Blood Gase Dr. Ambrisko Flashcards by Victoria Caccavone

What are the buffering systems of the body

Chemical

Respiration

Renal

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How fast do chemical buffers work

extracellular: in seconds (HCO3-)
intracellular: within hours (phosphate & proteins)

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How fast does respiration buffer work

adjusting CO2 within minutes

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How fast does the renal buffering system work

within hours to days by excreting H+ & retaining HCO3-

metabolic compensation

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What is the simple way to understand how changes in HCO3 influence pH

pH = HCO3-/PaCO2

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What are the measured blood gas variables

PaCO2

PaO2

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What are the calculated blood gas variables

HCO3

Oxygen content (CaO2)

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define -emia

applies to changes in blood

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define -osis

applies to physiological processes (conditions)

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What is assessed for respiratory component of pH

PaCO2

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What is assessed for metabolic component

BE or HCO3

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is there any metabolic compensation during anesthesia for pH changes

No! No time

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Normal blood pH

7.35-7.45

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define acidosis

a physiological process, that occuring alone, tends to cause acidemia

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define alkalosis

a physiological process, that occurring alone, tends to cause alkalemia

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what are mixed acid-base disorders

different kinds of acidosis a/o alkalosis occurring together

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what is a primary acid-base disorder

defined by the initial change in HCO3 or PaCO2

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What is compensation

secondary change in HCO3 or PaCO2 in order to attenuate the effect of the primary disorder on blood pH

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in respiratory acidosis would PaCO2 elevated?

what would the compensation be?

yes

HCO3 would elevate to compensate (metabolic compensation)

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in respiratory alkalosis would PaCO2 elevated?

what would the compensation be?

No!

Metabolic compensation would mean a decrease in HCO3

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in metabolic acidosis would HCO3 be elevated?

what would the compensation be?

Respiratory compensation would be a decr in PaCO2

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in metabolic alkalosis would HCO3 be elevated?

what would the compensation be?

Yes

the respiratory compensation should be an incr PaCO2

How to tell if an acid-base disorder is mixed

pH value is unexpected from a change in HCO3 or PaCO2

normal pH w/ abnormal HCO3 or PaCO2

normal HCO3

24 +/- 4 mEg/L

cats tend to be lower - think about diet, higher acid

herbivores tend to be higher - think about diet, higher base

normal PaCO2

35-45 mmHg cats tend to be lower (just weird animals)

What is Base excess (BE)

refers to an excess or deficit in the amount of base present in blood defines the metabolic component of acid-base disturbances

What does a positive BE signify

metabolic ALKALOSIS | (positive for excessive base in blood)

What does a negative BE signify

metabolic acidosis

Normal BE

0 +/- 4 mEq/L

How does CO2 exist in blood

as HCO3 & dissolved CO2

What is TCO2

Total CO2 almost the same as HCO3 can use interchangeably if HCO3 not available

What is P**_a_**CO2 equation

partial pressure (mmHG) of CO2 in the **_a_**rterial blood

What is important about PaCO2

it defines alveolar ventilation

What are the factors that can reflect (make up) any PaCO2 value

Any combo of RR, TV or breathing effort

A PaCO2 (mmHg) of \>45 would indicate which blood condition which state of ventilation

hypercapnia hypoventilation

A PaCO2 (mmHg) of 35-45 would indicate which blood condition which state of ventilation

eucapnia normal ventilation

A PaCO2 (mmHg) of \< 35 would indicate which blood condition which state of ventilation

hypocapnia hyperventilation

What will an incr PaCO2 cause | (hypoventilation)

lower P_AO₂ lower pH reflect respiratory acidosis reflect respiratory compensation for metabolic alkalosis \*P_AO₂ = partial pressure (mmHg) of O2 in Alveolar space

what do you need to remember when interpreting PaO2

does not reflect O2 content interpreted in light of * FiO2 * ambient pressure * PaCO2

what is FiO2

inspired O2 fraction ## Footnote * at 100% O2 ⇒ FiO2 = 1* * at air ⇒ FiO2 = .21*

what is PiO2

inspired O2 pressure (FiO2 x Pambient) ## Footnote * at 100% O2 ⇒ PiO2 = 760 mmHg* * at air ⇒ PiO2 = 160 mmHg*

What should the PaO2 be when breathing 100% O2 and if not what expected?

expect PaO2 \> 500 mmHg Lower than expected PaO2 values may indicate V/Q mismatch resulting from atelectasis

What is A-a difference

aka A-a gradient ⇒ is the real life difference between the **_P_**ressure of _O2_ in the **_A_**lveolar space vs the **_P_**ressure of _O2_ in **_a_**rterial blood

What is most likely cause for a high A-a difference (or gradient)

V/Q mismatch ⇒ #1 cause under anesthesia

reasons for V/Q mismatch

Atelectasis (common under anesthesia)

What can A-a difference be used for

to distinguish lung diseases (V/A mismatch) from hypoventilation as a cause of hypoxemia with hypoventilation: A-a difference normal with V/Q mismatch: A-a difference abnormal

What is normal PaO2/FiO2 ratio

\> 500 mmHg

Name 5 causes for hypoxemia (low PaO2)

Low FiO2 Hypoventilation Diffusion impairment V/Q mismatch R-L shunt

# define hypoxia causes

insufficient oxygenation of the tissues hypoxemia insufficient perfusion insufficient O2 uptake

where is most O2 carried in arterial blood

carried by Hb small portion dissolved in plasma

in a clinical situation if lactate is \>2 mmolL what is the significance

lactate \>2mmol/L is high & may indicate incr anaerobic metabolism

what is abnormally high lactate called most common causes

lactic acidosis Systemic: shock, sepsis (e.g. GDV, colic) Local: tournequet, under-perfusion of dependent muscles, intestinal torsion, etc.

what is the parameter that is a prognostic indicator when managing sick patients

lactate level