Fluids & Electrolytes. Body water and fluid volumes:. Water constitutes 50% to 70% of lean body weight . Total body water. intracellular fluid compartment (40% of body wt). Extracellular fluid compartment (20% of body wt). plasma 5% of body wt .
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plasma 5% of body wt .
An interstitial compartment 15% of body wt.
70 kg man has a TBW of 42 L.
ECF is 1/3 TBW ( 14 L ).
Plasma 1/4 (5%) ECF ( 3.5 L ).
Hematocrit of 40% >>> 1.5 L RBC volume
>>>> 3.5L + 1.5L = 5L
( if ATP depleted >>> cellular dysfunction).
- As osmolality > 300 mosm , osmoreceptor cells in the supra- optic nuclei of the hypothalamus signal the posterior hypothalamus to increase production of ADH.
- ADH increases water absorption from distal renal tubules.
The 1st 10 kg >>> 100 ml/kg/day
~ 4 ml/kg/hr
The 2nd 10 kg >>> 50 ml/kg/day
~ 2 ml/kg/hr
Wt. above 20kg >>> 20 ml/kg/day
~ 1 ml/kg/hr
( 1000 ml + 500 ml + 1000 ml )>>>>normal saline
Na+, K+, Cl- >>>> 1 mEq/kg/day each
Ca++ >>>> 2 g/day
Mg++ >>>> 20 mEq/day
N.B: neither Ca++ nor Mg++ is necessary in maintenance IV fluid.
- Respiratory>> 600ml/day
- Skin >> 400ml/day
( In fever, insensible skin loss can increase up to 250 ml/day/degree of fever ).
- Stool >> 200 ml/day
1- Physical examination: ( Signs)
2- Lab. Investigations:
3- Hemodynamic measurements:
A. CVP ( indicated when volume status is difficult to assess or when rapid or major alterations are expected).
B.Pulmonary artery pressure.
1- Crystalloids when given in sufficient amounts can be just as effective as colloids in restoring intravascular volume.
2-Replacing an intravascular volume deficit with crystalloids generally require 4 X the volume needed using colloid
3-Most surgical patients have an ECF deficit that exceeds the ICF deficit.
4- Severe intravascular fluid deficits can be more rapidly corrected using colloid solutions.
5-The rapid administration of large amounts of crystalloids (> 4-5 L ) is more
frequently associated with significant tissue edema.
( marked tissue edema can impair oxygen transport, tissue healing and return of bowel Function following major surgery ).
1- Crystalloid solutions:
( Hypotonic solutions in cases of primarily water deficit).
( Isotonic solutions in cases of both water and electrolyte deficits).
N.B: Glucose is provided in some solutions to maintain tonicity or to prevent ketosis and hypoglycemia due to fasting. ( Children and women more prone to hypogly.).
- slightly hypotonic and tends to lower serum Na+ to 130 mEq/L.
- Generally it has the least effect on ECF composition, and it is the
most physiologic solution when large volumes are needed.
- Lactate is converted by the liver into bicarbonate.
- When given in large volumes, it produces dilutional hyperchloremic acidosis bec. Of its high Na+ & Cl- contents ( Plasma bicarbonate conc. decreases as Cl- conc. Increases).
- Thus, NS is a preffered solution in for hypochloremic metabolic alkalosis and for diluting PRBCs prior to transfusion.
- Used for replacement of pure water deficits and as a maintenance fluid for patients on sodium restriction.
- Treatment of severe symptomatic hyponatremia.
NB: 3% - 7.5% saline solutions are used in resuscitation of patients in hypovolemic shock (they must be administered slowly , preferably through CVP, bec they readily cause hemolysis).
2- Colloid solutions:
- includes albumin (5% and 25% solutions) and plasma
protein fraction (5%).
- Both are heated to minimize the risk of hepatitis and
other virally transmitted diseases.
- Plasma protein fraction is associated with hypotensive
reactions ( allergic).
-include dextrose starch and gelatins.
( gelatins are associated with histamin mediated allergic reactions
and are not available in the USA).
- Dextrose starches include Dextran and Hetastarch.
1-Dextran is available as dextran 70 and Dextran 40. When infused in a rate more than 20ml/kg/d, they will be associated with certain complications.
- Interfering with blood typing.
- Prolong bleeding time ( antiplatelets effect).
- Renal failure.
- Anaphylactic reactions ( mild – severe).
2- Hetastarch is highly effective as a plasma expander and less expensive than albumin.
- It is non antigenic ( thus anaphylactic reactions are rare).
- Coagulation and bleeding times not significantly affected.
N.B. Na concentration and total body water are controlled by independent mechanism, As a consequence hypo and hypernatremia may occur in conjugation with hypovolemia, hypervolemia or euvolemia, thus it is necessary to measure the osmolality to evaluate the patient with hyponatremia.
- Gain of H2O.
- brain occupied lesion
- drug :acting centrally morphine –pethidine – NASID - Li+
- nausea , vomiting
- SIADH: low plasma osmolality (<280 mOsm/L),Hyponatremia (<135mmol/L),low urine output with concentrated urine (>100 mOsm/kg),elevated urine sodium (>20mEq/l), clinical euvolemia
Causes and diagnosis :
Hyponatremia may occur in conjunction with hyper tonicity ,isotonicity or hypo tonicity so it is necessary to measure the serum osmolility to evaluated patients with hyponatremia.
OSMOLILITY :280-290 mOsm
Note : measure blood glucose ,lipid , protein
2- Hypertonic hyponatremia (>290 mOsm ):
Note : measure blood glucose .
3- hypotonic hyonatremia: (<280 mOsm)
Is classified on basis of extracellular fluid volume Generally developed as a consequence of the administration and retention of hypotonic fluids [ dextrose 5% in water ,0.45% Nacl .
1. Hypovolemic hypotonic hyponatremia :
In the surgical patient most commonly results from replacement of sodium –rich fluid losses (from the GI tract, skin or lungs)with an insufficient volume of hypotonic fluid .
2.Hypervolemic hypotonic hyponatremia :
The edematous states of congestive heart failure , liver disease , nephrosis occur in conjunction with inadequate circulating blood volume renal retention renal retention of sodium and water disproportionate accumulation of water hyponatremia
3. Isovolemic hypotonic hyponatremia :
intracellular volume cerebral edema
In the presence of symptoms or extreme hyponatremia [Na<110mmol/L]:
Hypertonic saline (3%Nacl )is indicated to correct serum Na to 120mmol/L.
The quantity of 3% Nacl that is required to increase serum Na to 120mmol/L can be estimated by calculating the Na deficit:
Na deficit (mmol)=0.6xlean body weight (kg)x[120-measured serum Na (mmol/L)] .
Central pontine demylination occurs in the setting of correction of hyponatremia , the risk factors for demyelination are contraversial but appear to be related to chronicity of hyponatremia (>48hr) and the rate of correction .
Diagnostic approach to hypernatremia :
Clinically assess ECF volume
2. ECV normal : isovolemic hypernatremia :loss of water:
- a defect in the hypothalamic secretion of ADH .
- head trauma , intracranial tumors , infections, vascular disorders
(aneurysms ) , hypoxia , medications(clonidine ,phencyclidine ).
-renal insensitivity to normally secrection ADH
-familial, drug induced (Li , demeclocycline ), results of hypokalemia
,hypercalcemia , intrinsic renal disease )
1- Intercompartment shift of K+ ions
2. decreasedexcretion of K+ :
3- Increased K+ intake:
1- Intercompartmental shift of K+.
2- Increased K+ loss.
3- Inadequate K+ intake.
A- Intercompartmental shift of K+:
- Due to intracellular movement of K+.
B- Increased K+ losses:
- Renal (urinary K+ > 20 mEq/L):
- GI (urinary K+ < 20 mEq/L):
C - Decreased K+ intake:
- Marked reduction in K+ intake is required to produce hypo K+ bec.
Of the kidney’s ability to decrease urinary excretion to as low as 5-
Can produce widespread organs dysfunction:
Clinical manifestations of hypo K+:
T wave flattening & inversion.
Prominent U wave.
ST segment depression.
increased P wave amplitude.
Prolonged P-R interval.
The treatment of hypo K+ depends on the severity of any associated organ dysfunction:
Increased serum phosphate level :
of active vitamin D and renal phosphate retenion
Vitamin D deficiency :
End –organ resistance to PTH:
Tapping over the facial nerve in the region of the parotid gland causes twitching of facial muscles.
carpopedal spasm ( opposition of the thumb, extension of the interphalangel and flexion of the metacarpophalangeal joints induced by inflation of the sphygmomanometer cuff to level above systolic blood pressure .
- Symptomatic hypo Ca++ is a medical emergency and must be treated immediately with ca++ bolus:
then followed by a maintained infusion of 1-2 mg /kg elemental calcium /hr for 4 hr .
Excess PTH :
Excess action of vitamin D
Excess calcium intake
Other endocrine disease :
Management of severe hypercalcemia :
4-6 L of IV saline over 24 h and then 3-4Lfor several days .
and deposition of CaPo4 in bone and soft tissues.
note phosphate level : 0.8-1.5 mmol/l
redistrubitionof phosphate from extracellular fluid into cell :
decreased intestinal absorption :
Increased urine excretion :
If phosphate level <0.8 mmol/l
Severe hypophosphatenemia cause widespread organ dysfunction:
mmol slowly over 6-12 hrs ).
>>.>> ECG changes: Prolonged PR interval, widening QRS
If Mg+<0.7 mmol/L
Associated with other deficiencies like K+, PO4
Cisplatin, Cyclosporin, Amphotericin B).
hypomagnesemia increases renal excreation of k+ and inhibits secretion of parathyroid hormone and leads to parathyroid resistance , so many of symptoms of hypomagnesaemia are due to hypokalemia and hypocalcemia .
(aggrevated by hypo K+ ), AF.
(50mmol of MgCl in 1L of 5% dextrose over 12-24 h)
plus a loading dose (4 mmol over 10 min ).