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kjyhiuyujbm Fluids, Electrolytes & Acid-base Balance

‫فـكرّية فـريح‬

‫ حـسين الحيـص‬.‫د‬ 2-11-2008 8-11-2008

General Medicine 2-11-008 Fluids, Electrolytes and Acid-base Balance Fikria Freih

The fluids in the body or in the abdominal cavity are distributed into intra cellular and extra cellular compartments, The

dominant

electrolyte

in

the

intra

cellular

compartment is potassium (K+), while in the extra cellular is sodium (Na+), usually we divide the fluids in the abdominal cavity into the following sectors: gastric juice, bile, and the fluids in the intestine. List the normal range of the main electrolytes in serum: * mol/L=mEq/L. ◘Sodium Na+: normal is about 135-145 mEq/L. If 135 =hyponatremia.

If 145= hypernatremia.

◘Potassium K+: The normal serum level of potassium is 3.5 to 4 mEq/L. If 3.5 =hypokalemia.

If 4.5= hyperkalemia.

◘Bicarbonate HCO3-: 22-31 mEq/L. ◘Chloride Cl -: 100-108 mmol/L. Indicate how the electrolytes range in perspiration, gastric juice, bile & intestine content:

Perspiration (sweating): is a mechanism to dissipate fluids from

the

body.

It

participates

in

the

control

of

temperature .The center of temperature is in the

hypothalamus, this thermostat is set normally at 37 .but during infection via the production of IL-2 the

‫ء‬

thermostat is set at 38-39‫ء‬. Fever is a type of energy, so some of this energy is transformed to mechanical energy that appears as contraction of muscles in general and mostly in the contraction of muscles around the mouth. I.e. a patient with high fever, his body is trying to eliminate the fever by perspiration. So in infection the thermostat will change from 37 to 40. The human body tries to regulate his thermostat to decrease the 40 to the normal. The body tries to recompensate, if the body stays at high temperature, the metabolism rate will be high.

We need to dissipate the high energy/fever; so the body is trying to lose some of this energy by inspiration and contraction of mouth muscles others include rigor, chills, shivers and perspiration. Gastric juice: is secreted from the stomach; this secretion

is around 1.5-2L containing chloride and other non-organic factors like pepsin.

The small bowl: contains at least 8 L of fluids .Large bowl contains less fluids; it contains the hard stools. Fluids in the small bowl are subjected to excretion and absorption. Jejunum is the main site of absorption, while in terminal ileum different components are converted into triglycerides. The bile: (from the GallBladder) around 800ml and what is special for the bile is its enterohepatic circulation, ( entero=small bowl, hepatic =liver); The bile is secreted in the liver ,stored in GB ,passes from GB to the duodenum ,goes to the small bowl ,absorbed in the terminal ileum and part of the colon then absorbed back to the liver again. All These fluids stomach=1.5L, small bowl=8 L and bile =1L the body benefits from them. It means these fluids are the

reservoir of fluids in the body. List endogenous factors that affect renal control of Na+ and water excretion: The kidney is directed to excrete or retain sodium and water via the action of aldosterone, antidiuretic hormone (ADH, or vasopressin), atrial natriuretic peptide (ANP), and by Solvent drag (It is when solvents in the ultrafiltrate are transported back from the renal tubule by the flow of water rather than specifically by membrane transport proteins).

The urine output is around 1-1.5L daily (human body loses 1.5L of urine daily). A human should urinate ideally 50-60ml

urine/hour. Anybody should urinate more than 30ml /hour, if less than 30 he definitely needs fluids.

The kidney filters the body to the outside, while the liver is the filter from within the body. Kidney is composed of nephron and the nephron is composed of Bowman's capsule, proximal convoluted tubules, loop of Henle, distal convoluted tubules and lastly the collecting system. At each part there is exchange of electrolytes & organic materials. E.g. the main site of K

+

exchange is the

distal part of the distal convoluted tubules. All the electrolytes are distributed, absorbed and excreted in a proper way in the nephron. Once renal failure occurs the kidney will be unable to excrete toxic wastes to the outside so the patient starts to retain these toxic electrolytes in a large amount e.g. accumulation of Phosphorous and Calcium leads to itching. List 6 symptoms or physical findings of dehydration: Dehydration is caused by loss of normal fluids in the body. The main cause is upper GI loss of fluids by vomiting, lower GI loss by diarrhea, loss of fluids from intestine by abdominal trauma,

loss of fluids by fever or loss of fluids from the vascular compartment (hemorrhage).

Dehydration is the chronic loss of fluids from the body mainly by vomiting or diarrhea. The patient usually starts to recompensate that by thirst. So the 1st sign of

dehydration is

thirst ,2nd the patient will have all

the manifestations of cell dehydration; so he will be tired, fatigued, hypotensive, having tachycardia, will have sunken eyes and loss of subcutaneous fluids called loss of skin turgor. List & describe the objective ways of measuring fluid balance: the best indicator for dehydration is the urine output; if you would like to know if a patient is dehydrated or not look at the patient’s urine if the urine is more than 50ml/hour this means that the patient is not dehydrated, but if the urine is scanty

less than 30ml/hour this patient is dehydrated. Look at the color of the urine if it is dark this means that this urine is concentrated, contains ammonia and it means that this patient is dehydrated so that patient needs fluids. The 1st and best

criterion is to measure the urine output. If you go deep and ask about the electrolytes this will give information about the level of dehydration (at cellular or extra

cellular level) and to know if this dehydration is hyponatremic or hypernatremic. The other criterion is the Blood Pressure. In case of fluid loss the patient is expected to be hypotensive. This decrease in BP is balanced by tachycardia.

The solutions available to be given to a dehydrated patient:

If there is loss of fluids, the best way is to compensate for the same fluid component that is lost. Usually regarding pure fluid/water & electrolytes we have these available solutions: (all these fluids are given IntraVenously)  Normal (0.9%) saline: this is the ideal solution to be

given to a dehydrated patient. this saline is isotonic compared to the fluids of the body (this saline and body fluids are

equivalent

in

tonicity;

has

the

same

solute

concentration).This 0.9% normal saline contains 154Na & 154K.

In treatment usually start with normal saline but in

some situations like high BP, the normal saline can’t be given. 0.9% means that 0.9 of a Liter contains Na& K.

 ½ Normal saline: 1 L normal saline + 1 L Fluid (pure water). It contains 154/2=77 Na & K. 

Normal saline: 1 L normal saline + 2 L

fluid (pure

water). The previous 2 salines are used in pediatric age group and in hypertensive patients.  5% Dextrose in water: could be: 5%, 10% for diabetics, 20% or

30% for patient in need of glucose .5% means it

contains 5gm sugar /L. There is also dextrose saline which is mixture of NaCl with glucose. So we can mix these together; since there are daily requirements of Na and K .e.g. the body needs 100 mEq of K daily.  Ringer’s lactate: a fluid containing lactate and Potassium, it’s given in hypovolemic shock and burns. It contains 135 Na, 135 K &135 Cl.

So water + 0.9% NaCl = normal saline that is isotonic to the fluids in the body. If we can’t give NaCl because the patient is young or hypertensive so divide the Na in the normal saline by water. Or don’t give Na at all  dextrose water.

The daily requirements was calculated on a group of people with low metabolic rate, it was found to be more than 60ml/hour (usually in adult

2400/24100ml/hour). So 60-

100ml is the daily requirements of the human body. The amount of fluid given to the patient is equal to the estimated fluid loss + daily requirements of that patient. In the following situations, indicate whether serum electrolytes will remain stable, rise or fall:  Excessive gastric loss: the stomach contains a high mount of hydrochloric acid (HCl), so a patient with excessive gastric loss, will have loss of hydrogen and loss of chloride ions. 

High

volume

pancreatic

fistula: The pancreatic

secretion that is around 800ml /day will be lost, so this patient will lose Na+, K+ and HCO3 _.  Small intestinal fistula: The patient is losing fluids causing a considerable fall in the electrolytes.  Biliary fistula: Means that the bile goes from the body to out, a considerable fall in the electrolytes. *Fistula is an abnormal connection or passageway between two organs that normally do not connect (an opening to outside the body).  Diarrhea: Loss of electrolytes with substantial loss of K+.

In the following situations, indicate whether serum electrolytes will remain stable, rise or fall: Acute tubular necrosis: The kidney tubules are necrotic. The patient will lose the ability to excrete urine therefore the fluids & electrolytes will accumulate within his body leading to renal failure. A considerable rise in K+ at level of 8 mmol is expected, leading to arrhythmia.

High K+ in the body leads to arrhythmia. Dehydration: Causes Hypernatremia Inappropriate ADH secretion (Anti Diuretic Hormone): The patient will lose too much fluids by the kidney (3-4 L of urine is lost daily) so hypernatremia results.  Diabetes mellitus: Increase urination leads to decrease Na and retention of K+ .so hyponatremia & hyperkalemia. Note

Diabetes insipidus causes the exact opposite. Congestive Heart Failure: The patient tends to maintain fluids

in

the

subcutaneous

tissue

(peripheral

edema),

hepatomegaly and pulmonary effusion (the accumulation of fluids around the lungs).since this patient is having too much fluids in an abnormal anatomical location we expect to find hypernatremia. Describe the possible causes, appropriate laboratory studies needed and treatment of the following conditions:

Hypernatremia (Na above 145): The main cause is dehydration. The clinical manifestations of hypernatremia are (there is no fluids but Na+) thirst and fatigue. Hyponatremia (Na at 125 becomes pathological): It occurs in water intoxication; when a patient drinks a huge amount of water or if you put the patient on IV fluid and you leave the patient for 2-3 days ,he will have hyponatremia ,so the

hyponatremia is mainly by iatrogenic cause (caused by the medical staff) while hypernatremia

is a

pathological cause. Hyponatremia occurs with an increase in body water. In the presence of excess water the level of consciousness will deteriorate, the patient will get edema everywhere even in the brain thus decreasing the level of

consciousness. Hyperkalemia: Is caused by renal failure, once you have a patient with renal failure ask about the potassium you’ll find it high around 5.5- 6 you’ve to send him immediately to the hospital, he may die from arrhythmia and cardiac arrest Hypokalemia: The main cause is increased diuretic intake. If K+ is found 2.8-3 send the patient immediately to the hospital because he is having electrolyte disturbances and cardiac problems.

Cardiac problems occur in hyper & hypokalemia. The K+ interferes with the electrical activity of the heart.  Hyperchloremia: Occurs in renal failure. Hypochloremia: The main cause is vomiting.

Hyper

and

Hypochloremia

is

almost

always

associated with other electrolyte abnormalities; like K+ or mainly Na+ and the manifestations of abnormal Na+ are the dominant scenario of hypochloremia . Describe the concept of a “Third Space” & list conditions that can cause fluid sequestration of this type: Third space is a term applied to the accumulation of bodily fluids in abnormal anatomical location which doesn’t participate in the normal physiology of the body. Example: in case of perforation of a viscous or presence of peritonitis.  A patient with intestinal obstruction so the fluids will accumulate in a segment of the intestine; this fluid in this segment won’t be involved in the normal exchange of body fluids (no excretion non absorption), this fluid is accumulated /sequestrated.  Once you have fluids outside the intestine in the free

abdominal cavity this is a third space (With pancreatitis, fluids may leak out into the peritoneal cavity).

 With severe burns, the body losses the skin so the fluids with proteins may pool in the burn site.

Third spacing is pathological, that body fluids may collect in a "third" body compartment that isn't normally filled with fluids. What are the sequences of third space?? If the lost fluid is pure water  the patient will be dehydrated, hypotensive, tachycardic and with dry skin. If the lost fluid is blood the patient will be hypotensive.

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