carbon dioxide - effects during diving when descending and at depth

Last reviewed 01/2018

carbon dioxide

• the normal level of carbon dioxide in the alveoli is 40 mmHg (0.055 bar)
  • when diving the arterial and alveolar carbon dioxide tensions should be maintained at approximately 40 mmHg
  • with increasing depth, the alveolar pressures of nitrogen and oxygen increase and therefore the alveolar percentage of carbon dioxide decreases
  • however, when energy expenditure is high, the level of carbon dioxide can increase dramatically
    • most commonly encountered in divers using rebreather sets
    • may also be seen in the recompression chamber if there is inadequate flushing of the chamber with fresh gas
• if the level of carbon dioxide increases then clinical features of hypercapnia may occur:
  • breathlessness (carbon dioxide present at about 3%)
  • distress and dyspnoea (5-6%)
  • rise in blood pressure and heart rate, mental confusion and lack of coordination (10%)
  • followed by loss of consciousness and death (12-14%)
• although carbon dioxide is a respiratory stimulant, most of its effects are related to the metabolic acidosis it produces and are neurologically depressant

Reference:

• atmospheric pressure at sea level is 1 atm (equivalent to 101.3 kPa) and is the pressure that is experienced by all parts of the human body at sea level
• 1 atm = 1.01325 bar = 101.3 kPa

Reference:

• 1) Edge CJ. Recreational diving medicine.Current Anaesthesia Critical Care 2008; 19 (4): 235-246.