Advantages and scope of application
The main advantages of this technique are the rapid achievement of anesthetic sleep, the absence of an unpleasant excitation phase, and overall comfort for the patient during induction. The main limiting factor is the short duration of the drugs' action.
Due to its short-term effect, intravenous anesthesia is practically not used in its pure form (monoanesthesia) for long surgeries. The main niche for such drugs is:
- Short interventions (lasting 10–20 minutes): opening of abscesses and phlegmons, reposition of bone fragments, reduction of dislocations, laparostomic sanitation.
- Induction anesthesia prior to switching to inhalation anesthesia.
Barbituric acid derivatives
This group includes sodium thiopental and hexobarbital. Both drugs provide rapid onset of sleep and equally fast awakening, and their clinical picture is completely identical. The only difference is that hexobarbital depresses the respiratory center to a lesser extent.
Rules for working with barbiturates:
- Solutions must be strictly freshly prepared. Usually, 1 g of the drug is diluted in 100 ml of isotonic NaCl solution (resulting in a 1% solution).
- The drug is administered slowly — at a rate of about 1 ml per 10–15 seconds.
- A sensitivity test is mandatory: 3–5 ml is administered first, and waiting for 30 seconds. If no unexpected reactions occur, administration is continued until the surgical stage.
Sleep lasts about 10–15 minutes. To prolong the effect, the solution is administered fractionally (100–200 mg each), but the total dose should not exceed 1000 mg.
During anesthesia, roles are strictly distributed: the nurse monitors the pulse, BP, and respiration, while the anesthesiologist monitors the depth of anesthesia (pupils, corneal reflex, eye movements). The main dangers are a sharp drop in pressure with rapid administration (requires immediate cessation of injection) and respiratory depression (mask artificial ventilation is necessary).
Ketamine and Propofol
Ketamine differs from other agents in that it causes only superficial sleep while powerfully stimulating the cardiovascular system. It increases blood pressure and heart rate.
- Dosage: 2–5 mg/kg (intravenous and intramuscular administration possible).
- Indications: shock states with arterial hypotension.
- Contraindications: hypertension.
- Complications: unpleasant hallucinations are possible during the awakening phase.
Propofol is an ultra-short-acting agent, which is a 1% milky-white aqueous-isotonic emulsion (containing soybean oil and egg phosphatide).
- Dosage: 2.5–3 mg/kg.
- Effect: anesthetic sleep occurs in 20–30 seconds and lasts about 5–7 minutes.
- Risks: short-term apnea (up to 20 s) is possible during induction, so the physician must keep the anesthesia machine or Ambu bag ready. Bradycardia and allergies are recorded in rare cases.
Sodium oxybutyrate and Hydroxydione
These agents are usually used not in isolation, but in combination with other anesthetics.
- Sodium hydroxydione succinate is administered at a dose of 15 mg/kg (on average about 1000 mg). It is often used together with nitrous oxide for endoscopies and induction anesthesia. An important nuance: the drug is capable of causing phlebitis and thrombophlebitis, so it is administered exclusively into a central vein (as a 2.5% solution) and very slowly. In large doses, it can provoke hypotension.
- Sodium oxybutyrate requires extremely slow intravenous administration at a dose of 100–150 mg/kg. It provides superficial anesthesia and is therefore well suited for induction anesthesia in combination with the same barbiturates.
Briefly: answers to topical questions
What stages are distinguished in the clinical course of intravenous anesthesia?
Four main stages are distinguished in the clinical course of anesthesia; however, the main feature of intravenous anesthesia is the absence of the excitation phase.
- Stage I — Analgesia
- Stage II — Excitation (practically absent during intravenous administration)
- Stage III — Surgical stage (includes 4 levels)
- Stage IV — Awakening
Three periods are also distinguished: induction, maintenance, and emergence from anesthesia.
Which drugs belong to the barbituric acid derivative group for intravenous anesthesia?
Two main drugs belong to the barbituric acid derivative group for intravenous anesthesia.
- Sodium thiopental — used for induction of anesthesia; causes rapid onset of anesthetic sleep without an excitation stage.
- Hexobarbital (Hexenal) — used for induction and short-term procedures; causes less respiratory depression compared to sodium thiopental.
What are the absolute contraindications to the use of sodium thiopental?
Contraindications to the use of sodium thiopental include:
- Acute liver failure.
- Phlegmon of the floor of the mouth, root of the tongue, parapharyngeal space, and neck.
In dilated cardiomyopathy, sodium thiopental should not be used for induction due to its pronounced cardiodepressant and vasoplegic effects.
Which drugs are used for total intravenous anesthesia (TIVA)?
For total intravenous anesthesia, the following are used:
- Propofol combined with fentanyl.
A variant of combined total intravenous anesthesia is the combination of intravenous anesthetics (propanidid, etomidate, ketamine, or propofol) with benzodiazepine tranquilizers.
What is the mechanism of action of ketamine on CNS receptors?
The mechanism of action of ketamine on the central nervous system consists in blocking specific receptors.
- Blockade of NMDA receptors — the drug acts as an antagonist of these receptors.
- Elimination of glutamate influence — ketamine suppresses the excitatory effect of glutamate on CNS structures.
As a result, dissociative anesthesia develops, characterized by functional dissociation: depression of certain brain structures occurs while the activity of others is preserved.
To remember the effect of ketamine, use the phrase: "Ketamine — Keeps Blood Pressure Cruising Up". This will help you remember that the drug is indicated for hypotension, but strictly contraindicated in hypertensive patients.
Class and exam questions
Can sodium thiopental be used in patients with liver disease?
In the presence of acute liver failure in a patient, sodium thiopental is strictly contraindicated.
What is the essence of the sensitivity test during barbiturate anesthesia?
Before administering the main dose, 3–5 ml of the solution is injected into the patient and they wait for 30 seconds. This allows timely detection of an acute allergic or severe hemodynamic reaction.
Why does propofol look like milk?
The preparation contains specific solvents — soybean oil, purified egg phosphatide, and glycerin, which form a characteristic white emulsion.
What to do if blood pressure drops during rapid administration of thiopental?
In case of a sharp drop in blood pressure or cardiac depression, administration of the drug must be stopped immediately.
What else to study on this topic
- Clinical criteria for assessing the depth of anesthesia (pupillary and corneal reflexes).
- Technique of emergency mask artificial ventilation in drug-induced apnea.
- Features of fractional administration of anesthetics to prolong anesthesia.
- Interaction of intravenous drugs with inhalational anesthetics during combined anesthesia.
- Pathophysiology of hallucinatory syndrome during emergence from ketamine anesthesia.
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Other topics in the section "CHAPTER 3. ANESTHESIA"
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