Ventilator-associated pneumonia (VAP) has one of the highest death rates for any healthcare-associated infection, claiming around 6,000 lives in the UK alone, and can cause severe complications in surviving patients. KEITH TURNER, Cambridge Design Partnership, discusses the problems associated with current ventilation systems and looks at how humidification could be improved.
Healthcare-associated infection (HCAI) is one of the intractable problems facing the NHS and, as a result, it has issued research contracts to find a solution. These contracts are designed to focus some of the medical device industry’s brightest minds on finding a way of combating the big challenges in healthcare. Ventilator-associated pneumonia (VAP) is the most common infection in intensive-care units, affecting around 10% to 15% of patients. The condition puts serious financial pressure on the NHS by increasing the length of time patients spend in intensive care and in hospital. It is estimated that UK hospitals pay £370 m each year to contain and treat the infection.
Causes of VAP
A high proportion of intensive-care patients rely on a ventilator for breathing and so are at risk. VAP is caused by the micro-organisms that are normally found in the throat and the gut moving to the lungs, assisted by the action of the mechanical ventilation. There is no single cause of VAP, but a contributing factor appears to be condensation in the tubes of mechanical ventilators, as these pools of warm water provide ideal breeding grounds for pathogens. In a healthy person, the nasal airways are warm and moist and increase the humidity of the air before it reaches the lungs. In patients on ventilators, the nasal passageways are bypassed. Therefore, the humidification process must be performed artificially. Humidifiers that avoid condensation currently exist, but they only provide low levels of moisture. Over a short period, the human body is extremely resilient to variations in humidity, but exposure to low levels of humidity for long periods can have serious negative effects. Insufficient humidification causes a thickening of the mucus in the patient’s air passages, and these thick secretions can prevent correct functioning of the cilia. The subsequent build up of highly viscous mucus can cause cell damage and will ultimately suffocate the patient, so the consequences of under-humidification are as severe as the risk of VAP.
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