Unilateral spinal anesthesia. State of the art

The possibility to control the spread of intrathecal drugs, restricting the distribution of spinal block to the operated side is still controversial. Various authors reported that we can not predict the distribution of spinal block; however, other authors described how to restrict spinal block at the operated side in patients receiving surgical procedures involving one lower limb. Therefore, we reviewed clinical studies on this topic trying to outline the feasibility and potential clinical benefits of unilateral spinal anesthesia. The main results of studies recently published on peer reviewed journals concerning the clinical use of unilateral spinal anesthesia are reviewed. The main factors we must consider when attempting a unilateral spinal block are the use of small doses of local anesthetic solution injected through directional, pencil-point needles, together with a 15-20 min lateral decubitus position and the use of either hypo- or hyperbaric anesthetic solution. Using 6-8 mg of either hyper- or hypobaric bupivacaine provides a unilateral distribution of sympathetic and sensory blocks in 50 to 70% of patients, while unilateral motor block can be observed in up to 80% of cases. Attempting a unilateral spinal block results in a four-fold reduction in the incidence of clinically relevant hypotension with more stable cardiovascular parameters as compared with conventional bilateral spinal block. The small amount of local anesthetic solution injected, as well as the reduced extent of spinal block, also provide a favourable profile of the resolution of spinal block, which can be useful in the ambulatory setting. With simple technical skill we can reliably provide a preferential distribution of spinal block to the operated side. This results in a minimal delay in preparation time, but provides less hemodynamic side effects with higher cardiovascular stability, and increased autonomy after surgery with better patient acceptance.