Indications for Use and Modern Tactics
Classic respiratory analeptics are used in pathological conditions accompanied by a decrease in the excitability of structures responsible for regulating inspiration and expiration.
Key indications for their administration include:
- Depression of the respiratory center due to sedatives or general anesthetics.
- Neonatal asphyxia.
- Carbon monoxide poisoning (in these situations, drugs may be administered intravenously).
Despite these indications, modern management of patients with hypoxic conditions has changed significantly. Currently, respiratory stimulants are used quite rarely. The leading and most reliable method for correcting respiratory failure is assisted or mechanical ventilation (MV).
Carbogen: A Mixed-Type Stimulant
A well-known representative of mixed-type stimulants is Carbogen. Its efficacy is based on a strictly balanced gas mixture composition:
- Carbon dioxide ($CO_2$) — 5 to 7%.
- Oxygen ($O_2$) — 93 to 95%.
The mechanism of action of Carbogen is combined. First, it has a direct stimulatory effect on the neurons of the respiratory center. Second, it triggers a reflex stimulation mediated through chemoreceptors located in the carotid bodies.
From a pharmacodynamic perspective, the therapeutic effect of Carbogen is due exclusively to the carbon dioxide component. Upon inhalation, a clinically significant effect develops within 5–6 minutes after the procedure begins.
Specific Opioid Receptor Antagonists
In situations where pulmonary ventilation impairment is triggered by an overdose of central nervous system depressants, the use of nonspecific analeptics is impractical. In such cases, specific antidotes are used, the choice of which depends on the type of blocked receptors.
In opioid analgesic poisoning, the pathogenesis of depression is associated with the stimulation of $\mu$-opioid receptors on neurons of the respiratory center. $\mu$-receptor antagonists are used for treatment:
- Naloxone — an intravenous drug characterized by a rapid but relatively short duration of action (up to 1 hour).
- Naltrexone — an orally administered drug distinguished by a prolonged therapeutic window, with effects lasting up to 36 hours.
Reversing Benzodiazepine-Induced Depression
If respiratory failure is caused by the toxic effects of benzodiazepines, the specific benzodiazepine receptor antagonist flumazenil (trade name Anexate) is used as etiotropic therapy. The drug is administered via intravenous infusion.
An important feature of flumazenil is its broad spectrum of action within its receptor group. It demonstrates high clinical efficacy in overdoses of not only classical benzodiazepine tranquilizers but also so-called Z-drugs. The latter include, for example, zolpidem, a hypnotic agent that is a non-benzodiazepine agonist of the same receptor structures.