10. Intro to Blood Gas Analysis Flashcards
What is pH?
A scale of 1-14 of acidity or alkalinity of the blood
An inc of H+ = dec pH (acidotic)
A dec of H+ = In pH (alkalotic0
Normal body is 7.35-7.45
Normal cellular metabolism, enzymatic and cellular reactions require normal pH
What is acidosis?
dec pH
Dec exitability of cells
Clinical signs: alteration in cardiac contraction, dec vascular response to catecholamines, can lead to loss of consciousness
What is alkalosis?
inc pH, inc excitability of cells
clinical signs: impaired neurological and muscle func, tingling sensations, nervousness, muscle twitching
How do we know if its metabolic vs respiratory?
metabolic: caused by imbalances in the production and secretions of acids by the kidneys
Respiratory: caused primarily by the LUNGS or breathing abnormalities
What buffers are there to keep the pH balance?
chemical - immediate response (bicarb, phosphate, na, k/h ion exchange, bones, proteins (albumin, hemoglobin, plasma globulins)
Respiratory - seconds to minutes (Co2)
renal - hours to days (bicarb)
In acidosis, what is the chemical compensatory response?
H+ moves into the cell while K+ moves out of the cell
= hyperkalemia
In alkalosis, what is the chemical compensatory response?
H+ moves OUT of the cell while K+ moves INTO the cell
= hypokalemia
What is respiratory buffering?
normal byproduct of cell metabolism = C02
c02 travels via the blood to the lungs where it is excreted
excessive CO2 combines w/ H2O > H2CO3
Blod pH changes according to how much carbonic acid is present
Resp rate changes via stimulation of chemoreceptors in the carotic and aortic bodies
Chemoreceptors respond to changes in blood pH, PaO, PaCO2
What is renal buffering?
To maintain blood pH - kidneys retain or excrete bicard (HCO) to compensate
When pH dec (acidosis) - kidneys retain base (HCO3)
When pH inc (alkalosis) - kidneys excrete base (HCO3)
How is gas transported, what is the composition of it? What about Oxygen and carbon dioxide?
O2: transported via hemoglobin, taken up in lungs, delivered to tissues
inhale 21% O in atmosphere (FiO = 21%), exhale about 15% (ETO2 =15%
CO2: transport as bicarb ion in plasma, byproduct of metabolism of H ions
exhaled (ETCO2) = 5-6%
negligible amounts are inhaled from the atmosphere
What is dalton’s law of partial pressure?
the sum of all pressures of a gas = atmospheric pressure
* We breathe air which consists of:
* 20.95% O2
* 0.038% CO2
* 78.09% N2
* 0.247% H2O
* 0.93% Argon
* Other trace gases
What is the conversion of % to partial pressure? ETCO is 35-45, but how do we get there?
Atmostpheric pressure at sea lvl is 760mmHg
If all gasses in atmosphere add up to 760mmHg (100%) what is partial pressure of gases in the atmosphere?
* O2 = (20.95/100) x 760 = 159.22 mmHg
* CO2 = (0.038/100) x 760 = 0.28 mmHg
* What is exhaled (ETCO2)?
* (5-6/100) x 760 = 38 – 45.6 mmHg
Why might we sample arterial blood for a blood gas analysis?
Req to assess lung func. - take from any systemic artery, arterial blood has left the lungs and not passes through tissues, can examine any compensatory changes made by lungs/brain
A pulse oximeter will also provide arterial oxygenation status
Why might we sample venous blood for a blood gas analysis?
for indices of metabolism, look @ blod returning from the hole body (mixed venous blood), NOT the paw (peripheral being) - taken from pulmonary artery, but clinically can use a jug sample
A peripheral venous used for glucose, elytes, hemoglobin, gases and lactate only if good circulation
Do NOT assess a venous sample to look at resp compensation by the lungs - look at arterial sample
What are some blood sampling errors?
use pre-heparinized commercial syringes to avoid damaging analyzer
Blood sample taken from wrong site - peripheral venous sites do not reflect whole body in hypovolemic states, Venous do not assess lung func. need arterial sample
Air bubble - always remove air bubbles from blood sample - pO and PCO2 will reflect atmostpheric partial pressure from air bubble
Accidental sampling from artery and vein together
Erroneous low PaO and high PaCO2 - continuous metabolism in sample (white cells, avian cells); analyze immediately
What is fraction of inspired O2?
FI - Must know to assesss oxygenation status of animal
What is INHALED by the animal
What is partial pressure?
The driving force for O2 to attach to (saturate) a hemoglobin molecule with 4 molecules of o2
O2 dissolved in tissue or plasma
PO2(tissue),, PaO2 (artery), PvO2(vein)
What is the saturation of Hb with O2?
sO2 - relationship of sO with pO of blood
What is the oxygen content?
total number of mL’s O2/L of blood (arterial 200mL)
SUM of dissolved O2 ij plasma and O2, carried by hemoblobin
When we assess lung function, what are the values?
Mammals: PaO2 is less than atmospheric pO (150mmHg), normal PaO2 in mammals = 90-100mmHg
mammals can store 02 during breath hold
paO2 is dependant on lung function
some V/Q mismatch
arterial blood leaving the lung is mix of well oxygenated and poorly oxygenated blood
General rule: PaO2 = 5xFiO2 (%)
How is respiration controlled?
In the blood: conc of CO2, pH and O2 control the RR
Central chemoreceptors located on the ventral surface of the medulla respond to changes in PH of the CSF
Peripheral chemoreceptors loc. in the Carotid and aortic arches
What do electrodes measure?
pH, pCO, pO, does not measure nitrogen or nitrous oxide
What does the co-oximeter measure?
Hemoglobin content, saturation of hemoglobin molecule w/ o2
What does a typical BG analyzer measure?
Electrodes
Calculates bicarb, base excess
co-oximeter measure
re-calculates pO and pCO with body temp
Elytes: glucose, lactate, anion gap
For the blood gas analysis, what is the general rule of thumb?
1st - look at pH
2nd - look at paCO2
3rd - look at HCO3
When analyzing a BG sample, what does pH tell us?
tells us if blood is acidotic or alkalotic
normal is 7.35-7.45
When analyzing a BG sample, what does pCO2 tell us?
Tells us about RESPIRATORY component
Oppositeo of pH
normal is 35-45mmHg
<35 alkalosis
>45 acidosis
When analyzing a BG sample, what does HCO tell us?
Tells us what the KIDNEYS are doing (Metabolic component)
Follows the pH
normal 22-26 mEq/L
<22 acidosis
>26 alkalosis
What are the BG compensasion changes when compromising?
Acidosis: Resp PCO inc, hco dec
Metabolis: hCO dec, pCO dec
Alkalosis: Resp pCO dec, hCO inc
Metabolic: HCO inc, pCO inc
What is the oxygen content equation?
O2 delivery = O2 content × Cardiac Output
O2 content = (1.34 × SaO2 × [Hb]) + (0.003 × PaO2)
Cardiac output = Heart Rate (HR) x Stroke Volume (SV
