Lizard and Snake Respiration

Breathing is controlled differently in reptiles to mammals and this has important considerations for anaesthetics.

• Breathing process - Inspiration is due to the movements of the intercostal muscles and not by gulping air (gular breathing) into their lungs. The glottis is normally kept closed and is only opened by the dilator glottis muscle during active respiration. Snakes lack a cough reflex so conscious intubation is possible. This allows rapid induction of general anaesthesia. Snakes do not have a diaphragm and the intercostal and intrapulmonary muscles are used to vary the lung volume and intrapulmonary pressures. Intermittent positive pressure ventilation (IPPV) may be necessary during anaesthesia since anaesthetic agents affect these muscles.

• Metabolic control of respiration - Mammalian respiration is controlled to maintain blood CO2 and pH within narrow limits whereas blood oxygen partial pressure and temperature control reptilian respiration. Hypoxaemia increases the rate of breathing rather than hypercapnia. High oxygen environments (e.g. 100% oxygen during recovery from anaesthesia) suppress the spontaneous respiratory rate.

• Anaerobic metabolism - Reptiles can function to a large extent with anaerobic metabolism. They are able to survive with increased lactate due to their buffering system. Compensatory factors may conceal respiratory disease until it is advanced. Reptiles are capable of breath-holding and may be difficult to induce with volatile agents in an induction chamber.