Static Compliance (C S )

1. Static Compliance (CS) Bobbi Jimenez Sue Trapp

2. 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.

3. 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.

4. Equation • Cs= Vt Plateau- PEEP

5. 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

6. 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)

7. Compliance Changes • Decreased Cs • Seen in Restrictive Processes: • PNA • Pneumothorax • Loss of surfactant • Pulmonary Edema • Atelectasis • Pleural Effusions • Neuromuscular Diseases

8. 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.

9. RESTRICTIVE PROCESSES LEADING TO DECREASED VT AND/OR INCREASED PLATEAU PRESSURES

10. DECREASED STATIC COMPLIANCE Cs= Vt Plateau- PEEP We can see that: 1) Plateau=Cs 2) Vt= Cs

11. 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.

12. INCREASED STATIC COMPLIANCE Cs= Vt Plateau- PEEP We can see that: 1) Vt=Cs 2) Plateau=Cs 3) Auto-PEEP=Cs

13. Waveforms Plateau pressure decreases from Peak pressure as gas dispersion occurs in alveoli

14. Waveforms LOW COMPLIANCE= LOW VT HIGH COMPLIANCE= HIGH VT

15. SLOW RISE TO PEAK PRESSURE AND LOW PLATEAU PRESSURE QUICK RISE TO HIGH PEAK PRESSURE AND HIGH PLATEAU PRESSURE

17. AIR-TRAPPING CAN LEAD TO AUTO-PEEP, WHICH INCREASES MEASURED PEEP, WHICH CAN LEAD TO INCREASED Cs, SIMILAR TO WHAT HAPPENS IN EMPHYSEMIC PATIENTS

18. VOLUME-PRESSURE LOOP DECREASED COMPLIANCE LEADS TO HIGHER PRESSURES AND DUMPING OF VOLUME SO THAT THE HIGH PRESSURE SETTING IS NOT EXCEDED.

19. FLOW-VOLUME LOOP RESTRICITVE PROCESSES LEAD TO DECREASED VT, WHICH CAUSE Cs TO DECREASE.