5 acid_base_presentation.ppttttttttttttt

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1. ACID BASE
DISORDERS
DR A. K. SHERIFF

2. WHAT IS AN ARTERIAL BLOOD GAS?
The Components
•pH / PaCO
2
/ PaO
2
/ HCO
3
/ O
2
sat / BE
Normal Ranges
•pH - 7.35 - 7.45
•PaCO
2 – 4.5 – 6 kPa
•PaO
2
– 10.5 – 13.5 kPa
•HCO
3 - 21-27
•O
2
sat - 95-100%
•Base Excess - +/-2 mEq/L

3. ACID BASE BALANCE
The body produces acids daily
•15,000 mmol CO
2
•50-100 mEq Nonvolatile acids
The lungs and kidneys attempt to maintain balance
Buffering also occurs in the liver through ammonia
metabolism to urea / glutamate

4. ACID BASE BALANCE
Assessment of status via bicarbonate-carbon dioxide
buffer system
•HENDERSON-HASSELBALCH
•pH= pK + log ([HCO
3
-
] / [H
2CO
3 ])
•CO
2
+ H
2
O <--> H
2
CO
3
<--> HCO
3
-
+ H
+
•ph = 6.10 + log ([HCO
3] / [0.03 x PCO
2])

5. THE TERMS
ACIDS
•Acidemia
•Acidosis
•Respiratory
CO
2
•Metabolic
HCO
3
BASES
•Alkalemia
•Alkalosis
•Respiratory
CO
2
•Metabolic
HCO
3

6. RESPIRATORY ACIDOSIS
pH, CO
2, Ventilation
Causes
•CNS depression
•Pleural disease
•COPD/ARDS
•Musculoskeletal disorders
•Compensation for metabolic alkalosis

7. RESPIRATORY ACIDOSIS
Acute vs Chronic
•Acute - little kidney involvement. Buffering via titration via Hb
for example
•pH by 0.1 for 1.25 kPa  in CO
2
•Chronic - Renal compensation via synthesis and retention of
HCO
3
(Cl to balance charges  hypochloremia)
•pH by approx 0.05 for 1 kPa in CO
2

8. RESPIRATORY ALKALOSIS
pH, CO
2, Ventilation
 CO
2   HCO
3 (Cl to balance charges 
hyperchloremia)
Causes CHAMPS
•C – CNS Disease e.g. Intracerebral hemorrhage/
Cirrhosis
•H – Hypoxia
•A – Anxiety
•M – Over ventilation
•P – Progesterone
•S – Salicylate/Sepsis

9. RESPIRATORY ALKALOSIS
Acute vs. Chronic
•Acute - HCO
3
by 1.5 mEq/L for every 1 kPa  in PCO
2
•Chronic - Ratio increases to 3 mEq/L of HCO
3 for every 1 kPa
 in PCO
2
•Decreased renal bicarbonate reabsorption and decreased
ammonium excretion to normalize pH

10. METABOLIC ACIDOSIS
pH, HCO
3
12-24 hours for complete activation of respiratory
compensation
PCO
2
by 0.15 kPa for every 1 mEq/L HCO
3
The degree of compensation is assessed via the Winter’s
Formula
 PCO
2 = {1.5(HCO
3) +8  2 } x 0.133 [converts to kPa]

11. THE CAUSES
Metabolic Gap
Acidosis
•M - Methanol
•U - Uremia
•D – DKA - AKA
•P - Paraldehyde
•I – Isoniazid / Iron
•L - Lactic Acidosis
•E - Ethylene Glycol
•R-
Rhabdomyolysis
•S - Salicylate
Non Gap Metabolic
Acidosis
•H - Hyperalimentation
•A - Acetazolamide
•R - RTA
•D - Diarrhoea
•U - Uretero-pelvic
shunt
•P - Pancreatic Fistula
•S – Spironolactone

12. OSMOLAR GAP
OG = Measured osmolality – calculated osmolality
OG = 2 x [ Na mmol/L] + [glucose mmol/L] + [urea mmol/L] +
(1.25 x [Ethanol mmol/L])
Should be <10
Causes:
Methanol Glycine (TRUP)
Ethylene Glycol Propylene Glycol
Sorbitol Polyethylene Glycol
Mannitol Maltose (IV IG)

13. OG
For raised AG Metabolic Acidosis
Common Causes:
-Ketones
-Lactate
-Renal Failure
NO –
Ingestion possible
YES – Measure OG
Raised – Then likely Ethylene Glycol / Methanol
Normal – Salicylate, Paraldehyde, Iron + Isoniazid

14. METABOLIC ALKALOSIS
pH, HCO
3
PCO
2 by 0.1 for every 1mEq/L  in HCO
3
Causes – CLEVER PD
•C- Contraction
•L - Liquorice
•E - Endocrine: Conn’s / Cushing’s / Bartter’s
•V - Vomiting / NG Suction
•E - Excess Alkali
•R - Refeeding Alkalosis
•P - Post Hyper-capnoea
•D - Diuretics and Chronic diarrhoea

15. MIXED ACID-BASE
DISORDERS
Patients may have two or more acid-base disorders at one
time
Corrected Bicarbonate = AG – 12 + Serum HCO3-
If > 30 then there is also underlying metabolic alkalosis
If < 23 then there is an underlying non-AG metabolic acidocis

16. THE STEPS
Start with the pH – acidaemia or alkalaemia
Note the PCO
2
Look for disorders revealed by failure of compensation
Calculate anion gap
Calculate Corrected Bicarbonate

17. SAMPLE PROBLEM #1
An ill-appearing alcoholic male presents with nausea and
vomiting.
•ABG - 7.4 / 5.4 / 11.3 / 22
•Na- 137 / K- 3.8 / Cl- 90 / HCO
3- 22

18. SAMPLE PROBLEM #1
Winter’s Formula = {1.5(22) + 8  2} x 0.133
= {39  2} x 0.133 = 5.3 kPa
 compensated
Anion Gap = 137 - (90 + 22) = 25
 anion gap metabolic acidosis
Corrected Bicarbonate = 25 - 12 = 13
13 + 22 = 35
 metabolic alkalosis

19. SAMPLE PROBLEM #2
22 year old female presents for attempted overdose. She has
taken an unknown amount of Midol containing aspirin,
cinnamedrine, and caffeine. On exam she is experiencing
respiratory distress.

20. SAMPLE PROBLEM #2
ABG - 7.47 / 2.5 / 15.7 / 14
Na- 145 / K- 3.6 / Cl- 109 / HCO
3- 17
ASA level - 38.2 mg/dL

21. SAMPLE PROBLEM #2
Winters Formula = {1.5 (17) + 8  2} x 0.133
= 4.65 kPa
 uncompensated
Anion Gap = 145 - (109 + 17) = 19
 anion gap metabolic acidosis
Corrected HCO3- = 19 - 12 = 7
7 + 17 = 24
 no metabolic alkalosis

22. SAMPLE PROBLEM #3
47 year old male experienced crush injury at building site.
ABG - 7.3 / 4.2 / 12.8 / 15
Na- 135 / K-5 / Cl- 98 / HCO
3- 15

23. SAMPLE PROBLEM #3
Winters Formula = {1.5 (15) + 8  2} x 0.133
= 4 kPa
 compensated
Anion Gap = 135 - (98 + 15) = 22
 anion gap metabolic acidosis
Corrected Bicarb = 22 - 12 = 10
10 + 15 = 25
expected no additional deficit

24. SAMPLE PROBLEM #4
1 month old male presents with projectile vomiting for x 2
days.
ABG - 7.49 / 5.33 / 13 / 30
Na- 140 / K- 2.9 / Cl- 92 / HCO
3- 32

25. SAMPLE PROBLEM #4
Metabolic Alkalosis, hypochloremic
Winters Formula = {1.5 (30) + 8  2} x 0.133
= 53  2
= 7.3 kPa
 uncompensated

26. THANK YOU