TISSUE PERFUSION AND OXYGENATION
Oxygen is required for wound healing to occur, therefore, for healing to take place it is essential that there is an adequate perfusion and oxygenation of the tissues.
It is sometimes possible to identify patients who have poor tissue perfusion and/or oxygenation, just by looking at the patient’s skin. This is much easier to observe in fair-skinned individuals, when done in good lighting (Vuolo, 2009)
Cyanosis is a bluish purple discolouration of the skin, nail beds and mucous membranes and its presence is indicative of an abnormally high concentration of deoxyhaemaglobin in the arterial blood (Levitzky 2003, Martin 2015). The degree of cyanosis does not always reflect the degree of hypoxia as this is also dependent upon the concentration of haemoglobin in the blood.
Finger and toe clubbing is present in a number of respiratory diseases including bronchial carcinoma, bronchiectasis and pulmonary fibrosis (Davies et al. 2003, McMullen 2013). Central cyanosis usually suggests some severe disease of the heart or lungs (Ranjendran 2004, McMullen 2013).
An example of finger clubbing.
Nail widening characterises clubbing and occurs when the tissue under the nail plate becomes thicker. The medical conditions that can cause clubbing are generally associated with decreased oxygen levels. Further investigations may be required to determine the underlying cause.
Peripheral cyanosis is due to reduced and slow blood flow to the limbs because of vasoconstriction of the blood vessels. Peripheral cyanosis may disappear on massage or warming of the limb (Ranjendran 2004, McMullen 2013).
A particular area of the body may experience poor oxygenation/perfusion, for example in arterial disease. It is common for these patients to have hairless, shiny skin in the lower limbs and their nails may be hardened. Other methods of assessing the patient’s tissue perfusion and oxygenation include;
Oxygen saturation is a measure of the percentage saturation of haemoglobin in the blood. However, a patient who has a high percentage of oxygen saturation may still be hypoxic if they have a low concentration of haemoglobin in their blood (anaemia).
Capillary refill is the rate at which blood refills empty capillaries. This is a quick and easy way to measure peripheral perfusion. This can be measured by pressing a fingernail until it turns white and taking note of the time needed for colour to return once the nail is released. ‘Normal’ capillary refill is usually two seconds or less.
It is important to note that capillary refill alone is not a reliable indicator of vascular status and as such other observations and investigations should be undertaken.
The ability to perfuse and oxygenate tissues is affected by four main factors;
- Cigarette smoking
- Vascular disease
- Other disease
The long term systemic toxic effects of smoking, such as lung and respiratory diseases are widely acknowledged. Cigarette smoking is also acknowledged as having an adverse effect on blood vessels and platelets, which can ultimately impact wound repair at a cellular level (Storch & Rice 2005, McDaniel 2014). Hydrogen cyanide, carbon monoxide and nicotine found in smoke are believed to cause a number of problems
- Hydrogen cyanide inhibits oxygen transportation
- Carbon Monoxide binds to Haemoglobin in blood in place of oxygen
- Nicotine causes vasoconstriction and decreased tissue perfusion (Whiteford 2003, Cope 2014)
Smoking accelerates atherosclerosis by lowering HDL cholesterol levels and by increasing blood pressure. It can also impair fitness owing to a decreased pulmonary function and by directly damaging the epithelium (McConnel, 2006).
Atherosclerosis is a progressive disease and is the leading cause of obstructive arterial disease in the extremities of people over the age of 30 years. At least 95% of arterial occlusive disease is atherosclerotic in origin (Juall & Carpenito–Moyet, 2004) and will therefore be described in further detail in the vascular disease section.
The effect of these toxins significantly reduces the amount of oxygen available for wound healing, resulting in potential delays and increased risk of infection. Some research has been carried out which has shown that post-operative patients who smoke are also at higher risk of a variety of wound related complications such as infection, wound rupture and necrosis of the wound. (Ahn et al, 2008).