9 Shock, Water-Electrolyte and Acid Base Balance
WATER AND ELECTROLYTE BALANCE AND IMBALANCE
The input and output of water and electrolytes are finely balanced in the body.
The daily input of water is derived from two sources (Box 9.9):
• Exogenous in form of liquid intake and ingested solid food. The solids consumed contribute to the half of water requirement.
• Endogenous is released from oxidation of ingested food.
The daily output of water is by four routes (Box 9.9):
• Urine—daily output of urine is about 1500 ml/day.
Minimum 30 ml/hr urine is required to excrete the toxic metabolites from the body.
• Faeces—about 100 ml/day water is lost through this route normally.
• Lungs—about 400 ml/day water is lost in expired air from the lungs.
• Skin—about one liter water is lost daily through skin as perspiration meant for thermoregulation. The loss occurring through skin and lungs is called insensible loss.
This regulation is mainly done by the hormones:
• ADH (Antidiuretic hormone) secreted in response to rise in plasma osmolality that causes increased reabsorption of water in the distal renal tubules.
Box 9.9: Daily input output balance in an adult
Input Output
Liquids 1200 ml Urine 1500 ml
Solids 1000 ml Skin 1000 ml
Oxidation of food 300 ml Lungs 400 ml Faeces 100 ml
• Aldosterone—produced by the zona glomerulosa of the adrenal cortex.
• Renin-angiotensin mechanism—releases renin by the juxtraglomerular cells in response to decrease in renal plasma flow.
Osmolality: It is the osmotic pressure exerted by the number of moles per kg of solvent. Important electro-lytes which determine osmotic pressure of our body fluids are Na+, K+, Cl– and HCO3–. K+ is the most important electrolyte of intracellular fluid while Na+, Cl– and HCO3– are important for extracellular fluid.
Commonly carried out investigations show the status of ECF. Osmolality of plasma varies between 285-295 mOsm/kg.
Disturbances in Water Balance
• Hypovolemia
• Hypervolemia.
Hypovolemia
It is due to diminished water intake (pure water depletion).
Causes
• Decreased water intake—due to inability to swallow, e.g. painful ulcers in oral cavity, esophageal obstruction.
• Excess loss of water—loss from gut, e.g. vomiting, diarrhea.
Insensible loss from skin and lungs, e.g. fever
Loss from lungs, e.g. after tracheostomy.
Clinical features The patient complains of thirst, weakness and decreased urine output.
Investigations Raised hematocrit, increased specific gravity of urine, increased blood urea, increased serum sodium.
Treatment
• If swallowing is possible, increase oral intake of water.
• If there is difficulty in swallowing or in case of severe hypovolemia, give intravenous 5% dextrose or dextrose saline.
Hypervolemia
It is due to excess intake of water orally or excess infusion of fluids parenterally.
Causes
• Rapid and excess infusion of IV fluids
• Water retention enema
• Fluid retention due to cardiac or renal failure
• Excess absorption of fluid from prostatic fossa during transurethral resection of prostate
• ADH secreting tumor, e.g. oat cell tumor of lung.
Clinical features
• Nausea, vomiting, drowsiness, weakness, convul-sions and coma.
• Patient passes large amount of dilute urine.
• Although patient appears to be in shock, but on examination, pulse and blood pressure normal, neck veins distended, pedal edema.
Investigations Low hematocrit, blood urea normal, serum sodium may be low.
Treatment
• Restrict water intake.
• Very slow intravenous infusion of hypertonic saline.
Disturbances in Electrolyte Balance Four important disorders are:
• Hypernatremia
• Hyponatremia
• Hyperkalemia
• Hypokalemia.
Hypernatremia
It is the sodium excess in body (more than 150 mmol/l).
Causes
• Mismanaged fluid administration (excess saline in postoperative period)
• Mineralocorticoid excess.
Clinical features Puffiness of face, pitting edema, weight gain, distended jugular veins. Pulmonary edema may occur in neglected cases.
Treatment Water administration orally or through Ryle’s tube, 5% dextrose IV
Hyponatremia
It is the sodium depletion in body (less than 135 mmol/l).
Causes
• Excess vomiting or Ryle’s tube aspiration causing loss of intestinal secretions.
• Intestinal fistula.
• Severe diarrhea.
• Postoperative hyponatremia—it is due to prolonged administration of sodium free solutions (5%
dextrose) intravenously.
• Syndrome of inappropriate anti-diuretic hormone secretion (SIADH)—it is due to excess ADH secretion following surgery or trauma, more often seen in elderly patients. Excess ADH causes water retention and increase in ECF volume. This in turn leads to decreased aldosterone secretion and excess loss of sodium in urine.
• Pseudohyponatremia—serum osmolality depends on various solutes like sodium, glucose, urea, plasma lipids and proteins. Out of these, sodium is most abundant and others have less concentration.
However, when their concentration becomes very high, the relative concentration of sodium becomes less. So despite normal concentration, the serum sodium levels become less and it is termed as pseudohyponatremia.
Clinical features
• Unlike hypovolemia, thirst is not evident in hyponatremia
• Sunken eyes
• Drawn face
• Dry, coated tongue
• Dry and wrinkled skin
• Collapsed peripheral veins
• Low blood pressure
• Urine is small in amount and dark colored.
Investigations
• Hematocrit increased
• Serum sodium decreased
• Urine sodium decreased (In SIADH urine sodium increased)
• Urine specific gravity high.
Treatment
• Treat underlying cause.
• IV infusion of isotonic saline or Ringer’s lactate.
Hyperkalemia Causes
• Excessive K+ intake with diuretics (K+ sparing)
• Parenteral infusion of K+
• Transfusion of stored blood
• Acute renal failure (oliguric phase)
• Acidosis
• Addison’s disease
• Tissue damage (hypoxia, severe dehydration, hemolysis)
• Catabolic states (diabetes)
• Fallacious values because of hemolysed sample/
contamination.
Clinical features
• Vague muscle weakness
• Flaccid paralysis
• In severe cases (K+ levels >10 mmol/L), there can be ventricular fibrillation and death.
Investigations
• Serum K+ levels > 5.5 mmol/L
• ECG changes—Tall, peaked T-wave followed by absence of P-wave and finally formation of abnormal QRS complex.
Treatment
• Glucose and insulin to promote influx of K+ in cells.
• 10 ml of 10% of calcium gluconate IV.
• Retention enema.
• If above mentioned measures fail, peritoneal or hemodialysis is helpful.
• Treatment of the cause.
Hypokalemia Causes
• Diuretics
• Parenteral nutrition
• Diuretic phase of acute renal tubular necrosis and chronic renal failure.
• Renal tubular acidosis
• Alkalosis
• Mineralocorticoid excess
• Severe trauma
• Major surgical operation (increased ADH and aldosterone)
• Anabolic states
• Chronic diarrhea
• Excessive use of purgatives
• Intestinal fistulae
• Insulin administration.
Clinical features
• Muscle weakness
• Weakness of respiratory muscles causing rapid, shallow, gaping breathing
• Abdominal distention due to paralytic ileus
• Cardiac arrhythmias / congestive cardiac failure.
Investigations
• Serum K+ levels < 3.5 mmol/L (decreased serum K+ indicates much larger depletion of K+)
• ECG changes—depressed ST segment, low or inverted T-wave.
Treatment
• Dietary intake in mild cases (common foods have enough K+).
• K+ salts / I V KCl (Slow drip) in moderate to severe cases. Urine output should be adequate.
• Treatment of the cause.
Comparison between hyperkalemia and hypo-kalemia is given in Box 9.10.
Box 9.10: Comparison between hyperkalemia and hypokalemia
Hyperkalemia Hypokalemia
Clinical features Flaccid paralysis Muscle weakness
Ventricular fibrillation and death Abdominal distention
Cardiac arrhythmias / congestive cardiac failure
K+ levels > 5.5 mmol/L < 3.5 mmol/L
ECG changes Tall, peaked T-wave followed by absence of P-wave Depressed ST segment, low T-wave and finally formation of abnormal QRS complex.
Treatment Glucose and insulin to promote influx of K+ in cells. Dietary intake in mild cases.
10 ml of 10% of calcium gluconate IV. K+ salts / IV (Slow drip) in moderate to If above mentioned fails, peritoneal or hemodialysis. severe cases.
Treatment of the cause. Treatment of the cause.
Postoperative Fluid Therapy Period of Therapy
First 24 hours: Due to stress of operative trauma, adrenal steroids (aldosterone) and ADH are released in circulation resulting in retention of sodium and water and excretion of potassium from the kidneys (Sodium stays, potassium flees). The requirement of sodium and water is thus reduced. Moreover, due to body reserves of potassium, its replacement is also not required in first 24 hours.
In a healthy adult, approximately 2 liters of fluid (500 ml N saline and 1500 ml 5% dextrose) is required during first 24 hours.
After 24 hours: The fluid requirement after 24 hours is calculated by measuring previous days’ urine output and adding it to insensible loss from skin and breathing. In case, there is some additional loss, e.g. due to fever, diarrhea, Ryle’s tube aspirate, etc. then it is also taken into account. For example:
Insensible loss 1000 ml Urine output 1500 ml Total output 2500 ml
Thus, in a patient kept nil orally, replacement of 2500 ml IV fluids (equal to previous days’ output) is required during next 24 hours. It comes out to be 5 bottles of 500 ml each.
The daily need of sodium is 100 mmol and potassium is 40-60 mmol.
Thus requirement will be met by giving one bottle (500 ml) of N saline, four bottles (500 ml each) of 5%
dextrose and two ampoules (20 ml each) of KCL added to the infusion bottle. The potassium supplement should not be given as IV bolus as it can cause arrhythmia.
In case of electrolyte imbalance, serum levels of sodium and potassium will guide for calculating the requirements.
Once patient starts taking orally, the IV fluid supplement is decreased accordingly.
Types of IV fluids
Types of fluids used for IV use are:
• Crystalloids
• Colloids
Crystalloids These are solutions of electrolytes in water.
They are available as bottles containing sterile, pyrogen free solution without preservative and for single IV infusion. Routinely used solutions are:
1. 5% dextrose: It is isotonic solution that supplies calories without electrolytes. It is useful in early post-operative period when sodium excretion is reduced.
Its prolonged administration can lead to hypo-natremia.
A bottle contains 500 ml solution of dextrose is in the strength of 5% w/v.
Each 100 ml contains:
• Dextrose—5 gm
• Water for injection in QS
• Calories 17 kcal/100 ml
2 Isotonic saline (0.9%) solution: It is needed as replacement fluid when large amount of sodium has been lost, e.g. by vomiting, Ryle’s tube aspiration, intestinal fistula, etc.
Its other uses are:
• To dilute and dissolve drugs
• As irrigating fluid
• To toilet the body cavity
• Treatment of alkalosis (Hypochloremic) with dehydration
• Treatment of mild hyponatremia.
In a bottle of 500 ml, each 100 ml contains:
• Sodium chloride—0.9 gm
• Water for injection in QS.
3 Dextrose-saline solution: It contains 4.3% dextrose and 0.18% saline and is isotonic (5% dextrose in saline is hypertonic). It is also used as maintenance/
replacement fluid.
4. Ringer’s lactate solution: It contains sodium, potassium and chloride in almost same concen-tration as that of plasma. It also contains some calcium and bicarbonate as lactate. It does not contain dextrose. It is ideal replacement fluid in hemorrhagic shock due to trauma, surgery, etc. while awaiting blood (poor man’s white blood).
Contraindication to its use are:
• Liver disease, severe hypoxia and shock where lactate metabolism is impaired and lactic acidosis may occur due to infusion of Ringer’s lactate solution.
• Severe metabolic acidosis where conversion from lactate to bicarbonate is impaired. So it can worsen acidosis.
5. Other fluids used are:
• Isolyte P: It is designed to suit maintenance fluid requirement of children (more water and less electrolytes).
• Isolyte G: It is gastric replacement solution and is used to replace loss of gastric juice (in vomiting, Ryle’s tube aspiration) and in treatment of metabolic alkalosis.
• Isolyte M: It is ideal fluid for maintenance therapy.
• Isolyte E: It is used as extracellular replacement solution. It has electrolytes similar to ECF except double amount of potassium and acetate which will get converted into bicarbonate. It should be avoided in metabolic alkalosis.
Colloids These are fluids having substances of high molecular weight like proteins, starch or gelatin dissolved in water, efficient to produce oncotic pressure. They can be:
• Natural—albumin and plasma protein fractions.
• Synthetic/artificial—Dextran, Gelatin (Haemaccel), Hydroxy ethyl Starch (HES).
Synthetic colloids are preferred due to following advantages:
• Easily available
• Economic
• No transmission of diseases
• Low incidence of anaphylactic reactions.
The features of ideal colloid are given in Box 9.11.
Box 9.11: Features of ideal colloid
• Rapid replacement of blood loss
• Sustained hemodynamic parameters
• Sufficient long intravascular life
• Produces sufficient oncotic pressure
• Improve oxygen supply
• Improve organ functions by perfusion
• No transmission of disease
• Easily metabolized and excreted
• No effects on cross-matching of blood
• No effect on coagulation
• No anaphylactic or allergic reaction
1. Gelatins (Hemaccel): It contains polymer of degraded gelatin with electrolytes. Its intravascular stay time is 2-3 hr and it gives oncotic pressure of 21 mm Hg.
Its indication/uses are:
• As plasma expander in hypovolemic shock, burns, trauma.
• Perioperatively to replace blood loss.
• As preloading fluid in spinal anesthesia.
Dose 20 ml/kg/day (1000ml / 50 kg).
Contraindications
• Allergy to gelatin solutions
• State of fluid overload.
Side effects
• Anaphylactic /allergic reactions (0.146%).
Demerits
• Colloid osmotic pressure low (21)
• Water binding capacity low (15 ml/gm)
• Short stay in vascular compartment (2-3 hr)
• May interfere with coagulation.
2. Hydroxy ethyl Starch (HES): It is isotonic colloid derived from maize and is used as replacement fluid.
It is composed of amylopectin derived from starch.
Its preparations are:
• HES-200 (Pentastarch) molecular weight 200,000
• HES-450 (Hetastarch) molecular weight 450,000
• Tetrahes-130 (Tetrastarch) molecular weight 130,000
All preparations are in N saline.
Indications/Uses
• As plasma expander in hypovolemia, trauma, surgery
• Preloading in spinal anesthesia
• Hemodilution in cardiac and vascular surgeries
• Improves tissue perfusion and oxygen utilization in shock.
Contraindication
• Allergy to salt
• Fluid overload.
Side effects
• Allergic reactions
• Bleeding disorders.
Precautions
• HES may increase the renal toxicity of amino-glycoside antibodies.
• Interference with blood grouping and cross matching.
• Rapid infusion may cause circulatory disturban-ces and subsequent damage to tissues. So infusion should be given slowly.
Dose
• 20 ml/kg/hr for adult.
3. Dextran 40, 70: It is a polysaccharide (glucose polymer) synthesized by fermentation of sucrose that is ultimately degraded enzymatically to glucose.
Each 100 ml Dextran 40 contains:
Dextran-40—10 gm Sodium chloride—0.9 gm Water for injection—QS
Its water binding capacity is 25 ml/gm and osmotic pressure is 290 mOsm/L.
Dose – 20 ml/kg/day Intravascular stay period Dextran – 40 (10%)—2-4 hr Dextran – 70 (6%)—6 hr Uses
• As plasma expander
• As antithrombotic agent
• To improve perfusion in vascular surgeries (Dextran 40).
Contraindications
• Allergy to Dextran
• Overhydration
• Coagulation disorder Side effects
• Interfere with cross-matching due to rouleaux formation
• Increased bleeding time due to decreased platelet adhesiveness
• Anaphylactic reaction
• Noncardiogenic pulmonary edema (Direct toxic effect on pulmonary vasculature).
4. Human albumin: It is derived from pooled human plasma and is a costly preparation.
100 ml of 25% solution contains 25 gm albumin and half life of albumin is 16 hr.
Water binding capacity is 17 ml/gm of albumin.
Indications
• When crystalloids fail to sustain plasma volume for more than a few minutes because of low oncotic pressure.
• Abnormal loss of protein from vascular space as in peritonitis and burns.
Contraindication
• Allergy to albumin and fluid overload.
ACID BASE BALANCE AND DISORDERS