Isoflurane depresses ventilation in a dose-related fashion in spontaneously breathing volunteers. Subanesthetic concentrations of 0.1 times the minimal alveolar concentration (MAC) cause a 50 per cent depression of CO2 response, and concentrations well below this impair responsiveness to hypoxia. These effects are less important in the ICU because isoflurane is only used in patients supported by mechanical ventilation. As isoflurane is eliminated quickly, this ventilatory depression should not be a problem in the weaning period.
In normal human airways there is no effect on bronchomotor tone, but isoflurane may prevent the development of bronchospasm and has been used to treat patients with severe asthma or chronic obstructive pulmonary disease.
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If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.