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OSCE Data interpretation stations

Dr Cathy Armstrong Consultant Anaesthetist

Dec 2016


Objectives

• The stations

– Format

– Tips

• Blood tests

– Patterns to look for

• examples


Format

• Instructions

– Brief background

– Study data – ‘after 5 minutes the examiner will ask you some questions on diagnosis & initial management’


Format

• Data

– Blood tests incl blood gases

– ECG

– Imaging e.g xray or CT scan

– Observations


Format

• Questions from examiner

– Structured / standardised

• ‘what do the blood tests show?’

• ‘what does the CXR show?’

• What is your most likely diagnosis? What is your top differential?

• What will your initial management be?


Tips

• Use your thinking time wisely

• Use succinct language & be confident

– Likely to be some normal investigations also

• Show reasoning behind your thoughts

• Flag up potential dangers


Tips

• Differential diagnosis

– Start with your top & why

• Initial management

– Might include oxygen / fluids / nebulisers

– Remember management packages – e.g sepsis 6

– Further detailed history

– Other definitive investigations – e.g.echo, CT

– Don’t forget SENIOR HELP / INPUT


Investigations


Full Blood Count

• Hb

– Males 135 – 180g/l

– Females 115 – 160 g/l

• WCC

– 4.0 – 11 x 109/l

• Platelets

– 150 – 400 x 109/l


Anaemia classification by MCV

MCV – mean cell volume (76 – 96 fl)

• Normal MCV (Normocytic) – Acute blood loss

– Anaemia of chronic disease

• Low MCV (microcytic) – Iron deficiency

– Thalassaemia

• High MCV (Macrocytic) – B12 or folate deficiency


Anaemia quiz

• 1) Hb 86, MCV 80

• 2) Hb 82, MCV 70

• 3) Hb 89, MCV 102

• A) menorrhagia

• B) acute haemhorrage

• C) Vitamin B12 deficiency

MCV – 76-96 fl


Hyperkalaemia

• Mild 5.5 - 6.0 mmol/l

• Mod 6.1 – 7.0 mmol/l

• Severe > 7.0 mmol/l

• Causes – ↑ intake

• Food ingestion / supplements

• Rapid blood transfusion

– Intercompartmental shifts • Trauma / crush injuries

• Burns

• Acidosis

– Decreased excretion • Acute / chronic renal failure

• Adrenocortical insufficiency (e.g. Addisons disease)

– Medications • Potassium sparing diuretics, digoxin


Hyperkalaemia

ECG changes

Peaked T waves

Prolonged PR interval

Widened QRS

Loss of P wave

Loss of R wave amplitude

Sine wave pattern

Asystole

Management of mod / severe Treat underlying cause

Calcium gluconate

Insulin dextrose infusion

Nebulised salbutamol

dialysis


Hypokalaemia

• Mild 3.0 – 3.5 mmol/l

• Mod 2.5 – 3.0 mmol/l

• Severe < 2.5 mmol/l

• Causes – ↓ intake

• Iatrogenic (no K in IV fluids)

• Malnutrition

– Renal losses • Renal tubular acidosis

• Hyperaldosteronism (Conn’s syndrome)

– GI losses • Diarrhoea, vomiting

– Intercompartmental shifts • insulin

• Alkalosis

– Medications • Diuretics, β2 agonists


Diseases with electrolyte patterns

• Addisons disease (Primary adrenocortical insufficiency)

– Na K Ca

• Cushings syndrome (excess plasma cortisol)

– Na K Ca

• Conn’s Syndrome (hyperaldosteronism)

– Na K


Diseases with electrolyte patterns

• Addisons disease (Primary adrenocortical insufficiency)

– Na ↓ K ↑ Ca ↑

• Cushings syndrome (excess plasma cortisol)

– Na ↑ K ↓ Ca ↓

• Conn’s Syndrome (hyperaldosteronism)

– Na ↑ ↔ K ↓


Raised Urea & creatinine

• Both raised in renal failure

• Alternative causes of a raised urea with relatively normal Cr

– Dehydration

– GI haemhorrhage

– High protein diet


Deciphering between acute & chronic renal failure using blood results

Chronic renal failure

Anaemia of chronic disease

Low calcium

High phosphate


Liver Function tests

Non-specific

Bilirubin

AST (Aspartate transaminase)

ALP (Alkaline phophatase)

γ – GT (Gamma –glutamyl transpeptidase)

Albumin

Specific

ALT (Alanine aminotransferase)


LFT patterns

• Hepatocellular Damage

– Large ↑ in ALT with small ↑ in ALP

• Biliary obstruction

– Small ↑ ALT with large ↑ in ALP & γ -GT


Normal ABG Values

pH

PaO2

PaCO2

HCO3

Base Excess

7.35 - 7.45

10-12 kPa

4.5 - 6.0 kPa

22 – 26 mmol/l

-2 - +2 mmol/l

Many modern gas machines also measure

K+ Na+ Cl- SaO2 Hb COHb MetHb Lactate

IN AIR


Expected PO2 on oxygen

% oxygen – 10


Examples


Ryan

• Ryan is a 17 year old male. He has presented to A&E with a 2 month history of general malaise. Over the past few days he has been vomiting with stomach cramps.

• BP 110/70, Apyrexial, RR 39

• Review the investigations provided. You will then be asked questions on diagnosis and initial management.


Ryan


Ryan

• Hb 12.9 (9.0 – 13.0)

• Wcc 7.0 (4.0 – 11.0)

• Plt 395 (150-400)

• Na 139 (135-145)

• K 4.5 (3.5-5.5)

• Ur 15.0 (3.3-6.6)

• Cr 140 (80-120)

• Blood glucose 35mmol/l

• ABG on air

• pH 7.12 (7.35-7.45)

• PCo2 3.0 (4.5-6.0)

• PO2 11.0 (10-12 in air)

• HCO3 17 (22-26)

• BE -23 (-2- +2)


Ryan


Ryan (answers)

• What does the CXR ?

– Normal – nil significant

• What do the blood results show?

– FBC within normal range

– U&E’s – raised urea with moderately raised creatinine – suggesting dehydration, hypovolemia and possible acute kidney injury

– Extremely raised blood glucose

• What do the ABG’s show?

– Metabolic acidosis with respiratory compensation

• What does the ECG show?

– Sinus tachycardia

• What is the most likely diagnosis

– Diabetic ketoacidosis

• What would your initial management include – Follow local DKA policy which will include: insulin therapy, Fluid replacement, potassium

replacement

– Involve seniors

– May need monitoring in critical care area


Jack

• Jack is a 77 year old male. He has presented to A&E with a 2 day history of abdominal pain and vomiting.

• BP 90/45, T 38.5. RR 30

• Examination of the abdomen reveals a hard abdomen with generalised tenderness and guarding



Jack

• Hb 9.0 (9.0 – 13.0)

• Wcc 22.3 (4.0 – 11.0)

• Plt 170 (150-400)

• Na 139 (135-145)

• K 4.5 (3.5-5.5)

• Ur 10.0 (3.3-6.6)

• Cr 130 (80-120)

• ABG on air

• pH 7.22 (7.35-7.45)

• PCo2 6.1 (4.5-6.0)

• PO2 7.5 (10-12 in air)

• HCO3 18 (22-26)

• BE -10 (-2- +2)


Jack


Sepsis 6

• Oxygen

• Blood cultures

• IV antibiotics

• Lactate & FBC

• IV fluids

• Measure UO


Jack (answers)


– Air under right hemidiaphragm


– FBC – Borderline low Hb, elevated WCC

– U&E’s – raised urea with moderately raised creatinine – suggesting dehydration, hypovolemia and possible acute kidney injury ? Sepsis in this case


– Hypoxia

– Mixed metabolic & respiratory acidosis


– Fast AF

• What is the most likely diagnosis

– Perforated viscus intrabdominally causing air under the diaphragm. Hypoxia and Type 2 respiratory failure possibly due to diaphragmatic splinting, Sepsis from intra-abdominal perforation with hypotension and acute kidney injury. Fast AF may have been precipitated by acute illness or may have pre-existing AF. Borderline low HB may suggest anaemia due to chronic blood loss from bowel (? ?ulcer or Bowel malignancy)

• What would your initial management include (the list below is not exhaustive) – Oxygen therapy

– IV fluid resuscitation (part of sepsis six)

– Sepsis six protocol – need to be able to list these – see next slide.

– Involve seniors – in particular surgical opinion

– Establish whether AF old or new onset. May require treatment.


Dorothy

• Dorothy is a 82 year old female. She has presented to A&E with a 5 day history of productive cough with green sputum and worsening shortness of breath.

• BP 93/50, T 38.5. RR 32



Dorothy

• Hb 11.0 (9.0 – 13.0)

• Wcc 21.0 (4.0 – 11.0)

• Plt 250 (150-400)

• Na 139 (135-145)

• K 4.5 (3.5-5.5)

• Ur 8.0 (3.3-6.6)

• Cr 90 (80-120)

• ABG on 60% oxygen

• pH 7.35 (7.35-7.45)

• PCo2 4.2 (4.5-6.0)

• PO2 13 (10-12 in air)

• HCO3 23 (22-26)

• BE -3 (-2- +2)


Dorothy


CURB 65

• Confusion

• Urea – 7.0 or over

• RR 30 or over

• BP

– Systolic 90 or less OR

– Diastolic 60 or less

• Age 65 or over


Dorothy (answers)


– Inadequate film (rotated with apices & R costophrenic angle not included) however patchy shadowing throughout R lung field, particularly lower & mid zones, consistent with consolidation


– FBC – elevated WCC

– U&E’s – mildly raised urea& creatinine – suggesting dehydration.


– Relative hypoxia – oxygen significantly lower than would be expected on 60% O2



• What is the most likely diagnosis – Community acquired pneumonia – good to mention CURB-65 score at this point.(see next slide) You do not know if she is confused but she

triggers on 3 other criteria so definitely requires admission.

• What would your initial management include (the list below is not exhaustive) – Continue Oxygen therapy & adjust as appropriate

– Sepsis six protocol

– Involve seniors

.


Hyperinflation


Right sided

pneumothorax


Small bowel

obstruction


Thoracic Aortic

dissesction


Ruptured abdominal aortic aneurysm


Subarachnoid haemorrhage


Extradural

haematoma


Extra example - Tom

• Tom is a 22 year old male. He has presented to A&E with shortness of breath and an audible wheeze

• BP 135/90, T 36.5. RR 38



Tom

• Hb 11.0 (9.0 – 13.0)

• Wcc 6.0 (4.0 – 11.0)

• Plt 250 (150-400)

• Na 139 (135-145)

• K 4.5 (3.5-5.5)

• Ur 5.9 (3.3-6.6)

• Cr 80 (80-120)

• ABG on 15L oxygen via non-rebreath mask

• pH 7.35 (7.35-7.45)

• PCo2 5.9 (4.5-6.0)

• PO2 9 (10-12 in air)

• HCO3 23 (22-26)

• BE -3 (-2- +2)


Tom


Tom (answers)

• What does the CXR ? – Hyperinflation of the chest


– FBC – normal

– U&E’s – normal


– Relative hypoxia – oxygen significantly lower than would be expected on 15L non-rebreath mask. Tyoe 1 respiratory failure as CO2 just at higher end of normal limits. I would be concerned that the patient is starting to tire & that they will soon develop type 2 respiratory failure as their ventilation becomes inadequate and CO2 rises. This is a sign of severe asthma and may lead to intubation and ventilation being required. .



• What is the most likely diagnosis – Asthma exacerbation.

• What would your initial management include (the list below is not exhaustive) – Continue Oxygen therapy & adjust as appropriate

– Asthma management protocol – bronchodilators, steroids, magnesium

– Involve seniors early, may need critical care

.


summary

Read instructions carefully

Take time to look at data, formulate a differential diagnosis & initial management plan

Be confident in your approach

Remember senior input

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