EDAIC Basic Sciences 4 — Questions and Answers
Question 1: In a patient with renal failure, which muscle relaxant is MOST appropriate due to organ-independent elimination?
- Cisatracurium (Correct answer)
- Vecuronium
- Pancuronium
- Rocuronium
Correct answer: Cisatracurium
Cisatracurium undergoes Hofmann elimination (spontaneous non-enzymatic degradation at physiological pH and temperature), making it independent of renal or hepatic function.
Question 2: The cerebral metabolic rate for oxygen (CMRO2) is coupled to cerebral blood flow (CBF) through which mechanism?
- Metabolic autoregulation via local vasoactive metabolites (Correct answer)
- Myogenic response to pressure changes
- Neurogenic control via sympathetic nerves
- Baroreceptor reflex
Correct answer: Metabolic autoregulation via local vasoactive metabolites
Increased neuronal activity produces CO2, H+, K+, and adenosine, which act as local vasodilators coupling metabolic demand to blood flow.
Question 3: Propofol's mechanism of action primarily involves:
- Positive allosteric modulation of GABA-A receptors (Correct answer)
- NMDA receptor antagonism
- Opioid receptor agonism
- Alpha-2 adrenoceptor agonism
Correct answer: Positive allosteric modulation of GABA-A receptors
Propofol enhances inhibitory chloride currents by binding to GABA-A receptors at a site distinct from benzodiazepines, potentiating GABAergic neurotransmission.
Question 4: The pulmonary vascular resistance (PVR) is LOWEST at which lung volume?
- Functional residual capacity (FRC) (Correct answer)
- Total lung capacity (TLC)
- Residual volume (RV)
- Tidal volume peak
Correct answer: Functional residual capacity (FRC)
At FRC, both alveolar vessels (compressed at high volumes) and extra-alveolar vessels (collapsed at low volumes) are at their optimal diameter, minimizing total PVR.
Question 5: Which coagulation pathway is assessed by the prothrombin time (PT/INR)?
- Extrinsic pathway (factors VII, X, V, II, I) (Correct answer)
- Intrinsic pathway (factors XII, XI, IX, VIII)
- Common pathway only (factors X, V)
- Platelet function and primary hemostasis
Correct answer: Extrinsic pathway (factors VII, X, V, II, I)
PT measures the extrinsic pathway initiated by tissue factor (FIII) + FVII, then the common pathway; it is prolonged by warfarin which inhibits vitamin K-dependent factors II, VII, IX, X.
Question 6: Hypoxic pulmonary vasoconstriction (HPV) serves which physiological purpose?
- Diverting blood from poorly ventilated lung regions to better-ventilated areas (Correct answer)
- Increasing total pulmonary blood flow during hypoxia
- Decreasing airway resistance in hypoxic lung regions
- Stimulating surfactant production
Correct answer: Diverting blood from poorly ventilated lung regions to better-ventilated areas
HPV constricts pulmonary arterioles in hypoxic lung segments, redirecting blood to better-oxygenated alveoli to optimize V/Q matching and arterial oxygenation.
Question 7: The osmotic pressure exerted by plasma proteins (mainly albumin) across the capillary wall is termed:
- Colloid oncotic pressure (Correct answer)
- Hydrostatic pressure
- Oncotic hydrostatic pressure
- Crystalloid osmotic pressure
Correct answer: Colloid oncotic pressure
Colloid oncotic pressure (~25 mmHg) is generated by large plasma proteins that cannot freely cross the capillary membrane, opposing fluid filtration into the interstitium.
EDAIC Basic Sciences 4
In a patient with renal failure, which muscle relaxant is MOST appropriate due to organ-independent elimination?