The Effects Of Ephedrine And Phenylephrine On Intraocular Pressure During General Anesthesia

There are sometimes glaucoma attack after general anesthesia , what's more, children may not go with the examination ,so the intraocular pressure must be undertook under general anesthesia. Increasing efforts are focused on the effects of ephedrine and phenylephrine on intraocular pressure during general anesthesia, as well as the mechanism.The intraocular pressure is pressure of the contents on eyeball, including lens, vitreous, retina, aqueous fluid and blood. It is very important to keep normative intraocular pressure for the stability of eyes' appearance and utility of visual function. There are many reasons that could influence the intraocular pressure, such as induction of general anesthesia, tracheal intubation, and the drug used in general anesthesia.The intraocular pressure is affected by anesthesia drugs through the change of formation and flow of aqueous, muscular tension, and general haemodynamics. Besides, route and velocity of administration have an effect on intraocular pressure, inhalational and intravenous anesthesia have an obviously quick contribution to intraocular pressure, while IOP is less influenced by intramuscular, oral and per rectum administration. The effects of different drugs on IOP are varied.Adrenergic drugs are commonly used in general anesthesia with the ability to change the tension of vascular smooth muscle, regulate the blood pressure, affect the preload and aftercurrent load. Ephedrine have a immediate act on multiple adrenoceptors, while promoting the release of transmitter. Phenylephrine is a selectively agonist ofα1- receptor , which can increase the blood pressure through promotion of the contraction of peripheral vessels, and peripheral resistance. The boosting pressure of Phenylephrine is weaker but longer than deoxyepinephrine.The purpose of the study was to observe the change of patients'IOP while general anesthesia using different concentration of ephedrine and phenylephrine, and discuss the mechanism of it. So the ophthalmologist may evaluate the IOP correctly and guide the medication of general anesthesia.Methods : 48 patients of ASA I grade undergoing general anesthesia were chosen and randomly divided into 4 groups(n=12 each). Anesthesia was induced for each group. After tracheal intubations, group R1 received 5mg of ephedrine, while group R2 10mg.Group R3 received 50μg of phenylephrine, and group R4 100μg. IOP, SBP, HR were measured before anesthesia induction (T0),5min after tracheal intubations(Tl)and 10min after drug injection(T2). The data were done with statistical treatment and analysis.Results: Compared with the mean IOP at T0 and T1, IOP was significantly decreased in the ephedrine group at T2 (p<0.05), while in phenylephrine group, IOP was not significantly changed (p>0.05). Conclusions: The use of phenylephrine has little effect on IOP during general anesthesia, and the ephedrine may decrease the IOP. So the drugs could be used in patients who are old, glaucoma suspected, and have big surgical trauma.