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2025 Exam Block 4 > Exam 3: Lecture 21 - Blood Gas Interpretation > Flashcards

Exam 3: Lecture 21 - Blood Gas Interpretation Flashcards

(60 cards)

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1
Q

What is homeostasis?

A

-Maintenance of constant conditions through dynamic equilibrium of internal environment of body

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2
Q

What regulates homeostasis?

A

-Lungs
-Kidneys
-Liver/GI

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3
Q

Individual differences in amount of CO2 and excess H+ produced are influenced by:

A

-Species
-Diet
-Cellular basal metabolic rate
-Total protein
-Strong ions
-Body temperature

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4
Q

What are the differences in amount of CO2 & excess H+ produced between carnivores & herbivores?

A

-Carnivores -> produce CO2 & excess H+ precursors
-Herbivores -> produce CO2 & excess HCO3- precursors

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5
Q

What is the gas homeostasis equation?

A

CO2 + H2O <-> H2CO3 <-> H+ HCO3-

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6
Q

What are the 3 principal mechanisms to buffer H+?

A

-Chemical (extracellular buffering by bicarb works within seconds; phosphate, hemoglobin & proteins are intracellular buffers that work within 24 hours)
-Respiratory (Chemoreceptors in body monitor changes in [H+] & pCO2 to adjust resp. pattern & works within minutes to hours)
-Renal (increased renal excretion of H+ takes hours to days)

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7
Q

Many approaches to the diagnosis & treatment of acid-base disorders are based on what equation?

A

Henderson-Hasselbalch Equation

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8
Q

How many primary disturbances are there for acid-base abnormalities?

A

-4

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9
Q

What do we expect to see with a primary metabolic acidosis?

A

-Decreased pH
-Decreased HCO3- (primary)
-Decreased CO2

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10
Q

What do we expect to see with a primary metabolic alkalosis?

A

-Increased pH
-Increased HCO3-
-Increased CO2

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11
Q

What do we expect to see with a primary respiratory acidosis?

A

-Decreased pH
-Increased HCO3-
-Increased CO2

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12
Q

What do we expect to see with a primary respiratory alkalosis?

A

-Increased pH
-Decreased HCO3-
-Decreased CO2

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13
Q

What is a mixed disturbance?

A

-Two separate primary disorders occurring in a patient at one time

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14
Q

What are examples of a mixed disturbance?

A

-pCO2 & HCO3- changing in opposite directions
-Normal pH w/ abnormal pCO2 and/or HCO3-
-pH change in opposite direction to that predicted for primary disorder

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15
Q

What can disorders do to pH?

A

-Can have a neutralizing or additive effect on pH

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16
Q

What can a “triple disorder” be caused by?

A

-Metabolic acidosis, metabolic alkalosis, and either respiratory acidosis or alkalosis

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17
Q

What is one of the “other” methods to diagnose acid-base disorders?

A

Stewart’s approach determined by “independent variables”:
-PCO2
-Strong ion difference (SID) - Na+, K+, Cl-, Ca2+, Mg2+
-Total concentration of nonvolatile weak acid (Atot)

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18
Q

____ is more informative that H-H equation if mixed acid-base disorders & electrolyte disturbances co-exist

A

Stewart’s approach

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19
Q

What are causes of a respiratory acidosis?

A

-Pleural space disease, pneumothorax, severe pulmonary disease
-Upper airway obstruction
-Neurologic disease (central or peripheral)
-Anesthetic drugs & equipment dead space
-Decreased functional residual capacity (pregnancy or full stomach/rumen)
-Malignant hyperthermia
-Cardiopulmonary arrest

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20
Q

What are causes of respiratory alkalosis?

A

-Pain, fear, anxiety, stress (vet student feels)
-Hypotension, low cardiac output
-Sepsis or SIRS
-Pulmonary thromboembolism
-Overzealous IPPV
-Respiratory disease
-Hypoxemia
-Fever/hypothermia
-Severe anemia

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21
Q

What are causes of metabolic acidosis?

A

-Vomiting, diarrhea
-Renal loss of HCO3- or retention of H+
-IV nutrition
-Dilutional acidosis
-Ammonium chloride
-Hypomineralocorticism

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22
Q

What are causes of metabolic alkalosis?

A

-Vomiting due to pyloric obstruction
-Hypocholeremia & hypokalemia
-Furosemide
-Hypermineralocorticism
-Contraction alkalosis

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23
Q

What are some consequences of acidosis?

A

-Impairs cardiac contractility & response to catecholamines -> decreased cardiac output -> decreased renal & hepatic blood flow
-Ventricular arrhythmias or fibrillation
-Atrial vasodilation & venous constriction -> centralizes blood volume & causes pulmonary congestion
-Shifts oxygen-hemoglobin curve to right initially

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24
Q

What are consequences of alkalosis?

A

-CNS signs (agitation, disorientation, stupor, coma)
-Seizures or tetany due to hypocalcemia (rare)
-Hypokalemia due to transcellular shifting causes muscle weakness, cardiac arrhythmias, GI motility disturbances, & altered renal function
-Shifts oxygen-hemoglobin curve to the left, which impairs oxygen release from hemoglobin initially

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25
What do we use an arterial vs. venous blood sample for when sampling for acid base?
-Arterial sample used to evaluate respiratory gas exchange -Venous sample useful in determining acid-base status
26
Venous blood has a slightly ___ pH & ____ pCO2 than arterial blood due to local tissue metabolism
-slightly lower pH, higher pCO2
27
How do you know if it is an arteriole sample?
-PaO2 ~80-110 mmHg on room air or ~500 mmHg if on 100% O2 -SaO2 > 88% -Bright cherry color -Pulsatile flow if catheter placed & arterial waveform present when attached to pressure transducer
28
How do you know if it is a venous sample?
-PvO2 ~35-45 mmHg regardless of FiO2 -SvO2 65-75% -Darker color of red -No pulsatile flow from catheter & no arterial waveform present when attached to pressure transducer
29
What is needed to take an acid base sample (steps)?
1. Clip & clean site to be sampled 2. Dry lithium heparin syringe or heparinize 1-3 mL syringe w/ 22-25 g needle 3. Get rid of air bubbles quickly & analyze sample immediately (<10 min) or place rubber stopper on needle & store on ice (up to 1hr) 4. Apply pressure to sampling site so hematoma does not form
30
Where can we obtain an acid base sample in small animals?
-**Dorsal pedal artery** -Auricular artery -Femoral artery -Caudal artery -Lingual artery or **vein**
31
Where can we get an acid base sample in large animals?
-Facial artery (e.g horses, donkeys) -Transverse facial artery (horses, donkeys) -Lateral dorsal metatarsal artery -Auricular artery (e.g. ruminants) -Lingual artery -Femoral artery -Median artery (e.g. sheep)
32
Blood gas analyzers directly measure
-pH -Partial pressures of oxygen (PO2) -Partial pressure of carbon dioxide (PCO2)
33
Blood gas analyzers calculate
-HCO3- -BE -SaO2
34
What does the blood gas value pH tell us?
-Reflects overall balance of acid & base producing processes in body & the H+ concentration in extracellular fluid
35
One unit change in pH causes a ____ in [H+]
10-fold increase or decrease in [H+]
36
What does the blood gas value PaO2 tell us?
-Oxygen molecules dissolved in the plasma phase of an arterial sample (i.e. not bound to Hb), depends on FiO2 & barometric pressure
37
What does the blood gas value PaCO2 tell us?
-Reflection of respiratory component of acid-base balance, used to determine if patient is hypocapnic, hypercapnic, or eucapnic
38
PaCO2 is inversely related to
Alveolar ventilation
39
Bicarbonate is mainly responsible for regulating ____ & acts as ____
-The pH of body fluids -Acts as immediate buffer when fixed acids enter blood
40
Bicarbonate facilitates the transport of ____ from the body tissues to the lungs
CO2
41
What is total carbon dioxide (TCO2)?
Amount of carbon dioxide gas present in plasma -85% due to actual bicarbonate -10% from carbonic acid -5% CO2 in solution
42
What is BE?
-Base Excess -Amount of strong acid or alkali required to titrate 1L of blood to a pH of 7.4 at 37C while partial pressure of CO2 is constant at 40 mmHg
43
How is the BE in venous or arterial blood samples?
-Value is identical in venous or arterial blood sample
44
Base excess = Base deficit =
Base excess = metabolic alkalosis Base deficit = metabolic acidosis
45
BE is used to calculate
Bicarbonate therapy
46
A BE of ___ is mild, ____ is moderate, ___ is severe
Mild = +/- 5 Moderate = +/- 10-15 Severe = > 15
47
What is SaO2?
-Percentage of all available heme-binding sites saturated w/ oxygen from arterial sample -Calculated value based on position on the oxygen hemoglobin dissociation curve & PaO2
48
What are the **normal** values for **arterial** blood?
-pH = 7.35-7.45 (**7.4**) -PaCO2 = 35-45 mmHg (**40 mmHg**) -PaO2 = 80-110 (mmHg) room air (**100**) -HCO3- = 15-25 mmol/L carnivore, 20-28 mmol/L herbivore (**24 + 1-4**) -BE = 0 +/- 4 -SaO2 95-100% -Lactate < 2.0 mmol/L
49
What is the 1st step when determining acid/base status?
Determine if sample is arterial or venous -SaO2 > 88% = Arterial -SaO2 < 88% = Mixed sample, Venous, or Pulmonary disease
50
What is the 2nd step when determining acid/base status?
Determine acid/base status of the patient -pH = normal, acidemia, or alkalemia -pCO2 = normal, increased or decreased -HCO3- = normal, increased or decreased Is primary problem respiratory or metabolic? Any compensation occurring?
51
What is step 3 of determining acid/base?
Assess ventilatory status (PaCO2) -Hypoventilation = increased PaCO2 -Hyperventilation = decreased PaCO2 -Normal ventilation
52
What is step 4 of determining acid/base?
Assess how the animal is oxygenating -Is the patient breathing room air? -Is the patient on an FiO2 > 0.21?
53
How do we interpret PaO2:FiO2 ratio?
>400 = normal pulmonary functino 200-400 = Decreased pulmonary function <200 = Severe pulmonary dysfunction; ARDS
54
What is step 5 in determining acid/base status?
-Determine the Anion Gap -Normal = 12-24 mEq/L (dogs); 13-27 mEq/L (cats)
55
What can affect the accuracy of an acid/base sample?
-Air bubbles = increased PaO2 & decreased PaCO2 -Excess heparin = decreased pH -Delay in analysis = decreased PaO2 & pH; increased PaCO2 -Blood clot in sample (hemolysis) -Syringe type (glass preferred, plastic ok if analyzed within 10 minutes) -Temperature & barometric pressure (hyperthermia artificially lowers PaO2 & PaCO2, hypothermia artificially elevates PaO2 & PaCO2)
56
What is hypoxemia?
-Decreased PaO2, SaO2 or hemoglobin content -Amount of oxygen in the blood (CaO2) determines severity
57
What is hypoxia?
-General term for impairment of oxygen delivery to tissue (DO2) -Takes into account cardiac output (CO) & oxygen uptake at tissue level -Therefore, hypoxemia is one type of hypoxia
58
What are 5 causes of hypoxemia?
1. **Ventilation/perfusion (V/Q) mismatch** 2. Hypoventilation 3. Low FiO2 4. Right to left shunt 5. Diffusion impairment (less common in vet med)
59
Why would we want to use the oxygen content (CaO2) equation in our patients?
-CaO2 directly reflects the total number of oxygen molecules in arterial blood (both bound & unbound to hemoglobin) -Want to know your patient has enough hemoglobin to deliver oxygen to the tissues
60
Which patient is more hypoxemic, and how do we know? Patient A: Hb= 7 g/dL; SaO2 = 95%; PaO2 = 80 mmHg Patient B: Hb= 15 g/dL; SaO2 = 85%; PaO2 = 55 mmHg
-Patient A -Because lower hemoglobin (who's your daddy)

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