Shock

Fluid Replacement Therapy

nursebob 07/25/10

Lactated Ringer's solution is the resuscitation fluid of choice. It has advantages over solutions such as Dextrone (5% dextrose in lactated Ringer's solution) since the glucose is poorly metabolized in the presence, of the catecholamine response. The incremental elevation in blood glucose levels results in an osmotic diuresis, misleading urine output levels, and dehydration. Colloid solutions are expensive and do not equilibrate with the interstitial space as rapidly as Ringer's lactate. Even though smaller volumes of colloid are required for initial resuscitation, the consensus is that colloid-containing fluids have no significant advantage over Ringer's lactate for resuscitation of the shock casualty.

The shock patient should be given 1,000-2,000 cc of lactated Ringer's solution, infused as rapidly as possible. Another rule of thumb is an initial fluid challenge of 10-25 ml/kg given over a ten minute period. Some will respond promptly and remain stable with only this therapy. If the hemorrhage has been severe or is ongoing, the response will usually be only transient, but nevertheless may allow time for typing and crossmatching of blood. Lactated Ringer's Solution, in addition to providing a rapid increase in circulating volume, will begin the correction of the reduced extracellular volume space resulting front compensatory fluid shifts induced by the shock slate. Crystalloid solution rapidly equilibrates between the intravascular and interstitial compartments For this reason, adequate restoration of hemostatic stability may require large volumes of Ringer's lactate. It has been empirically observed that approximately 300 cc of crystalloid is required to compensate for each 100 cc of blood loss. This 3:1 rule is a good beginning point for fluid resuscitation, but obviously is not a hard and fast rule for those with massive hemorrhage. If the 3:1 ratio were adhered to in a casualty requiring 5,000 cc of blood replacement, inundation would result. About 3,000-4,000 cc of Ringer's lactate seems reasonable.

Several clinical parameters are utilized in determining the casualty's response to the therapeutic intervention. Assessment of clinical response can be made on the basis of changes in blood pressure, pulse rate, capillary refill, urine output, and mental status. Where large volumes of fluid and blood are required, the progress of therapy is facilitated by central venous pressure monitoring. The centrally-placed catheter affords all accurate measure of the right heart's volume requirement and its ability to accept additional fluid loading. Serial measurements are clearly of greater value than a single determination. Sophisticated systems that measure cardiac output and the pulmonary artery wedge pressure do not add a great deal to the early treatment or treatment assessment of the combat casualty.

Blood transfusion is all integral part of the resuscitation of casualties presenting with Classes III and IV hemorrhages and in those with continuing hemorrhage. Whole blood is preferred due to its lower viscosity, faster infusibility and potential provision of some of the clotting factors. Prior to hospital arrival, a more forward echelon may have already infused low-titer type O blood. Those casualties that have been started on type O blood should continue to receive type O. Switching to type-specific blood, especially after several units of type O blood have been given, can result in a transfusion reaction secondary to the reaction between anti-A and anti-B introduced into the recipient by donor O blood and the antigens A and B in the patient's blood. As a general rule, if four units or less of low-titer O blood have been given, a change to type-specific blood is possible without producing ill effects. It is recommended that type-specific blood be withheld for 2-3 weeks or longer if more than four units of type O was initially administered. Female casualties who require the immediate use of type O blood should be given Rh-negative, if available, to avoid the potential of future problems associated with sensitization. Ideally, the casualty is given type-specific, cross-matched blood. This was the practice of American forces in Vietnam, where 80% of the blood administered was type-specific. In the Korean conflict, the practice was to use type O, low-Rh titer blood.

Whole blood should be filtered during administration to remove small clots and other aggregations. A 160 micron macropore filter accomplishes this objective. Blood infusions should be warmed to prevent not only cardiac arrhythmias but also hypothermia. The incidence of cardiac arrhythmia is highest when almost-outdated old blood with high potassium levels is infused, when the blood is not warmed prior to infusion, and when the infusion catheter rests in a cardiac chamber. When rising packed cells, it is recommended that every fourth unit be followed by a unit of fresh frozen plasma. Banked blood in the combat zone, not uncommonly, is close to its expiration date. After an infusion of about ten units of this product, coagulation detects and bleeding diatheses often arise. They should be anticipated and may be avoided by interspersed transfusions of fresh frozen plasma and platelet packs, or by intermittently infusing freshly drawn local donor blood. The majority of those requiring blood transfusions do not require calcium supplementation; however, when infusion rates exceed 100 cc/minute, 250-500 mg of calcium chloride should be given as a slow bolus through a separate infusion line.

Adequate volume replacement is reflected by a normal central Venous pressure and a urine output of 0.5-1 cc/kg/hour. This level of urinary output should be substantially increase, in cases of crush injury.

The tachypnea of trauma tends to produce a state of respiratory alkalosis; however, this effect is more than overcome by the metabolic acidosis resulting from the perfusion deficit. Persistence of the shock state results in shifts to anaerobic metabolism, and further worsens the acidosis. Bicarbonate should be administered in those whose pH approaches 7.2. Serum potassium levels may rise to dangerously high levels as a result of acidosis-triggered potassium shifts. Hyperkalemia can in turn evoke cardiac arrest.

In situations in which infusion therapy fails to initiate a favorable response, conditions other than hypovolemia should be suspected. Cardiac tamponade, tension pneumothorax, myocardial injury, nerogenic shock, and acute gastric dilation may be responsible or contributory. Continued and unrecognized hemorrhage into the chest or abdomen is the most common cause of poor response to fluid therapy. In this sort of situation, the surgeon must operate to resuscitate rather than resiscitate to operate.

The following chart outlines the classes of shock, their presenting signs and symptoms, and the guidelines for resuscitation. These are guidelines only. The amount of blood lost is estimate only as a starting point for resuscitation. Clinical parameters must guide the response to therapy.

  Estimated Fluid and Blood Requirements in Shock
(Based on Patient's Initial Presentation)

  Class I Class II Class III Class IV
Blood Loss (ml) up to 750 750-1500 1500-2000 2000 or more
Blood Loss(%BV) up to 15% 15-30% 30-40% 40% or more
Pulse Rate 100 100 120 140 or higher
Blood Pressure Normal Normal Decreased Decreased
Pulse Pressure (mm Hg) Normal or increased Decreased Decreased Decreased
Capillary Blanch Test Normal Positive Positive Positive
Respiratory Rate 14-20 20-30 30-40 > 3.5
Urine Output (Ml/hr) 30 or more 20-30 5-15 Negligible
CNS-Mental Status Slightly anxious Mildly anxious Anxious & confused Confused-lethargic
Fluid Replacement (3:1 Rule) Crystalloid Crystalloid Crystalloid & blood Crystalloid & blood

 

Adequate volume replacement call be guided by urinary Output. Fifty cc per hour is a minimum objective of resuscitation for an adult. This figure should be doubled in cases of crush injury.

REFERENCE: Emergency War Surgery NATO Handbook: Part II: Response of the Body to Wounding: Chapter IX: Shock and Resuscitation

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