Pre-ICU length of stay in very old patients: interpreting prognosis within the ICU admission pathway

To the Editor,

Ahlström and Lipcsey provide an informative national analysis of how age modifies the association between pre-ICU hospital length of stay (LOS) and 30-day mortality [1]. They appropriately acknowledge that the flatter gradient in very old patients may reflect biology, selection, or age-dependent ICU triage. We suggest that its clinical interpretation depends on two related boundaries: the composition of the day-0 reference group and the point at which the cohort is defined.

Predicted mortality initially fell from day 0 to days 1 and 3 in several middle and older age groups before rising with longer LOS. Adjustment for SAPS3 Box III attenuated but did not remove this dip. Day 0 is therefore not necessarily a single clinical starting point: it may combine direct-from-emergency-room (ER) admissions with patients reaching ICU within the same hospital day through other pathways, whereas later strata require both continued hospitalization and survival to ICU admission. In very old patients, those pathways may encode particularly strong differences in acuity and selection.

Table 1 does not make the denominator used for reporting admission route fully explicit. It reports 98,685 ER admissions as 51.3%, although that count is 31.3% of 315,042; among patients aged 80 years or older, 14,695 is 29.3% of 50,109 rather than the reported 44.9%. The percentages may use available-case denominators, but route missingness and its distribution by age and LOS are not shown. Because direct-from-ER admission anchors the proposed explanation for the early dip, a compact display of ER, other, and unknown routes for LOS 0, 1, and 2–3 days by age would make the reference group clinically interpretable. If completeness permits, curves excluding direct-from-ER admissions could provide a focused sensitivity analysis.

The second boundary is cohort entry. All participants had reached ICU. The authors explicitly state that triage-related selection remains unresolved, yet the wording that pre-ICU LOS carries less prognostic information when triaging a very old patient could be read beyond this admitted population. At that earlier decision, patients assessed but not admitted and those dying before transfer also belong to the relevant denominator; frailty, reversibility, and goals of care shape admission [2]. Thus, the observed weaker prognostic association applies to very old patients admitted to ICU; evaluating pre-ICU LOS for admission decisions would require a population defined at referral or assessment.

Clarifying the admission-route denominator would connect the early non-monotonic pattern to the pathways generating it. Framing the conclusion within the ICU-admitted cohort would preserve the study's cautious message and help readers distinguish prognosis after admission from evidence about upstream triage.

Authors' contributions

XZ contributed to conceptualization and writing of the original draft. ZH contributed to supervision and writing - review and editing. Both authors approved the submitted version and agree to be accountable for the work.

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Declaration of Generative AI and AI-assisted technologies in the writing process

During the preparation of this work, the authors used OpenAI Codex to assist with manuscript organization, wording refinement, and editorial review. No data or analyses were generated. The authors reviewed and edited the output as needed and take full responsibility for the content of the publication.

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The authors declare no competing interests.