DIGITAL PRESSURE DURING INTERSCALENE BLOCK IS CLINICALLY INEFFECTIVE IN PREVENTING ANESTHETIC SPREAD TO THE CERVICAL PLEXUS

The application of digital pressure above the injection site during in terscalene block has been advocated to prevent cephalad spread of loca l anesthetic. In prior studies, radiographs taken immediately after in terscalene injection of radiographic contrast have supported this conc ept. However, the clinical efficacy of digital pressure has not been p reviously tested. If digital pressure were effective in inhibiting cep halad spread of local anesthetic, attenuation of both hemidiaphragmati c paresis and the resulting compromise in pulmonary function would be expected. Sensory, motor, and pulmonary effects were prospectively eva luated in 20 patients presenting for elective shoulder surgery. Patien ts were randomly assigned to receive interscalene block with or withou t digital pressure. No clinical differences were seen between groups. All 20 patients had ipsilateral hemidiaphragmatic paresis by ultrasono graphic evaluation and large mean decreases in forced vital capacity, 31.2% +/- 7.5% (with digital pressure), 33.7% +/- 12.8% (without digit al pressure), and forced expiratory volume at one second, 27.9% +/- 9. 3% (with digital pressure), 33.7% +/- 12.8% (without digital pressure) . Peak sensory level of anesthesia to pinprich was not significantly d ifferent between groups, each group having mean levels of C-2 to C-3. Digital pressure was ineffective in limiting the flow of local anesthe tic into the cervical plexus. Digital pressure influenced neither the incidence of diaphragmatic paresis nor the resulting large decreases i n pulmonary function that result from interscalene block.