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Y3 PPNP Finals > Acid Base Gas > Flashcards

Acid Base Gas Flashcards

1
Q

What is H used for

A

Cell membrane integrity and enzyme reactions

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2
Q

What are the 3 mechanisms that maintain normal pH?

A
  1. Buffer system (respond immediately)
    • change strong acid and bases into weaker ones = prevent drastic changes in pH of body
    • located in intracellular fluid (ICF) & extracellular fluid (ECF)
      > ECF: Carbonic acid bicarbonate (disintegrate into H and HCO3/bicarb), Hb
      > ICF: phosphate, proteins
  2. Respiration (within 1-3min)
    • CO2 produced as result of cellular respi
    • combine with water to form carbonic acid
    • before disintegrating into H & HCO3
    • resultant change in H changes pH
    • cause lungs to either increase/decrease rate & depth of ventilation
      > get rid of CO2 = increase RR
      > retain CO2 = decrease RR
  3. Kidney excretion (within hrs)
    • metabolic acids (except carbonic acid) can be excreted by kidney
    • adjust blood bicarbonate by:
      a) increase secretion/absorption
      b) produce new bicarb if necessary
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3
Q

What does acidosis cause?

A

Increased H+ & nervous system depression

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4
Q

What does alkalosis cause?

A

Decreased H+ & nervous system irritability

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5
Q

When is respi state acidotic

A

When PaCO2 >45mmHg

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6
Q

When is respi state alkalotic

A

When PaCO2 is <35mmHg

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7
Q

When is metabolic state acidotic

A

When HCO3 is <22mEq/L

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8
Q

When is metabolic state alkalotic

A

When HCO3 >26mEq/L

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9
Q

What is respi acidosis caused by?

A

Hypoventilation (lung cannot exhale excess CO2)
= accumulation of CO2 in body that combines with H2O to form carbonic acid
= breakdown into bicarbonate and H+ (where H+ change pH to acidic)

May req mechanical ventilator

Causes:
1. Brainstem trauma
2. CNS depressant
3. Impaired respi muscle function
4. Lung disorders (e.g pneumonia/emphysema)

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10
Q

What is the treatment for respi acidosis

A
  1. Tx underlying cause
  2. Hold/discontinue any respi depressant drugs
  3. Improve ventilation/respiration
  4. Reverse effect of respi depressants present
    • opiate = naxolone (*shd see response within 10min)
    • benzodiazepines = flumazenil (*max 5 doses per series, may repeat at 20min intervals)
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11
Q

What are the causes of metabolic acidosis

A
  1. Conditions when large amt of metabolic acids are produced
    • e.g. lactic acid -> lactic acidosis
      ketoacids -> diabetic ketoacidosis
      salicylic acid -> poisoning
  2. Impaired ability to excrete H+ by kidneys (e.g. severe kidney damage)
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12
Q

What is the treatment for metabolic acidosis

A

May req bicarbonate replacement (injection)

Na & H2O deficits must also be corrected

  1. Replace NaHCO3 (for pts with sodium bicarbonate loss due to diarrhoea, renal proximal tubular acidosis)

(*no definite evidence that it is beneficial for acute metabolic acidosis - incl DKA, lactic acidosis, septic shock, intranet metabolic acidosis/cardiac arrest)

  1. Monitor plasma e during course of therapy
    • k may decrease as pH increase
    • goal of HCO3 replacement: increase HCO3- to 10mEq/L & pH to 7.20 (*not to increase to normal)
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13
Q

What is the cause of respi alkalosis?

A

Hypoventilation due to:
1. Anxiety, fear, pain
2. Respi stimulants (e.g. doxapram)
3. Increased metabolic demands (e.g fever/thyrotoxicosis)
4. CNS lesions

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14
Q

What is the management for respi alkalosis?

A
  1. Identify & correct underlying cause
  2. Hold/discontinue any suspected drugs
  3. Initiate O2 therapy in pts with severe hypodermic (PaO2 <40mmHg)/change ventilator settings as needed
  4. Tx theophylline OD
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15
Q

What are the causes of metabolic alkalosis

A

Either H+ loss or excess HCO3

  1. Prolonged vomiting, repeated gastric suction = loss of gastric acid
  2. Excessive antacid usage (*not sole reason to pt having metabolic alkalosis)
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16
Q

What are the treatment for metabolic alkalosis

A

May req Cl-/K+ replacement

  1. Correct underlying disorder
  2. Hold/discounting any suspected drugs
  3. ECF vol contracted
    a) N/S at appropriate rate for degree of vol depletion
    b) replace K as needed
  4. ECF vol overload
    a) Acetazolamine (if not renal insufficiency)
    b) Haemodialysis/Peritoneal dialysis (for ARF/ESRD)
    - decrease bicarbonate bath if not alkalosis will worsen
  5. Hyperaldosteronism
    a) Spironolactone
    b) Amiloride
17
Q

What does pH test for

A

Tell if acidotic/alkalotic - measure of acid context/H+ in blood

18
Q

What does PaO2 test for

A

Amount of O2 dissolved in blood (O2 in arteries)

<80 = tissue hypoxia

Have a nonlinear r/s with SpO2 (not 1:1) = SpO2 & PaO2 lvls are diff
- only 1:1 when SpO2 is at 100%

*red flag when SpO2 <90% cos PaO2 will be <60mmHg
- as SpO2 goes down, PaO2 goes down drastically

19
Q

What does PaCO2 test

A

Measure CO2 in blood

Affected by CO2 removal in lung

*when PaCO2 is high, body compromises by vasodilating = flushed skin

20
Q

What does HCO3 test

A

Measure of bicarbonate content in blood

Affected by renal production of bicarb

21
Q

What does base excess test

A

Metabolic component of acid base balance reflected

Decreased or negative value = metabolic acidosis (primary/secondary to respi alkalosis)

Increased/positive value = metabolic alkalosis

*if ABG (pH, PaCO2, HCO3) is normal/body have compensated in a way but have diarrhoea etc, look at base excess

22
Q

What does SaO2 test

A

O2 sat

23
Q

What values are deranged in type 1 RF (hypoxemia without hypercapnia)

A

Only PaO2 (<60)

24
Q

What values are deranged in type 2 RF (hypoxemia with hypercapnia)

A

pH becomes acidotic

PaO2 is less than 60mmHg

PaCO2 is more than 45mmHg

25
Q

What values are deranged in a partial compensation ABG

A

Everything (except PaO2)

26
Q

What constitutes fully compensated ABG states

A

Respi acidosis -> pH normal but <7.40 + increased PaCO2 & HCO3

Respi alkalosis -> pH normal but >7.40 + decreased PaCO2 & HCO3

Metabolic acidosis -> pH normal but <7.40 + increased PaCO2 & HCO3

Metabolic alkalosis -> pH normal but >7.40 + decreased PaCO2 & HCO3

Y3 PPNP Finals (6 decks)

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