Ventilator Basics

The Pre-brief

In a world with amazing respiratory therapists, sometimes ventilator settings fall to the wayside for nurses. Each member of the health care team has a lot of responsibilities and nursing is no exception. But it is important that nurses understand various modes, settings, and alarms for their patients in times of emergencies.

First off, some settings jargon:

Fraction of Inspired Oxygen (FiO2) – percentage of oxygen delivered to the patient
Respiratory Rate (RR) – number of breaths per minute
Tidal Volume (Vt) – volume of air delivered to the lungs with each breath
Positive End Expiratory Pressure (PEEP) – positive pressure that remains in the lungs throughout expiration to keep alveoli open
Minute Ventilation – Vt x RR
Pressure Support Level – inspiratory pressure delivered by the ventilator
I:E ratio – ration of time between inspiration and expiration

MODES

Beginning with most to least supportive settings, starting with assist-control ventilation (A/C mode). A/C mode, a control mode, means the ventilator will deliver controlled breaths. A controlled breath is one where the machine initiates the breath, ends the breath, or both. If the patient breathes over the set RR the ventilator will deliver the preset controlled breath (either Vt in volume control, or the inspiratory pressure for a set inspiratory time in pressure control). The decision to set a Vt or an inspiratory pressure is made based on the patient’s pathophysiology, comfort, goals of ventilation, and clinician preferences. A controlled mode, such as A/C VC mode, is often used immediately after intubation. 

A/C mode Nursing Interventions:

• Assess level of sedation, RR, and Vt (knowing the Vt is especially important in pressure control, since it can change based on lung characteristics as well as patient effort. The Vt may be 500 ml when they are fully awake, but when sedated in PC this could fall precipitously!)
• Notify the clinician of changes in arterial blood gas (ABG) and assessment findings
• Consistently consider weaning the ventilator (according to facility policy)

The next setting, synchronized intermittent mandatory ventilation (SIMV) is similar to A/C mode because it also can provide full respiratory support. The patient receives a set number of mandatory breaths controlled/assisted by the ventilator but is able to breathe spontaneously over that rate. The difference is that in SIMV, when the patient initiates a breath over the set RR, the patient receives pressure support breaths. Again no setting is perfect, in SIMV it is important to assess that the RR is appropriate for the patient and they are not overexerting themselves due to increased work of breathing. This mode has largely fallen out of favor as its benefits are few, and it generally prolongs weaning when compared to pressure support or T-piece (https://criticalcarenow.com/the-landing-is-just-as-important-as-the-take-off-a-closer-look-at-assessing-a-patient-for-extubation/).

SIMV mode Nursing Interventions:

• Assess patient’s work of breathing to ensure appropriate RR and level of support
• If using for weaning, assess sedation levels (ideally minimal) and blood work closely

The final setting, pressure support ventilation (PSV) is the least controlled of the settings. This is often used for patients without cardiac/respiratory pathologies or weaning. PSV, a spontaneous mode of ventilation, provides only set inspiratory pressure, but without a set inspiratory time. The patient determines their own RR, Vt, and I:E ratio. If the patient becomes apneic for a set amount of time the ventilator will switch to a backup controlled mode to provide full ventilatory support.

PSV mode Nursing Interventions:

• Assess patients rate and work of breathing 
• THERE IS NO “automatic” BACKUP RR, but the ventilator will switch to a controlled mode if apnea alarms are triggered. Talk with RT and ensure personal understanding of alarms