Interaction of Lidocaine and Hypothermia in Bier Blocks in Volunteers

The present investigation was designed to study the interaction of temperature, lidocaine, and ischemia during intravenous regional anesthesia (IVRA) of the arm. Five volunteers were studied during exposure of one of their arms to four different experimental conditions: hypothermia and ischemia; hypothermia, ischemia, and lidocaine; normothermia and ischemia; normothermia, ischemia, and lidocaine. Each subject was tested on four different occasions with only one test condition imposed per occasion and with 3 or more days between experiments. Somatosensory evoked responses (SERs) and muscle responses to ulnar nerve stimulation were measured, and sensory testing was done to determine whether the neural effects of the particular treatments differed. Anesthesia developed sooner and was more extensive when local anesthetic was injected. A 5–10°C decrease in tissue temperature did not accentuate the anesthetic effects of lidocaine as determined by time to loss of pinprick and touch sensation. With ischemia alone, anesthesia of the finger tips with preservation of sensation on the arm was observed in all subjects 20 min after tourniquet inflation. Anesthesia at all cutaneous test sites was achieved in 7 of 10 lidocaine experiments; no systematic order of sensory loss, such as progression from distal to proximal sites, was observed. Decrease in limb temperature slowed the development of lidocaine effects on evoked responses and recovery from the effect. Under conditions of ischemia, deterioration of sensation generally began earlier under cold rather than warm conditions. Primary differences between changes in the SERs and muscle responses under condition of ischemia versus ischemia and lidocaine were the rate and magnitude of change of potential latency and amplitude. Venous lidocaine plasma levels were similar after tourniquet release with normothermia and hypothermia. Based on in vitro experiments, the expectation that cooling the arm would decrease time to onset of anesthesia and enhance the intensity and extent of the block was not met.