3. METODOLOGÍA
3.1. Marco Referencial
R Dayananda Babu
Fluid balance is the relationship between fluid output and fluid intake. Under normal circumstances fluid balance is maintained quite precisely, but in the surgical patient it has to be monitored carefully.
Fluid loss occurs in the following ways:
Urinary excretion 1500 ml (0.5- 2ml/kg/hr) Insensible loss 900 ml (0.35 ml/kg/hr)
Feces 100 ml
Total 2500 ml/day
Normal daily requirement for an adult is as follows: Water 2500 ml (30-40 ml/kg/day) Sodium 100-180 mEq/24 hr (1-2 mEq/
kg/day)
Potassium 40-60 mEq/24 hr (0.5-1 meq/ kg/day)
Glucose 100 gm (min. required to ward off ketosis)
POST
POST
POST
POST
POSTOPERAOPERAOPERAOPERAOPERATIVE FLUID MANATIVE FLUID MANATIVE FLUID MANATIVE FLUID MANATIVE FLUID MANAGEMENTGEMENTGEMENTGEMENTGEMENT
Pr
Pr
Pr
Pr
Practical Fluid Balance factical Fluid Balance factical Fluid Balance for the Operactical Fluid Balance factical Fluid Balance for the Operor the Operated Por the Operor the Operated Pated Pated Pated Patientatientatientatientatient
The calculation is based on:
1. The initial estimated loss (ie. the perioperative fluid loss)
2. The maintenance requirement 3. The on-going loss
Usually 50 percent of the calculated loss is corrected in the initial 24 hours.
The Initial Estimated Loss
The Initial Estimated Loss
The Initial Estimated Loss
The Initial Estimated Loss
The Initial Estimated Loss
• All peri-operative losses are isotonic and should be replaced by isotonic fluids, and all such losses must be rectified.
• Blood loss in excess of 15 percent of the blood volume in the adult is replaced by infusion of stored blood. • Smaller blood losses may be replaced by crystalloid
solutions.
Maintenance Requirement
Maintenance Requirement
Maintenance Requirement
Maintenance Requirement
Maintenance Requirement
• This is estimated after all the operative losses have been calculated and dealt with
• This is based on the estimated NORMAL requirements of the patient. For example, a normothermic 60 kg. adult with a normal metabolic rate would require about 2000 ml. of water, 100 mEq of sodium and about 50 mEq of potassium per day. Thus, this patient requires a daily fluid maintenance, under uncomplicated circumstances, consisting of:
• 1500 ml. of isotonic water as 5 percent Dextrose • 500 ml. of 0.9 percent Normal Saline
• 60 mEq of Potassium (K)
But, certain modifications have to be made in the first 24 hours when the stress response to surgery is the maximum, as:
• Stress—induced release of ADH, aldosterone and cortisol causes retention of sodium and water and increased renal excretion of potassium.
• Endogenous release of potassium from traumatized tissues and catabolism warrants restriction of potassium.
Therefore, in the first 24 hours, the patient requires no salt and less of water than normal.
2000 ml of 5 percent Dextrose is sufficient (when all the operative losses have been replaced) • By the second 24 hours metabolic response
diminishes:
Patient requires 2000 ml of 5 percent Dextrose and 1000 ml of isotonic saline in 24 hours.
• From the third post—operative day and thereafter: 20 mEq of Potassium is added to each 500 ml of intravenous fluid to give a total of 60 mEq in 24 hours.
On-going Losses
On-going Losses
On-going Losses
On-going Losses
On-going Losses
Additional fluid may be required in the following circumstances:
• If blood or serum is lost through drains
• If GIT losses continue; e.g. Nasogastric aspiration or fistula
• Continuing third—space losses in the first 24 to 48 hours after major surgery
• During rewarming, if the patient has become hypothermic during surgery
• These losses are replaced as Isotonic Saline(0.9% NS) In lower intestinal losses, ringer lactate is preferred (but this is best avoided in patients with hepatic disease as lactate is not converted to bicarbonate)
• For every 1000 ml of fluid loss, 20 mEq of potassium is added.
For example, a post-operative patient has a Ryle’s tube aspirate of 1000 ml., a biliary fistula of 1000 ml. and a urinary output of 1000ml. If the patient is not dehydrated, fluid calculation would be thus: Total fluid requirement is: 1000+1000+1000+500 (insensible losses) = 3500 ml.
(of this, Ryle’s tube aspirate and biliary loss is replaced as 0.9% NS; 2000ml.)
Potassium requirement is: 40 mEq.(for each 1000 ml of bile and gastric aspirate 20 mEq of Potassium is required).
To calculate the total fluid required for this patient in a day (including maintenance):
Saline Required
• On-going losses of bile and gastric aspirate is replaced as NS
2000 ml of 0.9 percent Normal Saline • Maintenance requirement of saline = 1000ml.
Total = 3000 ml
Potassium Required
• For on-going losses = 40 mEq • For maintenance = 60 mEq Total = 100 mEq
Glucose Required
• A minimum of 100 gm (500 ml of 5 percent Dextrose contains 25 gm of glucose)
Hence, this patient’s total requirement of 3500
ml can be administered as:
1500 ml of 0.9% NS 1500 ml of DNS 500 ml of 5 percent Dextrose 100 mEq of K (5 ampoules)
ASSESSMENT OF ADEQ
ASSESSMENT OF ADEQ
ASSESSMENT OF ADEQ
ASSESSMENT OF ADEQ
ASSESSMENT OF ADEQUUUUAUAAAACY OF FLUID ANDCY OF FLUID ANDCY OF FLUID ANDCY OF FLUID ANDCY OF FLUID AND
ELECTR
ELECTR
ELECTR
ELECTR
ELECTROLOLOLOLOLYTE REPLAYTE REPLAYTE REPLAYTE REPLAYTE REPLACEMENTCEMENTCEMENTCEMENTCEMENT
1. Clinical and biochemical parameters• General condition and sensorium • Signs of dehydration
• Hemodynamic stability; vital signs: pulse, blood pressure etc.
• Hematocrit, serum electrolytes, BUN, urine osmolality
2. Urine output
• A very sensitive index
• The ultimate goal of hydration is to obtain a minimum urine output of 0.5 ml/ kg/hr.
3. CVP
• Normal level is 4 to 8 cm of water
• Provides realistic information about fluid volume Low CVP >> decreased blood volume High CVP >> increased blood volume
• Should be monitored half-hourly
• Should be evaluated in the background of other data like pulse, blood pressure, respiration etc. For example, an increase in CVP parallels an increase in systolic BP indicating adequate fluid volume replacement.
After major surgery assessment of fluid and electrolytes is best achieved by the measurement of urine output, CVP and serum electrolyte concentration.
Judicious and appropriate administration of fluids in the postoperative period will reduce morbidity and mortality.
The following points should be always borne in mind with regard to intravenous fluid therapy:
1. Replacement fluids are used to replace abnormal losses of blood, plasma or other extracellular fluids in:
• Treatment of patients with established hypo- volemia: e.g. hemorrhagic shock
• Maintenance of normovolemia in patients with ongoing fluid losses: e.g. surgical blood loss. 2. Intravenous replacement fluids are the first-line
treatment for hypovolemia. Initial treatment with these fluids may be life-saving and provide some time to control bleeding and obtain blood for transfusion if it becomes necessary.
3. Crystalloid maintenance fluids, which contain dextrose, are not suitable for use as replacement fluids. Only crystalloid solutions with a similar concentration of sodium to plasma (normal saline or balanced salt solutions) are effective as replacement fluids. These should be available in all hospitals where intravenous replacement fluids are used.
4. Crystalloid replacement fluids should be infused in a volume at least three times the volume lost in order to correct hypovolemia.
5. All colloid solutions (albumin, dextrans, gelatines and hydroxyethyl starch solutions) are replacement fluids. However, they have not been shown to be superior to crystalloids in resuscitation.
6. Colloid solutions should be infused in a volume equal to the blood volume deficit.
7. Plasma should never be used as a replacement fluid.
8. Plain water should never be infused intravenously. It will cause hemolysis and will probably be fatal. 9. In addition to the intravenous route, the intraosseous,
oral, rectal or subcutaneous routes can be used for the administration of fluids.
REPLA
REPLA
REPLA
REPLA
REPLACEMENT FLUIDSCEMENT FLUIDSCEMENT FLUIDSCEMENT FLUIDSCEMENT FLUIDS
Replacement fluids are used to replace abnormal losses of blood or other extracellular fluids by increasing the volume of compartment. They are sometimes also called plasma substitutes.
Replacement fluids are used principally in:
• Treatment of patients with established hypovolemia: hemorrhagic shock
• Maintenance of normovolemia in patients with ongoing fluid losses: e.g. surgical blood loss. All colloid solutions are replacement fluids. However, only crystalloid solutions that contain a sodium con- centration similar to plasma are suitable as replacement fluids. Some of these crystalloids have a composition resembling extracellular fluid and are known as balanced salt solutions: e.g. Ringer’s lactate or Hartmann’s solution.
Examples of replacement fluids are:
• Crystalloids with a similar concentration of sodium to plasma:
Normal saline (sodium chloride 0.9%) Ringer’s lactate
Hartmann’s solution • All colloid solutions.
Intr
Intr
Intr
Intr
Intraaaaavvvvvenous Replacement enous Replacement enous Replacement enous Replacement enous Replacement TherTherTherTherTherapapapapyyyyyap
In hypovolemia, the primary goal of treatment is to restore the circulating blood volume in order to maintain tissue perfusion and oxygenation. The administration of replacement fluids achieves this by increasing the volume of the vascular compartment. A blood transfusion may also become necessary if there is extensive blood loss. However, even in cases of severe hemorrhage, initial treatment with intravenous replacement fluids may be life-saving and will allow time to obtain blood for transfusion. Intravenous replacement fluids are the first- line treatment for hypovolemia.
Intravenous replacement fluids are the first-line treatment for hypovolemia.
Intr
Intr
Intr
Intr
Intraaaaavvvvvenous Replacement Fluidsenous Replacement Fluidsenous Replacement Fluidsenous Replacement Fluidsenous Replacement Fluids
Crystalloids
Crystalloids are composed of crystalline substances such as dextrose or sodium chloride which, when dissolved in water, form a clear solution of electrolytes or sugars. These are aqueous solution of small molecules which easily pass through capillary membranes: e.g. normal saline, balanced salt solutions.
Crystalloid replacement fluids contain a similar concentration of sodium to that of plasma. This ensures that they are excluded from the intracellular compartment since the cell membrane is generally impermeable to sodium. However, they readily cross the capillary membrane from the vascular compartment to the interstitial compartment to become rapidly distributed throughout the whole extracellular compartment.
Normally, only a quarter of the crystalloid solution remains in the vascular compartment. For this reason, crystalloids should be infused in a volume at least three times the deficit in order to restore circulating blood volume (intravascular volume).
Crystalloids should be infused in a volume at least three times the blood volume deficit in order to correct hypovolemia
When large volumes of crystalloid fluid are admini- stered, edema develop as a result of the fluid that passes (or ‘leaks’) from the circulation into the interstitial compartment. Careful monitoring of the patient’s clinical condition is therefore essential. Crystalloid maintenance fluids, which contain mainly dextrose, are not recommended for use as replacement fluids (Table 13.1).
The dextrose rapidly becomes metabolized leaving only water, which readily crosses the capillary and cell wall membranes to become distributed throughout the extracellular and intracellular compartments. Only a small fraction remains in the vascular compartment, as shown in Figure 13.1.
Dextrose (glucose) solutions do not contain sodium and are poor replacement fluids. Do not use them to treat hypovolemia unless there is no other alternative
Colloids
Colloid solutions are composed of a suspension of particles that have a much larger molecular weight than crystalloids. These particles are generally too big to pass through the capillary membrane and initially tend to remain within the vascular compartment. They are used as a replacement fluid: e.g., gelatines, dextrans, hydroxy-
Table 13.1: Suitability of intravenous fluids as either maintenance or replacement fluids.
Fluid Crystalloids Crystalloids with high Colloids
composed mainly sodium content and of dextrose balanced salt solutions
Maintenance fluids × ×
Replacement fluids ×
Table 13.2: Advantages and disadvantages of crystalloids
and colloids
Advantages Disadvantages
Crystalloids Few side-effects Short duration of action Low cost May cause edema Wide availability
Colloids Longer duration of action No evidence that they are Less fluid required to more clinically effective correct hypovolemia Higher cost
May cause volume overload
May interfere with clotting Risk of anaphylactic reactions
ethyl starch.The effect of these particles in the circulation is to mimic plasma proteins, thereby maintaining or raising the colloid osmotic pressure of blood.
The molecular weight and number of particles in a colloid solution is important in determining its properties. The larger the particle sizes, the longer the duration of action of the solution in the vascular compartment. Also, the higher the number of particles in the solution, the greater the osmotic effect.
Solutions with an oncotic pressure greater than that of plasma have the capacity to draw water from the interstitial compartment into the blood. The increase in blood volume may thus exceed the infused volume. Colloids can be classified as:
1. Plasma-derived (natural): prepared from donated human blood or plasma (e.g. albumin). These should not be used simply as replacement fluids.
2. Synthetic: prepared from another source (e.g. bovine cartilage).
• Gelatines (Hemaccel, Gelofusine) • Dextran 60 and Dextran 70
• Hydroxyethyl starch (Hetastarch or hes) • Pentastarch
Colloids require smaller infusion volumes than crystalloids. They are usually given in a volume equal to the blood volume deficit.
However, in many conditions where the capillary permeability is increased, they may leak out of the circulation and produce only a short-lived volume expansion. Supplementary infusions will be necessary to maintain blood volume in conditions such as:
• Trauma
• Acute and chronic sepsis • Burns
• Snake bite (hemotoxic and cytotoxic).
Properties of an Ideal Intravenous Replacement Fluid
The most important property of an intravenous replacement fluid is simply to occupy volume in the vascular compartment. An ideal replacement fluid should do this for a sufficient length of time and without interfering with the normal functions of the blood. Furthermore, it should be:
• Easily available and inexpensive • Non-toxic
• Free of allergic reactions and risk of infection • Totally metabolized or eliminated from the body.
Unfortunately, no fluid yet satisfies all these requirements. It is important, therefore, to be familiar with the properties and characteristics of the replacement fluids used in the hospital and to be able to use them safely.
The Cr
The Cr
The Cr
The Cr
The Crystalloids or Colloids Controystalloids or Colloids Controystalloids or Colloids Controystalloids or Colloids Controystalloids or Colloids Controvvvvversyersyersyersyersy
Much has been written about the crystalloids or colloids controversy, but it can be summarized as follows. Most clinicians agree that, in hypovolemic patients, it is essential to restore blood volume with replacement fluids. However, they disagree on the type of fluid that should be used. Both crystalloids and colloids have advantages and disadvantages, as shown in the Table 13.2.
However, ensuring that an adequate volume of replacement fluid (of whatever type) is administered to a hypovolemic patient is more important than the choice of fluid.
There is no evidence that colloid solutions are superior to normal saline or balanced salt solutions in resuscitation.
If the supply of infusion fluids is limited, it is recommended that, wherever possible, the crystalloid normal saline (sodium chloride 0.9%) or a balanced salt solution such as Ringer’s lactate or Hartmann’s solution should be available in all hospitals where intravenous replacement fluids are used.
Before giving any intravenous infusion:
1. Check that the seal of the infusion fluid bottle or bag is not broken.
2. Check the expiry date.
3. Check that the solution is clear and free from visible particles.
Plasma-der
Plasma-der
Plasma-der
Plasma-der
Plasma-derivivivivived Colloidsed Colloidsed Colloidsed Colloidsed Colloids
These are prepared from donated blood or plasma. They include:
• Plasma
• Fresh frozen plasma • Liquid plasma • Freeze-dried plasma • Albumin
These products should not be used simply as replacement fluids. They can carry a similar risk of transmitting infection such as HIV and hepatitis, as whole blood. They are also generally more expensive than crystalloid or synthetic colloid fluids.
Table 13.3 shows the composition of replacement fluids and plasma
F
FF
FFactors Affactors Affactors Affactors Affactors Affected bected bected bected bected by Acid-base Imbalancey Acid-base Imbalancey Acid-base Imbalancey Acid-base Imbalancey Acid-base Imbalance
As a result of acid-base imbalance, the following four clinical entities can occur.
1. Respiratory acidosis may be produced by any condition or combination of conditions that result in inadequate ventilation (atelectasis, pneumonia, airway obstruction). The clinical signs of restlessness, hypertension, and tachycardia in the post- operative patient may indicate the presence of, hypercapnia. Treatment consists of providing adequate ventilation and correcting the pulmonary problem when possible. 2. Respiratory alkalosis in the surgical patient is caused, usually by hyperventilation secondary to apprehen- sion, pain, brain injury, or overventilation by mechanical respirators. If the condition is mild, no therapy is required. When the cause of hyperventila- tion can be determined and corrected, the problem is eliminated.
3. Metabolic acidosis may occur as a result of acute circulatory failure or renal damage, chloride excess, loss of lower gastrointestinal fluids, administration of unbalanced salt solutions, and uncontrolled diabetes
Table 13.3: Composition of replacement fluids and plasma
Fluid Na+ K+ Ca2+ Cl – Base Colloid osmotic
nmol/L nmol/L nmol/L nmol/L mEq/L pressure mmHg Crystalloids
Normal saline (sodium chloride 0.9%) 154 0 0 154 0 0
Balanced salt solutions
(Ringer’s lactate/Hartmann’s solution) 130-140 4-5 2 -3 109-110 28-30 0 Colloids
Gelatine (urea linked): 145 5.1 6.25 145 Trace 27
e.g. Hemaccel amounts
Gelatine (succinylated): 154 < 0.4 < 0.4 125 Trace 34
e.g. Gelofusine amounts
Dextran 70 (6%) 154 0 0 154 0 58
Dextran 60 (3%) 130 4 2 110 30 22
Hydroxyethyl starch 154 0 0 154 0 28
450/0.7 (6%)
Albumin 5% 130-160 < 1 V V V 27
Ionic composition of normal plasma 135-145 3.5-5.5 2.2-2.6 97-110 38-44 27 V=varies between different brands
mellitus., Correction of protracted metabolic acidosis may require the use of sodium bicarbonate. When cardiopulmonary arrest occurs, restoration of blood flow, pulmonary ventilation, and administration of sodium bicarbonate is required.
4. Metabolic alkalosis usually occurs when some degree of hypokalemia exists. It occurs when there is an uncomplicated loss of acids (H ion) or retention of bases. Because of the associated hypokalemia, cardiac arrhythmias, paralytic ileus, digitalis intoxication, and tetany may develop. Dangerous
hyperkalemia (greater than 6 mEq per liter) is unusual if kidney function is normal. Generally, it is unwise to administer potassium during the first 24 hours postoperatively unless there is a definite hypokalemia. These deficits should be replaced after an adequate urine output is obtained. The daily replacement of potassium for renal excretion is 40 mEq plus 20 mEq for gastrointestinal loss if indicated; it should not be administered parenterally in concentrations of more than 40 mEq per liter as potassium chloride.