Effects of isoflurane, ketamine-xylazine and a combination of medetomidine, midazolam and fentanyl on physiological variables continuously measured by telemetry in Wistar rats

Background: This study investigated effects on cardiovascular parameters during anaesthesia with isoflurane (ISO, 2 3 Vol%), ketamine-xylazine (MK, 100 + 5 mg.kg(-1)) or a combination of medetomidine-midazolamfentanyl (MMF, 0.15 mg.kg(-1) + 2.0 mg.kg(-1) + 0.005 mg.kg(-1)) in rats throughout induction, maintenance and recovery from anaesthesia. Rats were instrumented with a telemetric system for the measurement of systolic, diastolic and mean arterial pressure (SAP, DAP, MAP), pulse pressure (PP), heart rate (HR) and core body temperature (BT). The parameters were continuously measured before, during and after each type of anaesthesia. Forty minutes after induction, ISO delivery was terminated and IVIIVIF was antagonized with atipamezole-flumazenilnaloxone (AFN, 0.75 mg.kg(-1) + 0.2 mg.kg(-1)+ 0.12 mg.kg(-1)) whereas KX was not antagonized. Results: Differences were observed between anaesthesias with KX (301 min) lasting much longer than MMF (45 min) and ISO (43 min). HR in ISO (T< = 404 25 bpm) increased during the time of surgical tolerance whereas a HR decrease was observed in KX = 255 26 bpm) and MMF (7.\c = 209 24 bpm). In ISO (MAP during time of surgical tolerance: 7,c = 89 12.3 mmHg) and KX (MAP during wake up period: 7v = 84 8.5 mmHg) mild hypotensive values were observed, whereas blood pressure (BP) in MMF (MAP during time of surgical tolerance: 7 = 138 9.9 mmHg) increased. Despite keeping animals on a warming pad, a loss of BT of about VC was seen in all groups. Additionally, we observed a peaked increase of HR = 445 20 bpm) during the wake-up period with ISO and an increase of PP (7 = 59 8.5 mmHg) in IV11V1F during the time of surgical tolerance. Conclusion: The anaesthesias influenced very differently the cardiovascular parameters measured in Ws ar rats. ISO caused mild hypotension and increased HR whereas IVIIVIF produced a marked hypertension and a significant decrease of HR. The slightest alterations of BP, HR and BT were observed using KX, but the long wake-up and recovery period suggest the need for prolonged monitoring.