It is because it is crucial for decisions about fluid resuscitation. It is known that burn size is often overestimated by as much as 2× by referring hospitals. Computer-aided methods have improved the accuracy of estimating burned areas by including data analysis and reducing subjective differences. Computer planimetry and three-dimensional (3D) scanning allows to determine body dimensions rapidly and reproducibly. Representative efforts are the BurnCasev 3D, EPRI 3D Burn Vision, BAI, Chang Gung Whole Body Scanner and BurnCalc.20

Burn injuries of <20% TBSA can generally be resuscitated with oral hydration, except in cases of facial, hand and genital burns as well as burns in children and the elderly. Adults and children with burns of >20% TBSA should undergo formal intravenous fluid resuscitation.

Several formulas have been developed to optimise fluid delivery. We can use formulas:

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  based only in the contribution of crystalloids (Parckland, modified Brooke). Usually we use lactated Ringer's solution.

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  based in the contribution of colloids from the beginning (Evans, Brooke, Slater)

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  and based in hypertonic solutions (Monafo) or dextran (Demling).

Common formulas used to initiate resuscitation estimate a crystalloid need for 2–4mL/kg body weight/% TBSA during the first 24h (Table 1). The Parkland formula, which calculates the amount of fluid required to resuscitate a patient based on body size and surface area burned, is the most commonly used formula. According to this formula, the fluid requirement during the initial 24h of treatment is 4mL/kg of body weight for each percent of TBSA burned, given intravenously. Superficial burns are excluded from this calculation. An alternative to Parkland is the modified Brooke formula. According to one review, use of the modified Brooke formula may reduce the total volume used in fluid resuscitation without causing harm.21

Children may, in addition, require a maintenance fluid and dextrose in the resuscitation fluid.

To simplify calculations, Chung et al. have recently developed the ‘Rule of TEN’ (only applicable for adults). The estimated burn size in % TBSA is multiplied by 10 to derive the initial fluid rate in mL/h. For every 10kg above 80kg, 100mL is added to this rate.22

Neither Parkland formula nor others provides a precise method for determining the fluid requirements, these formulas provide only a starting point.4 Severity of burn, inhalation injury, associated injury, patient age and comorbidities can alter the fluid requirements of individual patients. Thus, the American Burn Association recommended monitoring urine output, pulse, blood pressure and oxygen saturations.23 Distal pulses, capillary refill and colour and turgor of uninjured skin along with serial laboratory determinations can assist the monitoring. Non-invasive blood pressure measurements by cuff are rendered inaccurate because of the interference of tissue oedema. Pulse rate is a much more sensitive monitoring parameter than arterial blood pressure. A pulse rate >120 beats/min usually indicates hypovolemia. However, urine output is the monitoring method most commonly used. Fluid resuscitation should be titrated to maintain an urine output of approximately 0.5–1.0mL/kg/h in adults and 1.0–1.5mL/kg/h in children, and in those patients at risk of rhabdomyolysis due to electrical burn or due to the association with crush injury, Although, now goals are reduced to 30–35mL/h for an average-sized adult.5 The infusion rate should be increased by approximately 20–30% when the urine output is insufficient or other clinical parameters suggest inadequate resuscitation. We can give fluids bolus, but any change to the infusion rate must be made as gradually as possible.

It is important to recognise when fluid resuscitation is not going well. If low urine output persists despite increasing fluid infusion rates, we must consider starting a continuous infusion of albumin 5%, use of vasopressors (vasopressin, norepinephrine) to support blood pressure and/or inotropes to support cardiac function. In these situations, the monitoring of cardiac output and filling pressures has shown a decrease in mortality with a trend towards less renal failure. Various studies demonstrated that urine output as a measure of resuscitation may not provide sensitive or specific monitoring and may not necessarily achieve the best prevention of organ dysfunction either.24,25 This is the reason because severity burned patients should be monitored by other methods. In addition, critically burn patients can have three simultaneous types of shock: cardiogenic, hypovolemic and distributive, and therefore, the use of hemodinamic monitoring is very important.

The finding that pulmonary artery occlusion pressure and central venous pressure are not good indicators of preload has led to increased resuscitation guided by data from the transpulmonary thermodilution (TPTD) method.26–28 This method measures cardiac output (CO), intrathoracic blood volume (ITBV), extravascular lung water (EVLW) and other dynamic parameters. Csontos et al. found that the mean ScvO2 was significantly lower and multiple organ dysfunction (MODS) was significantly higher in the hourly urine output group than in the ITBV group (with resuscitation goal of maintain ITBV Index between 800–850mL/m2). They suggest that ITBV Index may be a better target parameter than urine output.29 Our group found that monitoring TPTD and lactate was safe and avoided excessive fluid intake.30 Endorf et al. recommended monitoring dynamic data such as SVV and the response to the contributions of fluid (increased ITBVI percentage after a given contribution) without neglecting other supplementary data such as lactic acid clearance or intraabdominal pressure.31 In every critically burn patient, bladder pressures should be monitored to identify intraabdominal hypertension. Infusion of large fluid volumes (>250mL/kg) of crystalloid in the first 24h during burn resuscitation are considered a high risk for the development of Abdominal compartment syndrome. Early recognition can allow for timely descompressive (percutaneous or laparotomy).

There are patients with inadequate perfusion despite having achieved the objectives of blood pressure (compensated shock or microcirculatory shock). Thus, it is useful to add global perfusion parameters. A decrease in mixed venous oxygen saturation and an increase in serum lactate suggest inadequate end-organ perfusion. Base deficit and lactate have been shown to correlate with mortality and fluid resuscitation volumes. But so far physiologic manipulation does not change the outcome.32 Futhermore, in critically ill patients arteriovenous DeltaCO2 has been used as tissular perfusion parameter, but there are no studies on burn patients. Other technologies to guide fluid resuscitation are being used such as echocardiography, esophageal echo-Doppler and Doppler ultrasound measurement of renal perfusion. Another recently incorporated technology is the computer-guided infusion based upon urine output33.

Cancio et al. found that clinicians directing the resuscitation were significantly less likely to reduce the rate of fluid infusion when urine output was high than they were to increase fluid rates when urine output was low. In an effort to reduce the dependence on clinical decision making, some centres have been incorporating nurse-driven protocols or computer-based resuscitation algorithms. Some nurse-driven resuscitation showed a significant decrease in fluid volumes during resuscitation.

When it began the monitoring with pulmonary artery catheter high contributions of fluid were needed because we were trying to reach a normal preload. Some studies have shown that TPTD monitors results in more aggressive therapeutic strategies and is associated with a significant increase in fluid administration, but it does not improve preload. However, there are some study which found that when a fluid resuscitation is based on the arterial waveform analysis, the initial fluid volume provided was significantly lower than that delivered on the basis of physician-directed fluid resuscitation (by urine output and mean arterial pressure).

TPTD is a very beneficial tool in the estimation of amounts of fluid resuscitation, although the values of ideal end points need to be adjusted. The traditional values of ITVB, EVLW and cardiac index (CI) are associated with significant tissue oedema.34 In a study, Arlati et al. used a permissive hypovolemia protocol and reduced the volume given as low as possible by titrating the infusion rate to a minimum ITBV value that allowed for at least 2.2L/min/m2 of the CI. They found that this protocol was effective in reducing MODS.35 Zhang et al. did not found superiority in TPTD monitoring compared with that for central venous pressure, but in their algorithm, before administering vasoactive drugs seeks to achieve a minimum preload of 850mL/m2 of ITBV Index. We assume that a severely burn patient may not be adequate to achieve the optimal ITBV Index level36; therefore, it would be better to accept a slightly below-normal level to avoid excessive fluid intake. We studied 165 severely burn patients and found that CI and clearance of lactic acid significantly improved when ITBV Index levels reached 750mL/m2; however, further increases did not considerably improve the haemodynamics.37

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  Control of oxidative stress with high dose ascorbic acid (vitamin C, 66mg/kg/h) decreases systemic inflammation, decreases fluid requirements and decreases the days under mechanical ventilation.38 There is only one study in which high-dose vitamin C supplementation has been shown to cause secondary calcium oxalate nephropathy. In relation to its infusion is important to note that routine point-of-care glucose analysis can show fictitious hyperglycemia. Membrane-stabilising agents such as zinc, selenium and vitamin E could help in the recovery of burn patients.

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  Remove proinflammatory cytokines: whether continuous RRT or plasmapheresis exerts a beneficial effect during burn shock resuscitation remains to be determined.

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  Low doses of propranolol to severely burn patients reduce myocardial oxygen requirements without adversely affecting oxygen delivery, enhance wound healing and decrease the surface area requiring skin grafting.

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  Intensive insulin treatment improved biochemical markers of inflammation, decreased the catabolic response and decreased the incidence of infection and sepsis. Other drugs, as oxandrolone, are not yet standard-of-care therapies despite clear potential clinical benefit.

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  Other important aspects are pain management with morphine but avoiding excess that causes fluid creep. It should be also avoided over-treated with routine ventilation.39 Most severe patients need alternative ventilation modes and lung protective ventilation strategy combining lung recruitment maneuverer. Patients with inhalation injury may require mechanical ventilation and adjunctive therapies such as nebulised heparin and tissue plasminogen activator that have demonstrated efficacy through the breakdown of fibrin deposition, maintenance of alveolar structure and reduced obstruction.40 Antithrombin III has also been used in inhalation injury. Other therapies that should be considered are aggressive pulmonary toilet, nitric oxide, N-acetylcysteine, modified tetracycline, nebulised vitamin E and/or bronchodilators.

Finally, new therapeutic strategy to prevent microvascular permeability should be emphasised and developed in future, which may hopefully act as the most basic approach to prevent burn shock and the complications associated with it.