ITE Flashcards
What spinal level does the great radicular artery (artery of Adamkiewicz) most commonly originate?
T9-12
Paraplegia following open thoracoabdominal aortic aneurysm repair occurs in 10-20% of pts due to cross clamping and hypoperfusion of spinal cord anteriorly.
Most likely side effect of celiac plexus neurolytic block?
Orthostatic hypotension from splanchnic vasodilation caused by sympatholysis. Can also cause diarrhea from unopposed parasympathetic tone.
How do you improve spinal cord perfusion pressure in aortic surgery?
Increase MAP and reduce CSF pressure using lumbar CSF drain.
SCPP = MAP - CSF pressure (same as CPP = MAP-ICP)
What is the blood supply to the spinal cord?
Vertebral arteries –> single ASA that supplies anterior 2/3rds of spinal cord.
Two PSAs from PICA supply posterior 1/3rd of spinal cord.
Cervical cord is supplemented by radicular branches from vertebral arteries. Thoracolumbar cord supplemented by radicular arteries, especially great radicular artery of Adamkiewicz.
What movement is preserved after lumbar plexus block via posterior approach?
Plantar flexion of foot (lumbar plexus block spares sciatic nerve)
What muscles does sciatic nerve innervate?
gastrocnemius, soleus, plantaris, digital flexors
What is lumbar plexus formed by?
Ventral divisions of first four lumbar nerves (L1-L4), small contribution from T12 (subcostal nerve)
What nerves does lumbar plexus block?
femoral, lateral femoral cutaneous, obturator
What muscles does obturator nerve innervate?
Hip adduction (adductor longus, brevis, magnus muscles)
What muscles does femoral nerve innervate?
Hip flexion (iliopsoas, quadriceps femoris) and extension of lower leg at knee (quadriceps femoris)
How to visualize the ascending aorta on TEE?
Long axis view of ascending aorta, mid-esophageal, at about 100-110 degrees
How is PDA treated medically?
Fluid restriction and indomethacin - nonselective COX inhibitor. Inhibits prostaglandin synthesis. Prostaglandins usually aid in smooth muscle relaxation within ductus arteriosus and prevent closure.
Pathophys of PDA? What can PDA lead to if untreated?
allows a portion of oxygenated blood from the left heart to flow back to the lungs by flowing from the aorta, which has a higher pressure, to the pulmonary artery. Symptoms are uncommon at birth and shortly thereafter, but later in the first year of life there is often the onset of an increased work of breathing and failure to gain weight at a normal rate. With time, an uncorrected PDA usually leads to pulmonary hypertension followed by right-sided heart failure.
What causes increased risk of DVT during pregnancy?
Increase in circulating levels of fibrinogen - fibrinogen levels double in pregnancy.
Other increased coagulation factors are: factors VII, VIII, IX, X and XII.
Prothrombin time (PT) and partial thromboplastin time (PTT) are shortened by about 20% in pregnancy
Pt presenting with flushing, diarrhea, wheezing, right-sided cardiac abnormalities (fibrous deposits on tricuspid valve) - diagnosis? How to test for it?
Carcinoid syndrome from carcinoid tumor. Excrete large amts of serotonin, which is broken down and excreted as 5-hydroxyindoleacetic acid in urine (test for this in urine).
Lung metabolism of serotonin leads to right sided (but prevents left sided) involvement of the heart.
What nephron segment absorbs majority of sodium?
Proximal tubule (65-80% of Na absorbed here)
What factors can result in variable activated clotting times?
Hemodilution, hypothermia, platelet counts below 30-50K/ml and concomitant administration of other medications which affect platelets.
Induction strategy for peds pt with congenital emphysema going for resection of emphysematous bleb?
Mask induction with sevoflurane, spontaneous respiration. Nitrous oxide is contraindicated.
What are the pKa of common opioids (fentanyl, sufentanil, alfentanil, remifentanil, morphine)?
Fentanyl - 8.4 Sufentanil - 8.0 Morphine - 8.0 Remifentanil - 7.1 Alfentanil - 6.5
What is duration of effect of opioids determined by?
Primarily by lipid solubility, not drug elimination as with many other drugs.
Morphine has a longer onset time and duration of action because more difficult time crossing blood-brain (or blood-spinal cord) barrier due to lower lipid solubility.
Are ionized or nonionized drugs more lipid soluble?
Ionized drugs are polar and do not readily pass through cell membranes. Nonionized drugs are significantly more lipid soluble.
What is the pKa of a drug refer to?
the pH at which it exists in equal parts of ionized and nonionized forms.
Opioid with pKa less than physiologic pH (~7.4) will have much greater NONionized fraction, whereas opioid with pKa >7.4 will have greater ionized fraction.
What is mechanism for neurogenic pulmonary edema a few hours after traumatic brain injury?
Massive sympathetic discharge. Presents with rapid onset, severe pulmonary vascular congestion, intra-alveolar hemorrhage and protein-rich edematous fluid. Tx - supportive and reduce intracranial hypertension
Accumulation of metabolites of meperidine in renal dysfunction can cause what?
Seizures - active metabolite is normeperidine and is neurotoxic.
What are morphine’s metabolites and consequences of accumulation?
In renal disease, metabolites can accumulate. Active metabolite (morphine-6-glucuronide/M6G) has nearly 100-fold higher potency than morphine but has equal or decreased affinity for mu-opioid receptors. Increased potency can lead to respiratory depression in renal failure due to accumulation from delayed excretion.
Morphine’s inactive metabolite, morphine-3-glucuronide M3G, has nearly 300-fold lower affinity for mu-receptors but it has neuroexcitatory effects -> myoclonus and allodynia are seen after large doses.
What are morphine’s metabolites and consequences of accumulation?
In renal disease, metabolites can accumulate. Active metabolite (morphine-6-glucuronide/M6G) has nearly 100-fold higher potency than morphine but has equal or decreased affinity for mu-opioid receptors. Increased potency can lead to respiratory depression in renal failure due to accumulation from delayed excretion.
Morphine’s inactive metabolite, morphine-3-glucuronide M3G, has nearly 300-fold lower affinity for mu-receptors but it has neuroexcitatory effects -> myoclonus and allodynia are seen after large doses.
What is common side effect of meperidine?
Tachycardia - meperidine molecule resembles atropine.
What is Gilbert disease?
Decrease in activity of bilirubin glucuronyltransferase (needed for hepatocyte uptake of unconjugated bilirubin). They have increased risk of jaundice, especially following multiple pRBC transfusions.
Distressed fetus with bradycardia is more susceptible to toxicity from what drug?
Lidocaine - crosses placenta and accumulates due to ion trapping from fetal acidosis.
In setting of decreased uterine blood flow (such as significant maternal blood loss) fetal pH will decrease further. A basic drug, like local anesthetic, crosses placental in un-ionized form accepts a H+ ion in more acidic environment and becomes ionized.
What common drugs don’t cross placenta?
“He Is Going Nowhere Soon” = Heparin, Insulin, Glycopyrrolate, Non-depolarizing muscle relaxants, Succinylcholine
Primary site of dexmedetomidine metabolism and excretion?
Dexmedetomidine undergoes extensive hepatic metabolism including conjugation, n-methylation, and hydroxylation followed by conjugation before being excreted in urine and feces. Its elimination half-life is 2-3 hours.
What is the order of plasma elimination half life of the following? (shortest to longest) Alprazolam Diazepam Flumazenil Lorazepam Temazepam Midazolam
Shortest: Flumazenil (0.7 - 1.3h) Midazolam (1.7-2.6h) Temazepam (10h) Alprazolam (6-27h) Lorazepam (11-22h) Diazepam (20-50h)
What are Boyle, Avogadro, Charles, and Guy-Lussac laws in relation to gases?
Boyle: P1 x V1 = P2 x V2 (changes in volume inversely related to changes in pressure)
Avogadro: equal volumes of all gases at the same pressure and same temperature will contain the same number of molecules
Charles: V1/T1 = V2/T2
Guy-Lussac: P1/T1 = P2/T2
What is the renin-angiotensin-aldosterone system?
RAAS is one of the primary regulators of volume and blood pressure. Angiotensinogen is synthesized in liver, circulates in plasma until cleaved by renin to angiotensin I. Renin is released by juxtaglomerular apparatus in response to B1 activation, decreased renal perfusion pressure (glomerulus) or decreased NaCl concentration at the macula densa (distal convoluted tubule). Angiotensin I is cleaved to form active angiotensin II by angiotensin-converting enzyme (ACE) in the lungs.
Side effects of methylergometrine and carboprost?
Methylergometrine = hypertension
Carboprost = bronchospasm
“methylergometrine makes the blood pressure go HYER (higher):
HY ER: metHYlERgometrine HYpERtension
Also, the double O’s go together:
OOS: carbOprOSt brOnchOSpasm”
What are estimated blood volumes by age for premature infant to adult male/female?
Age Group Blood Volume Premature infant 90-105 mL/kg Full-term newborn 80-90 mL/kg Infant 3-12 months 70-80 mL/kg Child 1-12 years 70-75 mL/kg Adult male 65-70 mL/kg Adult female 60-65 mL/kg
Indications for spinal cord stimulator?
accepted indications for spinal cord stimulation include (but are not limited to): thoracic and lumbar post-laminectomy syndrome (“failed back syndrome”), post-herpetic neuralgia, phantom limb pain, cauda equina syndrome, CRPS I and II, cardiovascular angina, lower extremity ischemic pain, chronic cervical radiculopathy, and nerve root injury.
Relative contraindications to spinal cord stimulator?
cognitive and psychological disability that interferes with proper usage and understanding of the device. This includes significant somatization/somatoform disorders and unmanaged substance abuse.
Absolute contraindications to spinal cord stimulator?
Absolute contraindications for spinal stimulation include (but are not limited to): sepsis, coagulopathy, previous surgery or trauma obliterating the spinal canal, localized infection, and spinal bifida.
