Table 2 . Glossary of useful respiratory terms not covered in this article .
Term Tidal volume ( TV )
Minute volume or minute ventilation
Functional residual capacity ( FRC )
Dead space
Ventilation / perfusion ratio or V / Q ratio
Definition / comments
Tidal volume refers to the volume of air breathed in and out during one breath . It is calculated as 10 – 15 ml / kg .
Minute volume ( or minute ventilation ) refers to the volume breathed in and out during 1 min . This is calculated as tidal volume multiplied by respiratory rate .
The FRC refers to the air left in the lungs between breaths , after the animal has breathed out . As there is always some air in contact with the alveoli , this air allows gaseous exchange to continue during expiration . It also holds the lungs open due to the percentage of nitrogen in room air . Rabbits and small animals have a very small FRC . This is why , when intubating rabbits , they can quickly turn blue ( a sign of hypoxia ) and preoxygenation is important .
Dead space refers to the volume of the respiratory tract that is not involved in gaseous exchange . You may also be familiar with this term in relation to anaesthesia . Anatomical dead space is the region from the nose to the terminal bronchioles . Mechanical dead space is the additional volume in the equipment beyond the tip of the patient ' s nose , such as an endotracheal tube that is excessively long before it meets the Y piece on the anaesthetic circuit .
V / Q is used to indicate the concentration of both oxygen and carbon dioxide in the bloodstream . A V / Q mismatch could indicate that oxygen is not getting into the bloodstream or carbon dioxide is not able to get out . This could be because the alveoli receive the oxygen but there is no blood flow to them , or there is blood flow without oxygen . This can be caused by an obstructed airway , blood clots or contusions to the lungs . A pulmonary shunt is where blood passes from the venous to the arterial circulation without taking part in gaseous exchange .
REFERENCES
1 Colville TP , Bassert JM . The respiratory system . In : Clinical Anatomy and Physiology for Veterinary Technicians . 3rd ed . St . Louis : Elsevier Health Sciences ; 2015 . p . 361 – 377 .
2 Fraser M , Girling S . Anatomy and physiology . In : Cooper B , Mullineaux E , Turner L . ( eds .) BSAVA Textbook of Veterinary Nursing . 6th ed . Gloucester : BSAVA Publications ; 2020 . p . 52 – 120 .
3 Fraser M . Physiology relevant to anaesthesia . In : Welsh E . ( ed .) Anaesthesia for Veterinary Nurses . Chichester : John Wiley & Sons ; 2013 . p . 19 – 27 . Available from : https :// doi . org / 10.1002 / 9780470752302 . ch2 .
4 Cooper B , Mullineaux E , Turner L . Appendix 2 . In : Cooper B , Mullineaux E , Turner L . ( eds .) BSAVA Textbook of Veterinary Nursing . 6th ed . Gloucester : BSAVA Publications ; 2020 . p . 910 .
5 Lynch A . Providing supplemental oxygen to patients . Today ' s Veterinary Practice . 2018 ; 8 ( 4 ), 44 – 50 . Available from : https :// todaysveterinarypractice . com / respiratory-medicine / providingsupplemental-oxygen-to-patients / [ Accessed 9 April 2024 ].
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