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Static Compliance (C S ). Bobbi Jimenez Sue Trapp. C S (ml/cmH 2 O). Compliance- The ability of the alveoli to stretch and accept a volume of air per a given pressure gradient. Air flows from high to low pressures into the lungs. - PowerPoint PPT Presentation
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S
Static Compliance (CS)Bobbi Jimenez
Sue Trapp
CS (ml/cmH2O)
Compliance- The ability of the alveoli to stretch and accept a volume of air per a given pressure gradient. Air flows from high to low pressures into the lungs.
Static compliance is determined during a time of no airflow by finding the plateau pressure.
During an I hold/breath hold, Plateau pressure can be measured. Plateau pressure is the pressure in the alveoli that disperses
through the Pores of Kohn, canals of lambert, and channels of martin when a breath is held.
Compliance vs Elastance
• Compliance in its most general form:• CL= ΔV
ΔP
• Elastance in its most general form:• E= ΔP ΔV
• Elastance opposes compliance; Elastance is the ability to recoil or return to its original position.
Equation
Cs= VtPlateau- PEEP
Compliance’s Role in Ventilation
When the diaphragm contracts, a negative intrapleural pressure of approximately -2cmH2O is generated.
This establishes the pressure gradient for air to flow into the lungs, since the intrapleural pressure is negative compared to atmospheric pressure. Air is a mixture of gases, so it will flow from an area of high to an area of low pressure.
The lungs can then accept a volume of air.Normal Values: 60-100 ml/cmH2O ( on vent) 0.1-0.2 L/cmH2O
More Normal Values
Pediatric patients 40 to 50ml/cmH20 Neonates 10 to 20 mL/cmH20 Static compliance with ventilator circuit: Tubing
compliance varies depending on the type of diameter of tubing used. Typically tubing compensation (Ct) 2 to 3 mL/cmH2O
Cs=Vt-[(plateau-PEEP) x Ct]/(Plateau – PEEP)
Compliance Changes
Decreased Cs Seen in Restrictive Processes:
PNA Pneumothorax Loss of surfactant Pulmonary Edema Atelectasis Pleural Effusions Neuromuscular Diseases
Decreased Cs
Why is Cs decreased with Restrictive Processes? Restrictive process= Volume problem Volume DECREASES Plateau Pressure can INCREASE on vent because the
same amount of delivered Vt is trying to disperse into a smaller volume area.
RESTRICTIVE PROCESSES LEADING TO DECREASED VT AND/OR INCREASED PLATEAU PRESSURES
Cs= VtPlateau- PEEP
We can see that: 1) Plateau=Cs2) Vt= Cs
DECREASED STATIC COMPLIANCE
Compliance Changes
Increased Cs Emphysema
Increased Air-trapping causes increased measured PEEP and greater dispersion of air in alveoli due to loss of elasticity, which causes a drop in plateau pressure.
Cs= VtPlateau- PEEP
We can see that: 1) Vt=Cs2) Plateau=Cs3) Auto-PEEP=Cs
INCREASED STATIC COMPLIANCE
Waveforms
Plateau pressure decreases from Peak pressure as gas dispersion occurs in alveoli
Waveforms
LOW COMPLIANCE= LOW VT HIGH COMPLIANCE= HIGH VT
SLOW RISE TO PEAK PRESSURE AND LOW PLATEAU PRESSURE
QUICK RISE TO HIGH PEAK PRESSURE AND HIGH PLATEAU PRESSURE
AIR-TRAPPING CAN LEAD TO AUTO-PEEP, WHICH INCREASES MEASURED PEEP, WHICH CAN LEAD TO INCREASED Cs, SIMILAR TO WHAT HAPPENS IN EMPHYSEMIC PATIENTS
VOLUME-PRESSURE LOOP
DECREASED COMPLIANCE LEADS TO HIGHER PRESSURES AND DUMPING OF VOLUME SO THAT THE HIGH PRESSURE SETTING IS NOT EXCEDED.
FLOW-VOLUME LOOP
RESTRICITVE PROCESSES LEAD TO DECREASED VT, WHICH CAUSE Cs TO DECREASE.