(1510) Immortality Bias and the Timing of Administration of Calcium During In-Hospital Cardiac Arrests

Introduction: Advanced Cardiac Life Support (ACLS) guidelines do not endorse routine calcium administration during cardiac arrest due to a myriad of studies that suggest its use is associated with untoward outcomes, including mortality. Despite this, calcium remains in broad use during arrest, particularly during in-hospital cardiac arrest (IHCA). This is likely due to the unique etiologies of in-hospital arrest, including hyperkalemia. We also suspect that existing data is skewed by “immortality bias,” or “immortal time bias,” where patients who achieve early return of spontaneous circulation (ROSC) are less likely to receive calcium (thus making no-calcium cohorts appear better), and where patients who are not achieving ROSC are given calcium as a “last-ditch” therapy (thus making calcium-cohorts appear worse). Specific insights about the timing of calcium administration during arrest may help address existing confounding related to the immortality bias in IHCA studies. We hypothesized that calcium use during IHCA would escalate as code duration increased.

Methods: The study evaluated IHCA events that occurred in 2022 at the University of Wisconsin Hospital. Codes were excluded if they did not last at least 5 minutes given the risk of aberrantly initiating CPR due to hard-to-palpate pulses.

Results: In total, 143 IHCA events met inclusion criteria. Calcium was administered in 81 (56.6%) events. As code duration increased, the proportion of arrests that were administered calcium also increased (for codes lasting at least 5 min: 60.8% received calcium; 10 min: 68.6%, 15 min: 75.6%, 20 min: 76.6%, 25 min: 80.0%, 30 min: 76.7%, 35 min: 81.8%, 40 min: 77.8%, 45 min: 76.5 % and 50 min: 85.7%).

Conclusions: Calcium use during IHCA remains ubiquitous at our institution. Since calcium use escalates with increasing code duration, retrospective studies assessing calcium use during arrest are susceptible to “immortality bias.” Future retrospective research efforts assessing calcium administration and mortality outcomes in IHCA should add time stratification of calcium use to other adjustment techniques like propensity matching to best associate its use with outcomes.