Lung Characteristics

Question 1

Lung Characteristics

Answer 1

-The Two primary characteristics of the lungs are compliance and resistance

-These two important parameters are evaluated for pts receiving mechanical ventilation

Question 2

Compliance

Answer 2

-The compliance of any structure in the relative ease with which the structure distends ( the ease of inflation)

-An old balloon that is easy to inflate us very compliant (increased compliance) and brand new balloon that has neer been inflated and harder to blow up would be considered non compliant (decreased compliance)

-Pulmonary physiology uses the term compliance to describe the elastic forces that oppose lung inflation

-C= Change in volume / change in pressure

-Volume is typically is measured in liters and milliliters and pressure is measured in centimeters of water( cmH20)

Question 3

Compliance Measurments

Answer 3

-In an spontaneously breathing individuals, the compliance is about 50-170 ml/ cmH20 or 0.05-.17 L/ cm H20

-For intubated and mechanically ventilated pts with normal lungs and normal chest wall, compliance varies from 40-50 ml/cmH20 in males and 35-45 ml/cmH20 in females

-Monitoring of change in compliance is a valuable means of assessing changes in the pts condition during mechanical ventilatory support

-Because compliance usually is measured under conditions of no gas flow, it is referred to as static compliance or static effective compliance

Question 4

Lung and Chest Walls Effect on Compliance

Answer 4

-Changes in the condition of the lungs or chest wall (or both) affect total respiratory system compliance and the pressure required to inflate the lungs

-Diseases that reduce the compliance of the lungs or chest wall increase the pressure required to inflate the lungs

-Ards is an example of such a disease

-Conversely, emphysema is an example of a pulmonary problems that leads to increased compliance

-With emphysema, less pressure is required to inflate the lungs

	-Because of the loss of elasticity in their lungs ( barrel chest)

Question 5

compliance calculation

Answer 5

-For Pt on mechanically ventilatory support, compliance calculates use the plateau pressure measured at static, or no flow, conditions

-Cst= Vt/ Pplat-PEEP

	-Vt=Tidal Volume

-Cst is expressed at ml/cmH20 or L/cmH20

Question 6

Compliance Examples

Answer 6

-Your male pt is on a tidal volume (VT0 of 500 ml with a Pplat of 25 cmH20 and 0 PEEP. What is the effective Cst?

- Answer 500/25-0 = 20ml/cmH20

Question 7

Dynamic Compliance

Answer 7

-Often called dynamic compliance or dynamic effective compliance

-The volume delivered by the ventilator divided by (PIP-PEEP)

-Cdyn is measured during airflow, therefore it is infused by the pts lung and chest all elastic recoil and by airway resistance, the ET, and the vent circuit

-The difference between static compliance and dynamic compliance is that the static compliance is telling you what the compliance is of the lungs itself, the dynamic cominace is tha compliance of the lungs plus the thorax (chest wall)

-Dynamic compliance should be less than static compliance

-Formula; Cdyn=Vt/ Ppeak-PEEP

Question 8

Airway resistance

Answer 8

-During Mechanical ventilation, airway resistance (Raw) is the factor most often evaluated

-The ability of air to flow through the conductive airways depends on the gas viscosity, the gas density, the length and diameter of the tube, and the flow of the gas through the tube

-In clinical situations, viscosity, density, and tube or airway length remain fairly constant. Careful attention is paid to the diameter of the airway lumen and the flow of the gas

-The diameter of the airway lumen and the flow of gas into the lungs can decrease as a result of bronchospasm, increased secretions, mucosal edema, or kinks in the endotracheal tube. The rate at which the gas flows knot the lungs can be controlled on most mechanical ventilators

Question 9

Airway Resistance equation

Answer 9

-The relationship of gas flow, pressure, and resistance in the airways is described by the equation for airway resistance

-Raw= (PIP-Ppat)/flow

-Raw is usually expressed in centimeters of water pressure per liter per second( cmH20/L/sec)

-In normal individuals, Raw is about .6-2.4cmH20/L/sec

-With an artificial airway in place,normal airway resistance is increased. The smaller internal diameter of the tube creates greater resistance to the flow , approximately 6 cmH20/L/sec

Question 10

Airway resistance Diseases

Answer 10

-Diseases in the airway can also increase resistance. In non intubated subjects with emphysema and asthma, resistance may range from 13-18 cmH20/L/sec. Still higher values can occur with other server types of obstructive disorders

-The disadvantage of higher airway resistance to breath is obvious. With higher resistance, more of the pressure for breathing goes to the airways and not the alveoli. With less pressure in the alveolus, a smaller volume of gas is available for gas exchange

-Another disadvantage of high resistance is that more force must be exerted to try to get the gas to flow through the obstructed airways.	

-To achieve this force, the vent excerpts more pressure to try to Blow the air into the pts lungs through obstructed airways of through small endotracheal tube

Question 11

Measure Raw

Answer 11

-Raw= (PIP-Pplat0/Flow

-Example: the PTs peak pressure is 40cmH20, plateau pressure is 25 smH20, and the flow rate is 60 Liters/minute

40-25/60mlp

Covert 60 minutes into sec so 60/60 is 1 15/1= 15

Question 12

Higher intubated RAW values

Answer 12

-For an intubated pt, this previous example produces a high value for RAW

-This may be due to:

	-Increased secretions

	-Mucosal edema

	-Bronchospasm

	-An endotracheal tube that is too small

-The therapist should take cate to listen to breath sounds and determine the possible cause of the increased resistance