocular pressure--physiology and implications for anaesthetic management

The major factors controlling intraocular pressure during surgery are the dynamic balance between aqueous humour production in the ciliary body and its elimination via the canal of Schlemm; the auto-regulation and chemical control of choridal blood volume; the extraocular muscle tone and vitreous humour volume. Prior to surgical incision of the anterior chamber in open intraocular procedures, a low-normal intraocular pressure is mandatory to avoid the hazards of iris or lens prolapse and vitreous loss associated with sudden decompression. In general, the central nervous system depressant drugs, hypnotics, narcotics, major tranquillizers, volatile anaesthetic agents are associated with a reduction in intraocular pressure, with the exception of ketamine and possibly trichloroethylene. The mechanism of action of anaesthetic agents in reducing intraocular pressure may involve a direct effect on central diencephalic control centres, reduction of aqueous production, facilitation of aqueous drainage or relaxation of extraocular muscle tone. Succinylcholine administration is associated with a significant rise in intraocular pressure, with a peak increase between two to four minutes following administration and a return to base line values after six minutes. The intraocular hypertensive effect may be due to a tonic contraction of the extraocular muscles, choroidal vascular dilatation or relaxation of orbital smooth muscle. Despite many claims to the contrary, no reported method to date has been shown to consistently prevent the intraocular hypertensive response to intravenous succinylcholine administration. Because the non-depolarizing relaxants are associated with a reduced intraocular pressure, a barbiturate-non-depolarizing relaxant technique utilizing preoxygenation and cricoid pressure has evolved as the most commonly employed induction technique for the emergency repair of a penetrating eye injury. The alternative non-depolarizing relaxant pretreatment-barbiturate-succinylcholine technique may offer the advantages of more rapid onset of relaxation with only minor increases in intraocular pressure and in a carefully controlled rapid sequence induction technique may be the most acceptable method of handling emergency penetrating eye injuries.

Outpatient sedation for ocular examination

Outpatient sedation of infants, uncooperative children and, rarely, adults provides an opportunity to perform certain ophthalmologic diagnostic procedures such as tonometry, ophthalmoscopy and various electrophysiological studies (e.g., electroretinography and visual evoked response testing) without the expense and usage of an operating room. Many drugs have been recommended and used; all have limitations. The advantages and disadvantages of the more commonly used agents are reviewed. The known effects of these drugs on ocular function are presented.

Normocapnic anaesthesia with enflurane for intraocular surgery

The intraocular pressure was measured by applanation tonometry in 13 patients undergoing lens extraction with normocapnic anaesthesia with 1% enflurane and controlled ventilation of the lungs with large tidal volumes (13 ml/kg). The intraocular pressure was consistently reduced by about 35% and was associated with a similar reduction in systolic arterial pressure. Provided care is taken with those patients with hypertension or heart disease who might become hypotensive, the technique is suitable for lens extraction surgery especially where it is desirable to avoid the administration of halothane.

Normocapnic anaesthesia with trichloroethylene for intraocular surgery

Measurements of intraocular pressure (IOP) by applanation tonometry in twelve patients undergoing lens extraction showed that a normocapnic anaesthetic technique using 0.4% trichloroethylene with controlled ventilation of the lungs (IPPV) with large tidal volumes (14 ml/kg) reduced IOP by 13--20%. There was only a small reduction in arterial pressure. Normocapnia was easy to achieve by use of the single-limb co-axial Penlon (Bain type) anaesthetic breathing circuit in conjunction with an electrically-driven, small and inexpensive lung ventilator. The anaesthetic technique described using trichloroethylene is suitable for lens extraction surgery when it is desired to avoid a halothane anaesthetic for any reason.

Normocapnic anaesthesia for intraocular surgery

Measurement of intraocular pressure (IOP) by applanation tonometry in 23 patients undergoing lens extraction showed that a normocapnic general anaesthetic technique with controlled ventilation of the lungs (IPPV) reliably reduced the IOP by 50% for the duration of the operative period. This was not associated with large falls in systemic arterial pressure which are often a feature of spontaneously breathing halothane anaesthesia for eye surgery. Normocapnia and IPPV were easy to achieve by use of the single-limb coaxial Bain anaesthetic breathing circuit in conjunction with an electrically driven, small, and inexpensive ventilator while the anesthetic mixture of 33% oxygen and 0.5% halothane in nitrous oxide was delivered at a rate of 70 ml/kg body weight per minute.

Effect of etomidate on intra-ocular pressure

Etomidate, a new short-acting non-barbiturate hypnotic, was administered to 40 patients between the ages of 12 years and 65 years. Intra-ocular pressure was measured before and after etomidate injection using a Schiotz tonometer. A significant reduction of intra-ocular pressure was found to follow etomidate injection in spite of the often associated myoclonic movements. The mechanism of reduction of intra-ocular pressure has not been determined in this study. It is suggested that etomidate will be a useful intravenous induction agent where elevation of intra-ocular pressure is undesirable.