[Anesthesia effects on ocular circulation. Synopsis of a study].

UNLABELLED: In a study of 280 patients (265 with cataract, 15 with strabismus), we investigated the ocular circulatory effects of 3 methods of anesthesia widely used in ophthalmic surgery, retrobulbar, peribulbar and general anesthesia. Retrobulbar anesthesia (RETRO) was performed with 2, 5 or 8 ml of a mixture (BLH-Mix) of bupivacaine 0.75%, lidocaine 2% and hyaluronidase; with 5 ml BLH-Mix and addition of adrenaline in a low (1:500,000) or a higher (1:200,000) concentration; with 5 ml bupivacaine 0.75% or lidocaine 2% or mepivacaine 2%; with 5 ml mepivacaine 2% and addition of 150 units hyaluronidase; or with 5 ml BLH-Mix plus adrenaline and additional oculopression. Peribulbar anesthesia (PERI) was performed with 8 ml BLH-Mix (5 ml inferotemporally/3 ml superonasally) or 10 ml BLH-Mix (8/4) injected outside the muscle cone. General anesthesia was performed using halothane (inspiratory concentration 0.5 vol%) and nitrous oxide (65 vol%); respiration was adjusted to produce slight hyperventilation (alveolar pCO2 33 mmHg) or forced hyperventilation (pCO2 20-25 mmHg), respectively. The following variables were measured; systolic ciliary perfusion and blood pressures (PPs,cil and Ps,cil, respectively) and ocular pulsation volume (PVoc) using oculo-oscillodynamography of Ulrich, and the intraocular pressure (IOD) using the Draeger handapplanation tonometer.

RESULTS: (1) Measured 15 min after injection, PVoc was reduced by all local anesthesia (LA) methods by a range of 17-65%. The changes were dependent on the following factors: (a) increasing injection volume: larger PPs,cil reduction; (b) addition of adrenaline: larger reduction of all hemodynamic variables; (c) addition of hyaluronidase: more pronounced PVoc reduction; (d) type of local anesthetic: most marked PVoc reduction induced by RETRO with mepivacaine and bupivacaine, smallest reduction by lidocaine; (e) site of injection: less marked reduction of all hemodynamic variables during PERI than during RETRO with equal (8 ml) or equipotent (PERI 10, RETRO 5 ml) injection volumes; (f) additional oculopression: more marked Ps,cil reduction. The IOP, measured 15 min after injection, was increased by most LA types. The degree of IOP elevation was dependent on the following factors: (a) increasing injection volume: higher IOP elevation; (b) type of local anesthetic: lowest IOP elevation induced by bupivacaine, more marked effect of lidocaine, highest elevation after mepivacaine injection. After additional oculopressure, the IOP was reduced as expected. (2) During general anesthesia with slight hyperventilation, PPs,cil and Ps,cil were reduced by 20.6 and 27.6 mmHg, respectively, measured 15 min after intubation. PVoc was decreased by 50.8% and the IOP by 7.6 mmHg. With forced hyperventilation, the reduction of PVoc was even more pronounced.

CONCLUSIONS: The anesthesia-induced lowering of both ocular perfusion and blood pressures as well as of the ocular pulsation volume, which is a measure of the pulsatile choroidal blood flow, can be interpreted as reflecting an inhibitory influence on ocular circulation. We suggest the following mechanisms to account for the changes during LA: elevation of IOP, adrenaline-induced retrobulbar vasoconstriction, LA-induced retrobulbar vasoconstriction (hypothetical), improved penetration of LA brought about by the orbital compression occurring during oculopression. The relative significance of the separate mechanisms differs, however, between the various LA types. The changes found during general anesthesia are attributable to the halothane-induced reduction of systemic blood pressure and cardiac stroke volume as well as to a relative hyperventilation-induced choroidal vasoconstriction. The results are relevant for ophthalmic surgery with respect to the prevention of complications and problems depending on pathologic or at least unphysiological changes in ocular circulation, e.g...