Ventilator Modes And Tips
VENTILATOR MODES
Assist control: vent delivers a minimum set number of breaths, and patient-initiated breaths trigger fully-assisted vent breaths. Tachypnea can lead to resp alkalosis, breath-stacking, and auto-PEEP
Synchronized Intermittent Mandatory Ventilation: vent delivers a minimum number of supported breaths synchronized with the patient’s efforts. Additional patient-initiated breaths are not vent supported, but the patient must overcome the resistance of the vent circuit during spontaneous breaths. SIMV=AC when patients are not spontaneously breathing.
Pressure support: vent supports patient-initiated breaths with a set inspiratory pressure. Partial vent support sometimes used to evaluate for weaning. Continuous positive airway pressure: patient breathes spontaneously while vent maintains constant airway pressure
Volume Targeted vs. Pressure Targeted
Volume-targeted: vent delivers a set tidal volume, the pressure depends on airway resistance and compliance. The patient remains at risk for barotraumas / volutrauma from high pressures.
Pressure-targeted: vent delivers volume until a set pressure is achieved. Now, tidal volume is dependent on airway resistance and compliance. The patient remains at risk for low tidal volumes and inadequate minute ventilation.
Remaining Variables
1. FiO2: the fraction of inspired oxygen
2. PEEP: positive end-expiratory pressure, to help prevent alveolar collapse and increase oxygenation. Will also increase intrathoracic pressure and decrease preload, usually to a greater degree than its reduction on afterload – MAY decrease cardiac output. Auto-PEEP can occur when the patient has inadequate time to exhale before the next breath is delivered, typically signaled by end-expiratory flow > 0 before the next breath is delivered.
3. Inspiratory time: Normal I:E ratio is ~1:2, but can be controlled on a ventilator, used for the management of obstructive diseases
4. Inspiratory flow rates: usually 60, increased inspiratory flow rates achieve set volume or pressure in a shorter amount of time, and decrease inspiratory time and allowing for a longer expiratory time before the next breath. This can prevent auto-PEEP in obstructive disease and allow better ventilation.
5. Peak inspiratory pressure: determined by airway resistance and compliance.
6. Plateau pressure: pressure at end of inspiration when the flow has ceased, dependent on compliance. Increased plateau pressure suggests decreased compliance
Ventilator TIPS
For Mechanically Ventilated Patients, always know/do the following:
Patient and family education
Date and time ventilatory assistance was started
Ventilator settings, including the following: Fio2, mode of ventilation, Vt, respiratory frequency (total and mandatory), PEEP level, I: E ratio or inspiratory time, PIP, dynamic compliance, and static compliance
Size of Tube
Peak/Plateau Pressure
Arterial blood gas results
Sao2 readings
Reason for initiation of Positive Pressure Ventilation (PPV)
Assessment of pain, interventions, and response to intervention
Patient responses to PPV (including the patient's indication of level of comfort and respiratory symptoms)
Depth of endotracheal tube at the teeth or gum or lip
Hemodynamic values
Vital signs
Respiratory assessment findings
Unexpected outcomes
Nursing interventions
Degree of head elevation
Humidifier change maintenance