Positive-pressure ventilation (PPV) is a medical technique used to support breathing when a person is unable to adequately move air into and out of their lungs on their own. This intervention involves actively pushing air into the lungs, assisting individuals experiencing respiratory difficulties.
Principles of Positive-Pressure Ventilation
Normal breathing relies on negative pressure, where the diaphragm and chest muscles create a vacuum that draws air into the lungs. In contrast, positive-pressure ventilation works by actively pushing air into the lungs, creating a pressure gradient that inflates them. This external force helps overcome the natural resistance of the airways and the elastic recoil of the lung tissue, facilitating gas exchange. As positive pressure increases the total alveolar gas exchange surface and functional residual capacity (FRC), it improves the lung’s ability to take in oxygen and release carbon dioxide. This process also helps recruit collapsed alveoli, improving oxygen and carbon dioxide exchange.
Common Applications
Positive-pressure ventilation is employed in various medical situations where a person’s natural breathing is compromised. It is frequently used during respiratory arrest and in cases of severe respiratory distress, such as from asthma exacerbations, chronic obstructive pulmonary disease (COPD), pneumonia, or drug overdose. PPV is also a component of resuscitation efforts during cardiac arrest. Furthermore, it is routinely used during surgical procedures under general anesthesia to maintain adequate breathing for the patient.
Techniques and Devices
Positive-pressure ventilation can be delivered through manual methods or by mechanical ventilators. Manual ventilation often involves devices like the bag-valve-mask (BVM). This handheld device consists of a self-inflating bag, a one-way valve, and a face mask that forms a tight seal over the patient’s nose and mouth. Squeezing the bag forces air or oxygen through the valve and into the patient’s lungs.
Alternative manual techniques include mouth-to-mask ventilation. Mechanical ventilation, on the other hand, utilizes machines called ventilators. These devices precisely control the delivery of breaths, adjusting factors like pressure, volume, and flow. PPV can be administered non-invasively, typically through a mask (e.g., CPAP or BiPAP machines), or invasively, via a tube inserted into the windpipe (endotracheal tube) or through a surgical opening in the neck (tracheostomy).
Essential Considerations for Safe Delivery
Safe and effective positive-pressure ventilation requires careful attention to several factors. Achieving a proper seal with the mask or device is paramount to prevent air leakage, which can reduce the effectiveness of ventilation. Delivering the appropriate ventilation rate and volume is equally important, as both over-ventilation and under-ventilation carry risks. Over-ventilation, which involves delivering too much air or at too high a pressure, can lead to gastric inflation, where air enters the stomach, potentially causing vomiting and aspiration of stomach contents into the lungs. It can also result in barotrauma, a lung injury caused by excessive pressure.
Under-ventilation, providing insufficient air, can lead to inadequate oxygenation. Observing the patient’s chest rise and fall is a visual cue to assess the adequacy of ventilation. Monitoring skin color and patient response, such as heart rate, also helps determine the effectiveness of oxygen delivery.
Optimal patient positioning, such as a head tilt-chin lift or jaw thrust, helps maintain an open airway, which is fundamental for effective ventilation. Airway adjuncts, like oropharyngeal (oral) or nasopharyngeal (nasal) airways, can further assist in maintaining an open passage, especially in unconscious patients or those with anatomical challenges. These adjuncts help prevent the tongue from obstructing the airway, allowing for more efficient air delivery.