Chapter 16 - Acid/Base Balance Flashcards
pO2 reference interval (arterial blood)
80-100 mm Hg
pH reference interval (arterial blood)
7.35-7.45
pCO2 reference interval (arterial blood)
35-45 mm Hg
HCO3 Reference interval (arterial blood)
22-26 mEq/L
Base Excess reference interval (arterial blood)
-2 to 2 mEq/L
What are the measurements that are directly measured by an electrode in arterial blood?
pH
pO2
pCO2
What are the measurements that are calculated in arterial blood?
HCO3
Base Excess
What does a negative base excess imply?
Acidosis
What does a positive base excess imply?
Alkalosis
What is base excess?
The amount of excess or insufficient bicarbonate?
Pulse oximetry reference interval
95-100%
What does pulse oximetry measure?
Oxygen saturation of hemoglobin
Boyle’s Law
At a constant temperature, the volume of a gas varies inversely to the pressure exerted to contain it
Charles’s Law
At a constant pressure, the volume of a gas varies with temperature (increases as it increases)
Dalton’s Law
Total pressure of gas mixture is the sum of the partial pressures of each gas
Henry’s Law
The amount of a dissolved gas is proportional to the partial pressure of the gas over the liquid
Specimens have to be contained (capped) or gas will escape. Which Law does this correspond to and why?
Boyle’s Law
At a constant temp, inc Vol. = dec Pressure
Blood gas assays are temperature dependent. Which Law does this correspond to and why?
Charles’s Law
At a constant pressure, inc temp = inc volume
Blood has more than one gas in it, and we can measure pressures individually. Which Law does this correspond to and why?
Dalton’s Law
Total Pressure = Sum of partial pressures
Gas that diffuses from the blood sample is proportional to the blood concentration. Which Law does this correspond to and why?
Henry’s Law
Dissolved gas = partial pressure of gas above liquid
Where are gasses in the blood that we use to measure partial pressures?
Dissolved in plasma
and
Combined with hemoglobin
Describe the process of gas transfer of O2 and CO2 at the tissue
O2 RBC –> O2 Tissues
CO2 Tissues –> CO2 RBC
CO2 + H2O (Carbonic Anhydrase) —> H2CO3 (Carbonic Acid)
Carbonic Acid —> HCO3 + H+
Chloride Shift
Hemoglobin buffers Hydrogen ion
Describe the process of gas transfer of O2 and CO2 at the lung
O2 Lung –> O2 RBC
Reverse Chloride Shift
Hemoglobin releases H+
HCO3 + H+
Carbonic Acid/H2CO3 (Carbonic Anhydrase) –> CO2 + H2O
CO2 RBC –> CO2 Lung
At pO2 of 30, what percent of hemoglobin is saturated?
50%
At pO2 of 50, what percent of hemoglobin is saturated?
80%
At pO2 of 60, what percent of hemoglobin is saturated?
90%
At pO2 of 80, what percent of hemoglobin is saturated?
100%
Hemoglobin behavior is influenced by what factors
pH
pCO2
Temperature
2,3 DPG levels
What happens to hemoglobin saturation at pO2 of 30, if in left shift?
Instead of 50% Hgb saturation, it’s increased at 70%.
How should you mix an ABG tube?
Roll on 3 axes for 2 minutes
Undermining = clots
Collection protocol for measurement of arterial blood gases
Dry heparin
Short bevel
No tournique
No air/bubbles
What makes effects of air/bubbles worse
Big difference between ambient air and patient pO2
Lower temperature
Agitated sample
Bubbles big or exposed to blood too long
Glass syringes for ABG should be analyzed when
No more than 1 hour on ice
Plastic syringes for ABG should be analyzed when
Within 30 minutes at room temperature
Why should plastic syringes not be put on ice
Cold makes the syringes more permeable to oxygen and increases hemolysis
PO2 electrode
Oxygen passes through gas permeable membrane
Reacts with polarized platinum electrode
Reduced and generates a current
Current = oxygen concentration
pCO2 electrode
CO2 passes gas permeable membrane
Enters sodium bicarbonate buffer soon
Reacts with buffer producing carbonic acid, changing pH
pH change sensed by internal pH electrode
pH decreases in proportion to CO2 present
pH electrode
H+ migrates into outer layer of glass, replacing sodium ions
Chrloide ions are drawn into the inner membrane surface
Silver ions are released by the internal silver/silver chloride element
Voltage changes in proportion to the H+ concentration
Henderson-Hasselback equation
Formula to determine bicarb
pH = 6.1 + log ( HCO3/ 0.0306 * pCO2)
Alternate ABG specimens
Venous
Arterialized capillary blood
How are arterialized capillary blood samples prepared
Finger warmed for 10 minutes
Systolic bp must be at least 95 mm Hg
How does a delay in analysis affect ABG specimens
Oxygen consumed
Acidic pH, Glycolysis produces CO2
Effects of metabolism worse when what cells are high?
Retics
Platelets
WBC
Species with high WBC and PLT need to be analyzed within how long?
5 minutes
When should specimen be analyzed at RT? Why?
Within 30 minutes
Bcz metabolism at RT causes non significant effect within first hour
How do bubbles in specimen affect ABG samples
pO2 false increase
pCO2 false decrease
pO2 false decrease if PT on oxygen therapy (PO2 > 150)
How do poorly sealed specimens affect ABG levels
Gases escape causing lower pO2 and pCO2
pH false increase
What temp are ABG specimens tested at?
37C
Pulse oximetry method
Red and Infrared lights shine into photo detector, difference between pulses = oxygenated vs deoxygenated blood
How much more tightly does CO bind hemoglobin than O2?
250 times more likely
Can carboxyhemoglobin bind oxygen?
NO
S/S of carbon monoxide poisoning
headache
dizziness
weakness
nausea
vomiting
chest pain
altered mental status
death
Diagnostic measurement of carboxyhemoglobin in nonsmokers vs smokers?
2% carboxyhemoglobin non
9% carboxyhemoglobin smokers
CO treatment?
100% oxygen inhalation for 4-5 hours
Reference Method for CO measurement
Gas chromatography
Gas chromatography advantages
More sensitive than spectrophotometry
More expensive, but not as fast
Best method for measuring CO levels >2-3%
Spectrophotometry
A pH of 6 is how much more acidic than 7?
10x
A pH of 5 is how much more acidic than 7?
100x
Each unit of pH change represents how much of a change in acidity or alkalinity?
10 fold
Calculated pH
-log (H+)
