Vergleich der kardiovaskulären Funktion bei spontan atmenden und künstlich beatmeten Pferden unter Isofluran/Medetomidin-Anästhesie

Künstlich beatmete, normokapnische Pferde weisen in Anästhesie eine schlechtere kardiovaskuläre Funktion auf als spontan atmende Pferde. Die vorliegende Studie untersuchte ob dies auch zutrifft, wenn beatmete Pferde leicht hyperkapnisch sind. Sechzig Pferde wurden untersucht. Nach Prämedikation mit Medetomidin und Anästhesieeinleitung mit Ketamin-Diazepam wurde die Anästhesie mit Isofluran-Medetomidin unterhalten. Die Gruppenzuteilung erfolgte zufällig. Dreissig Pferde atmeten spontan und dreissig wurden künstlich zu leichter Hyperkapnie (arterieller Kohlendioxidpartialdruck 50-60 mmHg) beatmet. Herzfrequenz, Atemfrequenz, intraarterieller Blutdruck und die Zusammensetzung der in- und exspiratorischen Gase wurden kontinuierlich gemessen und alle 5 Minuten protokolliert. Fünfzehn Minuten nach der Anästhesieeinleitung und danach alle 30 Minuten wurde eine arterielle Blutgasanalyse durchgeführt. Der Herzauswurf wurde 45 Minuten nach Anästhesieeinleitung bestimmt und anschliessend stündlich. Kontinuierliche Daten wurden mittels ungepaartem t-Test oder mittels Varianzanalyse analysiert und kategorielle Daten mithilfe eines Chi-Quadrat Tests. Unterschiede zwischen den Gruppen wurden mittels poc-hoc Test analysiert. Ein p-Wert < 0.05 wurde als signifikant bezeichnet. Es gab zwischen den 2 Gruppen keine signifikanten Unterschiede. Nur die Atemfrequenz der beatmeten Gruppe war signifikant höher als in der spontan atmenden Gruppe. Unsere Studie zeigt, dass künstlich beatmete Pferde in Anästhesie eine kardiovaskuläre Funktion aufweisen, die sich nicht von derjenigen von spontan atmenden Pferden unterscheidet, vorausgesetzt sie sind leicht hyperkapnisch. = In anaesthesia to normocapnia ventilated horses show worse cardiovascular function than spontaneously breathing horses. The present study assessed differencies in cardiovascular function between artificially ventilated and spontaneously breathing mildly hypercapnic horses. Sixty horses were included. Premedication with medetomidine was followed by ketamine and diazepam. Anaesthesia was maintained with isoflurane-medetomidine. Horses were assigned to either spontaneous breathing or controlled ventilation to mild hypercapnia (arterial partial pressure of carbon dioxide 50-60 mmHg). Heart rate, respiratory rate, intraarterial blood pressure and composition of in- and expiratory gases were recorded every 5 minutes. Arterial blood gases were measured 15 minutes after anaesthesia induction and then every 30 minutes and cardiac output 45 minutes after anaesthesia induction and hourly thereafter. Continous data were analysed using analysis of variance for repeated measures or unpaired t-test. Categorical data were analysed using Chi-square test and differences between groups were analysed using poc-hoc test. A p-value of < 0.05 was considered significant. There was no difference between the groups. Only respiratory rate was significantly higher with controlled ventilation. In conclusion, there is no difference in cardiovascular function in healthy horses with spontaneous ventilation in comparison to controlled ventilation, underlying the horses are maintained slightly hypercapnic

Minimum infusion rate of alfaxalone for total intravenous anaesthesia after sedation with acepromazine or medetomidine in cats undergoing ovariohysterectomy

Objective: To determine the induction doses, then minimum infusion rates of alfaxalone for total intravenous anaesthesia (TIVA), and subsequent, cardiopulmonary effects, recovery characteristics and alfaxalone plasma concentrations in cats undergoing ovariohysterectomy after premedication with butorphanol-acepromazine or butorphanol-medetomidine. Study design: Prospective randomized blinded clinical study. Animals: Twenty-eight healthy cats. Methods: Cats undergoing ovariohysterectomy were assigned into two groups: together with butorphanol [0.2 mg kg−1 intramuscularly (IM)], group AA (n = 14) received acepromazine (0.1 mg kg−1 IM) and group MA (n = 14) medetomidine (20 μg kg−1 IM). Anaesthesia was induced with alfaxalone to effect [0.2 mg kg−1 intravenously (IV) every 20 seconds], initially maintained with 8 mg kg−1 hour−1 alfaxalone IV and infusion adjusted (±0.5 mg kg−1 hour−1) every five minutes according to alterations in heart rate (HR), respiratory rate (fR), Doppler blood pressure (DBP) and presence of palpebral reflex. Additional alfaxalone boli were administered IV if cats moved/swallowed (0.5 mg kg−1) or if fR >40 breaths minute−1 (0.25 mg kg−1). Venous blood samples were obtained to determine plasma alfaxalone concentrations. Meloxicam (0.2 mg kg−1 IV) was administered postoperatively. Data were analysed using linear mixed models, Chi-squared, Fishers exact and t-tests. Results: Alfaxalone anaesthesia induction dose (mean ± SD), was lower in group MA (1.87 ± 0.5; group AA: 2.57 ± 0.41 mg kg−1). No cats became apnoeic. Intraoperative bolus requirements and TIVA rates (group AA: 11.62 ± 1.37, group MA: 10.76 ± 0.96 mg kg−1 hour−1) did not differ significantly between groups. Plasma concentrations ranged between 0.69 and 10.76 μg mL−1. In group MA, fR, end-tidal carbon dioxide, temperature and DBP were significantly higher and HR lower. Conclusion and clinical relevance: Alfaxalone TIVA in cats after medetomidine or acepromazine sedation provided suitable anaesthesia with no need for ventilatory support. After these premedications, the authors recommend initial alfaxalone TIVA rates of 10 mg kg−1 hour−1

A study of cardiovascular function under controlled and spontaneous ventilation in isoflurane-medetomidine anaesthetized horses

OBJECTIVE: To determine, in mildly hypercapnic horses under isoflurane-medetomidine balanced anaesthesia, whether there is a difference in cardiovascular function between spontaneous ventilation (SV) and intermittent positive pressure ventilation (IPPV). STUDY DESIGN: Prospective randomized clinical study. ANIMALS: Sixty horses, undergoing elective surgical procedures under general anaesthesia: ASA classification I or II. METHODS: Horses were sedated with medetomidine and anaesthesia was induced with ketamine and diazepam. Anaesthesia was maintained with isoflurane and a constant rate infusion of medetomidine. Horses were assigned to either SV or IPPV for the duration of anaesthesia. Horses in group IPPV were maintained mildly hypercapnic (arterial partial pressure of carbon dioxide (PaCO(2)) 50-60 mmHg, 6.7-8 kPa). Mean arterial blood pressure (MAP) was maintained above 70 mmHg by an infusion of dobutamine administered to effect. Heart rate (HR), respiratory rate (f(R)), arterial blood pressure and inspiratory and expiratory gases were monitored continuously. A bolus of ketamine was administered when horses showed nystagmus. Cardiac output was measured using lithium dilution. Arterial blood-gas analysis was performed regularly. Recovery time was noted and recovery quality scored. RESULTS: There were no differences between groups concerning age, weight, body position during anaesthesia and anaesthetic duration. Respiratory rate was significantly higher in group IPPV. Significantly more horses in group IPPV received supplemental ketamine. There were no other significant differences between groups. All horses recovered from anaesthesia without complications. CONCLUSIONS: There was no difference in cardiovascular function in horses undergoing elective surgery during isoflurane-medetomidine anaesthesia with SV in comparison with IPPV, provided the horses are maintained slightly hypercapnic. CLINICAL RELEVANCE: In horses with health status ASA I and II, cardiovascular function under general anaesthesia is equal with or without IPPV if the PaCO(2) is maintained at 50-60 mmHg