Emergencies always happen when you are away from home, after “office hours,” or over a holiday. Due to this helpful timetable, it is likely that, when an emergency occurs, patients will be seen by professionals who have no knowledge of them or of their (rare) disease. During a respiratory emergency, the first reaction of emergency personnel is to give oxygen. Giving oxygen, without proper monitoring, can be life threatening to a person with Duchenne. Several such emergencies happened this year, prompting revision of the “Respiratory Care” section of the emergency card.

 

The new section of the card reads:

Respiratory Care

Risk: respiratory failure

Do Not Give Oxygen without checking end-tidal or blood CO2 level. A low hemoglobin saturation may indicate CO2 retention and a need for positive pressure ventilation. IF supplemental oxygen is given, please monitor CO2. Non-invasive ventilation may be required.

Why can supplemental oxygen be so dangerous in patients with Duchenne?

Well, there are 2 parts of respiration: the mechanics of breathing and the exchange of oxygen for carbon dioxide. When breathing in, the diaphragm and intercostal muscles (muscles between the ribs) contract, the diaphragm moves down, and the ribs move up. This creates space within the chest; air rushes in to fill this space. When the air rushes in, the air goes to the lungs where the oxygen in the air is exchanged for carbon dioxide (CO2). The oxygen then goes into the blood, where it travels in the hemoglobin to the cells. The muscles of the chest relax and the air, now filled with CO2, is pushed out of the body. While breathing happens automatically, it is regulated by the respiratory center in the brainstem. When the body has too much carbon dioxide or not enough oxygen, the brainstem triggers the body to breathe.

 

Patients with Duchenne have weak respiratory muscles. A weak diaphragm does not move up and down well and weak intercostal muscles do not expand the ribs well. Therefore, as the disease progresses, it becomes difficult to cough and to take deep breaths. Shallow breathing can provide the body with adequate oxygen supply and adequate removal of carbon dioxide. That delicate balance of oxygen and carbon dioxide allows breathing to continue. When extra or supplemental oxygen is given, this delicate balance is disturbed. The respiratory center may get the false impression that the body has enough oxygen and no longer needs to breathe. Without breathing, carbon dioxide can build to dangerous levels (called hypercapnia) that can result in death. 

 

There are ways of giving supplemental oxygen and monitoring carbon dioxide safely. Oxygen should never be given without constantly monitoring the level of carbon dioxide CO2 in the expired breath (the “end-tidal CO2”) or the CO2 level in blood. A normal end tidal CO2 is between 30-45 mmHg.  A CO2 level of greater than 45 mmHg is too high, and indicated that CO2 is not being expelled from the body. Hemaglobin in the blood becomes saturated with oxygen that the blood takes to the body. If hemoglobin is tested and is found to not be saturated with oxygen, that too can be an indication that there is too much CO2 in the body and that not enough oxygen is getting into the blood. Non-invasive ventilation (Bi-PAP via mouthpiece or nasal cannula) will assist with the mechanical process of breathing, delivery of oxygen, and removal of CO2. 

 

Please keep this emergency card on hand. Presenting this information to professionals during an emergency will, hopefully, prompt them to monitor your child closely.

 


Kathi Kinnett, MSN, CNP
Vice President, Clinical Care
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