The following cases and commentary, which focus on perioperative care, are excerpted from ACP's Medical Knowledge Self-Assessment Program (MKSAP 16). Part A of MKSAP 16 was released on July 31.
Case 1: Preop evaluation
A 67-year-old man is seen for preoperative evaluation before elective total hip replacement. He has a mechanical bileaflet aortic valve and takes warfarin. He has no history of stroke.
Physical examination shows normal vital signs. There is a regular rhythm with mechanical S1. There is a grade 2/6 early peaking systolic ejection murmur at the right upper sternal border without radiation. Lungs are clear to auscultation bilaterally.
Which of the following is the most appropriate perioperative recommendation regarding anticoagulation for this patient?
A. Discontinue warfarin 3 days before surgery and bridge with heparin before and after
B. Discontinue warfarin 3 days before surgery and restart on evening of the surgery
C. Do not discontinue warfarin
D. Reverse anticoagulation with fresh frozen plasma transfusion 1 hour before surgery; restart warfarin on evening of surgery
Case 2: Post bowel resection
A 64-year-old man was admitted to the hospital 4 days ago for severe, acute abdominal pain and was found to have acute mesenteric ischemia. He underwent massive small-bowel resection, with 180 cm of small bowel remaining, and his colon was able to be salvaged. Over the past 4 days since surgery, he has been on parenteral nutrition with gradual progression of oral intake. He has significant diarrhea that wakes him up at night. He has been afebrile and has not had recurrent or worsening abdominal pain. His medications are low-dose low-molecular-weight heparin, ciprofloxacin, and metronidazole. He is also taking loperamide four times daily.
On physical examination, temperature is 36.2°C (97.2°F), blood pressure is 118/60 mm Hg, pulse rate is 68/min and regular, and respiration rate is 12/min. BMI is 25. Abdominal examination discloses a large scar from his recent surgery that is healing well. Bowel sounds are very active and there is mild tenderness throughout, as is expected postoperatively.
Laboratory studies, including serum electrolyte, glucose, and thyroid-stimulating hormone levels, are normal. Stool cultures and Clostridium difficile polymerase chain reaction are normal.
Which of the following is the most appropriate management?
A. Decrease the lipids in his parenteral nutrition
B. Increase the loperamide
C. Initiate cholestyramine
D. Initiate omeprazole
E. Stop oral intake
Case 3: Post-op abdominal pain
A 37-year-old woman is evaluated in the emergency department for a 1-day history of generalized abdominal pain. She has had no nausea, vomiting, diarrhea, melena, or hematochezia. She denies dyspnea or cough. One week ago she underwent laparoscopic Roux-en-Y gastric bypass for obesity, and she had an uncomplicated cholecystectomy 2 years ago. Her medications are vitamin B12 injections, oral iron, and a multivitamin that contains folate.
On physical examination, she is afebrile. Blood pressure is 110/75 mm Hg (without orthostatic changes), pulse rate is 130/min, and respiration rate is 12/min; BMI is 46. Cardiac examination reveals tachycardia. Bowel sounds are normal. There is diffuse abdominal tenderness but no guarding or rebound. There are well-healing trocar sites from her recent surgery. Rectal examination reveals normal-colored stool that is guaiac negative.
Laboratory studies, including a complete blood count, liver chemistry studies, and pancreatic enzymes, are normal. An electrocardiogram shows sinus tachycardia. A plain radiograph of the abdomen is normal.
Which of the following is the most appropriate next step in management?
A. CT angiography of the chest
B. Emergent surgical exploration
C. Upper endoscopy
D. Upper gastrointestinal oral contrast radiograph
Case 4: VTE management
A 28-year-old man is evaluated 24 hours after a new diagnosis of a left calf deep venous thrombosis. One week ago, he underwent orthopedic surgery. Two weeks ago, he returned from vacationing in Italy on an 8-hour flight. Current medications are enoxaparin, 80 mg subcutaneously twice daily, and warfarin, 5 mg/d.
On physical examination, temperature is normal, blood pressure is 145/85 mm Hg, pulse rate is 72/min, and respiration rate is 18/min. BMI is 25. His lungs are clear. His left calf is erythematous and edematous.
Duplex ultrasound obtained yesterday confirms a left posterior tibial vein thrombosis. Laboratory results from his emergency department visit reveal factor V Leiden heterozygosity.
The patient asks why he developed this blood clot and how long he will have to take warfarin.
Which of the following is the most appropriate management of this patient's venous thromboembolism?
A. Low-intensity warfarin (INR, 1.5-2) for at least 3 months
B. Standard-intensity warfarin (INR, 2-3) for at least 12 months
C. Standard-intensity warfarin (INR, 2-3) for at least 3 months
D. Standard-intensity warfarin (INR, 2-3) for life
Case 5: Post-op intensive care
A 71-year-old man is evaluated in the intensive care unit 11 days after undergoing surgery to relieve a bowel obstruction. His postoperative course has been complicated by septic shock and multiorgan failure, for which he has received intravenous fluids, broad-spectrum antibiotics, vasopressors, corticosteroids, and insulin. He has been on mechanical ventilation for 10 days. For the past 72 hours, he has been hemodynamically stable, but attempts at weaning him from the ventilator have been unsuccessful. The patient previously was given muscle relaxants and neuromuscular junction-blocking agents, but these have been withheld for the past 4 days.
On physical examination, the patient is alert, follows commands, and cooperates with the examiner. Vital signs are stable. Cranial nerves are intact. Flaccid quadriparesis of the upper and lower extremities is noted that is greater proximally than distally. Areflexia is present.
Results of laboratory studies show a serum creatine kinase level of 850 units/L and a plasma glucose level of 200 mg/dL (11.1 mmol/L).
Results of electromyography show absent sensory responses in the legs and low amplitudes in the hands. Short duration, low-amplitude motor units consistent with myopathy are noted.
Which of the following is the most likely diagnosis?
A. Corticosteroid myopathy
B. Critical illness myopathy
C. Guillain-Barré syndrome
D. Myasthenia gravis
Case 6: Cholecystectomy consult
A 16-year-old boy undergoes preoperative consultation prior to a planned elective cholecystectomy for symptomatic gallstones. The patient has sickle cell disease and experiences two to three painful episodes per year. He has no history of stroke, acute chest syndrome, or prior transfusion. He takes daily folic acid supplementation.
On physical examination, temperature is 36.7°C (98.2°F), blood pressure is 113/59 mm Hg, pulse rate is 78/min, and respiration rate is 16/min. The patient has scleral icterus.
Abdominal examination is normal.
Laboratory studies show hemoglobin 8.0 g/dL (80 g/L), leukocyte count 9900/µL (9.9 × 109/L) with a normal differential, platelet count 209,000/µL (209 × 109/L) and reticulocyte count 3.4%.
Blood typing and screening reveal blood type O positive, with a negative antibody screen. The erythrocyte phenotype is available on file.
Which of the following blood products will best minimize the risk for erythrocyte alloimmunization in this patient?
A. Hb S negative
C. Phenotypically matched
Answers and critique
Correct answer: B. Discontinue warfarin 3 days before surgery and restart on evening of the surgery.
This patient should discontinue warfarin 3 days before his hip surgery, and restart warfarin on the evening of the surgery, provided hemostasis is maintained. Although the annual risk of a thromboembolic event in a patient with a mechanical heart valve without therapeutic anticoagulation may be as high as 20%, the short-term risk of anticoagulation discontinuation is small. In addition to valve-related characteristics, such as type of mechanical valve and its position (aortic versus mitral), other factors that increase the risk of thromboembolism include atrial fibrillation, more than one mechanical valve, left ventricular systolic dysfunction (ejection fraction <30%), a hypercoagulable state, and previous thromboembolic event, including stroke or transient ischemic attack. The current recommendation is to stop warfarin 48 to 72 hours before the procedure to reduce INR to 1.5, and restart warfarin within 24 hours after the procedure. Bridging with heparin is usually not necessary.
In patients with a mechanical valve and an increased risk of a thromboembolic event, it is recommended that unfractionated heparin is begun intravenously when INR falls below 2.0, stopped 4 to 5 hours before the procedure, and restarted as early after surgery as possible along with warfarin and continued until INR is therapeutic again. This patient does not have an increased risk for a thromboembolic event, so bridging anticoagulation is not needed.
In patients with a mechanical heart valve and therapeutic INR who require emergent surgery, reversal of anticoagulation with transfusion of fresh frozen plasma may be performed. This option is not appropriate for nonemergent surgery, however.
- For patients with a mechanical valve in the aortic position and without additional risk factors, the current recommendation for periprocedural anticoagulation is to stop warfarin 48 to 72 hours before the procedure and restart it within 24 hours after the procedure; bridging with heparin is usually not necessary.
Correct answer: D. Initiate omeprazole.
This patient should receive a proton pump inhibitor (PPI) such as omeprazole. In patients who have undergone massive resection of the small intestine and are left with short-bowel syndrome, there is a tremendous surge of gastric acid in the postoperative period. The increased acid can inactivate pancreatic lipase, leading to significant diarrhea and possible ulceration in the remaining bowel. Therefore, all patients who have undergone significant bowel resection should receive acid suppression therapy in the postoperative period with a PPI.
Decreasing the lipids in this patient's diet, rather than in his parenteral nutrition, may provide some clinical improvement, because oral long-chain triglycerides may not be handled well in the state of bile-salt deficiency and may result in diarrhea.
Although increasing the loperamide may help with diarrhea control, it will not target the underlying pathophysiology of the increased acid production and will not prevent small-bowel ulceration. Overlooking that point may lead to adverse consequences for this patient if his acid hypersecretion is not controlled.
Because this patient has had resection of such a large amount of small intestine, there is likely significant disruption of the enterohepatic circulation of bile with resulting bile salt deficiency. Giving this patient cholestyramine will bind the remaining bile salts that are present and worsen the diarrhea.
Stopping this patient's oral intake may lead to some improvement of his diarrhea; however, it is often not recommended if the patient is otherwise tolerating oral intake, because continued oral intake will allow for bowel adaptation over time.
- Patients who have undergone significant bowel resection should receive acid suppression therapy in the postoperative period owing to the acid hypersecretion that occurs.
Correct answer: D. Upper gastrointestinal oral contrast radiograph.
The most appropriate next step is an upper gastrointestinal oral contrast radiograph. This patient has clinical features suggestive of an anastomotic leak, and an upper gastrointestinal radiograph with water-soluble oral contrast will be helpful to document the presence and location of the leak and guide surgical management. The clinical presentation of an anastomotic leak can be subtle and may include fever, abdominal pain, or tachycardia. Although her laboratory studies and plain radiograph of the abdomen are unremarkable, she does have unexplained tachycardia, which may be the only clinical feature and should not be overlooked. Sustained tachycardia with a heart rate greater than 120/min is an indicator of an anastomotic leak after bariatric surgery in the absence of gastrointestinal bleeding. CT of the abdomen could also be used to identify an anastomotic leak in place of a water-soluble oral contrast radiograph.
CT angiography of the chest may be used to evaluate for a pulmonary embolism in the postoperative period, but the presence of abdominal pain and absence of chest pain, cough, dyspnea, or tachypnea make this diagnosis much less likely than a leak.
Although this patient would require surgical intervention if an anastomotic leak were found, emergent surgical exploration would not be required at this time because the patient is hemodynamically stable. This allows time for diagnostic testing, which will better direct the appropriate surgical approach. However, even if imaging of the abdomen does not reveal an anastomotic leak or other postoperative complication (such as an internal hernia) and the index of suspicion remains high, exploratory surgery should still be considered because the morbidity and mortality associated with missing these diagnoses are greater than that of a negative surgical exploration.
An upper endoscopy would be contraindicated if a perforation or anastomotic leak is being considered.
- Sustained tachycardia with a heart rate greater than 120/min can be an indicator of an anastomotic leak after bariatric surgery in the absence of gastrointestinal bleeding.
Correct answer: C. Standard-intensity warfarin (INR, 2-3) for at least 3 months.
Standard-intensity warfarin (INR, 2 to 3) for at least 3 months is the most appropriate management of this patient with a triggered episode of venous thromboembolism (VTE). Although distal (calf vein) deep venous thrombosis (DVT) is associated with a low risk for pulmonary embolism, these thrombi confer a substantial risk for progression into the proximal deep venous system in the absence of anticoagulation. In one randomized study, 29% of patients treated with a 5-day course of unfractionated heparin alone developed recurrent VTE compared with none in the group receiving warfarin for 3 months.
This patient has several identifiable risk factors for VTE: recent major orthopedic surgery, recent travel, and factor V Leiden heterozygosity. Major inpatient surgery is associated with a 70-fold increased risk for VTE; ambulatory surgery is associated with a 10-fold increased risk. The risk associated with surgery is greatest in the first few weeks after surgery and declines thereafter, reaching baseline as long as 12 months later. Therefore, this patient's recent orthopedic surgery played a major role in the pathogenesis of his calf vein DVT. In comparison, travel is associated with a modest twofold increased risk for VTE, and factor V Leiden is associated with a fivefold increased risk of VTE. Although factor V Leiden is associated with a significant risk for initial VTE, it is not associated with a significant risk for recurrent VTE (1.5-fold). Consequently, the presence of factor V Leiden in this patient does not mandate prolonged therapy.
Low-intensity warfarin (INR, 1.5-2) for 3 months would not be the optimal choice for this patient's triggered episode of calf vein DVT. Low-intensity warfarin therapy was found to be inferior to standard-intensity warfarin therapy (INR, 2-3) for treatment of patients with idiopathic VTE. Low-intensity therapy was initiated after at least 3 months of standard-intensity therapy (INR, 2-3). Low-intensity warfarin therapy has never been tested for the initial 3 months of VTE treatment.
Life-long warfarin (INR, 2-3) is not the best management approach for this patient with a triggered episode of VTE. The bleeding risks of long-term warfarin (at least 1% to 2% per year) outweigh the risk of recurrence (0.7% per year).
- Standard intensity warfarin for at least 3 months is the most appropriate management for patients with risk factors for venous thromboembolism.
Correct answer: B. Critical illness myopathy.
This patient has critical illness myopathy, which is seen in severely ill patients after a prolonged (>7 days) stay in the intensive care unit (ICU). Inability to extubate and predominantly proximal flaccid limb weakness are classic findings. Critical illness myopathy is characterized by an elevated serum creatine kinase (CK) level. Predisposing factors include the patient's prolonged ICU stay, use of corticosteroids and neuromuscular junction-blocking agents, and hyperglycemia.
Corticosteroid myopathy presents with predominantly proximal weakness, preserved reflexes, a normal serum CK level, and normal or only mildly myopathic findings on electromyography (EMG).
Guillain-Barré syndrome can share the clinical presentation of critical illness myopathy. The serum CK level, however, would be normal.
Patients with generalized myasthenia gravis typically have limb weakness, diplopia, slurred speech, dysphagia, and dyspnea. Findings on neurologic examination include ptosis, impaired ocular motility, and limb weakness that increases with repeated testing (fatigable weakness). Deep tendon reflexes and sensory examination findings are normal. Results of EMG in myasthenia gravis would show characteristic decremental motor responses on repetitive stimulation. The patient's findings are not consistent with myasthenia gravis.
- Critical illness myopathy can occur in severely ill patients after a prolonged stay in the intensive care unit and is characterized by an inability to extubate, flaccid limb weakness, and an elevated serum creatine kinase level.
Correct answer: C. Phenotypically matched.
This patient requires phenotypically matched blood products. Preoperative transfusion to achieve a hemoglobin level of 10 g/dL (100 g/L) is typically performed to minimize the risk for acute chest syndrome and other major complications in patients with sickle cell disease (SCD). Transfusion in patients with SCD is associated with a high risk for erythrocyte alloimmunization compared with transfusion in patients without SCD. One possible explanation is differing frequencies of various erythrocyte antigens of the primarily white donor pool compared with the typical black patient with SCD. Erythrocyte alloimmunization can lead to an increased risk for a delayed hemolytic transfusion reaction. To minimize this risk, patients with SCD should receive erythrocytes phenotypically matched for the C, E, and K antigens whenever possible, as well as for any antigens to which they have already developed an alloantibody.
Using Hb S-negative units is appropriate to decrease the risk for vasoocclusive complications but would not affect the rate at which alloimmunization occurs.
Irradiation of erythrocytes minimizes the risk for transfusion-associated graft-versus-host disease in immunocompromised patients, but it is not indicated in patients with SCD.
Washing of erythrocytes decreases the risk for allergic reactions but does not affect the incidence of erythrocyte alloimmunization.
- Patients with sickle cell disease who require transfusion should receive erythrocytes phenotypically matched for the C, E, and K antigens whenever possible, as well as for any antigens to which they have already developed an alloantibody, to avoid the risk for alloimmunization and subsequent delayed hemolytic transfusion reaction.