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medyokaloka-blog · 7 years

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THE BODY FLUID COMPARTMENTS: ECF AND ICF; EDEMA

Homeostasis – maintenance

WATER IS ADDED TO THE BODY BY 2 MAJOR SOURCES:

· Form of liquids or water in food (which add about 2100 ml/day)

· Synthesized in the body by oxidation of CHO (which add about 200 ml/day)

2300 ml/day – total water intake

INTAKE OF WATER IS HIGHLY VARIABLE DEPENDING ON:

· Climate

· Habits

· Level of physical activity

Insensible water loss – not consciously aware of it

700 ml/day – evaporation from the respiratory tract and diffusion through the skin

300 to 400 ml/day – average water loss by diffusion through the skin (loss is minimized by the cholesterol-filled cornified layer of the skin) is also the same with diffusion through the respiratory tract

3 to 5 L/day – rate of evaporation in those who have extensive burns

As air enters the respiratory tract, it becomes saturated with moisture, to a vapor pressure of about 47 mmHg, before it is expelled.

<47 mmHg – vapor pressure of inspired air

Decreases to nearly 0 – in cold weather (this explains why there’s a dry feeling in the respiratory passages in cold weather)

100 ml/day – fluid loss in sweat

Increases to 1 to 2 L/hour – in very hot weather or during heavy exercise (this fluid loss would rapidly deplete the body fluids if intake were not also increased by activating the thirst mechanism)

100 ml/day – water loss in feces

The remaining water loss from the body occurs in the urine.

0.5 L/day – urine volume in a dehydrated person

20 L/day – in a person who has been drinking tremendous amounts of water

20 mEq/day to 300 or 500 mEq/day – sodium intake

If you’re a medical student or a doctor, and you’re reading this…you know what are the 2 body fluid compartments right? ECF and ICF. Yeah, right it’s written as the title.

ECF IS DIVIDED INTO:

· Interstitial fluid

· Blood plasma

Transcellular fluid – another small compartment of fluid that is usually considered to be a specialized type of ECF (it constitute about 1 to 2 L)

In a 70-kg adult man, the total body water is about 60% or about 42 L of the body weight.

PERCENTAGE DEPENDS ON:

· Age

· Gender

· Degree of obesity

50% of the body weight – women

70 to 75% of the body weight – premature and newborn babies

28 of the 42 L (40%) – ICF

14 of the 42 L (20%) – ECF

11 L (3/4) – interstitial fluid

3 L (1/4) – plasma

They both have the same composition except for proteins which have a higher concentration in the plasma.

Blood – considered to be a separate fluid compartment because it is contained in a chamber of its own, the circulatory system (The average blood volume of adults is about 7% of body weight, or about 5 L. 60%of the blood is plasma and 40% is RBCs.)

Hematocrit – packed RBC volume

3 to 4% - plasma that is entrapped among the cells

96% - true hematocrit

0.40 – NV for men

0.36 – women

0.10 – severe anemia (barely sufficient to sustain life)

0.65 – those who have polycythemia

I honestly don’t know what’s the definition for the Donnan Effect. I guess (based on my understanding) it just speaks of how opposite charges attract. :) (Please correct me if I’m wrong.)

The concentration of cations is slightly greater in the plasma than in the interstitial fluid. The plasma proteins have a net negative charge and therefore tend to bind cations, thus holding extra amounts of these cations in the plasma along with the plasma proteins.

Conversely, anions tend to have a slightly higher concentration in the interstitial fluid compared with the plasma, because the negative charges of the plasma proteins repel the anions.

CATIONS FOUND IN THE ECF:

· Na+

· Ca++

ANIONS FOUND IN THE ECF:

· Cl-

· HCO3

CATIONS FOUND IN THE ICF:

· K+

· Mg++

ANIONS FOUND IN THE ICF:

· PO4 and organic ions

· CHON

MEASUREMENT OF TOTAL BODY WATER:

· Radioactive water (tritium, 3H2O)

· Heavy water (deuterium, 2H2O)

Antipyrine – a very lipid soluble used also to measure total body water

MEASUREMENT OF ECF VOLUME:

· Radioactive sodium

· Radioactive chloride

· Radioactive iothalamate

· Thiosulfate ion

· Inulin

Sodium space or the inulin space

CALCULATION OF INTRACELLULAR VOLUME: Total body water – Extracellular volume

MEASUREMENT OF PLASMA VOLUME:

· 125I-albumin

· Evans blue dye (T-1824)

CALCULATION OF INTERSTITIAL FLUID VOLUME: ECF volume – Plasma volume

MEASUREMENT OF BLOOD VOLUME: Plasma volume / (1 – Hematocrit)

51Cr – a substance frequently used to label the RBCs

Osmolality – osmoles per kg of water

Osmolarity – osmoles per L of solution

ISOTONIC SOLUTIONS:

· 0.9% NaCl

· 5% glucose

HYPOTONIC SOLUTION: <0.9% NaCl (swells)

HYPERTONIC SOLUTION: >0.9% NaCl (shrinks)

Fluid usually enters the body through the gut. It usually takes 30 minutes to achieve osmotic equilibrium everywhere in the body after drinking water.

DIFFERENT FACTORS THAT CAN CAUSE EXTRACELLULAR AND INTRACELLULAR VOLUMES TO CHANGE MARKEDLY:

· Excess ingestion or renal retention of water

· Dehydration

· IV infusion of different types of solutions

· Loss of large amounts of fluid from the GI tract

· Loss of abnormal amounts of fluid by sweating or through the kidneys

Glucose solutions – are widely used in administering nutritive purposes (5% is often used to treat dehydration…well except for dehydration which have other causes like bacterial diarrhea)

Homogenized fat solutions – used to a lesser extent

Plasma sodium concentration – measurement that is readily available to the clinician for evaluating a patient’s fluid status (Why? You should probably know the answer. You’re a doctor after all!)

Hyponatremia – mEq < 142

Hypernatremia – otherwise

CAUSES OF HYPONATREMIA:

· Excess water (CONDITION THAT CAN CAUSE THIS: excessive secretion of ADH which could lead to hyponatremia – overhydration)

· Loss of sodium (CONDITIONS THAT CAN CAUSE THIS: diarrhea, vomiting, overuse of diuretics, Addison’s disease from decreased secretion of aldosterone which impairs the kidney to reabsorb sodium)

PRIMARY LOSS OF NaCl RESULTS IN:

· Hyponatremia

· Dehydration

Cell swelling – consequence of hyponatremia (DUH!)

RAPID REDUCTION IN PLASMA SODIUM CONCENTRATION:

· Brain cell edema

· Neurological symptoms (headache, nausea, lethargy, disorientation)

FALLS BELOW 115 TO 120 mmol/L:

· Seizures

· Coma

· Permanent brain damage

· Death

Glutamate (find out what is this for)

Demyelination – loss of the myelin sheath from nerves when hypertonic solutions are added too rapidly to correct hyponatremia (AVOIDED BY LIMITING THE CORRECTION: <10 to 12 mmol/L in 24 hours, <18mmol/L in 48 hours)

Hyponatremia (oh boy, this came out in our Surgery exam) – most common electrolyte disorder encountered in clinical practice and may occur in up to 15% to 25% of hospitalized patients

CAUSES OF HYPERNATREMIA:

· Water loss

· Excess sodium (hypernatremia-overhydration by excessive secretion of aldosterone)

Increased aldosterone secretion – stimulates the secretion of ADH and the reason why hypernatremia is not more severe

PRIMARY LOSS OF WATER:

· Hypernatremia

· Dehydration – more common cause of hypernatremia associated with decreased ECF volume

“Central” diabetes insipidus – inability to secrete ADH so the kidneys excrete large amounts of dilute urine causing dehydration and increased concentration of NaCl in the ECF

“Nephrogenic” diabetes insipidus – kidneys cannot respond to ADH

Cell shrinkage – consequence of hypernatremia

HYPERNATREMIA PROMOTES:

· Intense thirst

· Stimulates secretion of ADH

SEVERE HYPERNATREMIA CAN OCCUR IN:

· Hypothalamic lesions that impair the sense of thirst

· Infants who may not have ready access to water

· Elderly patients with altered mental status

· Persons with diabetes insipidus

CORRECTION OF HYPERNATREMIA:

· Hypo-osmotic NaCl

· Dextrose solutions

Edema – presence of excess fluid in the body tissues; occurs mainly in the ECF compartment

CONDITIONS ESPECIALLY PRONE TO CAUSE INTRACELLULAR SWELLING:

· Hyponatremia

· Depression of the metabolic systems of the tissues

· Lack of adequate nutrition to the cells

Inflammation – usually increases cell membrane permeability

CONDITIONS ESPECIALLY PRONE TO CAUSE EXTRACELLULAR EDEMA:

· Abnormal leakage of fluid from the plasma to the interstitial spaces across the capillaries

· Failure of the lymphatics to return fluid from the interstitium back into the blood (lymphedema)

Excessive capillary fluid filtration – most common clinical cause of interstitial fluid accumulation

FACTORS THAT CAN INCREASE CAPILLARY FILTRATION:

· Increased capillary filtration coefficient

· Increased capillary hydrostatic pressure

· Decreased plasma colloid osmotic pressure

Rise in CHON concentration – raises the colloid osmotic pressure of the interstitial fluid

SUMMARY OF CAUSES OF EXTRACELLULAR EDEMA:

I Increased capillary pressure

A. Excessive kidney retention of salt and water (acute or chronic kidney failure, mineralocorticoid excess)

B. High venous pressure and venous constriction (heart failure, venous obstruction, failure of venous pumps: paralysis of muscles, immobilization of parts of the body, failure of venous valves)

C. Decreased arteriolar resistance (excessive body heat, insufficiency of sympathetic nervous system, vasodilator drugs)

II Decreased plasma proteins

A. Loss of proteins in urine (nephrotic syndrome)

B. Loss of protein from denuded skin areas (burns, wounds)

C. Failure to produce proteins (liver disease, serious protein or caloric malnutrition)

III Increased capillary permeability

A. Immune reactions that cause release of histamine and other immune products

B. Toxins

C. Bacterial infections

D. Vitamin deficiency, especially vitamin C

E. Prolonged ischemia

F. Burns

IV Blockage of lymph return

A. Cancer

B. Infections

C. Surgery

D. Congenital absence or abnormality of lymphatic vessels

Heart failure – one of the most serious and common causes of edema; arterial pressure tends to fall causing decreased excretion of salt and water; blood flow to the kidneys is reduced

Renin – cause increased formation of angiotensin II and increased secretion of aldosterone, both of which cause additional salt and water retention by the kidneys

Left-sided heart failure – blood is pumped into the lungs normally by the right side of the heart but cannot escape easily from the pulmonary veins to the left side of the heart; can cause death within a few hours

MAIN EFFECTS OF LARGE AMOUNTS OF NaCl AND WATER ARE ADDED TO THE ECF:

· Widespread increases in interstitial fluid volume

· Hypertension

Acute glomerulonephritis – renal glomeruli are injured by inflammation and therefore fail to filter adequate amounts of fluid, serious ECF fluid edema also develops; along with the edema, severe hypertension usually develops

Cirrhosis – development of large amounts of fibrous tissue among the liver parenchymal cells

Liver cirrhosis – sometimes compresses the abdominal portal venous drainage vessels as they pass through the liver before emptying back into the general circulation

Ascites – a condition of transudation of large amounts of fluid and protein into the abdominal cavity

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medyokaloka-blog · 7 years

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PULMONARY EMBOLISM

A 57-year-old man Ganni is admitted to the hospital because of acute shortness of breath shortly after a 12-hour automobile ride. Findings on PE are normal except of tachypnea and tachycardia. He does not have edema or popliteal tenderness. An ECG reveals sinus tachycardia but is otherwise normal. Which of the following statements is correct?

a. A normal D-dimer level excludes pulmonary embolus.

b. If there is no contraindication to anticoagulation, full-dose heparin or enoxaparin should be started pending further testing.

c. Normal findings on examination of the lower extremities make pulmonary emoblism unlikely.

d. Early treatment of pulmonary embolism has little effect on overall mortality.

e. A normal lower extremity venous Doppler study will rule out a pulmonary embolus.

ANSWER: B. If there is no contraindication to anticoagulation, full-dose heparin or enoxaparin should be started pending further testing.

The clinical situation strongly suggests pulmonary embolism. In greater than 80% of cases, pulmonary emboli arise from thrombosis in the deep venous circulation (DVT) of the lower extremities, but a normal lower extremity Doppler does not exclude the diagnosis. DVTs often begin in the calf, where they rarely if ever cause clinically significant pulmonary embolic disease.

However, thromboses that begin below the knee frequently “grow”, or propagate, above the knee; clots that dislodge from above the knee cause clinically significant pulmonary emboli. Untreated pulmonary embolism is associated with a 30% mortality rate. Interestingly, only about 50% of patients with DVT of the lower extremities have clinical findings of swelling, warmth, erythema, pain, or palpable “cord”.

When a clot does dislodge from the deep venous system and travels into the pulmonary vasculature, the most common clinical findings are tachypnea and tachycardia; chest pain is less likely and usually indicates pulmonary infarction.

The ABG (arterial blood gas) is usually abnormal, and a high percentage of patients exhibit low pCO2 with respiratory alkalosis, and a widening of the alveolar-arterial oxygen gradient. The ECG usually shows sinus tachycardia, but atrial fibrillation, pseudoinfarction in the inferior leads, and acute right heart strain are also seen. Initial treatment for suspected pulmonary embolic disease includes prompt hospitalization and institution of IV heparin or therapeutic dose SQ LMW-heparin. It is particularly important to make an early diagnosis of pulmonary embolus, as intervention can decrease the mortality rate from 30% down to 5%. A normal D-dimer level helps exclude pulmonary embolus in the low-risk setting. This patient, however, has a high pretest probability of PE; further testing (CT pulmonary angiogram, V/Q lung scan) must be done to exclude this important diagnosis.

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