Lecture 21: Blood Gas Interpretation (Exam 3) Flashcards
Define homeostasis
The maintenance of constant condition through dynamic equilibrium of the internal envi of the body
What regulates the body
- Lungs
- Kidneys
- Liver/GI
Slide 3
What are the 3 principal mechanisms to buffer H+
- Chemical
- Respiratory
- Renal
Describe the chemical mechanism to buffer H+
Slide 4
Do this for the other two
What does henderson-hasselbalch equation doe
- Relates pH to components of the bicarbonate buffer system
Slide 5
Fill out the following chart
Slide 6
What is the primary disturbance of metabolic acidosis
HCO3- decreasing
What is the primary disturbance of metabolic alkalosis
HCO3- goes up
What is the primary disturbance of respiratory acidosis
CO2 has increased
What is the primary disturbance of Respiratory alkalosis
Decrease in CO2
What is a mixed disturbances
- Two separate primary disorders occurring in a px @ one time
- Can have a neutralizing or additive effect on pH
- Triple disorder can occur w/ MAC, MAL, & RAC/RAL
What will you see if there is a mixed disturbance
- PCO2 & HCO3- are changing in opposite directions
- Norm pH w/ abnorm PCO2 &/or HCO3
- pH changes in the opposite direction that predicted for the primary disorder
Slide 8
What causes RAC
- Pleural space disease, pneuomothorax, severe pulmonary disease
- Upper air way obstruction
- Neuro disease
- Ax drugs & equipment dead space
- Decreased functional residual capacity
- Malignant hyperthermia
- Cardiopulmonary arrest
What causes RAL
Slide 9
What causes MAC
- Vomiting
- Diarrhea
- Renal loss of HCO3- or retention of H+
- IV nutrition
- Dilutional acidosis
- Ammonium chloride
- Hypomineralcorticisim
What causes MAL
Slide 10
What are the consequences of acidosis
- Impairs cardia contractility & response to catecholamines (decrease CO -> decreased renal & hepatic blood flow)
- Ventricular arrhythmias or fibrillation
- Arterial vasodilation & venous constriction (centralizes blood vol & causes pulmonary congestion)
- Shifts Oxygen-hem curve to the right
- Insulin resistance that impairs uptake of glucose
- Hyperkalemia due to transcellular shift
- Increased iCa2+
- CNS depression & coma
- Osteodystrophy & hypercalciuria
What are the consequences of alkalosis
Slide 11
What is the diff btw/ the arterial & venous blood gas
- Arterial: is oxygenated & is used to eval respiratory gas exchange
- Venous: useful in determining AB status; slightly lower pH & high pCO2 than arterial blood due to local tissue metabolism. Can’t comment on oxygenation status
Describe the values seen in an arterial sample
- PaO2 ~ 80 - 110 mmHg on room air or ~ 500mmHg if on 100% Ox
- SaO2 > 88% (pulse ox)
- Bright cherry red color
- Pulsatile flow if catheter is placed and arterial waveform present when attached to a pressure transducer
Describe the values seen in an venous sample
- PvO2 ~ 35 - 45 mmHg regardless of FiO2
- SvO2 65 to 75%
- Darker red
- No pulsatile flow from catheter & no atrial wave form present when attached to pressure transducer
What is need to obtain a sample
What are good sites to get a sample from in small animals
- Dorsal pedal a
- Auricular a
- Femoral a
- Caudal a
- Lingual a or v
What are good sites to get a sample from in large animals
- Facial a
- Transverse facial a
- Lateral dorsal MT a
- Auricular a
- Lingual a
- Femoral a
- Median a
What do blood gas analyzers directly measure
- pH
- PO2
- PCO2
What do blood gas analyzers calculate
- HCO3-
- BE
- SaO2
Describe pH blood gas values
- Reflects the overall balance of acid/base producing processes in the body & the H+ concentration in the ECF
- log(1/H+)
- one unit change in pH = 10 fold increase or decrease in H+
- Range of 6.8 to 7.8 is compatible w/ life
Describe PaO2 blood gas values
Slide 18
Describe PaCO2 blood gas values
Slide 18
Describe bicarbonate (HCO3-)
Slide 29
What is total carbon dioxide (TCO2)
Amount of CO2 gas present in the plasma
What is base excess (BE)
Slide 21
How is BE used to calculate bicarb theraby
Slide 21
What is SaO2
The % of all ava heme binding sites saturated w/ oxygen from an arterial sample is calculated value based on the position on the oxygen hemoglobin dissociation curve & PaO3 (150 PaO2 = 100% SaO2) want to stay at or above 95%
Fill the chart out for the norm values of an arterial blood sample:
slide 23
What is the best way to know if a sample is venous or arterial
- Arterial: SaO2 > 88%
- Venous/mixed sample/bad pulmonary disease: SaO2 < 88%
Hypoventilation = what PaCO2
Increased
Hyperventilation = what PaCO2
Decreased
How do you get the Alveolar arterial O2 gradient (A-a)
- The efficiency of gas exchange
- Equation is for room air
Fill out the chart for the A-a gradients in the dog (ADS = acute respiratory distress syndrome)
Slide 29
How do we assess how the animal is oxygenating if the the px is on ax
- Use PaO2: FiO2 ration
Answer the following example
Slide 30
Fill out the chart
Slide 30
How do you determine the anion gap? what are the norms?
- Norm for dogs = 12 - 24 mEq/L
- Norm for cats = 13 - 27 mEq/L
- Is composed of phosphate =, sulfate, plasma proteins, & organic acid anions
- Increased AG more common & useful ID the cause of metabolic. acidosis
What effects sample accuracy
- Air bubbles (Increased paO2)
- Excess heparin (decreased pH)
- Delay in analysis (decreased PaO2 & pH)
- Blood clot in the sampe
- Syringe
- Temp & barometric therapy
Define hypoxemia
Slide 34
Define Hypoxia
slide 34
Causes of hypoxemia in ax
- V/Q mismatch
- Hypoventilation
- Low FiO2
- Right to left shunt
- Diffusion impairment
- Most common is a R to L shunt
What is V/Q mismatch
- Change in hemodynamics
- Not getting O2 but the arterioles are coming by (decrease in Ventilation w/ norm circulation)
- Change in circulation or blood flow in the px
- Contributes to px oxygen levels
What is the oxygen content (CaCO2) equation? Why use it?
- CaO2 directly reflects the total # of oxygen molecules in arterial blood (both bound & unbound to hemoglobin)
- Hemoglobin concentration is the main contributor
- Times it by cardiac output to get DO2
- DO2 is the what we care the most about (rate of oxygen delivery)
