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pulmonology > Pulmonary Acid Base and ABGs > Flashcards

Pulmonary Acid Base and ABGs Flashcards

1
Q

What is pH?

A
  • scale goes from 1-14
  • water is neutral and is equal to 7
  • normal blood pH: 7.35-7.45
    alkalotic above 7.45, acidic below 7.35
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2
Q

pH is the result of what?

A
  • result of the total amt of body acids
  • carbonic acid: levels fluctuate based on concentration of CO2 and HCO3
  • lactic acid, phosphoric acid, sulfuric acid and ketone bodies: levels fluctuate based on function of renal system
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3
Q

What are the physiologic changes that occur with pH changes (alkalosis and acidosis)?

A
  • acidosis: decrease in force of cardiac contractions, decrease in vascular response to catecholamines, and decrease in response to the effects and actions of certain meds
  • alkalosis: interferes with tissue oxygenation, normal neuro and muscular functioning
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4
Q

How are blood pHs measured?

A
  • arterial sample
  • typically drawn at radial artery (or femoral)
  • ABG
  • test collateral circulation to the hand prior to drawing a sample from the radial artery = allen’s test
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5
Q

What do ABG results include?

A
  • pH
  • PaO2
  • PaCO2
  • HCO3
  • anion gap
  • H+ concentration, not directly measured but can be calculated if needed
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6
Q

What are the normal reference ranges fo ABGs?

A
  • pH: 7.35-7.45
  • paCO2: 35-45 mm Hg
  • PaO2: 80-102 mm Hg
  • HCO3: 22-28 mmmol/L
  • anion gap: 6-12 mmol/L
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7
Q

What types of pts would you order ABGs on?

A
  • impending or current state of respiratory failure
  • critically ill
  • sudden unexpected deterioration
  • sepsis
  • multiorgan failure
  • drug overdose
  • assessment of pts with chronic lung disease to eval level of CO2 retention
  • CO poisoning need to run a carboxyhemoglobin level
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8
Q

What are the main characters of acid base disturbances?

A
  • pH
  • H+
  • Co2
  • HCO3
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9
Q

What is inversely proportional to the pH?

A
  • H+ concentration
  • H+ ions are product of cellular metabolism
  • CO2 is a byproduct of cellular metabolism
  • most of CO2 is transported in the blood as HCO3
  • converting CO2 into HCO3 frees a H+, so the more CO2 there is the more H+ that are produced
  • CO2 concentration is also inversely proportional to pH. the higher the CO2 the lower (more acidic) the pH becomes
  • CO2 is a weak acid that is constantly being produced through tissue metabolism which is eliminated from the body through the lungs, and increasing the minute ventilation will decrease CO2: blowing off CO2
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10
Q

What are the buffers in the body?

A
  • respiratory
  • renal
  • carbonic acid-bicarb buffer
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11
Q

What buffer works the fastest?

A
  • respiratory buffer
  • the blood pH will change according to the level of carbonic acid and HCO3-
  • this triggers an increase or decrease in the rate and depth of ventilation until the appropriate amt of CO2 has been reestablished
  • activation of the lungs to compensate for an imbalance starts to occur within 1-3 minutes
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12
Q

What is the renal buffer?

A

bicarbonate (HCO3-)

  • base
  • buffer for H+
  • renal system maintains the balance of HCO3- and H+
  • metabolic changes that result in changes in pH take several days
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13
Q

How does the Carbonic acid bicarb buffer system work?

A
  • if there is an increase in H+ concentration in the blood - the equation is driven toward the left to form carbonic acid
  • if H+ concentration decreases below desired level than carbonic acid dissociates into bicarb and H+
  • when CO2 levels increase the formation of more carbonic acid occurs
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14
Q

What are the 4 major acid base derangements?

A
  • resp acidosis
  • resp alkalosis
  • metabolic acidosis
  • metabolic alkalosis
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15
Q

What are the causes of resp. acidosis?

A
  • pH less than 7.35 and a PaCO2 greater than 45 mm Hg
  • CNS depression: meds - narcotics, sedatives, or anesthesia or head injury
    or
  • impaired respiratory muscle function; spinal cord injury, neuromuscular disease, or neuromuscular blocking drugs
    or
  • pulm disorders: atelectasis, pneumonia, pneumothorax, pulmonary edema, bronchial obstruction, massive pulmonary embolus
    or
    hypoventilation due to pain, chest wall injury/deformity, abdominal distension, obesity
    or trauma
  • CO2 is elevated because of lack of ventilation
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16
Q

What are the causes of resp. alkalosis? (pH greater than 7.45, and CO2 less than 35 mm Hg)

A
  • psychological responses: anxiety or fear
  • pain
  • increased metabolic demands: fever, sepsis, pregnancy, or thyrotoxicosis
  • meds: such as respiratory stimulants
  • CNS lesions - telling you to breathe fast
  • CO2 decreased because of overventilation
17
Q

Causes of metabolic acidosis? (bicarb level of less than 22 mEq/L with pH less than 7.35

A
  • renal failure
  • DKA
  • diarrhea
  • anaerobic metabolism: from tissue hypoxia
  • starvation
  • ***salicylate intoxication: ASA overdose
  • ** presence of metabolic acidosis should spur a surch for hypoxic tissue somewhere in body
18
Q

Causes of metabolic alkalosis? bicarb greater than 28 mEq/L with pH greater than 7.45

A
  • either an excess of base or loss of acid within body
  • excess base occurs from ingestion of: antacids, excess use of bicarbonate, use of lactate in dialysis
  • loss of acids can occur secondary to: protracted vomiting, gastric suction, hypochloremia, excess admin of diuretics, and high levels of aldosterone
19
Q

Definitions of hypoxemia and hypoxia?

A
  • hypoxemia: insufficient oxygenation

- hypoxia: low oxygen content in tissue

20
Q

What is SaO2 or SpO2?

A
  • blood gas
  • SpO2 = pulse oximeter
  • arterial oxygen saturation
  • % of hemoglobin that is bound to O2
  • normal depends on pt, ideally should be 95% or greater
  • PaO2: arterial oxygen tension in the plasma, measured by blood gas, in general less than 80 is abnormal
21
Q

What is an A-a gradient?

A
  • difference b/t the oxygen tensino in alveoli (PAo2) and the arterial oxygen tension
22
Q

What can the PaO2 from the blood gas tell us?

A
  • can aid in assessment of the function of the alveolar capillary membrane
  • determination of the difference b/t alveolar oxygen partial pressure (PAO2) and arterial oxygen partial pressure (PaO2)
  • measures the integrity of alveolar capillary unit
23
Q

What is the normal A-a gradient?

A
  • normal values change with age (increase), usually norm is less than 10 mm Hg
  • to calculate estimated A-a gradient: age/4 + 4
24
Q

What factors go into calculating A-a gradient?

A
  • PaO2 is measure of blood gas
  • PAO2 is calculated from the alveolar gas equation
  • PAO2= (FIO2x (Patm -PH20))-(PaCO2/R)
    FIO2: room air= 0.21 fraction of inspired oxygen
    Patm= at sea level: 760
    PH20= at norm bod temp = 47 mm Hg
    PaCO2= CO2 tension from blood gas
  • R: respiratory quotient which is 0.8 at steady state
25
Q

What does hypoxemia with a normal A-a gradient mean?

A
  • hypoventilation, high altitude
26
Q

What does hypoxemia with an increased A-a gradient mean?

A
  • diffusion defect, ventilation-perfusion mismatch, right to left shunt
27
Q

What are the most common causes of a V/Q mismatch?

A
  • most common cause of hypoxemia***
  • responds to O2
  • increased Aa gradient
  • most common causes with ventilation problems: COPD, asthma, and pneumonia
    perfusion: PE, pulm HTN, and cardiac arrest
28
Q

Step 1 of ABG anaylsis (PaO2)

A

assess the PaO2
- is the PaO2 less than 80 mm Hg?
0 if no then there is adequate oxygenation and proceed to step 2
- if yes than go to step 1A to determine the A-a gradient

29
Q

Step 1A (assess ventilation)

A
  • is pt hypoventilating:
    if CO2 is high= hypoventilation go to step 2
  • if CO2 normal than no hypoventilation so proceed to step 1B to calculate A-a - need to find etiology of hypoxemia to determin degree of abnormality of pulmonary capillary membrane (problem with diffusion)
30
Q

step 1B (A-a gradient)

A
  • if A-a gradient is elevated then there is a problem on either side of the alveolar capillary membrane
31
Q

Step 2: calculate pH

A
  • Acidosis if below 7.35

- alkalosis if above 7.45

32
Q

Step 3: what is CO2?

A
  • in primary respiratory disorders: pH and CO2 change in opp directions but in primary metabolic disorders: pH and Co2 change in same direction
33
Q

Step 4: is there any compensation?

A
  • if it is a respiratory problem what is happening with HCO3-?
  • if metabolic problem what is happening with Co2?
34
Q

Step 5: calculate anion gap

A

= Na- (Cl+HCO3)

  • number of anions and cations should be equal in theory but they arent all measured in equation so difference is between 6-12
  • this may be helpful sorting out causes of metabolic acidosis as some causes have increased anion gap and some have normal gap
35
Q

When pH is low and CO2 is high what is problem?

A
  • resp acidosis
36
Q

When pH is high and CO2 is low what is the problem?

A
  • resp alkalosis
37
Q

When CO2 is normal and pH and HCO3 are low what is problem?

A

-metabolic acidosis

38
Q

When both pH and HCO3 are elevated and CO2 is normal whats the problem?

A
  • metabolic alkalosis

pulmonology (20 decks)

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