The aim of fluid resuscitation is to replete the circulation. The primary objective is to identify the source of fluid loss and prevent further loss, whether overt bleeding or fluid sequestration to the extravascular space. An adequate intravascular volume is only part of fluid resuscitation and there are many other considerations.
Measurement of central venous pressure and pulmonary artery occlusion pressure are the most widely used guides to volume status. A pulmonary artery occlusion pressure of 12 to 15 mmHg should be the initial target. Further small fluid boluses of 100 to 200 ml should be given with regular reassessment of pulmonary artery occlusion pressure and cardiac output. Values of stroke volume and left heart work can be derived from hemodynamic information obtained from the pulmonary artery catheter, and fluid therapy may target an optimal stroke volume.
There is an unresolved controversy regarding the use of crystalloid or colloid in the initial phase of shock. If crystalloid is used, more must be given than colloid.
Hemoglobin is the only available oxygen-carrying molecule. There must be a compromise between oxygen-carrying capacity and blood viscosity to allow good capillary blood flow. A hemoglobin concentration of 10 to 12 g/dl and a hematocrit in the range of 30 to 40 per cent are probably optimal, but controversy exists as to whether these goals should pertain in all conditions
Correction of coagulopathy aids volume replacement and reduces further volume loss. Loss, consumption, and dilution of clotting factors during hemorrhage and disseminated intravascular coagulation (DIC) in septic shock can lead to intractable bleeding. Adequate correction with fresh frozen plasma, cryoprecipitate, and platelets may be required to correct this. Hematinics and vitamin K may also be required after massive blood transfusion.
Thus hypovolemia should be corrected by early aggressive fluid resuscitation with adequate crystalloid or colloid, blood, and clotting factors (if required), guided by hemodynamic monitoring to assess whether treatment is effective.
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