*ABG Basics* Flashcards
Normal ranges for all values?
pH = 7.35-7.45 pO2 = 11-13 (>10) pCO2 = 4.7-6.0 HCO3- = 22-26 BE = -2 to +2
What is normal pO2 and how is it calculated in patients on administered oxygen?
Normal should be >10 on room air (RA)
- normal for patients on delivered oxygen is calculated as roughly 10kPa below the %oxygen being administered
- e.g. patient on 20% oxygen should be at pO2 10kPa
What are the abnormal pO2 states defined as?
Hypoxaemia = pO2<10
Severe hypoxaemia/respiratory failure = pO2<8
What are the 2 types of respiratory failure and how are they defined?
Type 1 - hypoxaemia (<8) with normocapnia (<6)
Type 2 - hypoxaemia with hypercapnia (>6)
What is type 1 respiratory failure caused by and how does it form?
Ventilation/perfusion mismatch (V/Q mismatch)
- volume of air flowing in/out of the lungs does not match the flow of blood to the lung tissue
- as a result of the mismatch, pO2 falls and pCO2 rises (remember these are in the blood, not the lungs)
- the rise in pCO2 triggers an increase in the patients alveolar ventilation which corrects the pCO2 but not the pO2 (different dissociation curves)
Examples of V/Q mismatch?
Reduced ventilation with normal perfusion = pulmonary oedema, bronchoconstriction (e.g. severe asthma)
Reduced perfusion with normal ventilation = pulmonary embolism
What is type 2 respiratory failure caused by and how does it form?
Caused by alveolar hypoventilation
- patient can’t adequately oxygenate, and eliminate CO2 from, their blood
- pCO2 rises as it isn’t cleared
- pO2 falls as less is absorbed into the blood form the lungs
What are the causes of alveolar hypoventilation (i.e. causes of type 2 respiratory failure)?
- Increased resistance due to airway obstruction (COPD)
- Reduced compliance of the lung tissue/chest wall (pneumonia, rib fracture, obesity)
- Reduced strength of respiratory muscles (Guillain-Barré syndrome, motor neurone disease)
- Drugs acting on the respiratory centre reducing overall ventilation (opiates)
Evidence for source of pH derangement?
Imbalance in HCO3- = metabolic
Imbalance in pCO2 = respiratory
- these are the buffers the body uses to correct the pH if one of them is causing a deranged pH
What is a typical pH, pCO2, and HCO3- appearance for respiratory acidosis with no compensation?
pH - decreased (acidic)
pCO2 - increased (CO2 retention)
HCO3- - normal
What is a typical pH, pCO2, and HCO3- appearance for respiratory alkalosis with no compensation?
pH - increased (alkalotic)
pCO2 - decreased (hypocapnia)
HCO3- - normal
What is a typical pH, pCO2, and HCO3- appearance for respiratory acidosis with partial/complete metabolic compensation?
pH - low/normal (partial/complete comp)
pCO2 - increased
HCO3 - increased
What is a typical pH, pCO2, and HCO3- appearance for respiratory alkalosis with partial/complete metabolic compensation?
pH - high/normal (partial/complete comp)
pCO2 - decreased
HCO3 - decreased
Incomplete so will come back to this but GeekyMedics quiz link on back of this and in Practice Paper 3
https://geekyquiz.com/learn/quiz/336440/