Subspecialty Surgery Anesthesia Kingdom of Bahrain Arabian Gulf University College of Medicine and Medical Sciences Subspecialty Surgery Anesthesia Ali Jassim Alhashli

General Anesthesia What is the definition of General anesthesia? It is a drug-induced loss of consciousness during which the patient could no be awaked even with painful stimuli. In addition, there is impaired ability to ventilate thus patient must be intubated. What are the stages of anesthesia? Stage-I: analgesia. Stage-II: excitement. Stage-III: surgical anesthesia. Stage-IV: medullary depression. What are the steps taken during general anesthesia? Induction anesthesia: which can be IV or via inhalation (more details in next slide). Neuromuscular blockage (they only cause muscle relaxation; more details in next slides). Maintenance of anesthesia: either by using inhaled agents (e.g. NO) or IV agents (e.g. propofol and ketamine). Emergence: during which the patient gains back his consciousness. Make sure patient has full muscle strength and that protective airway mechanisms are present before extubation. What is malignant hyperthermia? It is an autosomal dominant (AD) disorder which is triggered by exposure to an anesthetic agent. Pathophysiology: there is impaired reuptake of calcium by sarcoplasmic reticulum in muscles. Clinical features: hyperthermia, hypercarbia, hypoxia, acidosis, muscle rigidity, tachycardia and ventricular arrhythmias. Management: discontinuation of anesthetic agent + dantrolene sodium/benzodiazepines General Anesthesia

General Anesthesia Neuromuscular blockage: It is considered as the 2nd step taken during general anesthesia. Mechanism of action: causing muscle relaxation via blocking post-synaptic acetylcholine receptors in the neuromuscular junction. This is needed to facilitate intubation, decrease muscle tone and allow access to the surgical field. There are two types: Depolarizing agents: Example: succinylcholine. Mechanism of action: acetylcholine receptor agonist. Use: they cause twitching/fasciculations followed by paralysis and used for SHORT procedures. Reversal: fresh plasma transfusion. Non-depolarizing agents: Example: pancuronium. Mechanism of action: competitive antagonist for acetylcholine receptors. Use: they cause muscle paralysis and used for LONG procedures. Reversal: acetylcholine-esterase inhibitors (e.g. neostigmine). Examples on IV medications used for: Amnesia: benzodiazepines (e.g. diazepam, lorazepam and midazolam), barbiturates or ketamine. Analgesia: IV acetaminophen, NSAIDs, opiates or ketamine.

Methods for airway support during general anesthesia: Non-definitive: Jaw thrust or head tilt-chin lift methods. Bag mask ventilation: Disadvantages: risk for aspiration if patient is unconscious, airway patency cannot be insured, operator fatigue, precise tidal volume cannot be delivered. Oropharyngeal airway or nasopharyngeal airway. LMA (Laryngeal Mask Airway): there is a risk for aspiration. Definitive: Cricothyrotomy or tracheostomy. Endotracheal intubation: Advantages: insuring patency of the airway, no risk for aspiration, positive pressure ventilation is provided. Disadvantages: difficult to insert and there is need for muscle relaxants. The 8 P’s of rapid sequence intubation: Prepare: equipments (endotracheal tube, suction, light source and laryngoscope). Pre-treat: drugs. Position: sniffing position. Pre-oxygenate: 100% oxygen. Pressure: Sellick. Placement of the tube. Position of the tube (confirmed by: inspection of bilateral chest movement, auscultation for breath sounds over both lung fields, CO2 detection and CXR). Notice that the tip of endotracheal tube must be 2 cm above the carina of the trachea. If it is pushed further, it might enter the right main bronchus resulting in right-side pneumothorax and left-side atelectasis. If the position of endotracheal tube is too shallow, this can result in: accidental extubation, trauma to vocal cords or laryngeal paralysis. General Anesthesia

General Anesthesia What are the complications which might occur during intubation? Dental damage. Esophageal intubation. Laryngeal trauma. Lacerations. When do you suspect esophageal intubation? Presence of gastric contents in endotracheal tube. Distention of the stomach with ventilation. Abnormal sounds with auscultation. Hypoxia.

IMPORTANT: in regional anesthesia, there is NO CNS depression (patient DOES NOT lose his consciousness) unless there is an overdose of the anesthetic agent. Most important two types of regional anesthesia are: Epidural anesthesia. Spinal anesthesia. They are used with most surgeries performed below the level of the umbilicus. The use of regional anesthesia is contraindicated when there is allergy of infection of the site, sepsis, increased intracranial pressure or long procedures. What are the structures penetrated during regional anesthesia? Skin → subcutaneous tissue → supraspinous ligament → infraspinous ligament → ligamentum flavum → dura and arachenoid. Notice that spinal cord extends to the level of (L2) while the nerve roots (cauda equine) extend from (L2 – S2). Epidural anesthesia: The anesthetic agent is produced between ligamentum flavum and dura. Effect is seen after 10 minutes. It is done using a catheter and is MORE DIFFICUL when compared to spinal anesthesia. ADR: infection, hematoma, hypotension and bradycardia. Spinal anesthesia: The anesthetic agent is introduced to subarachenoid space (CSF). Insert your needle between (L3 – L4) or (L4 – L5). Effect is seen after 5 minutes. No catheter is used and it is EASIER when compared to epidural anesthesia. ADR: infection and post-spinal headache. Regional Anesthesia

Local Anesthesia Mechanism of action: they block the transmission of nerve impulses by binding to Na-channels and inhibiting Na-influx. There are two types of local anesthetics: Amide (e.g. lidocaine). Ester (e.g. procaine or tetracaine). The selection of local anesthetics is mainly depending on: Liposolubility (the more lipid-soluble the faster is the effect and penetrance to the nerves). Duration of effect (if protein binding is more, effect will be more). Local anesthesia toxicity: Features: numbness of tongue and peri-oral area with metallic taste, CNS and respiratory depression, vasodilation and hypotension and drowsiness/tetanus/muscle twitching. Management: 100% oxygen. Diazepam. Intralipid (to bind the local anesthetic). Manage arrhythmia (if present).