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
What are the causes of proteinuria?
Transient: congestive heart failure in elderly
Intermittent: Asymptomatic as a result of prolonged vertical posture, exposure to cold, pregnancy and hypertension.
Persistent: Glomerular underlying disease, DM, myeloma, hypertension, connective tissue disease
What are the causes of glycosuria
Diabetes
Cushing’s syndrome
Liver and pancreatic disease
Fanconi’s syndrome
What are the causes of ketones in the urine?
Pregnancy
Diabetes
Starvation/rapid weight loss
What are the causes of urobilogen/bilirubin in the urine?
No bilirubin in normal urine
Conjugated: Liver disease, BDobstruction
What is the diagnosis for someone with: Urea ++ Creatinine ++ Sodium + Potassium- Normal
Renal failure
Causes: Chronic renal failure, DM, hyperT, Pyelonephritis / glomerulonephritis
What is the diagnosis for someone with: Sodium + Potassium - Creatinine- Normal Urea- Normal Associated: Hypertension
Hyperaldosteronism (Conn’s Syndrome)
Aldosterone causes the retention of sodium at the expense of potassium. It acts on the PCT causing the synthesis of more Na+/K+ exchange channels. Thus, in thepresence of excess of aldosterone there will be excess secretion of K+, and retention of Na+. The retention of Na+ will cause a secondary retention of water, resulting in hypertension.
What is normal urine output for an adult?
> 0.5mL/Kg/hr
What are the indications for a lumbar puncture?
- Infection: Meningeal, encephalitis, TB, Strep, Herpes
- Bleeding into the CSF: Sub-arachnoid
- Inflammation of brain/SC/CSF: Multiple Sclerosis
What are the contraindications for a lumbar puncture?
- RAISED INTRACRANIAL PRESSURE
- No consent
- Coagulopathy
- Local infection at needle site
Why is an LP not performed with raised ICP?
What is the one exception to this rule?
By removing fluid from the spinal canal, you lower the pressure in this area. The high pressure within the cranium may then cause herniation of the brainstem through the foramen magnum.
Benign raised ICP- usually young women without symptoms (headache, impaired consciousness, dec pulse & BP)
What are the complications of an LP?
- Headache: Very common
- Paraesthesia
- Permenant nerve damage: SERIOUS
What are the normal LP values?
Protein 40g/dl Cell count <4-5 Red cell count – depends on how much blood was lost during the procedure! Pressure <20cm Glucose 2/3 of serum glucose
How is a potential PE investigated?
Wells Score >2 = LIKELY CTPA
Wells Score <2 = UNLIKELY D-dimer
D-dimer +ve= CTPA
D-dimer -ve= No more investigations
What is a normal score on a D-dimer? Is it a good test?
<50
Sensitive but not specific
When should a cardiac troponin be carried out?
6hours after the onset of pain
Then 3hourly
Check local guidelines
What are the 2 types of lactic acidosis?
Type 1: Hypoxic, produce too much lactic acid.
DKA, starvation, CV/R depression
Type 2: Non-hypoxic, cannot breakdown lactic acid
Secondary to Metformin/ poisoning
What is cardiac output a function of?
Preload
Afterload
Contractility
What are the parameters in an LP for bacterial, viral and TB meningitis?
B: Cloudy/Turbid, ↑neutrophils, ↑protein, ↓ glucose, ↑ pressure
V: Clear, ↑ lymphocytes, normal protein, normal glucose, normal pressure
TB: Normal/slightly cloudy, ↑ lymphocytes, ↑↑protein, ↓↓ glucose
