The following cases and commentary, which focus on pulmonology, are excerpted from ACP's Medical Knowledge Self-Assessment Program (MKSAP 16). Part A of MKSAP 16 was released on July 31, 2012 and Part B on Feb. 1, 2013.
Case 1: Weaning from ventilation
A 66-year-old man is evaluated in the intensive care unit for possible extubation. He was admitted for a severe COPD exacerbation 3 days ago. His carbon dioxide remained markedly elevated despite a trial of noninvasive ventilation, and he was therefore intubated and placed on invasive mechanical ventilation. He has improved with treatment of his COPD. His medications are methylprednisolone, albuterol, ipratropium, propofol, and levofloxacin.
On physical examination, he is awake and responsive. Temperature is 37.0°C (98.6°F), blood pressure is 138/82 mm Hg, pulse rate is 96/min, and respiration rate is 20/min. Pulmonary examination reveals decreased breath sounds bilaterally with no wheezing. Accessory muscle use is noted. A small amount of thin secretions is noted with endotracheal suctioning.
Arterial blood gas levels have returned to baseline, with a pH of 7.36, a Pco2 of 55 mm Hg (7.3 kPa), and a Po2 of 70 mm Hg (9.3 kPa) on an Fio2 of 0.35. He tolerates a weaning trial well and the decision is made to extubate.
Which of the following interventions will decrease this patient's risk for reintubation?
A. Incentive spirometry every 2 hours
B. Inhaled helium-oxygen mixture
C. Nebulized N-acetylcysteine
D. Noninvasive positive pressure ventilation
Case 2: COPD patient with right-sided chest pain
A 67-year-old woman is evaluated for the abrupt onset of right-sided pleuritic chest pain and moderate dyspnea. She recently had symptoms typical of an upper respiratory infection (rhinorrhea, headache, sore throat, and nonproductive cough), and her chest pain and dyspnea seemed to be triggered by an episode of vigorous coughing. She has not had fever, chills, purulent sputum, or risk factors for thromboembolic disease. She smokes, and her medical history is significant for COPD without additional complications. Her medications are daily salmeterol and as-needed albuterol.
On physical examination, she appears uncomfortable but is not in respiratory distress. She is speaking in full sentences. Temperature is 37.0°C (98.6°F), blood pressure is 129/58 mm Hg, pulse rate is 78/min and regular, and respiration rate is 22/min. Oxygen saturation is 98% on 2 L of oxygen via nasal cannula. Pulmonary examination is significant for a prolonged expiratory phase but no wheeze; breath sounds are symmetric bilaterally. The trachea is midline. There is no accessory muscle use. Cardiac examination is normal with no murmurs. No edema is noted.
Electrocardiogram shows normal sinus rhythm without ischemic changes. Chest radiograph is shown.
In addition to hospital admission, which of the following is the most appropriate next step in management?
A. Evaluation for pleurodesis
B. Needle aspiration
C. Serial chest radiography
D. Tube thoracostomy
Case 3: Acute inflammatory demyelinating polyneuropathy
A 34-year-old man is evaluated in the hospital for a 3-day history of bilateral lower extremity weakness with subsequent onset of exertional dyspnea and upper extremity weakness. He also notes difficulty swallowing in the past 24 hours. He had a self-limited upper respiratory infection 10 days before admission, but his medical history is otherwise unremarkable.
On physical examination, he is awake, alert, and speaking in full sentences. Temperature is 37.0°C (98.6°F), blood pressure is 168/96 mm Hg, pulse rate is 88/min, and respiration rate is 18/min. The lungs are clear to auscultation with use of accessory muscles and decreased breath sounds at both lung bases. Diffuse symmetric weakness and hyporeflexia are noted in the extremities. He develops a weak cough after being given ice chips. A diagnosis of acute inflammatory demyelinating polyneuropathy is made, and he is transferred to the intensive care unit for closer monitoring of his respiratory status.
Oxygen saturation is 96% breathing ambient air. Chest radiograph shows low lung volumes but is otherwise normal. Bedside vital capacity is 2.1 L (50% of predicted).
Which of the following is the best management strategy to prevent respiratory failure in this patient?
A. Bilateral transcutaneous phrenic nerve pacing
B. Continuous positive airway pressure
D. Plasma exchange
Case 4: Heart failure and progressive dyspnea
A 62-year-old woman is admitted to the hospital for a 2-week history of progressive dyspnea. Her medical history is significant for heart failure with an ejection fraction of 25%. Her current medications are carvedilol, lisinopril, spironolactone, and furosemide.
On physical examination, temperature is 37.1°C (98.8°F), blood pressure is 80/48 mm Hg, pulse rate is 106/min, and respiration rate is 30/min. Oxygen saturation is 89% on 70% oxygen delivered by a nonrebreather mask. She is confused and periodically removes the oxygen mask. Pulmonary examination reveals bilateral inspiratory crackles. Heart sounds are regular with a grade 2/6 holosystolic murmur and an S3 gallop at the apex.
Laboratory studies show hemoglobin 12 g/dL (120 g/L), leukocyte count 8200/µL (8.2 × 109/L), platelet count 250,000/µL (250 × 109/L), blood urea nitrogen 52 mg/dL (18.6 mmol/L), creatinine 2.8 mg/dL (248 µmol/L), lactic acid 38 mg/dL (4.2 mmol/L). Arterial blood gas studies (on Fio2 of 0.7) show pH 7.48, Pco2 30 mm Hg (4.0 kPa) and Po2 58 mm Hg (7.7 kPa).
Chest radiograph shows bilateral perihilar infiltrates, cardiomegaly, and bilateral effusions.
Which of the following is the most appropriate next step in treatment?
A. Endotracheal intubation and mechanical ventilation
B. Nitroglycerin infusion
C. Noninvasive positive pressure ventilation
D. Placement of a pulmonary artery catheter
Case 5: Ventilation for severe asthma exacerbation
A 45-year-old woman is evaluated in the emergency department for the acute onset of dyspnea, wheezing, and progressive respiratory distress. She has a history of severe persistent asthma with two previous admissions to the intensive care unit, one of which required intubation. Her medications are a high-dose inhaled corticosteroid, salmeterol, and as-needed albuterol. She has not responded to aggressive bronchodilation therapy and intravenous corticosteroids.
On physical examination, she is in marked distress and is anxious. Temperature is 37.0°C (98.6°F), blood pressure is 145/100 mm Hg, pulse rate is 120/min, and respiration rate is 25/min; BMI is 35. Cardiac examination reveals a rapid and regular rhythm with no murmurs. Pulmonary examination reveals very faint wheezing.
Arterial blood gas studies breathing ambient air show a Pco2 of 80 mm Hg (10.6 kPa), a Po2 of 50 mm Hg (6.7 kPa), and a pH of 7.08. Chest radiograph shows hyperinflation but no infiltrates.
She undergoes rapid sequence induction and intubation and is started on mechanical ventilation.
Which of the following strategies in establishing ventilator settings is most appropriate for this patient?
A. Decreased inspiratory flow
B. Increased minute ventilation
C. Prolonged expiratory time
D. Prolonged inspiratory time
Answers and commentary
Correct answer: D. Noninvasive positive pressure ventilation.
The most appropriate intervention at the time of extubation is noninvasive positive pressure ventilation (NPPV). Application of NPPV shortly after extubation for a 24-hour period reduced the need for reintubation in previous trials of intubated patients with chronic lung disease and hypercapnia after a successful weaning trial. This population also appears to benefit from NPPV even if it is not applied until after the patient has developed respiratory failure following extubation. However, studies enrolling unselected patients with postextubation respiratory failure indicate that the use of NPPV may actually increase mortality.
The use of incentive spirometry reduces the risk of postoperative pulmonary complications but does not have a role in the routine management of nonsurgical patients following extubation.
The reduced gas density of helium-oxygen mixtures (heliox) reduces resistance to airflow, and thereby the work of breathing, in patients with obstructive lung disease. However, there is insufficient evidence to support the routine use of heliox in the management of COPD exacerbations.
N-acetylcysteine is a mucolytic agent that has been used to thin secretions in patients with excess mucus production. However, N-acetylcysteine is less likely to benefit this patient because he had minimal secretions prior to extubation. Furthermore, nebulized N-acetylcysteine may trigger bronchospasm.
- Application of noninvasive positive pressure ventilation shortly after extubation for a 24-hour period reduced the need for reintubation in trials of intubated patients with chronic lung disease and hypercapnia after a successful weaning trial.
Correct answer: C. Serial chest radiography.
The most appropriate next step in management is serial chest radiography. This patient presents with a small, spontaneous pneumothorax in the setting of known COPD. The pneumothorax is therefore classified as a secondary spontaneous pneumothorax. In this case, there is less than 2 cm between the chest wall and lung, and it is reasonable to observe the pneumothorax with serial chest radiography rather than intervene at this time. Given the decreased respiratory reserve and higher likelihood of progression and mortality in this patient group when compared with patients without known underlying structural lung disease (primary spontaneous pneumothorax), observation should be performed in the inpatient setting.
If a persistent air leak is noted after 3 to 5 days, it is reasonable to consider definitive treatment of the pneumothorax. Definitive management to prevent recurrence typically consists of chemical pleurodesis via thoracostomy (which is shown to reduce recurrence to 25%) or thoracoscopic repair with pleurodesis (which reduces recurrence to approximately 5%).
Needle aspiration is an option for treating secondary pneumothoraces, but it has been shown to be significantly less effective than tube thoracostomy in patients requiring therapeutic intervention.
If at any time the pneumothorax increases to greater than 2 cm, a small-bore chest tube should be placed, because the patient is experiencing dyspnea.
- For secondary spontaneous pneumothoraces, outpatient management is discouraged; even small (<2 cm) pneumo- thoraces are more safely observed in the inpatient setting.
Correct answer: D. Plasma exchange.
The most appropriate next step in management is plasma exchange. Plasma exchange and intravenous immune globulin are both recommended treatment options for patients with Guillain-Barré syndrome (GBS), including its most common variant, acute inflammatory demyelinating polyneuropathy. Previous trials indicate plasma exchange reduces the need for and duration of mechanical ventilation in patients with GBS compared with supportive care alone.
Phrenic nerve pacing is not appropriate in the setting of impaired phrenic nerve function, including in patients with GBS and lower motor neuron diseases such as amyotrophic lateral sclerosis. Its use is generally limited to patients with complete high-cervical injuries (C1 and C2 levels) and select patients with brainstem dysfunction with respiratory failure of greater than 3 months' duration.
This patient is at high risk of further respiratory compromise requiring the institution of invasive mechanical ventilation, but he is not a suitable candidate for continuous positive airway pressure (CPAP). His examination, vital capacity, and ability to maintain adequate oxygenation indicate that he is not currently in need of mechanical ventilatory support, and his bulbar dysfunction places him at increased risk of aspiration with use of noninvasive ventilation. Furthermore, bilevel noninvasive ventilation rather than CPAP would be needed to improve his ventilation because the primary issue is respiratory muscle weakness.
Systemic corticosteroids are no longer recommended for the treatment of GBS because previous trials from the 1990s demonstrated no benefit. A more recent study found that the addition of methylprednisolone, 500 mg/d for 5 days, to intravenous immune globulin offers no advantage compared with immune globulin alone.
- Studies indicate that plasma exchange reduces the need for and duration of mechanical ventilation in patients with Guillain-Barré syndrome compared with supportive care alone.
Correct answer: A. Endotracheal intubation and mechanical ventilation.
The most appropriate next step in treatment is intubation and mechanical ventilation. This patient has cardiogenic shock and acute pulmonary edema due to acute decompensated heart failure. Her severe hypoxemia and respiratory distress are the first priority in stabilizing this patient, and therefore the next step in management should be endotracheal intubation and invasive mechanical ventilation. This patient is not a candidate for noninvasive mechanical ventilation. Contraindications to noninvasive ventilation include respiratory arrest, cardiovascular instability (hypotension, arrhythmias, myocardial infarction), change in mental status (lack of cooperation), high aspiration risk, viscous or copious secretions, recent facial or gastroesophageal surgery, craniofacial trauma, fixed nasopharyngeal abnormalities, burns, and extreme obesity. Early trials indicated that noninvasive positive pressure ventilation (NPPV) reduced the need for intubation in the setting of acute cardiogenic pulmonary edema. However, a recently published study found similar outcomes among patients with acute heart failure managed with continuous positive airway pressure, NPPV, and standard oxygen therapy alone, although the discordance with previous studies may be related to study population and design.
Nitroglycerin infusion is commonly used in managing acute decompensated heart failure, but in this instance its use could worsen the patient's hypotension and multiorgan failure. Regardless, stabilizing this patient's respiratory status is a higher priority.
Placement of a pulmonary artery catheter in selected patients can assist in addressing hemodynamic derangements; however, use of a pulmonary artery catheter does not ultimately appear to affect survival in critically ill patients or those with decompensated heart failure and should never take precedence over managing respiratory failure.
- Contraindications for noninvasive ventilation include respiratory arrest, cardiovascular instability, change in mental status, high aspiration risk, viscous or copious secretions, recent facial or gastroesophageal surgery, craniofacial trauma, fixed nasopharyngeal abnormalities, burns, and extreme obesity.
Correct answer: C. Prolonged expiratory time.
This patient has severe airflow obstruction caused by status asthmaticus and should be managed with ventilation with a prolonged expiratory time. Ventilation in patients with severe airway obstruction may result in breath stacking and auto-positive end-expiratory pressure (auto-PEEP) if sufficient time is not allowed for the preceding breath to be completely emptied. The goal of managing ventilation in patients with severe airway obstruction is to maximize ventilation by allowing adequate time for exhalation and avoid auto-PEEP with resultant increases in end-expiratory pressures, decreased venous return, hypotension, and barotrauma. Ventilation strategies that increase expiratory time include decreasing the tidal volume and respiration rate, increasing inspiratory flow rates, and judicious use of sedation and analgesia. Clinical suspicion of hemodynamic compromise caused by auto-PEEP should be immediately treated by disconnecting the ventilatory circuit at the endotracheal tube to allow trapped intrathoracic air and pressure to escape and venous return to improve. When ventilating patients with severe airflow obstruction, allowing hypercapnia is a permissible strategy.
Prolonging the inspiratory time will shorten the time spent in the expiratory cycle and worsen auto-PEEP and ventilation. Similarly, decreasing the rate of inspiratory flow will prolong inspiratory time. Increasing the minute ventilation (hyperventilation) may seem like an appropriate strategy in this patient with respiratory acidosis; however, the physiologic limitation of expiratory flow is the primary determinant of minute ventilation in patients with severe obstruction. Attempts to increase minute ventilation (through increases in respiration rate and/or tidal volume) increase the risk for development of auto-PEEP and hemodynamic compromise.
- The primary ventilator strategy for patients with severe obstructive lung disease is to allow adequate time for exhalation before the next delivered breath and to minimize auto-positive end-expiratory pressure.