Introduction
Anesthesiologists have several strategies for reducing pain, consciousness, mobility, and hemodynamic derangements caused by stress due to surgery in patients. The most common gaseous anesthetics utilized presently are nitrous oxide and volatile fluorinated liquids (Isoflurane, Desflurane, Sevoflurane) administered through specialized vaporizers that convert the liquids into gases that reduce and, at higher doses, eliminate patient awareness. 1842 Diethyl ether was first injected into the patient, which marked the beginning of surgical inhalation anesthesia in the United States. Many chemical compounds have since been used to anesthetize patients and keep them pain-free during surgical procedures. Many anesthetic agents, including Diethyl Ether, Divinyl Ether, Cyclopropane, and Ethylene, were efficient in their application in different fields but presented a fire and explosion risk in the presence of enough oxygen and a source of ignition, such as a spark from electrical circuits or electrical devices. Developments in chlorofluorocarbon chemistry in the 1950s resulted in halogenated, nonflammable, volatile agents that changed the explosive agents.
What Are the Hazards of Anesthetic Gases?
-
Most healthcare workers are potentially subjected to waste anesthetic gases and are at risk of contracting an occupational disease. However, healthcare facilities have significantly improved in controlling anesthetic gas pollution over the years.
-
These have been achieved through using and improving scavenging systems, more effective general ventilation systems, and a strong emphasis on equipment maintenance, leak detection, and careful anesthetic practice.
-
Escape of the gaseous waste into the room air from different parts of the anesthesia delivery system, according to measurements taken in operating rooms (OR) during the clinical administration of inhaled anesthetics.
-
Tank valves, high- and low-pressure connections of the machine, connections in the breathing circuit, faults in rubber and plastic tubing, hoses, reservoir bags, ventilator bellows, and the Y-connector are all potential sources of leaks.
-
Furthermore, improper practices such as leaving gas flow control valves and vaporizers open after using them, liquid inhaled anesthetics leakage, and poorly fitting face masksor inadequately inflated tracheal tube and laryngeal mask airway cuffs can all make a significant contribution to the escape of waste anesthetic gases into the operating room atmosphere.
What Are the Indications of the Gaseous Anesthetics?
-
In the healthcare setting, anesthetic gases, also known as inhaled anesthetics, are used as primary therapy for preoperative sedation and as an adjunct to conventional anesthesia maintenance to intravenous (IV) anesthetic agents ( for example, Midazolam and Propofol).
-
Because of the chemical properties that allow for the rapid administration of an agent into the bloodstream through the pulmonary circulation as opposed to the more indirect route of venous circulation, inhaled anesthetics are commonly used in the clinical setting.
-
Rapid therapeutic effects enable the effective induction and withdrawal of sedation induced by these agents, resulting in proper amnesia, anesthesia, and a shorter recovery period in postoperative care.
-
Though these agents are only suggested for use in the perioperative setting, they significantly benefit critical care by improving the patient’s tolerance for endotracheal intubation, mechanical ventilation, and bedside techniques. In these cases, the recommended use of IV Benzodiazepines (Midazolam, Lorazepam, Diazepam) or Propofol induces the same level of sedation.
What Is the Mechanism of Action of Gaseous Anesthetics?
-
To provide adequate sedation, inhaled anesthetics depress neurotransmission of excitatory paths comprising glutamate, acetylcholine, and serotonin inside the central nervous system (CNS) and strengthen chloride and potassium channels' inhibitory signals.
-
These agents are classified based on their chemical properties as well as their postulated mechanisms of action:
-
Nitrous oxide (N2O) is a nonvolatile gas.
-
Halothane, Isoflurane, Desflurane, and Sevoflurane are volatile gases.
-
-
The primary difference between non-volatile and volatile gases was based on their chemical properties.
-
Non-volatile anesthetics have low boiling points and high vapor pressures, indicating that they exist in gas form at room temperature. In contrast, volatile anesthetics have low vapor pressures and high boiling points, indicating that they exist in liquid form temperature in the room and thereby need vaporizers during administration.
-
Because these agents act on many different receptors, physiologically differentiating these subclasses has proven more difficult.
-
Non-volatile agents, according to current understanding, primarily inhibit NMDA receptors (N-methyl D-aspartate receptors) and glutamate signaling, whereas volatile agents enhance GABA (gamma-aminobutyric acid) signaling.
What Is the Route of Administration of Gaseous Anesthetics?
-
Inhaled anesthetics are peculiar, and they have only one route of administration and various factors that determine the therapeutic index.
-
Every agent has unique administration characteristics:
-
N2O: greater than 100 percent minimum alveolar concentration (MAC), the blood-to-gas partition coefficient of about 0.47, and brain-to-blood partition coefficient of about 1.1
-
Halothane: 0.75 percent minimum alveolar concentration (MAC), a blood-to-gas partition coefficient of about 2.30, and a brain-to-blood partition coefficient of about 2.9
-
Isoflurane has a minimum alveolar concentration (MAC) of 1.4 percent, a blood-to-gas partition coefficient of 1.4, and a brain-to-blood partition coefficient of 2.6.
-
Minimum alveolar concentration (MAC) of Six to seven percent, a blood-gas partition coefficient of 0.42, and a brain-blood partition coefficient of 1.3 for Desflurane.
-
What Are the Adverse Effects of Gaseous Anesthetics?
-
Anesthetic gases have mostly been observed in particular people to induce malignant hyperthermia, despite being relatively benign for immediate adverse reactions. Patients particularly prone to this reaction have heritable modifications in various proteins involved in the modulation of muscular cytosolic concentrations of Ca2+ (calcium ions).
-
The most common modifications observed are the ryanodine receptor/channel encoded by gene RYR1 and the dihydropyridine receptor (DPHR) encoded by gene CACNA1S.
-
Because both sarcoplasmic proteins are involved in the transport of Ca2+, when they are altered and then exposed to volatile gases or succinylcholine, there is an increase in Ca2+ release in skeletal muscle.
-
The rigidity of muscles, increased basal body temperature, rapid onset of tachycardia, hypercapnia, increased potassium levels, and metabolic acidosis are all possible symptoms of this hypermetabolic process.
-
These drugs are also linked to postoperative nausea and vomiting (PONV).
How Are the Adverse Effects of Gaseous Anesthetics Managed?
-
The administration of Dantrolene is required to reverse the side effects quickly. The mode of action in the sarcoplasmic reticulum is depleting and, thereby, releasing Ca2+. Therefore, adequate measures to decrease body temperature and restore acid-base imbalances and electrolytes are advised in addition to Dantrolene administration.
-
Typically, anti-emetic agents (Ondansetron, Metoclopramide, and Dexamethasone) are administered prophylactically and can be administered postoperatively as "rescue" agents to correct nausea and vomiting.
What Are the Contraindications of Gaseous Anesthetics?
-
Anesthetic gases, especially volatile gases, have generalized contraindications in patients with earlier susceptibility to malignant hyperthermia and their use in patients with severe hypovolemia and intracranial hypertension due to the adverse effects of ligand-gated ion channels and cerebral blood flow increasing effects.
-
Halothane- Liver dysfunction after previous anesthetic exposure, decreased ejection fraction related to heart failure, or pheochromocytoma.
-
Isoflurane and Desflurane are contraindicated in patients with severe asthma or active bronchospasm.
-
Sevoflurane is a relative contraindication in patients with renal dysfunction who are undergoing extensive surgical procedures.
Conclusion
When gaseous anesthetics are used, every individual in the operating room must interact effectively to prepare for the onset of the gaseous anesthetic use and any potential adverse effects. The operating room nurse, anesthesiologist, and surgeon must pay close attention and be prepared to help secure the airway during all general anesthesia inductions. In a perfect scenario, the operating room nurse would be by the patient's side to help the anesthesiologist in case of any difficult airway. Likewise, the surgeon should be present and prepared to establish an invasive airway.
