Explanations include full description to correct answer choice

Explanations include full description to correct answer choice, image/diagram, explanation to incorrect answer choices, and educational objective!

Explanation :

Deep venous thrombosis (DVT) is a thrombosis of the deep veins of the extremities that can lead to pulmonary embolism. Clinical signs of DVT include swelling, tenderness, and redness or discoloration. Risk factors include the Virchow triad: endothelial damage (surgery/intravascular instrumentation), venous stasis (immobilization, obesity), hypercoagulable state (undetected malignancy, thrombophilia). DVT is a concern in chronically bed-ridden patients secondary to blood stasis. Warfarin can used for prophylaxis of venous thromboembolism.

Warfarin inhibits the vitamin K-dependent synthesis of biologically active forms of clotting factors II, VII, IX and X, as well as the regulatory factors protein C and protein S. The precursors of these factors require gamma carboxylation of their glutamic acid residues to become active clotting factors. The enzyme that carries out the carboxylation of glutamic acid is gamma-glutamyl carboxylase. This enzyme requires reduced form of vitamin K to function. Vitamin K epoxide reductase (VKOR) converts vitamin K to reduced form. Warfarin inhibits VKOR resulting in the inability of Vitamin K to be converted to reduced form, and inhibition of gamma-glutamyl carboxylase. This leads to decrease in active clotting factors and overall less risk of thrombosis. Warfarin is also used for stroke prophylaxis in atrial fibrillation, pulmonary embolism, and artificial heart valves.

[Answer Choice B]: Nitrous oxide (N2O) is an inhaled anesthetic used to provide analgesia and narcosis for induction and maintenance of general anesthesia. Its exact mechanism of action is unknown, but its effects take place within the pain centers of the brain and spinal cord. Adverse effects include peripheral vasoconstriction, nausea, malignant hyperthermia, and postoperative shivering.

[Answer Choice C]: Prostacyclin (PGI2) chiefly prevents formation of the platelet plug involved in primary hemostasis. It does this by inhibiting platelet aggregation. It is also an effective vasodilator. It is used to treat pulmonary arterial hypertension (PAH) and critical limb ischemia.

[Answer Choice D & E]: Protein C is a zymogen, the activated form of which plays an important role in regulating anticoagulation by proteolytically inactivating Factor Va and Factor VIIIa. Protein S functions as a cofactor to Protein C in the inactivation of Factors Va and VIIIa. Both of these proteins work towards creating an anti-coagulant state in body.

[Answer Choice F]: Thrombomodulin functions as a cofactor in the thrombin-induced activation of protein C in the anticoagulant pathway. This raises the speed of protein C activation thousand-fold, thus, producing an anti-coagulant state. Thrombomodulin is not direct used for DVT prophylaxis.

Educational Objective:

Warfarin is a vitamin K antagonist that inhibits hepatic epoxide reductase, thereby blocking synthesis (recycling) of the active, reduced form of vitamin K. Without reduced vitamin K, γ-carboxylation of glutamate residues cannot occur, which reduces the production of active coagulation factors II, VII, IX, and X, as well as anticoagulatory proteins C and S. Typically administered in patients with artificial heart valves, increased risk of deep vein thrombosis and pulmonary embolism, and/or valvular A-fib.