An atypical presentation of tourniquet pain

Sir, Pneumatic tourniquets are used to facilitate a bloodless surgical field. Tourniquet pain is defined as ‘a diffuse and moderate to severe dull aching kind of pain during otherwise satisfactory regional anesthesia which is promptly relieved by deflation of the tourniquet’ (1). We report a varied presentation of tourniquet pain. A young ASA grade I adult was posted for open reduction and internal fixation of the tibial plateau under combined spinal epidural (CSE) anesthesia. With an initial intrathecal bolus of 2 ml of bupivacaine (heavy), together with 25 mg of fentanyl, the patient had a sensory block up to T10 (to pin prick). A 7-cm tourniquet was inflated to 345 mmHg; 55 min later, the patient complained of severe bursting pain localized to the plantar aspect of the right foot. The sensory level (to pin prick) was at L1. Extension of the block to T10 with 10 ml of 0.5% bupivacaine and intravenous fentanyl up to 2 mg/kg did not give relief. At 90 min, the tourniquet had to be deflated as the pain became unbearable. The pain disappeared immediately, and the patient had a ‘pins and needles’ sensation with warmth in the foot. Thereafter, the surgery progressed uneventfully. The current literature supports the hypothesis that tourniquet pain transmits along unmyelinated C-fibers resistant to pressure effects of the tourniquet. The neural pathway of these fibers may be through the spinal nerves or along the sympathetic chain. This explains the nature of tourniquet pain and its occurrence in patients with adequate surgical anesthesia with a level of sensory blockade above the site of tourniquet application (2). Over a period of time, the conduction of impulses in larger fibers, decreased as a result of compression by the tourniquet, may release inhibition on C-fibers and thus accentuate tourniquet pain (3, 4). The lower incidence of tourniquet pain with subarachnoid block than with epidural anesthesia to the same sensory level may be a result of the higher concentration of local anesthetic delivered directly to nervous tissue (denser block) (5). Epidural block may be patchy depending on the catheter tip location (4). Our patient localized the site of pain distinctly. Yet, the other characteristics resembled tourniquet pain, i.e. surgical site anesthesia and immediate relief on tourniquet release. This atypical presentation of tourniquet pain may be a result of the initial low volume of intrathecal drug, which resulted in inadequate density of the block. Although adjuvants are known to reduce the incidence of tourniquet pain (6, 7), perhaps lipophilic fentanyl did not increase significantly the height or density of the block (8). It has been shown that sensory blockade to touch is a more reliable indicator to assess the incidence of tourniquet pain (9) (not performed by us). The localization of the pain in our patient as a result of the patchy epidural anesthesia or differential blockade of L5—S1 nerve roots (root jumping) is also a possibility. To prevent tourniquet pain, we recommend the following: (i) a neuraxial block of adequate depth and height (T10 dermatome); (ii) a catheter-based technique over single shot neuraxial blocks; (iii) a comparative evaluation of neuraxial opioids (fentanyl, sufentanil and morphine) in the prevention of tourniquet pain; and (iv) touch rather than pin prick to assess the level of block.