After the airway and breathing have been addressed in the hypovolemic patient, circulation must be evaluated. Not only does this involve evaluation of the cardiac status, but also the cessation of life-threatening hemorrhage. Although in most major centers antecubital large-bore intravenous cannulas are placed, the ability to place 9 Fr introducers into central veins (subclavian, internal jugular, and femoral) has allowed aggressive resuscitation to proceed. Strategic location of access is crucial in that a patient with an obvious pneumothorax should have a central catheter placed on that side, although in massive hemothorax the catheter should be placed on the opposite side. In individuals with clinical conditions such as tense ascites, the rapid administration of fluids is best done centrally from above rather than via the femoral route which, owing to inferior vena caval compression, may limit resuscitation.
According to Poiseuille's law, the flow through a catheter depends on the radius to the fourth power, the length of the catheter, the viscosity of the fluid, and the pressure at which it is infused. Thus, large-bore short cannulas are best. The fluid viscosity affects flow rate in that cold packed red blood cells are more rapidly infused if they are diluted in an equal volume of normal saline and warmed. External devices are available to allow for rapid transfusions. In addition, these devices allow fluids to be warmed rapidly to body temperature, helping to ameliorate the hypothermia that frequently accompanies massive resuscitation.
Irrespective of the location, all catheters put in under urgent and emergency circumstances in the field or the emergency department should be changed within 24 h to decrease the incidence of infection and sepsis.
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