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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
Q

When pH increases (renal buffering)

A
  • Excrete HCO3-
26
Q

Renal buffering

A
  • May take HOURS TO DAYS
27
Q

Conversion of % to partial pressure

A
  • O2 20.95%/100 multiple by 760mmHg=159.22mmHg
28
Q

Oxygen transport

A
  • Transported attached to Hg (4 molecules)
  • Taken up in lungs and used within body tissues
  • Inhale 21% oxygen in atmosphere
  • Exhale: 15%
29
Q

CO2 transport

A
  • Transported as bicarbonate ion in plasma
  • Byproduct of metabolism with H+ ions
  • Exhaled through lungs (5-6%)
  • Negligible amounts are inhaled form atmosphere
30
Q

FiO2

A
  • Fraction of inhaled gas that is O2
  • *must know to interpret arterial blood sample
31
Q

Partial pressure O2

A
  • 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
Q

Saturation of Hb with O2

A
  • *know graph
  • If shifted left=bind O2 more tightly at tissues
  • If shifted right=off load more O2 at tissues
33
Q

What causes the Hb O2 saturation curve to shift left?

A
  • Increase pH
  • Decrease DPG
  • Decrease temperature
34
Q

What causes the Hb O2 saturation curve to shift right?

A
  • Decrease pH (ex. exercise)
  • Increase DPG
  • Increase temperature
35
Q

Oxygen content (O2Ct)

A
  • Total number of mLs O2 per liter of blood
  • *includes both O2 Hb is carry and dissolved O2
  • Ex. arterial: 200mL
36
Q

Why is there a different in mammals arterial blood O2 and atmospheric pO2?

A
  • Some alveoli are not well ventilated (DEAD SPACE)
  • Some blood moves through lung w/o picking up oxygen (SHUNT)
37
Q

What is the equation of O2 delivery?

A
  • O2 delivery = O2 content x CO
38
Q

What are some factors affecting O2 delivery?

A
  • PaO2
  • *Hb concentration
  • CO
  • Diffusion from capillaries to mitochondria
  • Oxygen affinity of Hb
  • Local blood flow
39
Q

What are the 5 causes of hypoxemia?

A
  1. Decreased FiO2
  2. Hypoventilation
  3. Shunt
  4. V/Q mismatch
  5. Diffusion impairment
40
Q

When will hypoxic drive take over?

A
  • If PaO2 is less than 60mmHg
  • *may result in hypocapnia
  • Built in safety mechanism
41
Q

If you want to assess LUNG function, what kind of blood gas sample will you take?

A
  • Arterial
  • Arterial blood has left lungs and NOT passed through tissues
42
Q

If you want to assess BODY pH (acidosis-alkalosis) what kind of blood gas sample will you take?

A
  • 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
Q

What are some sampling errors?

A
  • 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
Q

Taking sample from wrong site

A
  • Peripheral venous sites do NOT give idea of whole body
  • Venous sites do NOT assess pulmonary function
45
Q

Air bubble (sampling error)

A
  • Remove air from sample
  • Results will reflect values found in air (150mmHg O2 and low CO2)
46
Q

What do the electrodes of a blood gas analyzer measure?

A
  • pH
  • pO2
  • pCO2
  • do NOT measure N or NO
47
Q

What does the co-oximeter measure? (blood gas analyzer)

A
  • Hg content
  • Saturation of Hg molecule with O2
48
Q

What is the function of a blood gas analyzer?

A
  • Calculate bicarbonate and base excess
  • Re-calculates pO2 and pCO2 for body temperature of patient
  • Electrolytes; glucose; lactate; anion gap
49
Q

Typical blood gas print out: what you need to do/add

A
  • But in arterial or venous sample
  • Input Inspired O2
  • Operator ID
  • Patient ID
  • Temperature
50
Q

Where do you start when evaluating a blood gas?

A
  • 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
Q

Venous sample difference compared to arterial sample on a blood gas printout

A
  • PCO2 slightly increased
  • PO2 decreased (O2 has been used)
  • *everything else is pretty much the same
52
Q

What will you see if there is pulmonary dysfunction with good CO?

A
  • Pulse oximeter (saturation): low
  • Arterial gas: low PaO2
  • Content: low
  • *not getting as much O2 across membranes
53
Q

What will you see if there is anemia with good CO?

A
  • Pulse oximeter (saturation): normal
  • Arterial gas: normal PaO2
  • Content: low
  • *even though only 1 blood cell going by the probe, it looks good!
54
Q

What will you see on a blood gas printout of a hypoxemic dog?

A
  • 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
Q

What will you see on a blood gas printout for a hypoxemic and anemic dog?

A
  • Low pO2
  • Low sO2
  • Very low O2Ct
  • Low Hct
  • Low Hb concentration
  • *give a blood transfusion! (need more Hb)
56
Q

What will you see on a blood gas printout for an anesthetised horse?

A
  • *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
Q

Horses: ventilation/perfusion mismatch

A
  • Not designed for dorsal recumbency
  • Lungs are compressed: atelectasis
  • Anesthetic drugs depress brain and ventilation
58
Q

What will you see on a blood gas printout (VENOUS SAMPLE) for a dog with renal failure?

A
  • Normal PvO2 and PvCO2
  • Low pH
  • Low HCO3-
  • *metabolic acidosis

ANESTHESIA - 2 (17 decks)

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