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The effect of pregnancy on temporal summation and pain at venous puncture
Abstract Number: 1
Abstract Type: Original Research
Introduction: Temporal summation (TS) has been shown to be a good predictor of acute postoperative pain in non-obstetric patients;1 however, it has not been studied in the pregnant population. The influence of pregnancy on TS is not known. Also unknown is whether there is any correlation between TS and other modalities of acute non-surgical pain in pregnant women.
Methods: Following REB approval and written informed consent, we enrolled 80 healthy women, divided into 4 groups of 20 each, as follows: a) Group 1: women at 12 weeks of pregnancy; b) Group 2: women at 28 weeks of pregnancy; c) Group 3: full-term pregnant women; d) Group 4: non-pregnant women. All underwent the following assessments: a) first, temporal summation, including pain scoring; b) second, venous puncture, followed by pain scoring. The mechanical TS was evoked with a 180g Von Frey filament applied on the skin of the volar aspect of the non-dominant forearm. Subjects received a single stimulus, followed by 10 more stimuli within 10 seconds, within a 1-cm diameter area, and pain scores were assessed according to a 0-10 cm VAS. The venous puncture was then performed by a laboratory technician using a 21G hypodermic needle, and pain scores were also assessed with a 0-10 cm VAS. The primary outcome of this study was: a) the difference in VAS scores between the 1st and 10th stimuli of the filament; b) the VAS scores at venous puncture.
Results: Eighty patients were studied. The incidence of temporal summation ≥ 1 cm VAS (TS+ women) in the overall population was 35%, and it was similar in all the groups. The magnitude of temporal summation was similar in pregnant and non-pregnant women (p=0.389). Pain scores at venous puncture were higher in pregnant than in non-pregnant women (p=0.015). Overall, TS+ women experienced higher pain scores at venous puncture compared to TS- women (p=0.027). There was a positive correlation between the magnitude of TS and pain at venous puncture in the overall population (r=0.35, p<0.05).
Discussion: Pregnancy does not change either the incidence or the magnitude of TS. The increased pain perception at venous puncture during pregnancy may be explained by phenomena other than TS alone. The magnitude of TS, however, correlates with the magnitude of pain at venous puncture, regardless of pregnancy. TS may be a useful screening method for identifying pregnant women at risk of pain.
References: J Pain 2009; 10: 628-636.