A 65-year-old woman with history of COPD, congestive heart failure with ejection fraction of 35%, Hepatitis C cirrhosis without ascites, and body mass index of 35 is intubated for hypoxemic respiratory failure after an aspiration event and transferred to the ICU for further management. A chest radiograph demonstrates bilateral patchy infiltrates, and initial PaO2 is 145 on FiO2 100%. The patient remains hypoxemic on standard ventilation with tidal volumes 6 mL/kg and PEEP titrated to 12 cm H2O on FiO2 100%.
Which clinical factor suggests this patient may benefit from esophageal pressure measurements to titrate ventilation parameters?
Correct Answer: D
The pressure in the lower third of the esophagus closely parallels the pressure in the adjoining pleura. The measurement is accurate when taken in the upright lung, without the pressure of the mediastinum compressing the esophagus. The esophageal pressure balloon can therefore be used to estimate the transpulmonary pressure (Ptranspulmonary = Pairway opening − Ppleura ). Referring to the transpulmonary pressure equation, elevated pleural pressure can result in negative end-expiratory transpulmonary pressure, which is clinically manifested as alveolar collapse. Esophageal pressure measurement as a proxy for pleural pressure allows for titration of PEEP to maintain positive transpulmonary pressure at end expiration, maintaining functional residual capacity and preventing airway collapse. Patients ventilated to achieve transpulmonary pressure 0 to 10 cm H2O had significantly improved oxygenation and lung compliance.
Esophageal pressure is most likely to be useful in patients with elevated pleural pressure due to a decrease in extrapulmonary compliance. Direct pulmonary causes of ARDS, such as aspiration or pneumonia, are associated with decreased lung compliance but often have normal chest wall compliance. They are characterized by alveolar consolidation, which is not typically responsive to changes in PEEP. By contrast, extrapulmonary decreases in compliance, caused by factors such as obesity, ascites, bowel edema, pancreatitis, peritonitis, or other intra-abdominal pathologies, manifest as atelectasis and have a greater potential for alveolar recruitment. COPD, congestive heart failure, and cirrhosis without ascites do not particularly decrease extrapulmonary compliance and thus are not likely to specifically benefit from esophageal pressure measurements.
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A 36-year-old man is admitted to the ICU intubated status post polytrauma, with trauma burden including multiple lacerations over the ventral chest wall and an uncleared c-spine. He develops progressive hypoxemia over the first 12 hours of admission, with PaO2 :FiO2 ratios decreasing to <150 on FiO2 100%. Mechanical ventilation with tidal volumes 6 mL/kg and PEEP titrated to 12 cm H2O is initiated; however, arterial blood gas persistently shows pH 7.25 with PaCO2 68 and PaO2 67 on FiO2 100% over the subsequent 6 hours. The patient is adequately sedated, paralyzed, and demonstrates no ventilator asynchrony.
What is the next best step?
Correct Answer: B
Mechanical ventilation can perpetuate lung injury in ARDS by overdistending ventilated alveoli and causing atelectrauma be repeated alveolar opening and collapse if PEEP is insufficient to maintain patency at end expiration. Venovenous ECMO can be used to bypass the pulmonary circuit in severe ARDS, performing gas exchange and minimizing further lung injury. It is typically a salvage therapy utilized when other rescue strategies such as prone positioning or neuromuscular blockade have failed or are contraindicated. Criteria for ECMO initiation include acute, reversible lung injury when conventional therapy is insufficient to sustain life in the setting of severe hypoxemia (PaO2 :FiO2 <80) or uncompensated respiratory acidosis (pH <7.20). Contraindications include irreversible lung disease with no indication for lung transplant and intracranial bleeding.
In this stem, the patient has already shown no improvement after paralysis to ensure ventilator synchrony. An unstable vertebral fracture is an absolute contraindication to proning, whereas significant lacerations or burns over the ventral chest or abdomen are a relative contraindication. Inhaled nitric oxide results in transient improvement in oxygenation in patients with ARDS while therapy is continued but has shown no benefit on mortality and is associated with acute kidney injury. Esophageal pressure measurement can be used to individualize PEEP titration for improved alveolar recruitment, particularly in patients with decreased extrapulmonary compliance, such as those with ascites or obesity. However, it is unlikely to salvage the degree of refractory hypoxemia and respiratory acidosis seen in this patient. Thus, venovenous ECMO seems to be the next best strategy in this patient.
A 29-year-old woman is admitted to the floor with a productive cough and fevers; her influenza swab is positive, and chest radiograph demonstrates bilateral patchy pulmonary opacities. She develops progressive hypoxemic respiratory failure requiring intubation on the first day of admission. On transfer to the ICU, her initial arterial blood gas shows:
Correct Answer: A
ARDS impacts as many as 10% of patients admitted to the ICU and 23% of mechanically ventilated patients, with a mortality of 46% in patients with severe ARDS. This patient clearly meets the diagnosis of severe ARDS by the Berlin criteria, which include:
For all patients with ARDS, NHBI ARDS Network guidelines strongly suggest ventilation with low tidal volumes (goal 4-6 mL/kg predicted body weight) with plateau pressures <30 cm H2O and a minimum of PEEP 5 cm H2O. In addition, patients should receive conservative fluid management, which has been shown to shorten the duration of assisted ventilation.
Venovenous ECMO can be used to support patients with severe ARDS when conventional therapy is insufficient to correct severe hypoxemia (PaO2 :FiO2 <80) or hypercapnia (pH <7.20.) An increasing number of centers use ECMO in ARDS, particularly after 2009 H1N1 influenza A epidemic, where the patient population was typically young and otherwise healthy. Initial study of ECMO use for ARDS in patients with H1N1 found a mortality of 21%, leading to speculation that early initiation of ECMO may improve mortality. The EOLIA trial published in 2018, however, showed no mortality benefit with early initiation of ECMO as compared to ARDS Network mechanical ventilation with conventional rescue strategies that included ECMO.
A chest CT can be useful to confirm ARDS when chest radiographs fail to demonstrate opacities consistent with the diagnosis, given the heterogeneity of radiographic presentation, but it is not the next best step in this hypoxic patient. Likewise, although she will need blood cultures to rule out a superimposed bacterial pneumonia on viral influenza, improving oxygenation takes priority.
A 66-year-old woman with Haemophilus influenzae pneumonia is intubated on the floor for hypoxemic respiratory failure and transferred to the ICU. Chest radiograph demonstrates bilateral patchy infiltrates; ABG is:
Mechanical ventilation is titrated to tidal volumes 6 mL/kg with PEEP 8 cm H2O, and plateau pressures remain <30 cm H2O. The patient is paralyzed and sedated with no ventilator asynchrony noted.
In patients with severe ARDS (defined as PaO2 :FiO2 <150 with an FiO2 of >60%, PEEP >5 cm H2O, and tidal volumes 6 mL/kg), changing from supine to the prone position is associated with decreased mortality. Best outcomes have been shown when performed early in the course (<48 hour), and in conjunction with neuromuscular blockade and tidal volume <6 mL/kg. It improves oxygenation and reduces the risk of ventilator-associated lung injury by homogenizing ventilation in the dependent and nondependent portions of lung, reducing ventral overdistension, and improving dorsal alveolar recruitment.
Contraindications to prone ventilation include patients with facial/neck trauma or spinal instability, patients with elevated ICP, recent sternotomy, large burns or lacerations over the ventral body area, massive hemoptysis, hemodynamic instability, or patients at high risk for needing CPR/defibrillation. Factors such as chest tubes, multiple lines, and large body habitus can require extensive coordination with the care team during turning but are not contraindications. Potential complications of the prone position include kinking or misplacement of the ETT, kinking of vascular access, temporary increase in oral or tracheal secretions that can occlude the ETT, facial pressure ulcers, facial edema, brachial plexus injury, and elevated intra-abdominal pressure, which can complicate enteral feeding. Venovenous ECMO can be used in patients with ARDS or other causes of reversible pulmonary failure who experience refractory severe hypoxemia (PaO2 :FiO2 <80) or hypercapnia (pH <7.20.) Early initiation has not been shown to have a mortality benefit in ARDS as compared to conventional low tidal volume ventilation strategies with standard supplementary maneuvers such as neuromuscular blockade, proning, and rescue ECMO. Inhaled nitric oxide transiently improves oxygenation in ARDS patients while therapy is maintained but has not been shown to improve mortality and is associated with acute renal injury. Esophageal pressure measurements can be used as a proxy for pleural pressure in patients with ARDS to titrate PEEP to maintain positive end-expiratory transpulmonary pressure, minimizing atelectotrauma and volutrauma, but has not been shown to have a mortality benefit.
A 54-year-old man with a history of moderate COPD is transferred from the floor to the ICU one day after a witnessed aspiration event for increased work of breathing. On examination, pulmonary auscultation reveals bilateral rhonchi but no wheezing, and chest radiograph shows new bilateral, patchy pulmonary opacities. Respiratory rate is 36, and the patient communicates in one to three word sentences between breaths. Initial arterial blood gas analysis shows:
Correct Answer: C
The patient meets criteria for ARDS, although severity stratification based on the Berlin criteria requires PEEP >5 cm H2O.
The Berlin Criteria for Acute Respiratory Distress Syndrome:
Given the signs of increased work of breathing, with difficulty managing full sentences on face mask, an ABG demonstrating an uncompensated acute-on-chronic respiratory acidosis indicating progressive CO2 retention, and persistent hypoxemia on non-rebreather, the patient should be intubated and receive mechanical ventilation with low tidal volumes (4- 6 mL/kg), plateau pressure <30 cm H2O, and PEEP >5 cm H2O.
NIV can be used as an initial ventilatory support in patients with acute respiratory failure to spare the risks associated with sedation, muscular paralysis, and ventilator-associated complications. Several concerns remain regarding its use in the ARDS population, and the subgroups of ARDS most likely to benefit from it remain unclear. In particular, the use of prolonged NIV in the absence of respiratory function improvement may delay intubation and mechanical ventilation in patients who would benefit from conventional ARDS ventilation strategies. Recent data suggest that increased ARDS severity based on PaO2 :FiO2 was associated with NIV failure, and that NIV used was associated with increased ICU (although not hospital) mortality. In particular, NIV use was associated with higher ICU mortality in patients with PaO2 :FiO2 <150 mm Hg. NIV use may best be reserved for patients with mild ARDS (PaO2 :FiO2 201-300 mm Hg.) Other contraindications to NIV use include inability to cooperate because of altered mental status, inability to protect the airway or clear secretions, recent facial surgery or trauma, and recent esophageal anastomosis.
This patient with COPD may benefit from an ipratropium/albuterol nebulizer, but given adequate air excursion and the absence of wheezing, bronchospasm is likely not the central pathophysiology driving his clinical decompensation. Similarly, furosemide bolus is unlikely to significantly improve his ventilation in the absence of signs of volume overload.
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