Acid-Base disturbances Physiological approach

Transcription

1 AcidBase disturbances Physiological approach Pieter Roel Tuinman, M.D., PhD, intensivist Department of Intensive Care, VU Medical Center, Amsterdam, The Netherlands

2 Content Introduction Regulation of acidbase balance Diagnosis of acidbase disturbances Examples

3 AcidBase balance definition: BronstedLowry (1923) Homeostasis Physiologic effects of ph on protein function normal A:B ratio 1:20 strength is defined in terms of the tendency to donate (or accept) the hydrogen ion to (from) the solvent (i.e. water in biological systems)

4 Relation ph and H + ph H + nanomol/l 7, , , , ,00 100

5 HendersonHasselbalch equation 0.03 PCO 2 H + = 800 x HCO 3 H + + HCO 3 K d = CO 2 disolved HCO 3 ph = log CO 2 disolved Metabolic by kidneys Respiratory by lungs

6 ph ph is and indirect measure of [H + ] CAVE! Hydrogen ions (i.e. protons) do not exist free in solution but are linked to adjacent water molecules by hydrogen bonds (H 3 O + ) [H + ] by a factor of 2 causes a ph of 0.3 normal plasma ph ph 7.4 ( ) normal Acidosis <7.35 ph 7.45> alkalosis Range compatible with life (H nm)

7 Acidbase disturbances Why of interest? Frequently encountered Are (first) sign of illness Can be used to diagnose the disease Require early treatment

8 Examples of diseases resulting in acidbase disturbance CZS: CVA, bleeding, trauma Circulation: hypotension, myocardial infarction Respiratory: COPD, asthma. Renal: acute / chronic kidney injury Tr dig: vomiting, chronic diarrhea. Liver: acute / chronic liverfailure

9 H + regulation Chemical buffering Control of PCO₂ Control of plasma HCO 3

10 Regulation of acidbase balance How? Dilution (distribution) Chemical buffering (intra and extracellular) Regulation of CO 2 concentration (respiratory) Regulation of H + and HCO 3 concentration (metabolic)

11 Acid excretion Lungs mol volatile acid/day (2 4 liter concentrated HCL) Kidneys 80 mmol/l nonvolatile, sulfate, phosphate, urineacid, citrate, ammoniumsalts. x 1000 times more acid trough lungs than kidneys

12 Respiratory system CO 2 differences in the stimulation of respiration by pco 2, H + and po 2 alveolar ventilation disturbances acidemia respiratory centre of the brain alveolar ventilation CO 2 alkalemia respiratory centre of the brain alveolar ventilation CO 2

13 Respiratory regulation Influence of ph on breathing Daily CO 2 production : mmol/day H + chemoreceptors medulla oblongata ph alveolar ventilation /Minute volume ph alveolar ventilation /Minute volume

14 Renal regulation Serum ph Urine ph = netto HCO 3 excretion Serum ph Urine ph = netto H + excretion

15 Regulation kidney in summary serum ph HCO 3 resorption H + secretion Urine buffers = Netto base loss serum ph HCO 3 resorption H + secretion = Netto acid loss Urine buffers

16 Quantative rules (see Berend et al. NEJM) Compensation of acidbase disturbance is bound by quantative rules Are this rules disregarded, than there is a mixedacidbase disturbance Over or undercompensation does not exist

17 Rules in general HCO 3 ( nier ) ph =pk + log CO 2 ( long ) Definition acidbase distubance ph, PCO 2 en HCO 3 Compensation is usually not complete ph < 7.35 acidosis ph > 7.45 alkalosis Inadequate compensation Mixed disturbance Direction compensation the same HCO 3 / CO 2 ratio.

18 Assessment of AB balance Arterial blood Mixed venous blood range range ph ph pco 40 mmhg pco po 2 95 mmhg po Saturation 95 % Saturation BE 2 BE HCO 3 24 meq/l HCO

19 Disorders of AB balance Acidosis: abnormal condition lowering arterial ph Alkalosis: abnormal condition raising arterial ph Homeostatic response predictable Simple AB disorders: there is a single primary aetiological acidbase disorder Mixed AB disorders: more primary aetiological disorders are present simultaneously

20 Causes Respiratory abnormal processes which tend to alter ph because of a primary change in pco 2 levels acidosis alkalosis Metabolic abnormal processes which tend to alter ph because of a primary change in [HCO 3 ] acidosis alkalosis

21 Stepwise approach 1. History 2. Look at the ph 3. Look at PCO2 and HCO3 4. In metabolic acidosis: what is anion gap? 5. With high AG: deltaratio? 6. Normal AG: calculate urine AG 7. Is compensation adequate? 8. In respiratory process: acute or chronic?

22 Metabolic acidosis (MA) primary disorder is a ph due to HCO 3 : fixed [H + ] = high anion gap loss or reabsorption of HCO 3 = normal anion gap Anion Gap

23 Use and limitations of Anion Gap [Na + ] [Cl ][HCO³ ] Calculate the excess of unmeasured anions Range 812 mm/l Correction for albumin (alb 1 g/l> 2.5 AG)

24 High Anion Gap Acidosis Berend K, et al. NEJM 2014 (oct): 371:15

25 Normal Anion Gap Acidosis Berend K, et al. NEJM 2014 (oct): 371:15

26 Primary acidbase disturbances Disturbance Compensation Classification ph HCO 3 PCO 2 metabolic acidosis with respiratory compensation PCO 2 HCO 3 respiratory acidosis with metabolic compensation ph HCO 3 PCO 2 metabolic alkalosis with respiratory compensation PCO 2 HCO 3 respiratory alkalosis with metabolic compensation

27 Diagnosis mixed acidbase disturbances There is a discrepancy between real and expected compensation compensation CO 2 : extra acidosis CO 2 : extra alkalosis compensation HCO 3 : extra alkalosis HCO 3 : extra acidosis

28 Berend K, et al. NEJM 2014 (oct): 371:15

29 Case 1 44 yr man dehydrated with sever diarrhea. ph 7.31/33/bic 16/93 Na 134/K 2.9/Cl 108/Cr 150/Ur 25 What is the acid base disorder?

30 Answer 1.Based on history: normal AG because of diarrhea or elevated AG because of lactic acidosis due to hypovolemia 2.Look at ph 3.Look at the process (HCO3 and PCO2) 4.Calculate the AG: =10 5.Compensation adequate PCO2= 1.5 x bic +8 (+/2)= 3034 C/ Normal AG acidosis with adequate compensation, most likely due to diarrhea

31 Case 2 22 yr female with DM1, N/V+, polyuria, abnormal breathing ph 7.27/23/bic 10 Na 132/K 6/Cl 93/gluc 36/Cr 200 What is acidbase disorder?

32 Answer 1.History: elevated AG because of DKA or lactic acidosis secondary to hypovolemia due to vomiting and polyuria; metabolic alkalosis due to vomiting 2.Look at the ph 3.What is the primary process (bic/pco2)? 4.Calculate AG=28 5.Is compensation adequate? = ± 2 = C/ High AG metabolic acidosis due to diabetic ketoacidosis

33 Case 3 70 yr man, with history of CHF, increased dyspnoe and leg swelling ph 7.24/60/bic 27/ 52 What is acidbase disorder?

34 Answer 1.History acute respiratory acidosis due to acute pulmonary edema 2.Look at ph 3.What is process? (PCO2/bic)? 4.Acute/chronic? 6040=20/10=2 +24=26 (is almost bic 27) so acute respiratory acidosis C/ Acute respiratory acidosis secondary to pulmonary edema

35 Questions? m/welcome.html