Introduction to Ventilator Management

Daniela Gomez Zubieta

Static Ventilator Readouts

Plateau pressure (Pplat): Measured with an end-inspiratory hold (assesses static 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). Should be equal. If not, assess for an air leak 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.

When you first have a ventilated patient, it is helpful 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.

Mode	Settings	Pros	Cons
PRESSURE SUPPORT (PS)
> Used for spontaneous breathing trials and vent weaning since the patient is breathing on their own and triggering breaths. > Like “invasive BiPAP” > PS added to overcome the inherent resistance of the circuit. T– pressure, flow. C– flow. L – pressure	Things you set: PS, PEEP, FiO2 Monitor: Volumes	More comfortable and allows patient to control ventilation.	There is not a guaranteed rate (and thus, no guaranteed minute ventilation)
ASSIST CONTROL – VOLUME CONTROL (AC/VC)
> Patient or ventilator can trigger a breath; the breath is initiated either by patient effort or time (for set ventilator breaths); the inspiratory cycle of the breath ends when a pre-set TV is delivered. T– time, pressure flow C– volume L– volume	Things you set: PEEP, RR, TV, FiO2 Monitor: Pressures	Guarantees a min ventilation and low tidal vol; will limit volutrauma.	Pressure varies; if lungs become less compliant, the pressure needed to deliver set tidal volumes can become dangerously high causing risk of barotrauma
SYNCHRONIZED INTERMITTENT MANDATORY VENTILATION (SIMV)
> Vent provides a set number of breaths at a set TV. Patient can trigger breaths above this rate that are only supported by designated PS/PEEP > The ventilator tries to synchronize w/ patient’s breathing, is “smart” and will not provide double breath	Things you set: RR, TV, PEEP, FiO2, PS (for patient breaths) Monitor: Pressures	May be more comfortable in some patients, allows for spontaneous breathing	Increased work of breathing if patient is tachypneic but not getting adequate TV with patient breaths, breath stacking if async w/ vent, > Numerous RCTs demonstrated that it’s worse for vent weaning – associated with longer weans and fewer liberations
ASSIST CONTROL – PRESSURE CONTROL (AC/PC)
> Patient or ventilator can trigger breaths. All breaths supported. Breaths are delivered as set pressure (inspiratory pressure) over set time (inspiratory time). The breath is cycled when the preset inspiratory time is reached > Use volume like “vital sign”	Things you set: RR, IP, PEEP, FiO2, Inspiratory time Monitor: Volume	Vent maintains a constant pressure during inspiration (flow decreases as the lungs fill with air) > theoretically better for oxygenation - maintains a more consistent mean airway pressure, limits barotrauma	TV, and therefore, MV is not guaranteed, requires close monitoring as TV and MV may drop if lung compliance decreases (need to increase low MV alarm threshold manually)
PRESSURE REGULATED VOLUME CONTROL (PRVC)
> Attempts to reach a set volume by adjusting the pressure (same triggers as AC/VC) > Vent will average the preceding few breaths to try and deliver a desired tidal volume at the lowest possible pressure	Things you set: RR, TV, PEEP, FiO2 Monitor: Pressure and volume	Tries to limit both volutrauma and barotrauma	If conflict between the VC and PC aspects (e.g. ARDS), PC will supersede - cannot guarantee MV. The more work the patient does, the less the ventilator does and patients may be prone to ‘tiring out’ – should monitor PCO2 with blood gases
AIRWAY PRESSURE RELEASE VENTILATION (APRV) / BILEVEL
> 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	Things you set: P_high, P_low (PEEP), T_high, T_low, FiO2 Monitor: Volumes and gas exchange	Used for refractory hypoxemia - increases mean airway pressure and alveolar recruitment	Does not guarantee MV, risk of air trapping and hyperinflation due to auto-PEEP and breath-stacking, often difficult to ventilate patients

ALARM TYPE: High Peak Pressure

What is causing the alarm?

Dynamic compliance issue (resistance of the circuit when there is air flowing)
vs.
Static compliance issue (stretch of the lung or chest - doesn’t change
with airflow).

Troubleshooting:

Step 1: Check plateau pressure by performing inspiratory hold. Must be in VC mode.
High Peak and Low Plateau: Dynamic compliance issue à High Resistance.
- Work outside -> in:
  - Check if pt is biting on the ETT
  - In-line suction to check for/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 à give bronchodilators.
High Peak and High Plateau: Static compliance issue à Worsening alveolar or chest wall rigidity 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 o STAT CXR, b-lines on US, tracheal aspirate, bronchoscopy, etc.

ALARM TYPE: Low Tidal Volume/Low Minute Ventilation (VE)

What is causing the alarm?

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.

Troubleshooting:

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 à sometimes need to do an ETT exchange.
Ensure ETT not high or out.
Airleak through chest tube / bronchopleural fistula

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.

ALARM TYPE: Apnea

What is causing the alarm?

No breaths are being triggered by the vent, which means the patient Is NOT breathing.

Troubleshooting:

***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.