From the Guidelines
The best indicator of adequate resuscitation in shock is the normalization of lactate levels and clearance rate, along with improvement in tissue perfusion markers. When treating shock, clinicians should monitor serial lactate measurements, targeting a decrease of at least 10-20% every 2-4 hours, with the goal of normalizing levels below 2 mmol/L 1. Additional important indicators include:
- Improved mental status
- Increased urine output (>0.5 mL/kg/hr)
- Normalization of vital signs (particularly heart rate and blood pressure)
- Warm extremities with good capillary refill (<3 seconds)
- Normalized base deficit These parameters collectively reflect restored tissue perfusion and oxygen delivery. Lactate serves as an excellent marker because it accumulates during anaerobic metabolism when tissues are inadequately perfused, making its clearance a reliable sign that oxygen delivery has been restored to tissues 1. While no single parameter is perfect, this multimodal assessment approach provides the most comprehensive evaluation of resuscitation adequacy in shock patients. The most recent guidelines suggest guiding resuscitation to normalize lactate in patients with elevated lactate levels as a marker of tissue hypoperfusion 1.
In clinical practice, it is essential to consider the patient's overall clinical picture and adjust the resuscitation strategy accordingly. The use of dynamic over static variables to predict fluid responsiveness and the assessment of cardiac function can help determine the type of shock and guide further management 1. Ultimately, the goal of resuscitation is to restore tissue perfusion and oxygen delivery, and lactate clearance is a reliable indicator of this process.
It is worth noting that other indicators, such as mean arterial pressure and urine output, are also important, but they should be used in conjunction with lactate clearance to get a comprehensive picture of the patient's response to resuscitation 1. The 2016 Surviving Sepsis Campaign International Guidelines for Management of Sepsis and Septic Shock recommend an initial target mean arterial pressure of 65 mmHg in patients with septic shock requiring vasopressors 1. However, the most recent and highest quality study suggests that lactate clearance is a more reliable indicator of adequate resuscitation 1.
From the Research
Indicators of Adequate Resuscitation in Shock
The best indicator of adequate resuscitation in shock is a topic of ongoing debate in the literature. Several studies have investigated various parameters to determine the most appropriate endpoint of resuscitation.
- Traditional endpoints, such as heart rate, blood pressure, mental status, and urine output, are useful in the initial identification of inadequate perfusion but are limited in their ability to identify ongoing, compensated shock 2.
- Urine output is often used as a marker of acute kidney injury and to guide fluid resuscitation in critically ill patients, but its interpretation can be influenced by neurohormonal factors and functional changes 3.
- Ideal resuscitation endpoints should assess the adequacy of tissue oxygen delivery and oxygen consumption, and be quantifiable and reproducible 4.
- Improving organ perfusion, particularly renal blood perfusion, is a direct indicator of shock resuscitation, and critical-care ultrasonography can provide the best evaluation of renal perfusion 5.
- A conservative, physiologically guided approach to fluid resuscitation, individualized based on the cause of shock and the patient's hemodynamic and respiratory status, is likely to improve patient outcomes 6.
Parameters for Evaluation
Some parameters that can be used to evaluate the adequacy of resuscitation include:
- Lactate level: a decrease in lactate level can indicate improved tissue perfusion and oxygenation 4.
- Central venous oxygen saturation (ScvO2): a measure of the oxygen saturation of blood returning to the heart, which can indicate the adequacy of tissue oxygen delivery 4.
- Urine output: while its interpretation can be complex, urine output can still be a useful indicator of renal perfusion and function 3, 5.
- Mental status: improved mental status can indicate adequate cerebral perfusion and oxygenation 2.
- Blood pressure: while not a perfect indicator, blood pressure can still be used to guide fluid resuscitation and evaluate the adequacy of circulatory function 6.