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Anesthesia & Analgesia > Lecture 21: Blood Gas Interpretation (Exam 3) > Flashcards

Lecture 21: Blood Gas Interpretation (Exam 3) Flashcards

1
Q

Define homeostasis

A

The maintenance of constant condition through dynamic equilibrium of the internal envi of the body

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2
Q

What regulates the body

A
  • Lungs
  • Kidneys
  • Liver/GI
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3
Q

What amount of CO2 & excess H+ do carnivores produce

A
  • Produce CO2
  • Excess H+ precursors
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4
Q

What amount of CO2 & excess H+ do herbivores produce

A
  • Produce CO2
  • Excess HCO3- precursors
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5
Q

What are the 3 principal mechanisms to buffer H+

A
  • Chemical
  • Respiratory
  • Renal
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6
Q

Describe the chemical mechanism to buffer H+

A
  • Extracellular buffering by bicarbonate works w/in seconds
  • Phosphate, hemoglobin, & proteins are intracellular buffers that work w/in 2 - 4 H
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7
Q

Describe the respiratory mechanism to buffer H+

A

Chemoreceptors in the body monitor changes in [H+] & pCO2 to adjust respiratory pattern & it works w/in mins to H

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8
Q

Describe the renal mechanism to buffer H+

A

Increased renal excretion of H+ takes H to days

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9
Q

What does henderson-hasselbalch equation doe

A
  • Relates pH to components of the bicarbonate buffer system
  • Any acid base disturbance is instantly reflected in one or both of its buffer components & their ratio determines pH (ideal ratio of HCO3: pCO2 is 20:1)
  • Many approaches to the dx & tx of acid base disorders are based on this equation
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10
Q

Fill out the following chart

A
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11
Q

What is the primary disturbance of metabolic acidosis

A

HCO3- decreasing

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12
Q

What is the primary disturbance of metabolic alkalosis

A

HCO3- goes up

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13
Q

What is the primary disturbance of respiratory acidosis

A

CO2 has increased

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14
Q

What is the primary disturbance of Respiratory alkalosis

A

Decrease in CO2

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15
Q

What is a mixed disturbances

A
  • Two separate primary disorders occurring in a px @ one time
  • Can have a neutralizing or additive effect on pH
  • Triple disorder can occur w/ MAC, MAL, & RAC/RAL
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16
Q

What will you see if there is a mixed disturbance

A
  • PCO2 & HCO3- are changing in opposite directions
  • Norm pH w/ abnorm PCO2 &/or HCO3
  • pH changes in the opposite direction that predicted for the primary disorder
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17
Q

What independent variables determine the stewart’s approach

A
  • PCO2
  • Strong ion difference (SID) - NA, K, Cl, Ca, Mg
  • Total concentration of nonvolatile weak acids
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18
Q

What causes RAC

A
  • Pleural space disease, pneuomothorax, severe pulmonary disease
  • Upper air way obstruction
  • Neuro disease
  • Ax drugs & equipment dead space
  • Decreased functional residual capacity
  • Malignant hyperthermia
  • Cardiopulmonary arrest
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19
Q

What causes RAL

A
  • Pain
  • Fear
  • Anxiety
  • Stress
  • Hypotension
  • Low cardiac output
  • Sepsis or SIRs
  • Pulmonary thromboembolism
  • Overzealous IPPV
  • Respiratory dx
  • Hypoxemia
  • Fever/hyperthermia
  • Severe anemia
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20
Q

What causes MAC

A
  • Vomiting
  • Diarrhea
  • Renal loss of HCO3- or retention of H+
  • IV nutrition
  • Dilutional acidosis
  • Ammonium chloride
  • Hypomineralcorticisim
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21
Q

What causes MAL

A
  • Vomiting due to pyloric obstruction
  • Hypochloremia & hypokalemia
  • Furosemide
  • Hypermineralocorticism
  • Contraction alkalosis
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22
Q

What are the consequences of acidosis

A
  • Impairs cardia contractility & response to catecholamines (decrease CO -> decreased renal & hepatic blood flow)
  • Ventricular arrhythmias or fibrillation
  • Arterial vasodilation & venous constriction (centralizes blood vol & causes pulmonary congestion)
  • Shifts Oxygen-hem curve to the right
  • Insulin resistance that impairs uptake of glucose
  • Hyperkalemia due to transcellular shift
  • Increased iCa2+
  • CNS depression & coma
  • Osteodystrophy & hypercalciuria
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23
Q

What are the consequences of alkalosis

A
  • CNS sx (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 fxns
  • Shifts oxygen-hemoglobin curve to the left which impairs oxygen release from hemoglobin initially
24
Q

What is the diff btw/ the arterial & venous blood gas

A
  • Arterial: is oxygenated & is used to eval respiratory gas exchange
  • Venous: useful in determining AB status; slightly lower pH & high pCO2 than arterial blood due to local tissue metabolism. Can’t comment on oxygenation status
25
Q

Describe the values seen in an arterial sample

A
  • PaO2 ~ 80 - 110 mmHg on room air or ~ 500mmHg if on 100% Ox
  • SaO2 > 88% (pulse ox)
  • Bright cherry red color
  • Pulsatile flow if catheter is placed and arterial waveform present when attached to a pressure transducer
26
Q

Describe the values seen in an venous sample

A
  • PvO2 ~ 35 - 45 mmHg regardless of FiO2
  • SvO2 65 to 75%
  • Darker red
  • No pulsatile flow from catheter & no atrial wave form present when attached to pressure transducer
27
Q

What is need to obtain a sample

28
Q

What are good sites to get a sample from in small animals

A
  • Dorsal pedal a
  • Auricular a
  • Femoral a
  • Caudal a
  • Lingual a or v
29
Q

What are good sites to get a sample from in large animals

A
  • Facial a
  • Transverse facial a
  • Lateral dorsal MT a
  • Auricular a
  • Lingual a
  • Femoral a
  • Median a
30
Q

What do blood gas analyzers directly measure

A
  • pH
  • PO2
  • PCO2
31
Q

What do blood gas analyzers calculate

A
  • HCO3-
  • BE
  • SaO2
32
Q

Describe pH blood gas values

A
  • Reflects the overall balance of acid/base producing processes in the body & the H+ concentration in the ECF
  • log(1/H+)
  • one unit change in pH = 10 fold increase or decrease in H+
  • Range of 6.8 to 7.8 is compatible w/ life
33
Q

Describe PaO2 blood gas values

A

Oxygen molecules dissolved in the plasma phase of an arterial sample (not bound to Hb) depends on FiO2 & barometric pressure

34
Q

Describe PaCO2 blood gas values

A

Reflection of the respiratory component of acid-base balance, used to determine if the px is hypocapnic, hypercapnic, or eucapnic. Inversely related to alveolar ventilation

35
Q

Describe bicarbonate (HCO3-)

A
  • Part of the bicarbonate-carbonic acid buffering system & is mainly responsible for regulating the pH of body fluids
  • Facilitates the transport of CO2 from the body tissues to the lungs & changes in respiration rate will alter the bicarbonate-carbonic acid ratio & pH
  • Is an assessment of the metabolic component of acid base status
36
Q

What is total carbon dioxide (TCO2)

A

Amount of CO2 gas present in the plasma

37
Q

What is base excess (BE)

A

Amount of strong acid or alkali req to titrate 1L of blood to a pH of 7.4 @ 37 degree C while the partial pressure of CO2 is constant 40 mmHg
* Is identical in venous or arterial blood same
* Base excess = metabolic alkalosis
* Base deficit = metabolic acidosis

38
Q

How is BE used to calculate bicarb theraby

A
  • mEq to infuse = base deficit x kg of BW x 0.3
  • Infuse 1/3 of calculated vol over 20 mins then reassess acid base status
  • Use of bicarb therapy is controversial due to potential for serious side effects
39
Q

What is SaO2

A

The % of all ava heme binding sites saturated w/ oxygen from an arterial sample is calculated value based on the position on the oxygen hemoglobin dissociation curve & PaO3 (150 PaO2 = 100% SaO2) want to stay at or above 95%

40
Q

Fill the chart out for the norm values of an arterial blood sample:

41
Q

What is the best way to know if a sample is venous or arterial

A
  • Arterial: SaO2 > 88%
  • Venous/mixed sample/bad pulmonary disease: SaO2 < 88%
42
Q

Hypoventilation = what PaCO2

43
Q

Hyperventilation = what PaCO2

44
Q

How do you get the Alveolar arterial O2 gradient (A-a)

A
  • The efficiency of gas exchange
  • Equation is for room air
45
Q

Fill out the chart for the A-a gradients in the dog (ADS = acute respiratory distress syndrome)

46
Q

How do we assess how the animal is oxygenating if the the px is on ax

A
  • Use PaO2: FiO2 ration
47
Q

Answer the following example

48
Q

Fill out the chart

49
Q

How do you determine the anion gap? what are the norms?

A
  • Norm for dogs = 12 - 24 mEq/L
  • Norm for cats = 13 - 27 mEq/L
  • Is composed of phosphate =, sulfate, plasma proteins, & organic acid anions
  • Increased AG more common & useful ID the cause of metabolic. acidosis
50
Q

What effects sample accuracy

A
  • Air bubbles (Increased paO2)
  • Excess heparin (decreased pH)
  • Delay in analysis (decreased PaO2 & pH)
  • Blood clot in the sampe
  • Syringe
  • Temp & barometric therapy
51
Q

Define hypoxemia

A
  • Decreased PaO2, SaO2, or hemoglobin content
  • The amount of oxygen in the blood (CaO2) determines the severity
  • Usually PaO2 < 60 mmHg &/or SpO2 < 90%
52
Q

Define Hypoxia

A
  • General term for impairment of oxygen delivery to tissue (DO2)
  • Takes into account cardiac output (CO) & oxygen uptake @ tissue level
  • Therefore, hypoxemia is on type of hypoxia
53
Q

Causes of hypoxemia in ax

A
  • V/Q mismatch
  • Hypoventilation
  • Low FiO2
  • Right to left shunt
  • Diffusion impairment
  • Most common is a R to L shunt
54
Q

What is V/Q mismatch

A
  • Change in hemodynamics
  • Not getting O2 but the arterioles are coming by (decrease in Ventilation w/ norm circulation)
  • Change in circulation or blood flow in the px
  • Contributes to px oxygen levels
55
Q

What is the oxygen content (CaCO2) equation? Why use it?

A
  • CaO2 directly reflects the total # of oxygen molecules in arterial blood (both bound & unbound to hemoglobin)
  • Hemoglobin concentration is the main contributor
  • Times it by cardiac output to get DO2
  • DO2 is the what we care the most about (rate of oxygen delivery)

Anesthesia & Analgesia (29 decks)

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