PULMONARY DIAGNOSITIC TESTING

Arterial Puncture

puncture of a peripheral artery to obtain an arterial blood gas sample for direct measurement of pH, PaCO2 and PaO2

Indications for blood gas sample

Evaluation of the adequacy of patients ventilations ( PaCO2 ) oxygenation ( PaO2 ) and or acid/ base status ( pH )

• assess the need for therapeutic intervention and or diagnostic evaluation

• monitor the severity and progression of a documented disease processes

Primary sites for obtaining an arterial blood gas

• Radial

• Brachial

• Femoral- if BP is low ( last option )

First choice for abg site

Radial is the first choice om most patients bc of its accessibility and collateral blood flow

The modified allen’s test is

used to assess the collateral circulation in the hand prior to drawing a radial ABG

A positive modified allen’s test confirms

that collateral blood flow is present

• the hand should be pink up within 1-2 seconds after releasing the ulnar artery

Sampling hazards and problems

• disruption of blood flow- hematoma

• clotting

• bleeding

• vessel spasm

• tissue trauma

• anticoagulant therapy ( heparin ) - apply pressure longer to site

• air bubble

• improper cooling

• too much liquid heparin

Air bubbles in ABG cause

• PaCO2 decreases to 0

• PaO2 increases or decreases toward 150 torr

• pH to increase

Improper cooling in ABG cause

• PaCO2 increases

• PaO2 decreases

• pH decreases

Too much liquid heparin in ABG causes

• PaCO2 decreases toward 0

• PaO2 increases or decreases towards room air ( 150 torr )

• pH decreases toward 7.0

In a capillary stick

PO2 values do not correlate well with actual arterial blood. This is especially true when the arterial PO2 is above 60 torr

• Results show a consistent correlation with arterial pH and PCO2

umbilical artery

PO2 may be used to regulate FiO2

Advantages of umbilical artery catheter

• allows continuous monitoring of blood pressure

• arterial samples for ABG and other lab analysis

• blood replacement ( transfusions )

Arterial line

Arterial catheters can be inserted into the radial, brachial or femoral artery to provide continuous monitoring of systemic blood pressure and assess for arterial blood sampling

A transducer is used to to

Convert pressure ( analog signal ) to an electrical signal ( digital signal ) which is measured displayed and recorded by a monitor

Transducer should be level with

the catheter for accurate measurement of pressure

Complications with art line

• thrombosis/embolism

• bleeding

• infection

• hematoma

• arterial spasm

Blood Gas Analyzers

PCO2

partial pressure of carbon dioxide in sample

Blood Gas Analyzers

PO2

partial pressure of oxygen in sample

( clark electrode )

Blood Gas Analyzers

pH

acid base status

( sanz electrode )

Calibration for Blood Gas Analyzer

• calibration is performed by inserting solutions or gases with known values ( one low and one high )

• the machine readings are then calibrated to these known values

• low calibration gas levels and insufficient buffer solution would affect auto-calibration

Typical malfunctions of blood gas analyzers

• electrode or sensor malfunction s

• temp control

• improper calibration

• mechanical problems

• improper sampling technique

Westgard rules

A common set of rules developed to differentiate between random error and true out of control situations

• this method of QC is called the multiple rule method

Quality control charts or levey jennings plots

used to monitor the result of quality control procedures

Proficiency testing

unknown control samples are sent to different laboratories using the same brand and model of analyzer

• the analysis of the data then allows labs to compare heir results to other labs

Multiple machine analysis

Laboratories that have more than one blood gas analyzer can run pt samples on two or more machines to compare the results

• if significant differences occur between machines, the cause of the discrepancy should be investigated

Tonometer

a device that allows precision gas mixtures to be equilibrated with whole blood or a buffer solution. After an equilibration period, the sample is transferred to a blood gas analyzer

Alveolar air equation

PAO2= ( PB- PH2O ) FiO2-PaCO2 divided by R

• calculates the partial pressure of oxygen in the alveoli

R is normally

0.8

PH2O is normally

47 torr

A-a gradient

Measures the difference ( gradient ) between alveolar and arterial PO2

Formula for A-aDO2

PAO2- PaO2

25- 65 torr on 100%

Normal value

66-300 torr

V/Q mismatch

( rec oxygen therapy )

> 300 torr

shunting

( lung problems )

P/F ratio

Ratio of the partial pressure of arterial oxygen to the inspired fractional concentration of oxygen

• used to determination of acute lung injury ( ALI ) or acute resp distress syndrome ( ARDS )

Normal value in P/F ratio

380 torr or greater

A ration less than 300 torr in PF indicates

ALI

• acute lung injury

A ratio less than 200 torr in PF signifies

ARDS

• acute resp distress syndrome

Arterial Oxygen Content ( CaO2 )

Best measurement of oxygen delivered to the tissues, or the best index of oxygen transport

• estimates the oxygen carried by the hemoglobin as well as that dissolved in the plasma

Normal CaO2

17-20%

Normal CVO2

12-16% vol

CVO2 values will decrease when cardaic