D is the correct answer. Why?

Explanation

Asthma is a chronic pulmonary condition that occurs secondary to bronchospasm and inflammation. Patients present with wheezing, dyspnea, and respiratory distress and can have absent or minimal breath sounds in severe exacerbations. Early and aggressive treatment with albuterol, ipratropium, magnesium sulfate, and steroids can reduce the need for positive pressure ventilation and intubation. However, if a patient requires intubation, managing the ventilator can be challenging.

Patients with asthma often air stack, meaning that with each inhalation, they have difficulty exhaling the same volume of air, leading to an accumulation of additional air. To prevent this, a lower respiratory rate with a prolonged expiratory phase can allow for full exhalation of air. The respiratory rate should be titrated to the patient’s acid-base status to avoid carbon dioxide accumulation.

The primary focus in ventilator settings for patients with asthma should be maintaining adequate oxygenation (targeting a PO₂ > 60 mm Hg and SpO₂ between 88% and 92%). This helps ensure sufficient oxygen delivery while minimizing the risk of barotrauma and volutrauma from high ventilatory pressures. Minimizing PEEP and keeping plateau pressures low is critical to avoid further exacerbation of airway pressures and the risk of pneumothorax.

Other strategies are paramount to prevent complications and improve outcomes. One of these strategies involves the concept of permissive hypercapnia. This approach accepts higher levels of PCO₂ rather than striving to maintain it within a normal range, which can be detrimental if it leads to increased ventilation pressures and high volumes. The goal is to avoid aggressive ventilation that can exacerbate air trapping, increase intrathoracic pressure, and reduce venous return, potentially leading to hemodynamic instability.

Higher lung volumes (A) could cause barotrauma in this patient. Lung protective strategies include lower lung volumes.

An increased fraction of inspired oxygen to 100% (B) is inappropriate for most patients, as the goal is to maintain PO₂ > 60 mm Hg, which can often be done without 100% oxygen. A patient with asthma has no automatic indication that a higher amount of oxygen is needed.

Respiratory acidosis could be improved by increasing the respiratory rate (C). However, increasing the respiratory rate automatically in a patient with asthma reduces the expiratory duration and may lead to air stacking. This increases the risk of auto-PEEP and barotrauma in a patient with obstructive lung disease.