Acid/base balance
Medhat Hashem, MD, FCARCSI, FRCA
Professor of Anaesthesia, Cairo University
Director of Surgical ICU
Objectives





Basic physiology
Definitions
How to read ABG
Examples
Normal concentration in ECF
(m mol/L)
Na
140





H+
0.00004

Normal H+ concentration: 40 n mol/L
Viable limits (20-16...
pH


[H+] concentration 40 n mol/L (20-160)



100 = (10)2
Log10 100 = 2
Log10 1000 = 3
pH; negative logarithm of recipr...
pH

[H+] (nmol/L)

7.6

25

7.5

32

7.4

40

7.3

50

7.2

63

7.1

80

7.0

100

6.9

125

6.8

160
pH of body fluids
Plasma

7.4

Gastric HCl

0.8

Urine

4.5

Pancreatic juice

8
Definitions







Acid: A substance that dissociates in water to H+.
Acidosis: A process that causes acids to
accum...
Buffers and compensation


Buffers: Hb, proteins, H2PO4 , H2CO3

H2O + CO2 → H2CO3 → HCO3- + H+


Respiratory compensati...
Henderson Hasselbach Equation

pH ≈ HCO3/CO2


pH
>7.44 → Alkalosis (alkalaemia)
 <7.36 → Acidosis (acidaemia)




PaC...
Blood gas analysis
Blood gas machine measures
 pH (7.36 - 7.44)
 PaO (75 -100 mmHg), room air
2


PaCO2 (35 – 45 mmHg)
...
Metabolic acidosis
↓pH (↑H+)
 ↓HCO (22-26 mmol/l) (↑Base deficit)
3
 PaCO → normal
2
 Compensation: Hyperventilation to...
Metabolic acidosis


Overproduction of organic acids
Lactic acid: shock, infection, hypoxia
 Urate: renal failure
 Keto...
Metabolic acidosis



Overproduction of organic acids
Excessive loss of bicarbonate:
Diarrhoea
 Pancreatic or small int...
Metabolic acidosis (CP)






of the cause
Tachypnea (↑rate and depth)
Severe acidosis → cardiovascular collapse →
car...
Rx of metabolic acidosis
Rx of the cause (e.g., insulin if DKA)
 Mild to moderate:
beneficial (shift O2 dissociation curv...
35 yrs, M, RTA, bilateral # femur &
pelvis,
pH ≈ HCO3/CO2









SaO2 98%
pH 7.25
PaCO2 37 mmHg
HCO3 17 mmol/L
BE ...
17 yrs, M, unconscious, syringe next to him
pH ≈ HCO3/CO2








SaO2 81%
pH 7.2
PaCO2 80 mmHg
HCO3 22 mmol/L
BE 0
P...
Respiratory acidosis



↓pH (↑H+)
↑PaCO2 (35-45 mmHg)



HCO3 (22-26 mmol/l) normal



Renal compensation (after 24 ho...
Respiratory Acidosis



Always associated with hypoxia
↑PaCO2 → ↑respiratory depression (CO2
narcosis) → more hypoxia
Respiratory Acidosis (causes)


↓Respiratory center
Drugs (opioids-anaesthesia)
 ICT brain tumours-head injury





...
Respiratory Acidosis (CP)


Acute CO2 retention:
restlessness
 flapping tremors




Further CO2 rise:
VD (warm limbs, ...
Respiratory Acidosis (treatment)





Depends on the cause and timescale
Patent airway
Oxygen therapy
Rx of the cause ...
69 yrs, M, smoker, COPD, SOB
pH ≈ HCO3/CO2








SaO2 91%
pH 7.36
PaCO2 61 mmHg
HCO3 32 mmol/L
BE 7
PaO2 79 mmHg (O...
Nurse story, post colecystectomy, 40 yrs, fit
pH ≈ HCO3/CO2








SaO2 98%
pH 7.55
PaCO2 36 mmHg
HCO3 31 mmol/L
BE ...
Metabolic alkalosis



↑pH (↓H+)
PaCO2 (35-45 mmHg) normal



↑ HCO3 (22-26 mmol/l)



Compensation: Respiratory inhib...
Metabolic alkalosis


Loss of gastric HCl
Repeated vomiting (pyloric stenosis)
 Gastric suction




Hypokalaemia (intr...
Metabolic alkalosis (CP)




The cuase
Bradypnea (Chyne Stokes respiration)
Tetany (↓ionized Ca)
Metabolic alkalosis (treatment)






Rx of the cause
Cl replacement (Normal Saline 0.9%)
Correcion of hypokalaemia (...
22 yrs, M, soldier, spasticity
pH ≈ HCO3/CO2







SaO2 98%
pH 7.55
PaCO2 25 mmHg
HCO3 25 mmol/L
BE 1
PaO2 189 mmHg ...
Respiratory alkalosis


↑ pH (↓H+)

 ↓PaCO2 (35-45 mmHg)
2



HCO3 (22-26 mmol/l) normal



Renal compensation (after ...
Respiratory alkalosis (causes)


Hyperventilation (wash out of CO2)
Hysteria
 Hyperpyrexia




Iatrogenic hyperventila...
Respiratory alkalosis (CP)





The cause
Short lived, well tolerated
↓Ca+ → carpopedal spasm, parasthesia
Severe resp...
Respiratory alkalosis (treatment)




Breath into paper bag (rebreathing)
Readjust ventilator parameters
Addition of CO...
Base Excess


“The amount of acid or base (mmol/l) required
to return the pH of 1L blood to normal at a
PaCO2 40 mmHg.”

...
Standard Bicarbonate



Not the actual bicarbonate in the sample
“Estimate of bicarbonate concentration after
eliminatio...
Thank You
QUESTIONS?
medhashem@yahoo.com
medhashem@yahoo.com
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Acid base

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Transcript of "Acid base"

  1. 1. Acid/base balance Medhat Hashem, MD, FCARCSI, FRCA Professor of Anaesthesia, Cairo University Director of Surgical ICU
  2. 2. Objectives     Basic physiology Definitions How to read ABG Examples
  3. 3. Normal concentration in ECF (m mol/L) Na 140     H+ 0.00004 Normal H+ concentration: 40 n mol/L Viable limits (20-160 n mol/L) Na ion conc is 1000 times higher. ECF Electroneutrality essential for cellular activity.
  4. 4. pH  [H+] concentration 40 n mol/L (20-160)  100 = (10)2 Log10 100 = 2 Log10 1000 = 3 pH; negative logarithm of reciprocal [H+] concentration. pH = - Log10 1/[H+]    
  5. 5. pH [H+] (nmol/L) 7.6 25 7.5 32 7.4 40 7.3 50 7.2 63 7.1 80 7.0 100 6.9 125 6.8 160
  6. 6. pH of body fluids Plasma 7.4 Gastric HCl 0.8 Urine 4.5 Pancreatic juice 8
  7. 7. Definitions       Acid: A substance that dissociates in water to H+. Acidosis: A process that causes acids to accumulate. Acidaemia; if pH<7.36 Alkali: a substance that accepts H+ Alkalosis; A process that causes bases to accumulate. Alkalaemia: if pH > 7.44
  8. 8. Buffers and compensation  Buffers: Hb, proteins, H2PO4 , H2CO3 H2O + CO2 → H2CO3 → HCO3- + H+  Respiratory compensation: Immediate  Hypo/hyperventilation to ↑or↓ CO 2   Renal compensation: After 24-48 hours  Excretion or retention of filtered HCO 3 
  9. 9. Henderson Hasselbach Equation pH ≈ HCO3/CO2  pH >7.44 → Alkalosis (alkalaemia)  <7.36 → Acidosis (acidaemia)   PaCO2 and HCO3 (and Base deficit)  PaCO2 → Respiratory  HCO3 → Metabolic
  10. 10. Blood gas analysis Blood gas machine measures  pH (7.36 - 7.44)  PaO (75 -100 mmHg), room air 2  PaCO2 (35 – 45 mmHg)  HCO3 calculated (22 – 26 mmol/L)
  11. 11. Metabolic acidosis ↓pH (↑H+)  ↓HCO (22-26 mmol/l) (↑Base deficit) 3  PaCO → normal 2  Compensation: Hyperventilation to wash CO 2 pH ≈ HCO3/CO2 pH HCO3PaCo2 Compensation  ↓ ↓↓ ↓ Hyperventilation ↓PaCO2
  12. 12. Metabolic acidosis  Overproduction of organic acids Lactic acid: shock, infection, hypoxia  Urate: renal failure  Ketones: DM, alcohol  Drugs/toxins: (salicylate, biguanide, methanol)   Excessive loss of bicarbonate
  13. 13. Metabolic acidosis   Overproduction of organic acids Excessive loss of bicarbonate: Diarrhoea  Pancreatic or small intestinal fistula  Renal tubular acidosis  Uretero-sigmodostomy  Addison’s disease 
  14. 14. Metabolic acidosis (CP)     of the cause Tachypnea (↑rate and depth) Severe acidosis → cardiovascular collapse → cardiac failure (↓BP) Death
  15. 15. Rx of metabolic acidosis Rx of the cause (e.g., insulin if DKA)  Mild to moderate: beneficial (shift O2 dissociation curve to Rt → ↑O2 delivery at tissue level).  Severe (↓pH < 7.2) → iv NaHCO 3   Amount of HCO3= Bwt x base deficit x 0.3 Start with half correction  Repeat assessment 
  16. 16. 35 yrs, M, RTA, bilateral # femur & pelvis, pH ≈ HCO3/CO2       SaO2 98% pH 7.25 PaCO2 37 mmHg HCO3 17 mmol/L BE -7 PaO2 130 mmHg (O2 by face mask) Hb 4.1 gm/dl Rx: Blood Tx, ( open book #pelvis)
  17. 17. 17 yrs, M, unconscious, syringe next to him pH ≈ HCO3/CO2      SaO2 81% pH 7.2 PaCO2 80 mmHg HCO3 22 mmol/L BE 0 PaO2 45 mmHg (O2 40%) Hb 14.5 gm/dl Respiratory acidosis (uncompensated)
  18. 18. Respiratory acidosis   ↓pH (↑H+) ↑PaCO2 (35-45 mmHg)  HCO3 (22-26 mmol/l) normal  Renal compensation (after 24 hours):  pH ↓ Reabsorption of filtered HCO3 HCO3- ↑ pH ≈ HCO3/CO2 PaCo2 Compensation ↑↑ Renal retention of HCO3-
  19. 19. Respiratory Acidosis   Always associated with hypoxia ↑PaCO2 → ↑respiratory depression (CO2 narcosis) → more hypoxia
  20. 20. Respiratory Acidosis (causes)  ↓Respiratory center Drugs (opioids-anaesthesia)  ICT brain tumours-head injury       Cervical spinal cord lesions: trans-section of SC AHC: e.g. poliomyelitis Chest wall: #ribs (flail), obesity Intercostal ms: Myasthenia Gravis Lung disease: severe COPD (blue bloater)
  21. 21. Respiratory Acidosis (CP)  Acute CO2 retention: restlessness  flapping tremors   Further CO2 rise: VD (warm limbs, papilloedema)  Drowsiness, confusion, coma   Chronic CO2 retention:   poor sleeping →day somnolence Cyanosis
  22. 22. Respiratory Acidosis (treatment)     Depends on the cause and timescale Patent airway Oxygen therapy Rx of the cause e.g., Naloxone (opioid overdose)  Drainage of hydrocephalus  fixation of flail ribs   Mechanical ventilation
  23. 23. 69 yrs, M, smoker, COPD, SOB pH ≈ HCO3/CO2      SaO2 91% pH 7.36 PaCO2 61 mmHg HCO3 32 mmol/L BE 7 PaO2 79 mmHg (O2 40%) Hb 21.5 gm/dl Compensated respiratory acidosis
  24. 24. Nurse story, post colecystectomy, 40 yrs, fit pH ≈ HCO3/CO2      SaO2 98% pH 7.55 PaCO2 36 mmHg HCO3 31 mmol/L BE 6 PaO2 111 mmHg (O2 40%) Hb 10.1 gm/dl Metabolic alkalosis (uncompensated)
  25. 25. Metabolic alkalosis   ↑pH (↓H+) PaCO2 (35-45 mmHg) normal  ↑ HCO3 (22-26 mmol/l)  Compensation: Respiratory inhibition but hypoxia limit rise of PaCO2 50 mmHg pH HCO3- ↑ ↑↑ pH ≈ HCO3/CO2 PaCo2 Compensation ↑ Hypoventilation ↑ PaCO2
  26. 26. Metabolic alkalosis  Loss of gastric HCl Repeated vomiting (pyloric stenosis)  Gastric suction   Hypokalaemia (intracellular K moves out exchange with K (maintain electro-neutrality)   diuretics Bicarbonate retention NaHCO3 administration  Milk alkali syndrome 
  27. 27. Metabolic alkalosis (CP)    The cuase Bradypnea (Chyne Stokes respiration) Tetany (↓ionized Ca)
  28. 28. Metabolic alkalosis (treatment)      Rx of the cause Cl replacement (Normal Saline 0.9%) Correcion of hypokalaemia (irritant, CVC) Iv ammonium chloride???? Rx of tetany: Ca (gluconate-chloride) 10ml SLOWLY
  29. 29. 22 yrs, M, soldier, spasticity pH ≈ HCO3/CO2      SaO2 98% pH 7.55 PaCO2 25 mmHg HCO3 25 mmol/L BE 1 PaO2 189 mmHg (O2 by face mask) Hb 13.6 gm/dl Respiratory alkalosis (uncompensated)
  30. 30. Respiratory alkalosis  ↑ pH (↓H+)  ↓PaCO2 (35-45 mmHg) 2  HCO3 (22-26 mmol/l) normal  Renal compensation (after 24 hours):  Increased renal excretion of HCO3 pH HCO3- ↑ ↓ pH ≈ HCO3/CO2 PaCo2 Compensation ↓↓ ↑Renal excretion of HCO3-
  31. 31. Respiratory alkalosis (causes)  Hyperventilation (wash out of CO2) Hysteria  Hyperpyrexia   Iatrogenic hyperventilation
  32. 32. Respiratory alkalosis (CP)     The cause Short lived, well tolerated ↓Ca+ → carpopedal spasm, parasthesia Severe respiratory alkalosis → respiratory arrest
  33. 33. Respiratory alkalosis (treatment)    Breath into paper bag (rebreathing) Readjust ventilator parameters Addition of CO2 ????
  34. 34. Base Excess  “The amount of acid or base (mmol/l) required to return the pH of 1L blood to normal at a PaCO2 40 mmHg.”  It is a measure of the magnitude of the metabolic component to the acid-base disorder
  35. 35. Standard Bicarbonate   Not the actual bicarbonate in the sample “Estimate of bicarbonate concentration after elimination of any abnormal respiratory contribution to HCO3 (i.e., an estimate of HCO3 at PaCO2 40 mmHg).
  36. 36. Thank You
  37. 37. QUESTIONS? medhashem@yahoo.com medhashem@yahoo.com
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