Background and Aims Total hip arthroplasty is one of the most painful orthopaedic surgery.Spinal anaesthesia is a gold standard for hip replacement.By adding low-dose Morphine to intrathecal Bupivacaine,could be prolonged analgesia and reduced postoperative pain.The objective of the study:to compare the effect of low-dose morphine(0.1 mg and 0.2 mg)addition to Bupivacaine for spinal anaesthesia on postoperative pain and incidence of side-effects.

Methods A prospective randomized study conducted at the “Hospital of Traumatology and Orthopedics” from 2020 June to 2021 April includes 90 patients, who met inclusion and exclusion criteria. Randomly on the internet site https://www.randomizer.org/patients were divided into 3 groups.Before surgery all patients received intrathecally Sol.Bupivacaine 15–18mg. Group I - control group. Group II and Group III received accordingly 0,1 and 0,2 mg of morphine intrathecally in addition to Bupivacaine. After surgery all patients had standardized multimodal analgesia. Resque medication-Morphine 10 mg subcutaneously(if NRS>5). Pain level measured by NRS at rest in a 4h, 7h, 12h and 24h. Respiratory rate(RR,x/min), SpO2(%), resque medication consumption,oxygen supply and adverse reactions (nausea, vomiting, itching, etc.) were noted during 24h. Data analysis performed using IBM SPSS 22.0.

Results Pain score in I,II and III groups accordingly: 4h- 1.21; 0.48; 0.17(p = 0.076); 7h- 2.90; 1.00; 0.17(p < 0.001);12h- 3.33; 0.80; 0.37(p < 0.001);24 h - 2.53; 1.17; 0.40(p < 0.001).Rescue medication request (incidence,%):Group-I 77%,Group-II:16.7%, Group III:13,3%(p < 0,001).RR (x/min)(min;max):Group-I 16.1(13.0; 20.0);Group-II:15.2 (10.5; 19.0),Group-III:15.4(11.5; 21.5)(p > 0.05).SpO2(%):Group-I 96,7%(92,0%; 100,0%);Group-II:96,0%(92,0%;99,5%);Group-III:96,0%(91,0;100).Incidence of morphine-related side-effects was not statistically significant:nausea&vomiting 10%(I),23.3%(II),10%(III).Statistically reliable itching only in the Group-III: 23% of patients (p< 0.001).No other adverse effects observed.

Conclusions Optimal dose of intrathecal morphine is 0.2 mg.