IV Anesthesia or intravenous anesthesia is when anesthesia is given through a vein through injections. Anesthesia is usually started or induced with intravenous or IV anesthesia drugs.
The different IV Anesthesia drugs are:
- Thiopental sodium
- Some Steroids
Ultra short acting barbiturates
The ultra-short acting barbiturates administered as IV Anesthesia to produce general anesthesia are the thiobarbituratcs (thiopental, thiamytal and thiobarbitone) and the methylated oxy barbiturates (hexobarbitone and methohexitone). The compound employed most commonly is thiopental.
THIOPENTAL IV anesthesia
Thiopental sodium is readily soluble in water but the solution deteriorates on keeping. The clinically used solution is intensely alkaline with a pH varying from 10.5 to 11. High alkalinity causes local irritation and venous thrombosis. Given IV, it rapidly induces hypnosis and anesthesia without analgesia.
The induction is very quick and pleasant. The subject passes through the stages of hypnosis and deep sleep to anesthesia. Consciousness is lost first, and then the reflex activity and muscle tone and lastly, the vital medullary centers are depressed.
Pupils react to light and remain contracted in light hypnosis. There may be nystagmus or divergent strabismus. The corneal reflex remains active until deep anesthesia is achieved. Cerebral blood flow and cerebral metabolic rate are reduced and there is a marked reduction of intracranial tension.
A fairly reliable sign of an adequate induction by thiopental is the absence of the eyelid reflex. Presence of swallowing, phonation and reflex movements of eyes during anesthesia also indicate need for further injection.
Though the reflexes return in 10-30 minutes, the patient remains disoriented for several hours after stoppage and hence, must not be left alone.
Absorption, fate and excretion of thiobarbiturates
The very short duration of action is attributed to its high lipid solubility. With successive doses, body fat depots get saturated with the drug. The rapid metabolism of the drug by liver may also contribute to its short duration of action.
Slow release of the stored drug back into the plasma is responsible for the continuation of drowsiness observed after the cessation of anesthesia. Thiobarbiturates readily cross the placental barrier and appear in breast milk.
Therapeutic uses of Thiopental IV anesthesia
- For induction of general anesthesia.
- As anesthetic agent for operations of short duration e.g. fracture reduction, dilatation and curettage, laryngoscopy and bronchoscopy.
- As an anesthetic in patients with history of malignant hyperthermia.
- As anticonvulsant in the emergency treatment of intractable convulsions.
Advantages of IV thiopental IV anesthesia
- Non-explosive and non-irritant; easy to administer.
- Rapid and smooth induction, and rapid recovery after small doses.
- Quiet respiration; no cardiac arrhythmias; and
- Nausea, vomiting, excitement and postoperative complications infrequent.
Disadvantages of thiopental IV anesthesia
- Conducting anesthesia and judging its depth are difficult as the usual stages of anesthesia are not discernible.
- Pharyngeal and laryngeal reflexes persist, permitting occurrence of coughing, apnea, laryngospasm and bronchospasm. Hence, equipment for controlled ventilation must be available.
- Depression of respiratory center which becomes less sensitive to CO2.
- Depresses myocardium and vasomotor center; hypotension and cardiac arrhythmias can occur. Must never be given to a patient who is sitting such as in a dental chair.
- Poor analgesic and muscle relaxant.
- Highly irritant if extravasated; nerve palsy and limb gangrene reported.
- Relaxes gastro esophageal sphincter, causing silent regurgitation; and
- Can precipitate an acute attack in acute intermittent porphyria.
- Barbiturate anesthesia is to be used with great caution in the presence of hepatic and/or renal damage, in shock, in airway obstruction, in individuals with a past history of bronchial asthma and severe cardiovascular disease.
Preparations of Thiopentone
Thiopental sodium 0.5 to 1.0 g. powder. It is used as a freshly prepared, 2.5% solution for IV anesthesia.
Twice as potent as thiopental and claimed to be shorter acting. It is used as 1 per cent solution and may be less irritant to veins but as damaging to the arteries as thiopental.
This short acting benzodiazepine is used either IM as a premedication or IV for sedation for endoscopic procedures and for induction of anesthesia. The IV dose is 2.5 to 7.5 mg; the usual 1M dose is 5 mg.
With administration of midazolam for IV anesthesia, the same precautions are required as with IV diazepam. It is water soluble and less irritant to the veins than diazepam. It has also been used by subcutaneous infusion (by means of a syringe pump) as an anticonvulsant. It is a relatively safe drug.
This non-barbiturate general anesthetic agent is related to phencyclidine. It acts as an antagonist at NMDA receptors. It probably acts on the cerebral cortex, particularly the limbic system.
It has analgesic property in sub narcotic doses, and light anesthesia usually does not cause depression of the protective pharyngeal and laryngeal reflexes. It is a potent bronchodilator.
Given as IV Anesthesia it is quick acting although the onset of action is slower than that of thiopental. Following a single dose, it induces a state of dissociative anesthesia characterized by complete analgesia combined with amnesia; the patient can open his eyes and can obey instructions.
Respiratory support is not needed. Analgesia lasts for about 40 minutes whereas anesthesia lasts for about 15 minutes only. The pattern of sleep is different from that which occurs with barbiturates.
Anesthesia can be induced by both IM (5-10 mg/kg) and FV (1-2 mg/kg) routes. A dose of 0.5 mg/kg IM or IV produces adequate analgesia which can be maintained by 0.25 mg/kg.
The drug increases the BP, heart rate and cardiac output by raising the blood levels of NA and can be used in patients in shock. However, it should be avoided in patients with ischemic heart disease.
Disadvantages of ketamine IV Anesthesia
- It sometimes causes nystagmus, involuntary movements and hypertonia.
- It may cause delirium, hallucinations and colorful dreams during induction and recovery, especially in adults. Diazepam or midazolam given rapidly abolishes these disturbances.
- Rarely, laryngospasm may occur; salivation may be troublesome.
- Muscular relaxation is inadequate.
- It increases intraocular and intracranial pressures.
- It is a drug of abuse (Day Rape Drug).
Therapeutic uses of Ketamine IV anesthesia
- The drug is advocated as an inducing agent and for maintenance of anesthesia during short-lasting diagnostic procedures like cardiac catheterization and bronchoscopy.
- It has been used in adults for such short procedures as the dressing of burns, forceps delivery, breech extraction, manual removal of the placenta and dental work.
- It can be used in children.
It is not used:
- In patients suffering from hypertension, cardiac decompensating or a cerebrovascular accident.
- For surgery of the pharynx, larynx or bronchi.
- In abdominal surgery, as it relieves visceral pain poorly.
- In thyrotoxic patients, in whom it may cause rise in blood pressure.
- In pregnant women at term, because of its oxytocic activity. However, it may be used during caesarian section as it causes less fetal and neonatal depression.
- During operations on the eye, as it causes a rise in the intra-ocular pressure; and
- In the presence of psychiatric disorders such as acute psychosis and schizophrenia.
- Barbiturates and diazepam are chemically incompatible with ketamine. They should never be administered from the same syringe or via the same infusion set.
This drug, a carboxylated imidazole, has potent hypnotic and anesthetic properties. A single IV dose of 300 mcg/kg produces loss of consciousness within 10 seconds and a state of anesthesia, followed by sleep. Recovery is rapid and complete.
Cardiovascular and respiratory changes are minimal. In fact, cardiovascular stability during and after induction is considered to be a major advantage of etomidate; hence it is preferred in patients prone to hemodynamic instability.
The drug, however commonly causes nausea and vomiting. Further, it inhibits certain adrenocortical enzymes, resulting in suppression of adrenocortical stress response. Rarely, it causes involuntary movements. It is primarily used for induction.
This intravenous anesthetic causes rapid induction and rapid recovery with small hangover effect. It is generally used for induction and maintenance of general anesthesia.
In equianesthetic doses, it produces a slightly greater degree of respiratory depression than thiopental. It causes dose- dependent cortical depression and is an anticonvulsant. It is largely (88%) metabolized by the liver.
Advantages of Propofol IV anesthesia
- It has specific antiemetic action and is less likely to cause bronchospasm.
- It has no effect on the hypoxic, pulmonary vascular reflexes.
- Because of quick recovery from anesthesia, it may be preferred to thiopental for day-care surgery.
- It is safe during pregnancy.
- It is used by IV infusion for maintenance of anesthesia.
Steroids IV anesthesia
Various steroids such as althesin introduced earlier have now been withdrawn because of their unacceptable adverse effects.
Pregnenolone (Etanolol) is a naturally occurring metabolite of 17-alpha-hydroxy progesterone and is 3 times as potent as propofol. It is not used in practice.