Anesthesia

General and Local Anesthesia

General Anesthesia

Terminology:

-Surgery
-Operation
-Operating room (theater)
-Anesthesia/ Anesthetist

• (Operating Room/ Theater)

• (Operating Room/ Theater)

(Endotracheal tube/Endotracheal intubation)

• (Endotracheal tube/Endotracheal intubation)

• (Endotracheal tube/Endotracheal intubation)

• (Endotracheal tube/Endotracheal intubation)

• (Laryngoscope)

• (Ambo Bag)

• (Ambo Bag)

• (Ventilator)

(Airway tube)

General Anesthesia:= Inducing

-Quick
-Safe
-Easily reversible
Unconsciousness for any desired period of time.

Drugs in Anesthesia are given:

1- Before surgery

2-During surgery:

-Unconsciousness
-Analgesia
-Muscle relaxation

3-After surgery:

-Reversal of neuromuscular block
-Relief of pain
other



Stages of General anesthesia:

Stage One: Analgesia

Stage two: Delirium
*Stage Three: Surgical anesthesia 4 plans
Stage Four: Medullary paralysis, death

*Ether to non Pre-medicated patient

1-Before surgery: (Premedication)

A- Anxiolysis and Amnesia.

Patient is apprehensive clear explanation of what to expect
-Reassurance.

Very anxious patient can be helped by benzodiazepines

B-Analgesia for patient in pain.
Or to:
Prevent post operative pain


-Parenteral opiates morphine

C-Drying of bronchial secretions.

Anti muscarinic drugs
Rarely used
Glycopyrronium is used one hour before surgery

Gastric content can lead to pulmonary aspiration:

-Single dose of anti acid
-Ranitidine
-Metoclopramide

*Fasting for at least 6 hours before anesthesia

2-During surgery:

The Aim is to induce:

-Analgesia
-Unconsciousness
-Muscle relaxation (Intra abdominal surgery)


General anesthesia will include two steps:

A- Induction of anesthesia.

B- Maintenance.

A-Induction: Usually IV (Pre-Oxygenated patient)

-Small doses of opiates
-Fentanyl
-Followed by Thiopental (Ultra short acting Barbiturate)
or: Propofol

----Airway patency is maintained

(Oral airway + face mask)
Or
(Endotracheal tube)

Endotracheal tube insertion require paralysis

with Neuromuscular Block

Inhalation induction Sevoflurane

*(less common)


B-Maintenance: (Inhalation)

-Nitrous oxide (N2O) and Oxygen

-Volatile agents +Oxygen + Air.
-Isoflurane
-Sevoflurane
-Halothane
Or

Continuous iv infusion of Propofol (IV)
*(Less Common)

3-After surgery:

-Patient is not left alone until consciousness regained:

-Effect of neuromuscular blockade either wane off or reverted by Antidote.

-Relief of pain

Dissociative Anesthesia:

-Profound Analgesia
-Antegrade Amnesia
-Minimal Hypnosis

Mode of action:

On brain primarily on midbrain reticular formation system.

Lipid solubility is important as the more lipid soluble is the drug the more its effect on the brain.

GABA receptor activation is also another proposed mechanism

Individual Anesthetics:

1-Gases and Volatile Agents:

(Inhalation anesthesia)

Effect correlate with the partial pressure of anesthetic agent.

*Agents with law solubility in blood provide rapid effect


-N2O (Nitrous Oxide)
-Sevoflurane

When discontinued it moves from the tissue to the blood to the alveoli.

10 % of the expired volume and can lead to hypoxia.

Treated by oxygen (Diffusion hypoxia)

*Fast Induction
*Fast Elimination

Nitrous Oxide (N2O):

Gas used since 1844

-Not inflammable

-Not explosive
-Light anesthesia

• (Nitrous Oxide)

Advantages of Nitrous Oxide: (N2O)

-Strong Analgesic action

50 % N2O in Oxygen provide profound analgesia.

-Recovery is very fast

-Around 4 minutes

Disadvantages of Nitrous Oxide : (N2O)

-Expensive
-Must be used with more potent drug to produce surgical anesthesia.
***Post operative nausea and vomiting

Uses:

Use d to maintain surgical anesthesia with other agents e.g. Isoflurane


Dosage of Nitrous Oxide (N2O):

-Maintain anesthesia mixed with at least 30 % O2

-Analgesia: 50 % N2O + 50% O2

Contra indications of Nitrous Oxide (N2O):

-Any closed distended air filled space will expand
-Intra ocular surgery
-Middle ear
-lung

Precaution of Nitrous Oxide (N2O):

Adverse reactions:

-Nausea and vomiting

*When used for more than 4 hours
-Megaloblastic changes in blood.
-Teratogenicity to staff?

Halogenated anesthetics:

(Volatile Agents)

-Halothane

-Isoflurane
-Sevoflurane

Isoflurane:

-Volatile colorless liquid
-Not flammable under normal conditions
-Pungent odor
-Can cause bronchial irritation
-Minimally metabolized (o.2 %)









• (Vaporizer)

Effects of Isoflurane:

-Respiratory depression
-Increased respiratory rate and tidal volume

CVS:

-Slight depression in CVS
-And cardiac output
-Reduce Blood Pressure and peripheral vasodilatation.

Sevoflurane:

Chemical analogue to Isoflurane
Enflurane causes more respiratory depression

Desflurane

Halothane (Fluothane):


-Slow recovery
-Decrease cardiac output
-Sensitize heart to catecholamine (Arrhythmia)
-20% metabolized and induce liver enzymes
-Fever, anorexia, nausea, vomiting

***Hepatic damage (rare but serious)
Hepatitis is reported adverse reaction in 1:50000
Immune reaction

Oxygen in anesthesia:

-Supplementary O2 is always useful
-With inhalation agents to prevent hypoxia
O2 concentration is 30%.... not exceed 80 %

Atmospheric pollution in operating theater:

-Fetal malformation
-Miscarriages increased
-Hepatitis

Intravenous anesthesia:

Extremely rapid induction

*It is common practice to use iv induction and inhalation agents for maintenance.

When volatile anesthesia is stopped it is eliminated quickly through the lungs.

Propofol:

-Inductions within 30 sec
-Recovery is rapid
-Nausea and vomiting are extremely rare

(Propofol Emulsion)

(Propofol Emulsion)

Thiopental (Pentothal) :

-Very short acting barbiturate

-Induces anesthesia smoothly
Dose is 3-5 mg /kg

-Half life = 4 min allows swift recovery after a single dosage (Patient is awake after 10-15 min)


-Terminal half = life is 11 hours very prolonged recovery after repeated dosage or infusion

(Thiopental)

Metabolized in the liver
Ph = 11 Can damage tissue if exrtravasated

CNS:

-No analgesia
-Decrease intracranial pressure

CVS:

-Hypotension
-Tachycardia
-Decrease respiratory rate

Ketamine (Ketalar):

-Hallucinogen
-Trance like state
-Dissociative anesthesia
-Sedation amnesia dissociation
-Analgesia
15 min after a single IV injection
Can be given IM

Used for Minor surgical interventions

Tachycardia
*Increased blood pressure
Cardiac output
Has an advantage in Shocked patients
Bronchodilatation.

(Ketamine)

Disadvantages of Ketamine:

-No muscle relaxation

*Increase intracranial and intra ocular pressure
-Hallucination during recovery
***Decrease by diazepam

Usage:

Induction as a soul agent in minimal surgery
1-2 mg/kg over 60 sec
5-10 mg/kg IM

Contra indication of Ketamine:

-Hypertension
-Congestive cardiac failure
-Cerebral trauma
-Increased intracranial pressure
-Pregnancy (Contra indication in pregnancy)

Muscle relaxants in Anesthesia:

***Abdominal surgery requires muscle relaxation
(Deep general anesthesia can cause relaxation)

Neuromuscular blocking agents

*Deep general anesthesia is not advised

Light general anesthesia + selective neuromuscular block

Tracheal intubation + Quick recovery

***Mechanical ventilation is always used

-Technical skill is required

***Neuromuscular block should only be given after induction of anesthesia

Curare was an arrow poison
Complete paralysis of all voluntary muscles
Movement is impossible

Mechanisms of muscle relaxants:

Acetylcholine is released after nerve impulse
Leads to activation of receptors on motor end plate

Natural substances that prevent release of ach at nerve ending:

Botulinum toxin

1- Competitive relaxants:

Atracurium, Mivacurium
Pancuronium, Vecuronium

-Competitive antagonists to ach.
-Flaccid paralysis
Reversal of anticholinesterases drugs is by
Neostigmine
Prevent destruction of ach
Pancuronium bromide =(trademarked as Pavulon)

Tubocurarine:

*Can cause Hypotension
*Not used in many countries

Atracurium (Atracurium besylate):

-Altered in the body spontaneously in the body to inactive form
-T ½ = 30 min
-By passive chemical process
(Hofmann elimination)
Duration of action = 15-30 min
Hepatic and renal disease
Vecuronium
Full blockade after 3 min
20-30 min duration

(Pancuronium/Pavulon )

2- By Depolarization:

Suxamethonium = Succinylcholine = Scoline

Contraction +relaxation

Shortest duration of action

Tracheal intubation in less than 60 sec
Total paralysis for 4 minutes
If intubation is impossible recovery is rapid

(succinylcholine = scoline)

Suxamethonium (succinylcholine)
=scoline

-Destroyed by pseudocholinesterase

-Hereditary deficiency
-Scoline apnea


-Muscle fasciculation then paralysis
-Muscle pain 1-3 days
***Most rapid onset

Antagonism of Neuromuscular Blocking agents:

-Anti cholinesterase drugs
Neostigmine IV + Glycopyrronium = (or Atropine)
Glycopyrronium bromide = Glycopyrrolate
Glycopyrronium bromide is a medication of the muscarinic anticholinergic group. It does not cross the blood–brain barrier and consequently has no to few central effects
*To prevent bradycardia due to parasympathetic action
-Act within 4 minutes-Effect lasts 30 min

-Neostigmine can itself cause paralysis in overdose = depolarization

Local Anesthesia

Local Anesthesia:

Cocaine 1884 Carl Koller;

-Water soluble
-Rapid onset
-Sterilizable by heat

Mode of action of local anesthesia:

Prevent the initiation and propagation of the action potential (nerve impulse)

Reducing the passage of sodium through voltage gated sodium channel

They rise the threshold for excitability and block conduction





(Mechanism of action of local anesthesia)

The distribution of a single dose la is determined by diffusion into the tissue

Plasma half life is few mints

By infiltration local anesthesia act within 5 min

And have a useful duration of effect for 1-1.5 hors

Can be doubled by vasoconstriction

Local anesthesia is used as an acid salt = HCL

Dissociate in Basic Media

Liberating the active compound HCL
Free base

In abnormally acidic media (abscess)

This dissociation can be delayed


***Also risk of spreading infection

Absorption of topical anesthesia on mucus membrane can be extremely rapid and give plasma concentration comparable to injection

*This is important specially in urethra

Chemical classification of local anesthetics:

1-Esters:

Cocaine, Procaine, tetracaine, Benzocaine

2-Amides:

Lignocaine (Xylocaine) Lidocaine
Prilocaine, Pupivacaine

(Xylocaine = Lidocaine)

Effect is terminated by removing the local anesthetic from the circulation.


Delaying this will increase the duration of action of la and decrease systemic absorption.

Most la cause dilatation with the exception of cocaine
Addition of epinephrine (Adrenaline) increase the duration of lidocaine

Never use adrenaline in

Extremities = fingertips
Nose , toes, ..etc

Can lead to Gangrene!

Uses of local anesthesia:

1- Surface anesthesia: solution jelly cream
2- Infiltration anesthesia
3- Regional anesthesia

-Nerve block

-Intravenous regional anesthesia
-Epidural anesthesia
-Intrathecal ( Spinal anesthesia)

(Sites of Anesthesia)