Respiratory and Critical Care Flashcards
1
Q
1. A 29 year old man is admitted to the intensive care unit (ICU) after a drug overdose. The patient is placed on a ventilator with a set tidal volume (VT) of 750 mL at a rate of 10 breaths/min. The patient is making no inspiratory effort. The measured minute ventilation is 6 L and the peak airway pressure is 30 cm H20. What is the compression factor for this ventilator delivery circuit? A. 1 mL (cm H20)-1 B. 2 mL (cm H20)-1 C. 3 mL (cm H20)-1 D. 4 mL (cm H20)-1 E. 5 mL (cm H20)-1
A
- E A volume-cycled ventilator set to deliver a volume of 750 mL at a rate of 10/min would deliver a minute ventilation of 7.5 L. The measured minute ventilation, however, is only 7L; therefore 1.5 L must be absorbed by the breathing circuit. This volume is known as the compression volume. If one divides the volume by 10 (number of breaths/min), then one determines the compression volume/breath. This number (mL) can be further divided by the peak inflation pressure (cm H2O) to determine the actual compression factor, which in this case is 5 mL (cm H2O)-1 .
Compression Volume = [(Vdelivered - V measured)/ Respiratory Rate]/ Peak Airway Pressure (cm H2O) = 5 mL (cm H20)-1 (Hall 91)
2
Q
2. A 62 year old male is brought to the ICU after elective repair of an abdominal aortic aneurysm. His vital signs are stable, but he requires a sodium nitroprusside infusion at a rate of 10 ug/kg/min to keep the systolic blood pressure below 110 mm Hg. The SaO2 is 98% with controlled ventilation at 12 breaths/min and an FiO2 of 0.60. After 3 days, his SaO2 decreases to 85% on the pulse oximeter. Chest x ray film and results of physical examination are unchanged. Which of the following would most likely account for his desaturation? A. cyanide toxicity B. thiocyanate toxicity C. O2 toxicity D. thiosulfate toxicity E. methemoglobinemia
A
- E The metabolism of nitroprusside in the body requires the conversion of oxyhemoglobin (Fe++) to methemoglobin (FE+++). The presence of sufficient quantities of methemoglobin in the blood will cause the pulse oximeter to read 85% saturation regardless of the true arterial saturation. Cyanide toxicity is also a possibility in any patient who is receiving nitroprusside. Cyanide toxicity should be suspected when the patient develops metabolic acidosis or becomes resistant to the hypotensive effects of this drug despite a sufficient infusion rate. This can be confirmed by measuring the mixed venous PaO2, which would be elevated in the presence of cyanide toxicity. Thiocyanate toxicity is also a potential hazard of nitroprusside administration in patients with renal failure. Patients suffering from thiocyanate toxicity display nausea, mental confusion, and skeletal-muscle weakness. (Hall 92).
3
Q
3. Maximizing which of the following lung parameters is the most important factor in prevention of postoperative pulmonary complications? A. tidal volume (VT) B. inspiratory reserve volume C. vital capacity D. functional residual capacity (FRC) E. inspiratory capacity
A
- D FRC is composed of expiratory reserve volume plus residual volume. It is essential to maximize FRC in the postoperative period to ensure that it will be greater than closing volume. Closing volume is that lung volume at which small-airway closure begins to occur. Maximizing FRC, therefore, reduces atelectasis and lessens the incidence of arterial hypoxemia and pneumonia. Maneuvers aimed at increasing FRC include early ambulation, incentive spirometry, deep breathing, and intermittent positive pressure breathing. (Hall 93)
4
Q
4. At the outpatient surgicenter, a 66 year old healthy woman had an uneventful laparoscopic cholecystectomy approximately 3 hours ago. The postanesthesia care unit nurses inform you that her SPO2 is 89% on room air. Her preoperative SPO2 was 98%. Which of the following therapies is MOST likely to improve her oxygenation? A. incentive spirometry B. deep breathing exercises C. continuous positive airway pressure D. chest physiotherapy
A
- C Hypoxemia is an extremely common complication; 30%-50% of all patients experience some period of hypoxemia (SPO2>93% at sea level) after uneventful abdominal surgery. The most common etiology of hypoxemia is atelectasis associated with the anesthesia and surgical procedure. A small segment of patients who undergo open upper abdominal surgery have persistent hypoxemia that requires tracheal intubation and mechanical ventilation, leading to prolonged intensive care unit stays and increased morbidity and mortality. The diagnosis of atelectasis is usually one of exclusion. Findings on physical examination include dyspnea and tachypnea, asymmetrical chest movement, or decreased breath sounds. The specificity of this exam is low and frequently the only finding is a persistent decreased SpO2. However, diagnostic tests can rule out other causes such as aspiration pneumonitis, pulmonary edema, or pneumothorax. The most readily available test is a simple chest radiograph, and the diagnostic criteria used for a radiographic diagnosis include- opacification of a lobe or lobar segment, displacement of the interlobar fissure, elevation of the hemidiaphragm and mediastinal shift, compensatory overinflation of aerated segments. With the current emphasis on outpatient procedures, aggressive efforts to prevent or treat pulmonary atelectasis are often used. Most therapies aim to produce a large and sustained increase in transpulmonary pressure to reexpand the collapsed alveoli. The most frequently employed therapies include intermittent positive pressure breathing, deep-breathing exercises, incentive spirometry, and chest physiotherapy. A meta-analysis of the effectiveness of these therapies for improving oxygenation in patients after upper abdominal surgery found that all the methods had equal effect; more precisely, none were found to be clinically or statistically effective. In fact, in the meta-analysis the most effective therapy to reverse atelectasis, particularly in patients who develop severe hypoxemia, is the use of supplemental oxygen and 7.5 cm H2O of nasal continuous positive pressure airway pressure. Patients receiving continuous positive airway pressure (CPAP) had a lower occurrence of pneumonia and reintubation than patients who only received oxygen therapy. Nasal CPAP may be a good, brief, first-line therapy for patients with unacceptable postoperative SpO2 on room air, particularly for patients who normally use CPAP or oxygen at night.
5
Q
5. An 83-year-old woman is admitted to the ICU after coronary artery surgery. A pulmonary artery catheter is in place and yields the following data: CVP 5 mm Hg, CO 4.0 L/min, MAP 90 mm Hg, mean pulmonary artery pressure (PAP) 20 mm Hg, pulmonary artery occlusion pressure (PAOP) 12 mm Hg, and HR 90. Calculate the patient’s PVR A. 40 dynes-sec-cm-5 B. 80 dynes-sec-cm-5 C. 160 dynes-sec-cm-5 D. 200 dynes-sec-cm-5 E. 240 dynes-sec-cm-5
A
- C PVR = 80 * (PAP-PAOP)/CO. Hall 94
6
Q
- A 72 year old male patient with a history of myocardial infarction 12 months earlier is scheduled to undergo elective repair of a 6 cm abdominal aortic aneurysm under general anesthesia. When would this patient be at highest risk for another myocardial infarction?
A. on induction of anesthesia
B. during placement of the aortic cross-clamp
C. upon release of the aortic cross-clamp
D. 24 hours postoperatively
E. on the 3rd postoperative day
A
- E For reasons that are not fully understood, patients who have sustained a myocardial infarction and subsequently undergo surgery are most likely to have another infarction on the third postoperative day. Hall 95
7
Q
7. Calculate the body mass index of a male 200 cm (6 feet 6 inches) tall who weighs 100 kg (220 pounds) A. 20 B. 25 C. 30 D. 35 E. 40
A
- B Calculation of the BMI is a convenient way to define obesity and morbid obesity (>31 kg/m2). Obesity, defined as a weight 25% greater than ideal body weight, would correspond to a BMI of 27 for women and 28 for men. BMI = mass (kg)/ height2 (meters). All major organ systems are affected as a consequence of obesity. The greatest concerns for the anesthesiology are, however, related to the heart and lungs. Cardiac output must increase about 0.1L/min for each extra kg of adipose tissue. As a consequence, obese patients frequently are hypertensive, and may ultimately develop cardiomegaly and left-sided heart failure. FRC is reduced in obese patients and management of the airway often can be difficult. Hall 96
8
Q
8. The normal FEV1/FVC ratio is A. 0.95 B. 0.80 C. 0.60 D. 0.50 E. 0.40
A
- B The forced expiratory volume in 1 second (FEV1) is the total volume of air that can be exhaled in the first second. Normal healthy adults can exhale approximately 75% to 85% of their forced vital capacity (FVC) in the first second, 94% in 2 seconds and 97% in 3 seconds. Therefore, the normal FEV1/FVC ratio is 0.75 or higher. In the presence of obstructive airway disease, the FEV1/FVC ratio is less than 70% reflects mild obstruction, less than 60% moderate obstruction and less than 50% severe obstruction. This ratio can be used to determine the severity of obstructive airway disease and to monitor the efficacy of bronchodilator therapy. Hall 97
9
Q
- Direct current (DC) cardioversion is not useful and therefore NOT indicated in an unstable patient with which of the following?
A. supraventricular tachycardia in a patient with Wolff-Parkinson-White syndrome
B. atrial flutter
C. multifocal atrial tachycardia
D. new onset atrial fibrillation
E. all of these rhythms should be DC cardioverted in an unstable patient
A
- C Multifocal atrial tachycardia (MAT) is a non-reentrant, ectopic atrial rhythm often seen in patients with chronic obstructive pulmonary disease (COPD). It is frequently confused with atrial fibrillation but, in contrast to A. fib, atrial flutter, and paroxysmal supraventricular tachycardia, DC cardioversion is ineffective in converting it to normal sinus rhythm. Ectopic atrial tachydysrhythmias are not amenable to cardioversion because they lack the reentrant mechanism, which is necessary for successful termination with electrical counter shock. Hall 98
10
Q
10. During the first minute of apnea, the PaCO2 will rise A. 2 mm Hg/min B. 4 mm Hg/min C. 6 mm Hg/min D. 8 mm Hg/min E. 10 mm Hg/min
A
- C During apnea, the PaCO2 will increase approximately 7 mm Hg during the first minute and then 3 to 4 mm Hg each minute thereafter. Hall 99
11
Q
11. Potential complications associated with total parenteral nutrition (TPN) include of the following except A. ketoacidosis B. hyperglycemia C. hypoglycemia D. hypophosphatemia E. increased work of breathing
A
- A TPN therapy is associated with numerous potential complications. Blood sugars need to be carefully monitored since hyperglycemia may develop due to the high glucose load and require treatment with insulin, and hypoglycemia may develop if TPN is abruptly stopped (i.e., infusion turned off or mechanical obstruction in the IV tubing). Other complications include electrolyte disturbances (e.g., hypokalemia, hypophosphatemia, hypomagnesemia, hypocalcemia), volume overload, catheter related sepsis, renal and hepatic dysfunction, thrombosis of the central veins, and nonketotic hyperosmolar coma. Increased work of breathing is related to increased production of CO2 most frequently due to overfeeding. Acidosis in these patients is hyperchloremic metabolic acidosis resulting from formation of HCl during metabolism of amino acids. Ketoacidosis is not associated with TPN therapy. Hall 100
12
Q
12. O2 requirement for a 70 kg adult is A. 150 mL/min B. 250 mL/min C. 350 mL/min D. 450 mL/min E. 550 mL/min
A
- B The O2 requirement for an adult is 3 to 4 ml/kg/min. The O2 requirement for a newborn is 7 to 9 mL/kg/min. Alveolar ventilation (VA) in neonates is double that of adults to help meet their increased O2 requirements. This increase in VA is achieved primarily by an increase in respiratory rate as VT is similar to that of adults (i.e., 7 mL/kg). Although CO2 production also is increased in neonates, the elevated VA maintains the PaCO2 near 38 to 40 mm Hg. Hall 101
13
Q
- The FRC is composed of
A. expiratory reserve volume and residual volume
B. inspiratory reserve volume and residual volume
C. inspiratory capacity and vital capacity
D. expiratory capacity and VT
E. expiratory reserve volume and tidal volume
A
- A A comprehensive understanding of respiratory physiology is important for understanding the effects of both regional and general anesthesia on respiratory mechanics and pulmonary gas exchange. The volume of gas remaining in the lungs after a normal expiration is called the FRC. The volume of gas remaining in the lungs after a maximal expiration is called the residual volume. The difference between these two volumes is called the expiratory reserve volume. Therefore, the FRC is composed of the expiratory reserve volume and residual volume. Hall 102
14
Q
- Which of the following statements correctly defines the relationship between minute ventilation (VE), dead space ventilation (VD), and PaCO2?
A. if VE is constant and VD increases, then PaCO2 will increase
B. if VE is constant and VD increases, then PaCO2 will decrease
C. if VD is constant and VE increases, then PaCO2 will increase
D. if VD is constant and VE decreases, then PaCO2 will decrease
E. none of the above
A
- A The volume of gas in the conducting airways of the lungs (and not available for gas exchange) is called the anatomic dead space. The volume of gas in ventilated alveoli that are unperfused (and not available for gas exchange) is called the functional dead space. The anatomic dead space together with the functional dead space is called the physiologic dead space. Physiologic dead-space ventilation (VD) can be calculated by the Bohr dead-space equation, which is mathematically expressed as follows: VD/VT= (PaCO2-PeCO2)/PaCO2 where VD/VT is the ratio of VD to VT, and the subscripts a and e represent arterial and mixed expired, respectively. Of the choices given, only the first is correct. A large increase in VD will result in an increase in PaCO2. Hall 103
15
Q
15. A 22-year-old patient who sustained a closed head injury is brought to the operating room (OR) from the ICU for placement of a dural bolt. Hemoglobin has been stable at 15 g/dL. Blood gas analysis immediately before induction reveals a PaO2 of 120 mm Hg and an arterial saturation of 100%. After induction, the PaO2 rises to 150 mm Hg and the saturation remains the same. How has the oxygen content of this patient’s blood changed? A. it has increased by 10% B. it has increased by 5% C. it has increased by less than 1% D. cannot be determined without PaCO2 E. cannot be determined without pH
A
- C The oxygen content of blood can be calculated with the following:
O2 content = (1.39 x hemoglobin x arterial saturation) + (0.003 x PaO2)
First oxygen content = (1.39 x 15 x 1.0) + 0.003 x 120 = 21.21 mL/dL
Second oxygen content = (1.39 x 15 x 1.0) + 0.003 x 150 = 21.30 mL/dL
The difference in the oxygen content is 0.09 mL/dL. this represents a change of 0.42%. Hall 104
