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Patient Care - Third-Space Fluid
THIRD-SPACE
FLUID
The so called "third-space" fluid loss is, due to sequestration of
fluids in the body. This can occur as a result of : Acute intestinal
obstruction (as much as 5 liters or more can accumulate within the lumen of the
obstructed) Acute gastric dilatation: Acute peritonitis, Acute pancreatitis;
Burns, crush injuries, acute spreading cellulitis; following abdominal surgery,
particularly pelvic surgery (the fluid accumulates in the peritoneum, bowel
wall and other traumatized tissues); Following surgery on the abdominal aorta
after the aortic clamp has been released (declamping phenomenon) (the fluid
accumulates in the ischemic area of the lower extremities).
The sequestration of fluids in these patients will
decrease the circulating blood volume and produce signs of hypotension or
shock. When plasma exudes out of the bloodstream into a sequestered third
space, the red blood cells are now suspended in a smaller volumes of plasma.
Therefore, the hematocrit rises. This rise in hematocrit can be used to
determine the extent of the plasma loss, viz:
Plasma deficit (ml.) = Normal blood
volume- Normal bl. vol. x Normal (or initial) HCT.
Measured HCT.
It is assumed that the normal blood volume
equals approximately 7 per cent of body weight, and that the normal hematocrit
is 45 per cent.
Example:
Patient with acute intestinal obstruction, weight 70 kg. measured HCT. 55%.
The normal blood volume in this patient is 70,000 X 0.07 = 4900 ml.
Plasma
deficit = 4900 X 0.45 0.55 = 4900 - 4000 = 900 ml.
Theoretically, a third-space fluid loss
should be treated with plasma or another colloid solution. A multiple
electrolyte solution, such as lactated Ringer's solution can be infused
instead. The volume of solution needed can be calculated in a general way by
infusing 21/2 times the estimated plasma volume deficit. A similar third-space
fluid loss occurs in medical patients with marked ascites or pleural effusion.
However, the decreased circulating blood volume and hypotension occur after the
fluid accumulates quickly. It is better to treat these patients medically,
using diuretics, water restriction if necessary, digitalis if indicated, and so
on.
WATER AND ELECTROLYTE MANAGEMENT DURING A SURGICAL OPERATION
During the operation, water
and electrolytes can be lost in the following ways:
1.Loss of blood. If 500 ml. or more of blood is lost,
it should be replaced immediately. (If whole blood cannot be given because of a
patient's religious convictions, for example, lactated Ringer's solution can be
infused. An amount equal to 21/2 times the volume of blood lost. However, if
more than 1000 or 1200 ml. of blood has been lost, the patient should also
receive supplemental plasma or another colloid solution, to maintain the
circulation. No specific rules can be given for the volume of colloid solution
needed. Empirically, one can give 500ml. colloid solution for each 1500 ml.
lactated Ringer's solution infused. A simple way to estimate blood loss during
a surgical operation is to weigh the sponges before and after use. The
difference in grams is equivalent to the volume in ml. of the blood they have
absorbed. Add to this the volume of blood in the operating-room suction bottle.
Then increase the total by one-half, to approximate the acual blood loss.
2. Insensible water losses and excessive perspiration.
The warm ambient temperature of the operating room and the heavy drapes that
enclose of the operating room and water loss of 40 ml. per hour. One method of
compensating for this loss of water (and electrolytes) is to infuse lactated
Ringer's solution at a rate of 100 ml. per hour. When major surgery is done on
a patient who may develop acute renal failure, or when surgery requires
temporary occlusion of the aorta (open-heart surgery, or resection of an
abdominal aortic aneurysm), which increases the tendency to acute renal
failure, mannitol can be used prophylactically during surgery, to maintain a
urinary flow between 50 (preferably 75) and 100 ml. per hour.
3. Intravenous fluids and electrolytes to compensate
for third-space losses and to prevent acute renal failure. In the past, during
an operation, surgeons have found that the intravenous infusion of
lactated Ringer's solution during an operation could prevent postoperative
hypotension or acute renal failure. There are no simple answers to this
problem. When tissue is traumatized, and third-space losses are minimal, there
is no need to use a large volume of fluids with or without electrolytes.
However, when third-space losses are either present or can be anticipated
postoperatively (see above), or when acute renal failure is a possibility, a
large volume of intravenous fluids and electrolytes may be very helpful
prophylactically and therapeutically. For patients undergoing major aortoiliac
reconstructive surgery: At the start of the operation, a liter of 5 per
cent dextrose in lactated Ringer's solution is infused as the abdomen is
opened and the initial dissection is started. The solution is given throughout
the operation at a rate of 500 ml. for every hour of surgery. Blood loss is
replaced volume for volume simultaneously with the infusion. The patient
also receives approximately 250 ml. of 5 per cent dextrose in water during
surgery. (This IV line is used to administer muscle relaxants and other
medication. ) The principal criterion for the rate of infusion of the lactated
Ringer's solution during the operation is to maintain a satisfactory blood
pressure without using vasoconstrictors, and a urinary output between 30
and 50 ml. per hour.
Postoperative
Water and Electrolyte Management:
There is also controversy about the volume and type
of intravenous fluids needed postoperatively. The immediate goal of
postoperative fluid therapy is to maintain a blood pressure of approximately
90/60, a pulse rate of less than 120 per minute, and an hourly urine flow
between 30 and 50 ml. in association with an adequate level level of
consciousness, pupillary size, patent airway and breathing pattern, warm skin
and skin and skin color, and normal body temperature. If an uncomplicated
operation has been performed, and if there have been no third-space fluid
losses and if acute renal failure is' not anticipated, it is necessary only to
supply an adequate amount of water.
If the patient is able to take 500 mI. water by mouth
and retain it the first day, there is no need for parenteral water. However, if
an abdominal or anastomotic operation has been performed and oral intake
is forbidden, from 500 to 1000 mI. of water is adequate. Water needs will be
greater if fever, dyspnea, or other causes of water loss are present.
Similarly, electrolytes will be needed if abnormal electrolyte losses are
present. For example, nasogastric suction drainage can be replaced volume
for-volume with half-strength saline. (Each liter contains 77 mEq. sodium and
77 mEq. chloride ions.) Potassium chloride should not be added the first
postoperative day. From the second postoperative day, 20 mEq. potassium
ions (1.5 gm. of potassium chloride) per liter can be added to the
half-strength saline. When pyloric obstruction or postoperative malfunction of
a gastrointestinal stoma is present, massive volumes of gastric juice can be
withdrawn by nasogastric suction. Attempts to replace this loss with a
large volume of intravenous fluids, particularly sodium- and
potassium-free fluids such as dextrose in water, can cause a
self-perpetuating, abnormal, high-output, high-intake cycle that is
similar to the situation that may develop during the diuretic phase of
acute renal failure when too many fluids are given intravenously.
Electrolyte balance does not occur in these patients
with a large volume of gastric aspirate. Instead, water excess with
hyponatremia, hypochloremia, and hypokalemia may develop, and renal blood flow
may decrease, so that the BUN concentration may rise and urine output may
decrease. Berry suggests that when the gastric aspirate reaches 2500 ml. or
more in a 24-hour period, the nasogastric suction should be stopped
temporarily, the volume of intravenous fluids should be decreased
one-half, and the patient's clinical condition and electrolyte
concentrations should be carefully observed. If severe water excess has
developed, hypertonic sodium chloride intravenously may be necessary. If
mechanical gastrointestinal obstruction is present, it must be corrected
surgically. Some surgeons give isotonic saline postoperatively, or lactated
Ringer's solution, even on the first postoperative day. It is advisable to use
a solution of quarter-strength saline in dextrose. Each liter supplies water
and, in addition, 38.5 mEq. sodium and 38.5 chloride ions. Most postoperative
patients are able to tolerate this amount of sodium chloride without developing
pulmonary edema or edema of the lower extremities. (This volume should be
considered as part of the total water intake. ) By the second or third
postoperative day, the routine maintenance requirements. If a complicated
operation has been performed with third-space losses or if there is a
possibility of acute renal failure, a large amount of fluids and electrolytes
may be required to prevent hypotension and renal failure.
Thompson uses the following regimen postoperatively
for his patients who have undergone abdominal aortic surgery:
1. The intravenous fluids are
continued at a rate of approximately 125 ml. per hour. The rate of
infusion is varied, depending on the blood pressure, urinary output, and any
unusual extrarenal losses.
2. In the first 24 hours
postoperatively, the patient receives approximately 1 liter of lactated
Ringer's solution and 2 1/2 liters of 5 per cent dextrose in water.
3. In the second 24 hours
postoperatively, the patient receives approximately 500 ml. of 5 per cent
dextrose in isotonic saline, and 2000 m!. of 5 per cent dextrose in water. 4.
On the third postoperative day, the nasogastric tube is removed and fluids are
given orally, but one to two liters of 5 per cent dextrose in water are
infused. There after the infusions are discontinued. Many other water,
electrolyte, and acid-base syndromes may occur in surgical patients. Acute
respiratory acidosis may occur during operation; metabolic acidosis is common
after any general surgical operation; operations on the upper gastrointestinal
tract may induce an acute hypokalemic alkalosis; respiratory alkalosis is
common, particularly if the patient is receiving assisted respiration; the
administration of fluids intravenously to postoperative patients
frequently produces hyponatremia due to water excess and occasionally
water intoxication.
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