MKSAP quiz on mechanical ventilation


Case 1: Weaning from ventilation after COPD exacerbation

A 65-year-old woman is evaluated for discontinuation of mechanical ventilation. She was placed on mechanical ventilation 5 days ago for respiratory failure secondary to an exacerbation of COPD. Ventilator settings are in the volume-controlled continuous mandatory ventilation mode, with a set respiration rate of 10/min, a tidal volume of 370 mL, an FiO2 of 0.35, and a positive end-expiratory pressure of 5 cm H2O. Current medications are albuterol/ipratropium, levofloxacin, prednisone, and fentanyl.

On physical examination, vital signs are normal. She is sleepy but arousable and can follow simple commands. Lung examination reveals distant breath sounds. The remainder of the examination is unremarkable.

Arterial blood gas studies show a pH of 7.46, PCO2 of 47 mm Hg (6.25 kPa), and a PO2 of 62 mm Hg (8.25 kPa). Other laboratory studies, including a leukocyte count, are normal.

Chest radiograph demonstrates hyperinflation but no infiltrates or evidence of heart failure.

Which of the following is the most appropriate test or evaluation to perform next?

A. 30-minute spontaneous breathing trial
B. Cuff leak test
C. Glasgow Coma Scale
D. Measure negative inspiratory force

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Case 2: Dyspnea after aspiration during endoscopy

A 52-year-old man is evaluated in the ICU for dyspnea that developed after aspiration of gastric contents during an upper endoscopy. The endoscopy was performed for evaluation of upper gastric bleeding due to peptic ulcer disease. His only medication is pantoprazole.

On physical examination, temperature is 37.3 °C (99.1 °F), blood pressure is 150/99 mm Hg, pulse rate is 110/min, and respiration rate is 28/min. Oxygen saturation is 90% on a 100% oxygen nonrebreather mask. He is awake, diaphoretic, and anxious. Lung examination reveals scant bilateral crackles and rhonchi as well as use of accessory muscles. The remainder of the physical examination is normal.

Arterial blood gas studies on a 100% oxygen nonrebreather mask show a pH of 7.35, a PCO2 of 46 mm Hg (6.1 kPa), and a PO2 of 55 mm Hg (7.3 kPa).

Chest radiograph reveals new bilateral opacities.

Which of the following is the most appropriate treatment?

A. Continue current therapy
B. High-flow humidified nasal cannula
C. Intubation and mechanical ventilation
D. Noninvasive mechanical ventilation

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Case 3: Confusion with respiratory failure

A 56-year-old man hospitalized for respiratory failure is evaluated for new-onset confusion. He has acute respiratory distress syndrome secondary to community-acquired pneumonia. He has been in the critical care unit for 3 days. He is orally intubated and placed on mechanical ventilation. Current medications are ceftriaxone, azithromycin, and propofol for light sedation according to protocol.

On physical examination, temperature is 38.3 °C (100.9 °F), blood pressure is 100/45 mm Hg, pulse rate is 112/min, and respiration rate is 24/min. He cannot focus his attention, does not follow simple commands, and has demonstrated fluctuating mental status during the past 8 hours. The neurological examination is otherwise normal. He appears to be comfortable and shows no signs of pain.

Arterial blood gas studies show a pH of 7.41, a PCO2 of 38 mm Hg (5.1 kPa), and a PO2 of 62 mm Hg (8.2 kPa). Serum sodium, serum creatinine, and blood urea nitrogen are normal.

Chest radiograph shows multifocal opacities consistent with pneumonia and acute respiratory distress syndrome.

In addition to orientation strategies and promoting a normal sleep-wake cycle, which of the following is the most appropriate management?

A. Add haloperidol
B. Add lorazepam
C. Early mobilization
D. Increase propofol

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Case 4: Dyspnea in ALS

A 70-year-old man is hospitalized for a 4-week history of dyspnea, orthopnea, and daytime sleepiness. He was diagnosed with amyotrophic lateral sclerosis 6 months ago. His only medication is riluzole.

On physical examination, blood pressure is 128/73 mm Hg, pulse rate is 90/min, and respiration rate is 28/min. Oxygen saturation is 87% breathing ambient air. He has right-hand atrophy, decreased mobility, and fasciculations. Lung examination reveals abdominal paradox with breathing, use of accessory breathing muscles, and shallow tachypnea. He is awake, alert, and interactive, but dozes off easily. His speech is clear with no secretions. He is able to move all extremities and shows no cranial nerve abnormality.

On arterial blood gas testing, pH is 7.30, PCO2 is 76 mm Hg (10.1 kPa), PO2 is 50 mm Hg (6.65 kPa), and bicarbonate is 36 mEq/L (36 mmol/L) on room air. The calculated alveolar-arterial oxygen gradient is normal.

Chest radiograph reveals bilateral basal opacities consistent with atelectasis and shallow inspiration.

Which of the following is the most appropriate treatment?

A. Invasive mechanical ventilation
B. Noninvasive ventilation with bilevel positive airway pressure
C. Noninvasive ventilation with continuous positive airway pressure
D. Oxygen administration through nasal cannula

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Case 5: Decreased responsiveness

A 22-year-old man is evaluated in the hospital for decreased responsiveness. He was hospitalized 4 days ago after a motor vehicle accident. He has multiple fractures and a chest contusion. He was intubated for respiratory distress in the emergency department and given morphine, propofol, and heparin. He is on volume-controlled continuous mandatory ventilation mode with an FIO2 of 0.7.

On physical examination, temperature is 37.7 °C (99.9 °F), blood pressure is 124/65 mm Hg, pulse rate is 89/min, and respiration rate is 27/min. Oxygen saturation is 93% on mechanical ventilation. He is unresponsive to voice or pain, and his pupils are 3 mm and reactive; the neurological examination is otherwise nonfocal. He has external fixators in both lower extremities. There are bruises on the anterior chest wall. The remainder of the physical examination is noncontributory.

Which of the following is the most appropriate management?

A. Change propofol to dexmedetomidine
B. CT of the head
C. Continuous electroencephalography
D. Stop sedation and analgesia

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Case 6: Progressive dyspnea

A 78-year-old woman is evaluated in the hospital for progressive dyspnea requiring increased oxygen. She was diagnosed with idiopathic pulmonary fibrosis 5 years ago. She was evaluated in the clinic 2 months ago; at that time she required 5 L/min of supplemental oxygen at rest and daily activities were limited to dressing and eating, both of which caused severe dyspnea. Currently, despite broad spectrum antibiotics and intravenous methylprednisolone, 1 g daily for 5 days, she is in severe respiratory distress requiring high-flow oxygen at 80%. She is alert and breathless, and understands her condition and treatment options.

On physical examination, blood pressure is 150/85 mm Hg, pulse rate is 110/min, and respiration rate is 36/min. Oxygen saturation is 88% on 80% high-flow oxygen. BMI is 24. Pulmonary examination reveals diffuse inspiratory crackles. She has clinical findings of pulmonary hypertension on cardiac examination, unchanged from 2 months ago. She has no edema or jugular venous distention.

Chest radiograph is unchanged.

Which of the following is the most appropriate management?

A. Increase methylprednisolone
B. Initiate albuterol
C. Mechanical ventilation
D. Palliative care

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Answers and commentary

Case 1

Correct answer: A. 30-minute spontaneous breathing trial.

A 30-minute spontaneous breathing trial (SBT) should be performed using low levels of pressure support (8 cm H2O or less). Weaning from mechanical ventilation can start when the precipitating event or underlying condition that caused respiratory failure has resolved or is resolving. Patients should be assessed daily for their readiness to be removed from mechanical ventilation by performing an SBT. There are several methods used to assess if an SBT is successful. One criterion is the ability to tolerate a weaning trial for 30 minutes (in most patients, SBT failure will occur within approximately 20 minutes). 2-hour SBTs and 30-minute SBTs have a similar ability to recognize patients who are unable to breathe spontaneously. However a 30-minute trial has the benefits of less time on mechanical ventilation and less risk of respiratory muscle fatigue. If the patient successfully completes an SBT, the ability to follow commands, clear secretions, and a patent upper airway are other criteria that should be met to increase extubation success.

A “cuff leak” refers to measurable airflow around the endotracheal tube after the cuff of the endotracheal tube is deflated. Absent or minimal cuff leak following deflation of the cuff indicates reduced space between the endotracheal tube and the larynx. Minimal or absent cuff leak may be due to laryngeal edema, laryngeal stenosis, and thick secretions. The test is not standardized and not performed routinely and is not an initial routine test in the process of liberating a patient from mechanical ventilation. It might be considered in a patient who has a successful SBT but is at high risk for edema and stridor following extubation.

The Glasgow Coma Scale is pertinent to the actual extubation process, in which lack of awareness and ability to clear secretions and follow simple commands may increase the risk of aspiration and cooperation in the postextubation period. However, this patient should be placed on an SBT before being evaluated for extubation.

Negative inspiratory force has been used as a marker of inspiratory muscle strength to identify patients who will be able to be liberated from mechanical ventilation. However, there are technical issues that lead to variable predictive performance. A low negative inspiratory force by itself is not useful; however, serial measurements (for example, in patients with Guillain-Barré or myasthenia gravis) along with other measures (FVC, maximum tidal volume) may give a better picture of muscle strength recovery.

Key Point

  • Patients should be assessed daily for their readiness to be removed from mechanical ventilation by performing a spontaneous breathing trial; one criterion for success is the ability to tolerate a spontaneous breathing trial for 30 minutes.

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Case 2

Correct answer: C. Intubation and mechanical ventilation.

The most appropriate treatment is intubation and mechanical ventilation. This patient has dyspnea, severe hypoxemia, bilateral opacities on chest radiograph, and acute hypoxemic respiratory failure after aspiration, all of which are diagnostic for acute respiratory distress syndrome (ARDS). ARDS is associated with heterogeneous but often widespread damage to the alveolar epithelium and vascular endothelium, as well as surfactant dysfunction leading to alveolar instability and collapse. The changes can severely reduce lung compliance, making adequate ventilation difficult and further worsening hypoxia. Most patients with ARDS require intubation and mechanical ventilation to ensure adequate delivery of high levels of inspired oxygen and positive end-expiratory pressure to stabilize alveoli.

Continuing oxygen through a face mask would not be appropriate. Although the patient is maintaining appropriate oxygen saturation, the presence of anxiety, diaphoresis, tachycardia, tachypnea, hypercapnia, and hypoxemia signal impending respiratory failure that should be treated with intubation and mechanical ventilation.

High-flow humidified nasal cannula devices decrease the work of breathing, provide heated and humidified air, provide a reliable FiO2, and decrease dead space. Their initial application should occur in the critical care setting with close monitoring for tolerance and effectiveness. A recent trial demonstrated that in patients with acute hypoxemic respiratory failure, the use of high flow nasal cannula led to decreased mortality compared to continuing face mask oxygen or noninvasive face mask ventilation; however, the study excluded patients with hypercapnia, such as this patient. This patient shows features of respiratory muscle fatigue, including rapid breathing, diaphoresis, use of accessory muscles of respiration, and an elevated arterial PCO2, all indications for mechanical ventilation.

Noninvasive positive pressure ventilation (NIPPV) is the delivery of positive airway pressure using a cushioned face mask or helmet or without the use of an invasive connection directly in a patient's airway. In patients with hypoxemic respiratory failure, the use of NIPPV is controversial. Select patients may benefit from short-duration NIPPV to avoid intubation and associated complications but some studies have demonstrated increased mortality, likely due to delay in the implementation of appropriate invasive mechanical ventilation. This patient with deteriorating ventilation should be intubated and mechanically ventilated.

Key Point

  • Most patients with acute respiratory distress syndrome require intubation and mechanical ventilation to ensure adequate delivery of high levels of inspired oxygen and positive end-expiratory pressure to stabilize alveoli.

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Case 3

Correct answer: C. Early mobilization.

Early mobilization with physical and occupational therapy and interruption of sedation should be used to decrease the duration of delirium. This patient has acute onset of cognitive dysfunction, impairment of attention, and fluctuating mental status, which are features of delirium. Increased or decreased psychomotor activity, disorganized thinking, disorientation, and perceptual disturbances are other supportive features. The use of a screening instrument (such as the Confusion Assessment Method) allows for improved recognition and diagnosis of delirium. Delirium contributes to length of ICU stay, morbidity, mortality, and post-intensive care cognitive impairment. A study of critically ill patients on mechanical ventilation demonstrated that an early physical and occupational therapy program reduced delirium by 2 days compared to controls.

Haloperidol is used to decrease hyperactive features of delirium. Currently, there is no strong evidence in favor of its use for treating delirium in critically ill patients.

Current guidelines for sedation in the ICU favor strategies that control pain, target lighter sedation, avoid benzodiazepines, and favor early mobility. The use of benzodiazepines is associated with an increased incidence of delirium, and would not be appropriate for this patient showing signs of delirium when compared with nonbenzodiazepine sedation strategies.

The practice of having all critically ill patients on mechanical ventilation receive continuous deep sedation is no longer followed, thus increasing the propofol dosage would not be appropriate. A practice-changing trial demonstrated that daily interruption of sedation decreased length of mechanical ventilation and stay in the ICU. Recent trials demonstrated that the use of a light sedation protocol had similar patient outcomes to daily interruption of sedation. Light levels of sedation using a protocol are associated with shorter length of mechanical ventilation and ICU stay.

Key Point

  • Early mobilization with physical and occupational therapy and interruption of sedation should be used to prevent and treat delirium in critically ill patients.

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Case 4

Correct answer: B. Noninvasive ventilation with bilevel positive airway pressure.

The use of bilevel positive airway pressure (BPAP) ventilation is the most appropriate treatment. This patient has features consistent with chronic hypercapnic respiratory failure secondary to neuromuscular disease. He has dyspnea and, more characteristically, orthopnea. The patient has chronic respiratory acidosis with a normal alveolar-arterial (A-a) oxygen gradient. BPAP delivers both inspiratory positive airway pressure and expiratory positive airway pressure and improves survival and quality of life of patients with neuromuscular disease. The settings generate a pressure difference that augments the patient's own respiratory muscle activity, leading to an increase in the size of each breath. The PCO2 level will decrease due to the increase in minute ventilation and efficiency of breathing.

Invasive mechanical ventilation (mechanical ventilation with airway intubation or tracheostomy) is a therapeutic option in the setting of acute hypercapnic respiratory failure due to neuromuscular disease. However, the patient is awake, has excellent bulbar control (swallows and gags), and has a chronic disease that responds well to noninvasive ventilation.

Continuous positive airway pressure (CPAP) delivers positive airway pressure at a level that remains constant throughout the respiratory cycle preventing upper airway collapse or narrowing during sleep. No additional pressure above the level of CPAP is provided and patients must initiate every breath. CPAP does not increase minute ventilation, and it is not helpful in patients with hypercapnic respiratory failure due to neuromuscular disorders.

The patient has a normal A-a oxygen gradient and hypercapnia, which confirm that the hypoxemia is secondary to hypoventilation rather than a ventilation-perfusion mismatch or shunt; therefore, oxygen administration should not be needed once his PCO2 improves. More importantly, the administration of oxygen in the absence of supportive ventilation should be avoided in patients with neuromuscular disease and chronic hypercapnic respiratory failure; it has been associated with acute hypercapnia, in some cases leading to death.

Key Point

  • Bilevel positive airway pressure ventilation improves survival and quality of life in patients with neuromuscular disease.

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Case 5

Correct answer: D. Stop sedation and analgesia.

The most appropriate management is to stop sedation and analgesia. Clinicians at the bedside may resist stopping sedation and analgesia in a patient with a clear need for both, or because of concerns with ventilator synchrony or oxygenation. Protocolized care can help guide nursing and respiratory therapy if these problems arise. In addition, daily protocolized interruptions of sedation and analgesia have been shown to decrease the incidence of delirium, the need for diagnostic testing, and the amount of time spent on mechanical ventilation and in the ICU. Stopping sedation and analgesia, rather than gradually decreasing them, allows for a faster return to awareness and titration of infusions to achieve the sedation and analgesia goal. Analgesia and sedation can be restarted, at lower doses, if the patient requires them later.

Dexmedetomidine has pharmacological properties that may benefit this patient (analgesia, allows arousal). However, there is currently no evidence that it is superior to appropriately titrated propofol.

Ordering a CT scan is not the most appropriate first step in management of an unresponsive patient with nonfocal physical examination findings currently being treated with propofol and morphine. Moreover, a CT would expose the patient to the risks of being moved while critically ill and unnecessary radiation. The rate of serious events during transport is important enough to warrant careful determination of need.

Ordering an electroencephalogram to assess his unresponsiveness would be part of the diagnostic evaluation if interruption of sedation did not lead to improved mental status. Nonconvulsive status epilepticus has been reported in up to 20% of patients with unexplained unresponsiveness. Current recommendations suggest continuous electroencephalogram as the diagnostic test of choice.

Key Point

  • Daily protocolized interruptions of sedation and analgesia have been shown to decrease the incidence of delirium, the need for diagnostic testing, and the amount of time spent on mechanical ventilation and in the ICU.

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Case 6

Correct answer: D. Palliative care.

This patient should receive palliative care including morphine for the symptom of dyspnea. Idiopathic pulmonary fibrosis (IPF) is the most common idiopathic interstitial pneumonia. It occurs predominantly in older individuals. Prognosis is poor, and individuals diagnosed with IPF have an estimated average survival of 3 to 5 years. The most common cause of death in IPF is respiratory failure. Patients with IPF may experience an acute exacerbation of IPF, diagnosed when the chest radiograph shows new alveolar infiltrates and medical evaluation does not reveal another cause for dyspnea such as infection, heart failure, or pulmonary embolism. Despite maximal supportive care during the past 5 days, this patient has progressed and is now on the brink of respiratory failure. Lung transplantation has been shown to provide a survival advantage in select patients with IPF. This patient gives a history consistent with severe and prolonged deconditioning associated with chronic respiratory failure. She now presents with frank respiratory failure and rapid progression of IPF with an unclear trigger. Consideration for transplant typically includes a full assessment of the patient for evidence of additional organ disease and education regarding the risks and benefits of the procedure. This is best accomplished long before the development of an acute exacerbation. Because of this patient's age, functional status, and lack of previous assessment by a transplant center, lung transplantation is not a viable option for her. At this time, she remains awake and alert and is able to participate in her end-of-life decision making. Patients with this presentation and functional status do not typically respond favorably to intubation and mechanical ventilation and, as such, recommending palliative medicines and comfort measures is most appropriate.

Although high-dose glucocorticoids are often used for acute exacerbation, their efficacy remains unknown. This patient has already been treated with glucocorticoids without apparent improvement; this indicates that administration of additional glucocorticoids is not likely to be of benefit.

Albuterol is a bronchial vasodilator. Unfortunately, the limitation in patients with IPF that results in hypoxemia and dyspnea is at the level of the interstitium, and bronchial dilators have little effect on these symptoms.

For individuals who develop severe respiratory distress that has no underlying reversible cause, supportive mechanical ventilation is of little long-term benefit. Therefore, the most recent evidence-based consensus statement recommends against mechanical ventilation for individuals with acute respiratory failure due to either progression or an acute exacerbation of IPF. In these circumstances, the focus should be on palliation of the patient's underlying dyspnea.

Key Point

  • For individuals with idiopathic pulmonary fibrosis who develop severe respiratory distress that has no underlying reversible cause, supportive mechanical ventilation is of little long-term benefit; in these circumstances, the focus should be on palliation of the patient's underlying dyspnea.