Purpose:
Intraocular pressure (IOP) elevation to over 100 mm Hg is a well accepted model of retinal ischemia. However, use of a precisely controlled elevation of IOP (CEI) at less extreme pressure levels offers opportunities to understand the acute responses of the optic nerve head (ONH) and retina to repeat IOP elevations that might cumulatively be manifested as glaucoma. CEI involves anterior chamber cannulation in anesthetized animals. Because systemic blood pressure (BP) can affect ocular perfusion, it is important to select an anesthetic agent with the least effect on BP.
Methods:
Under anesthesia, the femoral artery was exposed and cannulated with heparinized Tygon tubing (OD 0.030"), placing the tip in the abdominal aorta with the other end connected to a Transpac IV pressure transducer and a Grass polygraph. Blood pressure was continuously monitored during 2 types of anesthesia, inhalational isoflurane (8 rats) and intraperitoneal rat cocktail (3 rats). For isoflurane, 3% was used for induction of anesthesia and cannula placement. Then, following 20 minutes’ equilibration at each isoflurane level (3-7 per rat), BP readings were recorded. For cocktail, the dose was 37.5 mg ketamine, 7.5 mg xylazine and 1.5 mg acepromazine/kg, with blood pressure readings continuously monitored for 60 minutes.
Results:
Isoflurane, at surgical levels of 1.0% and 1.5%, reduced mean arterial blood pressure to 98±1 and 90±2 mm Hg, respectively, with greater reduction at higher percentages (Chart). Cocktail produced consistent blood pressure lowering to between 70-80 mm Hg, with repeated dosing required every 30 to 40 minutes to prevent signs of arousal and accompanying highly variable blood pressures.
Conclusions:
Surgical levels of inhalational isoflurane anesthesia result in stable, less profound blood pressure lowering than the use of injectable cocktail and, therefore, are better suited for long periods of anesthesia.
Keywords: blood supply • intraocular pressure • optic nerve