3.6: 3.6 Ventilator Alarms

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Every ventilator has alarms that are set for the safety of the patient. We have talked a lot about the danger of applying pressure to the fragile alveoli. Using alarms on the ventilator will make sure that the pressures and volumes stay in safe ranges. After setting up your patient and initiating ventilation with your settings, go into your alarm screen and ensure your alarms are appropriate to your settings and patient.

A red siren light that is not currently in use. — Ventilator alarms are a useful tool for keeping you aware of your patient’s status when not present at the bedside. Photo by TBIT, CC0.

The standard alarms that are set for all ventilation modes are as follows:

Table 3.6.1 Ventilator Alarms
Type of Alarm	Alert	Significance
Input Alarms	Loss of electric power	Activated when the power supply is interrupted while the ventilator is on
Input Alarms	Loss of pneumatic power	Activated when either the O₂ or air supply pressure is reduced below a specified point
Control Alarms	The set parameters are incompatible	Activated when operator makes errors in set up
	Part of the self-test failed	Activated during self test prior to initiating ventilation: Ex. Leak in the circuit, or failed flow sensor calibration
	There is something wrong with the ventilator control circuitry	Activated when ventilator microprocessor fails to function (usually alarms “vent inop”)
Output Alarms	Volume Alarms	High and Low Expired Tidal Volume
	Flow Alarms	High and Low Expired Minute Volume
	Time Alarms	High and Low Ventilatory Frequency
		Inappropriate Inspiratory Time
		Inappropriate Expiratory Time
	Pressure Alarms	High and Low Peak Airway Pressure
		High and Low Mean Airway Pressure
		High and Low Baseline Pressure

If you would like additional information about the ventilator alarms listed above, check out Ventilator Alarms in Mechanical Ventilation.

It is important that you ensure your alarms are adequately set for all patients. Do not set your alarms too close to what your normal numbers are. These alarms are your safety net that your patient will not be exposed to volutrauma or barotrauma, but if your alarm ranges are set too tightly, it could cause any patient movement or change to trigger an alarm. Frequent alarms are disturbing for patients as well as the clinician. We also know that if things are alarming too often, it can cause alarm fatigue in healthcare workers and sometimes important alarms can be overlooked. Suggested ranges for alarm settings are below, but always defer to your health centre’s guidance when it differs from these recommendations:

Table 3.6.2: Alarms and their Suggested Settings
Alarm	Suggested Setting	Rationale
High RR	$30\text{ - }35\text{ bpm}$	Patient can wake up or rouse from sedation and increase their RR. This alarm is mostly used for spontaneous modes
High Pressure	$35\text{ cmH}_2\text{O (max)}$ or $+10\text{ cmH}_2\text{O}$ above your Peak Pressure	If this limit is hit, it will cut off the breath that is being delivered. This can be very uncomfortable for the patient and cause coughing and asynchrony. Monitor your pressures carefully and try to stay below $30\text{ cmH}_2\text{O}$ if possible. This is just the maximum limit.
Low Pressure	Set $2\text{ cmH}_2\text{O}$ below PEEP	Not set on every ventilator. It is good for sensing a leak or disconnect in the circuit.
High Volume	$+200\text{ mL}$ from your target volume	Monitor your volumes breath to breath. This alarm is set wide to avoid alarm fatigue. We as clinicians want to monitor our tidal volumes tighter than this when we are present, but this alarm will come into play when clinicians are not present.
Low Volume	$-200\text{ mL}$ from target tidal volume	Not important in control modes. Usually used for spontaneous modes
High Minute Volume	$20\text{ Lpm}$	Set widely on purpose. Usually used in spontaneous modes
Low Minute Volume	$3\text{ - }4\text{ Lpm}$ or $-1\text{ Lpm}$ below the MV reading on the ventilator.	Set widely on purpose. Usually used in spontaneous modes
Apnea time	$20\text{ seconds}$	Standard used in adult patients.