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Short Self Test (SST)
ments, the ventilator then enters the exhalation phase and waits for the detection of patient inspiratory effort, a manual inspiration, or apnea detection.
10.12
Apnea Ventilation
When a patient stops breathing or is no longer being ventilated, it is called
apnea. When apnea is detected by the ventilator the ventilator alarms and
delivers apnea ventilation according to the current apnea ventilation settings.
10.12.1
Apnea Detection
The ventilator declares apnea when no breath has been delivered by the time
the operator-selected apnea interval elapses, plus a small increment of time
(350 ms). This increment allows time for a patient who has begun to initiate a
breath to trigger inspiration and prevent the ventilator from declaring apnea
when the apnea interval is equal to the breath period.
The apnea timer resets whenever an inspiration begins, regardless of whether
the inspiration is patient-triggered, ventilator-triggered, or operator-initiated.
The ventilator then sets a new apnea interval beginning from the start of the
current inspiration. To hold off apnea ventilation, another inspiration must be
delivered before (the current apnea interval + 350 ms) elapses. Apnea detection is suspended during a disconnect, occlusion, or safety valve open (SVO)
state.
Apnea is not declared when the apnea interval setting equals or exceeds the
breath period. For example, if the respiratory rate setting is 4/min, an apnea
interval of 15 s or more means apnea cannot be detected. The ventilator bases
apnea detection on inspiratory (not expiratory) flow, and allows detection of a
disconnect or occlusion during apnea ventilation. Apnea detection is designed
to accommodate interruptions to the typical breathing pattern due to other
ventilator features that temporarily extend the inspiratory or expiratory intervals (rate changes, for example) but still detect a true apnea event.
The following figure shows an apnea breath where TA equals the breath
period.
Operator’s Manual
10-41