Arterial Blood Gases Final Review
An average adult in the supine position should have on PaO2 of what on room air?
90 mm Hg + or - 10
Define Deadspace
Ventilation without perfusion
What relationship does PaO2 have with SaO2?
A direct relationship
What is an advantage of the dissociation portion of the oxy hemoglobin curve?
A large amount of oxygen can be supplied to the tissue by allowing venous PO2 fall below normal levels. Mechanism exists to deliver additional oxygen to the cells if metabolism increases or supply is compromised.
The relationship between dissolved oxygen and PO2 is best described as?
A linear relationship
Air bubble in an ABG sample with PaO2 >160 would cause what to happen?
It will cause a decrease in PaO2.
Define a Systematic Error
Recurrent measurable deviation away from the mean. Trending is an example: with progressive controls increasing or decreasing (4-13B) Shifting: an abrupt change in measurement outcomes.
Explain the difference between acute respiratory failure and chronic respiratory failure?
*Acute respiratory failure:* Is short-term condition. Patient has difficulty breathing and is either hypoxemic PaO2 <60mm Hg, or hypercapnic PaCO2 >50 mm Hg. pH <7.35. *Chronic Respiratory Failure:* Is long-term, and a long-term condition. The patient's airways become narrow or damaged. Chronic respiratory failure can still be classified as hypoxemic or hypercapnic.
Which best describes the PaO2 electrode function to measure PaO2?
*Polarography:* The direct relationship between PO2 and electrical current is true only when specific voltage is initially applied. Proper voltage is determined by polarogram which shows a relationship between voltage and current at a constant with PO2. *Clark Electrode:* Blood is separated from the electrode terminals by a membrane that is permeable to oxygen and good electrical insulator. Oxygen from blood can diffuse easy Terminals are bathed in a phosphate buffer solution with potassium chloride. Sample is warmed to 37C and protected from air.
What is the normal range for [BE]?
0 + or - 2
What is the normal value for dissolved oxygen?
0.003mL of O2/100mL of blood mmHg
Name 4 complications from an arterial blood gas puncture. (Know all 4)
1.) Air emboli 2.) Hematoma 3.) Arteriospasm 4.) Hemorrhage
What are 4 common conditions associated with dead space?
1.) COPD 2.) Pulmonary emboli 3.) Rapid, shallow breathing, (anatomic) 4.) Decreased CO
What are 4 common conditions of a shunt?
1.) Pneumonia 2.) CHF 3.) Congenital Heart disease 4.) Atelectasis
What are three symptoms of respiratory acidosis
1.) SOB 2.) Lethargy 3.) Delirium & confusion
Provide 2 examples of a pre-analytical error
1.) Sample inappropriately drawn or transported. 2.) ABG done on the wrong patient.
Name 3 electrolytes that can be measured from an ABG
1.) Sodium (Na) 2.) Potassium (K) 3.) Chloride (Cl-)
Describe 2 situations where an ABG should be re-drawn/re-ran?
1.) Venous puncture 2.) Time limited exceeded 3.) Not enough sample to do an ABG
What is normal arterial oxygen content?
20%/volume
What is the average value for P50?
26.6 mm Hg
Severe Hypoxemia would indicate?
A PaO2 <45 mm Hg. A pt should NEVER be in this state. Oxygen administration is needed.
Define a Random Error
An error that is characterized by in isolated result outside the control limits.
Why is a steady state crucial in a clinical setting?
Because it can cause inaccurate readings. Which can cause inappropriate treatment.
What is the equation used for Arterial Oxygen Content (CaO2)?
CaO2=[(Hb x 1.34)SaO2]+(0.003 x PaCO2)
Define solubility coefficients
Gases may diffuse freely between liquid and gaseous phases depending on the difference of partial pressure between the 2 phases.
What is the Modified Henderson Equation?
H+= 24 x PaCO2/HCO3
What are the 2 metabolic indices (the factors that determine a metabolic acid -base)?
HCO3 & [BE]
What best describes the PaCO2 electrode function to measure PaCO2?
Is a modified version of the pH electrode. Blood does not come in direct contact with the glass but a CO2 permeable membrane. The other side of the membrane is a bicarbonate solution that is in direct contact with pH sensitive glass. The bicarbonate is also in contact with Silver/ Silver Chloride solution. CO2 diffuses in the bicarbonate solution, known as hydrolysis reaction, resulting in Hydrogen ions and pH change. The pH change is in direct proportion to the PCO2 *Severinghaus electrode*
What is an example of an Internal Quality Control?
Making sure the electrodes are performing without any inconsistencies.
What factors affect the oxyhemoglobin curve?
Most importantly the PaO2. Beyond a PO2 of 60mmHg saturation increase is very slow and does not reach 100% until about 250mmHg. PO2 from 20 to 60mmHg, saturation 35% to 95% PO2 from 60 to 100mmHg, saturation 90% to 97%
[BE] negative would indicate?
Negative [BE], the value would be lower than <0 mEq/L. Metabolic acidosis.
What is the definition of PAO2?
PAO2 is the partial pressure of oxygen in the alveoli. The normal range is 95-100 mm Hg. However, the (normal) average is 100 mm Hg.
What is the proper direction, angel, and bevel position for an arterial blood gas draw?
Opposite of blood flow, 45* angle, bevel up.
How is Henry's law applicable to an ABG?
Oxygen in the air exposed to blood or water, there is an exchange of oxygen molecules between the liquid & gaseous phases until the retrospective partial pressures are equal.
What is the definition of PaO2?
PaO2 is the partial pressure of oxygen inside the arteries. The normal range is 80-100 mm Hg.
Define Shunt
Perfusion without ventilation
[BE] positive would indicate?
Positive [BE] indicates that it's elevated. That means that it is above normal range >2 mEq/L. It would signify metabolic alkalosis.
What is the definition of SaO2?
SaO2 is the saturation of oxygen in the arteries. The normal range is 97-98%. SaO2 is a calculation.
What is the reason to perform an Allen's Test?
The Allen's Test is used to determine the adequacy of ulnar circulation. (Verifies co-lateral circulation).
How is the association portion a defense mechanism?
The PaO2 may decrease substantially while the combination of O2 to hemoglobin will only be slightly decreased. Thus, the decrease in PaO2 observed in high altitude, or during the the aging process, does not significantly decrease the SaO2.
What best describes Association on the oxyhemoglobin curve?
The combination of oxygen with hemoglobin in the lungs. PO2 will increase fro 40 mm Hg in mixed venous blood to approximately 100 mm Hg. End oxygenation loading will occur on the flat/upper portion of the curve; this is known as association.
Dissolved oxygen in the blood can be described as?
The oxygen in the blood is uncombined or free state referred to as dissolved oxygen.
What best describes the Oxyhemoglobin Curve?
The percentage of hemoglobin that actually carries oxygen.
What is a steady state?
The point where the cardiopulmonary system reaches a new equilibrium.
What best describes Dissociation on the oxyhemoglobin curve?
The steep/lower portion of the curve. PaO2 decreases from 100 to 40 mm Hg in the systemic capillaries.
Arterial oxygen content can be best described as?
The total volume of oxygen present in arterial blood (CaO2).
Lung Zone 1 can be defined as?
Theoretically, Zone 1 is an area in the lung where no perfusion is present, because pulmonary arterial pressure is less than alveolar pressure. PA>Pa>Pv
What are the 2 greatest complications of an arterial blood gas draw?
Thrombi & Hemorrhage
What are clinical affects associated with shifting the Oxyhemoglobin curve?
To the left: Increased Hb-O2 Affinity: Hb could easily pick up oxygen. *This can impede off loading* To the right: Decreased Hb-O2 affinity: Enhances tissue delivery.
Does metabolism continue to occur after an ABG is drawn?
Yes
Lung Zone 2 can be defined as?
Zone 2 is a functional area where the flow of perfusion is moderate. Pa>PA>Pv
Lung Zone 3 can be defined as?
Zone 3 is the most "gravity dependent," zone. Blood flow is heavy & relatively constant. Pa>Pv>PA
What is the equivalency of torr to mmHg?
mm Hg and torr are both interchangeable. For example, 1 mm Hg is 1 torr.
What best describes the pH electrode function to measure pH?
pH electrode measures the voltage rather then the current. Requires 4 electrode terminals. A reference solution of a known pH is placed between the 2 terminals. A single pH sensitive glass electrode terminal serves as a common electrode terminal for both the reference and unknown solution. This glass allows Hydrogen ions to diffuse For each pH unit difference between the known and unknown a difference of 61.5mV develops.