BIS index¶

The BIS depth-of-anaesthesia index, computed from a window of EEG.

Stub

Imported from the time-source table; the full page is still to be written.


Name in the dataset	`BIS/BIS`
Type	numeric
Device	BIS monitor
Stamped by	BIS clock

Measurement space¶

Time side (as stamped): the true time lies between -65 s and -3 s from the stamp: the delay range plus the interval one value describes.

Time¶

From UTC to the stored time stamp¶

Derived from this signal's timing table; a written chain is still to come.

The clock path first (UTC to the clock that stamps or spaces the samples), then the signal's own path to its stored time. Each bar: the time shift or error the step introduces (pale) and what is left after the atlas's correction (solid), on a log scale; dashed when estimated or assumed.

UTC

The reference every chain starts from.

Recorder PC clock

sync assumed 3 ms – 900 ms · clock link, parameter

Windows time synchronisation to the hospital's time server every 8–24 h (assumed), drifting a few ppm in between. Not observable in the release: dates are shifted to 2100. No step of 0.5 s or more was found.

BIS clock

transport measured 3 s – 4 s

Delay from the end of the interval a value describes to its stamp.

Stored time stamp

window measured 16 s – 61 s

The width of the interval one value or sample stands for.

Timing¶

Against the working reference. Delay: from the end of the interval a value describes to its stamp. Interval: how wide that interval is.

Form	Delay	Interval	Clock domain	Status	Evidence
as stamped (default)	3 s – 4 s	16 s – 61 s	BIS clock	measured	3-4 s after its EEG window ends; window 16 s (48%) or 32-61 s (40%); half the weight older than 30 s

Combine it with other signals in the synchronisation planner.

Delays¶

From the EEG window end (3 s (p10–p90 3 to 4)): The same in every smoothing group.

Averaging window¶

Trailing average (16 s in 48% of good fits (the 15 s setting); 32–61 s in 40%; half the weight older than 30 s): Set per case on the monitor; not recorded.

Value¶

Its value side is still to be described.

Parameters¶

Parameter	Value	Status	From
BIS index delay	3 s (p10–p90 3 to 4)	measured	How the BIS index trails its EEG
BIS index averaging window	16 s in 48% of good fits (the 15 s setting); 32–61 s in 40%; half the weight older than 30 s	measured	How the BIS index trails its EEG

Observations¶

Observation	Status	Summary
Monitor numerics describe the past, never the future	established	Every monitor numeric describes a window of 3–30 s or more that ended 1–9 s before its stamp. None is stamped before its data exist, so the stamps already respect the availability rule.
The BIS index is slow	established	The BIS index averages 15–60 s of EEG ending about 3 s before its stamp, with half its weight older than 30 s. It cannot time anything faster than about a minute.

Studies¶

Study	Date	Status	Summary
Value resolution of every signal	2026-10-19	draft	How finely every waveform and numeric track in the release records its values. The SNUADC waveforms are 10-bit codes, though VitalRecorder's documentation describes the SNUADC as 12-bit; Primus waveforms use about 10 bits of 12; BIS EEG is a 16-bit grid of 0.05 µV. Numerics are 32-bit floats on decimal grids of 1, 0.1, 0.01 or 0.001, one per track; settings sit on coarser grids of 10 or 100.
How the BIS index trails its EEG	2026-10-13	current	Modelling the BIS index as a lagged mix of EEG features shows a trailing average starting about 3 s after its EEG window ends: about 16 s long in half the cases (the 15 s smoothing setting) and 32–61 s in most others. Half the response weight is older than 30 s.
Drug effects as a clock check	2026-10-13	current	Infusion pumps, the rapid infuser and the cerebral oximeter share no waveform with the reference. Drug effects that follow infusions at plausible delays (propofol to BIS in about 2 minutes, fluid to CVP in about 30 s) bound their clocks to well within a minute of the recorder.
What a BIS-mimic project says about the index's smoothing	2026-10-13	current	The openeeg project reproduces the BIS index from the raw EEG and infers each case's smoothing setting: about 80% of its cases come out at 15 s. Its alignment cannot serve as a timing reference.
Anaesthesia record times are rounded up	2026-10-12	current	Anaesthesia start and end entered on a 5-minute mark sit 90–290 s later, against device markers, than entries typed to the minute. Rounding up to the next 5 minutes fits every one of 11 markers better than rounding to the nearest or down.

Worked examples¶

Example	Side	Status	Summary
Post-induction hypotension, from the charted start and from the devices	time	draft	The charted anaesthesia start comes a median 14 minutes before the patient is induced; measured from it, "hypotension within 20 minutes of induction" is found in 27% of 2,913 patients, against 51% from the devices' induction, and the label changes for a quarter of patients.

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