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.
6. pH of body fluids
Plasma
7.4
Gastric HCl
0.8
Urine
4.5
Pancreatic juice
8
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. 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
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. Metabolic acidosis (CP)
of the cause
Tachypnea (↑rate and depth)
Severe acidosis → cardiovascular collapse →
cardiac failure (↓BP)
Death
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. 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 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)
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. 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
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. 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)
32. Respiratory alkalosis (CP)
The cause
Short lived, well tolerated
↓Ca+ → carpopedal spasm, parasthesia
Severe respiratory alkalosis → respiratory arrest
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. 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).