Effects of untreated preoperative essential hypertension on post-operative pain after major abdominal surgery

Hypertension has been associated with hypoalgesia. This prospective study was designed to test the effects of untreated preoperative essential hypertension on post-operative pain intensity and morphine requirement after major abdominal surgery.

Sixty subjects (30 untreated essential hypertensives and 30 normotensives) scheduled for abdominal surgery were included in this study. All subjects received standardized anaesthetic with intra-operative fentanyl and patient-controlled analgesia with morphine for 48 h post-operatively as the only analgesics. Pain intensity scores, cumulative morphine requirement and side effects were recorded until 48 h post-operatively.

All subjects with essential hypertension had systolic hypertension, 93.3% had grade 1 severity and 6.7% had grade 2 severity. 23.3% of essential hypertensive subjects had elevated diastolic blood pressure. Essential hypertensive subjects had significantly lower total post-operative morphine requirement (29.6 mg vs. 49.9 mg; p = 0.002), significantly lower verbal rating scale post-operative pain intensity scores at rest and with coughing (p = 0.000), and significantly less incidence of post-operative pruritus (p = 0.048) over 48 h than normotensive subjects. There were no post-operative differences in the incidence of post-operative nausea (p = 0.982) or vomiting (p = 0.644) between the two groups.

Untreated essential hypertension is associated with significantly reduced post-operative morphine requirement and pain intensity, suggesting hypertension-associated hypoalgesia.