Basic exam content Flashcards
AcH receptor upregulation and NMBA
Upregulation results in increased number of immature AcH receptors (fetal subunit) at NMJ that extend into adjacent membranes
- Increased sensitivity to AcH and Suxx
- Decreased sensitivity/increased resistance to NDNMBA (why? more receptors need to be antagonized)
ACLS treatment for symptomatic bradycardia
1st line: atropine, transcutaneous pacing
2nd line: epinephrine, dopamine
Active cardiac conditions that require perioperative evaluation
Unstable coronary syndrome
- acute MI (<7 days old)
- recent MI (7-30 days old)
- unstable angina
Decompensated heart failure
- NYHA class IV
- new onset HF
Symptomatic arrhythmias
- mobitz type II AV block
- 3rd degree AV block
- Afib with RVR
- symptomatic bradycardia
Severe valvular disease
- severe aortic stenosis (mean pressure gradient >40 mmHg, aortic valve area <1.0 cm2
Allergen associated with latex allergy
Banana
Avocado
Kiwi
Pineapple
Mango
Alternative hypothesis (Ha)
States a difference DOES exist between the variables being tested
Alveolar gas equation
PAO2 = [(Patm - PH20) *FiO2] - (PaCO2/0.8)
Patm = 760 mmHg at sea level
PH20 = water vapor pressure = 47 mmHg at 37C
Increased Patm and FiO2 increase PAO2
Decreased PH2O and PACO2 decrease PAO2
Ambient lights effect on pulse oximetry
Increase in ambient light exposure increases DC signal, creating a poor pulse oximeter waveform, limiting its accuracy
Amiloride: MOA, side-effects
Potassium-sparing diuretic that acts on distal collecting ducts leading to hyperkalemia and sodium excretion.
Amount of fibrinogen in cryoprecipitate
200 mg/unit
Arterial waveforms: central (aorta) vs. peripheral
Peripheral waveforms:
Steeper upstroke
Higher systolic peak
Later dicrotic notch
Lower end-diastolic pressure
Wider pulse pressure (diff btw SBP and DBP)
60msec delay in systolic upstroke
ASA classification of physical status: 2
Mild systemic dz ex: well controlled DM, HTN, asthma (on inhalers), PREGNANCY, SMOKERS W/O COPD
ASA classification of physical status: 3
Severe systemic dz (no immediate threat to life) ex: DM w/ complications (retinopathy), asthma w/ hospitalizations, MI or CVA >6 mo ago, STABLE ANGINA, controlled CHF, ESRD on dialysis
ASA classification of physical status: 4
Severe systemic dz with constant threat to life ex: symptomatic CHF, MI or CVA <6 mo ago, UNSTABLE ANGINA, ESRD NOT on dialysis
ASA classification of physical status: 5
Moribund pt who won’t survive without surgery ex: septic shock, multi-organ failure, ICH with mass effect
ASA classification of physical status: 6
Declared brain dead, organ donor
At what point is cartilage totally absent from the airway wall?
Terminale bronchioles
Bainbridge reflex
Increases HR by inhibiting parasympathetic activity when stretch receptors located in the right atrial wall sense increased pressure
Benefit of additing opioid to epidural solution
- able to use more dilute LA
- prolongs duration of analgesia
- improves quality of sensory blockade
Biggest predictor of difficult intubation in morbidly obese pts?
Thick neck circumference (>40 cm)
Boyle’s Law
Shows effect of change in volume or pressure when temp remains constant
P1 V1 = P2 V2
Brachial artery catheterization risks
#1: vessel thrombosis
Infection
Median nerve injury
Burn pts and NMBA: how is dosing affected, why?
Burn pts exhibit resistance to NDNMBA resulting in increased dosing requirements due to upregulation of AcH receptors and increase in plasma protein binding
Calculate minutes until hypoxemia
Assumptions:
- oxygen consumption in an adult ~3-4 mL/kg/min
- FRC 30 mL/kg
min. until hypoxemia = [FRC/O2 consumption] x %O2 in FRC
Cardiovascular complications due to use of ketamine in critically ill patients
Ketamine is a direct myocardial depressant and smooth muscle relaxant but also blocks neuronal reuptake of circulating catecholamines, thereby leading to elevation of BP, HR, CO and myocardial oxygen consumption.
However, critically ill patient’s who have depleted their catecholamine stores or lack the ability to compensate via the sympathetic nervous system will experience decreased BP and CO.
Cardiovascular effects due to laparoscopic surgery
Increased cardiac filling due to increased intrathoracic pressure
Arrhythmias
Decreased venous return due to vena cava compression
Decreased EF
Decreased renal blood flow (results in decreased UOP 2/2 increased ADH secretion)
Decreased splanchnic perfusion
Cardiovascular effects of desflurane
Decreases arterial pressure by decreasing afterload
Increases HR, especially after quick concentration change
Dose-dependent depression of myocardial fxn
Maintains CO
Cardiovascular effects of ketamine
Direct myocardial depressant and smooth muscle relaxant. HOWEVER, also decreases neuronal reuptake of circulating catecholamines. Therefore, net result is:
- elevated BP
- elevated HR
- elevated CO
- increased myocardial oxygen consumption
Cardiovascular effects of Propofol
Propofol decreases sympathetic activity, therefore…
- Decreased SBP and DBP w/o increase in HR (CO, SV and SVR all decrease lowering BP while propofol inhibits baroreceptor response, therefore no reflexive increase in HR occurs)
- Myocardium depression (due to altered intracellular Ca2+ balance/influx)
- Both arterial and venous vasodilation
Causes of a sudden drop in EtCO2
Cardiovascular collapse (decreased CO)
VAE
PE
Kinked/dislodged ETT
Esophageal intubation
Sample line disconnect
Causes of BOTH elevated peak inspiratory pressure and plateau pressure
- Intrinsic pulmonary dz
- Ascites
- Insufflation
- Tension PTX
- Trendelenburg positioning
Causes of decreased mixed venous oxygen saturation (SvO2)
- Increased oxygen consumption (fever, shivering)
- Decreased CO (cardiogenic shock)
- Decreased [Hgb] (anemia)
- Decreased arterial oxygen saturation (methemoglobinemia)
Fick Equation:
SvO2 = SaO2 - [VO2/(CO x Hgb x 1.36)]
Causes of elevated peak inspiratory pressures with unchanged plateau pressure.
Why?
- Bronchospasm
- Kinked ETT
- Airway secretions
- Mucous plug
Peak inspiratory pressures directly proportional to changes in airflow resistance, while plateau pressure changes vary with change in lung compliance/elastic changes.
Causes of increased mixed venous oxygen saturation (SvO2)
- Inadequate regional blood flow (PVD)
- Decreased VO2 (sepsis, CN toxicity, hypothermia)
- Increased SaO2 (L to R intracardiac shunt, AV fistula)
- Increased [Hgb] (polycythemia)
Fick Equation:
SvO2 = SaO2 - [VO2/(CO x Hgb x 1.36)]
Causes of non-anion gap acidosis
FUSEDCARS:
- Fistula
- Ureteral diversion
- Saline administration
- Endocrine dfxn
- Diarrhea
- Carbonic anhydrase inhibitors (acetazolamide)
- Ammonium chloride (TPN component)
- RTA
- Spironolactone
Causes of prolonged succinylcholine duration of action
- Pseudocholinesterase deficiency
- Liver dz (why? pseudocholinesterase produced by liver)
- Pregnancy
- Malnutrition
- Malignancy
- Hypothyroidism
Causes of rebreathing CO2
Depleted CO2 absorbent
Dysfunctional circuit valve
Low FGF
Improper calibration of bellows
Central action of opioids in CNS
- Activate descending inhibitory pain pathway via inhibition of GABA receptors in the brainstem
- Provide analgesia via mu1 receptors in periaqueductal gray matter, locus ceruleus and nucleus raphe magnus
Characteristics of depolarizing blockade
- No fade in response to repetitive stimuli
- No amplification in force of subsequent muscle contractions after period of high-frequency stimulus (tetany)
Characteristics of non-depolarizing blockade
- Progressive decrease (fade) in response to repetitive stimuli
- Potentiation of evoked responses with high-frequency stimulation (tetany) = increased amplitude and decreased fade of response
Characteristics of Propofol-infusion syndrome
Acute refractory bradycardia
Severe metabolic acidosis
Cardiovascular collapse
Rhabdomyolysis
Hyperlipidemia/hypertriglyceridemia
Renal failure
Hepatomegaly
Charle’s Law
Shows effect of change in V or T when pressure remains constant
V1 / T1 = V2/ T2
CNS effects of ketamine
- increases CMRO2
- increases CBF (therefore, increases CBV)
- elevates ICP
CNS effects of meperidine. Why?
Tremors
Muscle twitches
Seizures
Meperidine is a synthetic opioid, acts on mu-receptors, metabolized in liver to normeperidine- t1/2 15-30 hrs, no mu-receptor activity but is a CNS STIMULANT.
CNS effects of opioids
- reduce MAC of inhaled anesthetics
- normeperidine-induced seizures
- reduce cerebral metabolic oxygen requirement
- reduce CBF
- reduce ICP (except in TBI!)
- opioid induced respiratory depression and associated mydriasis
- stimulate area postrema in brainstem leading to N/V
- interfere with serotonin uptake causing serotonin syndrome
CNS effects of propofol
- hypnosis via agonism at beta subunit of GABA-A receptor and inhibition of glutamate binding site on NMDA receptors
- decreases IOP
- decreases CMRO2 and CBF, leading to decrease ICP
Common causes of anion-gap metabolic acidosis
MUDPILES
Methanol (formic acid)
Uremia
DKA
Paraldehyde
Iron, Isoniazid
Lactic acidosis
Ethanol
Salicylates
Common drugs associated with Serotonin syndrome
- Levodopa, Carbidopa-levodopa
- SSRI (citalopram, fluoxetine, sertraline)
- SNRI (duloxetine, venlafaxine)
- Dopamine-NE reuptake inhibitor (bupropion)
- Trazodone
- TCAs (amitriptyline, clomipramine)
- Valproate, Carbamezepine
- St. John’s Wort
- Dextromethorphan
Common trauma related causes of HoTN
- # 1 = hemorrhage
- Abnl cardiac pump fxn (myocardial contusion, tamponade, coronary artery dissection, valve injury)
- PTX
- Hemothorax
- Spinal cord injury
Complications associated with succinylcholine
- bradycardia, asystole (esp. in children)
- fasciculations, myalgias
- elevated IOP
- elevated ICP
- elevated serum K+
- rhabdomyolysis/fatal hyperkalemia in children with muslce dystrophies
- malignant hyperthermia (associated with concomittant IA use)
- masseter muscle spasm
Complications of neuraxial anesthesia
Hypotension
Bradycardia
Postdural puncture HA
Epidural hematoma (reqs emergent evacuation)
Infx- epidural abscess, meningitis
Urinary retention
Transient neurologic sx- spinal only, occurs 24hrs after block wears off, causes severe buttock pain but no sensory or motor deficits
LAST
Complications of sodium bicarbonate administration
- Left shift of oxygen dissociation curve due to increasing pH, leading to tissue hypoxia, subsequent anaerobic metabolism and worsening lactic acidosis
- Depression of LV contractility, as sodium bicarbonate will transiently decreased serum ionized [calcium]; LV contractility is proportional to serum ionized [calcium]
- Increased preload, as sodium bicarbonate is a hypertonic solution (~1,800 mOsm/L), leading to increased intravascular volume
- Risk of elevated ICP and ICH, especially in infants, due to volume expansion in setting of sodium bicarbonate conversion to PCO2 leading to cerebral vasodilation
Conditions associated with latex allergy. Why?
Spina bifida
Urogenital syndromes
Frequent exposure to latex foley catheters and surgical equipment with latex
Consideration for pt undergoing retinal detachment surgery with use of SF6 (sulfur hexafluoride)
AVOID NITROUS OXIDE FOR 4 WEEKS! N2O can raise IOP by expanding air bubble.
SF6 used as intraocular gas during retinal detachment surgery.
Contraindications for cricoid pressure
Active vomiting
Unstable cervical spine
Contraindications of ketamine
Increased ICP
Increased IOP or open eye injury
ICM lesion
Ischemic heart disease
Vascular aneurysm
Psych hx, including PTSD, Schizophrenia
Contraindications of LMA
Unknown PO status (pt can aspirate around LMA)
Restrictive pulmonary dz (decreased chest wall compliance, LMA not intended for positive pressure ventilation)
Non-supine positioning, ie: lithotomy
Obesity
Pregnancy
Intra-abdominal procedures
Prolonged surgical time
Contraindications of nasotracheal intubation
Severe coagulopathy
High-dose systemic anticoagulation
Nasal pathologies or mass lesions
Infection of paranasal sinuses
Basilar skull fracture
TBI with CSF leak
Contraindications to electrical defibrillation
- pulseless electrical activity (PEA)
- asystole
- VT with pulse and perfusable rhythm (once unstable, should receive cardioversion; only defibrillate once pulseless)
- wet environment
Contraindications to sugammadex
Pts with allergy to cyclodextrins
Pediatric pts
ESRD
Reversal of agents other than rocuronium/vecuronium
Contraindications to use of EMLA cream
Allergy to amides (lidocaine, prilocaine)
Use of class III antiarrhythmics (amiodarone, sotalol, dofetilide)
Hx of congenital methemoglobinemia
Contraindications to use of N2O
Venous/arterial air embolism
PTX
Intestinal obstruction with bowel distention
Pneumocephalus
Pulmonary blebs
Intraocular procedures
Tympanic membrane procedures
Coronary artery perfusion of left ventricle
LAD, diagonals:
- medial aspect anterior wall
- anterior 2/3 septum
- apex
Left circumflex, marginals:
- anterior/posterior aspect of lateral wall
RCA:
- medial posterior wall
- posterior 1/3 septum
Critical side-effect of Naloxone administration
Pulmonary edema
CSF flow
Produced in lateral ventricles —> third ventricle via intraventricular foramina —> fourth ventricle via cerebral aqueduct —> subarachnoid space to surround brain and spinal cord
Cushing’s triad
HTN
Bradycardia
Respiratory changes
*sign of elevated ICP and impending uncal herniation.
CYP2CP metabolism
- Phenytoin
- Warfarin
- Ibuprofen
CYP2D6 metabolism
- Beta blockers
- Amiodarone
- Codeine
- Tramadol, Fentanyl, Oxycodone
Effect of damage to Recurrent Laryngeal nerve, unilateral
Hoarseness
Ddx: Large R wave in lead V1
- Right ventricular hypertrophy
- Posterior wall MI
- WPW
- Muscular dystrophy
- Right atrial enlargement
Define critical pressure
The pressure required to liquefy a gas at its critical temperature.
Remember, critical temperature is the temperature above which no amount of pressure can convert a gas to liquid.
Define critical velocity
Critical velocity is the velocity at which flow turns from laminar to turbulent flow.
Critical velocity is dependent on:
- radius of the tube (r)
- viscosity (Π)
- density (þ)
- Reynolds number (k)
Critical velocity = kΠ ÷ þr
Definition mixed venous oxygen saturation, SvO2
Measure of peripheral tissue perfusion signified by %O2 bound to Hgb in blood returning to right atrium (blood captured from SVC, IVC, coronary sinus)
Definition of critical temperature
Highest temperature at which a gas can exist in liquid form
Definition of efficacy
Maximum effect produced by a drug.
Efficacy does not depend on dose.
Definition of neurogenic shock
Hypotension and bradycardia caused by the loss of vasomotor tone and sympathetic innervation of the heart as a result of functional depression of the descending sympathetic pathways of the spinal cord.
It is usually present after high thoracic and cervical spine injuries and improves within 3 to 5 days.
Definition of potency
Dose required to produce a given effect.
Related to receptor affinity. S
maller dose needed for given effect, the higher the potency.
Definition of viscosity
Resistance to flow. Also, internal friction between adjacent fluid layers sliding past each other. Increases based on opportunity for hydrogen bonding, components of fluid and molecular size.
Definition: Difficult endotracheal intubation
>3 attempts or >10 minutes
Definition: Difficult mask ventilation
Inability of unassisted anesthesiologist to maintain SpO2 >92% or prevent/reverse signs of inadequate ventilation.
Definition: General Anesthesia
GA occurs when pt loses consciousness and ability to respond purposefully, whether or not airway instrumentation occurs
Definition: Monitored Anesthetic Care
MAC = varying levels of sedation, analgesia, anxiolysis; provider must be prepared to convert to general anesthesia when necessary
Describe Alveolar-arterial gradient
A-a gradient measures pulmonary shunt to determine the efficacy of pulmonary oxygenation of arterial blood.
A-a gradient in healthy pt < 10mmHg
Normal gradient exist due to physiologic shunting through bronchial and coronary veins that drain deoxygenated blood directly into left heart.
Describe blood/gas coefficient
It is the ratio of the concentrations of a compound in one solvent to the concentration in another solvent at equilibrium.
The blood/gas partition coefficient describes how the gas will partition itself between the two phases (blood/alveoli) after equilibrium has been reached.
High solubility = more anesthetic needs to be dissolved = slower onset
MAC decreases as blood gas partition coefficient increases, generally speaking
Describe boiling point
Boiling point is reached when vapor pressure is in equilibrium with external ambient pressure exerted on liquid surface.
Describe cardiac side-effect of isoflurane
Isoflurane has been shown to dilate coronary arteries that can lead to coronary steal syndrome. Coronary steal refers to narrowed coronary arteries with collateral microvasculature that becomes bypassed leading to myocardial ischemia in that distribution.
Describe dampening of a system.
What are signs of increased dampening?
Name causes of system dampening.
Dampening refers to the decrease of signal amplitude that accompanies a reduction of energy in an oscillating system.
Signs of increased dampening include:
- decrease in SBP
- increase in DBP
In a pressure transducer system, most dampening arises from factors that decrease energy in the system:
- friction between tubing and fluid within the tubing
- 3-way stopcock
- bubbles
- clots
- arterial vasospasm
- large catheter size
- narrow, long or compliant tubing
Describe “defibrillation”
During defibrillation, a RANDOMLY timed high-voltage electric current is discharged across two electrodes in attempt to SIMULTANEOUSLY DEPOLARIZE a large critical mass of myocardium. This would cause nearly all ventricular myocytes to enter their absolute refractory periods where no action potentials can be generated. At this point, the pacemaker with the highest automaticity (SA or AV node) will take control of ventricular pacing and contraction.
Describe dibucaine-resistant cholinesterase deficiency study
- Examines pt serum in those with suspected genetic mutations in pseudocholinesterase (homozygous, heterozygous)
- Dibucaine is a local anesthetic that inhibits pseudocholinesterase by 80% (Dib # = 80)
- If pseudocholinesterase is atypical due to homozygous mutation, dibucaine will inhibit it by only 20% (Dib # =20)
- If pseudocholinesterase is atypical due to heterozygous mutation, dibucaine will inhibit it by 40-60% (Dib # = 40-60)
- Pts with homozygous mutation, Dib # 20, will have an extremely prolonged block with phase II characteristics. Heterozygous pts will have a moderately prolonged block.
Describe discovery of meperidine and why this is important in understanding its side-effects
First used for its anticholinergic activity, as it has a structure similar to atropine.
Side-effect is tachycardia.
Describe effects of bradykinin
Promotes vasodilation by increasing production of arachidonic acid metabolites and nitric oxide.
Increases natriuresis (sodium excretion) via direct tubular effects.
Usually degraded by ACE
Describe features of NMDA receptor activation
Cell membrane must be depolarized
Mg2+ removed by depolarization
Glutamate (+/- glycine) bind to ligand-gated channel
Sodium and CALCIUM influx (Ca2+ responsible for 2nd messenger signaling cascade)
Potassium efflux
Describe fluoride-induced nephrotoxicity
Related to hepatic metabolism of IA and production of fluoride ions causing direct toxicity to collecting ducts leading to high-output renal failure that is unresponsive to vasopressin.
Describe function of carotid body (ies)
Chemoreceptors that respond to reductions in arterial partial pressure of oxygen (PaO2), “hypoxic drive”.
Associated with afferent glossopharyngeal n. that are stimulated when PaO2 < 60-65mmHg, leading to increased MV.
Describe Henry’s Law.
Name a common application of Henry’s Law.
States that for a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
Therefore, at equilibrium, there will be the same number of molecules existing in the gaseous phase and in the dissolved (liquid) phase, both exerting the same kinetic energy.
Common application = solubility of gases
- As temperature drops, gas solubility increases
Describe Hepatic Artery Buffer Response system
Mediated by adenosine, used to maintain total hepatic blood flow when reciprocal changes occur in portal vein
ie: portal vein blood flow increases –> hepatic artery will vasoconstrict
Describe laminar flow
Particles flow in one direction, parallel to tube/wall and down a pressure gradient.
Flow is fastest in the center and decreases parabolically due to friction.
Resistance directly related to flow rate.
Poisseuille’s law follows laminar flow.
Describe landmarks for Femoral nerve block
Bony structures = ASIS (lateral), pubic tubercle (medial)
Inguinal ligament
Femoral vein –> Femoral artery –> Femoral nerve (medial –> lateral)
Femoral nerve lies superficial to psoas muscle, fascia iliaca draps its anterior
Describe MOA of antiplatelet activity of dipyridamole
Dipyridamole inhibits both PDE and adenosine reuptake. Normally, PDE breaks down cAMP. When cAMP levels are high, PLT unable to aggregate due to cAMP inhibition of thromboxane A2.
Describe origin and pathway of cardiac sympathetic fibers
Originate at T1-T4, traveling to the heart through cervical (stellate) ganglia.
Describe pharmacology of fenoldopam
- Selective peripheral dopamine-1 receptor agonist
- Causes systemic arteriolar vasodilation leading to reduced afterload
- Improves renal blood flow, diuresis, natriuresis
- Short duration of action and elimination half-time
- Indicated for short-term management of HTN emergency
- Side-effects include HA, flushing, reflex tachycardia, elevated IOP (related to arteriole dilation)
- Contraindicated in pts with allergy to sulfa due to preservative, sodium metabisulfite
Describe production of CSF
- Produced in the lateral ventricles by choroid plexus
- 20 mL/h (500 mL/d)
- Total CSF volume 100-150 mL, maintained via absorption at arachnoid villi in cerebral venous sinuses
Describe redistribution. Why is it an important concept?
[tissue]=[plasma] causes redistribution in which drugs return from tissues back into plasma, therefore, slowing the rate of decline in [plasma drug]. Redistribution generally delays emergence as tissue reservoirs continue to feed [plasma drug]
Describe relationship between volume of distribution and drug plasma concentration
Inverse relationship: Large VOD = lower [drug plasma]
Describe resonance of a system.
Name factors that increase the natural frequency of the system, and therefore minimizes resonance.
Every system has a frequency at which it oscillates, called the natural frequency. If a force with similar frequency to the natural frequency of a system is applied, the system will oscillate at maximum amplitude. This is resonance. Resonance produces excessive amplification that distorts the electrical signal. In an invasive arterial BP monitoring system, this results in greater SBP, lower DBP and increased pulse pressure.
Factors that minimize resonance:
- Reduce tubing length
- Reduce compliance of tubing
- Reduce density of fluid in tubing
- Increase diameter of tubing
Describe surfactants role in non-respiratory functions of the lung
Produced by type II alveolar epithelial cells, surfactant plays many roles outside of decrease surface tension within alveoli:
- increases bacterial cell wall permeability
- stimulates macrophage migration
- stimulates synthesis of IgX and cytokines
Describe the basal ganglia:
- site of input
- site of output
- associated dz state
- Basal ganglia is part of the extrapyramidal system important for control of movement and posture
- Basal ganglia are made up of the caudate nucleus, putamen, globus pallidus and substantia nigra
- Site of input is via the striatum made up of the caudate nucleus and putamen
- Site of output is via the globus pallidus and substantia nigra
- Globus pallidus sends inhibitory outputs to the thalamus
- Degeneration of the pars compacta substantia nigra alters basal ganglia neurotransmission causing Parkinson’s disease (dfxn dopaminergic pathway)
- Degeneration of the caudate and putamen causes Huntington’s disease
Describe the Bezold-Jarisch cardiovascular reflex
Parasympathetic-mediated reflex occurs when stretch receptors located in the LV respond to an acute decrease in LV preload, resulting in bradycardia and reduced contractility.
Describe the corticospinal tract
- Descending pathway involved in limb and axial motor movement
Precentral gyrus—> corona radiata and internal capsule—> pons—> 85% decussate to form pyramids and descend as the lateral corticospinal tract—> synapse in anterior/ventral horn onto lower motor neurons—> limb motor movement
…pons—>15% don’t decussate in brainstem but rather continue to descend ipsilaterally as the anterior corticospinal tract—> decussate at the anterior white commissure and synapse in anterior/ventral horn onto lower motor neurons—> axial motor movement
Describe the dorsal column/medial lemniscus pathway
- Ascending pathway carries fibers that control fine touch and proprioception
- 3 neuron system (DRG, cunate/gracile nucleus, VPL)
Peripheral receptors (Meissner’s and Pacinian corpuscles, muscle stretch receptors, golgi tendon organs)—> cell body located in DRG—> fibers travel up dorsal column (cunate or gracile fasciculus)—> terminate at cell body in medulla oblongata (nucleus of cunate or gracile)—> decussate to become the medial lemniscus—> synapse on the ventral posterior lateral (VPL) nucleus in thalamus—> travel through internal capsule—> terminate in postcentral gyrus
Describe the effect that disease states causing decrease in AcH receptors (ie: MG) has on NMB agents
Fewer AcH receptors demonstrates a sensitivity to depolarizing agents (sux, fewer receptors to depolarize) and increased sensitivity to non-depolarizing agents (fewer receptors to impose conformational change on)
Describe the Haldane effect
Describes CO2 transport from tissues to lungs
Based on fact that deoxyhgb has 3.5x more capacity for CO2 than oxyhgb
- Once CO2 enters RBC (Hgb), it combines with H20 to form carbonic acid via carbonic anhydrase
- Carbonic acid rapidly releases H+ protons, forming bicarbonate, which diffuses from the RBC into plasma; H+ protons bind to histidine residue of Hgb
- Chloride ions replace bicarbonate to maintain neutrality
- Once RBC reaches lungs, Hgb is met with high [O2], which decreases Hgb affinity for H+ ions
- H+ then binds with bicarbonate to form CO2 + H20, CO2 is exhaled
Describe the lateral spinothalamic tract
- Ascending pathway carries fibers involved in pain and temperature
- 3 neuron system (DRG, substantia gelatinosa, VPL)
Peripheral receptors–> cell body in DRG—> ascend spinal cord through Lissauer’s fasciculus (white matter) 1-2 levels—> synapse onto cell body in dorsal horn = substantia gelatinosa (rex lamina II)—> axons decussate to the lateral spinothalamic tract—> synapse on the ventral posterior lateral (VPL) nucleus of the thalamus—> internal capsule—> postcentral gyrus
Describe the most important feature of CO2 absorbent. Why?
Granule size - Smaller granules have greater surface area for absorption but increased resistance to air flow.
Ideal granule size is 4-8 mesh
Describe the oculocardiac reflex (OCR)
Reflex that results in bradycardia, possible cardiac arrest secondary to traction on the EOM or pressure on the eyeball.
Stimuli at the eye –> ciliary ganglion –> ophthalmic division of trigeminal n –> gasserian ganglion –> trigeminal nucleus –> vagus n –> bradycardia
Describe the pattern of CNS symptoms in lidocaine toxicity
Perioral and tongue numbness > tinnitus > lightheadedness, dizziness > muscle twitching > seizures > coma > respiratory depression > cardiovascular collapse
Describe the Sciatic nerve, including origin and branches
Origin = L4-S3, lumbosacral nerve, travels down posterior thigh into popliteal fossa
Branches = Tibial nerve and Common Peroneal nerve
Describe therapeutic window
The range of a drug between the concentration associated with desired therapeutic effect and the concentration associated with a toxic drug response.
Describe Transient Neurologic Symptoms following spinal anesthesia.
Name risk factors.
Associated with lidocaine spinal anesthesia, causing LBP, buttocks and LE pain/sensory changes.
Risk factors include lidocaine anesthetic, lithotomy, ambulatory anesthesia.
Describe turbulent flow
Particles move in all directions, flow rate is the same across the diameter of the tube.
Pressure difference will increase to maintain flow and in turn increases resistance.
Gas density more important than viscosity.
Describes features of Fentanyl CSHT
Long and variable CSHT:
Highly lipophilic (hydrophobic) –> large VOD –> rapid redistribution–> requires metabolism by liver enzymes–> slower decrease in plasma drug concentration
Desflurane and impact on MAC delivered due to altitude changes
Desflurane Tec 6 vaporizer is a dual-gas blender that will deliver anesthetic directly proportional to the atmospheric pressure change.
In other words, MAC delivered will be inversely proportional to altitude change
(6% des (1 MAC) at 1 atm = 3% des (0.5 MAC) at 0.5 atm)
Desflurane has lower blood:gas coefficient number than N20 but slower rate of induction. Which concept explains this disparity?
Concentration effect of N20
Difference between carotid sinus vs. carotid body
Carotid sinus is a mechanoreceptor, responding to changes in pressure.
Carotid body is a chemoreceptor, responding to changes in oxygen/CO2 levels in blood.
Difference between physiologic dead space ventilation vs. physiologic shunt
Physiologic dead space ventilation applies to areas of the lung that are ventilated but poorly perfused, physiologic shunt occurs in lung that is perfused but poorly ventilated.
The physiologic shunt is that portion of the total cardiac output that returns to the left heart and systemic circulation without receiving oxygen in the lung.
Difference in vapor pressure between volatile anesthetics at 20 C
Desflurane 670 >>> Isoflurane 240 > Sevoflurane 160
Differential diagnosis: Hypoxemia and normal CXR
Pulmonary embolism
Obstructive lung dz (asthma)
Mucuos plugging
Intrapulmonary shunt
Methemoglobinemia
Downregulation of AcH receptors and NMBA
Downregulation causes decreased number of AcH receptors at NMJ due to sustained/chronic receptor agonism (chronic neostigmine use, organophosphate poisoning)
- Decreased sensitivity/increased resistance to AcH/Suxx
- Extreme sensitivity to NDNMBA
Drug used in post-op shivering
Meperidine
(Demerol)
Drug used to reverse central anticholinergic and also, hypnotic effects of ketamine
Physostigmine
Drugs that follow zero-order kinetics
THE PAW
Theophylline
Heparin
Ethanol
Phenytoin
Aspirin
Warfarin
Drugs that interfere with CSF production
Decrease CSF production:
- acetazolamide
- furosemide
- thiopental
Increase CSF production:
- desflurane
- halothane
- ketamine
E-cylinder gas and corresponding color (U.S.)
Oxygen: Green
Nitrous oxide: Blue
Carbon dioxide: Gray
Air: Yellow
Helium: Brown
Nitrogen: Black
ECG: Left anterior descending artery ischemia
Effects septal and/or anterior left ventricle
V1-V4, often V5-V6
ECG: Left circumflex artery ischemia
Effects lateral left ventricle.
I, aVL, V5-V6
ECG: Left main artery ischemia
Involves territory of LAD and LCx
I, aVL, V1-V6
ECG: Right coronary artery ischemia
Inferior territory
II, III, aVF
Effect of anti-epileptic drugs on neuromuscular blockade
Acute administration –> potentiates blockade
Chronic administration –> decreases duration of action of aminosteroid NDNMBA
Effect of co-administration of Ketamine and Mg2+. Why?
Potentiates effect of ketamine.
Mg2+ blocks NMDA receptor channel at rest, therefore, will assist in “antagonizing” the receptor.
Effect of damage to Recurrent Laryngeal nerve,
bilateral
Aphonia
Airway obstruction
*Partial injury to nerve = leads to bilateral adduction of vocal cords
Complete transection = paralyzed cords in paramedian position but act as “curtains” so still able to pass ETT
*partial nerve injury is worse
Effect of hypermagnesemia on NMBA blockade
Prolongs duration of action of NMBA blockade by inhibiting Ca2+ channels both pre and post-synaptically
Effect of hypokalemia on NDNMBA blockade and reversal
Hypokalemia potentiates blockade and decreases effectiveness of anticholinesterase antagonism of nondepolarizing blocks.
Effect of ionotropy
Positive ionotropes increase contractility, augment cardiac output and thereby enhance end-organ perfusion.
Effect on output and IA concentration if IA agents are placed into the wrong vaporizer
Vaporizers are IA agent specific based on differences in vapor pressure
- if a vaporizer calibrated for high vapor pressure (ie: iso) is filled with an agent with low vapor pressure (ie: sevo), less output/lower agent concentration will be delivered
- if a vaporizer calibrated for low vapor pressure (ie: sevo) is filled with an agent with high vapor pressure (ie: isoflurane), increased output/higher agent concentration will be delivered
Effects of Dobutamine
High affinity for beta-1 receptors, also acts on alpha-1 and beta-2 receptors but with equal affinity thereby resulting in no net effect on vascular tone
Increases conductance through the SA node
Effects of epinephrine on local anesthetic
- prolongs duration of block
- increases intensity of block
- decreases systemic absorption of LA
How? Epinephrine causes vasoconstriction that counteracts the vasodilatory effects inherent to LA. Therefore, epinephrine causes decreased systemic absorption, decreases intraneural clearance of LA and may have direct analgesic effects vvia alpha 2 receptors in brain and spinal cord.
Effects of nitric oxide (NO)
Also known as Endothelium-derived relaxing factor (EDRF)
Vasodilation
Antiaggregation of PLTs
Stimulates insulin release in pancreas
Modulates pain response
When bound to Hgb, causes pulm vasodilation
Effects of Phosphodiesterase inhibitors (PDIs) (Milrinone, amrinone, enoximone)
1) increase inotropy thereby improving cardiac output
2) improved lusitropy (myocardial relaxation)
3) decrease pulmonary vascular resistance thereby improve right ventricular outflow
4) vasodilation and reduced afterload
EKG finding for right ventricular hypertrophy
Large R wave in lead V1
Electrolyte abnormalities caused by thiazides
Hyponatremia
Hypokalemia
Hypomagnesia
Hypercalcemia
Hyperglycemia
Hypercholesterolemia
Hyperuricemia
Elimination of methohexital
Feces
All other barbiturates are renally excreted
Elimination of neostigmine
50% renal excretion, therefore, duration of action is likely to be prolonged in renal failure pts.
Endocrine effects of opioids
Suppresses FSH, LSH, ACTH, TSH, GH
Elevates prolactin
Enzyme inhibited by SSRIs?
CYP2D6
Equation for coronary perfusion pressure of left ventricle (CPPLV)
CPPLV = ADP - LVEDP
(Aortic diastolic pressure - LV end-diastolic pressure)
Equation: CO
CO= HR x SV
How to measure CO?
PA catheter
TEE
Esophageal doppler
Equation: Estimate time remaining in an E-cylinder
Time remaining (t)= Remaining cylinder pressure (PSi)/ (200 x Flow rate L/min)
(t) is measured in hours
Ex: 1000PSi remaining at Flow rate 5 L/min means you have 1 hr left to use that E-cylinder
Equation: MAP
MAP= SVR x CO
Equation: SVR
SVR= 80 x (MAP - CVP) / CO
Expected challenges in patients with Ankylosing Spondylitis (AS)
Difficult endotracheal intubation- AS as/w atlantoaxial instability and decreased ROM in cervical spine.
Difficult mask ventilation- TMJ hypomobility leads to ill-sealing facemasks.
AS as/w pulmonary fibrosis.
Epidural hematoma- lumbar spine fusion leads to increased attempts.
Many AS pts rely on NSAIDs for pain relief, resulting in plt dfxn and increased bleeding risk.
Explain difference between total body sodium and sodium concentration in vivo
Total body sodium caused by increase/decrease in ECV/plasma; involves aldosterone, ANP
Sodium concentration disorders due to excess/deficit of free water; involves ADH
*think: hyperaldosteronism as/w hypervolemia (increased ECV) resulting in HTN but is NOT as/w abnormal [Na+]
Facial nerve muscle innervation and TOF monitoring
Facial nerve innervates orbicularis oculi (moves eyelid) and corrugator supercili (moves eyebrow).
Neuromuscular blockade recovery time at the eyelid is similar to that of the adductor pollicis muscle (peripheral muscle), whereas recovery time at the eyebrow is similar to that of laryngeal muscles and diaphragm (central muscles).
Factors that affect the likelihood of terminating ventricular fibrillation via defibrillation (electrical current)
Low success:
- time spent in dysrhythmia (longer time = worse outcome)
- non-ischemic causes of cardiac arrest (tamponade, Tptx, PE, etc)
Higher success:
- ischemic causes of cardiac arrest (MI)
- applying firm pressure on paddles (~25 lbs)
- using proper paddle size, conductive gel
- defibrillating on end-expiration
- stacked shock strengths
Factors that affect the rate of diffusion of gases across a membrane
Based on Fick’s Law of Diffusion
Vgas = A x D X (P1-P2) ÷ T
- A = surface area of barrier
- D = diffusion cofficient (directly proportional to solubility and inversely proportional to sq root of molecular wt)
- P1-P2 = partial pressure difference across the barrier
- T = barrier thickness
Factors that increase diffusion:
- low molecular weight
- increased solubility
- increased partial pressure gradient
- increased barrier surface area
- decreased thickness of barrier
Factors that contribute to volume of distribution
Lipophilicity and protein binding
Lipophilic drugs and high tissue protein binding drugs have higher VoD
Increased plasma protein binding has smaller VoD
Factors that decrease MAC
IV anesthetics
Acute EtOH intoxication
Chronic amphetamine use
Lithium
Advanced age
Hyponatremia
Anemia
Hypercarbia
Hypoxemia
Hypothermia
Factors that determine resistance to gas flow in laminar flow
Gas viscosity and radius of the airway
Factors that determine resistance to gas flow in turbulent flow
Gas density and increasing flow rate
Factors that enhance alveolar concentration of inhaled anesthetic
Low blood solubility, decreased cardiac output, increased ventilation
Factors that increase insulin release
Enteral feeds
beta-adrenergic stimulation
alpha-adrenergic blockade
Nitric oxide
Factors that increase likelihood that flow in a tube will become turbulent
- increased velocity
- increased tube diameter
- increased fluid density
- decreased fluid viscosity
Reynolds number describes turbulent vs laminar flow
Reynolds number = (velocity x density x diameter) / viscosity
- Reynolds number <2000 = laminar flow
- Reynolds number >4000 = turbulent flow
Factors that increase MAC
Amphetamines
Cocaine
Ephedrine
Chronic EtOH use
Hypernatremia
Hyperthermia
Factors that increase risk of emergence rxn with ketamine
Adults > pediatrics
Womyn > men
Larger doses with rapid administration
Factors that increase risk of nausea with spinal anesthesia
Hx of motion sickness
Block above T5 (sympathectomy)
Hypotension
Opioid use
Factors that increase risk of post-op urinary retention
- Pelvic/GU/rectal surgery
- Hernia repairs
- Periop urinary catheterization
- Hx of urinary retention
- Neuraxial anesthesia (increased risk with hydrophilic opioids, ie: morphine)
Factors that increase risk of pressure neuropraxia with LMA use
Overinflation of cuff
Prolonged operative times
Lidocaine lubrication
Difficult insertion
Use of nitrous oxide (displaces air within cuff and can increase cuff pressure by 30 mm Hg)
Cervical joint dz
Factors that potentiate (prolong) the action of NMBA
- Volatile anesthetics
- Local anesthetics
- CCB
- Beta blockers
- Antibiotics (aminoglycosides)
- Magnesium
- Chronic steroid use
- Dantrolene
- Respiratory acidosis
- Metabolic alkalosis
- Hypothermia
- Hypokalemia
- Hypercalcemia
- Hypermagnesemia
Factors that predict degree of nerve blockade by local anesthetic
Drug concentration and volume
Fasting guidelines
Clear liquids, 2H
Breast milk, 4H
Infant formula, 6H
Cows milk, 6H
Solids, 6H
Fried food, 8H
Features of stage 1, GA
- induction stage, ends with LOC
- respiration is slow but regular
- eyelid reflex INTACT
Features of stage 2, GA
- “excitement” phase- disinhibition, delirium, spastic movements
- loss of eyelash reflex
- divergent gaze
- reflex pupillary dilatation
- airway irritability- risk of cough, vomiting, laryngospasm, bronchospasm
- irregular respirations and breath holding
Features of stage 3, GA
- period when target level of surgical anesthesia is reached
- cessation of eye movement
- skeletal muscle relaxation
- respiratory depression
Fentanyl and propofol are both highly lipophilic with large VOD. Why then does propofol have a shorter CSHT?
The rapid redistribution of fentanyl back to plasma prevents the plasma concentration from quickly falling after the infusion is stopped, even though fentanyl is rapidly cleared (1530 mL/min).
Fick equation for cardiac output
CO = O2 uptake by lungs (ml/min) / (O2 artery - O2 vein)
*arterial oxygen is from left heart, venous oxygen is from right heart
Fick equation: SvO2
SvO2 = SaO2 - [VO2 / (CO x Hgb x 1.36)]
Full E-cylinder: volume, pressure
Oxygen- 625 L, 2200 Psi
Air- 625 L, 2200 Psi
Nitrous- 1,590 L, 745 Psi
General causes of metabolic alkalosis
Vomiting (NG suctioning)
Diuretic use
GI side-effects of succinylcholine
Increased intra-gastric pressure and increased LES tone (LES tone effect > gastric pressure, therefore, as long as LES is competent, there is no increased risk of aspiration)
Graft Versus Host Disease (GVHD):
Pathology, S/Sx, Timing, Ppx
Pathology = Viable lymphocytes in DONOR blood attack recipient tissues. Recipient is IMMUNOSUPPRESSED so can’t mount response
S/Sx = fever, rash, cytopenia, liver dfxn, diarrhea
Timing = 3-4 wks post-transplant
Ppx = irradiated blood to reduce donor WBCs or leukoreduction filter use
Hepatic acinus zone most susceptible to toxins, ie: acetaminophen overdose
Zone 1, hepatocytes closest to hepatic arterioles and therefore, first zone to come in contact with blood toxins
Hering-Breuer reflex
Prevents overinflation of the lungs
How do changes in atmospheric pressure affect boiling point? Why?
Lower atmospheric pressure will lower boiling point. Boiling point is reached when vapor pressure of liquid is equal to the external pressure exerted on its surface. Therefore, if external pressure is lower, vapor pressure is lower.
How do changes in cardiac output effect uptake of volatile anesthetics in blood?
Higher CO > greater volume of blood perfuses the lungs > removes more inhalation anesthetic from alveoli > decreases concentration of anesthetic in lungs > lowers alveolar, arterial and therefore brain partial pressures of inhaled agent > delay in anesthetic induction
How does a right-to-left cardiac shunt effect IA induction? Why?
Slows induction.
First, anesthetic gas leaving pulmonary arteries are diluted by deoxygenated blood from the right heart.
Second, FA/FI is not effected much.
Even though there is a higher gradient between mixed venous partial pressure and alveolar partial pressure (favoring uptake), less lung is perfused to participate in gas exchange, so overall there is decreased uptake.
How does alkalinization speed onset of local anesthetics?
Alkalinization increases the percentage of molecules in their unionized form, therefore, molecules that can cross lipid bilayers and act on voltage-gated sodium channels
How does half-life of a drug relate to volume of distribution and drug clearance?
Half-life to clearance= inverse relationship, faster clearance= shorter half-life
Half-life to VOD= proportional relationship, larger VOD, longer half-life
How does HR influence hypotension?
Either tachycardia or bradycardia can cause hypotension if CO is decreased.
Bradycardia–> enhanced ventricular filling, increased SV but based on CO equation (CO= HR x SV), severely slow HR can lead to decreased CO
Tachycardia–> insufficient time for left ventricular filling resulting in low CO
How does plasma clearance effect context-sensitive half-time of a drug?
High plasma clearance = faster/shorter context-sensitive half-time (think Remifentanil)
How does PTH raise serum calcium levels?
- stimulates osteoclastic bone resorption
- activates distal tubule calcium reabsorption
- conversion of vitamin D to calcitriol, which increases gut absorption of calcium
How does redistribution effect context-sensitive half-time of a drug? Why?
Slower redistribution = faster/shorter context-sensitive half-time
Drug is being cleared from plasma faster than drug returning to plasma from tissue compartments.
How does single administration epidural morphine compare to fentanyl?
Fentanyl is much more lipophilic than morphine, and will cross out of the epidural space resulting in a more restrictive segmental spread!
Since morphine is more hydrophilic, it does not cross out but rather remains within the epidural space with greater chance of rostral spread. This is why we worry about delayed respiratory depression with neuraxial morphine!
How long after the last dose of LMWH can neuraxial procedure be performed?
Therapeutic doses- 24 hrs
Prophylactic doses- 12 hrs
How much CO2 can soda lime absorb?
23-26L of CO2 per 100g of absorbent
How to calculate appropriate metabolic compensation for respiratory alkalosis
Acute = 24 - 0.2 x (40 - PaCO2)
Chronic = 24 - 0.5 x (40 - PaCO2)
How to calculate appropriate metabolic compensation for respiratory acidosis
Acute = 24 + 0.1 x (PaCO2 - 40)
Chronic = 24 + 0.4 x (PaCO2 - 40)
How to calculate appropriate respiratory compensation for metabolic derangement
Metabolic acidosis: Winter’s Formula
PaCO2 = (1.5 x HCO3-) + 8
Metabolic alkalosis: Summer’s Formula
PaCO2 = 40 + 0.6 x (HCO3- - 24)
Indication if CO2 absorbent cannister is too hot
Excessive CO2 production is occuring
Indications for arterial line
Surgery requiring deliberate HoTN, HTN- vascular, intracranial, trauma
Pts with severe valvular dz
CAD
CHF who can’t tolerate alterations in BP
Need to monitor ABG- pHTN, ARDS
Expected large volume shifts
Indications for perioperative non-invasive cardiac stress test
1) intermediate or high risk elective surgery
2) poor functional status (<4 METS) or unknown functional status
3) pt would agree to angiography if test were positive
4) care team agrees it would change pts overall care/outcome
Indications for prophylactic antibiotics to prevent infective endocarditis
Used in high-risk patients undergoing high-risk operations
High-risk factors:
- prosthetic heart valves
- prior hx of IE
- unrepaired congenital cyanotic heart dz
- repaired congenital heart dz (within first 6 mo of repair)
- repaired congenital heart dz with residual defect
- valvular dz in transplanted heart
High-risk operations:
- dental work EXCEPT routine cleanings
- respiratory tract biopsy
- skin, MSK procedures
Inhalation anesthetic agent potentiation of neuromuscular blockade
Desflurane > sevoflurane > isoflurane > halothane > nitrous oxide
Inhaled anesthetic with highest vapor pressure
Nitrous oxide (3,800 mmHg)
Signs of cranial base skull fracture
Battle sign (mastoid ecchymosis)
Raccoon eyes
Bleeding from ears or nose
Uptake of inhaled anesthetics into different tissues from highest to lowest
Circuit > brain = alveoli > muscle > fat
