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Normal values for humans are in the range 35–45 mmHg. Values less than this may indicate hyperventilation and (if blood pH is greater than 7.45) respiratory alkalosis. Values greater than 45 mmHg may indicate hypoventilation, and (if blood pH is less than 7.35) respiratory acidosis. [2] [3]
The values of pH and HCO3 of venous blood are close enough to arterial blood for direct comparison. The pCO2 of venous blood is less reliably compared to arterial blood but may be used in some cases. The PO2 level of venous blood is always significantly lower that arterial and should be reported, labeled and interpreted as venous PO2.
Arterial blood oxygen tension (normal) P a O 2 – Partial pressure of oxygen at sea level (160 mmHg (21.3 kPa) in the atmosphere, 21% of the standard atmospheric pressure of 760 mmHg (101 kPa)) in arterial blood is between 75 and 100 mmHg (10.0 and 13.3 kPa).
Hypoventilation exists when the ratio of carbon dioxide production to alveolar ventilation increases above normal values – greater than 45mmHg. If pH is also less than 7.35 this is respiratory acidosis .
The actual values in the lung vary depending on the position within the lung. If taken as a whole, the typical value is approximately 0.8. [4] Because the lung is centered vertically around the heart, part of the lung is superior to the heart, and part is inferior. This has a major impact on the V/Q ratio: [5] apex of lung – higher; base of ...
Acute respiratory acidosis occurs when an abrupt failure of ventilation occurs. This failure in ventilation may be caused by depression of the central respiratory center by cerebral disease or drugs, inability to ventilate adequately due to neuromuscular disease (e.g., myasthenia gravis, amyotrophic lateral sclerosis, Guillain–Barré syndrome, muscular dystrophy), or airway obstruction ...
Hypercapnia (from the Greek hyper, "above" or "too much" and kapnos, "smoke"), also known as hypercarbia and CO 2 retention, is a condition of abnormally elevated carbon dioxide (CO 2) levels in the blood. Carbon dioxide is a gaseous product of the body's metabolism and is normally expelled through the lungs.
It usually occurs within minutes to hours and is much faster than renal compensation (takes several days), but has less ability to restore normal values. [citation needed] In metabolic acidosis, chemoreceptors sense a changed acid-base balance with a plasma pH of lesser than normal (<7.4). The chemoreceptors send afferent fibers to the ...