There are two pathways for the development of CO2 intoxication: either pCO2 is increased in inspired breathing gas, or expiration of produced CO2 is insufficient.
Increased pCO2 in inspired gas may occur when gas exchange in the hyperbaric chamber is insufficient to keep pCO2 at physiological level. To prevent raised pCO2 levels, hyperbaric chambers have to be flushed continuously with breathing gas. The flushing rate has to be adapted to the number of chamber occupants and to the total pressure of chamber atmosphere.
Anxiety can lead to frequent and shallow ventilation and so may cause insufficient expiration of CO2. Physical exhaustion due to strenuous work and increased CO2 production may have similar effects. Increased gas density and increased breathing resistance supports this mechanism.
The most common and primarily occurring symptom of CO2 intoxication is headache. In addition, palpitation, increased blood pressure, or agitation may occur. At pCO2 over 6kPa (0.06bar) air hunger, tachycardia, and loss of consciousness may occur ("CO2 narcosis").
Table 1.3-4. Symptoms at different levels of increased pCO21_
pCO2 in inspiration gas_Symptoms_
0.38kPa (0.0038bar) None (normal atmospheric pCO2 value)
1.5kPa (0.015bar) Increased ventilation frequency
2.5kPa (0.025bar) Headaches, dizziness, vertigo, nausea, air hunger, disturbed vision
6.5kPa (0.065bar) Loss of consciousness_
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