內(nèi)科學(xué)課件：33 酸堿平衡

1、 Acid production in the body Carbonic acid: the metabolism of carbohydrates and fats (primarily derived from the diet) results in the production of approximately 15,000 mmol of CO2 per day. Non-carbonic acid: Organic: lactate, metabolized by the liver and kidney Inorganic : the metabolism of protein

2、s and other substances results in the generation of noncarbonic acids (50 100 mEq, 1mEq/kg). Methionine glucose + urea + SO4(2-) + 2 H+ Arginine+ glucose (or CO2) + urea + H+ R-H2PO4 + H2O ROH + 0.8 HPO42- / 0.2 H2PO4- + 1.8 H+ 機(jī)體對(duì)酸負(fù)荷的反應(yīng) The homeostatic response to acid load 1. Chemical buffering by

3、 the extracellular and intracellular buffers. 2. Changes in alveolar ventilation to control the PCO2. 3. Alterations in renal H+ excretion to regulate the plasma HCO3- concentration. Chemical buffering Extracellular buffers Intracelluar: bone Henderson-Hasselbalch equation (Eq. 1) H+ + HCO3- H2CO3 H

4、2O + CO2 PCO2 (Eq. 2) H+ = 24 x HCO3- or by the Henderson-Hasselbalch equation HCO3- (Eq. 3) pH = 6.10 + log 0.03 PCO2 Henderson-Hasselbalch equation (Eq. 1) H+ + HCO3- H2CO3 H2O + CO2 PCO2 (Eq. 2) H+ = 24 x HCO3- or by the Henderson-Hasselbalch equation HCO3- (Eq. 3) pH = 6.10 + log 0.03 PCO2 Acido

5、sis: PCO2=1.5 X HCO3 + 8 Chemical buffering Extracellular buffers Intracelluar buffer: bone, Ca+ release, osteoclast activation The homeostatic response to acid load 1. Chemical buffering by the extracellular and intracellular buffers. 2. Changes in alveolar ventilation to control the PCO2. 3. Alter

6、ations in renal H+ excretion to regulate the plasma HCO3- concentration. The homeostatic response to acid load 1. Chemical buffering by the extracellular and intracellular buffers. 2. Changes in alveolar ventilation to control the PCO2. 3. Alterations in renal H+ excretion to regulate the plasma HCO

7、3- concentration. RENAL HYDROGEN EXCRETION (1) reabsorption of the filtered HCO3- (2) excretion of the 50 to 100 meq of H+ produced per day 1.Formation of titratable acid 2.Excretion of NH4+ in the urine Collecting tubuleTubular LumenPeritubular capillary H+ H2O2 OH- + CO23HCO3- CA H+ Cl- ATPase ATP

8、ase H+ K+ Excretion of H+ in a intercalated cells H+ H+ Collecting tubuleTubular LumenPeritubular capillary H+ H2O2 OH- + CO23HCO3- CA H+HPO42- H2PO4 Cl- ATPase ATPase H+ K+ Excretion of H+ in a intercalated cells Collecting tubuleTubular LumenPeritubular capillary H+ H2O2 OH- + CO23HCO3- CA H+ + NH

9、3 NH4+ Cl- H+-ATPase NH3 Excretion of H+ in a intercalated cells Can be stimulated by low K Acid-base balance The kidneys must excrete the 50 to 100 meq of noncarbonic acid generated each day. The daily acid load is excreted as NH4+ and H2(PO4). The daily acid load also cannot be excreted unless vir

10、tually all of the filtered HCO3- has been reabsorbed, because HCO3- loss in the urine is equivalent to adding H+ ions to the body. Regulation: The extracellular pH the effective circulating volume, aldosterone, and the plasma K+ concentration Can be independent of serum pH 酸堿測(cè)定指標(biāo) pH PaCO2 標(biāo)準(zhǔn)碳酸氫鹽 實(shí)際碳

11、酸氫鹽 緩沖堿 堿剩余、堿缺乏 CO2CP AG Anion Gap AG=Na+-Cl-HCO3- = 122 albumin: negative charged. Low serum albumin will reduce AG. Paraprotein (Ig or light chains, MM): positive charged. Presence of large amount of paraprotein reduces AG. Metabolic acidosis Influx of organic acid into plasma (high anion gap) Ket

12、oacidosis Lactic acidosis Poisoning Accumulation of endogenous acids (high anion gap) Renal failure External losses of bicarbonate (normal anion gap; hyperchloremic). GI loss Renal loss Anion Gap Renal failure With mild to moderate reductions in GFR, the acidosis reflects decreased ammoniagenesis an

13、d is therefore hyperchloremic. As kidney failure worsens, the kidney loses its ability to excrete various anions, and the accumulation of sulfate, phosphate, and other anions, produces an elevated AG. Renal failure Despite a daily net positive acid balance, it is unusual for HCO3to fall lower than 1

14、5 mmol/L. The buffering of protons by bone results in loss of calcium and a negative calcium balance. Chronic acidosis causes protein breakdown, muscle wasting, and a negative nitrogen balance. Maintenance of the acid-base balance close to normal can prevent these consequences Treatment Alkali repla

15、cement NaHCO3 Sodium citrate Causes: Renal loss of alkali RTA GI loss of alkali Reciprocal changes in Cl and HCO3 result in normal AG In the absence of such a relationship suggests a mixed disturbance Diarrhea Metabolic acidosis Metabolic acidosis and hypokalemia increase renal synthesis and excreti

16、on of NH4+, thus urinary pH is around 6 Urinary NH4 levels are high: urine anion gap is negative Proximal RTA (type 2) The threshold for HCO3- reabsorption in the proximal tubule is lower (normal: 26 -28 mmol/l). The distal nephron has a low capacity for HCO3 reabsorption. In the steady state, the s

17、erum HCO3 concentration usually is 16 18 mmol/l, when all the filtered HCO3 is reabsorbed. Despite systemic acidemia development, the urine pH is alkaline. However under steady state, the urine can be acidified to a pH of less than 5.5. HCO3 HCO3 HCO3 Proximal RTA (type 2) The threshold for HCO3- re

18、absorption in the proximal tubule is lower (normal: 26 -28 mmol/l). In the steady state, the serum HCO3 concentration usually is 16 18 mmol/l, when all the filtered HCO3 is reabsorbed. Despite systemic acidemia, the urine pH is alkaline. However under steady state, the urine can be acidified to a pH

19、 of less than 5.5. Proximal RTA: hypokalemia Increased distal Na+ delivery (NaHCO3) Increased aldosterone levels (dehydration because of loss of Na in the urine). Treatment of acidosis with HCO3 improves the acidosis but worsens the degree of hypokalemia. Causes of Proximal RTA Inherited pRTA: NBCe1

20、/SLC4A4) mutation, accompanied by ocular abnormalities such as cataracts, glaucoma. Carbonic anhydrase inhibitor: acetazolamide Fanconi syndrome: inherited and acquired Adult with Fanconi: dysproteinemic condition such as multiple myeloma dRTA (type 1) HCO3 HCO3 HCO3 dRTA Hyperchloremic acidosis Kid

21、ney stone Hypokalemia Sjogren syndrome dRTA: kidney stone Urinary calcium excretion is high Acidosis induced bone mineral dissolution Low intraluminal concentration of HCO3- because of acidosis Urinary citrate levels are low citrate serve as the major Ca+ chelator in the urine High urine pH decrease

22、 the solubility of calcium phosphate complexes. dRTA Primary: idiopathic or inherited (SLC4A1 mutation) Systemic disease: Sjogren syndrome dRTA-diagnosis NH4Cl Furosemide + mineralocorticoid (fludrocortisone) Type 4 RTA Renal function compromised Hyporeninemic hypoaldosteronism Hyperkalemia Urinary

23、ammonium excretion depressed Metabolic Alkalosis An elevated arterial pH An increase in the serum HCO3- and a increase in PCO2 Often accompanied by hypochloremia and hypokalemia Pathogenesis Generative stage: loss of acid Maintenance stage: volume contraction, a low GFR or depletion of Cl or K Diffe

24、rential diagnosis Mineralocorticoid excess Bartters or Gitelmans Diuretics Gastrointenstinal HCO3 retention + volume contraction Renal origin Diuretics Nonreaborbable anions and magnesium deficiency Potassium depletion After treatment of lactic acidosis or ketoacidosis posthypercapnia Mineralocortic

25、oid administration or excess production Related electrolyte abnormalities: hypokalemia 治療原則 治療原發(fā)病 糾正容量、低血鉀 補(bǔ)酸 Respiratory acidosis Severe pulmonary disease, respiratory muscle fatigue or abnormalities in ventilatory control Acute: immediate compensatory elevation in HCO3, which increases 1 mmol/L fo

26、r every 10 mmHg increase in pCO2 Chronic (24h): renal adaptation increases the HCO3 by 4 mmol/L Clinical features The clinical feature varies according to Severity and duration Underlying disease Whether there is hypoxemia A rapid increase in pCO2: anxiety, dyspnea, confusion coma Chronic hypercapne

27、a: sleep disturbances, loss of memory, . Treatment Acute respiratory acidosis can be life-threatening, measures to reverse the underlying cause should be undertaken simultaneously with restoration of adequate alveolar ventilation Chronic respiratory acidosis Improving lung function Respiratory alkalosis Alveolar hyperventilation decreases PaCO2 and increases the HCO3/PCO2 病因 中樞性 非低氧性：癔癥、腦外傷、藥物、溫度過高、肝性 腦病、酸中毒 低氧因素：高原、肺部疾病、供血不足 外源性：呼吸機(jī)管理不當(dāng)、胸廓腹部手術(shù)、呼 吸道阻塞突然解除 The effect of respiratory alkalosis vary according to duration and severity but are primarily those of the