A 60-year-old man comes to the emergency department complaining of bright red blood per rectum. The bleeding began abruptly several hours prior to his visit. He has light-headedness when he stands up rapidly, but has no abdominal pain, cramping, fever, nausea, or vomiting. He has no history of previous episodes of bleeding or abdominal pain, but has a history of coronary artery disease and takes aspirin as a "blood thinner." He is afebrile, slightly hypotensive and tachycardic, but stable. On examination, he has decreased skin turgor, and dry mucous membranes. He has no abdominal tenderness. Rectal examination is positive for gross blood.
Q 1
Which of the following is the most likely diagnosis?
/ A. Arteriovenous malformation
/ B. Diverticulitis
/ C. Infectious colitis
/ D. Ischemic colitis
/ E. UIcerative colitis
Q 2
After the patient has stabilized, a colonoscopy is performed to elucidate the origin of the bleeding. Several star-shaped branching vessels
measuring 0.2 to 1.0 cm are seen in the colonic submucosa. BIeeding is stopped by electrocoagulation. A diagnosis of lower gastrointestinal
bleeding is given. Which anatomic landmark demarcates upper gastrointestinal bleeding from lower gastrointestinal bleeding?
/ A. IIeocecal valve
/ B. Ligament of Treitz
/ C. Papilla of Vater
/ D. Pylorus
/ E. Splenic flexure of the colon
Q 3
The aspirin taken by this patient represents a contributor to his condition. Which of the following best describes the mechanism of action of
aspirin?
/ A. Aspirin decreases the serum level of factor VIII
/ B. Aspirin decreases the serum level of factor IX
/ C. Aspirin irreversibly inhibits platelets
/ D. Aspirin irreversibly inhibits thrombin
/ E. Aspirin reversibly inhibits platelets
/ F. Aspirin reversibly inhibits thrombin
Q 4
Which of the following is an important mechanism in short-term blood pressure maintenance?
/ A. BIood pressure regulation occurs slowly by endocrine mechanisms only
/ B. Decreased stretch in the carotid bodies decreases sympathetic and increases parasympathetic discharge to the heart
/ C. Decreased stretch in the carotid bodies increases sympathetic and decreases parasympathetic discharge to the heart
/ D. Decreased stretch in the carotid sinus decreases sympathetic and increases parasympathetic discharge to the heart
/ E. Decreased stretch in the carotid sinus increases sympathetic and decreases parasympathetic discharge to the heart
Normal saline is administered to this patient and his blood pressure and heart rate normalize. One of the goals in fluid resuscitation is to
optimize cardiac parameters according to Starling's Law. Starling's Law describes which of the following?
/ A. The relationship between end diastolic volume and contractility
/ B. The relationship between heart rate and stroke volume
/ C. The relationship between preload and afterload
/ D. The relationship between stroke volume and end systolic volume
/ E. The relationship between systemic vascular resistance and cardiac output
A1
The correct answer is A. Painless hematochezia or bright red lower GI bleeding can come from many sources. While bright red lower GI bleeding tends to indicate lower GI bleeding (bleeding distal to the ligament of Treitz), brisk upper GI bleeding can also be the source. The clinical manifestations of such bleeding range from negligible to hemodynamic instability, depending upon the rate of bleeding. The differential diagnosis for painless hematochezia includes AV malformations, gastric erosions, esophageal varices, esophagitis, duodenal or gastric ulcer, hemorrhoids, diverticulosis, and colonic neoplasm.
Diverticulitis (choice B) occurs when a colonic outpouching or diverticulum becomes inflamed. Patients tend to be elderly and present with fever, abdominal pain, and abdominal tenderness on examination. While painful, these lesions do not bleed significantly (unlike their uninflamed counterparts in diverticulosis).
Infectious colitis (choice C) may present as rectal bleeding, but this bleeding is typically accompanied by pain, cramping, and fever. Causative organisms may include Salmonella, Shigella, Campylobacter jejuni, E. coli, and Entamoeba histolytica.
Ischemic colitis (choice D) may have rectal bleeding, but the hallmark of ischemic colitis is severe abdominal pain out of proportion to examination findings.
Ulcerative colitis (choice E) presents as abdominal pain and diarrhea, which may be bloody or nonbloody. In addition, the onset of the disease tends to be earlier, so this patient would likely have had previous episodes of pain
A2
The correct answer is B. The ligament of Treitz, or the peritoneal ligament, which separates the third (retroperitoneal) portion of the duodenum from the fourth (peritoneal) portion of the duodenum, traditionally demarcates upper GI bleeding from lower GI bleeding. Bleeding proximal to this landmark tends to produce melena or black tarry stools. Bleeding distal to this landmark tends to produce hematochezia or red blood per rectum.
The ileocecal valve (choice A) separates the terminal ileum from the cecum.
The papilla of Vater (choice C) is where the pancreatic duct and common bile duct empty into the duodenum.
The pylorus (choice D) is the sphincter separating the stomach from the duodenum.
The splenic flexure of the colon (choice E) marks the transition from transverse colon to the descending colon.
A3
The correct answer is C. Patients with gastrointestinal bleeding must be assessed for anatomic as well as physiologic and pharmacologic sources of bleeding. Aspirin acts as an anticoagulant by irreversibly inhibiting platelets, preventing the formation of a clot by blocking platelet adhesion and aggregation. Since this platelet mass acts as a matrix for fibrin clot formation, blocking platelets prevents clot formation. This mechanism has been utilized in patients with atherosclerotic disease to prevent intravascular clot formation, but may aggravate bleeding conditions such as this.
Aspirin does not decrease the serum level of factor VIII (choice A). Factor VIII deficiency is the pathophysiology behind hemophilia A.
Factor IX deficiency (choice B) is associated with hemophilia.
Aspirin does not inhibit thrombin (choices D and F). Thrombin is the enzyme responsible for cleaving fibrinogen to fibrin.
Aspirin's effects on platelets are not reversible (choice E), and a new population of functional platelets must replace the inhibited platelets before coagulation is fully restored.
A4
The correct answer is E. As blood pressure falls in this patient with hypovolemia, many short term and long term mechanisms work to raise the falling pressure. In the short term, the baroreceptors found in the carotid sinus and aortic arch regulate blood pressure by modulating the autonomic nervous system. As pressure falls in this patient, the baroreceptors sense this change as a decrease in stretch in the vessel walls. Afferent fibers from the baroreceptors then "report" this change to the medullary cardiovascular center. This center responds by increasing sympathetic discharge and decreasing parasympathetic discharge to the heart and resistance vessels. This acts to restore the blood pressure by increasing heart rate, stroke volume, and vascular resistance.
While endocrine mechanisms (choice A) restore mean arterial pressure for the long term, the sympathetic mechanisms outlined above restore pressure toward baseline much more rapidly.
Choices B and C are incorrect. The carotid bodies contain chemoreceptors (not stretch receptors) that detect changes in PO2, PCO2, and pH. They restore these parameters to normal by acting through the medullary centers to change heart rate, stroke volume, vascular resistance, and ventilatory parameters.
The decrease in pressure triggers an increase in sympathetic discharge and decrease in parasympathetic discharge (compare with choice D).
A5
The correct answer is A. Starling's law of the heart describes the relationship between end diastolic volume or preload and cardiac contractility. It states that cardiac contractility is maximized at a particular preload. It also states that cardiac contractility declines as the preload is increased or decreased from this optimum. The basis for this principle is that at a particular preload, the myocardium is "stretched" to a point that maximizes the number of actin and myosin units that may interact in a given contraction.
Choice B is incorrect. Heart rate x stroke volume = cardiac output
Choice C is incorrect. Preload is related to end diastolic volume and passive wall tension exerted on the diastolic ventricle.
Choice D is incorrect. End diastolic volume - end systolic volume = stroke volume
Choice E is incorrect. Mean arterial pressure = cardiac output x total peripheral resistance.
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