الفهرس 
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Abstract
There are some studies regarding role of sex differences and its effect on pain perception modulation and response to pain therapies. The results are variable and not conclusive. This may be related to biological, physical, environmental, and genetic factors. Studies regarding effect of sex difference on pain perception and response to analgesic among Egyptian population are scanty.
So, the aim of this study was to assess whether there was an effect of sex difference among Egyptian population on pain perception and response to the analgesic nalbuphine on post-operative pain after major orthopedic surgery patients admitted to intensive care unit (ICU), at Ain Shams University hospitals. Also, adverse effects of nalbuphine were compared in both sexes.
This comparative prospective analytical study enrolled 100 postoperative patients admitted to ICU after major orthopedic surgery; 50 females and 50 males. Post-operative pain was assessed using visual analogue scale (VAS) on admission and at 1,2,4,8,12,24 hours post-operative, Sedation was assessed by Ramsay sedation score on admission and at 3,6,12,24 hours post-operative, Adverse effects were recorded and compared. In the present study, there was no significant statistical difference regarding body mass index (BMI) and comorbidities except that hypertension and smoking were more in males than females.
Regarding the primary outcome of the present study, males required significantly a higher dose of nalbuphine than females with p-value=0.001. The VAS score was lower in females than males although the difference in VAS did not reach statistical significance. This might be because females tolerance to pain was more than males.
Multiple mechanisms contribute to the observed sex differences in pain, including sex hor¬mones, endogenous opioids, brain responses, mood and affect, pain coping, and gender roles. Notably, several studies have demonstrated that biological and psycho¬social factors interact to influence sex differences in pain responses. Thus, sex differences in pain are best concep¬tualized in the context of the biopsychosocial model of pain.
There was no statistically significant difference between females and males regarding Ramsy sedation score at 3 hours, 6 hours, and 24 hours with p-value = 0.437, 0.641 and 0.132 respectively except at 12 hours which showed higher Ramsy sedation score in females than males with p-value < 0.001.
There was no statistically significant difference between females and males regarding postoperative analgesia adverse effects including nausea, vomiting, headache, and dyspnea.
In conclusion: Egyptian males required nalbuphine for post-operative analgesia, in doses more than Egyptian females, with no significant differences between them regarding adverse effects of nalbuphine.
Of the limitations of this study is the relatively small sample size and it is one center study and the mechanisms underlying this difference were not studied. So, we recommend, further studies on the relationship between the analgesic effect and other factors like comorbid conditions mental disorders, hormonal effects and genetic factors. Also, further studies are required to know whether sex difference regarding pain perception and response to analgesics are applied to all types of narcotics and all classes of analgesics or not.