title: Effects of tramadol, morphine or their combination in dogs undergoing ovariohysterectomy on peri-operative electroencephalographic responses and post-operative pain.
abstract: OBJECTIVE
  To compare the peri-operative electroencephalogram (EEG) responses and post-operative analgesic efficacy of pre-operative morphine or tramadol with a combination of low-dose pre-operative morphine and post-operative tramadol, in dogs undergoing ovariohysterectomy.
  
  
  METHODS
  Dogs undergoing routine ovariohysterectomy were treated with either pre-operative morphine (0.5 mg/kg S/C, n=8), or tramadol (3 mg/kg S/C, n=8), or pre-operative low-dose morphine (0.1 mg/kg S/C) and post-operative tramadol (3 mg/kg I/V, n=8). All dogs received routine pre-anaesthetic medication, and anaesthesia was induced with I/V thiopentone to effect and maintained with halothane in oxygen. Respiratory rate, heart rate, end-tidal halothane tension (EtHal) and end-tidal CO₂ tension (EtCO₂) were monitored throughout surgery. The EEG was recorded continuously in a three electrode montage. Median frequency (F50), total power (Ptot) and 95% spectral edge frequency (F95) of the EEG power spectra were compared during different 100-second periods of surgery: prior to and during skin incision, ligation of each ovarian pedicle, ligation of uterine body and skin closure. Post-operatively, pain was assessed using the short form of the Glasgow composite measure pain scale (CMPS-SF).
  
  
  RESULTS
  There was no difference in F50 or Ptot of the EEG between baseline and noxious surgical events within each treatment group, or between the three groups (p>0.05). The mean F95 was higher during the first three periods of surgery for dogs administered tramadol and low-dose morphine than those that received 0.5 mg/kg morphine (p=0.001). Dogs that received low-dose morphine and tramadol had lower CMPS-SF pain scores after ovariohysterectomy than those that received either tramadol or morphine alone (p=0.001). There was no difference in pain scores between dogs in the latter two groups.
  
  
  CONCLUSIONS
  Tramadol and morphine administered pre-operatively provided an equal degree of post-operative analgesia in dogs after ovariohysterectomy. A combination of pre-operative low-dose morphine and post-operative tramadol produced better post-operative analgesia than either drug administered alone pre-operatively. Administration of analgesics pre- and post-operatively could result in improved post-operative well-being of ovariohysterectomised dogs.
authors.affiliation: Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand. k.kongara@massey.ac.nz
authors.forename: K
authors.initials: K
authors.lastname: Kongara
authors.forename: J P
authors.initials: JP
authors.lastname: Chambers
authors.forename: C B
authors.initials: CB
authors.lastname: Johnson
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D000818:Animals; D004285:Dogs; D004359:Drug Therapy, Combination; D005260:Female; D007044:Hysterectomy / Q000009:adverse effects / Q000662:veterinary*; D009020:Morphine / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D010149:Postoperative Pain / Q000188:drug therapy / Q000662:veterinary*; D014147:Tramadol / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*
chemical_list: D000701:Analgesics, Opioid; D014147:Tramadol; D009020:Morphine