Respiratory Flashcards
Normal pH
7.35 - 7.45
Normal PaO2
Normal PaCO2
11-13kPa (note this is for room O2 - 21%)
4.7-6.0kPa
Rule of thumb to estimate PaO2 using the inspired O2 concentration
Ten less
i.e. if inspiring 21% O2 as in the air then PaO2 estimate around 11 kPa
If 60% O2 then 50kPa and so on
This is why PaO2 must always br interpreted with FiO2 in mind
Type 1 Respiratory failure PaO2 & PaCO2
PaO2 under 8kPa
PaCO2 under 6.5 kPa
(T1 only 1 abnormality)
Type 2 Respiratory failure PaO2 & PaCO2
PaO2 under 8kPa
PaCO2 over 6.5 kPa
(T2 only 2 abnormality)
Causes of T1RF (All the P’s)
Pulmonary oedema
Pneumonia
PE
Pulmonary fibrosis
Due to VQ mismatch
Causes of T2RF (more to do with mechanics of breathing)
COPD
Resp centre depression
Resp muscle weakness
Abnormal chest wall
What is quicker, resp or metabolic compensation
For resp pH problems, metabolic compensation occurs but this takes some time
For metabolic pH problems, resp compensation occurs and this is quick (resp rate change)
Steps of determining cause of pH imbalance
Look at pH (acid or alkali)
Assess PaCO2
If normal / high in alkalosis or normal / low in acidosis then go on to look at HCO3 as the potential cause of imbalance
pH acidic and bicarb low
Metabolic acidosis
pH alkaline bicarb high
Metabolic alkalosis
pH acidic and CO2 high
Resp acidosis (resp failure)
pH alkaline and CO2 low
Resp alkalosis (hyperventilation)
What is anion gap and when is it used
(Na+ + K+) - (Cl- + HCO3-) used to determine cause of metabolic acidosis
Normal anion gap metabolic acidosis causes
HCO3- loss from gut (e.g. diarrhoea)
Renal tubular acidosis
Na and K not increased (may be lost in diarrhoea)
Raised anion gap metabolic acidosis causes
Ketoacidosis (high K) Renal failure Lactic acidosis Salicylate toxicity Methanol ingestion Antifreeze ingestion
All factors are where extra metabolites are added or ingested
Metabolic alkalosis causes
Loss from gut (e.g. vomiting causes hypochloraemic met alk)
Hyperaldosteronism (due to lower levels of potassium in blood + more H+ excretion)
What is PEFR compared against
Predictive value using age, sex and height
FEV1 / FVC use in spirometry
Distinguish between obstructive (COPD and Asthma) and Restrictive (Pulmonary fibrosis) lung disease
(less than 70% = obstructive, over 80% = restrictive)
What is Kco
Common causes of a low Kco
This measures the ease of diffusion of carbon monoxide into capillary blood
Interstitial lung disease Emphysema Pulmonary oedema PE Anaemia (lower binding capacity - this will also have normal spirometry)
