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Wednesday, July 2, 2014

COPD-CO2 retainers: How should they be managed?

The evidence suggests that supplemental oxygen may increase CO2 levels in some COPD patients, particularly CO2 retainers.  While rare, it is still something that should weigh on the minds of medical professionals.

Based on this evidence, Schmidt and Hall recommended COPD-CO2 retainers be maintained on as little oxygen as possible to maintain an adequate oxygen saturation, or an SpO2 of 88-92%.  Many modern textbooks, including the Textbook of Canadian Medical-Surgical Nursing, support this view. (1)(2)

On the other hand, Schmidt and Hall also remind us that oxygen is essential to survival.  Oxygenation at or below critical levels, such as a PO2 of 40 and SPO2 of 70, this increases the risk of an anoxic brain injury that may cause life altering changes, including death.

For this reason, they recommend COPD-CO2 retainers be monitored and treated based on clinical assessment and work of breathing "rather than by arbitrary laboratory values."

Likewise, Chris Moulton and David W. Yates in their 2006 book "Lecture notes:  Emergency Medicine" recommend setting a goal "to raise the PaO2 above 50 mmHg without worsening the acidosis."  (17)

Savi et al, in 2014, reported that, while "the PaCO2 commonly rises somewhat when a patient with COPD receives supplemental oxygen... carbon dioxide narcosis due to oxygen therapy is uncommon, and patients should not be kept hypoxemic for fear that oxygen therapy could aggravate carbon dioxide." (4, page 385)

Moreover, the report notes: "This expected rise (in PaCO2) should not be specifically treated unless it is excessive, resulting in a trend toward acute respiratory acidosis on serial arterial blood gas analysis, with central nervous system or cardiovascular side effects." (4, pages 385-386)

They also reiterate the obvious: "Carbon dioxide narcosis may occur with excessive FiO2, but is much less likely with low-flow, controlled oxygen therapy." (4, page 386)

Generally, if a COPD-CO2 retainers lose their drive to breathe, it's going to occur whether in the presence of oxygen or not.  Therefore, it is essential to closely monitor oxygenation levels and adjust them accordingly.

Although, should the patient's drive to breathe become tapped out, with CO2 levels rising to critical levels, the best treatment option may be to support ventilations with positive pressure breaths by noninvasive positive pressure ventilation or mechenical ventilation.

  1. Schmidt, Greggory A., Jesse B. Hall M.D "Oxygen Therapy and Hypoxic Drive to Breath: Is There Danger in the patient with COPD?" Critical Care Digest, 1989, 8, pages 52-53
  2. Day, Rene A, Beverly Williams, Brunner and Suddarth's Textbook of Canadian Medical-Surgical Nursing, 2009, page 654. Source #8 above also supports the veiw that the hypoxic drive is not responsible for hypercarbia in COPD patients given too much oxygen, and likewise supports the Haldane and V/Q mismatching theories (Cooper, op cit, page 24)
  3. Moulton, Chris, David W. Yates, "Lecture notes:  Emergency Medicine," 3rd ed., 2006, pages 215-16
  4. Savi, Augusto, et al, "Influence of FiO2 During Noninvasive Ventilation in Patients with COPD," Respiratory Care, March, 2014, Volume 59, Number 3, pages 383-387

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