Acid-Base Overview Flashcards by 4/20 mg

What are the causes of pseudohyponatraemia?

All true hyponatraemia will have intravascular hypotonicitiy

If omsolality is normal (275-295) = increased protein (MYELOMA) or increased lipids

If osmolality is high (>295) = glucose OR mannitol

Waldenstrom macroglobulinaemia can also caus high protein

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How do you correct sodium for hyperglycaemia?

Corrected Na = glucose/3.5 + measured Na

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What are 6 diagnostic criteria of SIADH?

Na <135 mmol/L
Urine sodium > 20mmol/L
Blood osmolality <275 mOsm
Euvolaemic/fluid replete
Normal thyroid function
Not steroid deficient

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What are the causes of SIADH?

Malignancy = lung
Infection = pneumonia/TB
Neurogenic = traumatic SIADH/CVA/SAH
Medications = SSRIs/sodium valproate
Cystic fibrosis
Chronic lung disease e.g COPD

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Which drugs cause hypernatraemia?

Lithium = nephrogenic diabetes insipidus -> polyuria, hypotonic urine

Mannitol

Furosemide (if water intake inadequate)

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What is the single underlying reason for almost all hypernatraemia?

Volume depletion

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How quickly should Na be normalised in hypernatraemia?

Slowly!

Cerebral oedema if corrected quickly (just like hyponatraemia)

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What’s the mortality for symptomatic hypernatraemia?

50%!!

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Which drugs can cause hyponatraemia?

SSRIs/TCAs/antipsychotics
Morphine
NSAIDs
Carbamazepine
Furosemide
Thiazides
MDMA

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What are the three main causes of hypercalcaemia

Malignancy
Hyperparathyroidism
Thiazides

Rarer = sarcoid/PAgets disease/adrenal insufficiency

Normal Calcium = 2.15-2.55

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What are the symptoms of hyperCalcaemia?

Stones - renal colic/polyuria/polydipsia
Bones - bone pain
Groans - abdo pain/constipation
Psychic moans - confusion/hallucinations

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When should treatment for hypercalcaemia be initiated?

Symptomatic patients
OR
Ca > 3.5 mmol/L

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What are the 4 primary treament goals in hypercalcaemia?

Hydration = NaCl 0.9%

Enhanced renal Ca excretion = Furosemide

Inhibition of bone resorption = bisphosphonates

Avoid hartmann’s as it contains calcium

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Which group of hypercalcaemic patients do corticosteroids help in?

Haematological malignancies
Vit D deficiency
Sarcoid

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Which diuretic can you NOT give in hypercalcaemia?

Thiazides!

They cause hypercalcaemia = increased DCT Ca reabsorption

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What ECG abnormalities do you see in hypercalcaemia?

Depressed ST segment
Wide T waves
SHORT QT

Bradyarrythmia | bunble branch block | CHB

Hypocalcaemia = prolonged QTc

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How do you correct anion gap for hypoalbuminaemia?

For every 10g/L under 40 need to add 2.5 to anion gap

Therefore in hypoalbuminaemic states someone with a HAGMA may appear to have a NAGMA

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What is a low anion gap and what causes it?

< 4 mmol/L

hypercalcaemia
hypermagnesaemia
Lithium OD
Myeloma
Iodine toxicity
Aspirin OD can also cause an apparent normal or low anion gap acidosis because the blood gas analyzer can read the aspirin as chloride ions

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How do you measure anion gap and what is normal?

Na - (Cl + HCO3)

4-12

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How do you measure delta gap?

AG - 12 / 24 - HCO3

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What delta ratios indicate which concomitant pathologies?

< 0.4 = pure NAGMA
0.4-0.8 = NAGMA + HAGMA
0.8-2 = HAGMA
>2 = HAGMA + metabolic alkalosis or resp acidosis

What are the causes of metabolic alkalosis?

EVER PEe?

Endocrine: Conn’s/Cushings/barterrs/gitelamns
Vomiting (loss of H+)
Excess alkali - bicarb/antacids
Refeeding syndrome

Post hypercapnia
Excess diuretics - loop or thiazide

What are the two types of metabolic alkalosis?

Chloride responsive = vomiting/diuretics/cystic fibrosis

Chloride NON-responsive = endocrine i.e. Conn’s/Cushings/renal artery stenosis

Extracellular volume is already expanded in Conn’s/cushings/renal artery stenosis so extra saline is not going to help - the metabolic alkalosis is perpetuated by ongoing hypokalaemia

What urine test helps differentiate chloride responsive and non-responsive metabolic alkalosis?

Urine chloride <15mmol/L = chloride responsive

Urine chloride >20mmol/L = non-responsive

How do you calculate expected CO2 in metabolic acidosis?

8 + 1.5[HCO3]

How do you calculate expected CO2 in metabolic alkalosis?

21 + 0.7[HCO3]

How do you calculate expected HCO3 in resp acidosis and resp alkalosis?

The only way I could remember this is by substituting the numbers "14" and "25" into the Fetty Wap song "1738" and that C comes before L in the alphabet Resp acidosis: 1 - acute 4 - chronic Increase the bicarbonate by the above for every 10mmHg over 40 the CO2 is Resp alkalosis: 2 - acute 5 - chronic Decrease the bicarbonate for every 10mmHg under 40mmHg the CO2 is

What is a normal osmolar gap?

<10 mmol/L

How do calculate osmolality?

2Na + Ur + Glu

Which toxins can produce a HAGMA with high osmolar gap?

Methanol Ethanol Acetone Ethylene glycol

What electrolyte abnormality do beta-blockers |digoxin | addison's all cause?

HYPERKALAEMIA

What causes prolonged QTc?

Electrolytes: HYPO - K/Ca/Mg Metabolic: hypothermia/hypothyroidism Drugs: Ia/b/c antiarrythmics / antipsychotics / TCAs (amitryptiline) / antidepressants (venlafaxine/citalopram) / antibiotics (fluroquinolone) CVS disease: myocarditis/rheumatic heart disease Ceberovascular: ICH/CVA Hereditary: Romano-ward + lange nielsen ## Footnote NOT hyponatraemia

What ECG changes occur at which K levels?

6-7: Tented T waves/PR prolongation/Shortened QTc 7-8: QRS widening / P wave flattening 8-9: Sine wave >9: AV dissociation / ventricular tacharrythmias/ asystole ## Footnote These can all happen at lower potassium levels - more proportional to how fast the change is

What are some complications of sodium bicarbonate therapy?

Pulm oedema/overload (high osmotic load IV) Alkalosis (overshoot) CSF acidosis (generates CO2) Hypercapnoea/resp failure Hypokalaemia/hypocalcaemia ## Footnote BICARB DOES NOT cause dehydration

What is sodium bicarbonate dosing?

1-2 mmol/kg IV

What can sodium bicarbonate be used for?

TCA OD: aim QRS <120msec + pH 7.45-7.55 Salicylate toxicity: alkalinise urine - increase excretion Quinidine/cocaine OD Severe hyperkalaemia DKA ONLY IF pH < 6.9

What electrolyte disturbance does pyloric stenosis cause?

Hypchloraemic hypoklaemic metabolic alkalosis

What are the causes of NAGMA?

D - diarrhoea R - RTA F - Fistula U - ureterostomy C - carbonic anyhdrase inhibitor (acetazolamide) K - K sparing : spironolactone/renal failure S - SALINE H - hyperparathyroidism A - addison's T - TPN

How do you calculate expected CO2 in metabolic alkalosis?

21 + 0.7[HCO2]

How do you calculate Aa gradient

713 x Fi02 - (PaO2 - 1.25[PaCO2]) ## Footnote 713 from atmospheric pressure at sea level (760mmHg) - H20 pressure (47mmHg)

What concentration of Na and Cl do NaCl 0.9% and hartmanns have in them?

NaCl = 154 mmol/L each of Na & Cl Hartmanns: 130mmol/L Na 109 mmol/L Cl

What are the causes of HAGMA?

Cyanide Alcoholic ketoacidosis + Alcohols - ethylene glycol/methanol Toluene Metformin Uraemia DKA Paracetamol Iron/isoniazid Lactic acidosis (e.g. sepsis/ischaemia) Salicylates

What process does rapid correction of hyponatraemia cause? Can it cause cardiac arrythmias?

Central ponteine myelinolysis Doesn't typically lead to cardiac arrythmias

Which group of hyponatraemic patients are at highest risk of central pontine myelinolysis?

Chronic hyponatraemics Alcoholics Malnourished Elderly

What are the causes of hypocalcaemia?

CAL-CAL! C - CKD A - Albumin low (pseudo) L - Low vitamin D C - chelation (pancreatitis + transfusion) A - Acute Rhabdo L - Low PTH (post surgery) ## Footnote Pancreatitis causes calcium deposition due to saponification in necrotic fat tissue

What causes pseudohypocalcaemia?

Hypoalbuminaemia 40% of serum calcium is bound to albumin so if albumin drops - apparent hypocalcaemia

What causes rhabdomyolysis?

Drug abuse e.g. cocaine/amphetamines Trauma Sepsis Heat-related and strenous exercise

What complications occur in rhabdomyloysis?

AKI Metabolic (next slide) DIC Compartment syndrome

What electrolyte abnormalities occur in rhabdomyloysis?

HYPOCALCAEMIA (main one) Elevated phosphate (initially) then hypophosphataemia Hyperuricaemia - urate levels correlate well with CK HYPERKALAEMIA (proportional to extent of kidney injury) ## Footnote Calcium is deposited in necrotic tissue