Morphologic effects on the retina of massive exchange transfusion with stroma-free hemoglobin solution

Retinal morphology serves as an extremely sensitive end point to hypoxic and ischemic conditions manifested by circulatory perturbations. Therefore, the effect of massive transfusion of stroma-free hemoglobin solution (SFHS) on retinal morphology of rats was evaluated. Seventy-three rats were divided into three groups. Two groups were transfused to 75% blood volume replacement--one (n = 30) with 7% SFHS one (n = 26) with 7% albumin solution and the third group (n = 17) was cannulated, not transfused (controls). Animals in each group were killed at 1, 5, 12, and 24 hours and 2 months after the procedure. In the transfused rats, focal and perivascular regions of edema, axonal swelling, and vacuoles were observed by light and transmission electron microscopy in the nerve fiber layer of the central retina. These conditions progressively decreased from 1 to 12 hours in the albumin-treated group. The retinas of SFHS-treated rats killed at 12 and 24 hours had similar but more severe morphologic changes than any of the albumin-treated animals; swelling was more severe in those obtained at 24 than at 12 hours, whereas vacuoles were larger in animals obtained at 12 hours. Abnormalities were observed in the prelaminar portion of the optic disc of the SFHS-treated groups killed at 12 and 24 hours. Subretinal hemorrhaging occurred in about 50% of the SFHS-treated animals killed at both 12 and 24 hours and was associated with swelling, vacuolization, and disruption of the photoreceptor outer segments and retinal pigment epithelium. Below normal levels of glycogen were present in the Müller cells of the retinas of albumin-treated rats killed at 5, 12, and 24 hours. At 12 hours after transfusion the Müller cells in lesions of the retinas obtained from the SFHS-treated rats were devoid of glycogen. High glycogen levels, however, appeared in a zone peripheral to the lesions. The latter effect was not apparent in the specimens obtained at 24 hours. The damage observed was probably due to hypoxic and ischemic effects secondary to urinary hemoglobin excretion and concomitant blood volume loss. No abnormalities were seen in the controls. The retinas of SFHS-treated rats killed at 1 and 5 hours showed normal retinal morphology and glycogen levels. Presumably, SFHS exerted a protective effect during this time period. If the current formulation of SFHS is to be used clinically, it will have to be administered continuously until blood is available for transfusion, and the patient's intravascular volume should be monitored carefully to prevent hypovolemia.