Blood Gas Analysis Flashcards
Acid-base homestasis =
maintaining normal H+
acid-base homestoasis involves which organs (systems)
lung, kidney, liver, and GI
chemical buffers
extracellular: HCO3-; acts within seconds
intracellular: phosphate, proteins; act within hours
respiration buffer systemm
adjusting CO2; acts within minutes
respiratory compensation
how does the renal system buffer the body
excreting H+, retaining HCO3-
acts within hours - powerful but slow
metabolic compensation
Henderson-Hasselbalch equation
pH≈ HCO3- / PaCO2
what are the measure vaiables with blood gas analysis
pH
PaCO2
PaO2
what variables are calculated with blood gas analysis
HCO3-
BE
oxygen content (CaO2)
- emia
changes in blood
-osis
physiological processes
what variable should be assess respiratory component
PaCO2
which variable assess the metabolic component
BE (or HCO3-)
T/F there is no time for metabolic compensation during anesthesia
True
normal pH
7.35-7.45
primary acid-base disorder
the initial change in HCO3- or PaCO2
compensation
secondary change in HCO3- or PaCO2 in order to attenuate the effect of the primary disorder on blood pH
no classifed in the terms of acidosis/alkalosis
how are mixed acid-base disorders diagnosed
pH value is unexpected from a change in HCO3- or PaCO2
normal pH with abnormal HCO3- or PaCO2
HCO3- and PaCO2 are changing in opposite directions
normal HCO3-
24 +/- 4 mEq/L
cats tend to be lower, herbivores tend to be higher
normal PaCO2
35-45 mmHg
cats tend to be lower
what is base excess
refers to excess or deficit in the amount of base present in the blood
defines the metabolic component of acid-base dustrubances
what does a positive BE indicate
metabolic alkalosis
what does a negative BE indicate
base deficit - metabolic acidosis
what is normal BE
0 +/- 4 mEq/L
TCO2 is…
BICARB!
PaCO2 is
partial pressure (mmHg) of CO2 in the arterial blood
defines alveolar ventilation (CO2 production is normally stable)
PaCO2 > 45
hypercapnia and hypoventilation
PaCO2 < 35
hypocapnia and hyperventilation
T/F any combination of RR, tidal volume, or breathing effort can reflect any PaCO2 value
True
increased PaCO2 will
lower th PAO2 (hypoxemia) -partial pressure of O2 in alveolar space
lower the pH
refelect respiratory acidosis
reflect respiratory compensation for metabolic alkalosis
T/F PaO2 does not reflect O2 content and needs to be interpreted in light of FiO2
True
what is FiO2
inspired O2 fraction
at 100% O2 → FiO2 = 1
at air → FiO2 = 0.21
lower than expected PaO2 values may indicate
inadequate gas exchange (V/Q mismatch) resulting from pulmonary atelectasis
if breathing 100% O2 expect PaO2…
>500 mmHg
if gas exchange was perfect…
PAO2 = PaO2
T/F PaO2 is always lower than PAO2
True
normal values of A-a difference
breathing air → < 14 mmHg
breathing 100% O2 → <110 mmHg
causes for high A-a
V/Q mismatch (#1 cause under anesthesia)
right to left shunt
diffusion impairment
reasons for V/Q mismatch
Atelectasis (common under anesthesia)
lung disease
when is A-a difference used
clinically to distinguish between lung disease (V/Q mismatch) from hypoventilation as a cause of hypoxemia
A-a difference with hypoventillation
normal
A-a difference with V/Q mismatch
abnormal
PaO2 / FiO2 ratio
same purpose as A-a difference but easier to interpret
normal: >500 mmHg
5 causes of hypoxemia (low PaO2)
low FiO2
hypoventilation
diffusion impairment
V/Q mismatch
right to left shunt
causes of hypoxia
hypoxemia
insuffient tissue perfusion (e.g. low CO)
insufficient O2 uptake
CaO2 is mostly defined by
[Hb] and SaO2
O2 is carried by Hb
T/F while PaO2 is important in diagnosing V/Q mismatch, it has little impact on O2 content
high lactate (>2 mmol/L) may indicate
increased anaerobic metabolism
high lactate leads to
increased anaerobic metabolism and produced lactate and acids
symptom is called: lactic acidosis
lactate can be used as..
a prognostic indicator
high lactate level that does not decrease after treament indicates poor prognosis
