Every vasopressor protocol for spinal anaesthesia is defined against a baseline systolic pressure, and the baseline is usually whichever reading the monitor happened to take while the patient was being positioned, anxious, or in pain. A baseline recorded 20 mmHg high turns a normal pressure into a treated hypotension; one recorded low leaves a genuinely hypotensive patient untreated for several minutes.
Take three readings before the block, a minute apart, with the patient settled and the cuff on the arm you will keep using. Discard the first. Announce the number you are going to work from, write it on the chart, and state the threshold that follows from it — 'baseline 128, so I am treating below 115'. In a busy obstetric theatre, saying it aloud is what stops the assistant using a different number when you are occupied.
It also makes the record interpretable afterwards. A chart showing pressures without a declared baseline cannot be reviewed, because nobody reading it can tell whether a given value was a fall or a normal state for that patient.
- Take three pre-block readings a minute apart and discard the first.
- Use the same arm and cuff throughout; switching arms invalidates the comparison.
- Announce the baseline and the resulting treatment threshold to the room.
- Write both on the anaesthetic chart before the block, not afterwards.
- Re-declare the baseline if the patient's position changes substantially.
Why it matters
Every vasopressor threshold in spinal anaesthesia is relative to a baseline that is usually never agreed or recorded.
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