Abstract
ObjectiveA simple but reliable and safe anaesthetic procedure is required for surgical interventions in small rodents. Combined ketamine and xylazine injections are often used in rats for less invasive surgery, possibly with spontaneous breathing and without airway management. However, there are important pitfalls to be avoided by special precautions and monitoring, as shown subsequently.Study designObservational study.AnimalsTwenty-four anaesthetic procedures for bile duct ligation, sham operation or carotid artery dilatation in 20 male Sprague-Dawley rats, preoperatively weighing between 440 and 550 g.MethodsIntolerable high mortality rates occurred in the first 7 postoperative days while establishing a new experimental model in rats using ketamine-xylazine anaesthesia. Rats were spontaneously breathing ambient air during the first 12 surgeries without airway management. An observed high mortality rate in these animals led to a change in the trial protocol: the insufflation of 2 litres of oxygen per minute via nose cone during the following 12 rat surgeries. Retrospective comparison of the outcome (without oxygen vs. with oxygen insufflation) was conducted.ResultsThe perioperative mortality rate could be significantly reduced from 58% (7/12) to 17% (2/12) (p = 0.036) by oxygen insufflation via nose cone. Significantly different levels of intraoperative oxygen saturation (SpO2; 89 ± 4% [without oxygen] vs. 97 ± 0.5% [with oxygen], p < 0.0001), but no significant differences in heart rate (HR; 267 ± 7 beats minute–1 [bpm] [without oxygen] vs. 266 ± 6 bpm [with oxygen], p = 0.955) were observed.Conclusions and clinical relevanceIn summary, rats under ketamine-xylazine anaesthesia are susceptible to hypoxia. This may lead to increased delayed mortality related to hypoxia induced lung failure. Apparently, this is an underestimated problem. We highly recommend using additional oxygen insufflation in spontaneously breathing rats under ketamine-xylazine anaesthesia with basic monitoring such as measurement of oxygen saturation.
Highlights
A new experimental rat model investigating the impact of liver cirrhosis on the healing of vascular damages was employed in our research group
Rats under ketamine-xylazine anaesthesia are susceptible to hypoxia
Our results show the importance of oxygen supply during ketamine and xylazine (KX) anaesthesia, as hypoxia leads to increased mortality rates during surgery and up to seven days later
Summary
A new experimental rat model investigating the impact of liver cirrhosis on the healing of vascular damages was employed in our research group. Establishing new surgical animal models requires the selection of appropriate anaesthetic procedures. Selection criteria are the wellbeing of the trial animal, possible research interference, as well as financial and practical considerations such as ease of use or personal experience and preference [1, 2]. Intraperitoneal (IP) or inhalational anaesthetic induction is used in rats, as intravenous and intramuscular induction are inferior because of increased technical difficulty or painfulness [2]. We chose IP application, mainly because we planned to investigate the impact of liver cirrhosis on the heart, and inhalational anaesthetics such as fluranes are known to be cardioprotective [3,4,5].
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