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Lab D > Lab 2 Acid base - Blood gas > Flashcards

Lab 2 Acid base - Blood gas Flashcards

1
Q

Isohydria

A

pH

The conc of H-ions in the body

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2
Q

Normal pH in blood

A

7.35-7.45

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3
Q

Isohydria is essential for two things in the body:

Any pH change can lead to:

A

Cell membranes
Enzyme activities

Electrolyte imbalance

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4
Q

Why is a buffer system needed in the body

A

Because hydrogen ions are constantly produced from chemical reactions, these can lead to alterations in pH

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5
Q

Definition of a buffer system

A

A solution that can maintain a nearly constant pH if diluted, or if small amounts of strong acids or bases are added: they resist pH changes

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6
Q

What does a buffer solution typically consist of?

A

Weak acid/base and one of its salts
If H+ in the body starts to increase, the conjugate base can uptake this excess.
If H+ starts to decrease, more weak acids can dissociate

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7
Q

What is the most important buffer system in all fluid compartments of the body?

A

Carbonic acid - bicarbonate system

Phosphate buffer, protein buffer

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8
Q

Three most important buffer systems of blood plasma

A

Carbonic acid - bicarbonate system
Primary - secondary phosphate buffer
Albumin - albumin + H+

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9
Q

Three most important buffer systems of RBCs

A

Carbonic acid - bicarbonate system
Primary - secondary phosphate buffer
Haemoglobin + O2 - haemoglobin - H+

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10
Q

Three most important buffer systems of tissue cells

A

Carbonic acid - bicarbonate system
Primary - secondary phosphate buffer
Cytoplasmic proteins

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11
Q

What does the vital buffer system consist of?

A

The kidneys and lungs

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12
Q

Buffering capacity of lungs

A

Can retain or excrete CO2 to regulate pH acutely
Reduced ECF pH - hypercapnia
Ventilation is stimulated (huge capacity)
Kussmaul breathing is observed (deep exp/ins)

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13
Q

Buffering capacity of kidneys

A

Can retain or excrete H+ and effectively regenerate the HCO3- via complex tubular mechanisms
Takes hours/days

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14
Q

Acid base sample

A

Sample: Ca-equilibrated Li-heparinised blood
Arterial: shows respiratory function
Air contamination must be avoided (false high pO2)
CO2 can evaporate into air: false low pCO2
Long storage: metabolism of RBCs: false high pCO2

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15
Q

Acid base method

A

ISE to measure pH and CO2
Based on the measured parameters, HCO3- and ABE can be calculated
Measured at 37 C
Solubility of gas is dependent on temp - has to be corrected according to temp of patient (hypo/hyper-thermia)

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16
Q

Give respiratory parameters

A

pCO2

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17
Q

Give metabolic parameters

A

HCO3- (depends on pCO2)
ABE
SBE

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18
Q

TCO2

A

Total CO2
5% higher than plasma HCO3-
Gives no direct information about respiratory function

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19
Q

SBE

A

Standard base excess

Same as ABE but calculated value

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20
Q

ABE

A

Actual base excess

the amount of acid/base needed to equilibrate blood to pH 7.4

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21
Q

Evaluation of Acid/Base state

A
  1. Evaluate acidosis/alkalosis according to pH!
    Most important step
  2. Search for cause of pH alteration
    Respiratory/metabolic changes
    Resp: pCO2 change Met: HCO3-, ABE change
  3. Evaluate whether compensation effort is visible
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22
Q

Compensated state

A

Within 7.35-7.45

Below or above and it is decompensated

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23
Q

Respiratory background of pH alteration

A

pCO2 shows a strong shift in the same direction as pH

High pCO2 = bound to water = H2CO3 (carbonic acid)
= shift in acidic direction

Low pCO2: hyperventilation, too much CO2 is exhaled

24
Q

Metabolic background of pH alteration

A

Lactic acid production: acidic shift of both parameters

ABE: positive in alkalosis, negative in acidosis

25
Q

Evaluation of respiratory and metabolic parameters compared to pH

A

Evaluate whether the change of parameters correspond to the alteration of pH

26
Q

How to detect compensatory effect?

A

The given parameter is shifted in the opposite direction compared to the pH
EXAMPLE:
Metabolic acidosis, the lungs will try and compensate by Kussmaul breathing. Result:
pH acidic
CO2 alkaline

27
Q

Mixed acidosis

A

Advanced acidosis

All parameters are shifted significantly in the same direction as pH

28
Q

Metabolic acidosis causes (8)

A 
HCO3- loss
Increased acid intake
Increased acid production
Grain overdose in cattle (VFA overproduction)
Increased ketogenesis
Decreased acid excretion
Ion exchange (hyperkalaemia)
Ethylene-glycol toxicosis
29
Q

Metabolic acidosis effects (5)

A 
Kussmaul breathing
Hypercalcaemia: mobilization (long term)
Vomiting, depression
Hyperkalaemia
Acidic urine
30
Q

Metabolic acidosis treatment:

A

Adequate ventilation

if pH <7.2: alkaline (NaHCO3) infusion therapy (based on ABE calculation)

31
Q

Anion gap

A

Cations:anions

Useful when attempting to determine cause of metabolic acidosis

32
Q

Maintaining electroneutrality (anion gap)

A

Conc of cations and anions must be equal in plasma
Decrease in HCO3- has to be balanced by an increase in Cl- or Unmeasured anions
Direct HCO3- loss: Cl- replaces HCO3-
Normal anion gap: hyperchloraemic metabolic acidosis

If reduction of HCO3- is due to acc of Ua, Cl- stays normal
Increased anion gap: normochloraemic metabolic acidosis

33
Q

Normal anion gap: hyperchloraemic metabolic acidosis

CAUSES

A

Diarrhea
Early kidney failure
Renal tubular acidosis
Acidifying substances

34
Q

Increased anion gap: normochloraemic metabolic acidosis

CAUSES

A

Azotaemia/uraemia
Lactoacidosis
Ketoacidosis
Toxicosis

(basically substances in the blood that aren’t measured)

35
Q

Metabolic alkalosis causes (5)

A

Increased alkaline intake (rotten/bicarbonate)
Increased ruminal alkaline prod (high prot, low carb)
Decreased hepatic ammonia catabolism (liver failure)
Increased acid loss: vomiting, GDV, abomasal displacement
Ion exchange: hypokalaemia (HCO3- retention)

36
Q

Metabolic alkalosis effects (4)

A 
Breathing depression
Muscle weakness - hypokalaemia
Hypocalcaemia (ø bind to albumin)
Ammonia toxicosis
Arrythmia
37
Q

Metabolic alkalosis treatment

A

Treatment of underlying electrolyte imbalance

38
Q

Respiratory acidosis causes (7)

A

Upper airway obstruction
Pleural cavity disease
Pulmonary disease
Depression of central control of respiration
Neuromuscular depression of respiratory muscles
Muscle weakness
Cardiopulmonary arrest

39
Q

Respiratory acidosis effects (5)

A 
Dyspnoea
Cyanosis
Suffocation
Muscle weakness
Tiredness
40
Q

Respiratory acidosis treatment

A

Assisting ventilation
Treatment of cause (oedema of lungs)
Milk anxiolytic/sedating drugs to decrease fear/excitement caused by hypoxia

41
Q

Respiratory alkalosis causes (5)

A 
Hyperventilation:
Excitation
Forced ventilation (anaesthesia)
Epileptic seizures
Fever, hyperthermia
Interstitial lung disease
42
Q

Respiratory alkalosis effects

A

Hyperoxia, decreased pCO2:pO2 ratio

Increased elimination of HCO3- by kidneys

43
Q

Respiratory alkalosis treatment

A

Anxiolytic drugs

Breathing into paper bag

44
Q

Why do we analyse blood gas?

A

Assess effectiveness of gas exchange (esp during dyspnoea or anaesthesia

45
Q

Blood gas analysis sample

A 
Arterial blood
(venous blood only gives indication of how much oxygen was consumed by body)
Ca-equilibrated Li-heparinised plasma
Closed sampling method
(Avoid air contamination)
46
Q

Blood gas analysis method

A

ISE

Standardized temp 37C (must be temp corrected!)

47
Q

paO2

A

Arterial partial pressure of oxygen

Indicates the lungs ability to oxygenate blood

48
Q

paCO2

A

Arterial partial pressure of carbon dioxide

Indicates the ability of alveolar gas exchange to remove CO2

49
Q

SAT/SatO2

A

Oxygen saturation %
Indicates fraction of oxygen-saturated hemoglobin relative to total hemoglobin in the blood
Venous: 75-80%
Arterial: 90-100%

50
Q

FiO2

A

Fraction of inspired oxygen
The assumed % of O2 concentration participating in gas exchange in the alveoli
Room air: 20.9%
>0.5 risk of O2 toxicity

51
Q

What can be the case when paO2 is under 40-50 mmHg?

A

Cyanosis

52
Q

Which is higher, pvCO2 or paCO2

A

pvCO2

53
Q

Hypoventilation causes (5)

A

Upper airway obstruction
Pleural effusion
Disturbance to central control of respiration
Neuromuscular disease which affects resp system
Overcompensation of metabolic alkalosis

54
Q

Hypoventilation effects

A

Dyspnoea, cyanosis

55
Q

Hypoventilation treatment

A

Assisting ventilation
Diuretic treatment (fluid acc in lungs or thoracic cav)
Mild anxiolytic/sedative treatment

56
Q

V/Q

A

Ventilation-perfusion mismatch

57
Q

Hyperventilation causes

A

Iatrogen
Seizures
Excitation (mild/extreme)
Compensation of severe metabolic acidosis

Lab D (8 decks)

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