American Thoracic Society (ATS) and European Respiratory Society (ERS) guidelines were relied upon in devising this algorithm. A paucity of well-designed trials in this area mandated the use of consensus.

A. Using Oximetry, Titrate O₂ by Venturi Mask (24 to 35 Percent) to an SaO₂ of 90 Percent -The goal of oxygen therapy is to optimize oxygenation and minimize respiratory acidosis, if present. Thus, all patients presenting with Acute Exacerbation of Chronic Obstructive Pulmonary Disease (AECOPD) should receive oxygen by venturi mask (24 to 35 percent), which delivers a precise oxygen concentration, until the PaCO₂ is determined. The lowest fraction of inspired oxygen (FiO₂ ) resulting in an SaO₂ of 90 percent is optimal. A nasal cannula is to be avoided initially because of the inability to deliver a precise FiO₂. ABGs (Arterial Blood Gases) should be obtained initially. SaO₂ should be monitored continuously.

B. ABGs - Analysis of ABGs is to be used initially in all cases when it is unknown whether or not the patient is a chronic CO₂ retainer and to determine acid-base status. Pulse oximetry, which should be continuously monitoring SaO₂, is not sufficient by itself until it is clear that the CO₂ level is not elevated or is stable and the acid-base status is known and is stable.

C. Is SaO₂ > 90 Percent? - An SaO₂ of 90 percent is optimal. This corresponds to a PaO₂ of 55 to 60 mmHg. Pulse oximetry alone may be used in this situation once it is clear that CO₂ is not elevated and acid base status is known and stable.

D. Stepwise Increase in FiO₂   - Use of a venturi mask, with analysis of arterial blood gases after 20 minutes (earlier if indicated clinically), is the most judicious approach to the oxygen management of acute exacerbation of COPD in a patient having an elevated PaCO_2. If chronic elevation of PaCO₂ is not demonstrated and repeated measurement of acid base status is not a clinical concern, pulse oximetry alone to assess adequacy of oxygenation is acceptable, as is the use of nasal prongs or a cannula to deliver oxygen. However, when CO₂ retention exists, or when the acid-base status is unclear, assessment of PaCO₂ and pH are required. Use of pulse oximetry alone in this situation is to be avoided.

E. Increase FiO₂  - Once it has been established that the acid-base status is acceptable and CO₂ retention is not present, oxygen delivery using a nasal cannula or prongs is acceptable, as is the use of pulse oximetry alone.

F. Decrease FiO₂ Stepwise - If the PaO₂ is more than 60 mmHg or the SaO₂ is more than 90 percent but the patient is not back to baseline FiO₂, attempts can be made to lower the FiO_2, providing that SaO₂ is at least 90 percent.

G. Decrease FiO₂ Progressively Keeping SaO₂ at 90 Percent - Monitor with oximetry or ABGs. If CO₂ retention has been worsened by the use of a high concentration of oxygen, it may be difficult to reverse the rise in PaCO₂ and improve acidosis without resorting to mechanical ventilation. A stepwise reduction in FiO₂ may be useful in this setting if clinical circumstances permit. An abrupt reduction in FiO₂ is unwise, since it may result in severe hypoxemia.

H. Does Patient Need Mechanical Ventilation? - A decision to initiate mechanical ventilation and endotracheal intubation can be made prior to measuring arterial blood gases. Advance directives should be considered prior to initiating these supportive measures.
 

1. Indications for mechanical ventilation (invasive or noninvasive) include:
 
• Severe respiratory or combined respiratory and metabolic acidosis
• Sustained respiratory rate greater than 40 per minute
• Abnormal breathing pattern suggestive of increased respiratory workload and/or respiratory muscle fatigue
• Depressed mental status
• Severe hypoxemia
  
  
2. Indications for tracheal intubation include:
 
• Suspected airway obstruction
• Depressed mental status
• High-risk of gastropulmonary reflux and aspiration
• Difficulty managing secretions

J. Are ABGs Acceptable? - Acceptable blood gases would include a PaO₂ close to 60 mmHg, a stable PaCO₂, and a 7.45 > pH > 7.25.

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