Performing the fluid challenge test is often in circulatory failure conditions, especially in hypovolemic shock. Although it is usually considered safe and without risk, the fluid challenge test can increase fluid overload risk when given under the wrong conditions. Until now, there has not been a standardized fluid challenge test technique.

The fluid challenge test principle is the administration of fluid with a small volume and a short time to determine the patient's preload reserve. Generally, the fluid challenge test is given under hypovolemia to determine the patient's fluid responsiveness.

Overview of the Fluid Challenge Test

Performing the fluid challenge test aims to select which patients will benefit from hemodynamics from fluid resuscitation. Until now, there has been no standardized technique for conducting fluid challenges. However, most clinicians perform the fluid challenge test by giving a 250-500 ml colloid or crystalloid fluid in 20-30 minutes. An increase in stroke volume and cardiac output by 10-15% is considered a sign of a positive response to giving a fluid challenge. This test is simple, secure, inexpensive, and can be performed in a short time.

The disadvantage of the fluid challenge test is the difficulty of determining with certainty the effect of fluid administration on hemodynamics. Of course, the best way is to directly measure cardiac output, and it cannot be based solely on arterial pressure changes. One study found that arterial pressure change was not significantly related to a cardiac output change in fluid challenges. Another study even reported a 22% false-negative if the response was only assessed based on arterial pressure alone.

Another disadvantage that needs to be watched out for is that administering fluids in a fluid challenge serves as a supplementary examination and as an intervention or therapy. In patients who require repeated fluid challenges close together, the accumulation of the amount of fluid given during a fluid challenge can increase the risk of overload and hemodilution.

Conditions That Require The Fluid Challenge Test

The Fluid challenge test is generally used in emergency conditions, which cause a decrease in blood pressure and urine output. Hypovolemic shock is one of them.

Hypotension is the most frequent indication of doing fluid challenge test. Other indications include termination of vasopressors, oliguria, hypoperfusion markers such as mottling of the skin, increased lactate, septic shock, and renal or hepatic dysfunction.

However, administering a fluid challenge test must be tailored to each patient's clinical course. In patients with chronic kidney disease, for example, the risk of excess fluid becomes greater. In the case of cardiogenic shock, administering a fluid challenge can increase the end-diastolic pressure of the left ventricle, which has increased and worsened pulmonary edema.

Liquid Choices in the Fluid Challenge Test

The Fluid challenge test can use crystalloid fluids, either isotonic or hypertonic, and colloidal fluids. About 74% of clinicians use crystalloids in the fluid challenge test.

In theory, colloids have the advantage of reducing the likelihood of extravasation of fluid in the lungs and increasing cardiac output. Also, colloids have a more extended period of intravascular compared with crystalloids. They are hyperosmotic so that they can draw fluid from the interstitial to intravascular space, which can increase plasma volume better than crystalloids.

The Cochrane Review seeks to compare colloids and crystalloids' effects in critically ill patients who require fluid therapy. Sixty-nine studies with a total of 30,020 samples were included in the analysis. The results of the study found no significant differences related to mortality risk. The meta-analysis of Toscani L et al. in 85 studies with 3601 patients also stated that the type of fluid in the fluid challenge test did not affect the patient's response to this test. Therefore, the use of fluids, both colloid and crystalloid, in the fluid challenge test can be used according to circumstances.

How to do Fluid Challenge Test

Although the fluid challenge test has been approved for use by many guidelines, up to now, there is no standardization of giving. Several decades ago, the technique used was based on rules 2-5 using central venous pressure (CVP) and ruled 3-7 using pulmonary artery occlusion pressure (PAOP). Pressure observation is carried out at 10-minute intervals with 200 ml of initial liquid being given for 10 minutes. If there is a change in PAOP <3 mmHg or CVP <2 mmHg, then the liquid can be continued. However, if PAOP is in the range of 3-7 mmHg, or CVP 2-5 mmHg, the liquid is stopped first and re-evaluated within 10 minutes. The liquid is immediately stopped if there is an increase in PAOP pressure> seven mmHg or CVP> 5 mmHg.

At present, there is a modification in the administration of fluid challenge using mean arterial pressure (MAP) as a clinical target and CVP as a safe limit target for pulmonary edema complications. The recommended liquid is ringer lactate crystalloid fluid because it has an adequate electrolyte composition and economical price. Administration of 500 ml of lactate ringers for 30 minutes and evaluation of MAP and CVP are performed every 10 minutes. If there is an increase in MAP and CVP in the normal range, the fluid challenge test is considered successful, and the fluid can be continued. However, if there is a decrease in MAP accompanied by an increase in CVP, the fluid challenge can be considered unsuccessful, and the fluid is stopped.

Mini Fluid Challenge

Because the fluid challenge test has various disadvantages, as mentioned earlier, several studies have tried to see whether administering smaller volumes of fluid is capable of measuring fluid responsiveness.

Muller et al. conducted a study related to the mini fluid challenge by administering 100 ml of colloidal hydroxyethyl starch for 1 minute, followed by 400 ml for 14 minutes. Increased subaortic velocity time index (VTI) ≥ 15% becomes the standard of success. Of the total, 39 patients, 21 patients (54%) had an increase in VTI ≥ 15%. Variations in VTI after administration of 100 ml of fluid (ÄVTI) ≥ 10% have been found to have a sensitivity and specificity of 95% and 78%. [9,10]

Another study by Biais M et al. attempted to assess the mini fluid challenge test's efficacy. In this study, stroke volume index and pulse pressure variations were monitored before and after administering fluids. Initially, 50 ml of normal saline is given by infusion for 1 minute and measured. Then, continued giving 50 ml again and so on until reaching 250 ml. Fluid responsiveness is assessed by changes in stroke volume index of more than 6%. The study found that administering 100 ml fluids had a sensitivity of 93% and specificity of 85%.

The Mukhtar A et al. study also reported that using a mini fluid challenge test using 150 ml of 5% albumin for 3 minutes could predict the fluid response of patients after liver transplantation. However, the mini fluid challenge test has not yet been validated, and the samples in these studies are still minimal. [12]

Recommendations Perform the Fluid Challenge Test in a Variety of Clinical Conditions

Based on The Scottish Intensive Care Society's guidelines regarding administration of intravenous fluids in adults, administration of fluid challenges can be done if the patient has signs of hypovolemia, such as low blood pressure, central venous pressure or low jugular venous pressure, oliguria, decreased skin turgor, low tissue perfusion, tests capillary refill> 4 seconds. There is no suspicion of right ventricular dysfunction or cardiogenic shock. Based on this guide, a fluid challenge test can be administered with 250-500 ml of crystalloid or colloidal intravenous fluids for 5-15 minutes.

Meanwhile, in the case of septic shock, it is generally recommended that a fluid challenge be undertaken and followed by fluid administration if the hemodynamics are found to be improved. Fluid challenge tests can be given by giving crystalloid 30 ml/kg (approximately 2 liters) in 30-60 minutes. Hydroxyethyl starch is not recommended for fluid challenges in sepsis shock.

Based on the guidelines for acute heart failure from the European Society of Cardiology, new fluid challenges can be given to patients without signs of congestion and adequate peripheral perfusion.

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