Intermittent Positive Pressure Ventilation (IPPV) is a technique used in medicine to assist or completely take over a person’s breathing when they cannot do so effectively. This therapeutic support is widely employed in both emergency situations and intensive care settings to sustain life and improve gas exchange. IPPV is a fundamental method of artificial respiration where air is delivered into the lungs at set intervals using a machine or a manual device. This process ensures oxygen reaches the bloodstream and carbon dioxide is successfully removed from the body.
The Core Mechanism of Positive Pressure
Normal human breathing relies on a mechanism called negative pressure ventilation. The diaphragm and chest wall muscles contract, expanding the chest cavity and creating a vacuum, or negative pressure, inside the lungs relative to the atmosphere, drawing air in passively. Intermittent Positive Pressure Ventilation inverts this natural process by actively pushing air into the lungs under a controlled amount of force. The ventilator generates a positive pressure gradient at the airway opening, forcing a specific volume of gas into the thoracic cavity until a set volume or pressure is reached.
This forced inhalation is followed by an “intermittent” phase, which is the passive exhalation. Once the machine stops delivering the positive pressure, the natural elastic recoil of the lungs and chest wall pushes the air out. The amount of air delivered with each machine-assisted breath is known as the tidal volume. Controlling the tidal volume and the resulting airway pressure is necessary to overcome resistance in the airways and improve the expansion of the small air sacs, or alveoli.
Methods of Administration
IPPV can be administered through both manual and mechanical means, depending on the urgency and setting of the patient’s respiratory needs. In emergency situations, manual IPPV is frequently performed using a Bag-Valve Mask (BVM), often called an Ambu bag. A healthcare provider squeezes this self-inflating bag to deliver breaths. This technique is a rapid, life-saving measure used during cardiopulmonary resuscitation (CPR) or initial response to respiratory arrest.
For continuous, long-term support, mechanical ventilators are used, which precisely control the timing, volume, and pressure of each breath. Delivery is classified as either non-invasive or invasive. Non-invasive positive pressure ventilation (NIPPV) uses a tightly sealed mask over the nose or face, suitable for patients who are conscious and can protect their own airway.
Invasive IPPV is required for critically ill patients and involves securing an artificial airway. This is typically an endotracheal tube (ETT) inserted into the windpipe or a tracheostomy tube placed directly into the neck. The tube has an inflatable cuff that creates a closed system, preventing air from escaping and ensuring the full tidal volume is delivered to the lungs. This invasive method allows the machine to completely take over the patient’s breathing, which often requires the patient to be sedated.
When IPPV is Medically Necessary
The requirement for IPPV arises when a patient’s own respiratory system fails to maintain adequate levels of oxygen and carbon dioxide in the blood. The primary indication is acute respiratory failure, which can be due to the lungs’ inability to oxygenate the blood (hypoxemic failure) or to remove enough carbon dioxide (hypercapnic failure). Conditions such as severe pneumonia, acute respiratory distress syndrome (ARDS), or trauma can severely compromise lung function, necessitating mechanical support.
IPPV is also used when the muscles responsible for breathing are exhausted, paralyzed, or impaired, such as in cases of neurological diseases like amyotrophic lateral sclerosis (ALS) or Guillain–Barré syndrome. Furthermore, a complete cessation of breathing, known as apnea, or a patient with a compromised airway due to a reduced level of consciousness requires IPPV. In the context of cardiac arrest, positive pressure ventilation is an integral part of the resuscitation effort to oxygenate the patient during chest compressions.
Associated Risks and Side Effects
While IPPV is a life-sustaining therapy, the application of continuous positive pressure carries inherent risks and side effects. One significant concern is ventilator-associated lung injury, which includes barotrauma and volutrauma. Barotrauma refers to injury caused by excessive pressure, which can lead to air leaks from the lungs into the chest cavity, potentially causing a collapsed lung, or pneumothorax.
The constant positive pressure within the chest cavity also generates hemodynamic effects. Increased pressure can impede the return of blood to the heart, reducing the amount of blood the heart can pump out. This can result in hypotension, or low blood pressure, especially in patients who have circulatory issues. For patients requiring prolonged intubation, there is also the risk of ventilator-associated pneumonia (VAP), a serious infection that develops due to bacteria colonizing the artificial airway and lungs.