1、水电解质平衡失调的处理水电解质平衡失调的处理Department of Surgery2002.9lThe surgical patient is liable to develop numerous disorders of body fluid volume and composition, some of which may be iatrogenic. Understanding the physiological mechanisms that regulate the composition and volume of the body fluids and the princip
2、les of fluid and electrolyte therapy is therefore essential for patient management. Body water & its distribution lTotal body water (45-60% body weight)l Intracellular (ICF) 2/3(40%bw) Extracellular (ECF)1/3l Plasma 25%(5%bw) Interstitial fluid75%(15%bw) Body water & its distributionComposition ECF
3、ICFl Electrolyte = l Proteins l (Albumin Colloid osmotic pressure)lIons of body fluidlCation sodium Na+ potassium K+ l magnesium Mg2+ l Anion chloride Cl- organic phosphate P3l bicarbonate HCO3- proteins lby kidneys:l(1) filtration and reabsorption of sodium, which adjusts urinary sodium excretion t
4、o match changes in dietary intake l(2) regulation of water excretion in response to changes in secretion of antidiuretic hormone. lto keep the volume and osmolality of body fluid constant within a few percentage points despite wide variations in intake of salt and water. A corollary is that analysis
5、 of the composition. l(1) filtration and reabsorption of sodium, which adjusts urinary sodium excretion to match changes in dietary intake l(2) regulation of water excretion in response to changes in secretion of antidiuretic hormone. These two mechanisms allow the kidneys to keep the volume and osm
6、olality of body fluid constant within a few percentage points despite wide variations in intake of salt and water. A corollary is that analysis of the composition. lThe stability of fluid (hypothalmus-posterior pituitary-antidiuretic hormone system) and electrolytes (rennin- aldosterone) is regulate
7、d by neuroendocrine system. lIn normal human body, when H+ concentration or pH7.35-7.45 is maintained, normal physiometabolic function can be carry out.lDuring body metabolism, producing acid and base , H+ concentration often changes.l Relative steady state is maintained by buffer system of body flu
8、id, lung and kidney. lHCO3- and H2CO3 is the most important buffer system. When HCO3- / H2CO3 =20/1 palsma pH keeps normal. lLung excretes CO2 regulatesPCO2 and H2CO3 concentration. lLung functional disturbance causes acid-base imbalance and fail to regulate acid base balance. lKidney can excrete fi
9、xed acid and excess alkaline material. Abnormality of renal function can not regulate acid base balance and cause acid base imbalance.lKidney regulates acid-base imbalance by 1) H+ and Na+ exchange 2) HCO3- reabsorption 3) Excreting NH3+ H+ NH4 4) Excreting H+(acidification of urine) lVolume disturb
10、ance (isotonic dehydration)lConcentration (hypotonic or hypertonic dehydration)lComposition (hypokalemia or hyperkalemia, hypocalcemia or hypercalcemia etc) lWater and sodium have close interrelationship. Water deficit and sodium deficit are certainly concomitant in surgical practice. lBut the defic
11、it proportion may be different. According to different deficit proportion, water deficit may be divided into three types: Isotonic water deficit (dehydration) Hypotonic water deficit Hypertonic water deficit lAcute water deficit or mixed water deficit most often occur in surgical patientslProportion
12、 of water and sodium deficit is equal in plasma lNo change in ECF osmolality and ICF volumelStimulation of rennin- aldosterone and aldosterone increaseCommon causesAcute gastrointestinal losses: vomiting, enteric fistulas, nasogastric suction, enterostomiesFluid into infected area or peritoneal cavi
13、ty: peritoneal or retroperitoneal infection, intestinal obstruction, burns and so on.Clinical manifestation lnausea, anorexia, weakness, Urine decrease, without severe thirst. lDry tongue, sunken eye, dry skin, and decreased elasticity of skin. lfluid loss 5% of body weight or 20% extracellular flui
14、d causes small and rapid pulse, moist cooling extremity, unstable or decreased blood pressure. l6-7% of body weight (30-35% of extracellular fluid) causes severe shock often with acidosis.lIf much gastric juice loss, with metabolic alkalosis. Diagnosis lHistory: alimentary fluid or other fluid lossl
15、Clinical manifestationlLaboratory exam. Increase of RBC, HCT and Hb Sodium and chloride in plasma is normal. Increase of urine specific gravity. Artery blood gas analysis may show acidosis. Treatment lRemove causeslReplenish blood volume by balanced salt fluid or isotonic saline. lIf pulse increase,
16、 blood pressure decrease 5% of body weight fluid loss, give 3000ml solution.l If no manifestation of decreased blood volume, give 1/2-2/3 namely 1500-2000ml or of calculated volume.lDaily requirement should be given. Two kinds of balanced salt fluidsl 1.86% sodium lactate + Ringers solution (compoun
17、d sodium chloride), ratio is 1:2.l (2)1.25% sodium bicarbonate + isotonic saline, ratio is 1:2. Isotonic saline l Contains 154mmol/L Na+ and 154mml/L Cl-, but serum 142mmo1/L Na+ and 103mmo1/L C1-.l In isotonic saline, Cl- concentration is 50mmo1/L higher than that in serum.l If give much isotonic s
18、aline without normal renal function can cause hyperchloremic acidosis.l Giving balanced salt fluid is better for treating isotonic water deficit. After correcting dehydrationl Potassium excretion increases, fluid replenishment makes potassium concentration decrease, so we must pay attention to hypop
19、otassemia.l If urine is more than 40m1/h, give potassium lIt is also called chronic water deficit or secondary water deficit. lSodium deficit is more than water deficit. lExtracellular fluid is at lower osmotic pressure.lBlood volume severely decreases and causes shock called hyponatrimia shock. lan
20、tidiuretic hormone decrease and urine increase, ECF ostolality increaseCauseslContinual loss of gastrointestinal juice: repeated vomiting, gastrointestinal suction long timelChronic exudation from major wound arealExcess excretion sodium from kidney, (some diuretics without sodium placement)lIsotoni
21、c dehydration with more water placement Clinical manifestationlWithout thirst. Nausea, vomiting, giddiness, visual disturbance, weakness, rapid small pulse, and orthostatic hypotension (giddiness, faint).l Blood volume falls obviously and renal filtration decreases. There are metabolic product reten
22、tion, mental obtundation, unconsciousness, muscle spasm pain, decreased tendon reflexes and coma. Mild sodium deficit lThere are fatigue (lassitude), giddiness and numbness of the extremities, lSodium in urine falls. lSerum sodium is less than 135mmo1/L. Sodium loss is about 0.5g/kg. Moderate sodium
23、 deficitlAbove mentioned symptoms lNausea, vomiting, rapid small pulse, unstable blood pressure or decreased, lower pulse pressure, collapsed superficial vein, vague vision and orthostatic faint. lUrine volume falls. There are no sodium and chloride in urine.l Serum sodium is less than 130mmol/L. 0.
24、5-0.75g/kg sodium is lost Severe sodium deficitlThere are unconsciousness, muscle spasm pain, decreased tendon reflexes or negativelstupor, coma and shock.lSerum sodium is less than 120mmo1/L, about 0.75-1.25g/kg sodium is lost. Diagnosisl Historyl Clinical manifestation l Na+ and Cl- in urine fall,
25、 spgr1.010l Serum sodium is less than 135mmo1/L.l RBC, Hb (hemoglobin) and Hct (hematocrit) increase.l NPN (non-protein nitrogen), and BUN (blood urea nitrogen) increase. TreatmentlRemove causes lhypertonic saline infusionlMethod Na=(142PNa) TBWSodium(mmol)=normal serum sodium value (142mmol/L)-exam
26、ined sodium value (mmol/L) body weight(kg)0.60 (female 0.5) Treatmentl17mmol Na+=lg sodium saltlReplenish 1/2 of calculated volume plus daily requirement 4.5glFor 2/3 of calculated volume, give 5% sodium chloride. For the rest, give isotonic salinel Later infusion according to Na+, K+, Cl- and arter
27、y blood gas analysisTreatmentlCrystal (Ringers solution, Saline, balanced salt solution) and Colloid (plasma, albumin, dextran) togetherlvolume of crystal used is as 2-3 times as colloidlSodium deficit with acidosis may disappear. If acidosis still exists, give 1.25% sodium bicarbonate 100-200ml or
28、balanced salt solution 200ml. lIf urine output is more than 40ml/h, give potassium. l Primary water deficitl Water deficit is more than sodium deficitl Extracellular fluid is at hyperosmotic statelCompensation Thirst drinkAntidiuretin urineAldosterone secretion Causes 少进多出少进多出lWater intake decreases
29、 such as dysphagia in esophageal cancer. lNot Give enough water for severe patient. lInfusion of hypertonic saline and nasogastric tube feeding with hypertonic food. lMuch water loses such as high fever or perspiration, burn with exposure therapy, diabetes Clinical manifestation lMild hypertonic wat
30、er deficit. Thirst. Water deficit is 2-4% of body weight.lModerate hypertonic deficit Fatigue, lower urine output, dry tongue, decreased elasticity of skin, sunken eye, and restlessness. Water deficit is 4-6% of body weight.lSevere hypertonic water deficit. Above mentioned symptoms plus mania, hallu
31、cination, delirium even coma. These cerebral symptoms are due to water deficit of cerebral cells. Water loss is more than 6% of body weight. Diagnosisl Historyl Clinical manifestation Laboratory exams Increased urine specific gravity RBC, Hb and Hct increase. Serum sodium is more than 150mmol/L Trea
32、tment Remove causes Intravenous infusion of 5%glucose or 0.4%sodium chloride. Estimation of replenished fluid volume:lA. Per 1% loss of body weight, give 100-500ml.lB. Calculation according to Na+ concentrationlWater (ml)=examined serum sodium volume (mmol/L)-normal serum value (mmol/L) kg(body weig
33、ht) 4. lReplenish 1/2 of calculated volume + daily requirement (2000ml).lIf urine is more than 40ml/h, give potassium. lIf there is acidosis, give sodium bicarbonate. lECF constitutes only 2% of total body potassium; the remaining 98%is within body cells.lThe serum potassium concentration is determi
34、ned by the pH of ECF and the size of the ICF K+ pool. lWith extracellular acidosis, a large proportion of the excess hydrogen is buffered intracellularly by an exchange of intracellular K+ for extracellular H+; this movement of K+ may produce hyperkalemia. lAlkalosis has an opposite effect: as the p
35、H rises, K+ moves into cells.l Hypokalemia and hyperkalemia CauseslNot enough intake of potassium lDiuretics make kidney excrete potassium.lPatient having infusion without potassium, iv. nutrition without enough potassium.lVomiting, persistent gastrointestinal suction, fast or bowel fistula. lShift
36、into cells in alkalosisClinical manifestationlMuscle weakness is the earliest manifestation, first extremities, then trunk, respiratory, sometimes dyspnea, even choke and cough at eating and drinking, negative or decreasing of tendon reflexes and flaccid paralysis.lNausea vomiting, bowel paralysis.l
37、Impaired heart, abnormality of conducing and rhythm .ECG: Lower and broad T wave with double summit or inversion, depression of ST segment, lengthening QT interval, U wave appearance. Some patients are without abnormal ECG. Clinical manifestationlSevere patients have diuresis because hypokalemia can
38、 block secretion of ADH.lAt serum hypopotassium state, exchange 2Na+ and 1H+ in ECF for 3K+ in ICF, H+ in ECF decreases, which causes alkalosis.lWhen K+ in ECF decreases, excretion of K+ decreases while excretion of H+ increases in distal involuted tubule. As a result, the urine is acidic for alkalo
39、sis patient, which is called unusual acid urine. DiagnosislHistorylClinical manifestationlDecreased serum potassium3.5 mmol/LlECG accessory diagnostic methodTreatmentlRemove causeslGive K+ l13.4mmol K+=1glInfusion speed 20mmol/h, 100-200mmol/dl40mllComplete correction needs long time, oral intake Se
40、rum K+ 5.5mmol/LCauseslOral intake, infusion, blood transfusionlPoor renal function e.g. acute renal failure, K+ retention diuretics (antisterone), poor adrenal cortical functionlAbnormal K+ distribution (acidosis , crush injury, haemolysis) Clinical manifestationlNausea and vomiting, colicky abdomi
41、nal pain and diarrhealCirculatory disturbance, pale, cooling and bluish, hypotension, slower heart rate and/or arrhythmia, even stopslECG: peaking of the T waves, prolonged QT interval, widening of the QRS complex, depression of the ST segment DiagnosislCauses lClinical manifestationlECGlSerum K+ 5.
42、5mmol/L Treatment Stop giving potassium Decrease serum K+ concentrationA. Make K+ into cellsa) 60-100 ml of 5% NaHCO3 iv. to increase volume , dilute potassium, correct acidosis, K+ goes into cells, Na antagonize K+ b) 25-50% glucose + RI (1u/3-4g glucose) 100-200 ml ivc) For renal insufficiency: 10
43、% calcium gluconate 100ml + 11.2% sodium lactate 50ml + 25% glucose 400ml + RI 30u iv for 24h at 6drops/min. TreatmentB. Cation exchange resin, orally or by enema, 50-80g/d, binding K+ in intestine to exchange with Na+, with oral sorbital to induce diarrhia and enhance K+ removalC. Dialysis: peritoneal dialysis or hemodialysis Anti-arrhythmia: 10% calcium gluconate 20ml iv injection
