Chapter 38 Critical Care Medicine
Mechanical ventilation
1. List the typical indications for mechanical ventilation in the ICU.
2. What are some common causes of respiratory failure?
3. What are some common causes of ventilatory failure?
4. What are some indications for the need for airway protection?
5. What are some common modes of mechanical ventilation?
6. Describe the key ventilator settings in continuous mandatory ventilation (CMV) mode.
7. How can the inspiratory and expiratory time be adjusted in CMV mode?
8. What effect does a patient’s breathing effort have when mechanically ventilated in CMV mode?
9. Describe the key ventilator settings in synchronized intermittent mandatory ventilation (SIMV) mode.
10. What effect does a patient’s breathing effort have when mechanically ventilated in SIMV mode?
11. Describe the key ventilator settings in pressure support ventilation (PSV) mode.
12. What is positive end-expiratory pressure (PEEP)?
13. How does PEEP improve oxygenation?
14. What are some possible adverse effects of PEEP?
15. What are some criteria that must be met before a patient can be considered ready for a trial of weaning from mechanical ventilation?
16. What is the preferred method of protocol-driven weaning from mechanical ventilation?
Noninvasive positive-pressure ventilation
17. What is noninvasive positive-pressure ventilation (NIPPV)? What are two modes of NIPPV?
18. What is continuous positive airway pressure (CPAP)? What are some benefits of CPAP?
19. What is bilevel positive airway pressure (BiPAP)?
20. What are some advantages of NIPPV?
21. What are some indications for NIPPV?
22. What are three contraindications to noninvasive mechanical ventilation?
Acute respiratory distress syndrome
23. What are the American-European Consensus Conference Definitions for acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS)?
24. List three direct causes and three indirect causes of acute respiratory distress.
25. What are the basic principles for the treatment and the management of mechanical ventilation of patients with ALI or ARDS?
Sedation and analgesia in the intensive care unit
26. What are some indications for patient sedation in the intensive care unit (ICU)?
27. What are the components of the Ramsay sedation scoring system?
28. What are the common side effects of the use of opioids for the sedation of critically ill patients?
29. What are the common side effects of the use of benzodiazepines for the sedation of critically ill patients?
30. What are the common side effects of the use of propofol for the sedation of critically ill patients?
31. List the common clinical findings in propofol infusion syndrome.
32. What are the advantages of ketamine as a sedative in the ICU?
33. What is the mechanism of action of dexmedetomidine? What are its hemodynamic effects?
Shock
35. List three major categories of shock. How can they be differentiated using central venous pressure (CVP) and cardiac output (CO) measurements?
36. What are some common causes of hypovolemic shock?
37. What are the common clinical findings of hypovolemic shock?
38. What is the treatment for hypovolemic shock?
39. What are the causes of cardiogenic shock?
40. What are the common clinical findings in cardiogenic shock?
41. What is the treatment for cardiogenic shock?
42. What are some common causes of vasodilatory shock?
43. What are the common clinical findings of vasodilatory shock?
44. What is the treatment for vasodilatory shock?
45. Upon which receptor subtypes does dopamine have agonist activity?
46. Upon which receptor subtypes does epinephrine have agonist activity?
47. What are the advantages of norepinephrine use in septic shock?
48. Upon which receptor does phenylephrine have agonist activity?
49. What are the hemodynamic effects of dobutamine infusion?
50. How does vasopressin differ in its mechanism of action when compared to norepinephrine?
Delirium
55. What is the incidence of delirium in the adult ICU population?
56. How is mortality impacted by the presence of delirium in the critically ill?
57. What are some common causes of delirium in a patient in the ICU?
58. What is the common method of delirium assessment in the ICU?
59. What is the treatment for delirium in a patient in the ICU?
Answers*
Mechanical ventilation
1. Mechanical ventilatory support is typically initiated for the treatment of respiratory failure due to impaired oxygenation, impaired carbon dioxide excretion (ventilatory failure), and airway protection. Patients receive mechanical ventilatory support to (1) reduce the work of breathing, (2) reverse progressive respiratory acidosis or hypoxemia, (3) reduce the risk for aspiration, or (4) ensure a patent airway with severe neck and facial swelling or trauma. (666)
2. Common causes of respiratory failure may include trauma, ARDS, sepsis, pneumonia, and cardiogenic and noncardiogenic pulmonary edema. (666)
3. Ventilatory failure may be due to chronic obstructive pulmonary disease (COPD), asthma, and/or drug intoxication. (666)
4. Airway protection indications are usually limited to conditions such as altered mental status, head and neck trauma or swelling, or significant neuromuscular disorders. (666)
5. Common modes of mechanical ventilation include continuous mandatory ventilation, synchronized intermittent mandatory ventilation, pressure support ventilation, and PEEP. (666-667)
6. In CMV mode, the ventilator is programmed to deliver a set tidal volume at a set respiratory rate, thereby resulting in the delivery of a predictable minute ventilation. The ventilator will deliver its preset tidal volume at its preset time. (666)
7. To regulate the amount of time that the ventilator spends cycling in inspiration and expiration, the inspiratory flow rate is set. By increasing inspiratory flow, the set tidal volume is delivered in a shorter time, which allows more time for exhalation. (666)
8. The patient’s breathing efforts are unsupported in CMV mode. The ventilator continues to deliver its preset tidal volume at its preset time regardless of patient effort. (666)
9. In SIMV mode, the ventilator is programmed to deliver a set tidal volume and respiratory rate. In SIMV mode, however, the ventilator attempts to synchronize mandatory breaths to the patient’s own spontaneous breaths. If the patient does not initiate a breath within a set time, the ventilator delivers the set tidal volume as in CMV mode. Therefore a minimum minute ventilation is maintained in SIMV mode. (666)
10. If a patient initiates a breath during the preset time for a mandatory breath, a preset tidal volume will be delivered. Additional breaths initiated by the patient beyond those set in the SIMV mode are supported by the ventilator with an augmentation of the tidal volume by a preset pressure. It is therefore a pressure-supported breath. (666)
11. In pressure support ventilation, the ventilator does not deliver a preset tidal volume but, instead, relies on the patient’s intrinsic respiratory drive. Typically, the amount of pressure support is set between 5 and 20 cm H2O pressure to ensure adequate tidal volume and minute ventilation. In this mode, tidal volume will vary with patient effort. To use pressure support ventilation, the patient must possess an intact respiratory drive, and no residual skeletal muscle paralysis can be present. (666)
12. PEEP is positive airway pressure that is applied at the end of expiration during mechanical ventilation. The typical PEEP range is between 5 and 20 cm H2O pressure. (667)
13. PEEP functions to increase mean airway pressure and thereby minimize atelectasis. PEEP increases the functional residual capacity of the lungs and, in patients with a lung injury, results in improved pulmonary compliance. The recruitment of alveoli, or the inflation of previously collapsed alveoli, by PEEP can lead to improved oxygenation in a mechanically ventilated patient. (667)
14. Excessively high levels of PEEP can overdistend and damage alveoli. Excessive PEEP may also cause hemodynamic collapse by reducing preload to both the right and the left ventricles with a resultant fall in cardiac output. Finally, if there is inadequate time allowed for the exhalation of the delivered tidal volume, there can be a buildup of end-expiratory pressure that can lead to hemodynamic collapse. (667)
15. To consider weaning from mechanical ventilation, a patient must have recovered from the process that originally required mechanical ventilatory support, be hemodynamically stable, be able to manage their pulmonary secretions, and be able to protect their airway against the aspiration of gastric contents with an intact mental status and gag reflex. The patient should be maintaining adequate oxygen saturation with an inspired oxygen concentration of 40% or less, be able to initiate breaths, and be strong enough to generate an adequate tidal volume. The patient’s respiratory strength is usually considered sufficient for weaning if the patient is able to generate a negative inspiratory force of at least −20 cm H2
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