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ANESTHESIA - 2 > 31 – Intro to Blood Gas Analysis > Flashcards

31 – Intro to Blood Gas Analysis Flashcards

1
Q

Acidosis

A
  • Decrease excitability
    o Alteration in cardiac contractions
    o Decreased vascular response to catecholamines
    o Can lead to loss of consciousness
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2
Q

Alkalosis

A
  • Increased excitability
    o Impaired neurological function
    o Impaired muscular function
    o Tingling sensations, nervousness, muscle twitches
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3
Q

What is metabolic acidosis/alkalosis caused by?

A
  • Imbalance in production and excretion of acids or bases by KIDNEYS
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4
Q

Metabolic acidosis: pH and HCO3 levels

A
  • pH<7.35
  • HCO3 <22mmol/L
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5
Q

Too much acid build up (metabolic acidosis)

A
  • Shock
  • DKA
  • Renal failure
  • Diarrhea
  • Diuretics
  • Lactic acidosis
  • Ethylene glycol poisoning
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6
Q

Clinical signs of metabolic acidosis

A
  • Headache
  • Lethargy
  • Nausea
  • Anorexia
  • Vomiting
  • Diarrhea
  • Coma
  • Death
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7
Q

Metabolic alkalosis: pH and HCO3 levels

A
  • pH>7.45
  • HCO3 >26mmol/L
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8
Q

Excess loss of acid in blood (metabolic alkalosis)

A
  • Excessive vomiting
  • GI obstruction
  • *not as common)
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9
Q

Clinical signs of metabolic alkalosis

A
  • *chronic vomiting dog
  • Dizziness
  • Lethargy
  • Weakness
  • Muscle twitching
  • Cramps
  • Tetany
  • Coma
  • Death
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10
Q

What is respiratory acidosis/alkalosis caused by?

A
  • Primarily by LUNGS or breathing abnormalities
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11
Q

Respiratory acidosis: pH and PaCO2 levels

A
  • pH<7.35
  • PaCO2 >45mmHg
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12
Q

What is respiratory acidosis caused by

A
  • Hypoventilation
    o Obstruction of gas exchange
    o Respiratory depression
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13
Q

What are the clinical signs of respiratory acidosis

A
  • Dyspnea
  • Respiratory distress
  • Shallow respirations
  • Tachycardia
  • Dysrhythmias
  • Headache
  • Restlessness
  • Confusion
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14
Q

Respiratory alkalosis: pH and PaCO2 levels

A
  • pH > 7.45
  • PaCO2 <35mmHg
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15
Q

What is respiratory alkalosis caused by?

A
  • Hyperventilation
    o Pain
    o Fear
    o Anxiety fever
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16
Q

What are the clinical signs of respiratory alkalosis?

A
  • Dyspnea
  • Nausea
  • Vomiting
  • Headaches
  • Restlessness
  • Lethargy
  • Coma
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17
Q

What are some chemical buffers?

A
  • Bicarbonate, phosphate, sodium
  • Potassium/hydrogen ion exchange
  • Bones
  • Proteins (albumin, Hg, plasma globulin)
  • *IMMEDIATE RESPONSE TO CHANGES IN ACID/BASE BALANCE
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18
Q

Acidosis: compensatory response of chemical buffering

A
  • H+ moves into cell, K+ moves out of cell
  • RESULTS in HYPERKALEMIA
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19
Q

Alkalosis: compensatory response of chemical buffering

A
  • H+ move out of cell, K+ moves into cell
  • RESULTS IN HYPOKALEMIA
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20
Q

Respiratory buffering

A
  • Normal biproduct of cell metabolism=CO2
  • Excessive CO2 combines with water: H2CO3
    o Blood pH change according to how much carbonic acid is present
  • *lungs can increase OR decrease RR depending on pH
    *RESPONDS IN SECONDS TO MINUTES (slight delay, but pretty immediate)
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21
Q

What in blood stimulates the RR?

A
  • CO2
  • pH
  • O2
  • Central and peripheral
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22
Q

Central chemoreceptors

A
  • Ventral surface of medulla
  • Respond to changes in pH in CSF
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23
Q

Peripheral chemoreceptors

A
  • Carotid and aortic arches
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24
Q

When pH decreases (renal buffering)

A
  • Retain HCO3-
25
When pH increases (renal buffering)
- Excrete HCO3-
26
Renal buffering
- May take HOURS TO DAYS
27
Conversion of % to partial pressure
- O2 20.95%/100 multiple by 760mmHg=159.22mmHg
28
Oxygen transport
- Transported attached to Hg (4 molecules) - Taken up in lungs and used within body tissues - Inhale 21% oxygen in atmosphere - Exhale: 15%
29
CO2 transport
- Transported as bicarbonate ion in plasma - Byproduct of metabolism with H+ ions - Exhaled through lungs (5-6%) - Negligible amounts are inhaled form atmosphere
30
FiO2
- Fraction of inhaled gas that is O2 - *must know to interpret arterial blood sample
31
Partial pressure O2
- Amount O2 dissolved in plasma - *depends on lung function - Driving force to get O2 onto the Hb molecule - *if lung function is normal: PaO2=5xFiO2=100mmHg
32
Saturation of Hb with O2
- *know graph - If shifted left=bind O2 more tightly at tissues - If shifted right=off load more O2 at tissues
33
What causes the Hb O2 saturation curve to shift left?
- Increase pH - Decrease DPG - Decrease temperature
34
What causes the Hb O2 saturation curve to shift right?
- Decrease pH (ex. exercise) - Increase DPG - Increase temperature
35
Oxygen content (O2Ct)
- Total number of mLs O2 per liter of blood - *includes both O2 Hb is carry and dissolved O2 - Ex. arterial: 200mL
36
Why is there a different in mammals arterial blood O2 and atmospheric pO2?
- Some alveoli are not well ventilated (DEAD SPACE) - Some blood moves through lung w/o picking up oxygen (SHUNT)
37
What is the equation of O2 delivery?
- O2 delivery = O2 content x CO
38
What are some factors affecting O2 delivery?
- PaO2 - *Hb concentration - CO - Diffusion from capillaries to mitochondria - Oxygen affinity of Hb - Local blood flow
39
What are the 5 causes of hypoxemia?
1. Decreased FiO2 2. Hypoventilation 3. Shunt 4. V/Q mismatch 5. Diffusion impairment
40
When will hypoxic drive take over?
- If PaO2 is less than 60mmHg - *may result in hypocapnia - Built in safety mechanism
41
If you want to assess LUNG function, what kind of blood gas sample will you take?
- Arterial - Arterial blood has left lungs and NOT passed through tissues
42
If you want to assess BODY pH (acidosis-alkalosis) what kind of blood gas sample will you take?
- Can take a MIXED VENOUS SAMPLE - Must have mixed blood from all body regions - *take from pulmonary artery, but NOT easy - **CLINICALLY ACCEPTABLE to use jugular vein o Head and neck receives 30% CO
43
What are some sampling errors?
- Taking sample from wrong site - Air bubble - Blood clots - Arterial and venous mixed samples - *run samples immediately or put on ice (not longer than 2 hours)
44
Taking sample from wrong site
- Peripheral venous sites do NOT give idea of whole body - Venous sites do NOT assess pulmonary function
45
Air bubble (sampling error)
- Remove air from sample - Results will reflect values found in air (150mmHg O2 and low CO2)
46
What do the electrodes of a blood gas analyzer measure?
- pH - pO2 - pCO2 - do NOT measure N or NO
47
What does the co-oximeter measure? (blood gas analyzer)
- Hg content - Saturation of Hg molecule with O2
48
What is the function of a blood gas analyzer?
- Calculate bicarbonate and base excess - Re-calculates pO2 and pCO2 for body temperature of patient - Electrolytes; glucose; lactate; anion gap
49
Typical blood gas print out: what you need to do/add
- But in arterial or venous sample - Input Inspired O2 - Operator ID - Patient ID - Temperature
50
Where do you start when evaluating a blood gas?
- Look at pH - Does pCO2 explain change in pH? o What other conditions will produce H+? - Define respiratory or metabolic acidosis - Look at pO2, sO2, O2Ct - What concentration of O2 is patient breathing? - Patient on hypoxic drive? - Enough Hb? - How is O2 delivery to the tissue maintained?
51
Venous sample difference compared to arterial sample on a blood gas printout
- PCO2 slightly increased - PO2 decreased (O2 has been used) - *everything else is pretty much the same
52
What will you see if there is pulmonary dysfunction with good CO?
- Pulse oximeter (saturation): low - Arterial gas: low PaO2 - Content: low - *not getting as much O2 across membranes
53
What will you see if there is anemia with good CO?
- Pulse oximeter (saturation): normal - Arterial gas: normal PaO2 - Content: low - *even though only 1 blood cell going by the probe, it looks good!
54
What will you see on a blood gas printout of a hypoxemic dog?
- Low pO2 - Low sO2 - Low O2Ct - Hyperventilating dog on hypoxemic drive - Exhales more CO2 o Lower pCO2 o Higher pH - *O2 therapy will help to a point, but need to treat what is going on with the lung
55
What will you see on a blood gas printout for a hypoxemic and anemic dog?
- Low pO2 - Low sO2 - Very low O2Ct - Low Hct - Low Hb concentration - *give a blood transfusion! (need more Hb)
56
What will you see on a blood gas printout for an anesthetised horse?
- *respiratory acidosis - Low pH - High pCO2 - High HCO3- - Normal PO2 (or is it?) - *can’t give more O2 as it is already on 100% O2 - *can VENTILATE IT: give adequate tidal volume o Ventilation/perfusion mismatch
57
Horses: ventilation/perfusion mismatch
- Not designed for dorsal recumbency - Lungs are compressed: atelectasis - Anesthetic drugs depress brain and ventilation
58
What will you see on a blood gas printout (VENOUS SAMPLE) for a dog with renal failure?
- Normal PvO2 and PvCO2 - Low pH - Low HCO3- - *metabolic acidosis

ANESTHESIA - 2 (17 decks)

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