Resuscitation endpoints and monitoring
Key Points
- Urine output of 30-50 mL/hr in adults remains the primary resuscitation endpoint but is an imperfect surrogate for global tissue perfusion [1][3]
- Invasive hemodynamic monitoring improves cardiac index and urine output at 24 hours but has not demonstrated mortality benefit in randomized trials of burn patients [2]
- Serum lactate, base deficit, and central venous oxygen saturation serve as adjunctive markers of resuscitation adequacy [4]
- A personalized stepwise protocol integrating clinical, laboratory, and hemodynamic endpoints has been proposed but lacks multicenter validation [3]
- Overresuscitation driven by excessive reliance on urine output contributes to fluid creep and its complications including abdominal and extremity compartment syndromes [6]
Overview
Resuscitation endpoints guide the titration of intravenous fluid during the first 24 hours after major burn injury. The goal is to deliver the minimum fluid volume required for adequate tissue perfusion while avoiding the complications of overresuscitation. Hourly urine output of 30-50 mL/hr in adults (1 mL/kg/hr in children) has been the traditional "gold standard" endpoint since the development of modern resuscitation formulas [1][3]. However, urine output reflects renal perfusion and may not accurately represent global tissue oxygenation, leading to both under- and overresuscitation in individual patients [1][3]. The search for better endpoints has driven investigation of hemodynamic monitoring, laboratory markers, and computerized decision support systems.
Traditional Endpoints
Urine output remains the most widely used titration target. Its advantages are simplicity, universal availability, and continuous measurement via Foley catheter. Burns resuscitation protocols typically adjust crystalloid infusion rates in response to hourly urine output, increasing rates when output falls below 30 mL/hr and decreasing when output exceeds 50 mL/hr [3][6]. Mean arterial pressure and heart rate are supplementary clinical endpoints used to identify gross hemodynamic instability.
The limitations of urine output are well documented. It is a lagging indicator that reflects renal perfusion rather than global oxygen delivery [1]. Glycosuria from high-dose vitamin C or hyperglycemia can produce osmotic diuresis that mimics adequate resuscitation [6]. Peeters et al. argued that urine output is a poor resuscitation target and proposed that modern less-invasive hemodynamic monitoring should supplant it [3][4].
Advanced Hemodynamic Monitoring
Invasive hemodynamic monitoring, including pulmonary artery catheterization, transpulmonary thermodilution, and transesophageal echocardiography, has been evaluated in major burns. Davenport et al. conducted a systematic review and meta-analysis of 10 studies involving 401 major burns patients and found that invasive monitoring was associated with significantly improved cardiac index and urine output at 24 hours compared with non-invasive endpoints [2]. However, when limited to randomized controlled trials only, the survival advantage of invasive monitoring over hourly urine output did not reach statistical significance [2].
Paratz et al. performed a systematic review of endpoints beyond urine output, finding limited evidence that hemodynamic monitoring improved outcomes, though all studies lacked assessor blinding [1]. They concluded that a large multicenter study investigating alternative endpoints is warranted [1].
Bak et al. studied 10 patients with burns exceeding 20% TBSA using simultaneous transesophageal echocardiography, pulmonary artery catheterization, and transpulmonary thermodilution. Preload variables showed central circulatory hypovolemia at 12 hours that resolved by 24 hours with Parkland formula resuscitation, supporting more rapid early infusion but not increased total volume [5].
Laboratory Endpoints
Serum lactate and base deficit reflect global tissue perfusion and are commonly used as adjunctive markers. Elevated lactate indicates anaerobic metabolism from inadequate oxygen delivery, while base deficit quantifies the degree of metabolic acidosis [4]. Central venous oxygen saturation (ScvO2) provides a continuous measure of the balance between oxygen delivery and consumption.
Peeters et al. proposed a personalized stepwise resuscitation protocol that integrates urine output, mean arterial pressure, lactate, cardiac index, and global end-diastolic volume index from transpulmonary thermodilution as successive escalation tiers [3]. This protocol has not been validated in a prospective multicenter trial.
Computerized Decision Support
Computerized decision support systems use rule-based algorithms to automatically recommend fluid rate adjustments based on urine output trends. Cartotto et al. noted that these systems show promise in reducing total resuscitation volumes but an RCT comparing them to conventional nurse-driven titration has not been completed [6].
Controversies and Evidence Gaps
Urine output is the most accessible endpoint but is increasingly recognized as inadequate for complex resuscitations, particularly in patients with burns exceeding 40% TBSA, inhalation injury, or significant comorbidities [1][3]. Advanced hemodynamic monitoring provides more physiologic data but adds cost, invasiveness, and complexity without proven mortality benefit in burns [2]. No validated multiparameter protocol has been tested in a large multicenter trial. The optimal integration of traditional and advanced endpoints remains an unsettled question. Whether computerized decision support can standardize resuscitation quality across institutions is an active area of investigation [6].
References
[1] Paratz JD et al. "Burn resuscitation--hourly urine output versus alternative endpoints: a systematic review." Shock 2014;42(4):295-306. PMID: 24978885 [2] Davenport LM et al. "The role of invasive monitoring in the resuscitation of major burns: a systematic review and meta-analysis." Int J Burns Trauma 2019;9(2):28-40. PMID: 31149390 [3] Peeters Y et al. "An overview on fluid resuscitation and resuscitation endpoints in burns: Part 2." Anaesthesiol Intensive Ther 2015;47 Spec No:s15-26. PMID: 26480868 [4] Peeters Y et al. "An overview on fluid resuscitation and resuscitation endpoints in burns: Part 1." Anaesthesiol Intensive Ther 2015;47 Spec No:s6-14. PMID: 26480867 [5] Bak Z et al. "Hemodynamic changes during resuscitation after burns using the Parkland formula." J Trauma 2009;66(2):329-36. PMID: 19204504 [6] Cartotto R et al. "Burn State of the Science: Fluid Resuscitation." J Burn Care Res 2017;38(3):e735-e751. PMID: 28328669