Describe the advantages of spinal anesthesia over general anesthesia.
Although general anesthesia frequently provides airway control for the anesthesiologist, spinal anesthesia offers many advantages over general anesthesia. Both orthopedic and vascular surgeries on the lower extremities are associ-ated with diminished blood loss under spinal anesthesia compared with general anesthesia. The inference, which has been proven to be true, is that patients undergoing these procedures with spinal anesthesia receive less transfused blood. The risk of receiving the human immunodeficiency virus (HIV) and other communicable diseases through blood transfusion is therefore reduced also (Table 56.2).
Metabolic alterations associated with general anesthesia and surgery are well described. Increases in energy-liberating hormones, such as epinephrine, norepinephrine, cortisol, and growth hormone occur. Glucose levels may also increase in patients undergoing surgery and general anes-thesia. Spinal anesthesia to the upper thoracic levels is associated with decreased epinephrine and norepinephrine concentrations, while lower thoracic levels allow epineph-rine and norepinephrine levels to remain essentially unchanged. Surgery under spinal anesthesia is associated with depressed levels of cortisol, insulin, and free fatty acids. Glucose concentrations under spinal anesthesia increase slightly and then tend to fall slightly.
It is postulated that spinal anesthesia prevents increases in metabolic hormone concentrations by afferent and efferent neural blockade. Inhibition of adrenal medullary catecholamine release is probably secondary to efferent autonomic blockade. Inhibition of pituitary hormone release is probably due to afferent pathway interruption.
Ablation of the hyperglycemic response seen under spinal anesthesia may be secondary to efferent sympathetic block-ade to the liver as well as inhibition of catecholamine release from the adrenal medulla.
The incidence of deep vein thrombosis following lower extremity orthopedic surgery is reduced under spinal anesthesia compared with general anesthesia. Although one would anticipate the incidence of pulmonary emboli to be reduced following spinal anesthesia, this has not been documented.
Elderly patients undergoing surgery for femoral neck fractures under spinal anesthesia demonstrate an improved short-term survival rate. Interestingly, the long-term sur-vival rate of patients undergoing similar surgery under spinal anesthesia is approximately the same as that for patients who had undergone general anesthesia. Pulmonary embolism was a frequent cause of death for those who received general anesthesia and who died within 1 month of surgery.