Blood Gases 1 Flashcards
Arterial/venous blood gases/ Circuit arterial/venous blood gases are an invaluable tool in assessingthe following 3 things?
- ventilation
- acid-base balance
- oxygenation
Arterial Blood Gas It is an invasive procedure, it helps to differentiate oxygen deficiencies from
primary ventilatory deficiencies from
primary metabolic acid-base abnormalities
PaO2
partial pressure of oxygen dissolved in the plasma only. 90 - 100
SaO2
measured degree to which oxygen is bound to hemoglobin.
> 95%
PaCO2
-partial pressure of carbon dioxide dissolved in the plasma. - The rest is inside the red blood cells on a hemoglobin molecule 35 - 45
HCO3
Bicarbonate buffer 24 + or - 2
pH
Negative logarithm of the number of hydrogen ions (H+) in a solution, expressed as a number between 1 and 14 7.35 - 7.45
BE
Base Excess (-2) - (+2)
Acid/Base Relationship is critical for homeostasis, Significant deviations from normal pH ranges are
poorly tolerated and may be life threatening
Acid/Base Relationship is Achieved by ?
Respiratory and Renal systems
There are two buffers that work in pairs that are linked to the Respiratory and Renal compensatory system
H2CO3 Carbonic acid NaHCO3 base bicarbonate
Respiratory Component
H2CO3 Carbonic acid CO2 + H2O = H2CO3
Approximately 98% normal metabolites are in the form of ?
CO2
Metabolic Component Function of the kidneys
Na HCO3 base bicarbonate
carbonic anhydrase
an enzyme that accelerates hydration/dehydration CO2 in renal epithelial cells
active exchange of Na+ for H+ happens between the ____ ___ and the _____ ______.
tubularcells and glomerular filtrate
6 Normal ABG values
pH 7.35 – 7.45 PCO2 35 – 45 mmHg PO2 80 – 100 mmHg HCO3 22 – 26 mmol/L BE -2 - +2 SaO2 >95%
pH < 7.35 PCO2 > 45 HCO3 < 22
Acidosis
pH > 7.45 PCO2 < 35 HCO3 > 26
Alkalosis
Think of CO2 as an acid, failure of the lungs to exhale adequate CO2 results in what ?
Respiratory Acidosis
pH < 7.35 PCO2 > 45
Respiratory Acidosis
CO2 + H2CO3 =
decrease in pH
5 Non CPB Causes of Respiratory Acidosis
- emphysema - drug overdose - narcosis - respiratory arrest - airway obstruction
2 Causes of Respiratory Acidosis while on CPB?
- Gas flow rate - Sweep rate
5 Non CPB Causes of Metabolic Acidosis
- renal failure - diabetic ketoacidosis - lactic acidosis - excessive diarrhea - cardiac arrest
1 Cause of Metabolic Acidosis while on CPB?
Poor perfusion
too much CO2 exhaled (hyperventilation) causes what ?
Respiratory Alkalosis
pH > 7.45 PCO2 < 35
Respiratory Alkalosis
What are 6 Causes of Respiratory Alkalosis
- hyperventilation - panic d/o - pain - pregnancy - acute anemia - salicylate overdose
pH > 7.45 HCO3 > 26
Metabolic Alkalosis
3 Causes of Metabolic Alkalosis Non CPB ?
• Increase loss of acid from stomach or kidney • hypokalemia • excessive alkali intake Tums overdose
1 cause of Metabolic Alkalosis while on CPB?
Too much Bicarb
Step 1 in ABG interpretation, Examine the PaO2 & SaO2 to determine ?
oxygenation status
Low PaO2 (<80 mmHg) & SaO2 means what?
hypoxia
NL/elevated oxygen means
adequate oxygenation
Step 2 in ABG interpretation, evaluate the ___?
PH
Step 3 in ABG interpretation, evaluate whether its a ___ or ___ component?
Respiratory / Metabolic
Step 4 in ABG interpretation, determine if there is a ?
compensatory mechanism working to try to correct the pH.
What is the main functional substance of RBCs.
- Hemoglobin, consists of 4 heme molecules. responsible for blood’s red color - Contain iron in the Ferrous state
Male normal hgb ? hct ?
13-16 gm/dl 42-50%
Female normal hgb ? hct ?
12-15 gm/dl 40 -48%
Hemoglobin makes up _____ of the dry weight of RBC’s
95 %
destruction of red blood cell membrane.
Hemolysis
When the RBC membrane ruptures Hb is released into the plasma these subunits can block the ____ of ____ __ ____causing impairment/failure of these organs..
micro vasculature of kidneys and lungs
3 Primary forms of CO2 Transport
- 5% dissolved in plasma -15% combine w/ Hb (Carbamino hemoglobin -80% enters the RBC and converted to H2CO3
80% of CO2 enters the RBC and is converted to?
H2CO3
15% of CO2 combines with _____ as it enters the blood stream?
Hb (Carbamino hemoglobin)
5% of CO2 is dissolved in ___ as it crosses the capillary wall?
Plasma
The “Haldane Effect”
Increase in CO2 Displaces oxygen from the hemoglobin which causes an increase in O2 delivery.
The reverse “Haldane Effect”
binding of O2 to hemoglobin tends to displace CO2 from the blood
combination of O2 and HB in the lungs causes
Hb to become a stronger acid.
combination of O2 and HB in the lungs causes Hb to become a stronger acid, this displaces CO2 from the blood and into the aveoli in 2 ways.
- Acidic Hb is less likely to form carbaminoHb - Acidic Hb releases excess H+ ions, these bind to bicarb, this dissociates to CO2 & H2O
2 Compensatory Mechanisms
- Respiratory Compensation - Renal compensation
Pink Urine ?
Concern for breaking of the RBC.
Normal value of pO2 on CPB ?
150 - 250 mmHg
pO2 value on CPB is 100 mmHg. What will your actions as a perfusionist be ?
Increase my FiO2 to reach pO2 values between 150 - 250 mmHg.
A Base Excess > -2 indicates what ?
How would you the perfusionist treat this on CPB?
Metabolic Acidosis.
Treat by increasing pump flow.
A pH of 7.3 & a pCO2 of 52 mmHg on CPB means what?
How would you the perfusionist correct this ?
Respiratory Acidosis
Correct by turning up the Sweep.
