Fluid Therapy

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Chapter 7 Fluid Therapy

Elizabeth Cox, MD , Keith Baker, MD, PhD

1 How is water distributed throughout the body?

Total body water comprises 60% of body weight in males and 50% of body weight in females. The distribution of this water is 40% in intracellular space (30% in females because of larger amounts of subcutaneous tissue and smaller muscle mass) and 20% in extracellular space. The extracellular fluid is broken down into 15% interstitial and 5% plasma. Total body water decreases with age; 75% to 80% of a newborn infant’s weight is water.

2 What are sensible and insensible fluid losses? How are maintenance fluid requirements calculated?

image Insensible losses (nonmeasurable)

image Skin: 600 mL
image Lungs: 200 mL

image Sensible losses (measurable)

image Fecal: 200 mL
image Urine: 800-1500 mL
image Sweat: Variable

These losses account for 2000 to 2500 mL/day, giving a 24-hour fluid requirement of 30 to 35 mL/kg to maintain normal fluid balance.

3 What are fluid maintenance requirements for children?

Twenty-four–hour fluid requirements for children have been formulated on the basis of weight:

image 4:2:1 rule: 4 mL/kg per hour for the first 10 kg

image Then add additional 2 mL/kg per hour for the next 10 kg to 20 kg

image Then add 1 mL/kg per hour for every kilogram after that

EXAMPLE: 30-kg child

40 + 20 + 10 = 70 mL/hr maintenance

4 Describe the clinical features of volume deficit and volume excess

image Deficits (low volume)

image Central nervous system: decreased mentation in severe cases
image Cardiovascular: tachycardia, hypotension (in later stages)
image Skin: decreased turgor in subacute volume loss
image Renal: decreased urine output

image Excesses (volume overload)

image Distended neck veins
image Pulmonary edema
image Peripheral edema

5 What are the classes of hemorrhagic shock, and what fluid should be administered in each class?

See Table 7-1.

Table 7-1 Severity of Hemorrhagic Shock

image

6 What is the 3:1 rule in fluid therapy after acute blood loss?

Three milliliters of crystalloid is given for each milliliter of blood loss to compensate for administered fluid that is lost into the interstitial and intracellular spaces. This is a starting dose. Most patients need more than this and will need 5:1 to restore normovolemia. Please see Chapter 54 for description of blood replacement in patients who require massive transfusions (greater than 10 U of packed red blood cells).

7 What empiric replacement fluids can be used for fluid losses?

image Sweat: 5% dextrose (D5) ¼ normal saline solution with 5 KCl/L

image Gastric, colon: D5 ½ normal saline solution with 30 KCl/L

image Bile, pancreas, small bowel: lactated Ringer’s solution

image Third space (interstitial loss): lactated Ringer’s solution

8 What is the difference between crystalloids and colloids? Give examples of each

image Crystalloids: Crystalloids are mixtures of sodium chloride and other physiologically active solutes. The distribution of sodium will determine the distribution of the infused crystalloid. Examples are normal saline solution, lactated Ringer’s solution, and hypertonic saline solution.

image Colloids: High-molecular-weight substances that stay in the vascular space and exert an osmotic force are colloids. Examples are albumin, hetastarch, dextran, and blood.

9 Describe the composition of normal saline and lactated Ringer’s solution. Which should be used for acute resuscitation?

Table 7-2 summarizes the composition of normal saline and lactated Ringer’s solution. Lactated Ringer’s solution is preferable for acute volume replacement because normal saline solution can result in hyperchloremic metabolic acidosis.

Table 7-2 Composition of Crystalloids

image

10 What evidence-based data exist to support the use of various resuscitation fluids?

image Lactated Ringer’s solution: This remains the least expensive and best fluid for trauma resuscitation.

image Albumin, hetastarch and other colloids: No evidence from randomized controlled trials exists to demonstrate that resuscitation with colloids reduces the risk of death, pulmonary edema, or hospital stay compared with resuscitation with crystalloids in patients with trauma or burns, or after surgery. Because colloids are more expensive, it is difficult to justify their continued use in this setting.

image Hypertonic saline solution: The only benefit is shown in patients with head trauma–cerebral edema.

Acknowledgement

The editors gratefully acknowledge the contributions of James E. Wiedeman, MD, and Mark W. Bowyer, MD, DMCC, COL, USAF, MC, authors of this chapter in the previous edition.

Key Points Fluid Therapyimage

1. Total body water is 60% of body weight (40% intracellular and 20% extracellular). Plasma (blood) volume is 5% of body weight.

2. Diagnose volume deficit or excess by clinical examination, not laboratory study results.

3. Avoid fluid and electrolyte abnormalities by measuring and replacing ongoing gastrointestinal losses with appropriate fluids.

4. Use lactated Ringer’s solution for acute volume resuscitation.

5. There is no proved benefit to colloid over crystalloid in acute resuscitation.

Bibliography

1 Alderson P., Bunn F., Lefebvre C., et al. Albumin Reviewers: Human albumin solution for resuscitation and volume expansion in critically ill patients. Cochrane Database System Rev. 4, 2004. CD001208

2 Fan E., Stewart T.E. Albumin in critical care: SAFE but worth the salt? Crit Care. 2004;8:297–299.

3 Perel P., Roberts I. Colloids versus crystalloids for fluid resuscitation in critically ill patients. Cochrane Database System Rev. 3, 2011. CD000567

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