Pathophysoilogy of Diarrhea and Dehydration

Pathophysiology of Diarrhea and Dehydration

All diarrhea-causing agents interfere with the normal physiological functions of the gastro­intestinal tract. Some of these changes are brought about by direct action (invasion) and others indirectly through the production of toxins. Intestinal physiology. Disturbances in the transport mechanism of water are at the root of diarrhea. Since diarrhea fluid is derived mainly from the extracellular fluid space, its composition is closely similar to the composition of plasma water i.e. rich in sodium. potassium and chloride in the upper intestine which becomes further enriched by secretion of bicarbonate and potassium in the lower part of the intestine and colon. It may be mentioned here that normally small and large intestines handle over 9 liters of water each day from secretion and ingestions, whereas only about 200 ml of water is lost through stool. Diarrhea occurs wherever the secretions in the intestines, particularly the fluid entering the large intestine, exceed those of their absorptive capacities. A poorly absorbed but osmotically active substance, when ingested, may cause diarrhea due to increased solute load within the intestinal tract.




Mechanism of Diarrhea

    Abnormal or excessive secretion of water and electrolytes occurs whenever there is impaired absorption of sodium, by the villi of the small intestine while the secretion . of chloride in the small intestinal crypt Cells’ continues. Toxins from enterotoxigenic E. colt and, V. cholera produce the above action.

Rotavirus causes patchy destruction of small intestinal mucosal epithelium leading to diarrhea and loss of fluid and electrolytes. Consequences of diarrhea. The primary consequences of watery diarrhea are the loss of fluid and electrolytes (viz. sodium chloride, potassium, and bicarbonate) clinically known as dehydration. It is the main cause of death due to diarrhea, and therefore clinical recognition of different degrees of dehydration is of the utmost. importance in the management of acute diarrhea. The clinical signs of dehydration are restlessness, sunken eyes, an absence of tears, dry mouth, and going back of pinched skin slowly. The patient is thirsty and drinks eagerly, but in severe dehydration, he/she is lethargic and drinks poorly. Dehydration may be categorized into three groups: no dehydration, some (mild) dehydration, and severe dehydration. The average concentration of various fluids is given in Table.

Table-Electrolyte contents of plasma water. diarrhoeal stool, intravenous solution, and oral rehydration solution.

Average electrolyte content mmol/l-  Na+ K+ CI- HCO3 Plasma water 138 4.5 98 25 Cholera stool Adults 140 13 104 45 Children 100 25 90 30 Intravenous Solution 120 13 90 48 (Dhaka Solution)         Oral Rehydration 90 20 80 30 Solution        

It may be noticed that in cholera (and those due to toxigenic E. coli) diarrhea) secretions while. passing through the lower part of the intestine and colon acquires bicarbonate and potassium: The net result of a loss of bicarbonate from plasma is acidosis and loss of potassium is hypokalemia or low level of potassium in plasma. Acidosis causes deep and rapid breathing and hypokalemia causes_ weakness of muscles and partial paralysis of the’ intestine, both the symptoms are nearly always’ present in the severe watery diarrheal condition.





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Management and Treatment of Diarrhea

Until some 30 years ago, it was common to observe death in over 50% of cholera patients despite attempts to treat them. A dramatic breakthrough took place when the pathophysiology of diarrhea was investigated and a new approach to treatment was made. This took place in the middle of the 1950s and 1960s with a substantial contribution by -ICDDR, B.Intravenous therapy. It clearly explains the foundation of modern diarrhea therapy. The objective is to replace whatever has been lost by injecting the intravenous solution containing the missing electrolytes. This will result in the rapid restoration of fluid balance and return to the normal physiological status. Prompt use of the famous “Dhaka Solution” or a version of this, manufactured at the Institute of Public Health in Dhaka, called the ”Diarrhoea Treatment Solution” also restores physiological normalcy correcting dehydration, acidosis, and hypokalemia. During the last 40 years or so the solution has been used in scores of epidemics due to cholera with less than 1% mortality. The solution is equally effective in all other kinds of severe dehydration clue to diseases other than cholera.

Once the existing dehydration is corrected, maintenance of hydration status has to be continued `with. ORS solution till the end of diarrhea. In addition to the replacement of ongoing losses due to diarrhea, the normal daily fluid recOrenient of the body must also be considered.

Oral rehydration therapy. A search was made to replace expensive intravenous solutions for diarrhea therapy. A series of studies conducted at the Cholera Research Laboratory in Dhaka (now called the International Centre for Diarrhoeal Disease Research, Bangladesh—icddr,b) in the middle of 1960s showed that when electrolyte solution similar to the intravenous Dhaka Solution was administrated by oral route to patients with cholera, the solution simply passed through the intestine without being. absorbed. However, when glucose, was added up to a 3% level, a substantial amount of water and electrolytes were absorbed producing a net positive balance. The glucose component was considered to produce a partial reversal of the secretory process by enhancing the absorption of water and electrolytes. Ordinary sugar was also found to act as good as glucose but needed a higher concentration. since only the glucose portion acts after the breakdown of the sugars.

All cases of mild dehydration and most cases of moderate dehydration can be corrected with the ORS solution. Rehydration therapy. The following steps (or rehydration of acute watery diarrhea patient have been suggested byWHO:


Step I. Assess diarrhea for rehydration    

1  LOOK AT:           Condition Well, alert * Restless irritable Lethargic or  unconscious; floppy     Eyes Normal Sunken Very sunken and dry     Tears Present Absent Absent     Mouth and tongue Most Dry-Very dry-     Thirst Drinks normally, not normal Thirsty drink eagerly Drinks  poorly or not able to drink   2  FEEL: Skin pinch Goes back quickly Goes back slowly Goes back very slowly   3  DECIDE: Patient has NO signs of dehydration the patient  has two or more sign, including at least one sign, there is some dehydration If the patient  has two or more sign, including at least one sign, there is severe dehydration            

Step 2. Rehydrate the patient and reassess hydration status

For’ severe dehydration: For the patient, one year and older: IV fluid 30 11)1/kg within 30 ml/kg within 30 minutes; then 70 ml/kg in the next two and a half hours. For patients less than one year: IV fluid 30 ml/kg in the first hour; then 70 ml/kg in the next 5 hours. Give ORS (about 5 ml/kg/hour) as soon as the patient can drink.

Step 3. Maintenance of hydration until diarrhea stops.

Give ORS solution as indicated below:

Age               Amount of ORS solution after each loose stool <24 months   50-100 ml 2-9 years       100-200 ml >= 10 years    As much as wanted

Antibiotics in watery diarrhea

Except in cholera and dysentery due to shigella. antibiotics play almost no role in the management of diarrhea. It may be mentioned here that it takes nearly 36 hours (one and a half-day) for an effective antibiotic like tetracycline to reduce the purging in cholera; most other forms of enterotoxigenic watery diarrhea has only a short duration. Therefore, cholera should be only diarrhea where tetracycline may be recommended: in adults, 250 mg 6 hourly or 500 mg twice a day for 5 days. In tetracycline-resistant cases, trimethoprim­sulpharnethoxazole combination (Co-trimoxazole) should be used: 2 tablets twice a day for 5 days. Pregnant women and children should not receive tetracycline.


Feeding during Diarrhea

    Numerous studies have shown that digestive and absorptive processes continue at near-normal levels even during acute diarrhea. Only minor impairment may take place. Therefore, there is the consensus that the age-old belief, present even amongst the medical community that depriving food during diarrhea is like “giving rest” to the intestines, is no longer valid. It is a common practice now to give normal or easily digestible food to all patients suffering from diarrhea. A patient with diarrhea when given food. diarrhea lasts for a shorter period. As a matter of fact, once physiological normalcy is restored in sick diarrhea] patient by intravenous or ORS therapy the patient feels hungry and demands to be fed. Infants on breast must be sucked even during acute diarrhea and in between ORS therapy.



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