Blood Gas Interpretation Flashcards
Oxygenation
Is defined through PaO2 and SaO2 or more specifically CaO2 which will also look at Hb
CaO2
CaO2 is that total content of oxygen in the body
CaO2 Formula
(1.34HbSaO2)+(0.0031*PaO2)
Where 1.34 is the saturation capacity
0.0031 is your solubility coefficient
DO2
The delivery of oxygen to the tissues
DO2=CaO2 x CO (cardiac Output)
Oxygenation Determined Through
Spontaneous Breathing: (FiO2)
Positive Pressure Ventilation: (FiO2 and Mean Airway Pressure)
SaO2 and PaO2
Oxygen Dissociation Curve
Ventilation
Separate from oxygenation
Defined by PaCO2 and pH
Determined by
Alveolar minute ventilation= (RR x VT)
pH Normal Range
7.35-7.45
pH Goal Range
7.35-7.45
PaCO2 Normal Range
35-45 mmHg
PaCO2 Goal Range
35-45 mmHg
PaO2 Normal Range
80-100 mmHg
Partial Pressure of oxygen
PaO2 Goal Range
Greater than or equal to 60 mmHg
HCO3 Goal Range
22-26
Bases Excess
+/- 2
SaO2 Normal Range
95-100%
Should be very close to SpO2 (peripheral oxygen saturation)
Oxygen saturation in hemoglobin
SaO2 Goal Range
Greater than 90
Normoxemia
PaO2 80-100 mmHg
Mild Hypoxemia
PaO2 60-79 mmHg
Moderate Hypoxemia
PaO2 40-59 mmHg
Severe Hypoxemia
PaO2 less than 40 mmHg
Hyperoxemia
Oxygen in high levels which can be toxic
Hydrolysis Equation
CO2 + H2O H2CO3 HCO3- + H+
As CO2 production increases the bicarbonate will naturally increase as well
Do not confuse this with compensation
PaCO2 and HCO3
Acute changes in PaCO2 will cause a fairly immediate For every 10 mmHg increase in PaCO2 there is a 1 mmol/L increase in HCO3
For every 10 mmHg decrease in PaCO2 there is a 2 mmol/L decrease in HCO3
Acid Base Disorders
Metabolic (Non-Respirtory)
Respiratory (Ventilation)
Respiratory Acid Base Disorders
A normal PaCO2 will be 35-45 mmHg
< 35 will cause pH to increase/alkalemia
>45 will cause pH to decrease/academia
If PaCO2 is abnormal and in the opposite direction of pH then it is the primary cause
Respiratory Acid Base Disorders
A normal HCO3 will be 22-26 mmol/L
< 22 will cause pH to decrease/academia
>26 will cause pH to increase/alkalemia
If HCO3 is abnormal and in the same direction of pH then it is the primary cause
Henderson-Hasselbalch Equation
Relationship between metabolic and respiratory acid base disorder
For every 10 mmHg increase in PaCO2 there is a _______ increase/decrease in pH
For every 10 mmHg increase in PaCO2 there is a corresponding decrease in pH by 0.06
For every 10 mmHg decrease in PaCO2 there is a _______ increase/decrease in pH
For every 10 mmHg decrease in PaCO2 there is a corresponding increase in pH by 0.10
Base Excess
Change in the total blood buffer base above or below normal
Base Excess and HCO3
The total quantity of buffer anions in the blood is approximately twice that of HCO3
HCO3 accounts for only about half of the total buffering capacity of the blood, which means that BE will provide a more complete picture of blood buffering
Acute changes in PaCO2 will not affect BE
This is why BE is considered to be a pure measure of metabolic components of the acid base balance
A positive BE
Excess base or excessive loss of acid
Negative BE
Excessive Acid or Excessive loss of Base
Acidemia
< 7.35
Alkalemia
> 7.45
pH= 7.35-7.45:
Normal
Fully compensated disorder
Mixed disorder
Compensation
Compensation will occur as the body tries to maintain a normal (or closer to normal) pH
The body does not over compensate
Compensation in Respiratory Disorders
The metabolic system compensates by either increasing or decreasing the HCO3- levels to “correct” the pH back to normal
This occurs in the kidneys through the excretion/retention of bicarbonate
Full compensation may take several days
While this results in both HCO3- and PaCO2 levels being abnormal it brings the pH back to (or closer to) normal
Compensation in Metabolic Disorders
The respiratory system responds by either increasing or decreasing minute volume resulting in a decrease or increase in PaCO2
The new PaCO2 will counteracts the metabolic problem and “corrects” the pH, resulting in both PaCO2 and HCO3 being abnormal but the end result is a pH that is normal or closer to normal
Predicted pH
If PaCO2 = 40: Predicted pH should = Measured pH
Predicted pH when PaCO2 > 40
Predicted pH = 7.40 – [(PaCO2 – 40) * .006]
Predicted pH when PaCO2 < 40
Predicted pH = 7.40 + [(40 - PaCO2)* .01]
Co-Oximetry
Will should hemoglobin levels and types
Types of Hemoglobin
Normal Methemoglobin Carboxyhemoglobin Sulfhemoglobin Fetal hemoglobin
Methemoglobin
Fe+++ reduced Hb carrying capacity
Carboxyhemoglobin
Up to 8% in cities
Half life of 4-6 hours in room air, as low as 35min without HBOT
Sulfhemoglobin
Sulfur atom blocks heme (drugs)
Fetal hemoglobin
Curve shift left
Normal Hemoglobin
Fe++
Uncompensated (Acute) Respiratory Acidosis
PaCO2 is high, causing a low pH
HCO3 is normal
Partially Compensated Respiratory Acidosis
PaCO2 is high, causing a low pH (not as low as expected for a high PaCO2
HCO3 is high in an attempt to being pH back to normal range (but has not yet done this)
Fully Compensated (Chronic) Respiratory Acidosis
pH is within normal range
PaCO2 and HCO3 is high
Uncompensated (Acute) Respiratory Alkalosis
PaCO2 is low, causing a high pH
HCO3 is normal
Partially Compensated Respiratory Alkalosis
PaCO2 is low, causing a high pH
HCO3 is low in an attempt to being pH back to normal range (but has not yet done this)
Fully Compensated (Chronic) Respiratory Acidosis
pH is within normal range
PaCO2 and HCO3 is low
Uncompensated (Acute) Metabolic Acidosis
HCO3 is low, causing a low pH
PaCO2 is normal
Partially Compensated Metabolic Acidosis
HCO3 is low, causing a low pH
PaCO2 is low in an attempt to being pH back to normal range (but has not yet done this)
Fully Compensated (Chronic) Metabolic Acidosis
pH is within normal range
PaCO2 and HCO3 is low
Uncompensated (Acute) Metabolic Alkalosis
HCO3 is high, causing a high pH
PaCO2 is normal
Partially Compensated Metabolic Alkalosis
HCO3 is high, causing a high pH
PaCO2 is high in an attempt to being pH back to normal range (but has not yet done this)
Fully Compensated (Chronic) Metabolic Alkalosis
pH is within normal range
PaCO2 and HCO3 is high
Uncompensated (Acute) Metabolic Acidosis
HCO3 is low causing a low pH
PaCO2 is normal
Partially Compensated Metabolic Acidosis
HCO3 is low causing a low pH
PaCO2 is low
Fully Compensated (Chronic) Metabolic Acidosis
pH is within normal range
PaCO2 and HCO3 is low
Combined Respiratory and Metabolic Acidosis
pH is low and both PaCO2 and HCO3 are contributing to this
High PaCO2 and a low HCO3
Combined Respiratory and Metabolic Alkalosis
pH is high and both PaCO2 and HCO3 are contributing to this
Low PaCO2 and a high HCO3