Intermittent positive pressure ventilation (IPPV) is a form of mechanical breathing support for individuals who cannot adequately breathe on their own. It helps ensure enough air enters the lungs to maintain oxygen levels and remove carbon dioxide. IPPV takes over or supplements the natural breathing process, allowing respiratory muscles to rest and recover.
Fundamentals of Positive Pressure Ventilation
Natural breathing involves the diaphragm and intercostal muscles contracting, creating negative pressure within the chest cavity that draws air into the lungs. In contrast, positive pressure ventilation pushes air into the lungs. A ventilator generates a controlled stream of air, often mixed with oxygen, delivering it into the patient’s airways and inflating the lungs.
The ventilator creates a positive pressure difference between the airway opening and the alveoli, the tiny air sacs in the lungs. This pressure gradient causes air to flow from the ventilator, through the breathing circuit, and into the patient’s lungs. Once the desired volume or pressure is delivered, the ventilator allows for passive exhalation, where the lungs naturally recoil and push the air out.
Medical Conditions Requiring IPPV
IPPV is used for individuals experiencing acute respiratory failure, where the lungs cannot adequately perform gas exchange. Conditions like severe pneumonia, which causes widespread inflammation and fluid accumulation, can impair oxygen uptake and carbon dioxide removal. Acute Respiratory Distress Syndrome (ARDS) also leads to widespread lung inflammation and fluid leakage, making the lungs stiff and difficult to inflate.
Neurological conditions that weaken or paralyze breathing muscles also necessitate IPPV. Disorders such as Guillain-Barré syndrome or amyotrophic lateral sclerosis (ALS) can progressively impair the diaphragm and intercostal muscles, making spontaneous breathing impossible. In these cases, the ventilator entirely takes over the work of breathing. During major surgical procedures, especially those involving the chest or abdomen, IPPV is used to maintain stable breathing and oxygenation while the patient is under anesthesia and muscle relaxants.
Understanding IPPV Delivery Methods
IPPV can be delivered through various methods, categorized by how the ventilator interacts with the patient’s breathing efforts. In controlled ventilation modes, the ventilator initiates and delivers every breath at a preset rate and volume, irrespective of patient effort. This approach is used when a patient has no spontaneous breathing effort or is heavily sedated, ensuring consistent breath delivery.
Assist-control ventilation, a widely used mode, allows the ventilator to deliver breaths based on patient effort while also guaranteeing a minimum respiratory rate. If the patient attempts to take a breath, the ventilator senses this effort and delivers a full breath at the preset tidal volume or pressure. If the patient does not initiate a breath within a set time, the ventilator will automatically deliver a breath to ensure adequate ventilation. This mode balances patient autonomy with guaranteed support.
Adjusting specific parameters on the ventilator is important to customize support for each patient’s needs. The respiratory rate, set between 10 to 20 breaths per minute for adults, determines how many breaths the ventilator delivers per minute. Tidal volume refers to the amount of air delivered with each breath, set between 6 to 8 milliliters per kilogram of ideal body weight to prevent lung injury. Positive End-Expiratory Pressure (PEEP) is another setting that maintains a small amount of pressure in the lungs at the end of exhalation, between 5 to 10 cm H2O, to keep the air sacs open and improve oxygen exchange.
The inspiratory-to-expiratory (I:E) ratio dictates the relative duration of inhalation versus exhalation. A common ratio is 1:2, meaning exhalation is twice as long as inhalation, allowing sufficient time for air to leave the lungs. Peak inspiratory pressure (pMax) is the maximum pressure reached during inhalation and is monitored to avoid lung damage; it is kept below 30 cm H2O. These settings are continuously adjusted based on the patient’s response, blood gas measurements, and overall clinical picture, ensuring optimal ventilatory support and minimizing potential complications.
Potential Adverse Effects and Monitoring
While IPPV is beneficial, it carries potential risks and adverse effects that require careful management. One concern is ventilator-associated pneumonia (VAP), a lung infection that can develop when bacteria enter the airways through the breathing tube. This risk is managed through infection control protocols, including regular oral hygiene and head-of-bed elevation. Another potential complication is barotrauma, lung injury caused by excessive pressure or volume from the ventilator, leading to conditions like pneumothorax, where air leaks into the space between the lung and chest wall.
Patients on IPPV are continuously monitored to detect and manage potential issues. Vital signs, including heart rate, blood pressure, and body temperature, are observed to assess overall stability. Oxygen saturation levels, measured non-invasively with a pulse oximeter, provide immediate feedback on how well the lungs are oxygenating the blood. Arterial blood gas analysis, which involves drawing a blood sample, provides precise measurements of oxygen, carbon dioxide, and pH levels, giving a detailed picture of the patient’s respiratory and metabolic status. These monitoring efforts allow healthcare providers to fine-tune ventilator settings and address complications as they arise.