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

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