Fluid and Electrolyte Balance


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1 : Fluid and Electrolyte Balance Dr Michael Hadjigavriel Department of Nephrology and dialysis – Larnaca GH
2 : Water Balance In: food, drink, metabolism, etc Out: urine, feces, breathing, skin, etc
3 : kidneys They regulate excretion of water. They conserve water concentrating urine (compared to plasma) They excrete water diluting urine (compared to plasma)
4 : Water excretion Regulated by ADH (antidiuretic hormone) secreted by the hypothalamus Works through the reabsorption of water through the tubular cells of the collecting ducts
5 : ADH ADH excretion is influenced by: Receptors in the hypothalamous sensitive to plasma osmolarity (if osmolarity rises >ADH) Stretch receptors in the heart atrium sensitive to increased blood return (if increased blood return ADH)
6 : Osmolarity(amount of solute per unit volume) Kidneys regulate total volume but also osmolarity of body fluids Extreme variations in osmolarity make cells shrink or swell and damage their functions Regulation of osmolarity is correlated to regulation of volume because changes in water volume have diluting or concentrating effects on body fluids
7 : Example 1 Dehydration > reduced water in the body> Increased Na > increased osmolarity of body fluids > increased ADH excretion > Increased water reabsorbtion
8 : Example 2 Reduced blood from trauma or surgery (the looses of Na and water are proportionate to the composition of body fluids so, the body must conserve both water and Na) > increased ADH > increased water reabsorption> increased body water. In order to prevent osmolarity from decreasing below normal > increased aldosterone > increased reabsorption of Na in distal tubule
9 : Aldosterone Produced from Adrenal cortex Secretion controlled by: receptors on adrenal cortex that sense plasma osmolarity receptors on kidney that sense low blood pressure
10 : Example 3 If osmolarity increases > decreased secretion of Aldosterone > decreased reabsorption of Na in distal tubule And at the same time Increased ADH secretion > conserve water EFFECT: decreased urine excretion increased urine osmolarity
11 : Example 4 Low BP > reduced filtration rate > stimulation of Juxtaglomerular apparatus (in the afferent arterioles) >increased renin production > renin/angiotensin mechanism > Angiotensin II > increased production of aldosterone
12 : To remember Body attempting to conserve volume: Increases ADH production >increased water reabsorption Increases Aldosterone production >increased plasma Na EFFECT: Fluid retention (Isosmolar to plasma) Reduced urine output (of lower osmolarity)
13 : Fluid and electrolyte balance is extremely important and complicated
14 : It is important because: We need to take a decision regarding fluids in almost every hospitalized patient. Fluid administration can save lives in certain conditions. Acute or chronic loss of body water may cause a range of problems from mild headache, to dizziness, to convulsions, to coma and in some cases to death. Fluid administration can be very harmful if not done properly.
15 : Kinds of IV Fluid solutions Hypotonic -½NS (0.45%) Isotonic -NS (0.9%), albumin Hypertonic - Hypertonic saline (3%). 2 categories: Crystalloid Colloid
16 : Crystalloid vs ColloidType of particles (large or small) Fluids with small “crystalizable” particles like NaCl are called crystalloids Fluids with large particles like albumin are called colloids because they don’t pass quickly through the vascular pores and they stay “stick” longer in the circulation. Much smaller amounts of colloids can be used for same volume expansion: 250ml Albumin = 4 lt NS For the same reason edema resulting from colloids tends to stay longer. Albumin can cause severe allergic reactions.
17 : Fluid therapy Fluid therapy can be divided into 2 components: Maintenance therapy which replaces the normal ongoing losses Replacement therapy which corrects water and electrolyte deficits.
18 : 1st PartMaintenance therapy Is usually undertaken when a patient is not expected to eat or drink normally for some time (perioperatively or on a ventilator). Note: Patients who won’t eat for one to two weeks should be considered for parenteral nutrition. Maintenance therapy
19 : Maintenance Requirements Maintenance Requirements: water electrolytes Maintenance therapy
20 : Water In eating patients (adults) Most of the necessary water derives from the water content of food and from the water of oxidation It has been estimated that only 500ml of water is necessary to be given in normal diet patients without increased losses. These sources of are markedly reduced in patients who are not eating and so water must be replaced by maintenance fluids. Maintenance therapy
21 : Water Requirements water requirements increase with: fever, sweating, burns, tachypnea, surgical drains, polyuria, significant gastrointestinal losses,etc. Example: water requirements increase by 100 to 150 ml/day for each °C degree of elevation in body temperature. Maintenance therapy
22 : Several formulas can be used to calculate maintenance fluid rates. Maintenance therapy
23 : To remember Different formulas produce a variety of fluid recommendations Fluid needs, no matter what formula is used, are at best an estimation. Maintenance therapy
24 : 4/2/1 rule (Weight in Kg + 40) Better 4/2/1 rule because it is the same in adults and children over 20 kg of bw. Top Limit: 120 ml/hr Maintenance therapy
25 : 4/2/1 rule 4 ml/kg/hr for first 10 kg (=40ml/hr) then 2 ml/kg/hr for next 10 kg (=20ml/hr) then 1 ml/kg/hr for any kgs over that This always gives 60ml/hr for first 20 kgthen you add 1 ml/kg/hr for each kg over 20 kg This results in: Weight in kg + 40 = Maintenance IV rate/hour. (For any person weighing more than 20kg) Maintenance therapy
26 : What to put in the fluids Maintenance therapy
27 : Start: D5% ½NS+20 meq Kcl/lt @ rate: Wt+40/hr a reasonable approach is to start ½ normal saline to which 20 meq of potassium chloride is added per liter (½NS+20 Meq Kcl/lt). Glucose in the form of dextrose (D5%) can be added to provide some calories while the patient is NPO. So,start: D5% ½NS+20 meq Kcl/lt at a rate equal to their weight + 40ml/hr, but not greater than 120ml/hr. then adjust as needed. Maintenance therapy
28 : Start D5% ½NS+20 meq Kcl/lt, then adjust: If sodium falls, increase the concentration (to NS) If sodium rises, decrease the concentration (to ¼NS) If the plasma potassium falls add more potassium. If the plasma potassium rises add less potassium. If things are good, leave as they are. Maintenance therapy
29 : Usually kidneys regulate well, but: in the Hospital there is altered homeostasis In Hospital: Usually stress, pain and surgery can alter the normal mechanisms: Increased Aldosterone, Increased ADH Water and salt retention Increase tendency to edema Hypokalemia. Maintenance therapy
30 : 2nd part:Replacement therapy Hypovolemia or Fluid Volume Deficit (FVD) is a result of water and electrolyte loss Compensatory mechanisms include: Increased sympathetic nervous system stimulation with an increase in heart rate & cardiac contraction Increased thirst Increased release of ADH & Aldosterone Severe condition may result in hypovolemic shock and prolonged condition may cause acute renal failure Replacement therapy
31 : Causes of FVD (hypovolemia) Gastrointestinal losses: vomit,diarrhea Renal losses: diuretics Skin losses: burns Respiratory losses: tachypnea Third-spacing: intestinal obstruction, pancreatitis Replacement therapy
32 : To remember Hypovolemia: A variety of disorders may lead to fluid losses that deplete the extracellular space. This can lead to a potentially fatal decrease in tissue perfusion. Fortunately, early diagnosis and treatment can restore normovolemia in almost all cases. Replacement therapy
33 : Hypovolemia and Hypovolemic shock There is no easy formula for assessing the degree of hypovolemia. Hypovolemic Shock, the most severe form of hypolemia, is characterized by tachycardia, cold clammy extremities, cyanosis, a low urine output (usually less than 15 ml/h), and agitation and confusion due to reduced cerebral blood flow. This needs rapid treatment with isotonic fluid boluses (1-2lt NS), and assessment and treatment of the underlying cause. But hypovolemia that is less severe and therefore well compensated is more difficult to accurately assess. Replacement therapy
34 : History for assessing Hypovolemia The history can help to determine the presence and etiology of volume depletion. Weight loss Early complaints include lassitude, easy fatiquability, thirst, muscle cramps, and postural dizziness. More severe fluid loss can lead to abdominal pain, chest pain, or lethargy and confusion due to ischemia of the mesenteric, coronary, or cerebral vascular beds, respectively. Nausea and malaise are the earliest findings of hyponatremia, and may be seen when the plasma sodium concentration falls below 125 to 130 meq/lt. This may be followed by headache, lethargy, obtundation and in more severe cases by lethargy, confusion, seizures, and coma. Replacement therapy
35 : Basic signs of Hypovolemia Urine output (less than 30ml/hr) Hypotension Increased pulse Replacement therapy
36 : Physical examination for assessing volume The physical exam generally is not sensitive or specific Acute weight loss Decreased skin turgor - if you pinch it stays up Dry skin, particularly axilla Dry mucus membranes Low arterial blood pressure (relative to patient's usual BP) Orthostatic hypotension (can occur with significant hypovolemia). It is also common in normovolemic elderly patients. Decreased intensity of both the Korotkoff sounds (when the blood pressure is being measured with a sphygmomanometer) and the radial pulse ("thready") due to peripheral vasoconstriction. decreased Jugular Venous Pressure The normal venous pressure is 1 to 8 cmH2O and a low value alone may be normal and does not establish the diagnosis of hypovolemia. Replacement therapy
37 : Lab findings of Hypovolemia a variety of changes in urine and blood often accompany extracellular volume depletion. In addition to confirming the presence of volume depletion, these changes may provide important clues to the etiology. Replacement therapy
38 : BUN/Cr BUN/Cr ratio normally around 10 Increase above 20 is suggestive for “prerenal azotemia” which means that the pathologic process is unlikely to be due to intrinsic kidney damage. rise in BUN without rise in Cr might be a response to a relative decrease of blood flow to the kidney (as seen in heart failure or dehydration, hypovolemia) Replacement therapy
39 : Hgb/Hct Acute loss of EC fluid causes hemoconcentration (if not due to blood loss) Acute gain of EC fluid causes hemodilution Replacement therapy
40 : Plasma Na Decrease in Intravascular volume leads to greater avidity for Na (through Aldosterone) and water (through ADH), Plasma Na concentration tends to decrease from 140 mmol/l when hypovolemia is present. Replacement therapy
41 : Urine Na Urine Na decreases in “prerenal state” as body tries to hold on to water. Lasix gives false results Replacement therapy
42 : Basic Signs of Fluid Volume Excess (FVE) Orthopnea Edema & weight gain Distended neck veins & tachycardia Increased blood pressure Crackles & wheezes pleural effusion
43 : Thank you

 

Add as Friend By : Dr. Michael Hadjigavriel - Tansplant Nphrologist,
Added On : 4 Years ago.
Step by step practical quide to treating water and electrolyte abnormalities in the hospitalized pa    more
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