4 - General Anaesthetics Flashcards
General Anaesthetics Parameters (5) That Are Reversible
Analgesia
Amnesia
Loss of consciousness
Inhibition of sensory and autonomic reflexes
Skeletal muscles relaxation
Stages of Anesthesia (Guedel’s Signs): 1 - Stage of Analgesia (3)
Analgesia
Amnesia
End of this stage there is LOC and goes to next stage
Stages of Anesthesia (Guedel’s Signs): 2 - Stage of Excitement (6)
LOC and begins to respire on own
Disinhibition
Delirious excitement
Irregular respiration
Amnesia
Reflexes enhanced, unpleasant stage that is reduced
Stages of Anesthesia (Guedel’s Signs): 3 - Stage of Surgical Anesthesia (5)
Deep unconsciousness
Respiration is regular
Muscle relaxation
Planes 1,2,3, and 4 depending on patient size, eyeball reflexes, and diaphragmatic/chest muscles paralysis
Most surgeries are performed in plane 3
Stages of Anesthesia (Guedel’s Signs): 4 - Stage of Medullary Paralysis/Toxic (2)
Severe respiratory and cardiovascular depression
Toxic
Types of General Anaesthesia (2)
Intravenous - used to induce anaesthesia
Inhalation - used to maintain anaesthesia
Intravenous Anaesthetics: Barbiturates (2 Drugs + statement)
Thiopental
Methohexital
Used to INDUCE anaesthesia
Intravenous Anaesthetics: Benzodiazepines (2)
Midazolam
Diazepam
Intravenous Anaesthetics: Opoid Analgesics (4)
Morphone
Fentanyl
Sufentanil
Alfentanil
Intravenous Anaesthetics: Others (3)
Propofol
Ketamine
Etomidate
Inhaled Anaesthetics: Gas (1 and Taken up by?)
Nitrous Oxide (Less soluble in blood (low coefficient), so faster induction of anesthesia)
Take up by alveoli by gas exchange
Inhaled Anaesthetics: Volatile Liquids (5 and Taken up by?)
Halothane (More soluble in blood (high coefficient), so slower induction of anesthesia)
Enflurane
Isoflurane
Desflurane
Sevoflurane
Take up by alveoli by gas exchange
Balanced Anaesthesia Defined
Combination of intravenous and inhaled drugs
Inhaled Anaesthetics: Pharmacokinetics (Steps)
Anaestheic machine –> Breathing circuit via FGF –> Lungs –> Arterial and Venous blood –> Brain and back
Factors Affecting Uptake and Distribution (2)
The concentration of an inhaled anesthetic in a mixture of gases is proportional to its partial pressure –> Higher the partial pressure of the gas in alveoli –> faster uptake of gas into the blood and into brain, faster inducing
Increase partial pressure by increasing the dose (concentration) of anaesthetic
The speed of induction of anesthesia depends on blood gas solubility
Blood Gas Solubility: Gas Partition Coefficient Defined (Long)
Relative Affinity of an anesthetic/gas towards the blood compared with that of INSPIRED GAS
So, if the anaesthetic agent has more affinity towards the blood, it means it’s more soluble in blood (higher coefficient); if towards inspired air, less soluble in blood (lower coefficient)
An agent with a high coefficient that’s more soluble in blood, the MORE of the agent MUST BE DISSOLVED to RAISE the PARTIAL PRESSURE (so it takes time) –> INDUCTION of ANESTHESIA WILL BE SLOWER
On the other hand…
An agent with low coefficient that’s less soluble in blood diffuses from inspired air to the alveoli to blood, the rise in partial pressure will be much quicker (since it’s not soluble in blood) and rate of inducing anaesthesia will be faster
Blood Gas Solubility: Coefficient
Less than 1 ==> Less soluble in blood, arterial tension rises quickly, fast onset of action of anesthesia (e.g. NO)
Greater than 1 ==> Highly soluble in blood, arterial tension rises slowly (takes time), slow onset of action of anesthesia
Minimum Alveolar Concentration (MAC) Defined (4)
Measure of potency
Concentration of anesthetic at which 50% of subjects do not show a motor response to a surgical incision (so basically, dose of anesthesia required to perform surgery) –> Usually MAC of 1
If MAC value is low: potency is high (so only a small dose required for anasthesia)
1.3 MAC –> nearly 100% will NOT respond to stimuli
Minimum Alveolar Concentration (MAC): Values (3)
Nitrous Oxide: >100 (LEAST POTENT)
Halothane: 0.75 (Very potent)
Methoxyflurane: 0.16
Properties of Inhaled Anesthetics: Nitrous Oxide (4)
MAC > 100% (INCOMPLETE anesthetic, so need large doses)
Good analgesia
Rapid onset and recovery due to low blood-gas coefficient
Used along with other anesthetic
Properties of Inhaled Anesthetics: Halothane (5)
Not pungent (used for induction in children)
Bronchodilator
Medium rate of onset and recovery
Sensitizes the heart to epi-induced arrhythmias
HALOTHANE INDUCED HEPATITIS several days after procedure
Properties of Inhaled Anesthetics: Desflurane (4)
Most rapid onset of action and recovery of the halogenated GAs
Widely used for outpatient surgery
Irritating to the airway (pungent) in awake patients and causes coughing, salivation, and bronchospasm (poor induction agent)
Used in maintenance of anesthesia
Properties of Inhaled Anesthetics: Sevoflurane (5)
Very low blood: gas partition coefficient with relatively rapid onset of action and recovery
Widely used for outpatient surgery
NOT irritating to the airway
Bronchodilator
Useful induction agent, particularly in children
Properties of Inhaled Anesthetics: Isoflurane (3)
Medium rate of onset and recovery
Used for induction and maintenance of anesthesia
Can cause irritation to airway
Adverse Effects of Inhalational GAs: Nephrotoxicity (2 points and 3 drugs)
Chances in renal concentrating ability
Formation of fluoride form: Methoxyflurane, Enflurane, and Seveflurane
Adverse Effects of Inhalational GAs: Malignant Hyperthermia Defined, Volatile Agents + Muscle Relaxants, and Side Effects (Effects are 6)
Genetic disorder - AD
Volatile agents (e.g.Halothane) + muscle relaxants (Succinyl Choline)
Rapid onset of tachycardia and hypertension, severe muscle rigidity, hyperthermia, hyperkalemia, and acid-base imbalance
Adverse Effects of Inhalational GAs: Malignant Hyperthermia Rx Drug (1)
Dantrolene
IV Anesthetics: Barbiturates - Thiopental/Methohexital (5)
Can produce unconsciousness and surgical anesthesia in
anesthesia in < 1 min
Rx: induction of anesthesia and short procedures
With single bolus - emergence from GA occurs in 10 min
Cerebral metabolism, oxygen utilization, cerebral blood flow decreased
Can precipitate porphyria
IV Anesthetics: Benzodiazepines Drugs (3)
Diazepam
Lorazepam
Midazolam
IV Anesthetics: Benzodiazepines Use (1)
Used as premedication for surgery prep: produce anxiolysis, amnesia, and sedation prior to induction of GA
IV Anesthetics: Benzodiazepines Midazolam has a more?
Rapid onset, a shorter elimination of half-life and is an inducing agent
IV Anesthetics: Propofol (5)
Rate of onset of action is similar to that of the intravenous barbiturates but recovery is more rapid and no hangover
Patients subjectively “feel better” in the immediate postoperative period
Both induction and maintenance of anesthesia as part of total intravenous or balanced anesthesia techniques
Agent of choice for ambulatory surgery
Effective in producing prolonged sedation in patients in critical care
IV Anesthetics: Propofol Adverse Effects (5)
Apnea
Marked decrease in BP during inducation from vasodilation of veins and arteries
Pain at site of injection
Muscle movements/Hypotonus
Clinical Infections may occur –> due to propofol containin lecithin (from eggs), which can cause infections
IV Anesthetics: Etomidate (5)
Rapid induction (~1 min)
Short duration of action (3-5 mins)
Little effect on CV and Respiration
Maintains cardiovascular stability in patients with coronary artery disease, cardiomyopathy, cerebral vascular disease, or hypovolemia.
Can cause post-op nausea
Opioids: Drugs (5)
Morphone
Fentanyl
Sufentanil
Alfentanil
Remifentanil
Opioids: High doses can cause?
Post-op-respiratory depression
Opioids Used For?
Post-op analgesia and premedication
Opioids: Neuroleptanalgesia Defined
State of analgesia and amnesia: Fentanyl + Droperidol
Opioids: NeuroleptanesTHIA (Drugs)
Fentanyl + Droperidol +N20 (Nitrous Oxide)
Opioids: Remifentanil is very?
VERY Potent but with a short half life
Ketamine: Defined
“Dissociative anesthetic” that produces a cataleptic state that includes intense analgesia, amnesia
Ketamine: Acts by?
Blocking NMDA receptor of glutamate
Ketamine: Increased Cardiovascular Effects (3)
Increased Heart Rate
Increased arterial BP
Increased cardiac output
Ketamine: Increased Neurological Effects (4)
Increased cerebral blood flow
Increased oxygen consumption
Intracranial pressure
Can’t use on patients with intracranial lesions
Ketamine: Emergence Phenomena (3)
Postoperative disorientation
Sensory and perceptual illusions
Vivid Dreams
