Introduction to Vent Management
Seth Alexander
Ventilator Settings
Trigger: what initiates a breath; time, flow, or pressure
- Patient-initiated triggers are flow and pressure
- Ventilator breaths are triggered by time
Cycle:
Mode | You set | Not set | Comments |
|---|---|---|---|
| Pressure support (PS) | PEEP PS above PEEP FiO2 | TV RR Inspiratory flow | Used for spontaneous breathing trials (see intubation and extubation) and vent weaning Patient is breathing on their own and will trigger each breath, setting their own flow, RR and TV PS added to overcome the inherent resistance of the circuit |
| Volume Control (AC/VC) | PEEP RR TV Inspiratory flow FiO2 | Inspiratory pressure | Patient or ventilator can trigger a breath; the breath is initiated when a preset tidal volume is delivered Pros: Guarantees a minute ventilation and low tidal volume; will limit volutrauma Cons: Pressure varies and may lead to lower mean airway pressure and thus less alveolar recruitment; if lungs become less compliant, the pressure needed to deliver set tidal volumes can become dangerously high causing risk of barotrauma |
SIMV Synchronized Intermittent Mandatory Ventilation | PEEP RR FiO2 If vent triggered breaths, TV If pt triggered breaths, PS above PEEP | Vent provides a set number of breaths at a set tidal volume. Patient can trigger breaths above this rate that are only supported by designated PS/PEEP (no set TV) The ventilator tries to synchronize with the patient’s breathing effort Pros: more comfortable, allows for spontaneous breathing Cons: Increased work of breathing if patient is tachypneic but not getting adequate TV with spont breaths, breath stacking if async w vent, does not guarantee MV Numerous RCTs demonstrated that it’s worse for vent weaning, associated with longer weans and fewer liberations | |
| APRV / Bilevel | PEEP (PLow) Pressure High Time Low Time High FiO2 | TV | The ventilator cycles between P(high) and P(low) based on preset times but the patient is allowed to breathe spontaneously at any time Usually, long periods of inspiratory holds with brief expirations Pros: Used for refractory hypoxemia - increases mean airway pressure and alveolar recruitment Cons: Does not guarantee MV, risk of air trapping and hyperinflation due to auto-PEEP and breath-stacking, often difficult to ventilate patients |
Static Ventilator Readouts
- Plateau pressure (Pplat): Measured with an inspiratory hold (assesses lung compliance)
- Auto-PEEP: Measured with an expiratory hold; occurs when volume of previous breath is not entirely expelled before the next breath is initiated
Dynamic Ventilator Readouts
- Measured RR: In most modes, patients may trigger breaths more frequently than the set RR; if set and measured RR match, consider ↓ respiratory drive (sedation, neurologic injury) or iatrogenic over-ventilation
- Tidal volume of inspiration (VTi) and expiration (VTe)
- VTi should approximately equal VTe. If not, then assess for an air leak (e.g. cuff leak or pneumothorax) or auto-PEEP
- Minute ventilation: calculated from VTe x RR; higher MV = more CO2 clearance
- Peak (Inspiratory) pressure (PIP): Highest pressure reached in the entire ventilator cycle
Critical non-ventilator hemodynamic readouts
- SpO2: If poor waveform or discordant with measured PaO2, exchange the probe or consider serial ABGs
- HR: Can be an indicator of emergencies such as pneumothorax, PE, ventilator disconnection
- Blood pressure: Positive pressure ventilation decreases preload and has mixed effects on afterload (pulmonary vascular resistance vs. systemic afterload) by altering intrathoracic pressure gradients.
- Depending on the patient’s pathophysiology, increases in positive pressure may be detrimental or beneficial for BP
It is helpful, when you first have a ventilated patient, to review the equipment that makes up the “circuit” from the ventilator to the patient and back with an RT or bedside nurse.
Key things to know: How to inline suction, perform an inspiratory hold, reconnect/disconnect the circuit to the ETT if needing to bag the patient, etc.
Troubleshooting vent alarms
Alarm type | What is causing the alarm? | Troubleshooting |
|---|---|---|
| High Peak Pressure | Dynamic compliance issue (resistance of the circuit when there is air flowing)vs. Static compliance issue (stretch of the lung - doesn’t change with airflow) | Step 1: Check plateau pressure by performing inspiratory hold. Must be in VC mode. High Peak and Low Plateau: Dynamic compliance issue -> High Resistance Work outside -> in Check if pt is biting on the ETT Incline suction to clear secretions or proximal mucous plug Check circuit tubing for excess water condensation, mucous plug, or a kink. Ask RT to disconnect and clear circuit Auscultate for wheezing/stridor to indicate bronchospasm or obstruction -> give bronchodilators High Peak and Low Plateau: Static compliance issue -> Worsening alveolar process Emergencies: tension PTX, mainstem intubation Work outside -> in Obesity/chest wall rigidity Abdominal Compartment syndrome/ascites Single Lung: mucous plug, large pleural effusion/atelectasis Worsening alveolar process - pulmonary edema, PNA, DAH, ARDS - CXR, b-lines on US, tracheal aspirate, bronchoscopy, etc. |
| Low Tidal Volume/Low Minute Ventilation (VE) | Patient is not getting the desired (set) tidal volume/VE. The alarm reports exhaled VE. This may cause inadequate ventilation, CO2 retention, and potentially hypoxia. | 1. Put patient back on VC, assess for high peak pressures (-> low volume in certain vent modes) 2. Compare inspiratory tidal volumes (Vti) with expiratory tidal volumes (Vte) on the ventilator. If Vti>Vte, check for a leak in the system Check circuit for connection leaks w RT Listen for a cuff leak - can have RT check a cuff pressure and if low re-inflate -> sometimes need to do an ETT exchange Ensure ETT not high or out 3. Consider disconnecting vent and bagging pt If normal resistance: Leak in ventilator, tubing, or Y-adapter If low resistance: Cuff leak, ETT above cords, or bronchopleural fistula If low tidal volumes and no leak (ie. Vti = Vte) and RR WNL Patient may need more support (i.e. switching to a different vent mode (PS to PRVC)). Discuss with RT or fellow If low RR and no leak and Vt at goal Patient may be over-sedated May need to increase set/back-up ventilator respiratory rate |
| Apnea | No breaths are being triggered by the vent… in other words, your pt is NOT breathing -> this is an emergency… | ***Check that the patient hasn’t self-extubated, their trach hasn’t fallen out, or they haven’t been unhooked from vent*** If self-extubated or tracheostomy decannulated, then immediately start bagging the pt (may need to bag from trach stoma if s/p laryngectomy) Have nurse call staff assist for re-intubation if necessary or have trach team called to replace a fresh (<7 days old) trach |