Fluids and Electrolytes
Dr. Raju Khatiwada
Resident 1st year
General surgery
Moderator: Dr. Sushil Dhungel
CONTENTS
• Introduction
• Body fluids
• Principle of fluid management
• Electrolytes
INTRODUCTION
• Osmolality : Refers to the number of osmoles of solute particles per
kilogram of water and is comprised of both effective and ineffective
components.
• The plasma osmolality (Posm) is determined by the ratio of plasma
solutes and plasma water.
• The normal Posm is 275 to 290 mosmol/kg.
• Posm = 2 x [Na] + [Glucose]/18 + Blood urea nitrogen/2.8 (mmol/L)
• Posm = 2 x [Na] + [Glucose] + [Urea]
• Tonicity: The parameter the body attempts to regulate. Also known as
effective plasma osmolality, determines the transcellular distribution of
water
✔ Example: Neurological symptoms of Hypo/Hypernatraemia
✔ Plasma tonicity = 2 x [Na] + [Glucose]/18 (if glucose is measured in mg/dL)
✔ Plasma tonicity = 2 x [Na] + [Glucose] (if glucose is measured in mmol/L)
✔ Regulation of water and sodium balance- ADH and Thirst
• A mole is the molecular weight of the substance in grams.
• Each mole (mol) consists of 6 × 10 ^23 molecules.
• The millimole (mmol) is 1/1000 of a mole, and the micromole (μmol)
is 1/1,000,000 of a mole.
• mEq/L: number of electrical charges
• mOsm/L: number of osmotically active particles or ions
TBW (60% of body
weight) 42 L
The total body water (TBW) as
a percentage of lean body
weight varies with age
The principal extracellular
cation is Na +, and the
principal extracellular anions
are Cl− and HCO3
Extracellular = 1/3
(20% body weight)
14 L
Intracellular fluid = 2/3
(40% body weight)
28 L
the principal intracellular
cations are K+ and Mg2+, and
the principal intracellular
anions are phosphates and
negatively charged proteins.
Interstitial = ¾
(15% body weight)
Plasma = ¼
(5% body weight)
The Washington Manual of Surgery 8th Edition
Normal fluid balance in the body
• Water gain: 2-2.5 Lit/day
• Water Loss:
✔ Urine- 1-1.5 Lit/day
✔ Stool: 250 ml
✔ Insensible loss: 750 ml
Shift of water between compartment
Y-axis: solutes/ osmolality
X-axis: Volume of ICF and ECF
Disturbances in Fluid Balance
• Extracellular volume deficit is the most common fluid disorder in
surgical patients
• Acute: cardiovascular and central nervous system sign
• Chronic: Tissue signs, such as a decrease in skin turgor and sunken
eyes,
Fluid and electrolyte therapy
• Parenteral solutions
• Alternative resuscitative fluids
Parenteral solutions
Schwartz’s Principles of Surgery -11th edition
Alternative resuscitative fluids
• Hypertonic saline solution (7.5%): closed head injuries
• Colloids: albumin, dextrans, hetastarch, and gelatin
Why fluid
management is
important?
• The surgical patient is at risk for multiple
derangements of fluid balance and
electrolyte composition.
• Blood loss, volume deficit and shift of fluids
from intravascular space
Principle of fluid management
• Maintenance therapy replaces the ongoing losses of water and
electrolytes under normal physiologic conditions via urine, sweat,
respiration, and stool.
• Replacement therapy corrects any existing water and electrolyte
deficits. These deficits can result from gastrointestinal, urinary, or skin
losses, bleeding, and third-space sequestration.
Maintenance Fluid Therapy
• The goal of maintenance fluid therapy is to preserve water and
electrolyte balance and to provide nutrition.
• Example: periopearatively or under ventilator
• Ideal fluid is unknown
• The current standard is to use 5% dextrose in half-normal saline with
20 mEq per liter of potassium (9gm of Nacl, 400 kilocalorie)
• serum sodium concentration provides the best estimate of water
balance in relation to solute, does not provide any information on
volume status
Sabiston textbook of surgery- 21st edition
Intraoperative fluid management
• Replacement of preoperative deficit as well as ongoing losses.
Intraoperative insensible and third-space fluid losses depend on incision
size, extent of tissue trauma, and preoperative physiology.
• Small incisions with minor tissue trauma (e.g., inguinal hernia repair) -1
to 3 mL/kg/hr.
• Medium-sized incisions with moderate tissue trauma (e.g.,
uncomplicated sigmoidectomy) - approximately 3 to 7 mL/kg/hr.
• Larger incisions and operations with extensive tissue trauma and
dissection (e.g., pancreaticoduodenectomy) - approximately 9 to 11
mL/kg/hr or greater.
Post operative fluid management
• titrated to maintain an adequate urine output (0.5 to 1.0 mL/kg/hr)
• GI losses that exceed 250 mL/day from nasogastric tube suction
should be replaced with an equal volume of crystalloid
Replacement fluid therapy
Volume
deficit
Rate of
replacement
Choice of
replacement
fluid
• The goal of replacement
therapy is to correct
existing abnormalities in
volume status and/or
serum electrolyte
Electrolytes
ECF - Sodium
ICF - Potassium
The Washington Manual of Surgery 8th Edition
The Washington Manual of Surgery 8th Edition
The Washington Manual of Surgery 8th Edition
Management of Hypernatremia
Fluid: Hypotonic fluid such as
5% dextrose,
5% dextrose in one quarter normal saline,
or enterally administered water
The rate of fluid administration:
• Acute hypernatremia: no more than 1
mEq/h and 12 mEq/d decraese
• chronic hypernatremia: (0.7 mEq/h)
decrease
Potassium
• Hypokalaemia causes:
✔ GI losses, renal losses, and cutaneous losses (e.g., burns).
✔ Other causes of hypokalemia include conditions associated with acute
intracellular K+ uptake, such as insulin excess, metabolic alkalosis,
myocardial infarction, delirium tremens, hypothermia, and
theophylline toxicity.
✔ Hypokalemia may also occur in refeeding syndrome
Clinical manifestation- hypokalaemia
• Mild hypokalemia (K+ >3 mmol/L [11.7 mg/dL]) is generally
asymptomatic.
• Symptoms occur with severe K+ deficiency (K+ < 3 momol/L)
• Early electrocardiogram (ECG) manifestations include ectopy, T-wave
depression, and prominent U waves. Severe depletion increases
susceptibility to reentry arrhythmias.
Hyperkalemia
• Pseudohyperkalemia is a laboratory abnormality that reflects K+
release from leukocytes and platelets during coagulation.
• Spurious elevation in K+ may result from hemolysis.
• Abnormal redistribution of K+ from the intracellular to the
extracellular compartment may occur as a result of insulin deficiency,
β-adrenergic receptor blockade, acute acidemia, rhabdomyolysis, cell
lysis (after chemotherapy), digitalis intoxication, reperfusion of
ischemic limbs, and succinylcholine administration.
ECG abnormalities:
• Symmetric peaking of T waves,
•
reduced P-wave voltage, and
•
widening of the QRS complex.
•
If untreated, severe hyperkalemia
ultimately may cause a sinusoidal
ECG pattern
Sabiston textbook of surgery- 21st edition
• Bailey’s and love -27th edition
• Sabiston’s textbook of surgery-21st Edition
• Maingot’s Abdominal Operations- 13th edition
• Schwartz’s Principles of Surgery -11th edition
• PubMed
• UpToDate
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