Variables Exposed group Non-exposed group P-value Frequency Percent Frequency Percent Amount of blood loss <500 ml 21 67.74 37 63.79 0.76 500-1000 ml 9 29.03 20 34.48    1000-1500 ml 1 3.23 1 1.72   >1500 ml 0 0 0 0   Total 31 100 58 100   Type of anaesthesia         0.33  General 16 51.61 27 46.55    Spinal 15 48.39 31 53.45    Total 31 100 58 100   IV induction agent used         0.93  Ketamine  7 43.75 12 44.44    Thiopental 9 56.25 15 55.56    Total  16 100 27 100   Dose of reversal agent used           <the recommended dose 4 25 7 25.93 0.65  recommended dose 12 75 20 74.07   >the recommended dose 0 0 0 0    Total 16 100 27 100   Duration of surgery<1 hour 11 35.48 18 31.03 0.88  1-2 hrs 20 64.52 40 68.97   >2 hrs 0 0 0 0   Total 31 100 58 100    Duration of anaesthesia<1 hour 11 35.48 18 31.03 0.88  1-2 hrs 20 64.52 40 68.97   >2 hrs 0 0 0 0   Total 31 100 58 100   Mean systolic blood pressure change 7.058 5-10% 8.11% 1-Jul 0.76

Table 2: Clinical factors which affect the incidence of post-operative nausea and vomiting, in Ayder referral hospital Mekelle, northern Ethiopia, 2013.