RCP 100 - ABG Analysis and Monitoring of Gas Exchange

• Analysis and monitoring focuses on gas exchange

What to Record

• Date, Time and Site should be recorded
• Results of the Modified Allen Test should be recorded
• Patients body temperature, position, activity level and respiratory rate (RR) should be recorded
• FiO2 and/or all ventilator settings should be recorded
• Recording all of the above will aid in interpreting the results

Clinical Scenario

• A respiratory therapist (RT) changed Mr. Hampton from a 2L NC to a 6L Simple Mask
• Mr. Hampton was admitted for pneumonia without a prior lung history
• Arterial blood gas (ABG) analysis is required to asses the situation

Oxygenation Status

• PaO2 represents the partial pressure of O2 dissolved in the plasma of the arterial blood, reflecting gas exchange between the lung and the blood
• PaO2 levels are categorized as mild, moderate, or severe
• SaO2 represents the degree to which hemoglobin is saturated with O2
• CaO2 represents the content of O2 in arterial blood, based on the amount of Hb present and its saturation level

Acid-Base Status

• Determined by:
  • pH
  • PaCO2
  • HCO3

Clinical Indications for Gas Exchange Analysis

• Sudden, unexplained dyspnea
• Cyanosis
• Abnormal breath sounds
• Severe, unexplained tachypnea
• Heavy use of accessory muscles
• Changes in ventilator settings
• Cardiopulmonary resuscitation (CPR)
• Acute hypotension
• Acute deterioration in neurologic function

Arterial Line

• Used to measure the indications of gas exchange

Analyzing Blood Gases

• The primary parameters of pH, PCO2, and PO2 are measured using a blood gas analyzer
• Secondary values such as HCO3, BE/BD, and Hb Saturation are computed from these primary values
• Actual measurement of total Hb saturation, Methemoglobin, or Carboxyhemoglobin requires a special analyzer

Electrochemical O2 Analyzers

• Utilize a Polargraphic electrode (Clark electrode) which includes a battery
• Galvanic fuel cell analyzers do not have batteries and create their own current
• Galvanic analyzers do not have batteries, and generates its own current
• Polargraphic analyzers rely on an O2 mediated chemical reaction to produce a current from a Clark electrode, resulting in a faster response due to the battery
• Temperature and pressure increase and humidity and altitude decrease affect both types of analyzers and require recalibration

Analyzing Blood Gases continued

• The Clark polarographic electrode is used by blood gas analyzers to measure PO2
• The Sanz electrode is used to measure pH
• The Servinghaus electrode is used to measure CO2

Quality Control

• QC processes are more detailed than automatic QC
• Control media analysis results are plotted on a graph
• Results are compared with statistically derived limits, typically within ± 2 standard deviations (SD)
• Results falling outside these limits indicate analytic error which can be random or systemic

Point of Care Testing

• Moves blood gas analysis from the lab to the patient's bedside
• Enables quicker diagnosis and treatment
• Can measure chemistry, hematology, LA, PT, PTT, and troponin levels
• Requires testing within 1-2 minutes
• Uses a disposable cartridge

Transcutaneous Blood Gas Monitoring

• Provides continuous, noninvasive estimates of arterial PO2 and PCO2 through a surface skin sensor
• Heats the skin, similar to capillary gas measurement
• Primarily used with babies

Pulse Oximetry

• Measures blood Hb saturations using spectrophotometry
• Combines spectrophotometry and photoplethysmography called POX
• Utilizes one red light (660 nm) and one infrared light (940 nm)
• Is unreliable when SpO2 is less than 80%
• Appropriate alarms should be set