Pain after abdominal surgery study

A number of clinical, psychological, neurophysiological and genetic variables will be collected preoperatively to ascertain which are significant, independent predictors of acute postoperative pain in the first 14 days after surgery. The predictor variables will be 1. Comorbid Pain - Pain > 2/10 on numerical rating scale (0 = no pain; 10 = worst pain imaginable) that has been present on at least a weekly basis for 1 month or longer. Count number of anatomical locations apart from abdomen where this is true (e.g. n = 3). 2. Pain expectation - measured using the following question "Please indicate the level of pain you think you will experience 1 day after your surgery?" 0-10 Numerical rating scale (0= no pain; 10 = worst pain imaginable)" and 2. Pain expectation - measured using the following question "Please indicate the level of pain you think you will experience 2 weeks after your surgery?" 0-10 Numerical rating scale (0= no pain; 10 = worst pain imaginable)". The average of these scores will be taken. 3. Pain Catastrophising - measured using the Pain Catastrophsing Scale 4. Social support - measured using the Social network index 5. Temporal summation of mechanical pain - assessed through the repetition of 10 standardised punctuate stimuli at a frequency of 1 Hz, applied to an area of the skin 1cm lateral to the planned incision site using a 225.1g Von Frey filament. Patients will be asked to rate the pain intensity of the first and last stimuli on a 0-10 numerical rating scale (0 = no pain; 10 = worst pain imaginable). The difference in pain intensity between the last and first stimuli will be calculated to indicate the magnitude of temporal summation. 6. Conditioned Pain Modulation Efficacy - The electrical stimulation intensity (mA) required to get a pain rating of 60/100 will be measured 1cm lateral to the planned incision site and will be assessed alone (test stimulus) and while the contralateral hand is submerged in cold water (conditioning stimulus). The difference in stimlulation intensities (mA; mean of 2 measures) with and without the conditioning stimulus will be used as a measure of conditioned pain modulation efficacy. 7. Single nucleotide polymorphisms for the Catechol-O-methyl transferase (COMT), mu opiod receptor (OPRM-1), tumor necrosis factor alpha (tnf-alpha); interleukin-1 (IL-1) and interleukin-6 (IL-6) genes - obtained through a single blood sample that will be taken at the same time as routine preoperative bloods. Standard DNA extraction, polymerase chain reaction, microarray and detection methods will be used to identify single nucleotide polymorphisms.