Q: How do I choose a ventilation mode?
A: There is no mode of ventilation that has been proven to be superior in acute respiratory distress syndrome (ARDS). Start with assist control, either in pressure control or volume control, depending on your experience and comfort level
Q: What tidal volume should be targeted?
A: A high priority should be to target a tidal volume of 6 to 8 mL/kg of the patient's ideal body weight. (The maximum volume of the lungs is not affected by adipose tissue, so an obese patient should get the same volume as an underweight one of the same height.)
Q: What pressure should be targeted?
A: Target a plateau pressure of less than 30 cm H2O. This may be difficult in patients with poor lung compliance, that is, stiffer lungs due to inflammatory exudates and fibrosis.
Q: If I'm using pressure control, how do I set peak inspiratory pressure (PIP) and positive end-expiratory pressure (PEEP)?
A: Set PIP to 20 cm H2O and PEEP to 5 cm H2O and adjust PIP to obtain the target tidal volume. Adjust PEEP and fraction of inspired oxygen (FiO2) to achieve oxygen saturation of 92% to 96% and partial pressure of oxygen greater than 55 mm Hg. Both FiO2 and PEEP can be used to increase oxygenation; however, patients with ARDS require higher PEEP than other patients with respiratory failure. Excessive oxygen may lead to free radical damage and worsen lung disease.
Q: Anything else I should target?
A: If possible, target a driving pressure less than or equal to 15 cm H2O. In volume control ventilation the driving pressure is the plateau pressure minus the PEEP, while in pressure control it is the PIP minus the PEEP.
Q: What if my patient continues to have low saturation despite following these recommendations?
A: If the patient is synchronous with the ventilator, consider increasing the inspiratory time or inspiratory-to-expiratory ratio to increase the time spent at higher pressure. If not, consider increasing sedation or giving a bolus dose of paralytic to improve synchrony with the ventilator.
Q: What if I cannot achieve the target tidal volume without exceeding the recommended plateau pressure?
A: Decrease the tidal volume by 1 mL/kg to a minimum of 4 mL/kg. Ensure there is no cardiogenic or hydrostatic component, and use diuretics if hemodynamics are favorable and/or there is concern for volume overload. However, sometimes this goal is not achievable.
Q: How often should I order an arterial blood gas?
A: If there is a clinical change or if ventilator changes are made, it is reasonable to get one. If frequent arterial blood gases are expected, consider placing an arterial line to minimize the number of arterial punctures.
Q: What do I do if my patient remains acidotic?
A: Mild hypercapnia is tolerated, and even encouraged, in ARDS. Try to maintain pH of 7.25 to 7.35. If significant respiratory acidosis persists due to low tidal volume, consider using bicarbonate to maintain a pH greater than 7.15 to 7.2.
Q: What if my patient has high PIP despite achieving target plateau pressure?
A: This likely indicates an airway issue. Evaluate for bronchoconstriction (such as wheezing, prolonged exhalation, history of asthma or chronic obstructive pulmonary disease) and obstruction (for example, mucus plug), kinking, or biting of the tube.
Q: What other problems can cause high plateau pressure aside from ARDS?
A: This can be caused by anything that increases the amount of force required to inflate the lungs, so it is very important to investigate. Intrathoracic causes include pulmonary edema, pulmonary fibrosis, pleural effusion, and pneumothorax. Extrathoracic causes include high abdominal pressure, severe obesity, burns or scarring of the chest wall, severe kyphoscoliosis, and rib deformity.