Question 26

A 48 year old woman presents with 2 days of vomiting. She is confused and unable to give a clear history. Her current examination shows:

BP 100/82 mmHg

HR 144 bpm

Temp 36.5 C

RR 24 bpm

O2 Sat 98% RA

GCS 13 (E4 M5 V4)

pH 7.38 (7.35- 7.45)	low normal (N, corrected, balanced)

pCO2 36 (35-45)	low normal

HCO3 21 (22-26)	low (just)

BE -3 (-1- 1)	matches low Bic

Lactate 3.3 (0-2)	mildly elevated

Glucose 22 (3-6.5)	elevated ++

Na 129 (135-145)	low (uncorrected)

Cl- 79 (3.5-5-0)	low ++

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“The blood gas question” = OMG or yeah!! = Your choice!

Read the stem – all of it. Every word for a reason.

What is there	(left foot in)	relevant +ve and -ve

What isn’t there	(left foot out)	what should be / expect

Put it all together	(shake it all about)

Matches

Doesn’t match

Who am I, where am I, when am I? If time/place mentioned, why?

Why is this question in a fellowship exam? common, commonly deadly if missed, both

What would I do if this were a real patient in front of me? remember the patient

Expecting:

Vomiting – hypochloraemic metabolic alkalosis

Shocked – metabolic acidosis

Missing:

K, Osmolarity, urea

Physical findings

Medications

Not matching:

Confused – normal pH, temp, SBP 100, 98% sats

pH normal – fully corrected, two conditions, two effects

Arterial Blood Gas (ABG) Interpretation Chart - LITFL

Potassium

Serum K is inversely related to serum pH

Serum K decreases by 0.3mEq/L for every 0.1U increase in pH above normal

Alkalosis:

Correction of an alkalotic pH will produce a rise in serum K

Alkalosis (increase pH) shifts K intracellularly, lowering serum K

Acidosis

Shifts K to intravascular space so increasing the serum K

Correction of acidosis will produce a decrease in serum K (may drop precipitously eg correction of DKA)

Osmolarity = (1.86 x [Na+]) + [glucose] + [urea] + 9 (using values measured in mmol/l)

or use (2 x Na) + glucose + urea normal osmolar gap (measured - calc) is < 10

noting measured = Osmolality mOsm/kg solvent, calculated = Osmolarity mOsm/L solution

a) Provide two (2) calculations to assist with your interpretation of these investigations.

(2 marks)

b) State your interpretation of these results. Give three (3) points in your answer. (3

marks)

c) State your three (3) initial treatments, including aims where appropriate. (3 marks)

Pass = 2 + 2 + 2 = 6/8 (Basic, vital knowledge for a junior FACEM)

Calculations

AG, corrected Na, expected CO2, expected Bic, Delta ratio

Interpretation

HAGMA, delta > 2 = metabolic acidosis + metabolic alkalosis

Hypochloraemia from vomiting

Corrected Na normal

Hyperglycaemia – not typical of DKA or HHS or stress response

Clinical (confusion) disproportionate to gases

Possible single cause – aspirin

Initial treatments INCLUDING aims (1/2 marks if treatment without aim)

Fluids: improvement in haemodynamics (target SBP/MAP +/-pulse), perfusion parameters (skin perfusion, mental state, JVP, urine output, lactate, ketones)

Insulin: rate, target sugar

Anti-emetics

K – with rationale, rate, target (correct K not paid)

Antibiotics - no

Issues / Themes to avoid

Blank or partially blank answers

Gases are common and potentially deadly if wrong so like to have relatively high cut point. DO NOT SKIP THE GAS QUESTION. Zero is very bad!!

Calculations wrong

Trying to make findings fit e.g. DKA as sole Dx (despite normal pH and Bic)

Ignoring / forgetting the clinical stem (there for a reason – shock is easy to give treatments for!)

Investigations or History instead of Treatments

Aims of treatment already met e.g. SBP 90 or 100

Treatment generic without dose, rate, endpoints e.g. ‘fluids’ or ‘correct K’

Multiple answers when 2 or 3 asked for (after the required doesn’t count)

Interpretation in the calculation section (usually repeated)

Read the stem carefully

Skim the whole question before answering

might give you clues and allow for shorter responses e.g. in this one just give the calculations then interpret over the page