Imputed times, conformance failures and exclusion rules¶

About one in twelve op ends was set from the recording rather than charted, and a small set of times fail basic conformance checks; all are encoded as exclusion rules.

Background¶

• Vital Recorder stops recording 10 minutes after the heart-rate and SpO₂ signals disappear.
• Imputed times measure when monitoring stopped, not when surgery ended, and would bias any accuracy analysis towards agreement with the signals.

Data¶

• All charted times and dates in clinical_data.csv. The machine-readable rules are in exclusion_rules.json.

Method¶

• Checked gaps from op end to recording end, whole-second and whole-minute structure, event order, extreme values and placeholder dates.

Results¶

• 537 op ends (8.4%) fall 598–604 s before the end of the recording; most often 601 s (346 cases) or 602 s (129 cases). They are excluded as imputed.
• Anaesthesia ends derived from those op ends are stored with floating-point noise (e.g. 599.999999 s) and sit an exact multiple of 5 minutes after op end: 300 s (9 cases), 600 s (35), 900 s (9), 1,200 s (9) and others.
• Two dates default to 1900: case 4476 (anaesthesia end) and case 1563 (admission and discharge), near −3.69 × 10⁹ s.
• Op end comes after anaesthesia end in 52 cases and equals it in 108.
• Anaesthesia end is +720 min from recording end in case 3980 (12-hour error?) and +1,441 min in case 4959 (date error?).
• No case has op start before anaesthesia start, op end before op start, or anaesthesia end before anaesthesia start.
• Op end equals recording end minus 10 minutes (598–604 s) in 537 of 6,388 cases (8.4%). By department: thoracic 16.6% (184 of 1,111), general 6.9% (341 of 4,930), gynaecology 3.5%, urology 3.4%. By anaesthesia: sedation 41.7% (30 of 72), spinal 30.0% (82 of 273), general 7.0%. By operation type it ranges from 15.2% (minor resection) to 2.3% (breast). Emergency 9.8%, elective 8.2%. (Op end was filled in from the recording end in 537 cases)

Discussion¶

• Anaesthesia end was most likely charted as an interval after op end and inherited the imputed op end.
• Excluded values return a status rather than a distribution; flagged values are fitted and returned with the flag.
• The 1900 dates are the "missing time stored as zero" bug from §5.5 of the review.

Observations it supports¶

Limitations¶

• The derived anaesthesia ends were missed in an earlier fit, because their noise (about 10⁻⁶ s) slipped under the test threshold.

Open questions¶

• Was op end imputed deliberately? (next step). Was op end imputed from recording end deliberately? This is to be asked of the VitalDB team.
• Why imputed op ends cluster in thoracic and non-general cases (unexplained phenomenon). Imputed op ends are twice as common in thoracic surgery as in general surgery, and four to six times as common under sedation or spinal anaesthesia as under general anaesthesia. Cases without a charted op end are not spread at random; why these groups lack one (a different charting workflow, a different person recording, the operation's end not being marked) is not known, and the VitalDB team could say.

Tags: from the resolution work