Respiratory failure (lack of, or ineffective breathing) is the most common anaesthetic complication likely to be encountered in tigers. It can occur during anaesthesia or in any severely injured, shocked or diseased animal at any time, especially in cases of severe respiratory infections. Large doses of potent alpha-2 adrenoceptor drugs such as medetomidine in induction mixtures often produce a degree of respiratory depression. During anaesthesia, respiratory failure is often caused by the administration of too much anaesthetic agent. It can also be caused by obstruction of the airway, or even by severe pain. Respiratory failure persisting for more than a few minutes leads to inadequate oxygenation of the blood resulting in cellular death.
Monitoring of respiration is achieved by observing the depth, rate and character of breathing; by checking the colour of the mucous membranes and by ensuring that no obstructions develop within the mouth or pharynx. Signs of impending respiratory failure include a fall in the rate of breathing to less than 50% of normal, a progressive fall in the depth of breathing, and pallor or a blue appearance of the mucous membranes. Obstruction of the airway in conscious animals may be indicated by violent and frequent attempts by the animal to draw in breath. However, during deep anaesthesia, obstruction can cause inadequate ventilation without dramatic inspiratory efforts. As a rough “rule of thumb” complete respiratory failure in a medium sized animal may be considered as having occurred if there is a lack of breathing for 1 minute, with continued beating of the heart.
On recognizing the problem, discontinue administering any anaesthetic drugs including gaseous agents, and position the tiger on its side.
- Check that the passage of air into the lung is unobstructed.
- Check that the head is extended straight out from the body to ensure that the airway is not kinked.
- Ensure that the throat is not lying across a rock, stick, or radio-transmitter which may be pressing on the trachea.
- Check that any radio collar fitted is not too tight.
- Pull the tongue forward to ensure that it isn’t lodged against the back of the pharynx, obstructing the larynx.
- Remove any vomit, mucous, blood clots or foreign bodies from the mouth. It is wise to use a mouth prop to keep the jaws open during this process.
- Where possible, pass an endotracheal tube and inflate the cuff to safeguard the airway. Details of how to intubate a tiger are given here. If already fitted, ensure that an endotracheal tube is not blocked or kinked.
- Establish and maintain an effective pattern of breathing by either attaching an Ambu bag to the endotracheal tube and begin compressions of the Ambu bag which will inflate the lungs, or by blowing intermittently through the endotracheal tube which can be surprisingly effective. In extreme circumstances where no endotracheal tube is fitted, breathing can be established by blowing intermittently with your mouth placed around an animal’s nostrils whilst keeping its mouth closed. Whichever method is chosen, one respiratory movement should be established every 5-6 seconds in medium sized animals, more frequently in smaller individuals.
- Provide oxygen if available via the Ambu bag. With most designs of Ambu bag an oxygen line can be attached so that every compression delivers oxygen to the animal. If no Ambu bag or endotracheal tube is available, insert a lubricated small bore plastic tube from the oxygen cylinder into a nostril keeping close to the mid-line, and tape in place. Keep ventilating as above. DONT FORGET TO TURN THE OXYGEN ON!
- Intermittent pressure on the chest wall can be used to establish airflow in and out of the lungs but is extremely inefficient for anything more than a couple of minutes. However, if an animal has just stopped breathing, pressing down on and then releasing the chest wall can sometimes trigger spontaneous respiration.
- Respiratory and circulatory failure often occur together and therefore it is essential to ensure that the animal’s heart is still beating and that an effective pulse is present.
- If artificial respiration attempts did not restore spontaneous breathing, stimulate with intravenous doxapram hydrochloride (“Dopram-V”) at 0.5 – 1mg per kg (equivalent to 0.25 – 0.5mls “Dopram-V” solution per 10 kgs). Pushing on the chest wall sometimes triggers a breath after intravenous doxapram. Keep ventilating as above until the doxapram takes effect.
- If there is no effect, repeat the doxapram, and keep ventilating.
- If you are unable to administer a dose of doxapram intravenously it can be injected into the muscle of the tongue – but avoid damaging blood vessels in the process.
- Where reversible anaesthetic agents have been used, consider using the antidote. However, if a full reversal dose is given the safety consequences of recovery to consciousness must be considered. In cases where breathing was depressed but hadn’t ceased altogether, and measures detailed above have re-established a reasonable pattern of respiration, consider giving a small dose of the reversal agent (say 20%) to prevent respiratory failure recurring.
If breathing is re-established and stabilised, an anaesthetic can be continued, but monitor the animal closely and try to lighten the anaesthesia. Close monitoring will be required for a prolonged period following the episode – respiratory failure may recur and the effects of doxapram are often short lived.