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 the regulation of inspiration and expiration.
The main indications for their prescription include:
- Depression of the respiratory center due to the use of hypnotics or general anesthetics.
- Neonatal asphyxia.
- Carbon monoxide poisoning (in such situations, drugs may be administered intravenously).
Despite the presence of indications, modern management tactics for patients with hypoxic conditions have 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: mixed-type stimulant
One of the well-known representatives of mixed-type stimulants is carbogen. Its effectiveness is based on a strictly balanced gas mixture composition:
- Carbon dioxide ($CO_2$) — from 5 to 7%.
- Oxygen ($O_2$) — from 93 to 95%.
The mechanism of action of carbogen is combined. First, it exerts a direct stimulating effect directly on the neurons of the respiratory center. Second, a reflex stimulation is triggered, mediated through chemoreceptors located in the area of the carotid bodies.
From the perspective of pharmacodynamics, the therapeutic effect of carbogen is due exclusively to the presence of carbon dioxide in the mixture. Upon inhalation administration, a clinically significant effect develops 5–6 minutes after the start of the procedure.
Specific opioid receptor antagonists
In situations where ventilation impairment is provoked by an overdose of central nervous system depressants, the use of nonspecific analeptics is inappropriate. 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 of respiratory center neurons. $\mu$-Receptor antagonists are used for treatment:
- Naloxone is an intravenous drug. It is characterized by a rapid but relatively short effect (duration of action is up to 1 hour).
- Naltrexone is an oral drug. It features a prolonged therapeutic window, with its effect lasting up to 36 hours.
Reversal of benzodiazepine-induced depression
If respiratory failure is caused by the toxic effect of benzodiazepines, the specific benzodiazepine receptor antagonist flumazenil (trade name — Anexate) is used as etiotropic therapy. The drug is administered as an intravenous infusion.
An important feature of flumazenil is its broad spectrum of action within its receptor group. It demonstrates high clinical efficacy in overdose not only with classical benzodiazepine tranquilizers but also with so-called Z-drugs. The latter include, for example, zolpidem, a hypnotic agent that is a non-benzodiazepine agonist of the same receptor structures.
Briefly: answers to topical questions
Which drugs belong to direct-acting respiratory analeptics?
Direct- (central-) acting respiratory analeptics include pentetrazol, bemegride, and caffeine.
- Pentetrazol is a direct-acting drug.
- Bemegride is a centrally acting analeptic used in mild hypnotic poisoning.
- Caffeine is a centrally acting stimulant with a relatively wide therapeutic window.
These drugs directly stimulate the respiratory center, reducing the depressing effect of hypnotics and anesthetics.
Which drugs belong to reflex-acting analeptics?
Reflex-acting drugs include cytisine and lobeline, which are nicotinic acetylcholine receptor agonists.
- Cytisine excites the receptors of the sinocarotid zone.
- Lobeline stimulates nicotinic acetylcholine receptors, from where impulses are directed to the medulla oblongata.
These medications are used to restore respiratory function during its depression, acting not directly on the respiratory center, but via reflex stimulation.
What is the exact mechanism of action of flumazenil at the molecular level?
The mechanism of action of flumazenil involves the competitive blockade of benzodiazepine receptors.
This leads to the elimination of agonist effects, such as hypnotic and sedative actions. The drug is a specific antagonist administered intravenously and effectively restores breathing and consciousness in drug-induced depression. It is used in overdoses of both classical benzodiazepines and Z-drugs (e.g., zolpidem).
What side effects are characteristic of classical analeptics in overdose?
Overdose with classical analeptics can lead to dyspeptic, neurological, and severe convulsive complications.
- Dyspeptic disorders — nausea and vomiting.
- Neurological disorders include muscle twitching.
- Severe complications include the development of seizure syndrome (convulsions).
What are the absolute contraindications to the use of respiratory analeptics?
An absolute contraindication to the use of respiratory analeptics (e.g., bemegride) is severe hypnotic poisoning and severe forms of respiratory depression.
In such states, breathing is not restored, but the stimulation of brain neuron metabolism increases their oxygen demand. In the presence of uncorrected hypoxia, this leads to exacerbated nerve cell damage and general deterioration of the patient's condition. Instead of analeptics, mechanical ventilation is indicated in these cases.
To remember the composition of carbogen: carbon dioxide makes up exactly 5–7% of the mixture — this is the optimal concentration to stimulate breathing without causing poisoning.
Class and exam questions
How long does it take for the effect of Carbogen inhalation to appear?
The effect caused by carbon dioxide develops on average 5–6 minutes after inhalation.
What is preferable in severe hypoxia: analeptics or mechanical ventilation?
Modern tactics give unconditional priority to assisted or mechanical ventilation (MV); stimulants are rarely used.
What is the main difference between naloxone and naltrexone?
Naloxone is administered intravenously and has a short duration of action (up to 1 hour), whereas naltrexone is taken orally and provides a prolonged effect (up to 36 hours).
Can flumazenil be used for zolpidem poisoning?
Yes, flumazenil is effective in Z-drug overdoses (including zolpidem), as they are non-benzodiazepine agonists of benzodiazepine receptors.
What else to study on this topic
- Mechanism of reflex stimulation via carotid bodies
- Pathogenesis of respiratory depression by $\mu$-opioid agonists
- Pharmacokinetics and features of intravenous flumazenil administration
- Specifics of Z-drug action on the central nervous system
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