Target Alveolar Ventilation; Intelligent Backup Rate (Ibr) - ResMed AirCurve 10 ST-A Clinical Manual

Target alveolar ventilation

iVAPS targets alveolar ventilation. Alveolar ventilation was chosen because gas exchange occurs at
the alveoli level. Total ventilation includes the ventilation devoted to the conducting airways,
whereas alveolar ventilation best represents the useful portion of ventilation that reaches the alveoli.
Alveolar ventilation cannot be measured directly, so iVAPS estimates it using a height approximated
value of anatomical deadspace as shown in the graph below. Anatomic deadspace is the amount of
breath that remains in the conducting airways, that does not reach alveoli and does not contribute to
gas exchange. Its contribution is proportional to breath rate. By using alveolar ventilation as a servo-
ventilation target, as opposed to tidal volume or minute ventilation, the effect of respiratory rate
change on effective ventilation is negated.

intelligent Backup Rate (iBR)

ST and iVAPS modes only
Instead of mandating a fixed backup rate, the intelligent Backup Rate (iBR) will shift automatically
between two limits.
During sustained apnoea, the iBR will adopt a pre-configured Target Patient Rate. This Target Patient
Rate defines the upper boundary for iBR. Set the Target Patient Rate to match the patient's average
spontaneous rate (unlike a traditional backup rate).
During spontaneous ventilation, the iBR adjusts to remain in the background, at two-thirds of the
Target Patient Rate. This 'background' backup rate is lower than a traditional S/T rate, so gives the
patient maximum opportunity to spontaneously trigger.
When spontaneous triggering ceases (eg, at the onset of an apnoea/hypopnoea), the iBR adjusts
from its background frequency to its Target Patient Rate in iVAPS mode and adjusts quickest (within
4 to 5 breaths) when ventilation is below the target ventilation. In ST mode, iBR adjusts to the
Target Patient Rate at a fixed 5 breaths.
A single spontaneous triggered breath resets the iBR to its background rate (two-thirds of Target
Patient Rate).
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