Is anyone able to tell me why my anaesthetized rats often do a 'double breath', or diaphragmatic breath, like a hiccup (see video). This often begins after 1-2 hours under anesthesia, and can occur every 4th to 10th breath. The rats are anaesthetized with isoflurane (usually set to 1.5L/min). They are ventilated with a mixture of O2 and air (about 30:70). The ventilator is on volume control. When the rats 'double breathe' like this, I can sometimes stop it by turning the tidal volume right up, but this then leads to severe hypocapnia. There is no obvious cause for the development of this abnormal breathing (end tidal CO2 is in the normal range and the rats are not getting light in terms of anesthesia). Can anyone help?
Thank you very much, very interesting to see the same phenomenon in pediatrics. I should have mentioned that open tracheostomy is performed, rather than intubation, so the pharyngeal reflex is unlikely to play a role.
Hi Lakshmi - No, we just use isoflurane for anaesthesia, and buprenorphine for analgesia
Human patients sometimes show this pattern of breathing, specially when they are inadequately anaesthetised. I don’t know what the MAC value for rats is. In my practice, if I want to ventilate patients using only inhalational agents, I do it with concentrations above 1.3 MAC, which is about MAC95. In some patients, you need to go even higher.
The reason for the hitch in the breath (double breath) is that the diaphragm has dual innervation, with the central part through the vagus and peripheral parts through the intercostal nerves. When there is a loss of coordination between the two, you get this hitch. Very common in inadequate anesthesia. Even if you use neuromuscular blockers, a delay in giving the top up dose can lead to it.
And as you probably suspect, a rise in CO2 due to hypoventilation can stimulate the respiratory center and precipitate this phenomenon.
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