General Medicine Flashcards
Causes of respiratory alkalosis?
High pH, low H+
Low C02: Anxiety- hyperventilation Pain Sepsis Fever
Causes of metabolic alkalosis:
High pH, low H+
Loss of H+:
Burns
Vomiting
Gain of bicarbonate:
Drugs
Calculating the anion gap:
[Na+] - [Cl] - [HC03]
Should be between 4-16
What needs to be factored in when measuring the anion gap in liver disease?
Albumin is a negatively charged anion which contributes to nearly all the anion gap, which will be low in liver disease. If albumin is low, anion gap will appear low even if all the other anions are raised.
Anion Gap + (0.25 x (40-[albumin]))
Causes of metabolic acidosis with normal anion gap:
[Na+] - [Cl] - [HC03] = 4-16
Addisons disease + renal tubule Acidosis
Bicarbonate loss- renal failure
Chloride excess- too much saline or ammonium chloride
Diarrhoea + Drugs- acetazolamide (altitude)
In Addison’s, ENaC normally cause loss of K+, less K+ means more H+ excreted in exchange for Na+ uptake.
In chloride excess- less Cl reabsorption into the body via the HCl cotransporter= more H+ lost.
Metabolic acidosis with high anion gap?
[Na+] - [Cl] - [HC03] = 4-16
KARMEL: Ketones Aspirin Renal failure Metformin Ethanol/ethylene glycol (antifreeze) Lactate
Causes of respiratory acidosis?
Low pH, high H+
High C02:
COPD
Low respiratory drive
Brain injury
Drugs- opioids
Patient has high total calcium levels, how can you determine if it due to primary hypercalcaemia or malignancy?
PTH- normal or high despite raised Ca2+ =
Primary hypercalcaemia
A patient has raised PTH and Ca, you suspect primary hyperparathryoid. How can familial hypocalciuric hypercalaemia be excluded?
Altered Ca receptor sensing reduces sensitivity to high calcium, so PTH is suppressed less and less is excreted.
Calcium creatinine clearance will be low (despite high Ca)
Magnesium will be normal or high
How does pH affect free ionized calcium levels?
Ca++ > Calcium-bound-albumin
When H+ increases (low pH) then equilibrium is pushed towards albumin bound to neutralise unbalanced charge
When H+ decreases (high pH) equilibrium is pushed towards free ionized Ca++
How is mild, moderate or severe hypercalcaemia defined:
Mild: <3mmol (or 0.25 above normal range)
Moderate: 3-3.5 (may be asymptomatic)
Severe: >3.5 mmol
How is mild hypercalcaemia managed?
<3mmol of Ca++
Often due to ^PTH, no need for surgery unless under 50 years old and renal damage (nephrocalcinosis, nephrolithiasis) or bone damage (fractures, reduced density)
Management of chronic hypercalcaemia with a Ca concentration of 3-3.5mmol (secondary to primary parathyroidism)?
Refer for surgery
Management of severe hypercalcaemia (>3.5mmol)
Massive fluid replacement: 3-4L over 24 hours
High calcium causes diabetes insipidis, vomiting and fluid loss
Zoledronic acid 4g over 15 minutes IV (bisphosphonate)
Patient is given bisphosphonates and massive fluid replacement and still has dangerously high Ca levels. What Rx may be given?
Danusomab (monoclonal Ab to RANK ligand, preventing maturation and differentiation of osteoclasts)
Haemodialysis- useful if renal function is very reduced
What creatinine clearance is needed if you are going to give zoledronic acid for severe hypercalcaemia?
> 60mL/min
What K+ level is a medical emergency?
> 6.5mmol/L
ECG changes in hyperkalaemia
Small little P waves
Tall tented T waves
Wide QRS
And ventricular fibrillation
Which bloods should you take first, FBC or U+Es?
Can get a wrong result if taking U+Es after FBC because the EDTA corrupts the sample
So do U+Es first
For non urgent hyperkalaemia (<6.5mmol) what can be given to lower it:
Fluids + medication review (ACEi, suxamethonium)
Rx: Polystyrene sulfonate resin
Binds K+ in the gut
Low K+ exacerbates toxicity of which drug?
Digoxin
ECG signs of low K+
Everything is down: K+, hypotonic, hyporeflexic, ECG waves pointing down
Inverted T waves (opposite of tall tented in hyperkalaemia)
Prominent U waves
Long PR (slow because it’s down)
Depressed ST
Which other electrolyte needs to be checked in low K+?
Magnesium- low potassium won’t correct until Mg normalises
Patient with low K+, high BP and alkolosis, but is not on diuretics. What syndrome should be suspected?
Low K+ and potentially high Na+ causing high BP, more H+ loss
Suspect Conn’s (aldosteronism > more ENaC channels > more K+ lost and Na+ gained)
