Prediction of postoperative pain after percutaneous nephrolithotomy: can preoperative experimental pain assessment identify patients at risk?

Postoperative pain remains a significant problem and the individual variance in postoperative pain is not fully understood. In recent years, there has been focus on identifying risk factors predicting patients with high postoperative pain intensity or consumption of analgesics, which may facilitate an improvement in rehabilitation. This study evaluates the relationship between preoperative experimental pain assessment and postoperative pain and opioid consumption. Forty-four patients with uni- or bilateral kidney stone disease scheduled for percutaneous nephrolithotomy were included. The preoperative pain thresholds were measured using electrical (single and 5 repeated) and pressure pain stimulation over the flank bilaterally (stone-side = operation side and control-side = non-operation side). Postoperative pain scores were recorded on a numerical rating scale and analgesic consumption was registered. The responses to repeated electrical stimuli (temporal summation) were preoperatively increased on the stone-side compared to the control-side (P = 0.016). Preoperative electrical pain thresholds from the control-side correlated inversely with postoperative opioid consumption (single stimuli: ρ = -0.43, P < 0.01; repeated stimuli: ρ = -0.45, P < 0.005). This correlation was more pronounced for the 22 patients with unilateral renal calculi (single stimuli: ρ = -0.54, P < 0.02; repeated stimuli: ρ = -0.58, P < 0.01). There were no other correlations between the preoperative sensory tests and postoperative pain or opioid consumption. This study showed a correlation between the preoperative electrical pain thresholds on the control-side and postoperative opioid consumption after percutaneous nephrolithotomy. Preoperative measurement of the electrical pain thresholds may, therefore, be useful as a screening tool to identify patients at high risk of postoperative pain.