To the Editor: Two 35 cm long blue-tongue lizards live in the rockery above my home swimming pool (water temperature, 19ºC). While cleaning the pool, I was shocked to see one of them floating motionless on the surface, but with its head held out of the water. Rescue with a net revealed a sluggish but healthy lizard, that slowly crept into the ground cover.

Returning to my task, I was devastated to see the other lizard motionless on the bottom of the pool. After rescuing it, I thought it was dead, but a trace of slow muscular movement led me to action. With its head down, I rhythmically squeezed the upper body circumferentially with one hand, expelling an amazing amount of water and then saliva-like fluid. The abdomen, which had been distended to about 7 cm in diameter, reduced in size at least 1 cm. Gradually, there was more sluggish body and limb movement, but no discernible respiration and no opening of the mouth. After about 10 minutes, the eyes opened and I reduced my gentle efforts, but still fluid drained if the head was held down. Eventually, the lizard was placed on the rockery and observed. After a few minutes, it opened its mouth widely, revealing the oral cavity completely full of froth. More head-down draining and rest gradually improved the situation and, some time later, normal respiration seemed to have returned. Later in the day, it had moved about 30 cm and, before nightfall, it had gone. Next morning, both lizards were seen, appearing perfectly healthy and normal.

I have no idea how long they were in the pool, or why, but presumably they had had a tussle, a game of chasey or a fight and lost their bearings. After 3 years of retirement from general practice, I felt considerable personal and professional delight!

Comment: Lizards generally have simple lung structures compared with those of mammals. Their lungs are basically two membranous sacs, with no bronchial tree that leads to the alveolar sacs in mammals. This means their capacity for oxygen exchange is less than that of mammals. They have, however, many physiological adaptations to compensate for this limitation, including a capability for prolonged anaerobic metabolism and the ability to perform right-to-left cardiac shunting. Consequently, reptiles are much better able to cope with hypoxia than mammals. If hypoxia continues for more than an hour, heart rate may fall 50%, and a right-to-left shunting of up to 80% of cardiac output occurs.

Several species of lizards use their capacity to cope with hypoxia to advantage and will submerge themselves for several hours to escape predators. Blue-tongue lizards are a terrestrial species and generally avoid contact with water. If necessary, however, they are very good swimmers. They tend to inflate their lungs, and use their tails to propel themselves across the surface of the water. The lizard described by Darvall probably drowned because of exhaustion and hypothermia.

In reptile drowning, it is important to help remove water and respiratory secretions from the lungs using gravity and coupage, particularly as reptiles appear to lack a good mucociliary clearance system. The pool water, being chlorinated, would have had reduced microbial levels, making bacterial pneumonia, seen in accidental drowning in reptiles, less likely. Keeping the reptile warm is also important, to stimulate muscle activity and respiration.

Had this lizard failed to respond to drainage and coupage, it may have needed supplementary oxygen, a measure that warrants caution. The respiratory centre of reptiles responds mostly to low partial pressure of oxygen, unlike the respiratory centre of mammals, which normally responds to increased partial pressure of carbon dioxide. Thus, supplying 100% oxygen to reptile patients requiring resuscitation inhibits return to normal respiration. Reptile resuscitation is best provided with normal air, at a rate of six breaths per minute.