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.A PaCO2above 100 mm Hg may be well tolerated if the hypercapnia develops slowly andacidemia is minimized by renal compensatory changes, as is the case with this patient.Acute elevation in PaCO2 to 80 to 90 mm Hg may produce many neurologic signs andsymptoms, including confusion, headaches, seizures, and coma.A careful neurologicexamination of a patient with acute hypercapnia may reveal agitation, coarse tremor,slurred speech, asterixis, and, occasionally, papilledema.These effects of hypercapniaon the central nervous system are fully reversible, unlike the potentially permanentneurologic sequelae that are associated with acute hypoxemia.(Answer: C Acute hyper-capnic respiratory failure is defined as a PaCO2 greater than 45 to 50 mm Hg along with respiratoryacidosis)45.A 52-year-old man with severe emphysema presents to the emergency department with shortness ofbreath and altered mental status.A history is taken from the patient s wife.She states that the patientwas in his usual state of health until 24 hours ago, when he awoke with fever and shortness of breath.Since that time, he has experienced worsening fever, cough, and sputum production.She states that thepatient has been acting very funny for the past several hours.She does not believe the patient hascome into contact with anyone who was sick, and she states that he receives oxygen at home at a rateof 3 L/min via nasal cannula.On physical examination, the patient s temperature is found to be 101.1°F (38.4° C).The oropharynx and mucous membranes are dry, and rales with egophony are heard at theleft pulmonary base.Laboratory studies reveal leukocytosis with left shift.Results of arterial blood gasmeasurements are as follows: pH, 7.02; PaCO2, 80 mm Hg; and PaO2, 60 mm Hg.Which of the following statements regarding the management of respiratory failure in patients withCOPD is true?Q' A.The most common cause of acute respiratory deterioration inpatients with COPD is cigarette smoking 28 BOARD REVIEWQ' B.The first priority in the management of respiratory failure in thesepatients is to decrease PaCO2 to a normal valueQ' C.The level of PaCO2 at which ventilatory assistance becomes necessaryis approximately 70 mm Hg for males and 60 mm Hg for femalesQ' D.When invasive ventilation is required, PaCO2 levels should not belowered to the normal range in patients with chronic hypercapniaKey Concept: To understand the management of respiratory failure in patients with COPDThe first priority is to achieve a PaO2 level of 50 to 60 mm Hg but no higher.Intubationshould be performed if hemodynamic instability or somnolence occurs or if secretionscannot be cleared.It is important to remember that PaCO2 levels in patients with chron-ic hypercapnia should not be lowered to the normal range, because this could result inalkalemia, which increases the risk of cardiac dysrhythmias and seizures.In addition,overventilation for more than 2 to 3 days may result in renal restoration of the pH tonormal.As a consequence, during subsequent trials of spontaneous ventilation, as thePaCO2 rises to the baseline hypercapnic level, the patient becomes acidemic or thepatient s respiratory muscles become fatigued because of the greater minute ventilationrequired for the reset baseline pH and PaCO2.(Answer: D When invasive ventilation isrequired, PaCO2 levels should not be lowered to the normal range in patients with chronic hypercapnia)46.A 29-year-old man with AIDS is admitted to the hospital for worsening shortness of breath.He was inhis usual state of health until 1 week ago, when he developed dyspnea on exertion, with cough pro-ductive of thick sputum.His dyspnea has worsened over the past week, and he has developed a fever aswell.He denies having been in contact with sick persons.He states that he received treatment for PCP 1 year ago.He also states that his last CD4+ T cell count was less than 10. He is not currently takingany medications, because he cannot afford them.On his second day of hospitalization, he developsacute respiratory failure and is moved to the critical care unit, where he is intubated and undergoesmechanical ventilation.Which of the following statements regarding complications of mechanical ventilation is true?Q' A.Ventilated patients with acute, worsening respiratory distress or oxy-gen desaturation should be disconnected from the ventilator; manu-al ventilation should be administered with an anesthesia bag and100% oxygenQ' B.Growth of cultures obtained by suctioning through an endotrachealtube leads to a reliable diagnosis of pneumonia in ventilatedpatientsQ' C.Subcutaneous emphysema is the most common life-threateningmanifestation of barotraumaQ' D.In a patient with whole-lung atelectasis, a chest radiograph willreveal increased opacity in the affected hemithorax, together with acontralateral tracheal shiftKey Concept/Objective: To know the complications of mechanical ventilationWorsening respiratory distress or arterial oxygen desaturation may develop suddenly asa result of changes in the patient s cardiopulmonary status or secondary to a mechani-cal malfunction.The first priority is to ensure patency and correct positioning of thepatient s airway so that adequate oxygenation and ventilation can be administered dur-ing the ensuing evaluation.The patient should be disconnected from the ventilator, andmanual ventilation should be administered with an anesthesia bag, using 100% oxygen.Tension pneumothorax is the most common life-threatening manifestation of barotrau-ma.Tension pneumothorax leads to worsening hypoxemia and decreased venous returnwith hypotension.With atelectasis of an entire lung, breath sounds are diminished orabsent on the affected side, and the trachea is shifted toward that side.(Answer: AVentilated patients with acute, worsening respiratory distress or oxygen desaturation should be dis- 14 RESPIRATORY MEDICINE 29connected from the ventilator; manual ventilation should be administered with an anesthesia bag and100% oxygen)For more information, see Kollef MH: 14 Respiratory Medicine: VIII Respiratory Failure.ACP Medicine Online (www.acpmedicine.com)
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