Controlled ventilation is a medical intervention that assists or completely takes over a patient’s breathing when they cannot do so adequately on their own. This process involves a machine, known as a mechanical ventilator, which helps move air into and out of the lungs. It is a supportive measure, providing the necessary respiratory function while underlying medical conditions are addressed. Controlled ventilation is used in various critical care settings, including intensive care units (ICUs), operating rooms, and emergency departments.
Understanding Controlled Ventilation
Controlled ventilation involves a mechanical ventilator, a machine that delivers breaths to a patient, either assisting their natural breathing efforts or completely replacing them. This mechanical assistance ensures oxygen reaches the bloodstream and carbon dioxide is effectively removed from the body. The ventilator acts as an external lung, precisely regulating airflow.
There are two primary ways ventilators assist breathing: positive pressure ventilation and negative pressure ventilation. Positive pressure ventilation, the most common method, pushes air into the lungs. Negative pressure ventilation, an older and less common technique, creates a vacuum around the chest to draw air into the lungs, mimicking natural breathing. Positive pressure ventilation is widely used for its versatility and greater control over respiratory parameters.
When Controlled Ventilation is Needed
Controlled ventilation is necessary in situations where the body’s natural ability to breathe is compromised, leading to insufficient oxygen levels or excessive carbon dioxide buildup. Respiratory failure is a common reason, stemming from conditions like pneumonia, chronic obstructive pulmonary disease (COPD) exacerbations, or acute respiratory distress syndrome (ARDS). These conditions can cause fluid to leak into the lungs, making breathing difficult or impossible.
Neurological conditions, such as stroke, traumatic brain injury, or coma, can also impair the brain’s ability to regulate breathing, necessitating ventilatory support.
Patients undergoing major surgeries, especially those requiring general anesthesia, often receive controlled ventilation because anesthesia can suppress spontaneous breathing. Additionally, severe trauma, drug overdoses that depress respiratory function, or conditions like anaphylaxis can lead to a need for mechanical assistance.
How Ventilation is Controlled
Ventilators offer various modes or strategies to control breathing, tailored to the patient’s specific needs. These modes dictate how the machine delivers breaths and interacts with any spontaneous breathing efforts. Key adjustable parameters include respiratory rate, tidal volume, inspiratory pressure, positive end-expiratory pressure (PEEP), and fraction of inspired oxygen (FiO2).
Volume Control (VCV)
Volume Control (VCV) is a mode where a set volume of air, known as tidal volume, is delivered with each breath, regardless of the pressure required. The ventilator adjusts the pressure to ensure this specific volume is delivered consistently. This mode is useful for maintaining precise ventilation and managing carbon dioxide levels.
Pressure Control (PCV)
Pressure Control (PCV) operates differently by delivering a set pressure to the lungs with each breath, allowing the volume of air delivered to vary based on the patient’s lung compliance and airway resistance. This mode can help protect the lungs from excessive pressure, making it a lung-protective strategy. Clinicians set an inspiratory pressure, and the ventilator maintains this pressure for a predetermined inspiratory time.
Synchronized Intermittent Mandatory Ventilation (SIMV)
Synchronized Intermittent Mandatory Ventilation (SIMV) combines controlled breaths with the patient’s spontaneous breathing efforts. The ventilator delivers a set number of mandatory breaths, synchronized with the patient’s own attempts to breathe, while also allowing the patient to take additional breaths on their own. This mode helps maintain respiratory muscle function and promotes a gradual transition towards spontaneous breathing.
Pressure Support Ventilation (PSV)
Pressure Support Ventilation (PSV) is a spontaneous mode where the patient initiates every breath, and the ventilator provides a preset pressure to assist that breath. In PSV, the patient controls their respiratory rate and tidal volume, with the ventilator offering support to make breathing easier. This mode is often used during the weaning process to gradually reduce ventilatory support. Parameters such as respiratory rate, tidal volume, FiO2, and PEEP are carefully managed to optimize oxygenation and carbon dioxide removal.
Goals of Controlled Ventilation
The primary clinical objectives of controlled ventilation are to ensure adequate gas exchange, reduce the patient’s work of breathing, and protect the lungs from further injury. Adequate gas exchange involves ensuring sufficient oxygen reaches the blood to supply the body’s tissues and effectively removing carbon dioxide, a waste product of metabolism.
Reducing the work of breathing allows the patient’s respiratory muscles to rest and recover, which is particularly beneficial in cases of respiratory muscle fatigue. Healthcare providers also aim to minimize ventilator-induced lung injury by carefully managing tidal volumes and pressures, thereby preventing stress and strain on delicate lung tissues.
The Weaning Process
Weaning from mechanical ventilation is the systematic process of gradually reducing and eventually discontinuing ventilatory support as a patient recovers. This transition is carefully managed to ensure the patient can breathe independently and safely.
Healthcare professionals assess a patient’s readiness for weaning daily, looking for improvement in the underlying condition that necessitated ventilation. Common methods include spontaneous breathing trials (SBTs), where the patient breathes with minimal or no ventilator support for a set period.
During SBTs, ventilator settings like pressure support may be lowered to a minimal level. The goal is to safely remove the endotracheal tube once the patient demonstrates sustained spontaneous breathing and their overall condition improves.