Anesthetics Flashcards
Pt receiving lidocaine for local anesthesia develops cyanosis, headache, tachycardia, shortness of breath, lightheadedness, and fatigue. Diagnosis?
Methemoglobinemia
Optimal distance above carina for an endotracheal tube
2 cm above carina
Relate lipid solubility, speed of induction, and potency for an inhalational agent with a low MAC
Low MAC means that agent is more lipid-soluble and more potent, but slower speed of induction
What inhalational agent has the fastest speed of induction, high MAC, and low potency?
Nitrous oxide (NO2)
Contraindications to use of nitrous oxide
Middle ear occlusion
Pneumothorax
SBO
Any other instance where there is air-filled body pocket
Which inhalational agent can cause eosinophilia, fever, increased LFTs, and jaundice, and is associated with the highest degree of cardiac depression and arrhythmias?
Halothane
Pleasant smelling and ideal for induction in children
Sevoflurane
What induction agent should not be used in pts with egg allergy?
Propofol
Induction agent contraindicated in head injury
Ketamine
Which induction agent can cause adrenocortical suppression with continuous infusion?
Etomidate
First muscle to be paralyzed after administration of paralytic
Face and neck muscles
Last muscle to be paralyzed after administration of paralytic
Diaphragm
Triggering agents for malignant hyperthermia
Volatile anesthetics (halothane, enflurane, isoflurane, sevoflurane, desflurane) and depolarizing paralytic succinylcholine
Mechanism leading to malignant hyperthermia
Mutation of ryanodine receptors on SR resulting in drastic increase in intracellular calcium levels inducing an uncontrolled increase in skeletal muscle oxidative metabolism
First sign seen with malignant hyperthermia
Increase in end-tidal CO2
[other signs: acidosis, fever, hyperkalemia, rigidity, tachycardia]
Use of succinylcholine should be avoided in which pts?
Extensive burns, crush injuries/extensive trauma, eye trauma or glaucoma, neuro disorders/injury, spinal cord injury, acute renal failure with increased potassium
Maximum dose of lidocaine without epinephrine
5 mg/kg
(Remember 1% of drug = 10 mg/mL)
[max dose of bupivacaine is 3 mg/kg]
Maximum dose of lidocaine with epinephrine
7 mg/kg
Earliest symptoms of lidocaine toxicity
Perioral numbness or tingling of the tongue
May progress to lightheadedness or visual disturbance, CV symptoms such as arrhythmias and arrest
In patients on MAOIs, the concurrent use of narcotics can cause _____ _____
Hyperpyrexic coma
Histamine release is characteristic of what narcotic?
Morphine
Which benzodiazepine is contraindicated in pregnancy because it crosses placenta?
Versed (midazolam)
What is the best determinant of esophageal vs. tracheal intubation?
End-tidal CO2
Risk factors for post-op MI
Age >70 CHF DM Previous MI Unstable angina
What is the risk in administering a depolarizing anesthetic agent such as succinylcholine in quadriplegics, paraplegics, or after burns and severe trauma?
Life-threatening hyperkalemia from release of intracellular potassium
Effects of inhaled anesthetics include ______ cardiac output, respiratory ______, and post-op atelectasis
Decreased; depression
Propofol 10 mg/mL dosage for general anesthesia induction
ASA-I, II — 2 to 2.5 mg/kg IV; Administer in approx. 40 mg increments every 10 seconds until onset of anesthesia
ASA-III, IV — 1-1.5 mg/kg IV; Administer in approx. 20 mg increments every 10 seconds until onset of anesthesia
Children age 3-16 — 2.5-3.5 mg/kg IV as single dose over 20-30 seconds
Propofol 10 mg/mL dosage for general anesthesia maintenance
Intermittent dosing: 20-50 mg IV as needed
Continuous infusion: 9-12 mg/kg/hr IV for 10-15 mins, then decrease to 6-12 mg/kg/hr; infusion rates of 3-6 mg/kg/hr should be achieved to optimize recovery times
Average continuous IV infusion rate of propofol for ICU sedation maintenance of mechanically ventilated pts
About 1.6 mg/kg/hr
MOA of propofol
Inhibits NMDA subtype of glutamate receptors
Agonist at GABA-A receptor
Propofol is highly _____ and is thus rapidly distributed to all tissues in the body. There is fast equilibration between plasma and brain.
It is metabolized in the ______ where it rapidly undergoes ___________ to inactive metabolites. The steady state concentration is generally proportional to the infusion rate.
Lipophilic
Liver; glucuronide conjugation
Elimination and terminal half life of propofol
Elimination half life: 3-12 hours
Terminal half life: 1-3 days
After IV administration of propofol, loss of consciousness usually occurs within 40 seconds. The duration of action of a 2-2.5 mg/kg bolus injection is __________.
Recovery from anesthesia is rapid, about _______ minutes for 2 hours of anesthesia, and is associated with minimal psychomotor impairment. Recovery times may vary depending on degree and duration of sedation
3-5 minutes
8-19 minutes
Fentanyl dose for general surgery induction
50-100 mcg/kg
Fentanyl dose for adjuvant management of general anesthesia maintenance and intraoperative pain and stress response during major surgery
2-20 mcg/kg
MOA of fentanyl
Strong agonist at mu and kappa opioid receptors
Fentanyl is highly _____, rapidly distributed to brain, heart, lungs, kidneys, and spleen. It is slower to redistribute to skeletal muscle and fat, where it is released more slowly into the blood.
It is metabolized in the ____ via _____and excreted by the ______
Lipophilic
Liver; CYP3A4; kidneys
Onset and duration of action of fentanyl
After IV admin, peak analgesia occurs within minutes and lasts 30-60 mins after single dose
Preop dosing of versed
1-5 mg IV over 2 minute period, then titrate up as needed
Versed dosing for general anesthesia induction and maintenance in adults <55 vs >55
Adults <55 = 200-350 mcg/kg IV
Adults >55 = 150-300 mcg/kg IV
[reduce if ASA III or IV, or if premedicated]
Versed dosing for sedation during rapid sequence intubation
0.2 to 0.3 mg/kg IV, allow 1-3 mins for onset prior to administration of paralytic
MOA of versed
GABA agonist
Metabolism and excretion of versed
Metabolized in liver via CYP3A4
Renally excreted
Half life of versed
2-6 hrs
Onset and duration of action of versed
Onset after IV admin is 1.5 to 5 mins
Duration 30-45 mins after single dose, recovery time of 2-6 hrs
MSMAIDS check for anesthesia setup
M = Machine (run low-circuit pressure test, adjust parameters to patient, check gas levels, bag valve mask ready)
S = Suction (have suction and OG tube ready)
M = Monitors (EKG leads, pulse ox, temp probe, BP cuff)
A = Airway (ET tube with stylette and cuff checked for leak, laryngoscope of choice, oral airway, LMA)
I = IV access
D = Drugs
S = Special (OG/NG tubes, bair hugger, fluid warmer, etc)
Elimination half time is the time necessary for the plasma concentration of drug to decrease 50% during elimination phase. How many elimination half times are typically required for almost complete elimination of drug?
5
[Note - as with elimination half times, the time necessary for a drug to achieve a steady state plasma concentration with intermittent doses is 5 elimination half times]
Maintaining a constant and optimal __________ of inhaled anesthetic is an indirect but useful method for controlling the brain partial pressure. This parameter is used as an index of anesthetic depth, reflection of the rate of induction and recovery from anesthesia, and a measure of equal potency
Alveolar partial pressure
The alveolar partial pressure of inhaled anesthetic is determined by input/delivery into alveoli minus the uptake/loss of drug from alveoli into pulmonary arterial blood. Input is determined by inspired partial pressure, alveolar ventilation, and characteristics of anesthetic breathing system. What 3 factors determine uptake/loss of drug into arterial blood?
Solubility
Cardiac output
Alveolar-to-venous partial pressure difference
What is the second gas effect?
The ability of the large volume uptake of one gas (first gas) to accelerate the rate of increase of the alveolar partial pressure of a concurrently administered companion gas (second gas)
[example: initial large volume uptake of nitrous oxide accelerates the uptake of companion gases such as volatile anesthetics and oxygen]
_______ ______ may occur at the conclusion of nitrous oxide administration if patients are allowed to inhale room air
Diffusion hypoxia
[initial high volume outpouring of nitrous oxide from blood into alveoli when inhalation of this gas is discontinued can so dilute the alveolar partial pressure of oxygen that arterial oxygen decreases. This can be prevented by filling the pts lungs with O2 at the conclusion of nitrous oxide administration]
Clinically, greater than 1 MAC is necessary because by definition 50% of pts respond to surgical stimuli at 1 MAC. Administration of approx. _____ MAC prevents skeletal muscle movement in response to surgical stimuli in nearly all pts during surgery
1.3
What are some physiologic and pharmacologic factors that increase the MAC necessary to prevent a response to surgical stimuli?
Hyperthermia
Drugs that increase CNS catecholamines (MAOIs, TCAs, cocaine, acute amphetamine ingestion)
Infants
Hypernatremia
Chronic ethanol abuse (?)
What are some physiologic and pharmacologic factors that decrease the MAC necessary to prevent a response to surgical stimuli?
Hypothermia Preop medications IV anesthetics Neonates Elderly Pregnancy Postpartum Alpha-2 agonists Acute ethanol ingestion Lithium Hyponatremia Cardiopulmonary bypass Systemic BP <40 mmHg Neuraxial opioids PaO2 <38 mmHg
Beta-1 receptors are associated with what effector organ and response to stimulation?
Heart
Increased HR, increased contractility, increased conduction velocity
Beta-2 receptors are associated with what effector organ and response to stimulation?
Fat cells —> lipolysis
Blood vessels —> dilation
Bronchioles —> dilation
Uterus —> relaxation
Kidneys —> renin secretion
Liver —> glycogenolysis, gluconeogenesis
Pancreas —> insulin secretion
Alpha-1 receptors are associated with what effector organ and response to stimulation?
Blood vessels —> constriction
Pancreas —> inhibition of insulin secretion
Intestine and bladder —> relaxation, constriction of sphincters
Alpha-2 receptors are associated with what effector organ and response to stimulation?
Postganglionic (presynaptic sympathetic nerve ending) —> inhibition of NE release
CNS (postsynaptic) —> increase in K+ conductance
Platelets —> aggregation
Dopamine-1 receptors are associated with what effector organ and response to stimulation?
Blood vessels —> dilation
Dopamine-2 receptors are associated with what effector organ and response to stimulation?
Postganglionic (presynaptic) sympathetic nerve endings —> inhibition of NE release
Clonidine is a centrally acting antihypertensive that stimulates alpha-2 receptors in the depressor area of the vasomotor center, leading to a decreased outflow of SNS impulses to the periphery. The net effect of this decreased SNS activity is a decrease in CO, SVR, and systemic BP. How does this affect the MAC?
MAC is decreased
Effects of propofol on systemic BP, HR, SVR, cerebral blood flow, and intracranial pressure
BP decreased
HR unchanged to decreased
SVR decreased
Cerebral blood flow decreased
Intracranial pressure decreased
Effects of midazolam on systemic BP, HR, SVR, cerebral blood flow, and intracranial pressure
BP unchanged to decreased
HR unchanged
SVR unchanged to decreased
Cerebral blood flow decreased to unchanged
Intracranial pressure unchanged to decreased
Steps of Rapid Sequence Intubation (RSI) in 70 kg adult
Preparation
Preoxygenation
Pretreatment (Fentanyl 200 mcg IV)
Paralysis with induction (Propofol 105-210 mg IV, Midazolam 14 mg IV, Succinylcholine 100 mg IV or Rocuronium 70 mg IV)
Passive oxygenation
Protection and positioning (cricoid pressure, sniff position)
Placement with proof (intubate and assess end tidal CO2)
Postintubation management (IV sedation, ventilator settings)
Succinylcholine produces significant myoclonal fasciculations on its own, prompting a rise in ICP and potential for increased O2 demand. How can this be avoided?
Administer defasciculating agent at 10% of paralyzing dose 3-5 mins prior to giving Succinylcholine
Common agents include rocuronium, vecuronium, and pancuronium
General guidelines for ET tube depth in adult women vs. adult men
Adult women = 21 cm
Adult men = 23 cm
[measured from corner of mouth]
Why is it common practice to administer an opioid 1-3 minutes prior to administration of induction drug for general anesthesia?
The opioid is intended to blunt the subsequent pressor and heart rate responses to direct laryngoscopy and tracheal intubation, and also to initiate preemptive analgesia
Stages of anesthetic depth
Stage I: Analgesia — pt is conscious and rational, with decreased perception of pain
Stage II: Delirium — pt is unconscious, body responds reflexively, irregular breathing pattern with breathholding
Stage III: Surgical anesthesia — increasing degrees of muscle relaxation, unable to protect airway
Stage IV: Medullary depression — there is depression of cardiovascular and respiratory centers
