Femoral Versus Radial Invasive Arterial Pressure Monitoring in Cardiac Surgery Patients

Acute circulatory failure or shock-typically characterized by arterial hypotension-is a major cause of ICU admission and a significant contributor to postoperative complications in surgery. This condition may result from various pathophysiological mechanisms such as arterial vasodilation, hypovolemia, or low cardiac output, frequently triggered by sepsis, inflammation, surgery, or hemorrhage. Hypotension leads to hypoperfusion of vital organs (kidney, brain, heart), significantly increasing patient morbidity and mortality. Consequently, numerous studies have focused on identifying critical blood pressure thresholds and optimizing therapeutic strategies to reduce associated organ dysfunction and mortality.

A key challenge in the management of hypotension is the accuracy of blood pressure (BP) measurement. In clinical practice, invasive arterial pressure is commonly monitored at radial, brachial, or femoral sites. The radial artery is often preferred for its accessibility and ease of catheterization. However, from a physiological standpoint, the radial artery's small diameter and peripheral location can result in discrepancies when compared to central aortic pressure-the actual pressure driving organ perfusion.

Several studies have shown that in states of shock or acute circulatory failure, radial artery pressure measurements often underestimate actual blood pressure compared to more central measurements such as femoral artery pressure. This difference is particularly pronounced in specific physiological and pathological conditions-e.g., during vasoconstrictor use-where systolic pressure gradients between radial and femoral sites may be significant.

As such, accurate blood pressure monitoring is critical in anesthesia and critical care to guide fluid resuscitation, vasopressor therapy, and interpretation of hemodynamic monitoring tools. Inaccurate measurements may lead to excessive exposure to hypotension or unnecessary administration of vasopressors, both of which carry associated risks.

Scientific literature comparing radial and femoral arterial BP monitoring is limited, outdated (mainly from the 1990s), and largely based on observational data. It is well-established that radial artery monitoring can lead to spuriously low BP readings, resulting in inappropriate hemodynamic management, including excessive fluid resuscitation or vasopressor administration.

Observational studies consistently report the following findings:

A systematic pressure gradient (at least 5-10 mmHg in mean arterial pressure) between femoral and radial sites.

The radial site underestimates femoral BP, and thus organ perfusion pressure. This gradient is more pronounced in critically ill patients, particularly those receiving vasopressors, women, or those with severe illness (e.g., refractory shock, sepsis).

These discrepancies in BP measurement are associated with overuse of hemodynamic drugs. Previous studies reported that over one-third of patients had a significant BP gradient between radial and femoral sites-often leading to excessive vasopressor administration. Other works further support this, indicating higher rates of adverse events, including acute kidney injury (AKI), and excessive vasopressor use in patients monitored at the radial site versus the femoral site.

AKI, frequently observed during shock or in surgical patients, is a key concern. In its severe form, it increases operative mortality by 3 to 8 times, lengthens ICU and hospital stays, and dramatically increases healthcare costs. Even mild AKI is a major predictor of long-term outcomes, particularly chronic kidney disease. The kidney is especially vulnerable to both hypotension and excessive vasopressor use. Multiple perioperative and ICU studies have demonstrated correlations between norepinephrine exposure (dose and duration) and increased AKI incidence.

Despite the importance of accurate BP measurement, the debate regarding the optimal site for arterial monitoring remains unresolved. Radial catheterization is less invasive and easier to perform but may result in excessive vasopressor use and associated complications. In contrast, femoral arterial monitoring may offer more precise pressure readings and thereby improve the safety and efficiency of hemodynamic optimization in critically ill or surgical patients.

The central hypothesis of this study is that invasive arterial pressure monitoring at the femoral site is associated with a reduced number of patients requiring vasopressor therapy (e.g., norepinephrine), compared to monitoring at the radial site.

While clinical guidelines address central venous access and the use of ultrasound guidance, no current recommendations specify the optimal arterial site for BP monitoring, primarily due to a lack of high-quality evidence. This study aims to fill that gap, focusing on a routine clinical practice-arterial pressure monitoring in perioperative and critical care settings.

A better understanding of the clinical implications of the measurement site could lead to more precise recommendations for invasive BP monitoring and improve patient care. Results from this trial may influence: the choice of arterial catheterization site, the use and duration of vasopressor therapy, the incidence of renal and cardiovascular complications.

Should this study demonstrate that femoral arterial monitoring improves clinical outcomes, it could lead to changes in clinical practice guidelines and initiate larger-scale investigations in various other critical care and surgical populations.