5.6 Respiratory stimulants
Respiratory stimulants are administered, at doses below the
convulsive threshold, to stimulate respiration. Their main
uses are to promote respiration in apnoeic newborn and preterm
animals and to reverse respiratory depression associated
with general anaesthetic, sedative, or hypnotic drugs.
These drugs should not be used as an alternative to patient
management because CNS stimulation my be followed by a
subsequent exacerbation of the depression. In drug-induced
respiratory depression maintenance of an adequate airway
and airflow by intubation and positive-pressure ventilation
are the recognised methods of treatment. While analeptic
drugs will temporarily increase tidal and minute volume,
the oxygen gain may be partly offset by increased brain
oxygen consumption.
All analeptics are CNS stimulants and may induce convulsions.
Doxapram is selective as a respiratory stimulant.
The principal mechanism of action of doxapram involves
stimulation of the peripheral aortic and carotid body chemoreceptors
rather than a central action.
The methylxanthines such as diprophylline and etamiphylline,
in addition to their bronchodilatory action,
increase respiratory drive by altering the sensitivity of the
respiratory centre to carbon dioxide. They are also non-specific
CNS stimulants.