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DEFINITIONS acidemia/alkalemia –an abnormal pH acidosis/alkalosis –a process that if uncompensated would lead to an abnormal pH.

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Presentation on theme: "DEFINITIONS acidemia/alkalemia –an abnormal pH acidosis/alkalosis –a process that if uncompensated would lead to an abnormal pH."— Presentation transcript:

1 DEFINITIONS acidemia/alkalemia –an abnormal pH acidosis/alkalosis –a process that if uncompensated would lead to an abnormal pH

2 HENDESON-HASSELBACH H + = 24 pCO 2 HCO 3 H + = 24lungs kidney H + =

3 HENDERSON-HASSELBACH H + of 40nmol = pH of 7.4 for each 0.1 increase in pH multiply normal H + x 0.8 for each 0.1 decrease in pH multiply normal H + x 1.25

4 EXPECTED COMPENSATION metabolic acidosis - 1 HCO 3 / 1 pCO 2 metabolic alkalosis - variable resp. acidosis –acute1 HCO 3 / 10 pCO 2 –chronic3-4 HCO 3 / 10 pCO 2 resp. alkalosis –acute2-3 HCO 3 / 10 pCO 2 –chronic5 HCO 3 / 10 pCO 2

5 ACID-BASE COMPENSATION ALKALOSES pH 7.4 ACIDOSES METABOLIC CHANGESRESPIRATORY CHANGES DECREASE pCO 2 INCREASE p CO 2 INCREASE HCO 3 DECREASE HCO 3

6 THE ANION GAP [Na] - (Cl + HCO 3 ) Na Cl HCO 3 albumin Anion gap

7 ANION GAP METABOLIC ACIDOSIS ketoacidosis lactic acidosis uremic acidosis intoxications –ASA –methanol –ethylene glycol –paraldehyde

8 ASSESSMENT OF ACID-BASE DISTURBANCES Arterial pH < 7.35 Acidemia> 7.45 Alkalemia Hx & Px Check pH Check pCO 2 and HCO 3 Expected compensation ACUTE CHRONIC Check Anion Gap Na-(Cl+HCO 3 ) Possible Diagnoses Low HCO3 Metabolic Acidosis High pCO 2 Respiratory Acidosis High HCO3 Metabolic Alkalosis Low pCO 2 Respiratory Alkalosis 1 HCO 3 : 1 pCO 2 10 Pco 2 :1 HCO 3 10 Pco 2 :3 HCO 3 1 HCO 3 : 0.5 pCO 2 10 Pco 2 :2 HCO 3 10 Pco 2 :5 HCO 3 =12-16>16 HCO3 Loss R.T.A. Diarrhea Ketoacidosis Lactic Acidosis Renal Failure Intoxications ASA Methanol Ethylene Glycol COPD Drugs-CNS/Resp Depressants May be increased due to increased negative charge of proteins NormotensiveHypertensive Urine Cl < 10 Vomiting Post-hypercapneia > 10 Diuretics Conns Cushings Renal Artery Stenosis Drugs High Altitude ASA Pregnancy Sepsis

9 ANION GAP - METABOLIC ACIDOSIS H + gaining acidoses –the H + is buffered by HCO 3 - so this is consumption of bicarbonate and a fall in plasma HCO 3 This process converts strong acids to weak acids –H 2 So 4 + NaHCO 3 NaHSO 4 + H 2 CO 3

10 ANION GAP METABOLIC ACIDOSES The consumption of bicarbonate by combining with a cation is electrically neutral and thus the Cl concentration stays normal as the bicarbonate falls and thus the anion gap [Na-(Cl+HCO 3 )] increases

11 NON-ANION GAP METABOLIC ACIDOSIS renal tubular acidosis diarrhea hyperailementation

12 ASSESSMENT OF ACID-BASE DISTURBANCES Arterial pH < 7.35 Acidemia> 7.45 Alkalemia Hx & Px Check pH Check pCO 2 and HCO 3 Expected compensation ACUTE CHRONIC Check Anion Gap Na-(Cl+HCO 3 ) Possible Diagnoses Low HCO3 Metabolic Acidosis High pCO 2 Respiratory Acidosis High HCO3 Metabolic Alkalosis Low pCO 2 Respiratory Alkalosis 1 HCO 3 : 1 pCO 2 10 Pco 2 :1 HCO 3 10 Pco 2 :3 HCO 3 1 HCO 3 : 0.5 pCO 2 10 Pco 2 :2 HCO 3 10 Pco 2 :5 HCO 3 =12-16>16 HCO3 Loss R.T.A. Diarrhea Ketoacidosis Lactic Acidosis Renal Failure Intoxication's ASA Methanol Ethylene Glycol COPD Drugs-CNS/Resp Depressants May be increased due to increased negative charge of proteins NormotensiveHypertensive Urine Cl < 10 Vomiting Post-hypercapneia > 10 Diuretics Conns Cushings Renal Artery Stenosis Drugs High Altitude ASA Pregnancy Sepsis

13 NON-ANION GAP MATABOLIC ACIDOSES These are HCO 3 losing type metabolic acidoses The loss of HCO 3 by the lower GI tract or the kidneys results in the need for increased Cl reabsorption to maintain electroneutrality Thus as HCO 3 falls, Cl increases and the anion gap [Na-(Cl+HCO 3 )] stays normal

14 RENAL TUBULAR ACIDOSIS Renal loss of HCO 3 –PCT a decrease in the tubular maximum for HCO 3 reabsorption –DCT a failure to be able to secrete H +

15 BICARBONATE RECLAMATION (PCT) NaHCO 3 URINE H 2 CO 3 pCO 2 + H 2 O CO 2 + H 2 O CA H 2 CO 3 HCO 3 H+H+ CA = Carbonic Anhydrase CA Na HCO 3

16 BICARBONATE REGENERATION(DCT) NaHPO 4 URINE CO 2 + H 2 O CA H 2 CO 3 HCO 3 H+H+ CA = Carbonic Anhydrase Na HCO 3 NaHSO 4 H 2 PO 4 H 2 SO 4 NH 3 NH 4 +

17 METABOLIC ALKALOSIS vomiting post-hypercapneic diuretics Bartters syndrome

18 ASSESSMENT OF ACID-BASE DISTURBANCES Arterial pH < 7.35 Acidemia> 7.45 Alkalemia Hx & Px Check pH Check pCO 2 and HCO 3 Expected compensation ACUTE CHRONIC Check Anion Gap Na-(Cl+HCO 3 ) Possible Diagnoses Low HCO3 Metabolic Acidosis High pCO 2 Respiratory Acidosis High HCO3 Metabolic Alkalosis Low pCO 2 Respiratory Alkalosis 1 HCO 3 : 1 pCO 2 10 Pco 2 :1 HCO 3 10 Pco 2 :3 HCO 3 1 HCO 3 : 0.5 pCO 2 10 Pco 2 :2 HCO 3 10 Pco 2 :5 HCO 3 =12-16>16 HCO3 Loss R.T.A. Diarrhea Ketoacidosis Lactic Acidosis Renal Failure Intoxications ASA Methanol Ethylene Glycol COPD Drugs-CNS/Resp Depressants May be increased due to increased negative charge of proteins NormotensiveHypertensive Urine Cl < 10 Vomiting Post-hypercapneia > 10 Diuretics Conns Cushings Renal Artery Stenosis Drugs High Altitude ASA Pregnancy Sepsis

19 VOMITING Lose NaCl Lose HCl Lose volume this loss of acid generates the metabolic alkalosis ECF volume contraction also leads to secondary hyperaldosteronism

20 VOMITING Renal reaction volume contraction leads to avid Na reabsorption –NaCl first with elimination of Cl from urine –Na-H exchange but alkalosis means not much H available –Na-K exchange but loss of K limits this –thus NaHCO 3 absorption which perpetuates the alkalosis

21 METABOLIC ALKALOSIS- POST HYPERCAPNEIA The primary problem is respiratory acidosis with the increased pCO 2 leading to increased HCO 3 to compensate If the pCO 2 is suddenly normalized (e.g. by a respirator) the HCO 3 is now in excess and there is a metabolic alkalosis. This metabolic alkalosis is called post-hypercapneic metabolic alkalosis

22 METABOLIC ALKALOSIS- POST HYPERCAPNEIA The kidney takes time to get rid of the excess HCO 3 and if the patient is volume contracted the kidney may not be able to get rid of the HCO 3 because it is avid for Na reabsorption.

23 RESPIRATORY ACIDOSIS Alveolar hypoventilation –Acute airway obstruction, drugs, CNS disease 1 mEq/l increase HCO 3 /10 mmHg pCO 2 –Chronic (>72 hr.) COPD, CNS disease 3-4 mEq/l increase HCO 3 /10 mmHg pCO 2

24 ASSESSMENT OF ACID-BASE DISTURBANCES Arterial pH < 7.35 Acidemia> 7.45 Alkalemia Hx & Px Check pH Check pCO 2 and HCO 3 Expected compensation ACUTE CHRONIC Check Anion Gap Na-(Cl+HCO 3 ) Possible Diagnoses Low HCO3 Metabolic Acidosis High pCO 2 Respiratory Acidosis High HCO3 Metabolic Alkalosis Low pCO 2 Respiratory Alkalosis 1 HCO 3 : 1 pCO 2 10 Pco 2 :1 HCO 3 10 Pco 2 :3 HCO 3 1 HCO 3 : 0.5 pCO 2 10 Pco 2 :2 HCO 3 10 Pco 2 :5 HCO 3 =12-16>16 HCO3 Loss R.T.A. Diarrhea Ketoacidosis Lactic Acidosis Renal Failure Intoxications ASA Methanol Ethylene Glycol COPD Drugs-CNS/Resp Depressants May be increased due to increased negative charge of proteins NormotensiveHypertensive Urine Cl < 10 Vomiting Post-hypercapneia > 10 Diuretics Conns Cushings Renal Artery Stenosis Drugs High Altitude ASA Pregnancy Sepsis

25 RESPIRATORY ALKALOSIS Alveolar Hyperventilation –Acute drugs, sepsis, CNS disease 2 mEq/l decrease HCO 3 /10 mmHg pCO 2 –Chronic altitude, pregnancy, liver disease, CNS disease 5 mEq/l decrease HCO 3 /10 mmHg pCO 2

26 ASSESSMENT OF ACID-BASE DISTURBANCES Arterial pH < 7.35 Acidemia> 7.45 Alkalemia Hx & Px Check pH Check pCO 2 and HCO 3 Expected compensation ACUTE CHRONIC Check Anion Gap Na-(Cl+HCO 3 ) Possible Diagnoses Low HCO3 Metabolic Acidosis High pCO 2 Respiratory Acidosis High HCO3 Metabolic Alkalosis Low pCO 2 Respiratory Alkalosis 1 HCO 3 : 1 pCO 2 10 Pco 2 :1 HCO 3 10 Pco 2 :3 HCO 3 1 HCO 3 : 0.5 pCO 2 10 Pco 2 :2 HCO 3 10 Pco 2 :5 HCO 3 =12-16>16 HCO3 Loss R.T.A. Diarrhea Ketoacidosis Lactic Acidosis Renal Failure Intoxications ASA Methanol Ethylene Glycol COPD Drugs-CNS/Resp Depressants May be increased due to increased negative charge of proteins NormotensiveHypertensive Urine Cl < 10 Vomiting Post-hypercapneia > 10 Diuretics Conns Cushings Renal Artery Stenosis Drugs High Altitude ASA Pregnancy Sepsis

27 ACID-BASE


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