Assess for Hypoxemia and Hypercapnia and Treat if Indicated
Key Points:
- Assess for hypoxemia and consider assessment for hypercapnia.
Hypoxemia
The evaluation of gas exchange status by ABG measurement is recommended for initiation of oxygen therapy as well as to determine PCO2 and acid-base status. Assessment for long-term oxygen needs by arterial blood gas analysis should be considered for stable outpatients with:
- Severe airflow obstruction
- Symptomatic dyspnea with polycythemia, pulmonary hypertension (by electrocardiogram or echo), or altered mental status
- Problematic heart failure
- Severe symptoms out of proportion to the degree of airway obstruction
Pulse oximetry cannot determine acid-base status and is not considered sufficiently accurate to replace ABG (available) measurement in an initial assessment. ABG measurement can be used to confirm the accuracy of pulse oximetry at rest and with exercise when oximetry is less reliable.
Evidence supporting this recommendation is of classes: A, C
Nocturnal Hypoxia
During sleep, even in individuals without COPD, minute ventilation decreases. In patients with COPD whose O2 saturation is already low or borderline, this hypoventilation results in hypoxia, which can exacerbate or precipitate pulmonary hypertension. Sleep disruption from hypoxia or sleep apnea can induce daytime hypersomnolence and may worsen symptoms of COPD.
Risk factors for hypoxia during sleep:
- Severe COPD, especially with resting oxygen saturation less than 88% or exercise-induced hypoxia
- Evidence of cor pulmonale
- Daytime hypersomnolence in the absence of sleep deprivation
- Polycythemia
Evidence supporting this recommendation is of classes: A, C, D
Screening for Nocturnal Hypoxia
Screening for nocturnal hypoxia can be done easily and inexpensively with overnight pulse oximetry in the home. The oximeter is returned to the clinic, where the overnight oximetry and heart rate data are downloaded. If a significant portion of the night's data indicates oxygen saturations below 88%, supplemental oxygen should be provided empirically at 1 to 2 L/min. Home oximetry can be repeated at that level to verify correction of hypoxia.
The patient should be referred to a sleep specialist to rule out sleep-related disordered breathing if additional abnormalities are present.
Evidence supporting these recommendations is of class: C
Hypercapnia
In an ambulatory, stable patient with COPD, assessment for hypercapnia by ABGs should be considered in the following circumstances:
- Clinical suspicion of hypercapnia (asterixis, headache, hypersomnolence, altered mental status)
- FEV1 less than 1.0
- Upon initiation of oxygen
- Morbid obesity
- Excessive daytime somnolence
- Problematic right heart failure/cor pulmonale
- Severe airflow obstruction
Carbon dioxide (CO2) retention may pose a threat in patients with impaired CO2 ventilatory drive. Careful titration of supplemental oxygen should be performed in these patients. A pH drop along with a rise in PaCO2 with initiation of oxygen therapy or an increase in inspired oxygen concentration is usually well tolerated in the ambulatory stable patient with COPD. If hypercapnia results in a decrease in mental status, the patient may need admission to a hospital for more intensive respiratory care and monitoring.
In the unstable patient with resting hypercapnia, initiation of supplemental oxygen should be titrated upward, as there is a small risk of worsening CO2 retention. Reassessment by ABG and clinical status looking for signs/symptoms of hypercapnia is suggested 30 minutes after initiation of oxygen.
Hypercapnia does not require specific therapy, but instead, therapeutic intervention should be directed at correcting the hypoxemia. Nonetheless, a pH drop along with a rise in PaCO2 with initiation of oxygen therapy, or an increase in inspired oxygen concentration is usually well tolerated in the ambulatory stable COPD patient. If hypercapnia results in a decrease in mental status, the patient may need admission to a hospital for more intensive respiratory care.
These recommendations are further clarified in the NGC summary of the ICSI guideline Diagnosis and Treatment of Obstructive Sleep Apnea.
Evidence supporting this recommendation is of classes: C, R
Oxygen Therapy
Important Points
- Long-term oxygen therapy (more than 15 hours per day) improves survival and quality of life in hypoxemic patients.
- ABG measurement is recommended for initiation of oxygen therapy as well as to determine PCO2 and acid-base status.
- Pulse oximetry is a good method for monitoring oxygen saturation and can be used in adjusting the oxygen flow setting.
- Indications for long-term oxygen therapy have been adopted by Medicare as reimbursement criteria. (Appendix B in the original guideline document contains a summary of Medicare Oxygen Coverage Guidelines.)
- Patients considered for long-term therapy may benefit from assessment by a pulmonologist.
- Supplemental long-term oxygen therapy should be provided at a flow rate sufficient to produce a resting PaO2 of greater than 55 mm Hg, or SaO2 greater than 89%.
- Titrate liter-flow to goal at rest: add 1 L/min during exercise or sleep or titrate during exercise to goal of SaO2 greater than 89%. Titrate sleep liter-flow to eight-hour sleep of SaO2 greater than 89%.
- Consider referral for sleep evaluation if patient experiences cyclic desaturation during sleep but is normoxemic at rest.
- Recheck SaO2 or PaO2 in one to three months if hypoxia developed during an acute exacerbation. Rechecks should be performed annually if hypoxia is discovered in an outpatient with stable COPD.
Oxygen Delivery Methods
The dual-prong nasal cannula is the standard means of continuous flow oxygen delivery for the stable COPD patient with hypoxemia. It is not only well-tolerated, but is also simple and reliable. Care must be taken when assigning an estimated FiO2 to patients as this low-flow system can have great fluctuations.
Reservoir cannulas, demand pulse delivery devices, and transtracheal oxygen delivery are oxygen-conserving devices that can improve the portability of oxygen therapy, reduce the overall costs of home oxygen therapy, especially in patients requiring higher flow rates, and can more effectively treat refractory hypoxemia. These devices function by delivering all of the oxygen during early inhalation. They reduce oxygen requirements by 25 to 75% compared to continuous flow oxygen. Disadvantages of these devices are that they are bulky on the face, mechanically more complicated, and require additional care as well as additional training of the user.
Evidence supporting this recommendation is of classes: C, D, M
COPD and Air Travel
Airline travel is safe for most patients with COPD. Hypoxemic patients should be evaluated clinically, and a decision should be made regarding oxygen requirements. Patients with COPD receiving continuous oxygen at home will require supplementation during flight. A doctor's order is required for patients who need supplemental oxygen during air travel. Special arrangements with oxygen or equipment suppliers and the airline must be made at least 48 hours prior to departure. Patients should check with airlines for restrictions and special arrangements that apply.
Evidence supporting this recommendation is of class: D
Use of Supplemental O2 for Patients with COPD and Not Currently on Supplemental O2
Regression equations have been validated which predict pO2 at usual atmospheric pressures in aircraft. These predict that patients with FEV1 less than 80% and pO2 less than 80 will have in-flight pO2 less than 55% and therefore should be prescribed supplemental O2 at 2 L/M (liters/minute). Patients with underlying cardiovascular or cerebrovascular disease should be prescribed O2 if their FEV1 and pO2 are even higher.
Evidence supporting this recommendation is of classes: D, R