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
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
There are a few things to keep in mind when caring for a ventilated patient, regardless of mode.
- The ventilator is not a cure, continuously assess the patient’s ability to wean and patient-ventilator synchrony
- Settings to alter oxygen – FiO2 and PEEP
- Settings to alter carbon dioxide – RR and Vt (thus altering minute ventilation)
- Assess work of breathing by physical exam and be mindful of fatigue
- Respiratory therapists (RT) are the keepers of the ventilator, it is their machine! Nurses should not alter the ventilator settings without notifying the RT.
Responding to alarms is the RT and nurse’s responsibility, notifying RT and/or the clinician of emergent alarms is also the nurse’s responsibility. The first alarm to be aware of is an apnea alarm, which as implied, indicates the patient is not taking any breaths within a set interval. This alarm is important in PSV and CPAP modes.
- Assess for over sedation and fatigue
- Look for a new leak in the ventilator circuit or an accidental disconnect
- Initiate ventilator support (a control mode) – usually the ventilator will do this automatically
- Notify clinician/RT
- If the ventilator is in the backup, controlled mode, it will stay in this mode until the alarm is reset.
Increased RR alarm is indicative of a patient fatiguing on a weaning mode and/or the patient is experiencing pain/anxiety. Most concerning, it could be due to impending shock (increased oxygen demand), worsening lung pathology (increasing dead space), or acidemia (respiratory or metabolic).
- Assess work of breathing and consider increasing sedation/analgesics
- Correct underlying physiologic derangements (especially acidemia)
- Consider switching to a mode with more support
- Notify clinician/RT
Peak pressure alarms are common and can occur with coughing, bronchospasms, increased secretions, condensation in the tubing, pneumothorax, and occlusion of the endotracheal tube (ETT).
- Check a plateau pressure to assess if there is a resistance issue or a compliance issue. More on this HERE
- Suction the patient and remove excess condensation in the tube
- Auscultate the lungs to ensure bilateral lung sounds and identify new/adventitious sounds
- Consider bite block and assess ETT measurement at the teeth
- Consider increasing sedation
- Notify clinician/RT
Low pressure alarms are also very common and indicate a cuff or circuit leak.
- Check all connections between the patient and the ventilator, assess pilot balloon, and consider a cuff leak
- Notify clinician/RT
If equipment failure is suspected, manually ventilate the patient with a bag-valve mask (BVM). At the beginning of each shift it is important to collaborate with your respiratory therapist to ensure alarm parameters are set appropriately based on current settings. Ensure understanding of ventilator alarms and discuss parameters set with respiratory therapy at the beginning of each shift. Know where the 100% FiO2 button is located and do not be afraid to use it.
- A/C mode has a set RR and Vt (or inspiratory pressure paired with inspiratory time in pressure control)
- SIMV mode has a set RR or Vt (or inspiratory pressure paired with inspiratory time in pressure control); any breaths above the set RR are delivered as “pressure support” breaths.
- PSV mode has no RR or Vt set, be mindful of work of breathing. CPAP, unlike PSV, has set inspiratory pressure of zero.
- Settings to alter oxygen are FiO2 and PEEP, to alter carbon dioxide are RR and Vt
- Find the 100% FiO2 button
- If equipment failure is suspected USE A BVM!
- Owens, W. (2018). The Ventilator Book. First Draught Press.
- Pham, T., Brochard, L., & Slutsky, A. (2017). Mechanical ventilation: State of the art. Mayo Clinic Proceedings, 92(9), 1382-1400. Doi: https://doi.org/10.1016/j.mayocp.2017.05.004
Well written and easy to understand.