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Acid Base DisordersAcid Base Disorders
A Practical ApproachA Practical Approach
Ass. Lecturer critical care medicineAss. L...
Regulation of acid-base balance:Regulation of acid-base balance:
Defense against the change in pH…
 because H+ react hig...
What information does ABG provide about the patient?What information does ABG provide about the patient?
ABG provide an as...
Diagnosis of acid Base disordersDiagnosis of acid Base disorders
•Arterial blood sample is common utilized clinically
but ...
Acid Base -Basic ConceptsAcid Base -Basic Concepts
 Hydrogen IonHydrogen Ion [H[H++
]]is tightly controlledis tightly con...
[H[H++
] pH] pH
pH = 6.1 + log ([PaCO2] / [0.03 x HCO3-])pH = 6.1 + log ([PaCO2] / [0.03 x HCO3-])
pH [H+
] pH [H+
]
7.80
...
Normal ValuesNormal Values
[H+] = 40 nEq/L[H+] = 40 nEq/L
pH = 7.40pH = 7.40 (7.35-7.45)(7.35-7.45)
PaCOPaCO22 = 40 mm ...
Keep It SimpleKeep It Simple
 PaCOPaCO22 = Acid= Acid
  PaCOPaCO22 ==  pH (Acidemia)pH (Acidemia)
  PaCOPaCO22 ==...
Simple Acid-Base DisordersSimple Acid-Base Disorders
Type of Disorder pH PaCO2 [HCO3]
Metabolic Acidosis ↓ ↓ ↓
Metabolic A...
EXPECTED CHANGES IN ACID-BASE DISORDERSEXPECTED CHANGES IN ACID-BASE DISORDERS
Primary DisorderPrimary Disorder ExpectedEx...
Acid-Base AnalysisAcid-Base Analysis
What do You Need?What do You Need?
 Arterial Blood gases (pH, COArterial Blood gases...
 A 39 year old woman was admitted with a history ofA 39 year old woman was admitted with a history of
generalized weaknes...
Simple Vs. MixedSimple Vs. Mixed
Compensation ConceptCompensation Concept
[H[H++
] = 24 (PaCO] = 24 (PaCO22 / HCO/ HCO33
-...
Respiratory CompensationRespiratory Compensation
 Compensate for metabolicCompensate for metabolic
disordersdisorders
 P...
Respiratory CompensationRespiratory Compensation
 Metabolic AcidosisMetabolic Acidosis
PaCO2 = [1.5 x HCOPaCO2 = [1.5 x ...
Metabolic CompensationMetabolic Compensation
 Compensation for respiratory disordersCompensation for respiratory disorder...
Metabolic CompensationMetabolic Compensation
 Chronic Respiratory AcidosisChronic Respiratory Acidosis
∆∆ HCOHCO33= 0.35...
Case Study - 1Case Study - 1
 A 39 year old woman was admitted with a history of generalizedA 39 year old woman was admit...
Metabolic AcidosisMetabolic Acidosis
Anion GapAnion Gap
 Metabolic acidosis is groupedMetabolic acidosis is grouped
accor...
Wide Anion Gap AcidosisWide Anion Gap Acidosis
 MethanolMethanol
 UremiaUremia
 Diabetic Ketoacidosis, KetoacidosisDiab...
Non (normal) Anion GapNon (normal) Anion Gap
AcidosisAcidosis
 HyperalimentationHyperalimentation
 Acetazolamide, amphot...
Non anion gap metabolic acidosis:
Metabolic acidosis associated with normal AG is
typically characterized by hyperchloremi...
BASE EXCESSBASE EXCESS
 It is an estimate of the amount of strong acid orIt is an estimate of the amount of strong acid o...
Study Case - 1Study Case - 1
 A 39 year old woman was admitted with a history ofA 39 year old woman was admitted with a h...
Metabolic AlkalosisMetabolic Alkalosis
 Characterized byCharacterized by
 PrimaryPrimary ↑↑ in HCO3 concentrationin HCO3...
Metabolic AlkalosisMetabolic Alkalosis
Chloride ResponsiveChloride Responsive
Urine ClUrine Cl--
>20 mEq/L>20 mEq/L
 Volu...
Metabolic AlkalosisMetabolic Alkalosis
Chloride UnresponsiveChloride Unresponsive
 Mineralcorticoid excessMineralcorticoi...
Case Study - 2Case Study - 2
 A 78 year old lady presented with at a 1 weekA 78 year old lady presented with at a 1 week
...
SolvingSolving
Acid Base DisordersAcid Base Disorders
Rule 1Rule 1
Validate the ABGValidate the ABG
[H[H++
] = 24 (PaCO] = 24 (PaCO22 / HCO/ HCO33
--
))
80 - [H80 - [H++
]] ~ t...
Another method
Determine if numbers fit:Determine if numbers fit:
H+ =H+ =
3
2
HCO
PCO24×
H+ = (7.8-PH)×100.H+ = (7.8-PH)×...
Rule 2Rule 2
 What is the pH?What is the pH?
 > 7.40 → 1° disorder is alkalosis> 7.40 → 1° disorder is alkalosis
 < 7.4...
Rule 3Rule 3
 Does theDoes the PaCOPaCO22 explains the pH?explains the pH?
 YesYes → 1° disorder is respiratory→ 1° diso...
Rule 4Rule 4
Apply compensation rulesApply compensation rules
 If calculated compensation:If calculated compensation:
 W...
There is no over correction orThere is no over correction or
compensation in acid base balance →compensation in acid base ...
Case Study - 1Case Study - 1
 A 39 year old woman was admitted with a historyA 39 year old woman was admitted with a hist...
Case Study - 2Case Study - 2
 A 78 year old lady presented with at least aA 78 year old lady presented with at least a
we...
Mixed Acid-Base DisordersMixed Acid-Base Disorders
 pH may be within normal (7.35-7.45)pH may be within normal (7.35-7.45...
 A 21 year old MS is brought to the ER at ~3A 21 year old MS is brought to the ER at ~3
am, stuporous and tachypneic. His...
 A 21 year old MS is brought to the ER at ~3 am, stuporous and tachypneic.A 21 year old MS is brought to the ER at ~3 am,...
Primary Respiratory DisordersPrimary Respiratory Disorders
Acute vs. ChronicAcute vs. Chronic
 ACUTEACUTE
 Δ PCO2 = 10 →...
 A 55 year old woman presented to the ERA 55 year old woman presented to the ER
with dyspnea and wheezes. She is heavywit...
 A 55 year old woman presented to the ER with dyspnea andA 55 year old woman presented to the ER with dyspnea and
wheezes...
Approach To ALL Acid/BaseApproach To ALL Acid/Base
ProblemsProblems
 Don’t get overwhelmed by all the numbersDon’t get ov...
METHODICAL SYSTEMMETHODICAL SYSTEM
 Get all your numbers in front you first…Get all your numbers in front you first…
 Lo...
SYSTEM…continuedSYSTEM…continued
 After you come up with “primary disturbance”,After you come up with “primary disturbanc...
CompensationCompensation
The Two Given Rules of Compensation:The Two Given Rules of Compensation:
1.1. METABOLIC = BICARB ...
Compensation…continuedCompensation…continued
2.2. RESPIRATORY = PCO2RESPIRATORY = PCO2
……So if you are dealing with respir...
SYSTEM…continuedSYSTEM…continued
 If the compensation is INAPPROPRIATE, thenIf the compensation is INAPPROPRIATE, then
yo...
Case 1Case 1
 A 75-year-old man presents to the ED after aA 75-year-old man presents to the ED after a
witnessed out of h...
ABG Analysis reveals:ABG Analysis reveals:
 FFiiOO22 0.50.5
 pHpH 7.107.10
 PaCOPaCO22 45 mmHg45 mmHg
 PaOPaO22 56 mmH...
Case 2Case 2
 A 65-year-old man with severe COPDA 65-year-old man with severe COPD
has just collapsed in the respiratoryh...
ABG Analysis reveals:ABG Analysis reveals:
 FFiiOO22 0.85 (estimated)0.85 (estimated)
 pHpH 7.207.20
 PaCO2PaCO2 151 mm...
Case 3Case 3
 A 75-year-old lady is admitted to the EDA 75-year-old lady is admitted to the ED
following a VF cardiac arr...
ABG Analysis reveals:ABG Analysis reveals:
 FFiiOO22 1.01.0
 pHpH 7.607.60
 PaCOPaCO22 20 mmHg20 mmHg
 PaOPaO22 192 mm...
Case 4Case 4
 An 18-year-old male insulin dependentAn 18-year-old male insulin dependent
diabetic is admitted to the ED.d...
ABG Analysis reveals:ABG Analysis reveals:
 FFiiOO22 0.40.4
 pHpH 6.796.79
 PaCOPaCO22 11.3 mmHg11.3 mmHg
 PaOPaO22 12...
Case 5Case 5
His vital signs are:His vital signs are:
 Heart rateHeart rate 120/min – sinus120/min – sinus
tachycardia – ...
ABG Analysis reveals:ABG Analysis reveals:
 FFiiOO22 0.4 (approx)0.4 (approx)
 pHpH 7.127.12
 PaCOPaCO22 36 mmHg)36 mmH...
AnyAny
Question?Question?
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Acid base disorders

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Acid base disorders

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Acid base disorders

  1. 1. Acid Base DisordersAcid Base Disorders A Practical ApproachA Practical Approach Ass. Lecturer critical care medicineAss. Lecturer critical care medicine Cairo University HospitalCairo University Hospital WALID KAMEL, MBChWALID KAMEL, MBCh
  2. 2. Regulation of acid-base balance:Regulation of acid-base balance: Defense against the change in pH…  because H+ react highly with cellular proteins resulting in alteration in their function. Avoiding acidemia and alkalemia by tightly regulation H+ is essential for normal cellular function.
  3. 3. What information does ABG provide about the patient?What information does ABG provide about the patient? ABG provide an assessment of the following: 1)PaO2 : Amount of o dissolved in the blood, it give initial information on efficiency of oxygenation. 2)PaCO2 : Adequacy of ventilation is inversely proportional to Paco2 (when ventilation increase PaCO2 decrease and vice verse). 3) Acid base status (pH, HCO3 , base deficit, anion gap). 4) Hb, Hct, oxygen saturation. 5) Electrolyte e.g. Na+ , K+ .
  4. 4. Diagnosis of acid Base disordersDiagnosis of acid Base disorders •Arterial blood sample is common utilized clinically but venous blood may be useful in determining acid base status. (Except in CHF and shock). •Blood sample should be in heparin coated syringe. •The sample should be analyzed as soon as possible. •Air bubble should be eliminated. •The syringe should be capped and placed in ice.
  5. 5. Acid Base -Basic ConceptsAcid Base -Basic Concepts  Hydrogen IonHydrogen Ion [H[H++ ]]is tightly controlledis tightly controlled  [H[H++ ]]is determined by the balance betweenis determined by the balance between PaCOPaCO22 and serumand serum HCOHCO33 (bicarbonate)(bicarbonate) Henderson-Hasselbalch EquationHenderson-Hasselbalch Equation [H[H++ ] = 24 (PaCO] = 24 (PaCO22 / HCO/ HCO33 -- ))
  6. 6. [H[H++ ] pH] pH pH = 6.1 + log ([PaCO2] / [0.03 x HCO3-])pH = 6.1 + log ([PaCO2] / [0.03 x HCO3-]) pH [H+ ] pH [H+ ] 7.80 7.75 16 18 7.30 7.25 50 56 7.70 7.65 20 22 7.20 7.15 63 71 7.60 7.55 25 28 7.10 7.00 79 89 7.50 7.45 32 35 6.95 6.90 100 112 7.40 7.35 40 45 6.85 6.80 141 159
  7. 7. Normal ValuesNormal Values [H+] = 40 nEq/L[H+] = 40 nEq/L pH = 7.40pH = 7.40 (7.35-7.45)(7.35-7.45) PaCOPaCO22 = 40 mm Hg= 40 mm Hg (35-45)(35-45) HCOHCO33 = 24 mEq/L= 24 mEq/L (22-26)(22-26)
  8. 8. Keep It SimpleKeep It Simple  PaCOPaCO22 = Acid= Acid   PaCOPaCO22 ==  pH (Acidemia)pH (Acidemia)   PaCOPaCO22 ==  pH (Alkalemia)pH (Alkalemia)  HCOHCO33 = Base= Base   HCOHCO33 ==  pH (Alkalemia)pH (Alkalemia)   HCOHCO33 ==  pH (Acidemia)pH (Acidemia)
  9. 9. Simple Acid-Base DisordersSimple Acid-Base Disorders Type of Disorder pH PaCO2 [HCO3] Metabolic Acidosis ↓ ↓ ↓ Metabolic Alkalosis ↑ ↑ ↑ Acute Respiratory Acidosis ↓ ↑ ↑ Chronic Respiratory Acidosis ↓ ↑ ↑↑ Acute Respiratory Alkalosis ↑ ↓ ↓ Chronic Respiratory Alkalosis ↑ ↓ ↓↓
  10. 10. EXPECTED CHANGES IN ACID-BASE DISORDERSEXPECTED CHANGES IN ACID-BASE DISORDERS Primary DisorderPrimary Disorder ExpectedExpected ChangesChanges Metabolic acidosisMetabolic acidosis PCO2 = 1.5 × HCO3 + (8 ± 2)PCO2 = 1.5 × HCO3 + (8 ± 2) Metabolic alkalosisMetabolic alkalosis PCO2 = 0.7 × HCO3 + (21 ± 2)PCO2 = 0.7 × HCO3 + (21 ± 2) Acute respiratory acidosisAcute respiratory acidosis delta pH = 0.008 ×delta pH = 0.008 × (PCO2 - 40)(PCO2 - 40) Chronic respiratory acidosisChronic respiratory acidosis delta pH = 0.003 ×delta pH = 0.003 × (PCO2 - 40)(PCO2 - 40) Acute respiratory alkalosisAcute respiratory alkalosis delta pH = 0.008 × (40 - PCO2)delta pH = 0.008 × (40 - PCO2) Chronic respiratory alkalosisChronic respiratory alkalosis delta pH = 0.003 × (40 -delta pH = 0.003 × (40 - PCO2)PCO2)
  11. 11. Acid-Base AnalysisAcid-Base Analysis What do You Need?What do You Need?  Arterial Blood gases (pH, COArterial Blood gases (pH, CO22))  Serum chemistry (Na, K, Cl, HCOSerum chemistry (Na, K, Cl, HCO33))
  12. 12.  A 39 year old woman was admitted with a history ofA 39 year old woman was admitted with a history of generalized weakness, dyspnea, continuous nauseageneralized weakness, dyspnea, continuous nausea and diarrhea. Bowel motions were frequent andand diarrhea. Bowel motions were frequent and watery.watery.  ABG: pH 7.29, PaCO2 25.6, PaO2 98ABG: pH 7.29, PaCO2 25.6, PaO2 98  NaNa++ =125, K=125, K++ =2.8, Cl=2.8, Cl-- =101, HCO=101, HCO33=14=14 Study CaseStudy Case MetabolicMetabolic Acidosis
  13. 13. Simple Vs. MixedSimple Vs. Mixed Compensation ConceptCompensation Concept [H[H++ ] = 24 (PaCO] = 24 (PaCO22 / HCO/ HCO33 -- ))  Is compensation appropriate?Is compensation appropriate?  Must know “rules of thumb” of compensationMust know “rules of thumb” of compensation
  14. 14. Respiratory CompensationRespiratory Compensation  Compensate for metabolicCompensate for metabolic disordersdisorders  Prompt responsePrompt response  Metabolic acidosisMetabolic acidosis  Hyperventilation - ↓ PaCOHyperventilation - ↓ PaCO22  Metabolic alkalosisMetabolic alkalosis  Hypoventilation - ↑ PaCOHypoventilation - ↑ PaCO22
  15. 15. Respiratory CompensationRespiratory Compensation  Metabolic AcidosisMetabolic Acidosis PaCO2 = [1.5 x HCOPaCO2 = [1.5 x HCO33 + 8] ± 2+ 8] ± 2  Metabolic AlkalosisMetabolic Alkalosis ∆∆PaCO2 = 0.9 ∆ HCOPaCO2 = 0.9 ∆ HCO33
  16. 16. Metabolic CompensationMetabolic Compensation  Compensation for respiratory disordersCompensation for respiratory disorders  Slow responseSlow response  Starts in 6-12 hoursStarts in 6-12 hours  Steady state in few daysSteady state in few days  Respiratory acidosisRespiratory acidosis  Stimulates HCOStimulates HCO33 reabsorption --reabsorption --↑ HCO↑ HCO33  Respiratory alkalosisRespiratory alkalosis  Inhibits HCOInhibits HCO33 reabsorption --reabsorption -- ↓ HCO↓ HCO33
  17. 17. Metabolic CompensationMetabolic Compensation  Chronic Respiratory AcidosisChronic Respiratory Acidosis ∆∆ HCOHCO33= 0.35 ∆ PaCO= 0.35 ∆ PaCO22  Chronic Respiratory AlkalosisChronic Respiratory Alkalosis ∆∆ HCOHCO33= 0.5 ∆ PaCO= 0.5 ∆ PaCO22
  18. 18. Case Study - 1Case Study - 1  A 39 year old woman was admitted with a history of generalizedA 39 year old woman was admitted with a history of generalized weakness, dyspnea, continuous nausea and diarrhea. Bowelweakness, dyspnea, continuous nausea and diarrhea. Bowel motions were frequent and watery.motions were frequent and watery.  ABG: pH 7.29, PaCO2 25.6, PaO2 98ABG: pH 7.29, PaCO2 25.6, PaO2 98  NaNa++ =125, K=125, K++ =2.8, Cl=2.8, Cl-- =101, HCO=101, HCO33=12=12 PaCO2 = [1.5 x HCO3 + 8] ± 2PaCO2 = [1.5 x HCO3 + 8] ± 2 PaCo2=[1.5X12]+8 ± 2PaCo2=[1.5X12]+8 ± 2 PaCO2 =PaCO2 = 2525 ± 2± 2 Simple (compensated) metabolic acidosis
  19. 19. Metabolic AcidosisMetabolic Acidosis Anion GapAnion Gap  Metabolic acidosis is groupedMetabolic acidosis is grouped according to the anion gapaccording to the anion gap  Anion Gap (AG)Anion Gap (AG)  The difference between measured cationsThe difference between measured cations and measured anions in the serumand measured anions in the serum AG= NaAG= Na++ - [Cl- [Cl-- + HCO+ HCO33 -- ]]  Normal (9 - 12 mEq/LNormal (9 - 12 mEq/L))
  20. 20. Wide Anion Gap AcidosisWide Anion Gap Acidosis  MethanolMethanol  UremiaUremia  Diabetic Ketoacidosis, KetoacidosisDiabetic Ketoacidosis, Ketoacidosis  ParaldehydeParaldehyde  Iron, Isoniazid (INH)Iron, Isoniazid (INH)  Lactic AcidosisLactic Acidosis  Ethanol, Ethylene glycolEthanol, Ethylene glycol  SalicylatesSalicylates
  21. 21. Non (normal) Anion GapNon (normal) Anion Gap AcidosisAcidosis  HyperalimentationHyperalimentation  Acetazolamide, amphotericinAcetazolamide, amphotericin  RTA –Renal Tubular AcidosisRTA –Renal Tubular Acidosis  DiarrheaDiarrhea  Ureteral DiversionsUreteral Diversions  Pancreatic fistulaPancreatic fistula  Saline resuscitationSaline resuscitation
  22. 22. Non anion gap metabolic acidosis: Metabolic acidosis associated with normal AG is typically characterized by hyperchloremia. Calculation of AG in urine: Urine AG = ( Na+ + K+ ) – CL- In a patient with a hyperchloraemic metabolic acidosis: •A negative UAG  GIT loss of bicarbonate (eg diarrhoea) •A positive UAG  impaired renal distal acidification (ie renal tubular acidosis).
  23. 23. BASE EXCESSBASE EXCESS  It is an estimate of the amount of strong acid orIt is an estimate of the amount of strong acid or base needed to correct the met. component of anbase needed to correct the met. component of an acid base disorder (restore plasma pH to 7.40at aacid base disorder (restore plasma pH to 7.40at a PacoPaco22 40 mmHg)40 mmHg) represent only the metabolic component of acid base disorders.  Its +ve value indicate metabolic alkalosis, wIts +ve value indicate metabolic alkalosis, while –ve value indicate metabolic acidosis.
  24. 24. Study Case - 1Study Case - 1  A 39 year old woman was admitted with a history ofA 39 year old woman was admitted with a history of generalized weakness, dyspnea, continuous nauseageneralized weakness, dyspnea, continuous nausea and diarrhea. Bowel motions were frequent andand diarrhea. Bowel motions were frequent and watery.watery.  ABG: pH 7.29, PaCO2 25.6, PaO2 98ABG: pH 7.29, PaCO2 25.6, PaO2 98  NaNa++ =125, K=125, K++ =2.8, Cl=2.8, Cl-- =101, HCO=101, HCO33=14=14 AG = Na – (Cl+HCO3) AG = 125 – (101+14) = 10 Normal anion gap metabolic acidosis
  25. 25. Metabolic AlkalosisMetabolic Alkalosis  Characterized byCharacterized by  PrimaryPrimary ↑↑ in HCO3 concentrationin HCO3 concentration  CompensatoryCompensatory ↑↑ in PaCO2in PaCO2  Classified according to urinary chlorideClassified according to urinary chloride  Chloride responsiveChloride responsive  Chloride resistantChloride resistant
  26. 26. Metabolic AlkalosisMetabolic Alkalosis Chloride ResponsiveChloride Responsive Urine ClUrine Cl-- >20 mEq/L>20 mEq/L  Volume Contraction:Volume Contraction:  Nasogastric suctioningNasogastric suctioning  VomitingVomiting  DiureticsDiuretics  Post HypercapniaPost Hypercapnia  HypokalemiaHypokalemia  HypomagnesemiaHypomagnesemia  PenicillinPenicillin
  27. 27. Metabolic AlkalosisMetabolic Alkalosis Chloride UnresponsiveChloride Unresponsive  Mineralcorticoid excessMineralcorticoid excess  Exogenous steroidsExogenous steroids  Alkali IngestionAlkali Ingestion  LicoriceLicorice  Too much wineToo much wine  Tobacco chewersTobacco chewers  Bartter’s SyndromeBartter’s Syndrome Urine Cl- < 20 mEq/LUrine Cl- < 20 mEq/L
  28. 28. Case Study - 2Case Study - 2  A 78 year old lady presented with at a 1 weekA 78 year old lady presented with at a 1 week history of abdominal pain and vomiting.history of abdominal pain and vomiting.  ABG: pH 7.49, PaCO2 52, PaO2 78ABG: pH 7.49, PaCO2 52, PaO2 78  Na 137, K 2.2, CL 91, HCO3 38Na 137, K 2.2, CL 91, HCO3 38  Urine CI 43Urine CI 43 mEq/LmEq/L Metabolic Alkalosis Vomiting and hypokalemia
  29. 29. SolvingSolving Acid Base DisordersAcid Base Disorders
  30. 30. Rule 1Rule 1 Validate the ABGValidate the ABG [H[H++ ] = 24 (PaCO] = 24 (PaCO22 / HCO/ HCO33 -- )) 80 - [H80 - [H++ ]] ~ the last two digits of the pH~ the last two digits of the pH  [H[H++ ] of 24: pH of (80-24=56) ~ 7.] of 24: pH of (80-24=56) ~ 7.5656  [H[H++ ] of 53: pH of (80-53=27) ~ 7.] of 53: pH of (80-53=27) ~ 7.2727
  31. 31. Another method Determine if numbers fit:Determine if numbers fit: H+ =H+ = 3 2 HCO PCO24× H+ = (7.8-PH)×100.H+ = (7.8-PH)×100. The Rt side of the equation should beThe Rt side of the equation should be within 10% of the Lt Side. If not so anotherwithin 10% of the Lt Side. If not so another ABG or chemistry panel for HCO3 should beABG or chemistry panel for HCO3 should be done.done.
  32. 32. Rule 2Rule 2  What is the pH?What is the pH?  > 7.40 → 1° disorder is alkalosis> 7.40 → 1° disorder is alkalosis  < 7.40 → 1° disorder is acidosis< 7.40 → 1° disorder is acidosis  Does theDoes the PaCOPaCO22 explains the pH?explains the pH?  YesYes → 1° disorder is respiratory→ 1° disorder is respiratory  No → 1° disorder is metabolicNo → 1° disorder is metabolic
  33. 33. Rule 3Rule 3  Does theDoes the PaCOPaCO22 explains the pH?explains the pH?  YesYes → 1° disorder is respiratory→ 1° disorder is respiratory  No → 1° disorder is metabolicNo → 1° disorder is metabolic
  34. 34. Rule 4Rule 4 Apply compensation rulesApply compensation rules  If calculated compensation:If calculated compensation:  Within the expected range → simpleWithin the expected range → simple acid/base disorderacid/base disorder  Less or more than expected → 2°Less or more than expected → 2° acid/base disorderacid/base disorder
  35. 35. There is no over correction orThere is no over correction or compensation in acid base balance →compensation in acid base balance → if the compensatory response is moreif the compensatory response is more or less than expected → it is mixedor less than expected → it is mixed acid base disorderacid base disorder
  36. 36. Case Study - 1Case Study - 1  A 39 year old woman was admitted with a historyA 39 year old woman was admitted with a history of generalized weakness, dyspnea, continuousof generalized weakness, dyspnea, continuous nausea and diarrhea. Bowel motions were frequentnausea and diarrhea. Bowel motions were frequent and watery.and watery.  ABG: pH 7.29, PaCO2 26, PaO2 98ABG: pH 7.29, PaCO2 26, PaO2 98  NaNa++ =125, K=125, K++ =2.8, Cl=2.8, Cl-- =101, HCO=101, HCO33=12=12 PaCO2 = [1.5 x HCO3 + 8] ± 2PaCO2 = [1.5 x HCO3 + 8] ± 2 PaCO2 = 25 ± 2PaCO2 = 25 ± 2 Simple (compensated) metabolic acidosis
  37. 37. Case Study - 2Case Study - 2  A 78 year old lady presented with at least aA 78 year old lady presented with at least a week history of abdominal pain and vomiting.week history of abdominal pain and vomiting.  ABG: pH 7.49, PaCO2 52, PaO2 78ABG: pH 7.49, PaCO2 52, PaO2 78  Na 137, K 2.2, CL 91, HCO3 38Na 137, K 2.2, CL 91, HCO3 38  Urine CI 43Urine CI 43 mEq/LmEq/L Metabolic Alkalosis ∆∆PaCO2 = 0.9 ∆ HCO3 : 0.9 X 14 = 17PaCO2 = 0.9 ∆ HCO3 : 0.9 X 14 = 17 PaCO2 = 53PaCO2 = 53 Simple
  38. 38. Mixed Acid-Base DisordersMixed Acid-Base Disorders  pH may be within normal (7.35-7.45)pH may be within normal (7.35-7.45)  Cannot over-compensateCannot over-compensate  Simultaneous co-existence ofSimultaneous co-existence of disordersdisorders  2 respiratory + 2 metabolic2 respiratory + 2 metabolic  Acute on top of chronicAcute on top of chronic  The pH determines which is primary:The pH determines which is primary:  pH < 7.40 – primary disorder is AcidosispH < 7.40 – primary disorder is Acidosis  pH > 7.40 – primary disorder is AlkalosispH > 7.40 – primary disorder is Alkalosis
  39. 39.  A 21 year old MS is brought to the ER at ~3A 21 year old MS is brought to the ER at ~3 am, stuporous and tachypneic. History isam, stuporous and tachypneic. History is remarkable for failing the respiratory moduleremarkable for failing the respiratory module in 2in 2ndnd year. An ABG and electrolytes haveyear. An ABG and electrolytes have been drawn by the ER nurse.been drawn by the ER nurse.  ABG: pH=7.38, PaCOABG: pH=7.38, PaCO22=18=18  NaNa++ =140, K=140, K++ =3.8, Cl=3.8, Cl-- =106, HCO=106, HCO33=12=12 Case Study - 3Case Study - 3
  40. 40.  A 21 year old MS is brought to the ER at ~3 am, stuporous and tachypneic.A 21 year old MS is brought to the ER at ~3 am, stuporous and tachypneic. History is remarkable for failing the respiratory module in 2History is remarkable for failing the respiratory module in 2ndnd year. An ABG andyear. An ABG and electrolytes have been drawn by the ER nurse.electrolytes have been drawn by the ER nurse.  ABG: pH=7.38, PaCOABG: pH=7.38, PaCO22=18=18  NaNa++ =143, K=143, K++ =3.8, Cl=3.8, Cl-- =106, HCO=106, HCO33=12=12 Case Study - 3Case Study - 3 AG = 143-106-12 = 25 Wide AG Metabolic acidosis PaCO2 = 1.5 X 12 +8 = 26 ±2 Wide AG metabolic acidosis and Respiratory Alkalosis Aspirin Overdose
  41. 41. Primary Respiratory DisordersPrimary Respiratory Disorders Acute vs. ChronicAcute vs. Chronic  ACUTEACUTE  Δ PCO2 = 10 → Δ pH=0.08 (~0.1)Δ PCO2 = 10 → Δ pH=0.08 (~0.1)  CHRONICCHRONIC  Δ PCO2 = 10 → Δ pH=0.03Δ PCO2 = 10 → Δ pH=0.03
  42. 42.  A 55 year old woman presented to the ERA 55 year old woman presented to the ER with dyspnea and wheezes. She is heavywith dyspnea and wheezes. She is heavy smoker. An ABG and electrolytes have beensmoker. An ABG and electrolytes have been drawn by the ER nurse.drawn by the ER nurse.  ABG: pH=7.33, PaCOABG: pH=7.33, PaCO22=65=65  NaNa++ =144, K=144, K++ =4.2, Cl=4.2, Cl-- =104, HCO=104, HCO33=32=32 Case Study - 4Case Study - 4
  43. 43.  A 55 year old woman presented to the ER with dyspnea andA 55 year old woman presented to the ER with dyspnea and wheezes. She is heavy smoker. An ABG and electrolytes havewheezes. She is heavy smoker. An ABG and electrolytes have been drawn by the ER nurse.been drawn by the ER nurse.  ABG: pH=7.33, PaCOABG: pH=7.33, PaCO22=65=65  NaNa++ =144, K=144, K++ =4.2, Cl=4.2, Cl-- =104, HCO=104, HCO33=32=32 Case Study - 4Case Study - 4 Chronic Respiratory Acidosis
  44. 44. Approach To ALL Acid/BaseApproach To ALL Acid/Base ProblemsProblems  Don’t get overwhelmed by all the numbersDon’t get overwhelmed by all the numbers at once!at once!  Use a methodical system to dissect theUse a methodical system to dissect the numbers.numbers.  Don’t jump ahead when doing calculations.Don’t jump ahead when doing calculations.
  45. 45. METHODICAL SYSTEMMETHODICAL SYSTEM  Get all your numbers in front you first…Get all your numbers in front you first…  Look at pH first: Acidotic or alkalotic?Look at pH first: Acidotic or alkalotic?  Metabolic or Respiratory?Metabolic or Respiratory?  Go straight to Bicarb!Go straight to Bicarb!  Correlate bicarb with PCO2 and it should beCorrelate bicarb with PCO2 and it should be obviousobvious  Calculate anion gap no matter what theCalculate anion gap no matter what the disturbance is!disturbance is!
  46. 46. SYSTEM…continuedSYSTEM…continued  After you come up with “primary disturbance”,After you come up with “primary disturbance”, your next question should ALWAYS BE =your next question should ALWAYS BE =  ““Is there compensation?”Is there compensation?”  For metabolic acidosis… do last two digits of pHFor metabolic acidosis… do last two digits of pH equal PCO2 or notequal PCO2 or not  For resp acidosis… is it acute or chronic, and isFor resp acidosis… is it acute or chronic, and is the HCO3 up appropriately?the HCO3 up appropriately?  For resp alkalosis… is it acute or chronic, and isFor resp alkalosis… is it acute or chronic, and is the HCO3 down appropriately?the HCO3 down appropriately?
  47. 47. CompensationCompensation The Two Given Rules of Compensation:The Two Given Rules of Compensation: 1.1. METABOLIC = BICARB (HCO3)METABOLIC = BICARB (HCO3) ……So if you dealing with figuring out yourSo if you dealing with figuring out your disturbance and it is metabolic (up or downdisturbance and it is metabolic (up or down HCO3), then the compensation will beHCO3), then the compensation will be RESPIRATORY (is the PCO2 appropriatelyRESPIRATORY (is the PCO2 appropriately up or down)up or down)
  48. 48. Compensation…continuedCompensation…continued 2.2. RESPIRATORY = PCO2RESPIRATORY = PCO2 ……So if you are dealing with respiratorySo if you are dealing with respiratory alkalosis or acidosis, you want to know ifalkalosis or acidosis, you want to know if the METABOLIC (HCO3) compensationthe METABOLIC (HCO3) compensation is appropriate or notis appropriate or not
  49. 49. SYSTEM…continuedSYSTEM…continued  If the compensation is INAPPROPRIATE, thenIf the compensation is INAPPROPRIATE, then you automatically have a SECONDyou automatically have a SECOND superimposed acid/base disordersuperimposed acid/base disorder
  50. 50. Case 1Case 1  A 75-year-old man presents to the ED after aA 75-year-old man presents to the ED after a witnessed out of hospital VF cardiac arrest.witnessed out of hospital VF cardiac arrest.  Arrived after 10 minutes, CPR had not beenArrived after 10 minutes, CPR had not been attempted.attempted.  The paramedics had successfully restoredThe paramedics had successfully restored spontaneous circulation after 6 shocks.spontaneous circulation after 6 shocks.  On arrival the man is comatose with a GCS of 3On arrival the man is comatose with a GCS of 3 and his lungs are being ventilated with 50%and his lungs are being ventilated with 50% oxygen via ET tube.oxygen via ET tube.  He has HR of 120/min and a blood pressure ofHe has HR of 120/min and a blood pressure of 150/95 mmHg.150/95 mmHg.
  51. 51. ABG Analysis reveals:ABG Analysis reveals:  FFiiOO22 0.50.5  pHpH 7.107.10  PaCOPaCO22 45 mmHg45 mmHg  PaOPaO22 56 mmHg56 mmHg  HCOHCO33 -- 14 mmol/l14 mmol/l  BEBE - 10 mmol/l- 10 mmol/l
  52. 52. Case 2Case 2  A 65-year-old man with severe COPDA 65-year-old man with severe COPD has just collapsed in the respiratoryhas just collapsed in the respiratory high-care unit.high-care unit.  On initial assessment he is found to beOn initial assessment he is found to be apnoeic but has an easily palpableapnoeic but has an easily palpable carotid pulse at 90/min.carotid pulse at 90/min.  A nurse is ventilating his lungs withA nurse is ventilating his lungs with an Ambu bag and supplementary O2an Ambu bag and supplementary O2
  53. 53. ABG Analysis reveals:ABG Analysis reveals:  FFiiOO22 0.85 (estimated)0.85 (estimated)  pHpH 7.207.20  PaCO2PaCO2 151 mmHg151 mmHg  PaO2PaO2 147 mmHg147 mmHg  HCO3-HCO3- 36 mmol/l36 mmol/l  BEBE + 12 mmol/l+ 12 mmol/l
  54. 54. Case 3Case 3  A 75-year-old lady is admitted to the EDA 75-year-old lady is admitted to the ED following a VF cardiac arrest, which wasfollowing a VF cardiac arrest, which was witnessed by the paramedics.witnessed by the paramedics.  A spontaneous circulation was restoredA spontaneous circulation was restored after 4 shocks, but the patient remainedafter 4 shocks, but the patient remained comatose and apnoeic.comatose and apnoeic.  The paramedics intubated her trachea,The paramedics intubated her trachea, and on arrival in hospital her lungs areand on arrival in hospital her lungs are being ventilated with an automaticbeing ventilated with an automatic ventilator using a tidal volume of 900 mlventilator using a tidal volume of 900 ml and a rate of 18 breaths/min.and a rate of 18 breaths/min.
  55. 55. ABG Analysis reveals:ABG Analysis reveals:  FFiiOO22 1.01.0  pHpH 7.607.60  PaCOPaCO22 20 mmHg20 mmHg  PaOPaO22 192 mmHg192 mmHg  HCOHCO33 -- 20 mmol/l20 mmol/l  BEBE - 4 mmol/l- 4 mmol/l
  56. 56. Case 4Case 4  An 18-year-old male insulin dependentAn 18-year-old male insulin dependent diabetic is admitted to the ED.diabetic is admitted to the ED.  He has been vomiting for 48 hours andHe has been vomiting for 48 hours and because he was unable to eat, he omittedbecause he was unable to eat, he omitted his insulin.his insulin.  He has HR of 130/min and his bloodHe has HR of 130/min and his blood pressure is 90/65 mmHg.pressure is 90/65 mmHg.  He is breathing spontaneously with deepHe is breathing spontaneously with deep breaths at a rate of 35/min. His GCS is 12breaths at a rate of 35/min. His GCS is 12 (E3, M5, V4(E3, M5, V4).).
  57. 57. ABG Analysis reveals:ABG Analysis reveals:  FFiiOO22 0.40.4  pHpH 6.796.79  PaCOPaCO22 11.3 mmHg11.3 mmHg  PaOPaO22 129.2 mmHg129.2 mmHg  HCOHCO33 -- 4.7 mmol/l4.7 mmol/l  BEBE - 29.2 mmol/l- 29.2 mmol/l
  58. 58. Case 5Case 5 His vital signs are:His vital signs are:  Heart rateHeart rate 120/min – sinus120/min – sinus tachycardia – warm peripheriestachycardia – warm peripheries  Blood pressureBlood pressure 70/40 mmHg70/40 mmHg  Respiratory rateRespiratory rate 35 breaths/min35 breaths/min  SpOSpO22 on oxygenon oxygen 92%92%  Urine outputUrine output 50 ml in the last 6 hours50 ml in the last 6 hours  GCSGCS 13 (E3, M6, V4)13 (E3, M6, V4)
  59. 59. ABG Analysis reveals:ABG Analysis reveals:  FFiiOO22 0.4 (approx)0.4 (approx)  pHpH 7.127.12  PaCOPaCO22 36 mmHg)36 mmHg)  PaOPaO22 62 mmHg62 mmHg  HCOHCO33 -- 12 mmol/l12 mmol/l  BEBE - 15 mmol/l- 15 mmol/l
  60. 60. AnyAny Question?Question?
  61. 61. Thank YouThank You

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