Pharmacology in Anesthesia – Explained by Dr. Jannat Shayyan

📚 Content Table: Pharmacology in Anesthesia

1. Pre-anesthetic Medications

Explained by Dr. Jannat Shayyan
Before starting anesthesia, it’s essential to prepare the patient mentally and physiologically. Sedatives and anxiolytics such as midazolam and diazepam are given to relieve anxiety and promote calmness. These drugs act on GABA receptors in the brain, producing a calming effect without inducing full unconsciousness. Midazolam is preferred due to its rapid onset and short duration. These medications also cause amnesia, so the patient doesn’t remember the procedure. They help stabilize vital signs, especially in anxious patients, and reduce the required dose of induction agents. Care is taken with dosing to avoid respiratory depression. Proper selection enhances patient comfort and safety.

2. Induction Agents

Explained by Dr. Jannat Shayyan
Induction agents are used to quickly render the patient unconscious. Propofol is the most commonly used agent because of its rapid onset and short recovery time. It acts by enhancing GABA activity in the brain, leading to sedation. Thiopental, a barbiturate, is also used in specific cases, although less commonly now. These drugs cause a quick loss of consciousness, making them ideal for the start of general anesthesia. However, they can lower blood pressure and depress respiration, so close monitoring is essential. Induction agents are chosen based on the patient’s health status and surgical needs. Their effects are reversible and short-lived, making them ideal for initiating anesthesia.

3. Inhalational Agents

Explained by Dr. Jannat Shayyan
Inhalational agents maintain anesthesia after induction. Common examples include sevoflurane and isoflurane. These volatile anesthetics are delivered via mask or endotracheal tube, absorbed through the lungs into the bloodstream, and transported to the brain. They reduce consciousness and suppress reflexes, allowing safe surgical intervention. Sevoflurane is preferred for its pleasant smell and quick onset in both adults and children. Isoflurane, though slower, is more cost-effective. These agents are titrated carefully to avoid overdose, and monitoring is essential to manage depth of anesthesia. Their elimination is primarily through the lungs, so respiratory function must remain adequate post-surgery.

4. Muscle Relaxants

Explained by Dr. Jannat Shayyan
Muscle relaxants are essential for surgeries requiring complete muscle paralysis, such as abdominal or thoracic procedures. Succinylcholine is a depolarizing agent that causes brief muscle twitching followed by relaxation. It’s used for rapid intubation. Rocuronium and vecuronium are non-depolarizing agents that block acetylcholine at neuromuscular junctions, preventing muscle contraction. These drugs have different onset and duration times, chosen according to surgical needs. Muscle relaxants don’t cause unconsciousness or pain relief, so they must be used alongside sedatives and analgesics. Reversal agents are used at the end of surgery to restore muscle function. Close neuromuscular monitoring is critical to ensure safety.

5. Analgesics (Pain Control)

Explained by Dr. Jannat Shayyan
Pain control is a cornerstone of anesthesia. Opioids such as fentanyl and morphine are potent analgesics used intraoperatively to reduce pain perception. They act on opioid receptors in the brain and spinal cord. Fentanyl has a rapid onset and is ideal for short procedures, while morphine provides longer-lasting relief. NSAIDs like ketorolac are used for post-op pain and reduce inflammation. These drugs are combined with other anesthetics to ensure patient comfort during and after surgery. Overdose or inappropriate use of opioids can cause respiratory depression, so their administration is strictly controlled. Multimodal analgesia is now preferred to reduce opioid use and side effects.

6. Local Anesthetics

Explained by Dr. Jannat Shayyan
Local anesthetics block nerve impulses in a specific area, allowing minor surgeries without affecting consciousness. Lidocaine and bupivacaine are widely used. They block sodium channels in neurons, preventing pain transmission. Lidocaine acts quickly but for a shorter duration, while bupivacaine provides longer anesthesia. These drugs are used for dental, obstetric, and orthopedic procedures. They can be given via injection, topical creams, or nerve blocks. Care must be taken to avoid overdose, which can cause CNS or cardiac toxicity. Local anesthetics offer excellent pain control with minimal systemic effects, making them suitable for outpatient procedures and regional anesthesia.

7. Anticholinergics

Explained by Dr. Jannat Shayyan
Anticholinergics like atropine and glycopyrrolate are used to reduce secretions and prevent bradycardia during surgery. They block the parasympathetic nervous system, reducing saliva and mucus production, which improves airway visibility and reduces aspiration risk. Atropine also increases heart rate, helpful in cases of vagal stimulation during surgery. Glycopyrrolate is preferred for its lack of CNS side effects. These drugs are especially important in pediatric anesthesia and when using inhalational agents that can increase secretions. Dosing must be precise to avoid dry mouth, urinary retention, or excessive tachycardia. Their preventive role significantly improves surgical conditions and patient safety.

8. Reversal Agents

Explained by Dr. Jannat Shayyan
At the end of surgery, reversal agents are given to undo the effects of muscle relaxants and opioids. Neostigmine is used to reverse non-depolarizing muscle relaxants by increasing acetylcholine levels at the neuromuscular junction. It’s usually combined with glycopyrrolate to counteract unwanted side effects like bradycardia. Naloxone is used to reverse opioid overdose by competitively binding to opioid receptors. These agents must be administered carefully to avoid complications such as sudden pain return or muscle weakness. Their timely use ensures smooth recovery from anesthesia and helps patients regain normal function postoperatively. Proper reversal is crucial for safe patient discharge from anesthesia care.

9. Antiemetics

Explained by Dr. Jannat Shayyan
Nausea and vomiting are common side effects after anesthesia. Antiemetics such as ondansetron and metoclopramide are used to prevent and treat these symptoms. Ondansetron blocks serotonin receptors in the brain’s vomiting center, offering strong and safe relief. Metoclopramide enhances gastric emptying and also acts centrally. These drugs improve patient comfort and reduce complications like aspiration. They are often given prophylactically before the end of surgery. Antiemetics are especially important in high-risk patients, such as those with a history of motion sickness or after abdominal surgery. Proper use ensures faster recovery and better overall patient satisfaction postoperatively.

10. Emergency Drugs

Explained by Dr. Jannat Shayyan
Emergency drugs are vital for handling unexpected crises during anesthesia. Epinephrine is used in cardiac arrest and anaphylaxis; it increases heart rate and blood pressure. Ephedrine is used to treat hypotension by stimulating adrenergic receptors. Atropine is given in bradycardia to speed up the heart rate. These drugs must be readily available in the operating room and used with precision. They require a deep understanding of pharmacodynamics and pharmacokinetics to avoid worsening the situation. Timely administration can be life-saving. Training in their use is a mandatory part of anesthesiology practice to ensure patient survival in emergencies.