Introduction
Anesthesia is a medicine used to block pain messages to the brain. There are different modes by which anesthesia can be delivered to the human body. It can be intravenous or injectable routes or inhalation mode. There are different types of anesthesia. General, regional, and local anesthesia. Inhalation anesthetics are used in only general anesthesia, whereas injectable anesthesia is used in all three types of anesthesia. This topic gives a detailed view of inhalation anesthesia.
What Is Inhalation Anesthesia?
The anesthetics used in surgery and delivered by inhalation method in gaseous form are called inhalation anesthetics. Inhalation anesthesia is used in general anesthesia to make the patient unconscious during surgery. The commonly used inhalation anesthetics are Isoflurane, Sevoflurane, Nitrous oxide, and Desflurane, administered by a face mask, laryngeal mask, or tracheal tube connected to an anesthetic vaporizer and an anesthetic delivery system. There are three forms of inhalation anesthetics: volatile anesthetics, gasses form, and hyperbaric anesthetic.
What Are the Indications of Inhalation Anesthetics?
Inhalation anesthetics are commonly used in operation theaters to maintain general anesthesia. Some are used along with injectable anesthetics to keep the sedation. They are used in the ICU for the purposes given below:
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Sedation.
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Bronchospasm (muscle of lungs constrict).
How Does Inhalation Anesthetic Work?
The inhaled anesthetics work on the central nervous system. It blocks the nervous system signals to go to the brain by depressing neurotransmission. It makes the patient go to sleep while performing surgery on him. The patient feels nothing during surgery as he will be unconscious due to the anesthetic dosage working on the central nervous system. The patient breathes by the tube installed in the throat during surgery.
How Is Inhalation Anesthetic Administered?
They are mainly inhaled through a face mask, laryngeal mask airway, or a tracheal tube connected to an anesthetic vaporizer and an anesthetic delivery system. Mostly used in children to give them a pain-free environment for surgery. A gold standard to measure the potency of the inhaled anesthetic is called minimum alveolar concentration (MAC). Minimum alveolar concentration can vary depending upon old age, toxication of drugs, or hypothermia, which will decrease its levels, whereas Cocaine and alcohol abuse increases its level in patients. All inhaled agents have different minimum alveolar concentration properties. The higher the minimum alveolar concentration, the lower the gas potency needed for sedation. The inhaled anesthetics with minimum alveolar concentration values are Isoflurane (1.2 %), Sevoflurane ( 2.6 %), and Nitrous oxide (104 %).
What Are Different Types of Inhaled Anesthetics?
There are three different types of inhalation anesthetics. They are:
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Volatile Anesthetics - Volatile anesthetics agents are in liquid form at room temperature and evaporate on inhalation. They do not dissolve in water. These can be used in the induction and maintenance of general anesthesia with less effect on the organ systems. The volatile agents include Isoflurane, Desflurane, Sevoflurane, and Halothane. They are used because:
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They are odorless and pleasant to inhale.
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They are safe to use with all age groups.
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They can be used comfortably during pregnancy.
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They show rapid onset and offset.
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They are cheap and easy to transport.
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They have long shelf lives.
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They are easy to administer and monitor.
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They are non-inflammable and environmentally friendly.
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Gases - These anesthetic agents are in the form of gas. The gaseous anesthetic agents are the vapors that are inhaled. The gases are nitrous oxide, cyclopropane, and xenon. They are administered by flow meters and stored in cylinders. All the gases are unsuitable for use like cyclopropane is inflammable and xenon is expensive. So, the good use of nitrous oxide is done.
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Hyperbaric Anesthesia - Other gases like nitrogen come under it. But they are not often used in surgical procedures.
What Are the Adverse Effects of Inhalation Anesthetic?
Adverse effects of the use of inhaled anesthetics are:
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Postoperative nausea and vomiting are commonly present side effects. Usually, Dexamethasone is recommended to administer after surgery to reduce nausea and vomiting.
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Malignant hyperthermia in patients with a family history of malignant hyperthermia. So, the patient is not recommended for volatile agents and to go for injectable anesthetics.
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Bronchospasm in patients dealing with asthma due to the irritating smell of Desflurane and Isoflurane.
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Decrease in blood pressure by the Isoflurane, Sevoflurane, and Desflurane.
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Diffusion hypoxia by nitrous oxide discontinuation. The patient is recommended to have oxygen through a mask.
What Are Contraindications to Inhalation Anesthetics?
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Malignant hyperthermia - It is abnormally high body temperature.
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Severe hypovolemia - It is a condition in which there is low blood plasma.
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Pneumothorax - The condition in which air leaks into the lungs and chest wall.
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Pulmonary hypertension - The blood pressure affecting the arteries of the lung.
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Craniotomies - (surgery in which removal of the bone from the skull), bowel surgery (surgery related to intestines or bowel), and middle ear surgery for nitrous oxide.
Is Inhaled Anesthetic Toxic?
Yes, they can be toxic on overuse. If the inhaled anesthetic agents are used more than the required dose or overdose, they can become toxic. Several acute and chronic toxicities can occur with inhaled agents. Acute toxicity includes carbon monoxide poisoning, nephrotoxicity, and hepatotoxicity. Chronic toxicity has hematotoxicity, teratogenic effects, and carcinogenic toxicities. Some anesthetic agents with toxicity are :
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Nitrous oxide can cause hypoxia which can be managed by supplemental oxygen supply to the lungs.
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Halothane causes hepatotoxicity and hepatic failure.
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Sevoflurane can cause nephrotoxicity.
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Desflurane can cause carbon monoxide poisoning.
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Nitrous oxide also produces hepatotoxicity on prolonged use.
Can a Child and the Elderly Use Inhalation Anesthetics?
The inhalation anesthetics are mostly used in the pediatric population to give them a pain-free environment during surgery. Old age can also have the benefit of inhaled anesthetics. The dosage varies accordingly. The elderly requires reduced minimum alveolar concentration, and an infant below six months especially requires increased minimum alveolar concentration.
Conclusion
Inhaled anesthetics are the agents used to anesthetize the patient during surgery. They work on the body's central nervous system and block the brain's neurological signals. They make the patients asleep during surgical procedures to inhibit pain. They are indicated in the intensive care unit for sedation and, in some cases, status epilepticus. The most commonly used inhalation anesthetics are Sevoflurane, nitrous oxide, and Desflurane, administered with a face mask. They can be distributed to all types of patients. However, they cause postoperative nausea and vomiting after use. Contraindicated in cases of malignant hyperthermia. They have a toxic effect on overuse.
