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Patient Spirometry
●
x = Time
●
y =
1. Inspiration
2. Expiration
Compliance
The measurement of pressure and volume allows for the calculation of the lungs’
dynamic compliance - in other words, how well an additional volume enters the lungs
when pressure is exerted on the airway. Compliance describes the extensibility
of the lung-thoracic system but is dominated by alveolar (that is, purely peripheral)
properties.
Typical compliance for adults varies between 35 ml/cmH
2
O and 60 ml/cmH
2
O, and
typical compliance for children is more than 15 ml/cmH
2
O.
Decrease in compliance may indicate too high a PEEP level, acute lung injury, or
increased intra-abdominal pressure (bleeding, ascites). Decreased compliance
indicates a worsening ventilatory status.
Typical compliance
●
x = Paw
●
y = Vol
Low compliance
●
x = Paw
●
y = Vol
Airway resistance (Raw)
Airway resistance expresses the relationship between the pressure difference across
the airway (between the mouth and the alveoli) and the rate at which gas is flowing
through the airway. An increasing airway resistance usually indicates an airway
obstruction and may lead to barotrauma. In critically ill patients, factors causing
increased airway resistance should be identified as quickly as possible to avoid lung
overdistension or decreased oxygen delivery.
NOTE
An endotracheal tube greatly contributes to Raw. The
resistance of the tube is normally higher than that of the
remaining internal airways.
2062971-001 CARESCAPE Modular Monitors 333