Sepsis is a leading cause of critical illness worldwide, resulting in millions of hospitalizations and deaths annually [1]. In the United States alone, it accounts for approximately 1.7 million hospitalizations each year and is present in about 30 % of ICU admissions [2,3]. Effective management hinges on prompt recognition, followed by early interventions such as rapid administration of antibiotics, fluids, and vasoactive medications to restore tissue perfusion [[4], [5], [6]]. Precise hemodynamic monitoring is widely considered essential for guiding and tailoring therapy in real time. Although there has been a gradual shift away from invasive monitoring techniques such as central venous pressure or Swan-Ganz measurements, arterial lines remain common, used in 52 % to 84 % of critically ill patients with shock depending on the region [7].

There are many theoretical benefits of invasive blood pressure (BP) monitoring – it is thought to be more accurate in shock [8], allows for continuous measurements and practically, makes blood sampling for laboratory analysis more convenient. However, recent evidence challenges the long-held belief that arterial catheters yield more accurate BP measurements: one large retrospective study including over 50,000 measurements from over 1800 critically ill patients found a high degree of agreement between simultaneous arterial line and cuff measurements with a mean difference of only 6 mmHg [9]. While other previous studies were limited by single measurements, small sample sizes, or the inclusion of patients less critically ill than typical ICU populations, they also generally found a high correlation between the two measurement methods [[10], [11], [12], [13]].

To date, no trials have demonstrated a benefit of invasive BP monitoring. Observational studies of matched patients with and without arterial lines have not shown a mortality benefit, with corresponding longer ICU stays for those with arterial lines [14,15]. However, these studies primarily included mechanically ventilated patients with relatively stable hemodynamic profiles, leaving a gap in understanding the effects of arterial lines in patients with higher severity of illness [14,15]. Similarly, a matched case-control study of septic patients demonstrated no mortality difference, but this was a single-center study that included patients with relatively low Sequential Organ Failure Assessment (SOFA) scores (mean of 4) [16].

Arterial lines are not without risk. Initially thought to have a lower risk of infection due to brisk arterial flow, recent evidence shows similar bacterial colonization and catheter-related infections compared to central venous catheters [17]. Once placed, they may require ongoing sedation or immobilization and thereby interfere with interventions demonstrated to improve functional recovery, including early mobilization, sedative minimization and physical therapy [18,19]. Furthermore, their placement requires specialized expertise not universally available, especially in resource-limited settings [20]. Consequently, while the 2021 Surviving Sepsis Guidelines recommend early placement of arterial catheters for invasive monitoring of blood pressure in patients with shock, this is a weak recommendation based on very low-quality evidence [21]. As a result, there is a wide variability in practice [7], reflecting differences in institutional protocols and clinician preferences and underscores the need for robust evidence to guide clinicians on the efficacy and utility of arterial lines in septic shock management.

Therefore, we aim to determine whether invasive BP monitoring is associated with differences in all-cause inpatient mortality and length of stay in critically ill patients with septic shock. Additionally, we assess whether arterial catheter use affects the rate of shock resolution.