MCQs 2 21. Which of the following statements about head injury and concomitant hyponatremia are true? A. There are no primary alterations in cardiovascular signs. B. Signs of increased intracranial pressure may be masked by the hyponatremia. C. Oliguric renal failure is an unlikely complication. D. Rapid correction of the hyponatremia may prevent central pontine injury. E. This patient is best treated by restriction of water intake. Answer: A DISCUSSION: Acute symptomatic hyponatremia is characterized by central nervous system signs of increased intracranial pressure. Changes in blood pressure and pulse are secondary to increased intracranial pressure. In the absence of hypovolemia, asymptomatic patients may be treated by restriction of water intake; however, in such patients, hyponatremia should be partially corrected by parenteral sodium administration. Rapid correction, particularly to hypernatremia, may lead to central pontine myelinolysis. Oliguric renal failure may rapidly develop in severe hyponatremia. 22. Which of the following statements about total body water composition are correct? A. Females and obese persons have an increased percentage of body water. B. Increased muscle mass is associated with decreased total body water. C. Newborn infants have the greatest proportion of total body water. D. Total body water decreases steadily with age. E. Any persons percentage of body water is subject to wide physiologic variation. Answer: CD DISCUSSION: Since fat contains little water, lean persons with a proportionately greater muscle mass have a greater than expected volume of total body water. Likewise, the female body habitus and obesity contribute to decreased total body water percentage. The highest proportion of total body water is found in newborn infants, and total body water decreases steadily and significantly with age. The actual figure for a healthy person is remarkably constant. 23. Which of the following statements about extracellular fluid are true? A. The total extracellular fluid volume represents 40% of the body weight. B. The plasma volume constitutes one fourth of the total extracellular fluid volume. C. Potassium is the principal cation in extracellular fluid. D. The protein content of the plasma produces a lower concentration of cations than in the interstitial fluid. E. The interstitial fluid equilibrates slowly with the other body compartments. Answer: B DISCUSSION: The total extracellular fluid volume represents 20% of body weight. The plasma volume is approximately 5% of body weight. Sodium is the principal cation. The Gibbs-Donan equilibrium equation explains the higher total concentration of cations in plasma. Except for joint fluid and cerebrospinal fluid, the majority of the interstitial fluid exists as a rapidly equilibrating component. 24. Which of the following statements are true of a patient with hyperglycemia and hyponatremia? A. The sodium concentration must be corrected by 5 mEq. per 100 mg. per 100 ml. elevation in blood glucose. B. With normal renal function, this patient is likely to be volume overloaded. C. Proper fluid therapy would be unlikely to include potassium administration. D. Insulin administration will increase the potassium content of cells. E. Early in treatment adequate urine output is a reliable measure of adequate volume resuscitation. Answer: D DISCUSSION: Each 100-mg. per 100 ml. elevation in blood glucose causes a fall in serum sodium concentration of approximately 2 mEq. per liter. Excess serum glucose acts as an osmotic diuretic, producing increased urine flow, which can lead to volume depletion. Insulin therapy and the correction of the patients associated acidosis produce movement of potassium ions into the intracellular compartment. 25. Which of the following statements about respiratory acidosis are true? A. Compensation occurs by a shift of chloride out of the red blood cells. B. Renal compensation occurs rapidly. C. Retention of bicarbonate and increased ammonia formation are normal compensatory mechanisms. D. Narcotic administration is an unusual cause of respiratory acidosis. E. The ratio of bicarbonate to carbonic acid is less than 20:1. Answer: CE DISCUSSION: Renal compensation for acute hypoventilation is relatively slow. Depression of the respiratory center by morphine can lead to respiratory acidosis. Renal retention of bicarbonate, ammonia formation, and shift of chloride into red cells combine to increase the ratio of bicarbonate to carbonic acid to 20:1. 26. Which of the following statements are true of elevated–anion gap metabolic acidosis? A. Hypoperfusion from the shock state rarely produces an elevated anion gap. B. Retention of sulfuric and phosphoric acids may lead to this form of acidosis. C. Copious diarrhea does not produce this condition. D. Rapid volume expansion may produce this form of acidosis. E. Use of lactated Ringers solution is inappropriate in the treatment of lactic acidosis. Answer: BC DISCUSSION: An elevated anion gap may be produced by lactic acidosis from shock or by retention of inorganic acids from uremia. Lactated Ringers solution rapidly corrects the lactic acidosis from hypovolemia, as lactate is converted to bicarbonate with hepatic reperfusion. Bicarbonate loss from diarrhea and “dilutional acidosis” are non–anion gap types of metabolic acidosis. 27. Which of the following is true of loss of gastrointestinal secretions? A. Gastric losses are best replaced with a balanced salt solution. B. Potassium supplementation is unnecessary in replacement of gastric secretions. C. Bicarbonate wasting is an unusual complication of a high-volume pancreatic fistula. D. Balanced salt solution is a reasonable replacement fluid for a small bowel fistula. E. A patient with persistent vomiting usually requires hyperchloremic replacement fluids. Answer: DE DISCUSSION: Gastric secretions are relatively high in chloride and potassium. Other than an isolated pancreatic fistula, gastrointestinal tract losses below the pylorus are best replaced by a balanced salt solution. Although potassium concentrations are low, copious losses require potassium supplementation to prevent hypokalemia. 28. Which of the following statements regarding hypercalcemia are true? A. The symptoms of hypercalcemia may mimic some symptoms of hyperglycemia. B. Metastatic breast cancer is an unusual cause of hypercalcemia. C. Calcitonin is a satisfactory long-term therapy for hypercalcemia. D. Severely hypercalcemic patients exhibit the signs of extracellular fluid volume deficit. E. Urinary calcium excretion may be increased by vigorous volume repletion. Answer: ADE DISCUSSION: Markedly elevated serum calcium levels produce polydipsia, polyuria, and thirst. Vigorous volume repletion and saline diuresis correct the extracellular fluid volume deficit and promote the urinary excretion of calcium. Metastatic breast cancer is the most common cause of hypercalcemia, from bony metastasis. The calcitonin effect on calcium is diminished with repeat administrations. 29. Which of the following statements about normal salt and water balance are true? A. The products of catabolism may be excreted by as little as 300 ml. of urine per day. B. The lungs represent the primary source of insensible water loss. C. The normal daily insensible water loss is 600 to 900 ml. D. Excessive cell catabolism causes significant loss of total body water. E. In normal humans, urine represents the greatest source of daily water loss. Answer: CE DISCUSSION: The skin is the primary source of insensible water loss. Including losses from the lungs, this averages 600 to 900 ml. per day. Catabolism liberates “water of solution.” In normal humans, urine represents the greatest source of water loss. The patient deprived of external access to water must still excrete a minimum of 500 to 800 ml. of urine per day to expel the products of catabolism. 30. Which of the following is/are not associated with increased likelihood of infection after major elective surgery? A. Age over 70 years. B. Chronic malnutrition. C. Controlled diabetes mellitus. D. Long-term steroid use. E. Infection at a remote body site. Answer: C DISCUSSION: Controlled diabetes mellitus has been shown repeatedly not to be associated with increased likelihood of incisional infection provided one avoids operations on body parts that may be ischemic or neuropathic. Uncontrolled diabetes mellitus, such as ketoacidosis, is associated with a dramatic increase in surgical infection. The other parameters noted—age over 70, chronic malnutrition, regular steroid use, and an infection at a remote body site—are well-recognized adverse predictive factors and are identified in tables within the chapter. 31. Which of the following are not determinants of a postoperative cardiac complication? A. Myocardial infarct 4 months previously. B. Clinical evidence of congestive heart failure in a patient with 8.5 gm. per dl. hemoglobin. C. Premature atrial or ventricular contractions on electrocardiogram. D. A harsh aortic systolic murmur. E. Age over 70 years. Answer: B DISCUSSION: Clinical evidence of congestive heart failure in a patient with 8.5 gm. per dl. hemoglobin concentration is a misleading sign. Evidence of congestive failure is ordinarily a major risk factor, but in this particular patient the anemia lends itself to correction by preoperative transfusion with packed red blood cells, and often it is found that congestive failure and the associated increased risks disappear when the hemoglobin concentration is returned to the 12 gm. per dl. or higher ratio. All other factors are overt signs of increased likelihood of a postoperative cardiac event, the most ominous being a myocardial infarction 4 months preoperatively or the presence of a harsh aortic systolic murmur suggesting the presence of aortic stenosis. Age over 70 years and the presence of premature atrial or ventricular contractions on the electrocardiogram are less strong determinants of a postoperative cardiac complication. 32. Rank the clinical scenarios in order of greatest likelihood of serious postoperative pulmonary complications. A. Transabdominal hysterectomy in an obese woman that requires 3 hours of anesthesia time. B. Right middle lobectomy for bronchogenic cancer in a 65-year-old smoker. C. Vagotomy and pyloroplasty for chronic duodenal ulcer disease in a 50-year-old who had chest film findings of old, healed tuberculosis. D. Right hemicolectomy in an obese 60-year-old smoker. E. Modified radical mastectomy in a 58-year-old woman who is obese. Answer: BDCAE DISCUSSION: If one considers the constellation of risk factors for pulmonary complications that is provided in tabular form in the accompanying chapter, one should readily recognize B, right middle lobectomy for bronchogenic cancer in a 65-year-old smoker, as the highest risk of a clinical situation for the likelihood of serious pulmonary complications. The next in rank may be properly debated between answer D and answer C. D, right hemicolectomy, is judged to have somewhat greater likelihood of complications since the patient is older, smokes, and is obese, although the procedure may be done through a transverse or lower abdominal incision. C, vagotomy and pyloroplasty, is viewed as being somewhat less serious since it is an upper abdominal operation on an elective basis in a 50-year-old whose only abnormalities include old, healed tuberculosis on a chest film. A very low risk of pulmonary complication should follow a transabdominal hysterectomy done through a lower abdominal incision in a woman whose only risk factors are obesity and a 3-hour anesthesia time. The lowest risk probably resides with the younger patient undergoing modified radical mastectomy, whose only risk factor is obesity. This is particularly true since this operation is conducted on the surface of the body, is associated with relatively little postoperative pain, and provides free and unrestricted respiratory function. 33. Rank the following laboratory tests and procedures in terms of their relative value to a 65-year-old woman who is to undergo elective resection of a sigmoid cancer. A. Carcinoembryonic antigen (CEA). B. Blood urea nitrogen (BUN). C. Electrocardiogram (ECG). D. Hemoglobin concentration (Hgb). E. Serum creatinine (Cr). F. Arterial blood oxygen tension (PaO 2) on room air. G. Serum sodium concentration (Na+). Answer: CDFEBAG DISCUSSION: The most important test by far is the electrocardiogram, with its capacity to indicate signs of occult heart disease. The second most important evaluation is the hemoglobin concentration, which in this patient may show an anemia related to chronic alimentary tract blood loss that would require correction prior to safe induction of a general anesthetic. Arterial blood gases vary from individual to individual depending primarily on smoking habits and age. Accordingly, each older person should have a resting baseline determination prior to operation. Serum creatinine may show evidence of occult renal disease and is substantially more useful than blood urea nitrogen, which is more vulnerable to transient volume changes. Carcinoembryonic antigen is important to know in many patients with cancer with respect to postoperative follow-up since in some cases it may be an early herald of recurrent disease. However, it has little to do with the patients preoperative assessment in terms of risk and preparation for an elective operation. The presence of liver metastases, for example, can be discovered with significant accuracy by palpation at the time of operation, and an elevated carcinoembryonic antigen in no set of circumstances would lead one to withhold colon resection with its relief of potential obstruction and bleeding. Finally, serum sodium concentration in a 65-year-old woman who is admitted electively for resection of the colon is always normal and would be of least value among these tests. 34. Which of the following statements regarding whole blood transfusion is/are correct? A. Whole blood is the most commonly used red cell preparation for transfusion in the United States. B. Whole blood is effective in the replacement of acute blood loss. C. Most blood banks in the United States have large supplies of whole blood available. D. The use of whole blood produces higher rates of disease transmission than the use of individual component therapies. Answer: B DISCUSSION: Whole blood is effective as a replacement fluid for acute blood loss because it provides both volume and oxygen-carrying capacity (red blood cells). It is rarely used in the United States nowadays, and most blood banks do not provide whole blood transfusions. It is significantly more efficient to separate donated blood into its components. In this manner, the red blood cell mass can be used to provide oxygen-carrying capacity, the plasma can be used for factor replacement, and the platelets and white cells can be used for patients deficient in these components. The use of whole blood to replace acute blood loss is associated with lower disease transmission rates than the use of packed red blood cells, fresh frozen plasma, and platelets, each from a different donor. 35. Which of the following statements about the preparation and storage of blood components is/are true? A. Solutions containing citrate prevent coagulation by binding calcium. B. The shelf life of packed red blood cells preserved with CPDA-1 is approximately 35 days at 1؛ to 6؛ C. C. There are normal numbers of platelets in packed red blood cells stored at 1؛ to 6؛ C for more than 2 days. D. The storage lesion affecting refrigerated packed red blood cells includes development of acidosis, hyperkalemia, and decreased intracellular 2,3DPG (diphosphoglycerate). Answer: ABD DISCUSSION: After blood has been collected from a donor, it is anticoagulated with a solution containing citrate, which acts by binding calcium. Blood is then separated into its components. Packed red blood cells stored at 1؛ to 6؛ C using CPDA-1 preservative have a shelf life of 35 days. There are essentially no functional platelets in refrigerated blood stored at 1؛ to 6؛ C after approximately 48 hours in storage. Refrigerated packed red blood cells undergo progressive changes termed a storage lesion. Such changes include acidosis, hyperkalemia, and decreased levels of 2,3-DPG, which are reversed after transfusion or produce effects other than those predicted based on the content of the unit of blood. 36. Which of the following is/are acceptable reasons for the transfusion of red blood cells based on currently available data? A. Rapid, acute blood loss with unstable vital signs but no available hematocrit or hemoglobin determination. B. Symptomatic anemia: orthostatic hypotension, severe tachycardia (greater than 120 beats per minute), evidence of myocardial ischemia, including angina. C. To increase wound healing. D. A hematocrit of 26% in an otherwise stable, asymptomatic patient. Answer: AB DISCUSSION: Currently accepted guidelines for the transfusion of packed red blood cells include acute ongoing blood loss, as might occur in an injured patient, and the development of symptomatic anemia with manifestations of decreased tissue perfusion related to decreased oxygen-carrying capacity of the blood. This includes situations in which the patient is unable to compensate for a decreased oxygen-carrying capacity by the usual mechanisms, such as increased cardiac output. Such patients develop myocardial dysfunction if an excessive demand is placed on the heart. The patient should be transfused with packed red blood cells, which afford added oxygen-carrying capacity. This decreases the workload on the myocardium while providing the necessary oxygen-delivery capability. The use of packed red blood cells to improve wound healing or to improve the patients sense of well-being is highly questionable. No data support such a practice. In general, the use of a transfusion trigger such as a hematocrit of 30% or hemoglobin of 10 gm. per dl. constitutes a questionable indication for transfusion. If a patient is asymptomatic and stable and has no risk of myocardial ischemia, packed red blood cell transfusion should not be given based solely or predominantly on a numerical value such as a hematocrit of 28%. 37. The transfusion of fresh frozen plasma (FFP) is indicated for which of the following reasons? A. Volume replacement. B. As a nutritional supplement. C. Specific coagulation factor deficiency with an abnormal prothrombin time (PT) and/or an abnormal activated partial thromboplastin time (APTT). D. For the correction of abnormal PT secondary to warfarin therapy, vitamin K deficiency, or liver disease. Answer: CD DISCUSSION: The use of FFP as a volume expander is not indicated. There are currently several preparations (both crystalloid and colloid) that are equally effective and do not carry the infectious and other risks associated with the use of FFP. The use of FFP as a “nutritional” supplement is to be condemned. Patients with specific deficiencies of coagulation factors generally benefit greatly from the infusion of FFP. In cases of specific factor deficiency, other preparations may be more appropriate, but FFP is generally immediately available and is effective in most patients. Patients receiving warfarin therapy, those who have vitamin K deficiency, and those with liver dysfunction have abnormalities of the vitamin K–dependent factors II, VII, IX, and X, as well as protein C and protein S. 38. In patients receiving massive blood transfusion for acute blood loss, which of the following is/are correct? A. Packed red blood cells and crystalloid solution should be infused to restore oxygen-carrying capacity and intravascular volume. B. Two units of FFP should be given with every 5 units of packed red blood cells in most cases. C. A “six pack” of platelets should be administered with every 10 units of packed red blood cells in most cases. D. One to two ampules of sodium bicarbonate should be administered with every 5 units of packed red blood cells to avoid acidosis. E. One ampule of calcium chloride should be administered with every 5 units of packed red blood cells to avoid hypocalcemia. Answer: A DISCUSSION: Patients who are suffering from acute blood loss require crystalloid resuscitation as the initial maneuver to restore intravascular volume and re-establish vital signs. If 2 to 3 liters of crystalloid solution is inadequate to restore intravascular volume status, packed red blood cells should be infused as soon as possible. There is no role for “prophylactic infusion” of FFP, platelets, bicarbonate, or calcium to patients receiving massive blood transfusion. If specific indications exist patients should receive these supplemental components. In particular, patients who have abnormal coagulation tests and have ongoing bleeding should receive FFP. Patients who have depressed platelet counts along with clinical evidence of oozing (microvascular bleeding) benefit from platelet infusion. Sodium bicarbonate is not necessary, since most patients who receive blood transfusion ultimately develop alkalosis from the citrate contained in stored red blood cells. The use of calcium chloride is usually unnecessary unless the patient has depressed liver function, ongoing prolonged shock associated with hypothermia, or, rarely, when the infusion of blood proceeds at a rate exceeding 1 to 2 units every 5 minutes. 39. Hemostasis and the cessation of bleeding require which of the following processes? A. Adherence of platelets to exposed subendothelial glycoproteins and collagen with subsequent aggregation of platelets and formation of a hemostatic plug. B. Interaction of tissue factor with factor VII circulating in the plasma. C. The production of thrombin via the coagulation cascade with conversion of fibrinogen to fibrin. D. Cross-linking of fibrin by factor XIII. Answer: ABCD DISCUSSION: Hemostasis requires the interaction of platelets with the exposed subendothelial structures at the site of injury followed by aggregation of more platelets in that area. Interactions between endothelial cell and subendothelial tissue factor with factor VII activate the coagulation cascade. The end product is large amounts of thrombin that catalyze the conversion of fibrinogen into fibrin. Fibrin thus formed is cross-linked by factor XIII to form a stable clot that incorporates the platelet plug and fibrin thrombus into a stable clot. 40. Which of the statements listed below about bleeding disorders is/are correct? A. Acquired bleeding disorders are more common than congenital defects. B. Deficiencies of vitamin K decrease production of factors II, VII, IX, and X, protein C, and protein S. C. Hypothermia below 32؛C rarely causes a bleeding disorder. D. Von Willebrands disease is a very uncommon congenital bleeding disorder. Answer: AB DISCUSSION: Acquired bleeding disorders are significantly more common than congenital bleeding defects. Vitamin K deficiency may be related to malnutrition or competitive inhibition of the production of the vitamin K–dependent factors II, VII, IX, X, protein C, and protein S by warfarin (Coumadin). Hypothermia causes significant platelet dysfunction with a significant bleeding disorder in many patients. It is among the least recognized causes of altered coagulation in surgical patients. Von Willebrands disease is a relatively common disorder of bleeding and is generally undetectable by routine screening methods.
Posted on: Wed, 12 Nov 2014 12:37:09 +0000
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