Drugs Flashcards
General anesthesia
a state of CNS depression
a complete absence of sensations and is unconscious
Stage I of anesthesia
analgesia and amnesia
good stage
less pain, and loss of consciousness
Stage II of anesthesia
Delirium
patient may be agitated or combative
breath-holding, vomiting
ideally, patient should move through this stage as fast as possible
Stage III of anesthesia
surgical anesthesia
good stage
respiration becomes regular
four substages based on eye movement, depth of respiration and muscular relaxation
Stage IV of anesthesia
Medullary depression
bad stage
stage of relative overdose
may result in cardiovascular suppression
Halothane
CNS effects
- Decrease brain metabolic rate
- Increase cerebral blood flow
- Increase intracranial pressure
CV effects
- Decreased myocardial contractility and stroke volume leading to lower arterial blood pressure
- Sensitizes myocardium to catecholamines
- ↑ automaticity
Isoflurane
Advantages
- Potent
- Induction in less than 10 minutes
- Doesn’t sensitize the myocardium to catecholamines
- Less hepatotoxicity and renal toxicity than halothane (may be related to lower rate of metabolism)
Disadvantages
- Rarely arrhythmias
- Pungent odor
- Potential for malignant hyperthermia
Desflurane
Halogenated Hydrocarbon Inhalation Anesthetic
CNS effects: Increase intracranial pressure
CV effects:
- Decreased myocardial contractility and stroke volume leading to lower arterial blood pressure
- Sensitizes myocardium to catecholamines
- ↑ automaticity
Watch for malignant hyperthermia!
Sevoflurane
- Newest approved inhalation agent for use in North America (1996)
- High potency (low % of inspired gas)
- Low blood solubility
- Rapid onset – 5-10 min
- Rapid recovery – same day surgery
- Almost perfect inhalation anesthetic
Nitrous oxide
Advantages
- Low blood solubility (rapid onset)
- Second gas effect
Disadvantages
- MAC = 104% - can’t use as sole anesthetic agent
- No muscle relaxing effect
- Diffusion hypoxia if rapidly discontinued
Thiopental
Barbiturate
- Facilitates GABA induced Cl- entry into neurons, leading to CNS depression
- Rapid onset (sec) after iv administration and short action (min) allows quick recovery
Propofol
- Rapid induction (50 seconds) and recovery (4-8 minutes) from anesthesia
- May be given alone to maintain anesthesia or used for induction as part of balanced anesthesia technique
- May result in injection site pain
- Causes Apnia (22-45%) –> don’t leave the room!
Midazolam
Benzodiazepine
- Facilitates GABA induced Cl- entry into neurons, leading to CNS depression
- Most important characteristic is amnestic action
- Insufficient for anesthesia when given alone
Ketamine
- Dissociative anesthetic (Patient appears to be awake - eyes open; Unaware of environment and doesn’t feel pain)
- Principal drawback is the occurrence of emergence reactions (delirium and hallucinations)
- Abuse - currently abused in the US
Fentanyl
Opioid
- Hemodynamic stability - good for patients with compromised myocardial function
- Respiration must be maintained artificially and may be depressed into the postoperative period
- Usually supplemented with inhalation anesthetic, benzodiazepine or propofol
Sufentanil
opioid
- Hemodynamic stability - good for patients with compromised myocardial function
- Respiration must be maintained artificially and may be depressed into the postoperative period
- Usually supplemented with inhalation anesthetic, benzodiazepine or propofol
Why is the partial pressure of an inhalation anesthetic is a more important variable in producing anesthesia than blood concentrations of the agent?
- Remember Dalton’s Law?
- (Pt = P1 + P2 + P3 …)
- Always have 21% O2!!
- So the remaining 79% is available
- Amount of undissolved drug in blood is related to the clinical effect
- Drugs dissolved in fluid do not raise the Panesthetic in that fluid
3 Factors affecting Parterial
- Concentration of anesthetic in inspired air
Higher = faster onset
- Pulmonary ventilation
Higher = faster onset
- Transfer of anesthetic from alveoli to blood
Solubility of anesthetic in blood
Really important number used in anesthesia: Minimum Alveolar Concentration (MAC)
ED50
What are the usual MACs for surgical anesthesia and deep anesthesia?
Surgical anesthesia is usually attained at 1.3 - 1.5 MACs
Deep anesthesia ensures at about 2 MACs
Potency in Anesthesia
DEF: Amount of drug necessary to produce effect of specified intensity
Function of lipid solubility
Conclusion: The more lipid soluble the anesthetic, the greater is its potency
Blood:Gas Partition Coefficient
Reflects solubility of an inhalation anesthetic in blood
Conclusion: **the more soluble a drug is in blood, the longer it takes to raise its partial pressure in blood (Pblood) **
Longer period of time for anesthesia
Halogenated Hydrocarbon Inhalation Anesthetics:
halothane, isoflurane, methoxyflurane (vet), sevoflurane
What are the CV effects?
- Decreased myocardial contractility and stroke volume leading to lower arterial blood pressure
- Sensitizes myocardium to catecholamines
- ↑ automaticity
- Halothane > isoflurane, desflurane, sevoflurane > nitrous oxide
Malignant hyperthermia may occur with all inhalation anesthetics…
Whis is MH?
Potential for MH with all inhalation anesthetics except what?
Antedote = ???
rapid increase in body temp due to hypermetabolic reaction in skeletal muscle (cool patient!!)
All except N2O
Dantroline – blocks Ca release from sarcoplasmic reticulum
Intravenous Anesthetics
- Act faster
- Best suited for induction of anesthesia
- Useful for short operative procedures
- Unsuitable as a single drug anesthetic for many surgical procedures (inhalation anesthetics maintain anesthesia for longer procedures)
