Mechanisms of toxicity and clinical picture
Barbiturates are characterized by a narrow therapeutic index. This means that the difference between the dose producing a therapeutic effect and the dose causing poisoning is minimal. Because of this, a high risk of acute intoxication persists in practice.
The clinical picture of severe poisoning is formed due to massive depression of central nervous system (CNS) functions. The patient loses consciousness, reflex activity is completely suppressed, and a deep comatose state develops.
The main threat to life is associated with the toxin's effect on vital centers located in the medulla oblongata:
- Respiratory center: its depression leads to a significant decrease in tidal volume. Ultimately, complete respiratory arrest is the direct cause of death.
- Vasomotor center: its suppression causes a sharp drop in blood pressure (BP). Hypotension is also aggravated by the ganglion-blocking action of barbiturates and their direct myotropic (relaxing) effect on the vascular wall.
Treatment principles: prevention of absorption
The treatment strategy is based on three key areas: preventing further entry of the poison into the blood, accelerating its elimination, and maintaining vital bodily functions.
The first stage consists of cleansing the gastrointestinal tract to stop the absorption of the drug. The following measures are performed for this purpose:
- Thorough gastric lavage.
- Administration of saline laxatives to accelerate the transit of contents through the intestine.
- Use of adsorbent agents that bind the toxin in the lumen of the digestive tract.
Detoxification: removal of the absorbed substance
To eliminate barbiturates that have already entered the systemic circulation, active detoxification methods are used:
- Forced diuresis. Large volumes of fluid (usually 1–2 liters of 0.9% NaCl solution) are administered intravenously to the patient, followed by potent diuretics such as furosemide or mannitol.
- Alkalinization of the filtrate. The use of alkaline drinks or administration of appropriate solutions is aimed at shifting the pH of the renal filtrate toward the alkaline side. This mechanism is fundamentally important: it prevents the reabsorption of barbiturates in the renal tubules, forcing them to be excreted faster with urine.
- Extracorporeal methods. At critically high concentrations of poison in the blood, drug therapy is insufficient. In such cases, extracorporeal blood purification — hemisorption or hemodialysis — is indicated.
Symptomatic therapy and resuscitation
The third direction of therapy is aimed at combating life-threatening symptoms and supporting organ function.
Respiratory support depends on the severity of the poisoning:
- In mild forms, the use of analeptics (e.g., bemegride) is acceptable to stimulate the respiratory center.
- In severe forms, analeptics are strictly contraindicated, as their administration only depletes the CNS and worsens the patient's condition. The only adequate method is transferring the patient to mechanical ventilation (artificial lung ventilation).
Hemodynamic support is required when collapse or pronounced hypotension develops. To stabilize blood pressure, intravenous administration of plasma expanders (to restore intravascular fluid volume) and vasopressors (e.g., norepinephrine) are used.
Briefly: answers to topical questions
What drugs and solutions are used for forced diuresis in barbiturate poisoning?
For forced diuresis in barbiturate poisoning, large volumes of fluid, potent diuretics, and alkalinizing solutions are used.
- Sodium chloride (NaCl) — 0.9% solution administered intravenously in a volume of 1–2 liters.
- Furosemide — used as a potent diuretic.
- Mannitol — used as an alternative potent diuretic.
- Alkaline solutions — necessary to shift the pH of the renal filtrate toward the alkaline side, which prevents the reabsorption of barbiturates in the renal tubules.
What trophic and infectious complications are characteristic of the comatose period of barbiturate poisoning?
The comatose period of severe barbiturate intoxication is characterized by:
- secondary pneumonia;
- deep pressure ulcers and sepsis during prolonged coma;
- high probability of aspiration due to loss of the pharyngeal reflex.
What analeptics, besides bemegride, can be used in mild forms of barbiturate poisoning?
In mild forms of poisoning with hypnotic drugs, besides bemegride, nikethamide (Cordiamin) can be used. In hypnotic poisoning, it is administered parenterally at 3–5 ml. In severe poisonings, analeptics are contraindicated.
The rule of three "P"s will help remember the directions of treatment: Prevent (absorption), Purge/Process (diuresis, dialysis), Protect/Provide (mechanical ventilation, hemodynamics).
Class and exam questions
Why does blood pressure drop sharply in barbiturate poisoning?
Hypotension is caused by three factors simultaneously: depression of the vasomotor center in the medulla oblongata, the ganglion-blocking effect, and the direct myotropic (relaxing) effect of the drug on the vascular walls.
Can analeptics be used if the patient is in a coma and not breathing?
No, in severe forms of poisoning, analeptics are strictly contraindicated as they worsen the condition. Mechanical ventilation (artificial lung ventilation) is required.
How does alkaline drinking help in poisoning?
Shifting the pH of the renal filtrate toward the alkaline side prevents the reabsorption of barbiturates in the renal tubules, accelerating their elimination from the body.
What else to study on this topic
- Mechanism of action of barbiturates on CNS receptors
- Features of analeptic use: indications and risks
- Principles of extracorporeal methods (hemisorption and hemodialysis)
- Pharmacology of potent diuretics in forced diuresis
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