Breathing bags in an anesthetic system are collapsible ellipsoid containers that serve as a reservoir for anesthetic gases and as a mean for manual ventilation. The reservoir bags, also known as counterlungs, allow visual assessment of the presence and estimation of the volume of ventilation. These bags form a crucial part of most anesthetic systems, since, during normal spontaneous inspiration, anesthetic machines are incapable of providing the needed peak inspiratory gas flow.
Breathing bags are elastic and are available as disposable and reusable variants. Disposable bags, in comparison to reusable variants, are usually thinner and lighter, yet they provide reasonable durability. Generally, the reservoir bags are made of natural rubber (latex); however non-latex versions are also available for subjects with latex allergies. To improve the grip, they are usually textured. However, hourglass-shaped breathing bags are also available to allow better grip.
Breathing bags are usually mounted at or near the carbon dioxide absorbent canister with the help of a T-shaped fitting or at the end of a corrugated tubing leading from the T-connector in a circle breathing system.
Apparatus and Equipment
Breathing bags are generally made of rubber although latex-free disposable versions are also available. The bag materials are non-slip, non-permeable and do not absorb or adsorb the gases. The neck of the reservoir is connected to the breathing system using two female conical fitting connectors having internal diameters 15 mm and 22 mm. The tail end of the bag has a tubular extension that is at least 2 cm long and functions as a relief mechanism. The size of the bag is dependent on the size of the subject.
|Weight of Animal (kg)||Bag Size (L)|
The selection of the reservoir is based on the tidal volume of the subject. The bag size can be calculated as follows,
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In case the pop-off valve has been accidentally kept in the closed position, and gas inflow continues, the pressure-volume characteristics play a crucial role when the breathing bag is inflated. Reservoir bags are one of the components that usually cause failure of anesthetic machines in the pressure test. Breathing bags deteriorate over time; thus, it is important to inspect them regularly. Cracks and holes around the neck of the breathing bag are often the cause of leakage.
Ehrenwerth, J., Eisenkraft, J. B., & Berry, J. M. (2013). Anesthesia equipment: Principles and applications. Philadelphia, PA: Elsevier Saunders.
Fish, R. E. (2008). Anesthesia and analgesia in laboratory animals. Amsterdam: Elsevier.
Križmarić, M. Functions of anesthesia reservoir bag in a breathing system. Retrieved from http://vestnik.szd.si/index.php/ZdravVest/article/view/2204/2156