A chronic wound is defined as a wound that has failed to progress through the stages of healing in an orderly fashion to produce anatomic tissue integrity and restored functional capability.1 Many factors are recognized as contributing to wound chronicity, but impaired tissue perfusion that results in poor tissue oxygenation and tissue hypoxia is often at the top of the list. This chapter will discuss the importance of oxygen in wound healing and the role of adjunctive technologies such as hyperbaric oxygen therapy (HBOT) in the management of the hypoxic wound.
Oxygen is the third most common element in the universe. In fact, approximately 21% of the air we breathe is composed of oxygen, and most of this exists in a biatomic form as O2 molecules. This is the form that living organisms can best use. The remaining composition of air consists of about 79% nitrogen and less than 1% inert gases such as argon, carbon dioxide, neon, helium, and hydrogen. Air enters the alveoli, diffuses into the pneumatocytes, and then moves into the bloodstream. Given an atmospheric pressure of about 760 mm Hg at sea level, the partial pressure of oxygen (PaO2) in the air is around 150 mm Hg. But when losses due to vapor pressure and pulmonary diffusion gradients are considered, the partial pressure of oxygen actually reaching the bloodstream is less than 100 mm Hg.2
Once in the blood, oxygen is preferentially bound to the hemoglobin molecules on the red blood cells, and at sea le vel the average person has essentially 100% saturation of the hemoglobin molecules. However, the plasma can also carry dissolved oxygen, and, in fact, this system provides a great reserve in oxygen-carrying capacity.
Under normal atmospheric pressure, the average person has about 0.3 volume percent of dissolved oxygen in his or her plasma. However the oxygen-carrying capacity of the plasma is immense, and this reserve capacity is exactly the target of the supraphysiological oxygen levels provided by HBOT.2,3
Oxygenated blood flows to distal tissues, and under normal physiological conditions the oxygen is off-loaded to provide the energy substrates to fuel tissue metabolism. Oxygen delivery can be negatively impacted by conditions that inhibit uncoupling of oxyhemoglobin (such as tissue acidosis) or, as mentioned previously, conditions that prevent adequate tissue perfusion (ie, peripheral arterial disease, edema, and conditions causing vessel sludging or trauma). With regard to wound healing, normal tissue oxygenation is critical to collagen synthesis, epithelialization, angiogenesis, and bacterial killing.4,5,6,7
Definition of the Hypoxia Wound and Chronic Ulcer
Wounds that have failed to progress through the normal stages of the wound healing process are considered to be chronic, nonhealing wounds, especially if they have persisted longer than 4 to 6 weeks. The ...