Laboratory Analysis is...
discrete measurements of fluids or tissue that has been removed from patient
Monitoring is defined as...
an ongoing process by which clinicians obtain and evaluate dynamic physiological processes in a timely manner (bedside)
Invasive procedures are...
insertion of a monitoring device into a patient
Noninvasive procedures are...
external monitoring without insertion of devices INTO the patient.
What is the benefit to invasive procedures over noninvasive procedures?
Greater accuracy
What is the downfall to invasive procedures?
Greater risk
What situation is noninvasive methods appropriate?
clinical decisions
What do most beside systems to measure FiO2 utilize?
electrochemical principles (O2 analyzers)
Why is the radial artery the most often used site for ABG puncture?
**near surface
**Collateral circulation usually exists
**No large veins nearby
**Radial puncture is RELATIVELY pain free
What can be used if frequent blood sampling is needed?
Arterial cannulation
Possible anatomical sites for blood draws
Brachial
Radial
Femoral
Posterior tibial
Dorsalis pedis
When do you do a modified Allen's test?
Prior to radial puncture ONLY.
What is the normal range for proper collateral circulation? (time wise)
Pink in 5-10 seconds
What should you do if you get a negative reading on the modified Allen's test?
Redo the test on the other hand and if you get another negative call the doctor.
How much blood is needed for an adequate ABG sample?
0.5-1 mL of blood. (usually enough to perform two tests)
Syringe safety precautions...
Do NOT recap the needle without a safety device, handle with both hands, point the needle at people when not performing a puncture, bend/break/remove needles from syringes by hand or dispose of used syringes in anything but an appropriate puncture resista
How is CO2 transported?
45-55 ml of CO2 per 1 dl blood is transported by ionized bicarb, dissolved in plasma, and plasma protein transport.
What is Hemoglobin (Hb or Hgb)
a protein (metalloprotein) with Fe+2 (ferric Iron) made up of globulin chains (2 alpha and 2 beta). Each of these chains have a central structure called the Heme molecule. Hb helps maintain the shape of the RBC. Abnormal Hb will change the shape of the RB
What is the importance of the Heme Molecule in Hb?
Heme molecule contains iron that transports O2 and CO2.
What is responsible for the color of our blood?
The Fe in Hb is responsible for the color of our blood which varies depending on the amount of O2 that is bound to it.
What is Hb measurements expressed as and what is its O2 capacity when compared to what is dissolved in plasma
Always expressed in grams/dl. dl=100 ml. The O2 capacity of Hb is 7x greater than what is dissolved in plasma.
Reasons for drawing an ABG
Sudden, unexplained dyspnea
Acute shortness of breath / tachypnea
Abnormal breath sounds
Cyanosis
Heavy use of accessory muscles
Changes in ventilator settings
CPR
Diffuse infiltrates in chest radiograph
New infiltrates in CXR
Sudden cardiac arrhythmias
A
How do you prevent pre-analytical errors in ABG samples?
Make sure the sample is:
Obtained anaerobically
Properly anticoagulated
Bubbles removed
Analyzed within 10 to 30 minutes
Pressure values for oxygenation
PaO2 (normal = 80-100)
PaO2 60-79 mm Hg = mild hypoxemia
PaO2 40-59 mm Hg = moderate hypoxemia
PaO2 <40 mm Hg = severe hypoxemia
SaO2 (normal = 95-100%)
CaO2 (normal = 18-20 vol%)
What are the benefits of indwelling catheters? (ie. A-Line)
**Provides ready access for blood sampling.
**Allow continuous monitoring of vascular pressures.
What is a downfall of indwelling catheters?
Infection and thrombosis are more likely than intermittent punctures.
What are the site locations for indwelling catheters?
Normal routes are peripheral arteries (radial, brachial, pedal), femoral artery, central vein, and pulmonary artery.
Procedure for initiating indwelling catheterization...
First sample of indwelling catheter would be a waste sample.
what can a good capillary blood gas sample provide and reflect?
estimated arterial oxygenation and PCO2
What value is useless in regards to Capillary blood samples
PO2 and SaO2. (SaO2 must be evaluated via pulse oximetry.
What are common technical errors associated with capillary blood sampling?
inadequate warming and squeezing of puncture site. Squeezing the puncture site may result in venous and lymphatic contamination of sample.
What are secondary values to ABGs that need to be CALCULATED?
Bicarbonate (HCO3-)
Base excess (BE) or deficit
Hemoglobin saturation (HbO2%)
In regards to accurate ABG results what are the components of quality control?
**Record keeping (policies and procedures)
**Performance validation (testing new instrument)
**Preventative maintenance and function checks
**Automated calibration and verification
**Internal statistical quality control
**External quality control (profici
What is Point-of-Care Testing?
Performing blood gas analysis at the patient's bedside.
Why do we use Point-of-Care Testing?
**Reduces turnaround time, thus should improve care and lower costs.
**Used for blood chemistry and hematology parameters.
**Used increasingly in hospitals and physician offices.
Benefits of Point-of-Care Testing...
Reduces turnaround time, thus should improve care and lower costs.
What does transcutaneous monitoring provide?
continuous, noninvasive estimates of PO2 and PCO2 using a skin sensor. Also PtcO2 levels
What are the 2 most important factors influencing accuracy of transcutaneous measurements?
Age and perfusion status
Intra-arterial (In Vivo) continuous blood gas analysis is beneficial because it provides...
Real time monitoring
**Reduction in therapeutic decision making time
**Less blood loss
**Lower infection risk
**Improved accuracy
**Elimination of specimen transport
What does Extra-arterial (Ex Vivo) blood gas analysis provide?
**Eliminates all problems associated with indwelling sensors.
**Provides quick results.
**Determine further justification of costs and patient benefits.
What is the drawback of Ex Vivo blood gas analysis?
Unable to provide real-time continuous data.
How can tissue O2 be measured?
Can be measured by invasive probes-Tissue Oxygen (PtO2) Monitor, inserted directly into organs, tissue, and body fluids.
What can PtO2 monitors indicate?
**Monitor brain tissue oxygen as an early sign of ischemia.
**Monitor adequacy of brain perfusion in patients with traumatic brain injury.
What does oximetry measure?
Hb saturation using spectrophotometry.
Why does Oximetry work?
each substance has its own unique pattern of light absorption. (ie each form of hemoglobin HbO2, HbCO)
What is hemoximetry?
laboratory analytical procedure requiring invasive sampling of arterial blood.
**Measures blood oxygen levels and hemoglobin saturations using a hemoximeter.
**Multiple lights pass through sample to measure multiple hemoglobin species such as HbO2, HbCO,
What is pulse oximetry?
noninvasive monitoring technique performed at bedside.
**Combines principles of spectrophotometry with photoplethysmography.
**Noninvasive portable monitoring device providing estimates of SaO2
**Results are reported as SpO2
**Pulse oximetry uses light ab
What is Tissue oximetry?
noninvasive (TCM) method of measuring saturation of hemoglobin at tissue level.
**Oxygen saturation at tissue level (StO2) assesses adequacy of circulation & oxygen delivery.
**Early detection of low StO2 can be used as an early detection method of tissue
What does capnometry measure?
CO2 in respiratory gasses
**Capnometer functions on basis that CO2 absorbs infrared light proportion to amount of CO2 present.
What is used to measure CO2 levels in capnometry?
Capnometer
What patients usually require capnometry?
patients undergoing general anesthesia or mechanical ventilation.
What are two techniques of capnometry?
1. Mainstream technique places an analysis chamber in patients breathing circuit.
2. Sidestream technique pumps small volume of gas from circuit into nearby analyzer.