Definition: what is hypercapnia?
Hypercapnia is defined by a CO2 arterial partial pressure above standards. This measure is never taken in isolation, since it is made as part of the analysis of “blood gases”which also measures oxygen concentration and blood pH.
Dr. Marie-Pascale Schuller, pulmonologist: Hypercapnia is one of the symptoms of respiratory diseases. It can be acute or chronic, and is most often associated with hypoxia, ie a decrease in the concentration of oxygen in the blood.
Acute hypercapnia
Hypercapnia is said to be acute when it is associated with decreased blood pH and hypoxia. This is a sign that the body can no longer adapt, and it is a vital emergency.
Chronic hypercapnia
Hypercapnia is considered chronic when thebody has managed to adapt. “Thanks to the kidneys which recover bicarbonate from the urine, the blood pH is maintained at 7.4 and acidosis is avoided” explains Dr. Schuller.
Norms of CO2 level in the blood: When do we speak of hypercapnia?
We speak of hypercapnia if the CO2 concentration in the arteries is greater than 45 mm of mercury.
Acute respiratory failure: what are the main causes of hypercapnia
Hypercapnia is a symptom that reflects a poor lung ventilation. It therefore testifies to respiratory failure, which can be acute or chronic, which can have several origins:
- The most common is the chronic obstructive pulmonary disease (COPD). This chronic inflammatory bronchial disease is characterized by progressive narrowing and obstruction of the airways and lungs, causing difficulty in breathing. It is relatively common since it affects 7.5% of the French population. In 80% of cases, it is attributable to smoking.
- A spine injuryscoliosis type or very important kyphosis, creating a deformation of the rib cage and compressing the lungs,
- A morbid obesity. Being overweight compresses the rib cage and makes it harder to breathe We talk about Obesity-hypoventilation Syndrome,
- A neuromuscular disease or myopathylimiting the proper functioning of the respiratory muscles,
- And severe sleep apnea syndromewhich can cause nocturnal respiratory failure,
- And respiratory virus such as Covid19, influenza viruses or metapneumovirus, which can cause severe respiratory damage,
- A drug poisoningincluding opiates and opioids.
Shortness of breath, fatigue, vasoconstriction, flapping tremor: What are the signs and consequences of hypercapnia?
Hypercapnia is not a pathology but a sign of respiratory dysfunction. “She is a biological witness of a bad adaptation of the ventilation to the needs of the body” explains the pulmonologist.
Symptoms associated with hypercapnia and its consequences are therefore those of the pathology which is the cause.
When combined with hypoxia in cases of chronic respiratory insufficiency, they may be: a thehigh blood pressureof the headachesand shortness of breatha great fatigueheavy sweating or involuntary muscle contractions called flapping tremor.
Treatment: How to correct hypercapnia?
L’hypercapnie acute is a life-threatening emergency and should therefore be dealt with immediately by respiratory support. Patients are either intubated or placed on assisted ventilation.
If the deficiency is chronicthe patient with hypercapnia is placed under ventilation non invasive. “This ventilator device connected to a mask placed on the patient is effective in reducing the respiratory rate and restoring gas exchange” explains Dr. Schuller.
At the same time, the cause of the respiratory failure (COPD, obesity, spinal deformity, drug intoxication, etc.) must be treated to solve the problem at the source.
Why not put too much oxygen on a COPD?
When COPD is very severe, it can progress to respiratory failure due to alveolar hypo-ventilation, which means that the pulmonary alveoli no longer carry out their gas exchange work correctly. Hypoventilation then combines hypercapnia and hypoxia – namely a decrease in the concentration of oxygen in the blood.
Dr. Schuller: Severe hypercapnia causes disturbances in alertness where the patient tends to fall asleep, but hypoxia keeps the patient awake. When too much oxygen is given to the patient, he loses this stimulation, with the risk that he falls asleep.
It is for this reason that home oxygen prescription should be done at low flow rates (1 to 2 l/min) by the pulmonologist according to codified rules with adaptation to the patient’s ambulation needs.
“However, for several years, for patients hospitalized in intensive care, new so-called “high flow” oxygen therapy techniques are used if necessary, under strict supervisionallowing patients to pass this difficult stage without having to resort to intubation, which is much more traumatic,” says Dr. Schuller.