When hypoxia leads to disease, the first thought that comes to mind is to provide more oxygen to the patient to alleviate the oxygen deficit. However, it is important to consider how much oxygen reaches the hypoxic tissues. Using Dalton’s and Henry’s laws, we can see that the physiologic effect of HBOT alters the concentration of oxygen in the plasma and assists hemoglobin to achieve full oxygen-carrying capacity.

 

Because the partial pressure of oxygen does not affect hemoglobin’s carrying capacity for oxygen, the maximum amount that hemoglobin can carry is unaltered and remains at 20 mL O2/dL of blood. The only change is in the amount of oxygen dissolved in the plasma. Oxygen partial pressure is 713 mmHg in the trachea when 100% oxygen is given to a patient (see Table 1). This partial pressure of oxygen is dissolved with a coefficient of 0.0024 mL O2/(dL of blood per mmHg), yielding 1.71 mL O2/dL of blood dissolved in plasma. A total of 21.71 mL O2/dL of blood is the oxygen content with the application of 100% oxygen. This is a net increase of 1.47 mL O2/dL of blood, or only a 7.26% increase. There are limitations to this application, as oxygen can only be delivered to areas receiving adequate blood supply. As in cases of ischemia, the oxygen does not reach the hypoxic tissues, and the administration of 100% oxygen to the patient is insufficient to correct the underlying pathology.

 

HBOT uses 100% oxygen in a setting of local artificially elevated pressures generally in the range of 1–3 atm.3,55 This has practical implications for treating conditions in which tissues are damaged due to oxygen deprivation. HBOT is the use of oxygen under pressure “as a drug to treat basic disease processes and their diseases”.56 The effects of hyper-baric oxygen lead to changes in the transcription of DNA, alterations in the organelles of the cell, improved structure of tissue, and more efficient function of the organ. These changes can become permanent within 25–35 treatments.42