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 VTHIGH 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.