Approach Considerations
Several types of fluids are available for resuscitation. They are generally divided into isotonic crystalloid solutions (most commonly used), colloids, hypertonic solutions, oxygen therapeutic agents and blood products (see the image below). Clinicians should adopt an individualized fluid approach based on the clinical scenario and best available evidence. [15]
Blood Transfusion
The American Society of Anesthesiologist set the lower threshold for blood transfusion at hemoglobin less than 6 g/dL or hematocrit less than 18% in a healthy individual. Transfusing a patient with a hemoglobin greater than 10 g/dL or a hematocrit over 30 is not recommended. [16, 17] This leaves a relatively wide range for practitioners to choose when blood transfusion is necessary based on the etiology of hypovolemia, comorbidities, and disease processes, in addition to the stability of the patient and their laboratory abnormalities.
The Transfusion Requirements in Critical Care (TRICC) trial showed that patients on a restrictive transfusion strategy where red cells were transfused for Hgb less than 7 g/dL and maintained at 7-9 g/dL showed a lower in-hospital mortality rate than a liberal strategy, although 30-day mortality was similar. [18] Also, literature exists that supports maintaining a hematocrit above 30 for patients with a history of coronary artery disease.
When time is available, typed and cross-matched blood is preferred. Unstable patients may be transfused with low-titer O-negative blood (see the image below). In the setting of hemorrhage, 4 classes exist for which specific clinical responses are demonstrated requiring different levels of fluid resuscitation.
Massive Transfusion
Massive transfusion is defined as a transfusion of more than 10 units PBRC at one given time. In the setting of massive hemorrhage, when large volumes of crystalloid and blood have been given, FFP and platelet transfusion may be required to address the effects of dilutional coagulopathy. Some debate exists in the literature, but it is generally suggested that when initiating a massive transfusion protocol, patients should be transfused PRBC, FFP, and platelets in a ratio close to 1:1:1 if multiple units of blood will be necessary. [19]
Whole blood should be considered only when dealing with a patient with an acute hemorrhage [20] and then only after the patient has received approximately 5-7 units of red cells plus crystalloids. [21] Reinfusion of autologous red cells is a good approach for patients for who have large quantities of blood collected from chest tubes or aspirated from peritoneal cavities reducing the need for an allogenic transfusion. Proper collecting devices are necessary for this type of transfusion but should be considered in patients who present with massive hemorrhage or patients such as Jehovah’s Witnesses who do not accept any donor products.
Crystalloids versus Colloids
Colloids have larger molecular-weight particles that give them oncotic plasma pressures similar to natural plasma proteins. This theoretically allows for better volume resuscitation by remaining in the intravascular space and supporting circulating volume as compared to crystalloids, which may have extravascular shift causing pulmonary and interstitial edema. However, in patients with increased vascular permeability as seen in sepsis and late hemorrhagic shock, leakage of these larger colloid molecules also exists. Physiologically balanced crystalloids may be the default fluid for critically ill patients, whereas the role for colloids remains unclear.
Several studies have compared the use of crystalloid and several different types of colloids as resuscitation fluids and have found no difference in mortality. [22, 23] Furthermore, most evidence shows there is no clear evidence that one colloid solution is more effective or safer than any other. [24] Newer studies have shown that differences in chloride load and strong ion difference appear to be clinically important. Quantitative toxicity can be mitigated when dosing is based on dynamic parameters that measure volume responsiveness. Qualitative toxicity for colloids and isotonic saline remain a legitimate concern. [25] Given the cost associated with colloids, no clear benefit exists to using these agents over the more affordable and generally available crystalloids.
Hypertonic Fluids
Hypertonic saline has been proposed as a crystalloid alternative that may have some benefit in head injury and trauma patients by limiting tissue edema effects associated with volume resuscitation. Recent studies have shown that hypertonic saline plus dextran does not reduce mortality or the risk of acute respiratory distress syndrome (ARDS) compared to resuscitation with lactated Ringer solution in trauma patients. [26] Evidence from the SAFE trial demonstrated that albumin and saline have similar outcomes for fluid resuscitation in patients receiving volume resuscitation in intensive care units. [27]
Oxygen-Carrying Fluids
Two classes of agents are under development in hopes of replicating the oxygen-carrying capacity of native RBC that may be lost during hemorrhage. [28, 29, 30] Hemoglobin-based oxygen carriers are not currently approved for human use in the United States and fluorocarbon-based oxygen carriers have yet to show any effectiveness in large-volume resuscitation.
Tranexamic Acid
Tranexamic acid (TXA) has been demonstrated to reduce bleeding in patients undergoing elective surgery. The CRASH-2 trial aimed to determine the effect of early administration of TXA on death and transfusion requirement in bleeding trauma patients. Early administration of TXA safely reduced the risk of death in bleeding trauma patients and may be cost-effective. However, treatment beyond 3 hours of injury is unlikely to be effective. [31]
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Table 1: Body Fluid Spaces
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Table 2: Causes of Intravascular Volume Loss
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Table 3: Types of Resuscitation Fluids
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Table 4: Classes of Hemorrhage
