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(4) Respiratory alkalosis

(4) Respiratory alkalosis. 1) Concept Respiratory alkalosis is defined as a primary decrease in [H 2 CO 3 ] ([CO 2 ], PaCO 2 ) in plasma Hypocapnia The secondary change is the decrease of [HCO 3 ¯ ] in plasma due to the renal compensation. 2) Causes and Pathogenesis.

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(4) Respiratory alkalosis

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  1. (4) Respiratory alkalosis 1) Concept Respiratory alkalosis is defined as a primary decrease in [H2CO3] ([CO2], PaCO2) in plasma Hypocapnia The secondary change is the decrease of [HCO3¯ ] in plasma due to the renal compensation.

  2. 2) Causes and Pathogenesis Increased alveolar ventilation Hypoxia due to high altitude Hysteria Fever Central nervous diseases Gram-negative septicemia Salicylate intoxication The basic reason of hyperventilation is the stimulation of respiratory center. Mis-operation of mechanical ventilator

  3. 3) Compensation The compensation of respiratory alkalosis is in the opposite direction of the compensation of respiratory acidosis. The main mechanisms are cellular and renal compensation (How about buffering system, respiration?)

  4. Cellular compensation for acute typea) H+-K+ exchange

  5. b)CO2 moves out of the cells

  6. (b)The renal compensation for chronic type • The renal compensation in respiratory alkalosis is the same as the renal compensation in metabolic alkalosis. • It may take 3~5 days to reach the maximal renal compensation.

  7. Changes of laboratory parameters • Primary decrease of [H2CO3]: • PaCO2 ? • Secondary compensation: • AB,SB,BB ??? • AB ?? SB • BE ? • pH ?

  8. Changes of laboratory parameters • Primary decrease of [H2CO3]: • PaCO2 decrease • Secondary compensation: • AB,SB,BB decrease • AB < SB • BE negative value increases • pH tends to increase.

  9. Predicted compensatory formula for acute respiratory alkalosis ΔHCO3- = 0.2x ΔPaCO2± 2.5 HCO3- = 24+0.2x (PaCO2 -40)± 2.5 Secondary compensation primary change Value measured > value predicted: with metabolic alkalosis Value measured < value predicted: with metabolic acidosis. Maximal compensatory value up to:18 mmol/L

  10. Predicted compensatory formula for chronic respiratory alkalosis ΔHCO3- = 0.5x ΔPaCO2± 2.5 HCO3- = 24+0.5x (PaCO2 -40)±2.5 Secondary compensation primary change Value measured > value predicted: with metabolic alkalosis Value measured < value predicted: with metabolic acidosis. Maximal compensatory value up to:12 mmol/L

  11. (3) Effects on the body •  1) Effects on the central nervous system. • 2) Effects on metabolism •  （hypophosphatemia）

  12. 1) Effects on the central nervous system • (a) Excitability is increased. • Manifestations are more severe than those of metabolic alkalosis.

  13. The reasons : • (a) Hyperventilation leads to low [CO2] in plasma and cerebral vasoconstriction, the oxygen supply to the brain is decreased. • (b) The left-shift of oxygen-hemoglobin dissociation curve leads to brain hypoxia.

  14. Glutamate decarboxylase r-GABA, r-aminobutyric acid Glutamic acid r-GABA transminase Succinic acid Kreb’s cycle (c) The production of GABA (gama aminobutyric acid, a inhibitory transmitter), is decreased due to the activity of enzyme for the production is reduced in alkalosis.

  15. 2) 低磷血症 hypophosphatemia • 细胞内碱中毒使糖元分解增多,在磷酸化酶作用下形成葡萄糖6-磷酸盐等磷酸化合物增多,需用磷增多, 细胞外磷进入细胞内。

  16. Treatment principle • For respiratory alkalosis: • Let the patient inhale the air that is exhaled by himself (herself) with a “mask”.

  17. Thinking method of diagnosis • (1) via pH: acidosis or alkalosis ? • compensatory or decompensatory ? • (2) via history: primary change • metabolic or respiratory ? • (3) via predicted compensatory value: • simple or mixed ?

  18. Case discussion A 32-year-old male presented with vomiting of one week’s duration. On examination, he appeared dysphoria and had a supine blood pressure of 90/60 mmHg and a pulse of 116/min. The laboratory results were: Arterial blood: pH=7.55 PaCO2=46 mmHg PaO2=90mmHg [HCO3-]=38 mmol/L.

  19. See pH See primary history ΔPaCO2=0.7xΔHCO3- ± 5 = 0.7x 14 ± 5 = 10 ± 5 (5~15)mmHg Predicted 40+ 5~15=45~55, measure: 46, Decompensatory metabolic alkalosis.

  20. Case discussion • A 58-year-old man with pulmonary heart disease had 3 days of diarrhea. • pH=7.12, PaCO2= 85 mmHg,HCO3 - =26 mmol/L • Na+=137 mmol/L, Cl- =85 mmol/L • ΔHCO3 -=0.4 xΔPaCO2± 3 = 18 ± 3 • Predicted 24+18 ± 3 = 39~45 (1) via pH: decompensatory acidosis (2) via history: primary change: respiratory (3) via predicted compensatory value: mixed Respiratory acidosis + metabolic acidosis (AG??)

  21. A patient with diabetes: Measured: pH = 7.32 PaCO2 = 30mmHg Checked: Chronic metabolic acidosis HCO3- = 16 mmol/L BE = -9 mmil/L

  22. A patient with CHD • Measured: • pH=7.22 • PaCO2 = 50mmHg • Checked: • Respiratory acidosis+metabolic acidosis

  23. Section 3. Mixed types of acid-base disturbances • （1） Double双重性 acid-base disorders • 1）呼吸性+代谢性混合型 • 呼酸+代酸 • 呼酸+代碱 • 呼碱+代酸 • 呼碱+代碱 • 2）代谢混合型 • 代酸+代碱 • 高AG代酸+高Cl代酸 • 3) 呼吸混合型？？

  24. Case discussion • A 45-year-old man had chronic cough for 20 years. He had a shortness of breath, orthopnea with edematous ankles for 1 month. The laboratory findings were: • pH = 7.26 PaO2=55 mmHg • PaCO2=60 mmHg AB = 22 mmol/L • See pH: Decompensated acidosis • See history: Respiratory disorder • Calculate:

  25. Predicted: ΔHCO3- = 0.4x ΔPaCO2± 3 HCO3- = 24+0.4x 20± 3=29~35 Measured: 22 Respiratory acidosis + metabolic acidosis pH?? HCO3- ??

  26. Respiratory alkalosis + metabolic acidosis • A patient with salicylic acid poisoning • (stimulating respiratory center) • pH= 7.45 • PaCO2=20mmHg • HCO3-=13 mmol/L ΔHCO3- = 0.2x ΔPaCO2± 2.5 Predicted HCO3- = 24 - 4 = 20 ± 2.5

  27. In metabolic acidosis + metabolic alkalosis • pH is in normal range, • [HCO3-] is in normal range.

  28. (2)Triple三重性 acid-base disorders • A 62-year-old woman with chronic bronchitis and emphysema for more than 15 years. was admitted to the hospital in a confused state. Her temperature was 38.5℃. • The laboratory data: • pH = 7.27 PaCO2=65 mmHg • AB=28mmol/L

  29. Respiratory acidosis + metabolic acidosis Predicted: ΔHCO3- = 0.4x ΔPaCO2± 3 HCO3- = 24+0.4x 25± 3=31~37 Measured:28

  30. The next day she presented with severe vomiting . The laboratory finding: • In venous blood: • [K+]= 3.3 mmol/L [Cl- ]= 54 mmol/L • pH= 7.4 AB=52 mmol/L

  31. Respiratory acidosis + metabolic acidosis • + metabolic alkalosis • (causes?)

  32. A patient with pulmonary heart disease treated by diuretics. pH= 7.43, PaCO2=61mmHg, HCO3-=38 mmol/L Na+=140mmol/L, Cl- = 74 mmol/L, K+ = 3.5mmol/L Predicted[HCO3-]=32.4 AG=140-(74+38)=28 Respiratory acidosis+metabolic alkalosis+metabolic acidosis with increased AG

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