Miguel Gozalo Marcilla

Influence of a constant rate infusion of dexmedetomidine on cardiopulmonary function and recovery quality in isoflurane anaesthetized horses

OBJECTIVE To investigate the influence of a dexmedetomidine constant rate infusion (CRI) in horses anaesthetized with isoflurane. STUDY DESIGN Prospective, randomized, blinded, clinical study. ANIMALS Forty adult healthy horses (weight mean 491 ± SD 102 kg) undergoing elective surgery. METHODS After sedation [dexmedetomidine, 3.5 μg kg(-1) intravenously (IV)] and induction IV (midazolam 0.06 mg kg(-1), ketamine 2.2 mg kg(-1)), anaesthesia was maintained with isoflurane in oxygen/air (FiO(2) 55-60%). Horses were ventilated and dobutamine was administered when hypoventilation [arterial partial pressure of CO(2) > 8.00 kPa (60 mmHg)] and hypotension [arterial pressure 70 mmHg] occurred respectively. During anaesthesia, horses were randomly allocated to receive a CRI of dexmedetomidine (1.75 μg kg(-1) hour(-1) ) (D) or saline (S). Monitoring included end-tidal isoflurane concentration, cardiopulmonary parameters, and need for dobutamine and additional ketamine. All horses received 0.875 μg kg(-1) dexmedetomidine IV for the recovery period. Age and weight of the horses, duration of anaesthesia, additional ketamine and dobutamine, cardiopulmonary data (anova), recovery scores (Wilcoxon Rank Sum Test), duration of recovery (t-test) and attempts to stand (Mann-Whitney test) were compared between groups. Significance was set at p < 0.05. RESULTS Heart rate and arterial partial pressure of oxygen were significantly lower in group D compared to group S. An interaction between treatment and time was present for cardiac index, oxygen delivery index and systemic vascular resistance. End-tidal isoflurane concentration and heart rate significantly increased over time. Packed cell volume, systolic, diastolic and mean arterial pressure, arterial oxygen content, stroke volume index and systemic vascular resistance significantly decreased over time. Recovery scores were significantly better in group D, with fewer attempts to stand and significantly longer times to sternal position and first attempt to stand. CONCLUSIONS AND CLINICAL RELEVANCE A dexmedetomidine CRI produced limited cardiopulmonary effects, but significantly improved recovery quality.

Effects of a constant rate infusion of detomidine on cardiovascular function, isoflurane requirements and recovery quality in horses

OBJECTIVE To examine the influence of a detomidine constant rate infusion (CRI) on cardiovascular function, isoflurane requirements and recovery quality in horses undergoing elective surgery. STUDY DESIGN Prospective, randomized, blinded, clinical trial. ANIMALS Twenty adult healthy horses. METHODS After sedation (detomidine, 10 μg kg(-1) intravenously [IV]) and induction of anaesthesia (midazolam 0.06 mg kg(-1) , ketamine 2.2 mg kg(-1) IV), anaesthesia was maintained with isoflurane in oxygen/air (inspiratory oxygen fraction 55%). When indicated, the lungs were mechanically ventilated. Dobutamine was administered when MAP<70 mmHg. The horses were randomly allocated to one of two groups and throughout anaesthesia, received either a detomidine (5 μg kg(-1)  hour(-1) ) (D) or saline (S) CRI, with the anaesthetist unaware of the treatment. Monitoring included end-tidal isoflurane concentration, arterial pH, PaCO(2) , PaO(2) , dobutamine administration rate, heart rate (HR), arterial pressure, cardiac index (CI), systemic vascular resistance (SVR), stroke index and oxygen delivery index (ḊO(2) I). For recovery from anaesthesia, all horses received 2.5 μg kg(-1) detomidine IV. Recovery quality and duration were recorded in each horse. For statistical analysis, anova, Pearson chi-square and Wilcoxon rank sum tests were used as relevant. RESULTS Heart rate (p=0.0176) and ḊO(2) I (p= 0.0084) were lower and SVR higher (p=0.0126) in group D, compared to group S. Heart rate (p=0.0011) and pH (p=0.0187) increased over time. Significant differences in isoflurane requirements were not detected. Recovery quality and duration were comparable between treatments. CONCLUSIONS AND CLINICAL RELEVANCE A detomidine CRI produced cardiovascular effects typical for α(2) -agonists, without affecting isoflurane requirements, recovery duration or recovery quality.

Cardiovascular effects of epidural administration of methadone, ropivacaine 0.75% and their combination in isoflurane anaesthetized dogs

OBJECTIVE To compare the cardiovascular effects of four epidural treatments in isoflurane anaesthetised dogs. STUDY DESIGN Prospective, randomized. experimental study. ANIMALS Six female, neutered Beagle dogs (13.3±1.0 kg), aged 3.6±0.1 years. METHODS Anaesthesia was induced with propofol (8.3±1.1 mg kg(-1)) and maintained with isoflurane in a mixture of oxygen and air [inspiratory fraction of oxygen (FiO(2))=40%], using intermittent positive pressure ventilation. Using a cross-over model, NaCl 0.9% (P); methadone 1% 0.1 mg kg(-1) (M); ropivacaine 0.75% 1.65 mg kg(-1) (R) or methadone 1% 0.1 mg kg(-1) + ropivacaine 0.75% 1.65 mg kg(-1) (RM) in equal volumes (0.23 mL kg(-1)) using NaCl 0.9%, was administered epidurally at the level of the lumbosacral space. Treatment P was administered to five dogs only. Cardiovascular and respiratory variables, blood gases, and oesophageal temperature were recorded at T-15 and for 60 minutes after epidural injection (T0). RESULTS Mean overall heart rate (HR in beats minute(-1)) was significantly lower after treatment M (119±16) (p=0.0019), R (110±18) (p< 0.0001) and RM (109±13) (p<0.0001), compared to treatment P (135±21). Additionally, a significant difference in HR between treatments RM and M was found (p=0.04). After both ropivacaine treatments, systemic arterial pressures (sAP) were significantly lower compared to other treatments. No significant overall differences between treatments were present for central venous pressure, cardiac output, stroke volume, systemic vascular resistance, oxygen delivery and arterial oxygen content (CaO(2)). Heart rate and sAP significantly increased after treatment P and M compared to baseline (T-15). With all treatments significant reductions from baseline were observed in oesophageal temperature, packed cell volume and CaO(2) . A transient unilateral Horners syndrome occurred in one dog after treatment R. CONCLUSIONS AND CLINICAL RELEVANCE Clinically important low sAPs were observed after the ropivacaine epidural treatments in isoflurane anaesthetised dogs. Systemic arterial pressures were clinically acceptable when using epidural methadone.

Transient unilateral Horner’s syndrome after epidural ropivacaine in a dog

OBSERVATIONS A left sided Horners syndrome (ptosis, prolapse of the nictitating membrane and miosis) was observed in a 4-year-old female, neutered Beagle dog after epidural injection of 0.22 mL kg(-1) ropivacaine (0.75%) in 0.01 mL kg(-1) of saline during isoflurane anaesthesia. Clinical signs disappeared gradually and resolved completely 4 hours and 10 minutes after injection. CONCLUSIONS The epidural injection of 0.22 mL kg(-1) ropivacaine (0.75%) in 0.01 mL kg(-1) of saline during isoflurane anaesthesia caused unilateral (left) Horners syndrome in a 4-year-old female, neutered Beagle dog.