Cairo: Pilbeam's Mechanical Ventilation, 6th Edition

Chapter 16: Extrapulmonary Effects of Mechanical Ventilation

WorkBook Answer Key

Key Terms Crossword Puzzle

Chapter Review Questions
1. (a) Cardiovascular function, (b) pulmonary function, (c) neurological function, (d) renal function, and (e) gastrointestinal function.
2. (1) The amount of pressure applied to the airways and (2) the patient’s cardiopulmonary status.
3. The negative intrapleural pressures that occur during spontaneous inspiration are transmitted to the intrathoracic vessels. A drop in pressure in the vena cava increases the pressure gradient back to the heart, and venous return increases.
4. Right ventricular preload is increased during inspiration, because more blood is returning to the right heart.
5. Left ventricular preload is decreased during passive expiration. When intrapleural pressure becomes less negative, venous return is decreased, and right ventricular stroke volume is also decreased, which causes a decrease in left ventricular preload.
6. Increase the pressure gradient.
7. Diagram “A” represents the largest gradient.
8. Diagram “C” represents the smallest gradient.
9. Diagram “A” represents the system with the largest venous return.
10. Because the pulmonary capillaries are interlaced with the alveoli, when the alveoli are overdistended, the pulmonary capillaries are stretched and narrowed. As a result, resistance to blood flow through the pulmonary circulation increases. The increased pulmonary vascular resistance increases right ventricular afterload.
11. High levels of positive pressure (>15 cm H2O) and volume depletion.
12. The reduction in cardiac output created by decreased venous return reduces the coronary artery perfusion pressure gradient for both sides of the heart. This, plus the direct effect of compression of the coronary vessels caused by increases in intrathoracic pressure, can ultimately lead to myocardial ischemia.
13. (a) Increase in sympathetic tone, (b) increase in systemic vascular resistance, (c) increase in peripheral venous pressure from arterial and venous constriction, and (d) peripheral shunting of blood away from the kidneys and lower extremities.
14. (any four of the following) Sympathetic blockade, spinal anesthesia, moderate levels of general anesthesia, spinal cord transaction, or severe polyneuritis
15. The respiratory therapist should measure the blood pressure soon after PPV is initiated.
16. >15 cm H2O
17. (a) The presence or absence of the normal compensatory mechanism for maintaining arterial blood pressure, (b) the lung and chest wall compliance and airway resistance, and (c) the duration and magnitude of the positive pressure.
18. PPV can reduce venous return and thus preload to the heart. This improves length-tension relationships within the heart and improves stroke volume.
19. Mean airway pressure
20. Mean airway pressure = ½[PIP × (TI/TCT)]; TCT = 60/12 = 5
= ½[25 × (1 sec/5 sec)]
= ½(5) = 2.5 cm H2O
21. Adding a 1-second inspiratory hold increases the TI to 2 seconds, so that:
Mean airway pressure = ½(25) × (2/5)
= ½(25) × 2/5
= 25/2 × 2/5 = 50/10 = 5 cm H2O
22. The mean airway pressure increases when an inspiratory hold is added. The longer the inspiratory time, the higher the mean airway pressure.
23. Mean airway pressure = ½[(PIP  PEEP) × (TI ÷ TCT)] + PEEP
= ½[(35  10) × (1/5)] + 10
= ½[25 × (1/5)] + 10
= ½(5) + 10
= 12.5 cm H2O
24. Adding a 1-second inspiratory hold increases the TI to 2 seconds.
Mean airway pressure = ½[(35  10) × (2/5)] + 10
= 25/2 × 2/5 + 10 = 50/10 + 10 = 15 cm H2O
25. High inspiratory flow rates are likely to cause uneven ventilation.
26. Values of 1:1, 2:1, and higher may result in significant increases in air trapping and significant hemodynamic complications.
27. A longer expiratory time.
28. The severity of a patient’s lung disease.
29. (a) Inspiratory flow and pattern, (b) I:E ratio, (c) inflation hold, (d) PEEP, and (e) ventilator mode.
30. Rapid flow rates deliver the desired VT in a shorter time. The faster the flow, the shorter the inspiratory time and the lower the mean airway pressure.
31. To affect cardiac output, the PEEP must transmit its pressure to the intrathoracic space and intrathoracic vessels. If this occurs, PEEP causes a decrease in cardiac output.
32. High levels of PEEP would not cause a decrease in CO when the patient has “stiff” lungs. This situation could exist because the “stiff” lungs do not allow the transmission of pressure to the intrathoracic space and intrathoracic vessels.
33. CPP = MABP  ICP; 85  18 mm Hg = 67 mm Hg.
34. PPV can increase central venous pressure, making it more difficult for blood to return to the right side of the heart from the head. This causes “backup” of pressure into the head, increasing the ICP.
35. Jugular vein distention is a clinical sign of increased ICP.
36. Hyperventilation lowers PaCO2, which temporarily constricts cerebral vessels.
37. (a) The kidneys respond to hemodynamic changes resulting from high intrathoracic pressures; (b) humoral responses also occur with PPV, including antidiuretic hormone (ADH), atrial natriuretic factor, and renin-angiotensin-aldosterone changes; and (c) abnormal pH, PaCO2, and PaO2 abnormalities affect the kidneys.
38. Urinary output is severely reduced when the glomerular capillary pressure drops below 75 mm Hg.
39. This redistribution of blood flow within the kidney will cause less urine, creatinine, and sodium to be excreted.
40. (a) Antidiuretic hormone; blood pressure changes caused by PPV precipitate the release of ADH, resulting in oliguria. (b) Atrial natriuretic factor, PPV, and PEEP can reduce the atrial filling pressure by reducing atrial stretch; this leads to decreased secretion of atrial natriuretic factor, causing water and sodium retention. (c) Renin-angiotensin-aldosterone; plasma renin activity is increased during PPV, which activates the renin-angiotensin-aldosterone cascade, resulting in retention of both sodium and water.
41. Decreased PaO2 values in patients with respiratory failure cause a reduction in renal function and a decrease in urine flow. Severe hypoxemia (PaO2 <40 mm Hg) dramatically interferes with normal renal function. A PaCO2 greater than 65 mm Hg can also severely impair renal function.
42. Many drugs (e.g., sedatives, neuromuscular blocking agents) and their metabolites are excreted by the kidneys. The altered renal function caused by PPV can prolong the effects of these drugs and affect patient care.
43. PPV and PEEP cause an elevation of serum bilirubin (>2.5 mg/100 mL), even when no evidence of preexisting liver disease is present. Several factors may lead to this effect on the liver. Liver malfunction may be a result of a drop in cardiac output, an increased diaphragmatic force against the liver, a decrease in portal venous flow, or an increase in splanchnic resistance. Any of these changes can lead to hepatic ischemia and impaired liver function.
44. Gastric distention during PPV can result from the swallowing of air that leaks around the endotracheal tube cuff. A gastric tube can be used to remove this air and decompress the stomach.
45. Seriously ill patients are at risk for malnutrition because of inadequate food intake and an increased metabolic rate associated with fever and wound healing.
46. (any of the following ) Reduced response to hypoxia and hypercapnia; muscle atrophy from prolonged bed rest and lack of use; muscle wasting, including respiratory muscles, from lack of nutrition; respiratory tract infections from impaired cell immunity and reduced or altered macrophage activity; decreased surfactant production and development of atelectasis; reduced ability of the pulmonary epithelium to replicate, resulting in slowed healing of damaged tissue; lower serum albumin levels, which affect colloid oncotic pressures and can contribute to pulmonary edema formation.
47. Overfeeding can lead to increased oxygen consumption, increased carbon dioxide production, and the need for increased minute ventilation, resulting in increased work of breathing.
48. (any of the following) Body composition, actual versus predicted body weight, anthropometric measurements, fat versus lean muscle mass, protein deficiencies, creatinine/height index, visceral protein malnutrition, serum albumin <3.5 g/dL, transferrin <300 mg, immunodeficiency, and decreased skin test response to known recall antigens.
49. Complications can be reduced through early recognition of the signs and symptoms of the problems associated with PPV, followed by appropriate intervention.
Critical Thinking Question
1. Arrow “A” represents decreased venous return resulting from the increase in intrapleural pressure. Arrow “B” represents the septal shifting that occurs when high levels of positive pressure are used and the patient is volume depleted. When this happens, left ventricular end-diastolic volume is encroached upon, and LV stroke volume may decrease because its ability to fill is limited. Arrow “C” represents compression of the heart between the expanding lungs. The transmission of positive pressure to the heart from the lungs exerts a cardiac tamponade effect. Arrow “D” represents the stretch and narrowing of the alveoli and pulmonary capillaries. As a result, resistance to blood flow through the pulmonary circulation increases, or pulmonary vascular resistance increases PVR, which will decrease right ventricular output.
Case Study
1. MAP = ½[(PIP  PEEP) × (TI ÷ TCT)] + PEEP
TI = VT ÷ Flow rate = 0.56 L ÷ 1.4 L/sec (84 L/min = 1.4 L/sec)
MAP = ½[(30  10) × (0.4 ÷ 5)] + 10
= ½[20 × (0.4 ÷ 5)] + 10
= 0.8 + 10 = 10.8 cm H2O
MAP = 10.8 cm H2O
2. The acid-base status is within normal limits. However, the patient still has mild hypoxemia with an FIO2 of 0.5 and PEEP of +10 cm H2O. The patient’s CSTAT is 43 mL/cm H2O. Therefore, his lungs are not stiff.
3. Because it was determined that the patient does not have stiff lungs, an increase in PEEP is not appropriate at this time. Looking at the patient’s ventilator settings, the RT can see from the calculation of inspiratory time that it is only 0.4 seconds. This is not a sufficient time for oxygenation. The inspiratory time should be at least 0.5 seconds. Therefore, the most appropriate ventilator change would be to decrease the set flow rate to increase the inspiratory time. This will increase the mean airway pressure and improve oxygenation. Decreasing the flow to 60 L/min (1 L/sec) will increase the mean airway pressure to 12 cm H2O.
NBRC-Style Questions
1. B
2. A
3. C
4. C
5. C
6. B
7. D
8. B
9. D
10. B