Is the PaO₂/PaCO₂ Ratio Associated With ICU Mortality Independent of Oxygen Saturation and Mean Arterial Pressure? (RATIO-MIMIC)

Association of the PaO₂/PaCO₂ Ratio With ICU Mortality Independent of Oxygen Saturation and Mean Arterial Pressure: Insights From the MIMIC-II Database

The goal of this observational study is to learn about the Association of the PaO₂/PaCO₂ Ratio with ICU Mortality Independent of Oxygen Saturation and Mean Arterial Pressure

Study Overview

• Status: Completed
• Conditions: Mortality in Intensive Care Units

• Study Type: Observational
• Enrollment (Actual): 1776

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

This study included adult patients admitted to intensive care units (ICUs) represented in the Medical Information Mart for Intensive Care II (MIMIC-II) database, a large, publicly available critical care database developed by the Massachusetts Institute of Technology (MIT) in collaboration with Beth Israel Deaconess Medical Center (BIDMC). The database contains detailed, de-identified clinical data from patients admitted to the BIDMC ICUs between 2001 and 2008.

All adult (≥18 years) ICU patients with at least one arterial blood gas measurement containing both arterial oxygen tension (PaO₂) and arterial carbon dioxide tension (PaCO₂) were eligible for inclusion. For each included ICU stay, corresponding measurements of oxygen saturation (SpO₂) and mean arterial pressure (MAP) were also extracted to allow adjustment for oxygenation and hemodynamic status.

Patients were excluded if they lacked valid PaO₂ or PaCO₂ measurements, had missing ICU mortality data, or had physiologically impla

Description

Inclusion criteria

Adult patients (≥ 18 years old) at time of ICU admission. Rationale: Restrict to adult physiology and consent/ethics comparability.

First ICU stay during hospital admission (index ICU admission). Rationale: Avoid within-hospital dependency and repeated measures bias.

ICU admission captured in the MIMIC-II dataset between the database start and end dates.

Rationale: Use all eligible records within the dataset timeframe.

At least one arterial blood gas (ABG) measurement with both PaO₂ and PaCO₂ available during the ICU stay.

Rationale: Primary exposure is PaO₂/PaCO₂ ratio; require both values to compute it.

Available outcome data for ICU mortality (discharge status from ICU). Rationale: Necessary to ascertain primary endpoint.

Available SpO₂ and mean arterial pressure (MAP) measurements in the same ICU stay (for confounder adjustment).

Rationale: Study aims to evaluate independence from SpO₂ and MAP; require at least one measurement of each during the stay. (If either is missing, see handling below.)

Exclusion criteria

Age < 18 years. Rationale: Exclude pediatric physiology.

Missing or unusable arterial blood gas values (PaO₂ or PaCO₂ absent or non-numeric) for the ICU stay.

Rationale: Cannot compute exposure.

No recorded ICU outcome (missing ICU discharge status) or lost/invalid mortality data.

Rationale: Cannot determine primary outcome.

Extreme or physiologically implausible ABG values that suggest data error (e.g., PaO₂ ≤ 0 mmHg, PaCO₂ ≤ 0 mmHg, or PaO₂ > 1000 mmHg or PaCO₂ > 300 mmHg - thresholds may be tightened after exploratory data review).

Rationale: Remove likely data-entry errors. Document thresholds and perform sensitivity analysis.

Patients on extracorporeal life support (ECMO) during ABG measurement (if identifiable in MIMIC-II).

Rationale: ECMO profoundly alters gas exchange and PaO₂/PaCO₂ physiology; consider exclusion or separate subgroup.

Repeat ICU admissions within the same hospital stay beyond the index admission (if you choose to restrict to single index admission).

Rationale: Prevent correlated observations - include only the first ICU stay per hospital admission.

ICU stays with no recorded SpO₂ or MAP at any time (if you insist on requiring these for adjustment).

Rationale: If primary models must adjust for SpO₂ and MAP, exclude records without those covariates or plan appropriate imputation.

Do-not-resuscitate (DNR)/comfort-care only status recorded before ABG measurement (optional exclusion depending on study question).

Rationale: Treatment limitation orders can confound mortality associations; you may choose instead to adjust or analyze separately.

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort

The Indwelling Arterial Catheter Clinical dataset contains clinical data for 1776 patients..........; The Indwelling Arterial Catheter Clinical dataset contains clinical data for 1776 patients from the MIMIC-II clinical database. It was the basis for the article: Hsu DJ, et al. The association between indwelling arterial catheters and mortality in hemodynamically stable patients with respiratory failure: A propensity score analysis. Chest, 148(6):1470-1476, Aug. 2015.This dataset was also used by Raffa et al. in Chapter 5 "Data Analysis" of the forthcoming book: Secondary Analysis of Electronic Health Records, published by Springer in 2016......................................................................................................................................................................................................................................................................................................................................................................................................................................................................

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
ICU mortality	Death occurring during the ICU stay	From October 2025 to January 2026.............................................................................................................................................................................................................................

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
28-day all-cause mortality	28-day all-cause mortality	From October 2025 to January 2026

Collaborators and Investigators

• Sponsor: Tanta University

Study record dates

Study Major Dates

• Study Start (Actual): March 20, 2015
• Primary Completion (Actual): March 20, 2016
• Study Completion (Actual): March 20, 2016

Study Registration Dates

• First Submitted: December 10, 2025
• First Submitted That Met QC Criteria: December 10, 2025
• First Posted (Actual): December 24, 2025

Study Record Updates

• Last Update Posted (Actual): December 24, 2025
• Last Update Submitted That Met QC Criteria: December 10, 2025
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Other Study ID Numbers: MIMIC-II

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No