This scoping review explores fluid management strategies for adult patients undergoing venoarterial extracorporeal membrane oxygenation (VA-ECMO), a life-saving technique used in cases of severe cardiogenic shock or cardiac arrest. Despite its critical role, optimal fluid management during VA-ECMO remains controversial, with limited evidence guiding decisions regarding fluid type, dosage, and strategies to achieve balance. This review analyzes 16 studies, including 14 clinical and two experimental studies, to map existing knowledge and identify research gaps.
VA-ECMO often necessitates fluid resuscitation to maintain adequate intravascular volume and ensure ECMO functionality. However, excessive fluid administration can lead to fluid overload, which has been consistently associated with negative outcomes. Among the studies analyzed, early fluid overload—measured in the first 24 to 72 hours after ECMO initiation—correlated with increased mortality, kidney injury, and prolonged hospital stays. For example, one study reported a sixfold increase in mortality risk for patients with fluid balance above the 75th percentile within the first three hours post-ECMO initiation. Another study identified a cumulative fluid balance threshold of 38.8 mL/kg in the first 24 hours as a significant predictor of mortality.
Fluid type is another critical consideration in VA-ECMO. Crystalloids, often used as first-line resuscitation fluids, can be classified into balanced and unbalanced solutions. Balanced crystalloids have shown renal protective effects in general ICU populations, but their specific benefits in VA-ECMO patients remain unexplored. Albumin, a colloid with theoretical anti-inflammatory and plasma-expanding properties, has shown potential benefits in retrospective studies. In one study, patients receiving albumin alongside balanced crystalloids exhibited improved survival rates compared to those receiving balanced crystalloids alone. However, no randomized controlled trials have directly compared the efficacy and safety of saline, balanced crystalloids, or albumin in VA-ECMO settings, leaving this area under-researched.
Fluid balance monitoring is crucial in critically ill patients on VA-ECMO. Methods include net fluid balance (input vs. output), weight-based measures, and cumulative fluid balance. Despite being widely used, these methods vary significantly across studies, creating challenges in standardizing definitions and thresholds for fluid overload. For example, a 10% increase in weight from baseline is commonly used as a marker for fluid overload, but this threshold may not fully account for individual patient variability or ECMO-related fluid shifts.
Acute kidney injury (AKI) is a common complication in ECMO patients, affecting up to 85% of cases, with 45% requiring renal replacement therapy (RRT). Fluid overload exacerbates AKI, creating a vicious cycle of worsening outcomes. Studies suggest that managing fluid balance aggressively—through de-resuscitation strategies like diuretics or RRT—could mitigate the risks of AKI. However, the timing and criteria for initiating such interventions remain unclear, particularly during the early, high-risk phases of ECMO support.
The review highlights a notable lack of high-quality evidence regarding the optimal fluid resuscitation strategy in VA-ECMO patients. Most studies are retrospective and heterogeneous, with varying patient populations, ECMO durations, and underlying conditions. Half of the clinical studies included mixed VA-ECMO and venovenous ECMO (VV-ECMO) populations, limiting their applicability to VA-ECMO-specific scenarios. Additionally, while animal studies provided insights into fluid dosing and tissue effects, their relevance to human patients is limited due to physiological differences.
The findings underscore the urgent need for prospective, randomized controlled trials to address key questions: (1) What is the ideal fluid type for resuscitation in VA-ECMO patients? (2) How does a restrictive fluid strategy compare to liberal or goal-directed approaches in this context? (3) What are the most accurate and clinically relevant endpoints for guiding fluid management? Future studies should focus on homogeneous patient groups, considering variables such as age, severity of illness, and ECMO indications, to generate reliable and actionable evidence.
In conclusion, while fluid management is a cornerstone of VA-ECMO therapy, the current lack of standardized practices underscores the need for robust research. Addressing these gaps could significantly improve survival and reduce complications for patients undergoing this critical intervention.
