Want to know about those anaesthetic drugs that will take you to the moon and back? While we strictly advise agaist the use of pharmaceuticals for recreational purpose, here’s a list of the most common anaesthetic drugs that will take you to another world while you’re undergoing surgery. You can read on the overview of anaesthesia to better understand these drugs.

Types of Anaesthetic Drugs

Anaesthetic drugs can be classified in different ways. But mainly according to the purpose. We classify the drugs used for general anesthesia as inducers, which induce anesthesia in the patient, and adjuvants, which supplement the effects of the inducers.

Inducers

The induction phase of anesthesia marks the transition from consciousness to unconsciousness, a critical step in ensuring patient comfort and safety during surgical procedures.

General anesthesia establishes a reversible state that includes:

●Hypnosis

●Amnesia

●Analgesia

●Akinesia

●Autonomic and sensory block

,Let’s delve into the world of induction agents, unraveling their diverse pharmacological properties and clinical implications.

Propofol A.K.A. Milk of Amnesia

Propofol serves as the preferred induction agent for the majority of patients due to its rapid onset and offset of anesthesia. Its primary mechanism of action is activation of the gamma-aminobutyric acid_A (GABA_A) receptor complex, the chief inhibitory neurotransmitter of the central nervous system. Propofol is also an antagonist of the N-methyl-D-aspartate (NMDA) receptor. Typically administered at a dose of 1 to 2.5 mg/kg, adjustments are made for older patients or those with hemodynamic compromise. Its advantages include rapid onset, along with antiemetic and antipruritic properties. Additionally, propofol facilitates bronchodilation and reduces cerebral metabolic rate of oxygen (CMRO2), cerebral blood flow (CBF), and intracranial pressure (ICP). However, potential adverse effects include dose-dependent hypotension and respiratory depression, along with pain during injection, microbial contamination risk, and rare instances of anaphylaxis in susceptible individuals.

Etomidate

Etomidate is preferred for patients experiencing hemodynamic instability from any cause. It is an imidazole derivative that acts directly on the gamma-aminobutyric acid_A (GABA_A)receptor complex to block neuroexcitation and produce anesthesia. Typically administered at a dose of 0.15 to 0.3 mg/kg, adjustments are made for profound hypotension. Its advantages include rapid onset and offset, as well as hemodynamic stability without changes in blood pressure (BP), heart rate (HR), or cardiac output (CO). Additionally, etomidate reduces cerebral metabolic rate of oxygen (CMRO2), cerebral blood flow (CBF), and intracranial pressure (ICP). However, potential adverse effects include a high incidence of postoperative nausea and vomiting (PONV), pain during injection, involuntary myoclonic movements, absence of analgesic effects, and transient acute adrenocortical suppression.

Ketamine

Ketamine is a valuable option for hypotensive patients or those at risk of hypotension, providing profound analgesic effects. Typically administered at a dose of 1 to 2 mg/kg, adjustments are made based on specific patient characteristics. Its advantages include rapid onset, cardiovascular stimulation resulting in increased blood pressure (BP), heart rate (HR), and cardiac output (CO), as well as profound analgesia, bronchodilation, and preservation of airway reflexes and respiratory drive. However, potential adverse effects include increased myocardial oxygen demand and pulmonary arterial pressure, neurologic effects such as psychotomimetic effects and increased cerebral blood flow (CBF) and intracranial pressure (ICP), as well as increased salivation.

Methohexital

Methohexital specifically induces electroconvulsive therapy (ECT) by lowering the seizure threshold and facilitating convulsions The primary mechanism of action is noncompetitive antagonism of glutamate at the N-methyl-D-aspartate (NMDA) receptor-cation channel complex, causing neuroinhibition and anesthesia. Also, ketamine excites opioid receptors within the insular cortex, putamen, and thalamus, thereby producing analgesia. Typically administered at a dose of 1.5 mg/kg, it offers advantages in ECT procedures by reducing cerebral metabolic rate of oxygen (CMRO2), cerebral blood flow (CBF), and intracranial pressure (ICP). However, it is noteworthy that methohexital has limited availability and is associated with potential adverse effects, including dose-dependent hypotension and respiratory depression, involuntary myoclonic movements, pain during injection, and contraindication in patients with porphyria.

Adjuvant Anaesthetic drugs

During the induction of general anesthesia, it’s common practice to administer one or more adjuvant IV agents. These serve to dull the sympathetic stress response and cough reflex during laryngoscopy and intubation, alleviate pain caused by the injection of irritating induction agents, and decrease the required dose of the primary sedative-hypnotic. Typically, healthcare providers opt for a short-acting opioid, lidocaine, or a benzodiazepine like midazolam or remimazolam for this purpose

Fentanyl

Fentanyl, a potent opioid, is commonly used in anesthesia induction. Its dosage ranges from 25 to 100 mcg or 0.5 to 1 mcg/kg, often administered in divided doses. It serves multiple purposes during induction, including the suppression of airway reflexes to prevent coughing and bronchospasm during laryngoscopy and intubation, attenuation of stress responses to prevent tachycardia and hypertension, and minimization of pain caused by the injection of other induction agents. However, caution is warranted as it can lead to dose-dependent respiratory depression, pruritus, and postoperative nausea and vomiting.

Sufentanil

Sufentanil, a highly potent opioid, shares similarities with fentanyl but is even more powerful. Its recommended dosage is 0.05 to 0.1 mcg/kg, often given in divided doses. Like fentanyl, it suppresses airway reflexes, attenuates stress responses, and reduces pain from induction agents. However, it also carries the risk of dose-dependent respiratory depression, emphasizing the need for careful dosing and monitoring.

Lidocaine

Lidocaine, a local anesthetic, has applications in anesthesia induction. It is a class 1B anti-arrhythmic agent that works by reversibly binding sodium ion channels and holding them open with a net effect of preventing depolarization. Typically, it is administered at a dose of 0.5 to 1.5 mg/kg for airway reflex suppression and 20 to 30 mg total to alleviate pain from the injection of other agents. Its primary functions include suppressing airway reflexes, reducing airway responsiveness, minimizing pain from induction agents, and supplementing sedation. However, caution is necessary due to its potential to mildly increase airway tone and increase ventricular rate in patients with atrial fibrillation.

Midozolam

Midazolam, a benzodiazepine, is commonly used for its anxiolytic and sedative properties during induction. Typically administered in 1 to 2 mg increments, it effectively reduces anxiety, induces amnesia, supplements sedation, and acts as an anticonvulsant. However, it may cause mild systemic vasodilation and decreased cardiac output, particularly in hemodynamically unstable or hypovolemic patients. Additionally, dose-dependent respiratory depression is a concern, especially when coadministered with opioids.

Inhalation Anaesthetic Drugs

Inhalation anaesthetics are maintainers. After induction of anaesthesia with an inducer such as propofol, these will keep the patient under at a constant level of anaesthesia.

Nitrous Oxide A.K.A Laughing Gas

Also known as laughing gas, nitrous oxide is a colorless, sweet-smelling gas with minimal pungency. It boasts a very low blood:gas partition coefficient, rendering it rapidly eliminated from the body and resulting in negligible effects on blood pressure and vascular tone. Nitrous oxide’s potency, as indicated by its oil:gas partition coefficient, is very low, contributing to its minimal inotropic and chronotropic effects. It is supplied in pressurized bottled gas form and delivered via flowmeter. While it is non-flammable, its use may be associated with nausea and emesis.

Halothane:

Halothane, once widely used but now less common, is a colorless, sweet-smelling liquid with moderate pungency. Its high blood:gas partition coefficient results in significant solubility, leading to dose-dependent hypotension and potential cardiovascular effects. The addition of 0.01 percent thymol maintains the stability of halothane, which can accumulate in the vaporizer and eventually cause the remaining liquid to turn yellow. Despite its negative inotropic and chronotropic effects, halothane is non-flammable and delivered via a vaporizer. However, its use has diminished due to associated adverse events such as nausea, emesis, bradycardia, and asystole. Despite this, its continued use persists in resource-challenged countries due to its affordability.

Isoflurane

Isoflurane, a colorless, sweet-smelling liquid with high solubility, is favored for its moderately high potency and vasodilatory effects. Its cardiovascular impact includes slight negative inotropic and chronotropic effects, making it suitable for use with a vaporizer. Like halothane, isoflurane may induce nausea and emesis, albeit potentially accompanied by significant tachycardia.

Sevoflurane

Sevoflurane, another colorless liquid with a sweet odor, exhibits low solubility and vasodilatory properties. It is delivered via a vaporizer mounted on the anesthesia machine. Its cardiovascular effects are similar to isoflurane, albeit with a higher likelihood of tachycardia at higher concentrations. Anesthesia providers commonly administer Sevoflurane through a vaporizer during inhalational inductions, and it often leads to nausea and emesis as common side effects.

Desflurane

Desflurane, characterizes initial vasoconstriction followed by vasodilation, as it is a colorless liquid known for causing airway irritation and sympathomimetic effects. Anesthesiologists typically administer it via an electric heated vaporizer, as it provides rapid onset and offset of anesthesia. However, its use may induce nausea, emesis, and airway irritation. Desflurane undergoes the least metabolism of all potent volatile agents.