Pulmonary Acid Base and Alterations in Gas Exchange Flashcards Preview

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Flashcards in Pulmonary Acid Base and Alterations in Gas Exchange Deck (55)
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What is the normal blood pH?

What is the equation to find pH?

Normal blood pH is 7.35 to 7.45

pH=6.1 + log10 ([HCO3-]/0.03 x PaCO2)


pH is the total amount of what in the body?

Levels flucuate based on what? 2

What other acids are we including in pH measurements? 4

All these acids flucuate based on what?


Levels fluctuate based on the concentration of CO2 and HCO3-

1. Lactic acid,
2. phosphoric acid,
3. sulfuric acid and
4. ketone bodies

Levels fluctuate based on the function of the renal system


Physiologic changes that occur with pH changes
Acidosis? 3
Alkalosis? 2

↓force of cardiac contractions
↓ vascular response to catecholamines
↓ response to the effects and actions of certain medications

1. interferes with tissue oxygenation
2. normal neurological and muscular functioning


How is blood pH measured?

The blood pH is measured with an arterial sample


What should we do before we draw a blood sample from the radial artery?

Test collateral circulation to the hand prior to drawing a sample from the radial artery = Allen’s Test


ABG results include the following 5

Is H+ concentration measured?

Anion gap

Not directly measured but can be calculated if needed


Normal reference ranges:
Anion gap

pH 7.35-7.45
PaCO2 35-45 mmHg
PaO2 80-102 mmHg
HCO3 22-28 mmol/L
Anion gap 6-12 mmol/L


Types of patients to order blood gases on include:

1. Impending or current state of respiratory failure
2. Critically ill
3. Sudden unexpected deterioration
4. Sepsis
5. Multiorgan failure
6. Drug overdose
7. Assessment of patients with chronic lung disease to evaluate level of CO2 retention
8. Carbon monoxide poisoning need to run a carboxyhemoglobin level


What are the main players in acid base disturbances?



1. Hydrogen ion concentration is inversely proportional to what?

2. What are hydrogen ions a product of?
3. CO2?
4, Most of the CO2 transported in the blood is what?
5. Converting CO2 into HCO3- frees a ______ ion
6. The more CO2 there is the ______hydrogen ions are produced

7. What is the equation for this reaction?

1. pH

2. cellular metabolism
3. cellular metabolism
4. HCO3-

5. hydrogen
6. more

7. H2O + CO2 ↔ H2CO3 ↔ HCO3- + H+


CO2 is proportional how to pH?



The higher the CO2, the ________ the pH becomes

CO2 is a ____ ___ that is constantly being produced through ____ _______?

Increase the minute ventilation will do what to CO2?

lower (more acidic)

weak acid
tissue metabolism

Increasing the minute ventilation will decrease CO2


What are the three different kinds of buffers we talked about in the lecture?

Carbonic acid-bicarbonate buffer


How would you describe the repsponse of the respiratory buffer?

The blood pH will change according to the what? 2

This triggers an increase or decrease in the ____ and ____ of _______ until the appropriate amount of CO2 has been re-established

Activation of the lungs to compensate for an imbalance starts to occur within ______?


level of carbonic acid and HCO3-

rate and depth of ventilation

1-3 min


What is the renal buffer?

What is it a buffer for?

Renal system maintains the balance of what? 2

Metabolic changes that result in changes in the pH take how long?

Bicarbonate (HCO3-)- base

Buffer for hydrogen ions

Renal system maintains the balance of HCO3- and H+

Metabolic changes that result in changes in the pH take several days


If there is an increase in the H+ concentration in the blood what happens?

If H+ concentrations in the blood drop below the desired level what happens?

What happens when CO2 levels increase?

Formation of carbonic acid (drives equation to the left)

Carbonic acid dissociates (drives the equation to the right)

Formation of more carbonic acid (drives the equation to the right)


The 4 major acid base derangements

Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis


What is respiratory acidosis defined as?

What causes it?

pH less than 7.35 with a PaCO2 > than than 45 mm Hg

1. Central nervous system depression

2. Impaired respiratory muscle function

3. Pulmonary disorders

4. Hypoventilation

5. Trauma


For respiratory acidosis what things could depress the central nervous system?

What could impair repsiratory muscle function? 3

What pulmonary disorders could cause this? 6

What would the hypoventilation be due to?

1. medications (narcotics, sedatives, or anesthesia)
2. head injury

1. spinal cord injury,
2. neuromuscular diseases
3. neuromuscular blocking drugs

1. Atelectasis
2. Pneumonia
3. Pneumothorax
4. Pulmonary edema
5. Bronchial obstruction
6. Massive pulmonary embolus

1. Pain
2. Chest wall injury/deformity
3. Abdominal distension
4. Obesity
5. Trauma


What is respiratory alkalosis defined as?

What causes it?

pH >7.45 with a PaCO2 less than 35 mm Hg.

1. Psychological responses
Anxiety or fear
2. Pain
3. Increased metabolic demands
Fever, sepsis, pregnancy, or thyrotoxicosis
4. Medications, such as respiratory stimulants
5. Central nervous system lesions


What are things that could increase metabolic demands?

pregnancy, or


Defintion and Causes (6)of Metabolic Acidosis

bicarbonate level of less than 22 mEq/L with a pH less than 7.35

1. Renal failure
2. Diabetic ketoacidosis
3. Diarrhea
4. Anaerobic metabolism
from tissue hypoxia
5. Starvation
6. Salicylate intoxication


Pearl: The presence of metabolic acidosis should spur a search what??

for hypoxic tissue somewhere in the body (need to save dying tissue)


Defintion and causes (8) of Metabolic Alkalosis

3 and 5

bicarbonate level > 28 mEq/L with a pH > 7.45

1. Either an excess of base or a loss of acid within the body
Excess base occurs from ingestion of:
2. antacids
3. excess use of bicarbonate
4. use of lactate in dialysis
Loss of acids can occur secondary to:
5. protracted vomiting
6. gastric suction
7. Hypochloremia
8. Excess administration of diuretics
9. High levels of aldosterone


What is hypoxemia?
What is hypoxia?

Insufficient oxygenation = hypoxemia

Low oxygen content in tissue = hypoxia


SaO2 (blood gas) or SpO2 (pulse oximeter) is defined as what?

What is the normal value?

Arterial oxygen saturation
% of hemoglobin that is bound with O2

Normal, depends on the patient, ideally should be ≥ 95%


What is PaO2 and what is the normal?

Arterial oxygen tension in the plasma

Measured by blood gas
In general less than 80mmHg abnormal


What is A-a gradient?

The difference between the oxygen tension in the alveoli (PAO2) and the arterial oxygen tension


The PaO2 from the blood gas can aid in assessment of what?

the function of the alveolar-capillary membrane


What does the different between alveolar oxygen partial pressure (PAO2) and arterial oxygen partial pressure (PaO2)
PAO2 – PaO2 measure?

Measures the integrity of the alveolar-capillary unit