Fluid and Electrolytes

2. Fluid and Electrolytes F . Mamdouhi M . D Mashhad University of Medical Sciences

7. اسمولالیته:غلظت ذره یا ماده محلول در یک مایع • اسمولالیته طبیعی پلاسما:275-290 • اختلالات هموستاز آب: هیپوناترمی یا هیپرناترمی • اختلالات هموستاز سدیم :ادم یا هیپوولمی

8. The major ECF particles are Na+ and its accompanying anions Cl– and HCO3–. • The predominant ICF osmoles are K+ and organic phosphate esters (ATP, creatine phosphate, and phospholipids).

9. REGULATION OF PLASMA OSMOLALITY • The normal plasma osmolality (Posm ) is 280 to 295mosmol/kg. • It usually is held within narrow limits as variations of only 1 to 2 percent initiate mechanisms to return the Posm to normal. • These alterations in osmolality are sensed by receptor cells in the hypothalamus which affect water intake (via thirst) and water excretion (via ADH, which increases water reabsorption in the collecting tubules).

10. The osmolality of human body fluid is between 280 and 295 mosmol/kg and regulated by : • Vasopressin secretion • water ingestion, and • renal water transport.

11. Osmolality • Hypoosmolality and hyperosmolality can produce serious neurologic symptoms and death,primarily due to water movement into and out of the brain, respectively. • To prevent this, the plasma osmolality (Posm ), which is primarily determined by the plasma Na+ concentration, is normally maintained within narrow limits by appropriate variations in water intake and water excretion. • This regulatory system is governed by osmoreceptors in the hypothalamus that influence both thirst and the secretion of antidiuretic hormone (ADH).

12. Vasopressin (AVP) is synthesized in the hypothalamus. • the distal axons of those neurons project to the posterior pituitary or neurohypophysis, from which AVP is released into the circulation. • AVP has a half-life in the circulation of only 10–20 min.

13. AVP secretion is stimulated as systemic osmolality increases above a threshold level of 285mosmol/kg, • Thirstsensation and thus water ingestion also are activated at 285 mosmol/kg. • Changes in blood volume and blood pressure are also direct stimuli for AVP release and thirst.

15. osmoregulation is almost entirely mediated by changes in water balance

16. WATER BALANCE • Water intake  • Obligatory water output 

17. هیپوولمی

18. علل: • از دست دادناب ازطریق GI • از دست دادن اب از طریق کلیوی • از دست دادن اب از طریق پوست • سکستراسیون به فضای سوم

19. از دست دادن ازطریق :GI • استفراغ • NG tube • اسهال • فیستول

20. Gastrointestinal losses • Only small amounts of water are normally lost in the stool, averaging 100 to 200 mL/day. • However, gastrointestinal losses are increased to a variable degree in patients with vomiting or diarrhea. • The effect of these losses on the plasma Na+ concentration depends on the sum of the Na+ and K+ concentrations in the fluid that is lost.

21. از دست دادن از طریق کلیوی: • اتلاف کلیوی آب • دیابت بیمزه(مرکزی یا نفروژنیک) • اتلاف کلیوی آب و سدیم • دیورتیک • دیورز اسموتیک • هیپوآلدوسترونیسم • نفروپاتی از دست دهنده سدیم

22. obligatory renal water • The obligatory renal water loss is directly related to solute excretion. • If a subject has to excrete 800 mosmol of solute per day (mostly Na+ and K+ salts and urea) to remain in the steady state, and the maximum Uosm is 1200 mosmol/kg, then the excretion of the 800 mosmol will require a minimum urine volume of 670 mL/day.

23. از دست دادن از طریق پوست: • اتلاف نامحسوس • تعریق • سوختگی

24. Insensible losses • The evaporativelosses play an important role in thermoregulation; the heat required for evaporation, 0.58 kcal/1.0 mL of water, normally accounts for 20 to 25 percent of the heat lost from the body, with the remainder occurring by radiation and convection. • The net effect is the elimination of the heat produced by body metabolism, thereby preventing the development of hyperthermia.

25. Sensible loss • Sweat is a hypotonic fluid (Na+ concentration equals 30 to 65 meq/L) • It also contributes to thermoregulation, as the secretion and subsequent evaporation of sweat result in the loss of heat from the body. • In the basal state, sweat production is low, but it can increase markedly in the presence of high external temperatures or when endogenous heat production is enhanced, as with exercise, fever, or hyperthyroidism. • As an example, a subject exercising in a hot, dry climate can lose as much as 1500 mL/h as sweat

26. سکستراسیون به فضای سوم: • هیپوآلبومینمی • سیروز • سندرم نفروتیک • نشت مویرگی • پانکراتیت حاد • روده ایسکمیک • رابدومیولیز

27. علایم هیپوولمی: • خستگی پذیری-ضعف-کرامپ-تشنگی-گیجی • ایسکمی اعضای انتهایی:اولیگوری-سیانوز-درد شکم-آنژین قلبی-خواب آلودگی • کاهش تورگور پوستی-خشکی غشاهای مخاطی • کاهش فشار ورید ژوگولر-هیپوتانسیون وضعیتی-تاکیکاردی وضعیتی

28. تعادل سدیم

29. 85-90% سدیم در بخش خارج سلولی قرار دارد. • تغییرات غلظت سدیم منعکس کننده بر هم خوردن هموستاز اب است. • تغییرات مقدار تام سدیم به صورت کاهش یا افزایش حجم ECF تظاهر می یابد.

30. دریافت سدیم : 150میلی مول • دفع سدیم : بستگی به GFRو بازجذب توبولی دارد. • بازجذب سدیم : 3/2در لوله پروگزیمال – 25-30%در هنله- 5% توبول دیستال- بقیه در مجاری جمع کننده

31. هیپوناترمی

32. تعریف:سدیم کمتر از 135 • علل: 1-هیپوناترمی کاذب 2-هیپوناترمی هیپواسمولار

33. Hyponatremia • In almost all cases, hyponatremia results from the intake and subsequent retention of water. • A water load willbe rapidly excreted as the dilutional fall in plasma osmolality suppresses the release of antidiuretic hormone (ADH), thereby allowing the excretion of a dilute urine. • The maximum rate of water excretion on a regular diet is over 10 liters per day.

34. هیپوناترمی کاذب: 1-اسمولالیته نرمال: • هیپرلپیدمی • هیپرپروتئینمی • پروستاتکتومی 2-اسمولالیته بالا: • هیپرگلیسمی • مانیتول

35. Pseudohyponatremia • Is associated with a normal plasma osmolality, refers to those disorders in which marked elevations of substances, such as lipids and proteins, result in a reduction in the fraction of plasma that is water. • In normal subjects, the plasma water is approximately 93 percent of the plasma volume. • A normal plasma sodium concentration of 142 meq/L (measured per liter of plasma) actually represents a concentration in the physiologically important plasma water of 154 meq/L (142 ÷ 0.93 = 154).

36. Ion-selective electrodes have been used to directly measure the plasma water sodium concentration in this setting but have variable accuracy.

37. HYPONATREMIA WITH A HIGH PLASMA OSMOLALITY • Hyponatremia with a high plasma osmolality is most often due to hyperglycemia. • A less common cause is the administration and retention of hypertonicmannitol. • The rise in plasma osmolality induced by glucose or mannitolpulls water out of the cells, thereby lowering the plasma sodium concentration by dilution.

38. Physiologic calculations suggest that the plasma sodium concentration should fall by 1 meq/L for every 62 rmg/dLrise in the plasma concentration of glucose or mannitol (which have the same molecular weight). • The 1:62 ratio applied when the plasma glucose concentration was less than 400 mg/dL. • At higher glucose concentrations, the ratio of 1:42 provided a better estimate of this association than the usual 1:62 ratio

39. Normal Plasma Osmolality • Isosmotic hyponatremia can be produced by the addition of an isosmotic (or near isosmotic) but non-sodium-containing fluid to the extracellular space. • This problem primarily occurs with the use of nonconductive glycine or sorbitol flushing solutions during transurethral resection of the prostate or bladder or irrigation during laparoscopic surgery, since variable quantities of this solution are absorbed.

41. DISORDERS IN WHICH ADH LEVELS ARE ELEVATED • The two most common causes of hyponatremia are: • effective circulating volume depletion and • the syndrome of inappropriate ADH secretion, disorders in which ADH secretion is not suppressed.

42. Effective Circulating Volume Depletion • Significantly decreased tissue perfusion is a potent stimulus to ADH release. • This response is mediated by baroreceptors in the carotid sinusand can overcome the inhibitory effect of hyponatremia on ADH secretion.

43. Heart Failure and Cirrhosis • Even though the plasma volume may be markedly increased in these disorders, the pressure sensed at the carotid sinus baroreceptors is reduced due to the fall in cardiac output in heart failure and to peripheral vasodilatation in cirrhosis. • The rise in ADH levels tend to vary with the severity of the disease, making the development of hyponatremia an important prognostic sign.

44. Syndrome of Inappropriate ADH Secretion • Persistent ADH release and water retention can also be seen in a variety of disorders that are not associated with hypovolemia. • These patients have a stable plasma sodium concentration between 125 and 135 meq/L.

45. Hormonal Changes • Hyponatremia can occur in patients with adrenal insufficiency (in which it is lack of cortisol that is responsible for the hyponatremia) and with hypothyroidism. • The release of HCG during pregnancy may be responsible for the mild resetting of the osmostat downward, leading to a fall in the plasma sodium concentration of about 5 meq/L.

46. DISORDERS IN WHICH ADH LEVELS MAY BE APPROPRIATELY SUPPRESSED • There are two disorders in which hyponatremia can occur despite suppression of ADH release: • advanced renal failure • primary polydipsia

47. Advanced Renal Failure • The relative ability to excrete free water (free water excretion divided by the glomerular filtration rate) is maintained in patients with mild to moderate renal failure. • Thus, normonatremia is usually maintained in the absence of oliguria or advanced renal failure.

48. Advanced Renal Failure • In the latter setting, the minimum urine osmolality rises to as high as 200 to 250 mosmol/kg despite the appropriate suppression of ADH. • The osmotic diuresis induced by increased solute excretion per functioning nephron is thought to be responsible for the inability to dilute the urine.

49. Primary Polydipsia • Is a disorder in which there is a primary stimulation of thirst. • It is most often seen in anxiousand in patients with psychiatric illnesses, particularly those taking antipsychotic drugs in whom the common side effect of a dry mouth leads to increased water intake. • Polydipsia can also occur with hypothalamic lesions (as with infiltrative diseases such as sarcoidosis) which directly affect the thirst centers

50. Primary Polydipsia • The plasma sodium concentration is usually normal or only slightly reduced in primary polydipsia, since the excess water is readily excreted. • These patients may feel asymptomatic or may present with complaints of polydipsia and polyuria. • In rare caseswater intake exceeds 10 to 15 L/day and fatal hyponatremia may ensue.