Investigations Flashcards
What is the formula for arterial blood gas?
CO2 + H2O H2CO3 H+ + HCO3-
Who should have an ABG?
Critically unwell
Unexpected/inappropriate hyperaemia (sats <94%)
Deteriorating sats or inc SOB
Deteriorating pt now needing O2 to maintain sats
Risk of hypercapnic resp failure
SOB & risk of metabolic condition
Poor peripheral circulation sats cannot be obtained
Any other evidence ABG would be useful
What are the risks associated with an ABG?
Nerve injury Digital ischaemia Infection Bleeding & haematoma Pseudoaneurysm AV fistula Injury to staff
What parameters show respiratory acidosis?
pH: Low
PaCO2: High
What parameters show respiratory alkalosis?
pH: High
PaCO2: Low
What parameters show metabolic acidosis?
pH: Low
HCO3-: Low
What parameters show metabolic alkalosis?
pH: High
HCO3-: High
What are the causes of respiratory acidosis?
Hypoventilation
CNS depression (drugs, narcotics, sedatives)
Dec chest wall movement (NM disorders, myasthenia, tension PT, upper airway obstruction)
COPD
Asthma attack
What are the causes of respiratory alkalosis?
Stimulated resp drive
Hyper metabolic state (sepsis, pregnancy, thyrotoxicosis)
Hyperventilation
Hyperthermia
Drugs (aspirin, OD, progesterone)
Hypoxaemia (PE, pneumonia, altitude, PO, asthma attack)
Liver failure
What are the causes of metabolic acidosis?
Increased anion gap: New acid added (OH-, uraemia, DKA, lactate, iron, salicylate)
Normal anion gap: retaining H+/loosing HCO3-, diarrhoea, Addison’s, RTA
Low anion gap: Li toxicity, hyperCa, hyperMg, HyperK, multiple myeloma
What are the causes of metabolic alkalosis?
Acid loss Chloride responsive (D&V, corticosteroids) Chloride resistant (hyperaldosteronism, Cushing's, hypoK)
How is hydration status assessed?
Hands: Temp, (collapsing) pulse, L&S BP, CRT
Head & neck: Sunken eyes, JVP, mucus membranes, carotid vol & character
Sternum: CRT, skin turgor, apex beat, auscultate heart&lung bases
Abdo: Ascites
Legs: Oedema
Extra: Weight, U&Es, Catheter, ABG&lactate
What can the colour of a urine sample mean?
Straw yellow- Normal
Dark- Bile pigments due to dehydration
Red- Haematuria, menstrual blood, food (beetroot & blackberries)
Green/blue- Pseudomonal UTI, triamterene (K sparing diuretic), asparagus
Orange- Dehydration (bile pigments), phenothiazines, carrots
What can frothy urine be indication of?
Proteinuria
What are the causes of haematuria?
Menstrual bleeding- MOST COMMON Trauma Prostate/urological exam Exercise induced Dehydration Glomerular/tubular pathology