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Blood Gas Flashcards

1
Q

What should the pH of blood be?

A

7.35-7.45

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2
Q

What does it indicate if the blood pH is below 7.35?

A

Acidosis

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3
Q

What does it indicate if the blood pH is above 7.45?

A

Alkalosis

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4
Q

What should the PaCO2 be in the blood?

A

4.5-6.0kPa

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5
Q

What does it indicate if the PaCO2 is above 6.0kPa?

A

Respiratory acidosis

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6
Q

What does it indicate if the PaCO2 is below 4.5kPa?

A

Respiratory alkalosis

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7
Q

What should PaO2 be in the blood?

A

10.5-13.5kPa

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8
Q

What should the BiCarb HCO3 be in the blood?

A

21-27mmols

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9
Q

What does it indicate if the Bicarb HCO3 is above 27?

A

Metabolic alkalosis

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10
Q

What does it indicate if the Bicarb HCO3 is below 21?

A

Metabolic acidosis

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11
Q

What should the base excess in the blood be?

A

+2 - -2

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12
Q

What does it indicate if the base excess is more than 2?

A

Metabolic acidosis

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13
Q

What does it indicate if the base excess is less than 2?

A

Metabolic alkalosis

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14
Q

What effect does respiratory acidosis have on an ABG?

A

pH decreases
CO2 increases
HCO3 normal
Base Excess normal

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15
Q

What effect does respiratory alkalosis have on an ABG?

A

pH increases
CO2 decreases
HCO3 normal
Base Excess normal

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16
Q

What effect does metabolic acidosis have on an ABG?

A

pH decreases
CO2 normal
HCO3 decreases
Base Excess decreases

17
Q

What effect does metabolic alkalosis have on an ABG?

A

pH increases
CO2 normal
HCO3 increases
Base Excess increases

18
Q

What does the pH in an arterial blood gas represent?

A

pH represents the hydrogen ion concentration in the blood

19
Q

What does the HCO3 (bicarb) in an arterial blood gas represent?

A

If there is metabolic contribution to acidosis/alkalosis

20
Q

What does Base Excess represent in an ABG?

A

Base Excess measure the amount of acid or base needed to return the pH to normal homeostasis (7.35-7.45)

21
Q

What are the systems that are responsible for maintaining pH called?

A

Buffer systems

22
Q

What are the buffer systems?

A

Bicarbonate, haemoglobin, phosphate, plasma proteins

23
Q

What are the buffer organs?

A

Lungs and kidneys

24
Q

What are the causes of respiratory acidosis?

A

Impaired gas exchange or ventilation caused by:
- Acute Obstructive Disorders (eg: croup, asthma, bronchiolitis)
- Chronic Obstructive Disorders (eg: Cystic Fibrosis)
- Pulmonary Restrictive Disorders (eg: pneumonia, aspiration, pulmonary oedema, pleural effusion)
- Neuromuscular disorders
- CNS depression
- Inadequate mechanical ventilation

25
What are the effects of respiratory acidosis?
- Increased then decreases respiratory rate with shallow breathing and tachycardia - Cyanosis - Wheezing, hyperinflation, decreased breath sounds, prolonged expiration (respiratory compensation) - Mental status may be affected by decreased oxygenation in the brain - Nausea and vomiting
26
What are the causes of respiratory alkalosis?
- Direct cause of hyperventilation - Increased metabolic rate - Brain tumour/injury - Aggressive ventilation
27
What are the effects of respiratory alkalosis?
- Low CO2 (hypocapnia) causes a reduction in serum levels of potassium and phosphate - Reduction in serum calcium as calcium binds to albumin - Cardiac rhythm disturbances - Hypocapnia reduces cerebral blood flow and can cause neurological symptoms - Tachycardia/tachypnoea
28
What are the causes of metabolic acidosis?
- Severe diarrhoea causing GI loses of bicarbonate - Renal disease causing inadequate re- absorption of bicarbonate and excretion of acids - DKA - Shock - Excess alcohol consumption - High extracellular potassium (Potassium enters the cell in exchange for H+ ion)
29
What are the effects of metabolic acidosis?
- Tachycardia - Poor perfusion - Decreased peripheral pulses - Increased capillary refill time - Decreased level of consciousness - Fatigue - Confusion - Seizures - Nausea and vomiting
30
What are the causes of metabolic alkalosis?
- Vomiting or gastric draining - Selected diuretics can cause potassium depletion and stimulate renal tubules (kidneys) to produce H+ ions - Constipation – increased bicarbonate is absorbed - Excess bicarb administration
31
What are the effects of metabolic alkalosis?
- Hypoventilation - Decreased perfusion - Confusion and lethargy - Unresponsiveness - Hyperreflexia - Diarrhoea and vomiting
32
How may an exacerbation of asthma affect an Arterial Blood Gas?
A patient may present with respiratory acidosis
33
How may sepsis affect a patient's Arterial Blood Gas?
A patient may present with metabolic acidosis
34
How may hypovolaemia affect a patient's Arterial Blood Gas?
A patient may present with metabolic acidosis
35
Why may a patient with hypovolemia and sepsis present with metabolic acidosis?
In shock there is a reduced delivery or increased consumption of oxygen as oxygen delivery is impaired due to inadequate numbers of red blood cells or haemoglobin to carry the oxygen Therefore cells move from aerobic to anaerobic metabolism which affects cell pH and causes metabolic acidosis as anaerobic metabolism produces lactic acid
35
Why may a patient with hypovolemia and sepsis present with metabolic acidosis?
In shock there is a reduced delivery or increased consumption of oxygen as oxygen delivery is impaired due to inadequate numbers of red blood cells or haemoglobin to carry the oxygen Therefore cells move from aerobic to anaerobic metabolism which affects cell pH and causes metabolic acidosis as anaerobic metabolism produces lactic acid
36
Why may a patient with asthma present with respiratory acidosis?
Asthma leads to respiratory acidosis due to the inability to get CO2 out of the blood and PaCO2 > 6 KPA Impaired expiration, hyperventilation and hyperinflation of the lungs leads to CO2 retention and respiratory acidosis

OSCE PREP (12 decks)

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