Respiratory Failure- it hurts to breathe
A 47-year-old male sustains multiple traumatic injuries after being struck by a vehicle while on the side of the road. He had severe thoracic trauma (bilateral pulmonary contusions), bilateral femur fractures and a liver laceration. He also had a severe TBI, requring intubation shortly after his arrival. 10 days into his hospital stay, he still requires ventilatory support.
What are some of the potential causes of the patients ongoing requirement for mechanical ventilatory support?
Pain from rib fractures, pneumonia, ARDS, pulmonary embolism, fat embolism, pulmonary contusions, loss of chest wall stability due to severe thoracic trauma, hypomagnesemia, volume overload, retained hemothorax, poor nutrition from inadequate protein delivery.
He is undergoing a trial of spontaneous ventilation, but he develops tachypnea and hypoxemia and appears to be struggling on the ventilator.
What are some of the initial steps in evaluating this patient?
Physical exam (pulmonary exam, assess for edema), bedside ultrasound (pleural effusion, pneumothorax). Chest x-ray- look for infiltrates. ABG, EKG, review volume status.
His chest x-ray is shown below.
What do you see?
Trachea midline, no effusions. Bilateral fluffy infiltrates.
His current ventilator settings and ABG results are shown below.
Ventilator settings: RR 12, TV 450, PEEP 10, FiO2 50.
Arterial blood gas: pH 7.34, PaCO2 42, PaO2 64, HCO3 24
What does this tell you about his oxygenation?
PaO2:FiO2 ratio is an indicator of oxygenation. This patients P:F ratio is 182. See below for explanation.
What diagnosis is this consistent with?
Acute respiratory distress syndrome.
What are the management principles when caring for a patient with ARDS? What are your initial ventilator management strategies?
ARDS is not a primary diagnosis, so it is important to treat the underlying cause (pancreatitis, pneumonia, etc).
Minimize further insults to the lungs.
Optimize ventilator strategies- low tidal volume, target PEEP/FiO2 combination to target SpO2 88-95%
Diagnosis and Management of ARDS
Etiologies of ARDS
Pneumonia, pulmonary contusions, aspiration, inhalation
Trauma, burn
Pancreatitis
Transfusion-related acute lung injury (TRALI)
ARDS diagnostic criteria: The Berlin Definition[1]
Onset of respiratory failure within 1 week of an insult that is known to cause ARDS
Bilateral fluffy infiltrates on CXR not explained by effusions/ infiltrates/ contusions/ lung collapse
Respiratory failure not related to heart failure or fluid overload
Oxygenation PaO2/FiO2 ratio with PEEP ≥5 cm H2O. Mild 200-300, moderate 100-200, severe ≤100.Â
Basic principles of ARDS management[2,3]
Low tidal volume ventilation- 4-8 mL/kg predicted body weight. Prevent volutrauma.
Permissive hypercapnia- low TV ventilation leads to decreased minute ventilation, which leads to CO2 retention (hypercapnia). Hypercapnia is tolerated as long as pH remains above 7.2.
Positive end-expiratory pressure (PEEP)- goal is avoiding overdistension and optimizing recruitment
If ↑PEEP→ ↓plateau pressure: recruitmentIf ↑PEEP→ ↑plateau pressure: overdistension
Optimizing mean airway pressure (MAP). Prolonged inspiratory:expiratory ratio
Target plateau pressure <30, driving pressure ≤15.
Recruitment manuevers
Advanced strategies for persistent hypoxemia
Prone positioning
Airway Pressure Release Ventilation (APRV)
Neuromuscular blockade
Inhaled vasodilators
Prostacyclin and nitric oxide
ECMO
High frequency oscillatory ventilation
Open lung ventilation
Dexamethasone
Extracorporeal carbon dioxide removal (ECCO2R)
References
 SCCM Clinical Practice Guideline. Fan E et al. ATS/ SCCM CPG: Mechanical Ventilation in Adult Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2017;195(9):1253-1263.
Basic Principles of Ventilatory Management of ARDS
