Positive Pressure Ventilation

Excerpt

Positive pressure ventilation is a form of respiratory therapy that involves the delivery of air or a mixture of oxygen combined with other gases by positive pressure into the lungs. As gas enters the lungs, the interalveolar pressure increases until a change in flow or pressure are detected by the machine delivering the mixture, or the set volume of gas was delivered to signal the end of a breath. Expiration of air happens passively secondary to the build-up of pressure in the alveoli that escapes into the less pressurized conductive airways. Historically, artificial lung ventilation based on the opposite to PPV physical principle – the negative pressure ventilation – was used widely to treat acute respiratory failure in poliomyelitis patients via hermetically sealing the patient’s torso inside the vacuum-producing “iron lung” machine. The overwhelming polio epidemic of Copenhagen in 1952 and insufficient availability of “iron lungs” led to the implementation of PPV into clinical practice.

Positive pressure ventilation can be delivered in two forms: non-invasive positive pressure ventilation (NIPPV), which is delivered through a special face mask with a tight seal (air travels through anatomical airways), or invasive positive pressure ventilation (IPPV), which involves the delivery of positive pressure to the lungs through an endotracheal tube or tracheostomy (or any other device that delivers gas bypassing parts of the anatomical airway). Each form of ventilation has its own benefits, risks, indications, and contraindications. NIPPV can be used in acute hypercapnic respiratory failure so long as the patient’s condition is responsive to this form of therapy. Conditions that respond the most to NIPPV include exacerbations of chronic obstructive pulmonary disease (COPD) and acute cardiogenic pulmonary edema. However, the need for emergent endotracheal intubation is a contraindication to NIPPV and may be required for conditions such as cardiac arrest, hemodynamic instability, the inability of the patient to cooperate, or maintain an open and protected by reflexes airway, as well as many others to be discussed further.