1. Dr.Arkan Jaafar , M.D. Anesthesiologist Medical college of Mosul
GENERAL ANESTHESIA
Dr.Arkan Jaafar , M.D.
Anesthesiologist
Medical college of Mosul

2. Definition of General anesthesia GA
Delivery of anesthetic drugs (inhaled or infused) to produce a level of CNS depression with the following goals :
Anesthesia :Hypnosis , loss of consciousness (reversible)
Analgesia : pain control
Amnesia : loss of recall
Areflexia : muscle relaxation ( this is not always required)
Autonomic Areflexia : decrease sympathetic nervous system (SNS) function
Anxiolysis : Intra-operative & Post-operative

4. INTRAVENOUS ANESTHETICS IV
Thiopental (sodium thiopentone)
Ultrashort acting thiobarbiturate
Most commonly used as an induction agent
Short duration of action 6-8 min
After IV bolus , rapidly distributes to vessel rich organs (brain,liver,heart,kidney) thus achieves unconsciousness in approximately 30 sec
Metabolism & elimination occur at a slower rate resulting in residual effects (usually sedation) during post-anesthesia recovery which may last hours

5. Propofol (Diprivan)
Used for induction and/or maintenance of anesthesia
Thick white soybean-based solution
Metabolism & elimination much more rapid due to increase rate of liver metabolism compared to thiopental
Less residual sedative effect, patients recover sooner, thus popular for outpatient surgery
More suited for continuous infusion than thiopental due to rapid elimination
More expensive

6. Ketamine: -
Cause dissociative anesthesia; - that the patient appears conscious (e.g. eye opening, swallowing, muscle contracture) but unable to process or respond to sensory input.
Use as i.v. & i.m. anesthetic agent.
Can cause hallucination, but it is less common in children & in patient premedicated with benzodiazepines.
Onset of anesthesia is slower than that with thiopental.
Duration of action longer than thiopental, its (10-15 min).
Cardiovascular stimulant (BP well maintained in poor risk patient e.g. shock state).
Bronchodilator

7. Etomidate: -
Onset is rapid.
There is pain at injection site.
It is least likely of commonly used agent to cause depression of the CVS or release of histamine.
It may depress the cortisol production especially if given by infusion

8. Oral & injectable formulations are available
Benzodiazepines ( eg. Diazepam.midazolam,lorazepam)
Used as a premedication prior to induction or as an induction agent in combination with other drugs
Oral & injectable formulations are available
Act on a specific brain GABA receptors to produce selective anti-anxiety & sedative effects
Duration of action long but variable/somewhat unpredictable
Benzodiazepine antagonist→→ Flumazenil

9. Opioids
Opioids used in anesthesia : morphine , codeine , meperidine , fentanyl, sufentanyl, alfentanyl, remifentanil
Indications
Opioids used for pre, intra, post-operative analgesia
Also used as an induction agent alone or as adjuvant
Can be administered IV , IM , PO

10. General effects of morphine (prototype opioid)
CNS (depression) :analgesia , mood changes ,sedation , respiratory depression , decreased cough reflex
CNS (excitation): miosis , nausea & vomiting ,hyperreflexia
CVS : vasodilatation , orthostatic hypotension
Respiratory :central depression , bronchial constriction
GI : constipation , biliary colic
GU : urinary retention
Other : histamine release ,smooth muscle contraction (e.g. biliary & bladder sphincters)
Opioid antagonists (e.g. naloxone , naltrexone)

11. Volatile inhalational agents :
Halothane , Isoflurane , Enflurane , sevoflurane
Characteristics : liquid , colorless, non-flammable ,non-explosive
vaporizer delivers controlled concentration of anesthetic agent to respiratory system of the patient via anesthetic machine

12. Nitrous oxide N2O
Characteristics : gas , colorless ,mild sweet odor at room temperature
Uses : Analgesia
Adverse effects :
During emergence , N2O can diffuse rapidly from the blood to the alveoli , resulting in a dilution of O2 in the alveoli (diffusion hypoxia) it is therefore necessary to provide 100% O2 for several minutes until N2O is eliminated
Bone marrow depression
Chronic neuropathy
Tends to diffuse into closed air spaces causing increased pressure & volume (important if there is trapped air e.g. air embolus , pneumothorax)

13. Muscle Relaxants

14. Muscle relaxants often required during surgical procedures for various reasons :
Prevent muscle stretch reflex & suppresses muscle resting tone
Facilitate intubation
Facilitate controlled ventilation
Allow access to the surgical field
Muscle relaxants classified on the basis of the neuromuscular blockade they provide :
Depolarizing
Non-depolarizing
And according to their duration of action
Short
Intermediate
long

15. Depolarizing
Succinylcholine (suxamethonium)
Onset :rapid (30-60 sec)
Duration : short (5 min)
Metabolism of sch by plasma cholinesterase
Side effects :
Sch also binds to autonomic cholinergic receptors
Muscarinic receptors in the heart can cause sinus bradycardia
Muscarinic receptors in the salivary glands result in increase secetions
Hyperkalemia
Other side effects
Increased intracranial ICP , intraocular IOP ,intragastric pressure
Triggers malignant hyperthermia
Sustained contraction in myotonia
fasiculations

16. Non-depolarizing muscle relaxants
Mivacurium , atracurium ,cis-atracurium , rocuronium ,pancuronium , doxacurium
Reversing agents for non-depolarizing blockade (neostigmine , pyridostigmine)
Reversible anticholinesterase
Inhibit enzymatic degradation of Ach , increases the amount of Ach at nicotinic receptors ,displacing the non-depolarizing muscle relaxants
With reversal ,Ach concentration will increase at muscarinic ( before nicotinic) sites causing bradycardia , salivation etc.
Therefore simultaneous administration of atropine or glycopurrolate is necessary to decrease cholinergic side effects