Biochemistry of acid-base disorders. Alice Skoumalová

Transcription

1 Biochemistry of acid-base disorders Alice Skoumalová

2 Main topics of the lecture: Measurement of acid-base dysbalance Classification of the acid-base disorders 4 basic acid-base disorders and their compensaiton Combined acid-base disorders Ions and acid-base disorders

3 Measured and calculated values of acid-base disorders Measured: ph, pco 2, po 2, saturation of hemoglobin Calculated: Actual bicarbonate The amount of HCO 3 - in 1 liter of blood saturated with oxygen under actual conditions (p a CO 2 and temperature) Standard bicarbonate The amount of HCO 3 - in 1 liter of blood saturated with oxygen at p a CO kpa and temperature 37 C Base excess The amount of bases in mmol (at p a CO 2 5,3 kpa and temperature 37 C) that would have to be added to the blood to titrate it to ph 7.4 ph 7.40 ± 0.04 p a CO ± 0.5 kpa p a O kpa Actual HCO ± 2 mmol/l Standard HCO ± 2 mmol/l Base excess (BE) 0 ± 2.5 mmol/l Saturation of hemoglobin (S a O 2 )

4 Classification of the acid-base disorders: Acidosis: a process leading to the accumulation of H + in the body Alkalosis: a process leading to a decrease in H + concentration in the body Two components of acid-base balance: respiratory, metabolic acute stage x compensated four main disorders x mixed acidemia x acidosis alkalemia x alkalosis

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6 The maintenance of ph: Correction of the acid-base disorders: Buffer reactions Compensations - Corrections processes in which one system compensates the alteration of the other one

7 Diagram of Henderson-Hasselbalch equation showing compensations for acid-base disorders:

8 Metabolic acidosis (MAc): 1. Increased production of H + : -lactasidosis (hypoxia, intensive muscular work, ethanol) -ketoacidosis (starvation, diabetes) -acid retention (renal failure) 2. Exogenous intake of H + : - methanol, ethylene glycol intoxication, salicylate poisoning 3. Loss of HCO 3- : -diarrhoea, burns, renal tubular disorders, diuretics 4. Increase Cl - or phosphate: - administration of NH 4 Cl, diuretics, renal disorders 5. Relative dilution of HCO 3- : -excessive infusion of isotonic solutions

9 physiological acute compensation -lungs -hyperventilation [HCO 3- ] 24 mmol/l pco 2 5,3 kpa N [HCO 3- ]/[H 2 CO 3 +CO 2 ] 20 : 1 < 20 : 1 20 : 1 ph 7,34 7,44 < 7,34 7,4

10 Metabolic alkalosis 1. Loss of Cl - : - vomiting, gastric lavage, diuretics 2. Input of HCO 3- : - bicarbonate overdosing 3. Hypoalbuminemia 4. Dehydratation

11 physiological acute compensation -lungs -hypoventilation [HCO 3- ] 24 mmol/l pco 2 5,3 kpa N [HCO 3- ]/[H 2 CO 3 +CO 2 ] 20 : 1 > 20 : 1 20 : 1 ph 7,34 7,44 > 7,44 7,4

12 Respiratory acidosis Hypoventilation: - depression of the respiratory center (opiates, sedatives, narcotics, CO 2 ) - failures -ventilation, diffusion, perfusion (respiratory diseases) -gass transport (anemia, circulatory failure, CO intoxication) -gass exchange between the blood and tissues (cyanide intoxication) -neuromuscular junction (pharmaceuticals, nikotine, botulin intoxication) -neural transmission (spinal cord injuries)

13 physiological acute compensation -kidney - excretion of H 2 PO - 4 and NH resorption of HCO - 3 [HCO 3- ] 24 mmol/l N, pco 2 5,3 kpa [HCO 3- ]/[H 2 CO 3 +CO 2 ] 20 : 1 < 20 : 1 20 : 1 ph 7,34 7,44 < 7,34 7,4

14 Respiratory alkalosis Hyperventilation: - mechanical ventilation - respiratory center stimulation: from CNS (hysteria, anxiety, infection), drugs (salicylates), from thermoregulation center (fever, physical effort)

15 physiological acute compensation -kidney - excretion of HCO - 3 [HCO 3- ] 24 mmol/l N, pco 2 5,3 kpa [HCO 3- ]/[H 2 CO 3 +CO 2 ] 20 : 1 > 20 : 1 20 : 1 ph 7,34 7,44 > 7,44 7,4

16 Mixed acid-base disorders 1. Antagonistic metabolic acidosis + metabolic alkalosis acid-base indicators are often physiological (hypochloremia discovers MAlk) 2. Synergic e.g. metabolic acidosis + respiratory acidosis Diagnosis: electrolytes, proteins, lactate, calculation from the iontogram, symptoms Examples: Vomiting and starving (metabolic acidosis + metabolic alkalosis) Heart and respiratory failure (respiratory acidosis + metabolic acidosis)

17 Other values derived from the iontogram of plasm Name Calculation Physiological range Comments Buffer base(bb S ) BB S = Na + + K + - Cl - 42 mmol/l To understand the role of chlorides in the acid-base disorders Anion gap (AG) AG = (Na + + K + ) (Cl - + HCO 3- ) 18 mmol/l The portion of metabolic acidosis on a combined acid-base disorder Residual anions (RA ) RA = (Na + + K + + Ca + + Mg + ) (Cl - + HCO proteins) 10 mmol/l The portion of metabolic acidosis on a combined acid-base disorder, including the role of hypoproteinemia Strong ion difference (SID) SID = (Na + + K + + Ca + + Mg + ) (Cl - + UA - ) SID = HCO ,28 x albumin + 1,8 x Pi 39 ± 1 mmol/l The value of SID is influenced mainly by changes of sodium, chlorides and unmeasurable anionts SID (retention of Cl -, UA -, dilution by water acidosis SID (loss of Cl - ) alkalosis Concentration of weak acids (A tot ) The sum of negative charges of albumin and phosphor The role in acid-base disorders Hypoalbuminemia metabolic alkalosis Retention of P i metabolic acidosis

18 Main topics of the lecture: Measurement of acid-base dysbalance Classification of the acid-base disorders 4 basic acid-base disorders and their compensaiton Combined acid-base disorders Ions and acid-base disorders