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Primus ETCO₂, PIP and RR

End-tidal CO₂, peak pressure and respiratory rate from the Primus, polled about every 7 s.

Stub

Imported from the time-source table; the full page is still to be written.
Name in the dataset Primus/ETCO2
Type numeric
Device Primus anaesthesia machine
Stamped by Recorder PC clock

Measurement space

Time side (after the per-case delay label): the true time lies between -30.57 s and -0.07 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.
Recorder PC clock
clock measured 750 ms – 7.6 s → 70 ms – 570 ms after correction
Delay or clock offset to the stamp; removed by the per-case delay label.
Stored time stamp
window measured 7 s – 30 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
after the per-case delay label (default) 70 ms – 570 ms 7 s – 30 s Primus clock measured numeric_delay label SE p10-p90 0.07-0.57 s (RR_CO2 weaker: SE ~1 s)
as stamped 750 ms – 7.6 s 7 s – 30 s Primus clock measured from window end: ETCO₂ 0.75-3.4, PIP 3.65-6.5, RR 1.6-7.6 s; 7 s polls, RR over 30 s

Combine it with other signals in the synchronisation planner.

Delays

Value

Its value side is still to be described.

Parameters

Parameter Value Status From
Primus ETCO₂ delay 1.55 s (p10–p90 0.75 to 3.4) measured Numeric delays are fixed within a case, different between cases
Primus PIP delay 4.6 s (p10–p90 3.65 to 6.5) measured Numeric delays are fixed within a case, different between cases
Primus RR delay 4.3 s (p10–p90 1.6 to 7.6) measured Numeric delays are fixed within a case, different between cases

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.
Numeric delays are fixed within a case but differ between cases established A numeric's delay does not drift through a recording, but 40–70% of its variance lies between cases. One delay per case describes it; one delay for the whole dataset is wrong by up to about 2 s.
Primus waveform gains are wrong in every recording, for CO₂ or for AWP established Recordings store the Primus waveforms with one of three sets of scale factors. Checked against the Primus's own ETCO₂ and PIP numerics in all 6,388 recordings, CO₂ fits only 0.075 mmHg per code and AWP only 0.1 mbar per code with offset −20, so most recordings overstate CO₂ by a third, and the others overstate AWP by about 3% (950 recordings) or understate it about fourfold (26).

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.
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.
Numeric delays are fixed within a case, different between cases 2026-10-12 current With each numeric's algorithm held fixed, delays were fitted for every case and every 30-minute block. They do not drift within a case, but 40–70% of their variance lies between cases, so a single population delay is wrong by up to 2 s for HR and 1 s for the others. Each case gets its own delay label.
How the monitors compute their numbers 2026-10-12 current Recomputing each monitor numeric from its own waveform finds a short, simple algorithm for every one (a median, an exponential average or a time mean over 3–30 s) and a delay of 2–9 s behind the newest data it uses. No value is stamped before its data exist.

Worked examples

Example Side Status Summary
End-tidal to arterial CO₂, and pulse oximetry against blood gas, at the right moment time draft For 4,281 blood gases, reading the monitor when the blood was drawn rather than at the lab stamp makes changes in end-tidal CO₂ track changes in arterial CO₂ far better (within-patient correlation 0.74 against 0.54), and agreement peaks exactly at the estimated draw. Oximetry shows the same timing (agreement peaks at the draw), but the 100% ceiling hides the size of the oximetry gradient for three gases in four.

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