To the Editor:—
It is unfortunate that Drs. Lee et al. 1and Warner2feel compelled to conclude that blindness may be an inevitable consequence of prolonged spine surgery in the prone position, and that patients should be warned of that possibility. While perhaps correct, my experience in supervising many hundreds of such cases without this complication leads me to believe that it is preventable. Although briefly considered by Dr. Lee et al. in the Discussion section, sufficient attention was not focused on the large average volume of crystalloid solution (9.7 ± 4.7 l) infused in the 83 patients who developed ischemic optic neuropathy. This volume of infusion is far in excess of what is necessary for maintenance of either blood pressure or urine output. In addition, it has a serious negative impact on the hematocrit, as well as promoting edema of the orbs and optic nerves. Although the etiology of blindness may be multifactorial, as anesthesiologists we must critically assess those aspects of care over which we have control. Limiting crystalloid administration, avoiding severe anemia (hematocrit < 26), and limiting the duration of controlled hypotension, if used, to the dissection period only (not the instrumentation period) are all controllable. I would urge anesthesiologists to limit crystalloid volume in prone spine surgical cases to no more than 40 ml/kg (approximately 3 l in adults) for the entire operative procedure regardless of duration. If additional fluid is deemed necessary, it should be hetastarch (not to exceed 20 ml/kg), albumin, or blood. If necessary, a low-dose dopamine infusion can be used to support circulation and improve urine output. Finally, urine output should not be the benchmark for fluid requirements in these patients. Urine output is commonly diminished while patients are in the prone position for reasons that have not been documented. Diminished urine output in this setting does not lead to renal insufficiency postoperatively.
David Geffen School of Medicine at UCLA, Los Angeles, California. firstname.lastname@example.org