SUPPRESSION OF VENTILATION  AND CO₂ TOXICITY IN COPD PATIENT

 

By: Kristal Rubio, Student 2005

COPD patients’ bodies learn to live in a state of elevated pCO₂ levels due to their oxygenation-perfusion mis-match.  Their bodies accept the higher level and adjust, making a new “balance” for themselves. 

Patients with COPD have a stimulus for respiration which is driven by the decrease in blood oxygenation, rather than an increase in CO₂ levels as seen in a patient with no respiratory problems.

 

Administration of a high amount of oxygen (over 2 L/ min) to a COPD patient causes in increased oxygenation in the blood, but blocks their breathing stimulus (respiratory drive).  While the higher level of oxygen helps the patient very briefly in the short term (by bringing up their O₂ levels), it causes the patient to breathe at a slower rate, causing a buildup of CO₂ in the blood stream.  Add this buildup to the already increased CO₂ level that the patient’s body is already accustomed to and the patient will very rapidly develop carbon dioxide narcosis (CO₂ toxicity) which will ultimately lead to the patient’s death.

 

Oxygen- induced hypoventilation is prevented by administering oxygen at low rates (1 to 2 L/ min).  (PG 601, Bruner & Suddarth).

 

 

Ex. (With hypothetical numbers):

 

Patient has the following levels prior to oxygen administration:         

 

pCO2   -   30

pO2     -    32

R Rate -    20

Oxygen is administered at 3L/min.

 

Due to the low O₂ concentration, the patient’s respiratory drive is activated and the respirations increase to 26.

 

The patient’s levels change.  The O₂ increases to 45, and the CO₂ decreases a little to 28 ( still above average, but closer to normal).

 

But, since the O₂ level is now up, the patient’s respiratory drive is shut off and the respirations now decrease to 17.

 

The patients O₂ level stays at a normal range because the oxygen is still being supplied at 3L/min; however, since the patient’s respirations have now decreased to a lower level, patient is not blowing off the CO₂  at as high of a rate as he previously was.  The CO₂ is now building up in the blood stream even higher (on top of the already elevated level of 28).  This causes the patient to develop carbon dioxide toxicity or narcosis, even though his oxygen saturation is at a good level.