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Acid-Base Disorders A Simple Approach BP Kavanagh, HSC.

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Presentation on theme: "Acid-Base Disorders A Simple Approach BP Kavanagh, HSC."— Presentation transcript:

1 Acid-Base Disorders A Simple Approach BP Kavanagh, HSC

2 1st Step Check the ABG result or validity: [H] nM = [PaCO 2 ]  24/[HCO 3 - ] In range : , pH = 7.X [80-X] = approx. [H] nM

3 Normal Values pH PaCO mmHg [HCO3 - ] mmol.L -1 Anion Gap10-14 mmol.L -1 [Assumes Protein 40 g/l - should reduce AG by 3, for every 10 g/l decrease in plasma protein]

4 pH = 7.4 There is no acid-base disorder OR There are more than one, and they’re perfectly balanced, not compensated [ Q: How many types can co-exist? ]

5 Hypoventilation Brain Injury CNS Depressants Myoneural Chest Wall Lung Parenchyma Airways Mechanical Ventilation Brain Lung

6 Hyperventilation Anxiety Drugs Encephalopathy Pregnancy Mechanical Ventilation Pulmonary Fibrosis Pulmonary Edema Brain Lung

7 Ventilation Alv. vent. = min. vent. - dead space vent = [f.V T ] - [f.V D ] = f.[V T - V D ] = [f / V T ].[1 - V D / V T ] Frequency Tidal Volume Physiologic Deadspace

8 Anion Gap No Osmole Gap Ketones Lactate Uremia ASA/Paraldehyde Rhabdomyolysis Osmole Gap Methanol Ethylene Glycol Ethanol

9 Non-Anion Gap Dilution of HCO 3 - Normal Saline TPN Loss of HCO 3 - GI Loss Renal Loss

10 Diarrhea Ureteric Diversion [ Cl - exchanged for HCO 3 - ] GI Loss of HCO 3 -

11 Renal Loss of HCO RTA 2. Acetazolamide 3. Steroid Deficiency

12 ECF Expansion HCO 3 - Cl - NS TPN HCO 3 - Cl - ECF Vol. Cl - mmol. HCO 3 - mmol. Cl - conc. HCO 3 - conc.

13 Metabolic Alkalosis - Causes ECF Contracted [Ur Cl - < 10] Remote Diuretics [ECF low, but no current Cl - spill] Gastric Losses [Aspiration or Vomiting] ECF Normal or Expanded [Ur Cl - > 20] Current Diuretics Excess Steroid Effect Excess Renin Effect Bartters Syndrome Administration of HCO 3 - Post Hypercapnia [Ur Cl - < 10]

14 ECF Contraction HCO 3 - Cl - Diuresis HCO 3 - Cl - ECF Vol. Cl - mmol. HCO 3 - mmol. Cl - conc. HCO 3 - conc. [Secondary Hyperaldo.] Cl -

15 2nd Step What's the pH, PaCO 2, & the HCO 3 - ? If the pH is > 7.45, there's a primary alkalosis If the pH is < 7.35, there's a primary acidosis

16 3rd Step Calculate the Anion Gap If > 20, Calculate Anion Gap ‘Excess’ Add the ‘Excess’ to the Bicarbonate

17 The Anion Gap If assess a patient for all known causes of an anion gap: AG [mmol/l]% Confirmed

18 Anion Gap Rules 1 If > 20, there’s likely a cause to find 2 AG does not rise to compensate 3 Changes in AG should be matched with changes in HCO 3 - [ titrated, mole for mole ]

19 If AG is increased > Assume it began normal [12 mmol/l] 2. Therefore an excess has developed 3. Assume the HCO 3 - began normal 4. If [HCO xs] < normal HCO 3 -  additional primary loss of HCO If [HCO AGxs] > normal HCO 3 -  additional primary source of HCO 3 -

20 Primary AG Metabolic Acidosis Only Na + Cl - AG HCO 3 - Cl - AG HCO 3 - AG xs Before After

21 Primary AG Metabolic Acidosis, With Primary Non-Gap Metabolic Acidosis Na + Cl - AG HCO 3 - Cl - AG HCO 3 - AG xs Before After

22 Primary AG Metabolic Acidosis, With Primary Metabolic Alkalosis Na + Cl - AG HCO 3 - Cl - AG HCO 3 - AG xs Before After

23 Summary Steps 1. Clinical Status 2. Verify Results 3. Determine the Primary Problem [pH, PaCO 2, HCO 3 - ] 4. Calculate AG 5. If AG > 20, calculate AG excess 6. Add to HCO 3 - [ compare to normal range ]

24 Case #1 pH 7.5 PaCO 2 29 HCO Case #2 pH 7.2 PaCO 2 70 HCO

25 Case #3 pH 7.55 PaCO 2 40 HCO Case #4 pH 7.34 PaCO 2 60 HCO

26 Case #6 pH 7.5 PaCO 2 20 HCO Na Cl - 103

27 Case #7 pH 7.4 PaCO 2 40 HCO Na Cl - 100

28 Case #8 pH 7.5 PaCO 2 20 HCO Na Cl - 100

29 Case #9 pH 7.1 PaCO 2 50 HCO Na Cl - 100

30 Case #10 pH 7.15 PaCO 2 15 HCO Na Cl - 110


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