Assessment of the level of sensory block after subarachnoid anesthesia using a pressure palpator

In a cross-over study, we compared two methods of assessing the level of se nsory block during subarachnoid anesthesia: the traditional pinprick sensat ion or a novel pressure palpator exerting a pressure of 650 g. Fifty patien ts scheduled for transurethral surgery under subarachnoid anesthesia were r andomly assigned to be tested for spread of sensory block. In Group 1, the pressure palpator was followed by pinprick; in Group 2, the reverse sequenc e was used. Evaluation was performed 15 and 25 min after the subarachnoid i njection of 2 mi, of 5% Lidocaine hyperbaric solution. In Group 1, the leve l of sensory block assessed with the pressure palpator was 1.7 +/- 3.2 cm ( 0.5 +/- 1.2 dermatomes) higher than that with the pinprick at 15 min, and 2 .2 +/- 3.4 cm (0.6 +/- 1.0 dermatomes) higher than that with the pinprick 2 5 min after the block. In Group 2, the difference was accentuated. The leve l of sensory block assessed by pinprick 15 min after subarachnoid lidocaine was 5.7 +/- 4.8 cm (1.2 +/- 0.9 dermatomes) lower than the level with the pressure palpator, and 4.2 +/- 3.3 cm (0.9 +/- 0.6 dermatomes) lower than t hat with the pressure palpator at 25 min. In all instances, the pressure pa lpator gave a significantly higher assessment than the pinprick. We conclud e that the pressure palpator, when preceded by the pinprick test, is associ ated with an increased threshold. This method may be useful in assessing th e sensory block produced by subarachnoid anesthesia. Implications: A novel pressure palpator that maintains the integrity of the epidermis was used to assess the level of sensory block after subarachnoid anesthesia and was co mpared with the standard method of the pinprick sensation. This method asse ssed the block consistently higher than the pinprick method, but it may hav e advantages as a noninvasive sensory test.