Mechanical ventilation is a medical therapy that assists or takes over breathing for individuals who cannot breathe adequately on their own. This support is provided by a machine called a ventilator, which moves air into and out of the lungs. The primary goal of mechanical ventilation is to ensure sufficient oxygen delivery to the body and removal of carbon dioxide. Synchronized Intermittent Mandatory Ventilation (SIMV) represents a specific mode of this support, designed to help patients breathe while encouraging their own respiratory efforts.
Understanding Synchronized Intermittent Mandatory Ventilation
SIMV delivers a set number of mandatory breaths at a predetermined volume or pressure. Between these, the patient can breathe spontaneously. The ventilator synchronizes its mandatory breaths with the patient’s own inspiratory efforts. Sensors detect the patient’s attempt to inhale, and the ventilator delivers its programmed breath in harmony with that effort.
The “intermittent” component refers to periods when the patient breathes independently. During these times, the patient controls the volume of their spontaneous breaths, which can be supported by pressure support (PS). This added pressure boosts self-initiated breaths, making them deeper or more effective. The “mandatory” aspect ensures a minimum number of breaths are delivered by the machine, guaranteeing baseline ventilation even if the patient’s own breathing efforts are weak or infrequent.
This combination balances machine support and patient participation. The ventilator delivers a mandatory breath if the patient does not initiate one within a specific “trigger window,” ensuring consistent ventilation. This synchronization improves patient comfort and reduces instances of patient-ventilator asynchrony.
Applications and Advantages
SIMV is used in intensive care units and other clinical settings for conditions like acute respiratory distress syndrome (ARDS), pneumonia, or chronic obstructive pulmonary disease (COPD). It also applies to post-operative care for patients needing support who retain some respiratory drive and muscle strength. This mode suits patients requiring partial ventilatory support, allowing a gradual shift from full machine control to more independent breathing.
An advantage of SIMV is its ability to promote patient comfort by synchronizing with breathing efforts. This synchronization helps reduce the risk of ventilator-induced lung injury, which can occur with full, continuous support. SIMV also allows patients to maintain and exercise their respiratory muscles, preventing muscle weakening from prolonged full ventilation.
SIMV’s flexibility allows clinicians to adjust ventilation frequency, adapting the work of breathing to the patient’s capabilities. This adaptability facilitates a transition from fully-controlled to largely spontaneous breathing, reducing the need for heavy sedation. By enabling patients to influence their own ventilation, SIMV also helps manage carbon dioxide levels in the blood, reducing the risk of hyperventilation or respiratory alkalosis.
Role in Weaning from Ventilation
SIMV plays an important role in weaning patients off mechanical ventilation, helping them transition back to breathing independently. This mode was developed in the 1970s, gaining popularity for weaning by the 1980s. The core strategy involves gradually reducing the number of mandatory breaths delivered by the ventilator.
As the mandatory breath rate decreases, the patient is encouraged to take on more breathing work. This gradual reduction allows respiratory muscles to strengthen, preparing the patient for full independence. The process can be further supported by adding pressure support to spontaneous breaths, reducing the effort of breathing through the endotracheal tube and ventilator circuit.
The goal of this gradual reduction is to assess the patient’s readiness for extubation, the removal of the breathing tube. By allowing patients to progressively take over breathing, SIMV helps minimize the risk of respiratory failure once the ventilator is removed. This approach maintains reflex control of breathing and helps prevent coordination problems with respiratory muscles during weaning.