Blood Gases Flashcards
What are the normal pH ranges?
7.35-7.45 kPa
What are the normal PaCo2 ranges?
4.5-6.0 kPa
What are the normal PaO2 ranges?
10.5-13.5 kPa
What are the normal HCO3 ranges?
21-27 kPa
What are the normal BE ranges?
-2 to +2 kPa
What would you expect to see in a respiratory acidosis?
Decreased pH
Increased CO2
Normal HCO3
Normal BE
What would you expect to see in a respiratory alkalosis?
Increased pH
Decreased CO2
Normal HCO3
Normal BE
What would you expect to see in a metabolic acidosis?
Decreased pH
Normal CO2
Decreased HCO3
Decreased BE
What would you expect to see in a metabolic alkalosis?
Increased pH
Normal CO2
Decreased HCO3
Increased BE
What does pH represent?
The hydrogen ion concentration
What does HCO3 represent?
Assesses the metabolic component- titrated against a constant temperature and CO2
What does Base Excess represent?
Is a measure of the amount of acid or base that needs to be added to a sample under standard conditions to return the pH to 7.4
What do acid base disturbances indicate?
A serious underlying pathology rather than being the pathology in themselves
How does pH affect the body?
Biochemical processes are very sensitive to even small changes in pH
What are buffer systems?
Systems responsible for maintaining pH- such as bicardbonate, haemoglobin, phosphate and plasma proteins
What are examples of buffer organs?
Lungs and kidneys
What are some causes of respiratory acidosis?
Impared gaseous exchange or lung ventilation i.e. asthma, croup
Pulmonary restrictive disorders i.e. COPD
Neuromuscular diseases
CNS depression
Iatrogenic causes (inadequate mechanical ventilation)
What are the effects of respiratory acidosis?
Decreases respiratory rate, shallow breathing, tachycardia
Cyanosis may be notes if accompanying hypoxaemia is present
Physical examination may demonstrate presence of wheezing, hyperinflation, decreased breath sounds, prolonged expiration etc
Mental status may be depressed in severe elevations of PaCO2- seizures may occur
Nausea and vomiting
What are some causes of respiratory alkalosis?
Direct cause is always hyperventilation (pain, anxiety)
Increased metabolic rate
Brain tumour or injury
Effects of respiratory alkalosis
Hypocapnoea causes a reduction in serum calcium (many of the symptoms are related to hypocalcaemia.) Calcium reduction is secondary to increased binding of calcium to albumin
Cardiac rhythm disturbances
Hypocapnoea reduces cerebral blood flow and can cause neurological symptoms, including dizziness, mental confusion, syncope and seizures
Anxiety, tachycardia and tachypnoea
Causes of metabolic acidosis
Severe diarrhoea (GI losses of bicarbonate)
Renal diseases (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)
What are the effects of metabolic acidosis?
Kussmaul respirations
Tachycardia
Poor perfusion
Decreased peripheral pulses
Increased capillary refill time
Decreased level of consciousness
Fatigue
Confusion
Seizures
Nausea and vomiting
What are the causes of metabolic alkalosis?
Vomiting or gastric drainage
Selected diuretics causing potassium depletion which stimulates the renal tubules to secrete H+ ions
Constipation leading to increased bicarbonate absorbed
Excess bicarbonate administration
What are the effects of a metabolic alkalosis?
Hypoventilation
Decreased perfusion
Confusion and lethargy
Unresponsiveness
Hyperreflexia
Tetany
Seizures
D&V
