What it makes
A blood gas result printed the way an analyser prints one: sections, a unit on every row, calculated values marked.
- Arterial or venous. A venous sample is the same patient sampled venously; its pCO₂ and pO₂ do not stand in for arterial values, and the slip says so.
- Computed, not typed. pH, SaO₂, base excess and the anion gap come from the same equations for every picture, so the slip always adds up.
- Adult values. The pictures and the teaching bands are adult ones.
- Three ways out. Copy it as text for a chat or a handout, save a picture, or print the slip at its real 80 mm width and cut it out.
The 14 pictures
Seven acid–base patterns in the order they are taught, then seven clinical pictures in the order a learner meets them.
Patterns
- Normal. The reference every other picture departs from.
- Metabolic acidosis (compensated). Low bicarbonate with the expected fall in pCO₂.
- Metabolic acidosis (uncompensated). The same bicarbonate with a normal pCO₂: the pair differs in pCO₂ alone.
- Metabolic alkalosis. High bicarbonate, a pCO₂ that rises to meet it, and the low potassium that travels with it.
- Respiratory acidosis (acute). High pCO₂ with the bicarbonate barely moved, so the pH falls.
- Respiratory acidosis (chronic). A similar pCO₂ on a raised bicarbonate: the acuity reads from the bicarbonate.
- Respiratory alkalosis (acute). Low pCO₂ from overbreathing, with the bicarbonate barely moved.
Clinical pictures
- Cardiac arrest / severe shock. A mixed acidosis: high pCO₂, low bicarbonate and a high lactate.
- Sepsis / hyperlactataemia. A lactic acidosis with a raised anion gap and a compensating low pCO₂.
- Type 2 respiratory failure (COPD, failing NIV). A very high pCO₂ on a raised bicarbonate, with hypoxaemia.
- DKA. A severe metabolic acidosis with a wide anion gap, high glucose and a raised potassium.
- Salicylate toxicity (mixed). A respiratory alkalosis with a raised-gap metabolic acidosis beside it.
- Hypochloraemic alkalosis (vomiting). A metabolic alkalosis with low chloride and low potassium, as after prolonged vomiting.
- Type 1 respiratory failure (PE / pneumonia). Hypoxaemia with a low pCO₂.
Editing a gas
Start from a picture and move what you need; the calculated values follow.
- A pH change moves one axis. Choose bicarbonate for a metabolic story or pCO₂ for a respiratory one; the editor shows which value moved.
- Guards, not silence. A value that would leave the teaching range stops at the edge and says where.
- Sodium, chloride and haemoglobin come with the picture. The anion gap depends on them, so they are not edited one by one.
- Units at the edge. kPa or mmHg, glucose in mmol/L or mg/dL, haemoglobin in g/L or g/dL; the values behind them do not change.
How the numbers are made
Teaching values. The pictures are authored teaching values, and NAP’s blood gases are still awaiting external clinical face validation.
The equations behind the slip
- pH from Henderson–Hasselbalch in its clinical form.
- Standard base excess from the Van Slyke equation at the haemoglobin of the extracellular fluid.
- SaO₂ from Severinghaus’ standard dissociation curve, uncorrected for temperature and pH.
- Anion gap without potassium: Na⁺ − (Cl⁻ + HCO₃⁻).
- The venous sample carries published venous offsets for pH and pCO₂; its pO₂ is a typical peripheral value.
- The pictures were built with the expected-compensation relationships, so each hangs together as one clinical story.
Sources and limits: Evidence & methodology.
Questions
- Are these real results?
- No. Every slip is generated from a simulated patient and is headed “NAP · Simulated result”.
- Why does the venous slip say pCO₂ does not stand in for arterial?
- Venous and arterial pCO₂ are not interchangeable, so the slip never suggests a conversion.
- Can I use kPa or mg/dL?
- Yes. Switch pressure, glucose and haemoglobin units with the toggles above the slip; the copy, picture and PDF follow the screen.
- Can I use the slips in teaching materials?
- Yes. Use them as they are, with the NAP mark left on.
- Why is there no interpretation line?
- Reading the gas is the learner’s job. The optional ↑ ↓ flags mark values outside NAP’s teaching bands and nothing more.
In a NAP session
The same gas is prepared on the controller’s Advanced tab and released to every monitor in the room as a frozen, timestamped result. Guide: blood gases
