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Updated: Sep 7, 2025
Anesthesia and Intubation of Preadolescent Mouse Pups for Cardiothoracic Surgery
Published on: June 2, 2022
Anesthesia and Intubation of Preadolescent Mouse Pups for Cardiothoracic Surgery
Jianxin Wu1, Amy M Nicks2, Justin J Skowno3
1Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute.
Insights
Anesthesia protocols using ketamine/xylazine/atropine in 10-day-old mice enable endotracheal intubation for cardiac surgery research. Higher pup weight correlated with increased survival rates, suggesting a minimum weight of 5.5g for successful procedures.
Area of Science:
- Cardiovascular Research
- Surgical Models
- Neonatal Mouse Physiology
Background:
- Murine surgical models are crucial for preclinical research, particularly for studying myocardial regeneration.
- Cardiothoracic surgery in young mice (0-14 days) is valuable as their cardiomyocytes retain proliferative capacity, unlike adult cells.
- Intubation is necessary for 8-14-day-old mouse pups but lacks established anesthesia protocols, leading to challenges and high mortality.
Purpose of the Study:
- To establish safe and effective anesthetic dosage regimens for endotracheal intubation in 10-day-old mouse pups.
- To optimize survival rates during cardiothoracic surgery in preadolescent mice.
- To provide guidance on anesthetic management for neonatal mouse cardiac surgery models.
Main Methods:
- Empirical titration of ketamine/xylazine/atropine dosages based on body weight in 10-day-old C57BL/6J mouse pups.
- Dosage regimens were determined for three weight groups: 3.15-4.49g, 4.50-5.49g, and 5.50-8.10g.
- Anesthesia for surgery involved isoflurane, with survival rates tracked post-intubation and post-surgery.
Main Results:
- Non-linear anesthetic responses to ketamine/xylazine/atropine were observed, with specific doses recommended per weight group.
- Lower-body-weight pups required more intubation attempts and had lower survival rates post-intubation (55-70%).
- Post-surgery survival rates were high and similar across weight groups (86-92%), but overall procedure survival correlated with body weight.
Conclusions:
- Specific ketamine/xylazine/atropine dosages facilitate intubation in 10-day-old mouse pups, with survival linked to pup weight.
- Given the challenges and mortality associated with intubation in younger/lighter pups, cardiothoracic surgery in 10-day-old pups is recommended for those weighing at least 5.5g.
- Refined animal handling and dam interaction are vital for improving overall survival in neonatal mouse cardiac surgical models.
Abstract:
Murine surgical models play an important role in preclinical research. Mechanistic insights into myocardial regeneration after cardiac injury may be gained from cardiothoracic surgery models in 0-14-day-old mice, the cardiomyocytes of which, unlike those of adults, retain proliferative capacity. Mouse pups up to 7 days old are effectively immobilized by hypothermia and do not require intubation for cardiothoracic surgery. Preadolescent (8-14-day-old) mouse pups, however, do require intubation, but this is challenging and there is little information regarding anesthesia to facilitate intubation. Here, we present dosage regimens of ketamine/xylazine/atropine in 10-day-old C57BL/6J mouse pups that allow endotracheal intubation, while minimizing animal mortality. Empirical titration of ketamine/xylazine/atropine dosage regimens to body weight indicated that the response to anesthesia of mouse pups of different weights was non-linear, whereby doses of 20/4/0.12 mg/kg, 30/4/0.12 mg/kg, and 50/6/0.18 mg/kg facilitated intubation of pups weighing between 3.15-4.49 g (n = 22), 4.50-5.49 g (n = 20), and 5.50-8.10 g (n = 20), respectively. Lower-body-weight pups required more intubation attempts than heavier pups (p < 0.001). Survival post-intubation correlated with body weight (59%, 70%, and 80% for low-, mid-, and high-weight groups, respectively, R2 = 0.995). For myocardial infarction surgery after intubation, a surgical plane of anesthesia was induced with 4.5% isoflurane in 100% oxygen and maintained with 2% isoflurane in 100% oxygen. Survival post-surgery was similar for the three weight groups at 92%, 86%, and 88% (p = 0.91). Together with refinements in animal handling practices for intubation and surgery, and minimizing cannibalization by the dam post-surgery, overall survival for the entire procedure (intubation plus surgery) correlated with body weight (55%, 60%, and 70% for low-, mid-, and high-weight groups, respectively, R2 = 0.978). Given the difficulty encountered with intubation of 10-day old pups and the associated high mortality, we recommend cardiothoracic surgery in 10-day-old pups be restricted to pups weighing at least 5.5 g.
