A Five-Step Framework for Any Data
Whether you are shown a capnography trace, an arterial blood gas table, a chest radiograph, or a cardiac output trend, the same framework applies. Practise it until it becomes automatic.
1. Identify the Source and Context
State what you are looking at and where it comes from. This orients both you and the examiner.
- "This is a capnography trace from an anaesthetised patient."
- "This is a table of arterial blood gas results."
- "This appears to be a chest radiograph, portable antero-posterior view."
- "This is a trend chart showing mean arterial pressure and heart rate over two hours."
If the examiner has given you a clinical stem, acknowledge it: "In the context of this patient who has just been intubated for emergency laparotomy…" This signals that you are integrating data with clinical reasoning, not pattern-matching in isolation.
2. Check Scale, Units, and Labels
Before you describe findings, confirm that you understand what the axes, columns, or annotations mean.
- On a waveform: What is the vertical scale (pressure in mmHg or cmH₂O, flow in L/min)? What is the time base?
- On a table: What are the units (mmol/L, kPa, g/dL)? Are reference ranges provided?
- On an image: Is there a date, a patient identifier, a projection label (AP, lateral, supine)?
If any of these are unclear, say so: "I note there is no scale marked on this trace; I would want to confirm the pressure range before interpreting absolute values." Examiners respect candidates who acknowledge limitations in the data.
3. Describe Before You Diagnose
This is the discipline that separates a safe clinician from a pattern-matcher. Describe the objective features you observe, using neutral language, before you offer an interpretation.
For a capnography trace, you might say:
- "The trace shows a square waveform with a plateau phase. The end-tidal value is approximately 4.5 kPa. There is a gradual upward slope during the plateau, and the baseline returns to zero between breaths."
For a blood gas table:
- "The pH is 7.28, PaCO₂ is 7.8 kPa, PaO₂ is 9.2 kPa on FiO₂ 0.4, bicarbonate is 18 mmol/L, base excess is –6, and lactate is 3.2 mmol/L."
For a chest radiograph:
- "There is increased opacification in the right lower zone with loss of the right hemidiaphragm silhouette. The trachea is midline. The cardiac silhouette is not enlarged. There are no rib fractures visible."
Only after you have described do you interpret: "This is consistent with a metabolic acidosis with partial respiratory compensation," or "This appearance suggests right lower lobe consolidation or collapse."
4. Interpret in Context and Integrate with Clinical Reasoning
Data never exist in a vacuum. The same PaCO₂ of 7.8 kPa means something different in a patient with chronic obstructive pulmonary disease at baseline than in a previously healthy patient one hour post-induction. The same capnography trace shape has different implications in a spontaneously breathing patient versus a mechanically ventilated one.
After describing, link your interpretation to the scenario:
- "Given this patient has just been intubated and the plateau is rising, I am concerned about inadequate minute ventilation or the development of bronchospasm."
- "In the context of sepsis and fluid resuscitation, this metabolic acidosis with elevated lactate suggests ongoing tissue hypoperfusion."
- "This radiographic appearance, combined with the sudden desaturation, raises the possibility of aspiration or acute respiratory distress syndrome."
This is anaesthesia viva data interpretation at its best: you are not reciting a textbook; you are thinking aloud as a safe clinician.
5. Name Uncertainty and Propose Verification
No single piece of data is diagnostic in isolation. Acknowledge what you do not know and what you would do next.
- "I would want to confirm this blood gas with a repeat sample and check the analyser calibration."
- "I would auscultate the chest and check the position of the endotracheal tube with a fibreoptic scope."
- "I would review previous imaging to see if this appearance is new."
- "I would correlate this waveform with the patient's clinical state—are they haemodynamically stable? Is there a change in airway pressure?"
Examiners are reassured by candidates who know the limits of their data and who propose sensible next steps. This is criterion-referenced assessment: you are demonstrating the standard of a safe, newly qualified specialist.
Common Data Types in the EDAIC Part 2 SOE
While the framework above is universal, it helps to know the categories of data you are likely to encounter.
- Capnography: shape (square, shark-fin, biphasic), plateau slope, baseline, end-tidal value.
- Arterial pressure: systolic, diastolic, mean, pulse pressure, waveform morphology (dicrotic notch, variation with respiration).
- Central venous pressure: mean value, waveform components (a, c, v waves), respiratory variation.
- Flow-volume loops: inspiratory and expiratory limbs, evidence of obstruction or restriction.
- Electrocardiography: rhythm, rate, intervals (PR, QRS, QT), ST segments, T waves, axis.
Tables and Laboratory Results
- Arterial blood gases: pH, PaCO₂, PaO₂, bicarbonate, base excess, lactate, electrolytes.
- Full blood count: haemoglobin, white cell count, platelets.
- Coagulation: PT, APTT, fibrinogen, D-dimer.
- Biochemistry: sodium, potassium, urea, creatinine, glucose, liver enzymes.
- Cardiac biomarkers: troponin, BNP.
Describe the values, note any that fall outside reference ranges, and interpret the pattern (e.g. metabolic acidosis, acute kidney injury, coagulopathy).
Imaging
- Chest radiographs: projection, quality (rotation, penetration, inspiration), systematic review (airway, breathing, circulation, diaphragm, everything else).
- Computed tomography: slice orientation (axial, coronal, sagittal), contrast, key structures, abnormalities.
- Ultrasound: probe position, structures visible, measurements (e.g. inferior vena cava diameter, left ventricular function qualitatively described).
Do not attempt a radiological diagnosis beyond your competence. Describe what you see and state that you would seek expert interpretation if needed.
Trends and Charts
- Haemodynamic trends: blood pressure, heart rate, cardiac output, systemic vascular resistance over time.
- Ventilator trends: tidal volume, peak pressure, plateau pressure, compliance, minute ventilation.
- Fluid balance: cumulative input and output, daily balance.
Look for patterns: stability, deterioration, response to intervention. Propose what you would do if a trend is concerning.
Exam tip: If you are shown a waveform or image you do not immediately recognise, do not panic. Fall back on the five-step framework: identify, check scale, describe, interpret in context, name uncertainty. The examiner is testing your method, not your ability to diagnose zebras.
