Intro to mechanical Ventilation pt 2

Mechanical Ventilation Operating Modes

• Mechanical ventilation modes are defined as sets of operating characteristics controlling ventilator function.
• Breath delivery options are referred to as ventilation modes.
• Ventilator modes are often combined to achieve desired effects (e.g., spontaneous plus PEEP = CPAP).
• Modes are described by how the ventilator is triggered or cycled, including variables limited during inspiration and whether modes permit mandatory, supported, or spontaneous breaths (or a combination).

Basic Operating Modes

• Controlled Mechanical Ventilation (CMV): The ventilator delivers a preset tidal volume at a set interval. Use only when the patient is sedated and/or has neuromuscular blockade. Patients cannot spontaneously breathe.
• Assist-Control Ventilation (A/C): The patient always receives a mechanical breath, triggered by either the ventilator or the patient (spontaneous breaths allowed). Full ventilatory support. Useful when a patient has a stable respiratory drive (10-12 breaths per minute).
• Intermittent Mandatory Ventilation (IMV): The patient can breathe spontaneously at any tidal volume between the delivered mechanical breaths. The primary disadvantage is possible breath stacking. Using this mode carefully sets the high-pressure limit to reduce barotrauma.
• Synchronized Intermittent Mandatory Ventilation (SIMV): Mandatory breaths are synchronized with spontaneous patient efforts to prevent breath stacking. SIMV has largely replaced IMV. A "synchronized window" is the time before the ventilator responds to spontaneous efforts.
• Pressure Support Ventilation (PSV): Used to reduce work of breathing and augment the patient's spontaneous tidal volume. When used with SIMV, this lowers oxygen consumption. This mode involves a preset pressure plateau during spontaneous breaths, is patient-triggered, pressure limited and flow-cycled. This aides overcoming resistance of artificial airways.
• Pressure-Controlled Ventilation (PCV): Pressure-controlled breaths are time triggered based on a preset respiratory rate. Inspiration starts with a pressure plateau, sustained for a set length of time. This mode is particularly useful for patients with acute respiratory distress syndrome (ARDS) or stiff lungs (low compliance) where excessive pressure is needed in volume-cycled modes to ventilate, potentially leading to barotrauma.

Adjuncts to ventilation modes

• Pressure Support (PS): A parameter added to various modes to lower the work of breathing and potentially augment spontaneous tidal volumes.
• Positive End Expiratory Pressure (PEEP): A parameter used in various modes to increase end-expiratory or baseline airway pressure above atmospheric pressure. It improves oxygenation for patients with refractory hypoxia, particularly in situations where functional residual capacity and lung compliance are reduced. PEEP is not a stand-alone mode but is used with other modes.

Spontaneous Breathing

• Spontaneously breathing and not a mode, since rate and tidal volume are self-determined by the patient (though ventilators can provide support).
• Apnea ventilation is a safety measure for patients in spontaneous breathing mode, providing breaths at a preset rate if the patient stops breathing.
• With PEEP, this becomes CPAP.

Inverse Ratio Ventilation (IRV)

• IRV uses a longer inspiratory time compared to the expiratory time (I:E ratio).
• IRV improves oxygenation by decreasing intrapulmonary shunting, improving V/Q matching, and decreasing deadspace ventilation.
• Two notable changes of IRV are increased mean airway pressure and auto-PEEP.

Alarm Fatigue

• Alarm fatigue is a risk across the entire hospital, triggered by numerous alarms from various devices, including IV pumps, ventilators, etc.
• The repeated and consistent exposure to alarms can lead healthcare workers to ignore them.
• Respond appropriately to alarms and be perceptive about potential concerns.

Alarms

• Alarms can be visual or audible, or both, including colored lights, messages, and input/output signaling. Input alarms include power issues for ventilation equipment, while control alarms signal malfunctions in mode settings. Output alarms monitor parameters, especially pressure and volume delivery. Consider important indicators such as inspired gas temperature, FiO2, etc.

Additional Considerations

• Complications of PEEP: Decreased venous return and cardiac output, barotrauma, increased intracranial pressure (especially important in patients with normal lung compliance), alterations in renal function and water metabolism.
• Barotrauma: Lung injuries caused by alveolar over-inflation beyond the rupture point. This is a concern with high pressures and PEEP.
• Increased intracranial pressure: High PEEP levels can increase pressure if the patient has normal compliance. But for patients with ARDS or non-compliant lungs, it has minimal effect.
• Renal response to PEEP: PEEP can cause fluid retention, affecting urine output and other renal indicators. There can be potential issues with ADH and blood redistribution impacting creatinine clearance and sodium excretion.

Test your understanding of the various operating modes of mechanical ventilation. This quiz covers key concepts, definitions, and the specific characteristics of modes like Controlled Mechanical Ventilation and Assist-Control Ventilation. Perfect for healthcare professionals and students in respiratory therapy.