Calculations

Question 1

What is the Parkland formula?

Answer 1

2ml x TBSA (%) x body weight (kg); 50% given in first eight hours; 50% given in next 16 hours.

In paediatric burns 3 ml/kg/%TBSA should be used, and 4 ml/kg/%TBSA used for electrical burns.

Question 2

What is osmolality?

Answer 2

2(NA+K) +urea + glucose

In SIADH, serum osmolality

Question 3

How to calculate CPP and MAP?

Answer 3

CPP= MAP -ICP
MAP= [(2 x Dia) + sys ] / 3 - normal is 70-100
Normal CPP is 60-80

Question 4

How to calculate anion gap?

Answer 4

(sodium + potassium) - (bicarbonate + chloride)

A normal anion gap is 8-14 mmol/L

Causes of a normal anion gap or hyperchloraemic metabolic acidosis
gastrointestinal bicarbonate loss: diarrhoea, ureterosigmoidostomy, fistula
renal tubular acidosis
drugs: e.g. acetazolamide
ammonium chloride injection
Addison’s disease

Causes of a raised anion gap metabolic acidosis
lactate: shock, hypoxia
ketones: diabetic ketoacidosis, alcohol
urate: renal failure
acid poisoning: salicylates, methanol

Question 5

How to calculate % cerebral blood blow

Answer 5

CBF= CPP/CVR
Normal in the human brain is 60 ml per 100 g per minute.
BP= CO X TPR
CO= HR X SV

Question 6

What is sensitivity?

Answer 6

=True positives/True positives+False Negatives

Question 7

What is specificity?

Answer 7

=True negatives/True negatives+ False postives

Question 8

How to calculate odds ration

Answer 8

from table= AD/BC

Question 9

How to calculate PPV?

Answer 9

True positives/Total postives

Question 10

How to calculate NNT?

Answer 10

1/Absolute risk reduction

=(c/C+D)- (A/A+B)

Question 11

Safe doses of Lidocaine?

Answer 11

Without adrenaline 3mg/kg
With adrenaline 7mg/kg
acts on sodium channels

Question 12

Safe doses of Bupivicaine?

Answer 12

Without adrenaline 2mg/kg

With adrenaline 3mg/kg

Question 13

Calculate GCS?