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METABOLIC ACIDOSIS
D8
HISTORY 45 year old Diabetic woman 4th day
Fever (39.5C) Chills Myalgia Diarrhea
Denies taking any medications, drugs or alcohol
PHYSICAL EXAMINATION BP: 84/52 (Supine) PR: 118 bpm RR: 42 breaths/ minute Dry mucous membrane Flat neck veins No edema Abdomen distended, firm & mildly tender Hyperactive bowel sounds
LABORATORY CBC
Result Reference range
Remarks
Hemoglobin 15.5 g/dL 12-16 Normal
Hematocrit 48% 38-48% Normal
WBC count 22,800 5,000-10,000
Normal
Segmenters 66% 50-70% Normal
Band forms 23% 0-5% Increased
LABORATORY CHEMISTRY
Result Reference range
Remark
Serum Na 138.0 meq/L
135-145 Normal
Serum Cl 108.0 meq/L
99-110 Normal
Serum K 4.2 meq/L 4-4.5 Normal
LABORATORY CHEMISTRY
Result Reference range
Remark
pH 7.39 7.35-7.45 Normal
pCO2 17.0 mmHg 35-45 Decreased
HCO3 10.0 meq/L 21-28 Decreased
LABORATORY CHEMISTRY
Result Reference range
Remark
BUN 28.0 mg/dL 7-20 Increased
Creatinine 2.4 mg/dL 0-8-1.4 Increased
LABORATORY CHEMISTRY
Result Reference range
Remark
Glucose 342.0 mg/dL
<100 Increased
Lactate 3.0 meq/L 0.5-1.0 Increased
Ketones None Negative Normal
INTRODUCTION Blood pH
7.35 – 7.45 Extracellular & intracellular buffering process Respiratory & renal regulatory mechanisms
Dispose the body’s normal physiologic load of carbonic acid (as carbon dioxide), non-volatile acids & defend against occasional addition of abnormal quantities of acids & alkalis
BODY SOURCES Volatile acid
Carbon dioxide Aerobic metabolism
Non-volatile acid From breakdown of protein & phospholipid
metabolism Ketoacids, lactic acid, from disease & anaerobic
metabolism
HYDROGEN REGULATION Chemical buffering
Extracellular & intracellular buffers Acts within a fraction of second
Respiratory regulation Altering rate of breathing affecting rate of CO2 removal Acts with minutes to days
Renal regulation Excreting either acid or alkaline urine Acts within hours to several days
QUESTION 1 What is the acid base disturbance present
in this case?
What is the acid-base disturbance present in this case?
Metabolic Acidosis
Metabolic Alkalosis
Respiratory Acidosis
Respiratory Alkalosis
pH
H+
PCO2
HCO3-
Arterial blood sample
pH < 7.40 pH > 7.40
HCO3 < 24 pCO2 > 40
Metabolic acidosis
pCO2 < 40
Respiratory acidosis
HCO3 > 24
HCO3 >24
Metabolic alkalosis
pCO2 > 40
pCO2 < 40
Respiratory alkalosis
HCO3 < 24
Disturbance Primary alteration
Defense mechanism
Metabolic alkalosis
plasma [HCO3-] Intracellular buffers
Hypoventilation to increase PCO2
Urinary excretion of HCO3-
Respiratory acidosis
blood pCO2 Intracellular buffersIncreased renal acid excretion
Respiratory alkalosis
blood pCO2 Intracellular buffers renal acid excretion
Metabolic acidosis
in plasma [HCO3]
Intracellular & extracellular bufferHyperventilation to pCO2
Urinary excretion of H+
Metabolic Acidosis
Metabolic Alkalosis
Respiratory Acidosis
Respiratory Alkalosis
Hx: hypercapnia, dyspnea, anxiety, delirium, obtundation
Hx: dizziness, mental confusion, seizures, tetany
Hx: palpitations, chest pain, visual changes, mental confusion, dyspnea, n/v, diarrhea, tachypnea, hyperpnea
Hx: weakness, myalgia, polyuria, vomitting, diarrhea, hypoventilation
METABOLIC ACIDOSIS Addition of non-volatile acids Loss of non-volatile alkali (Diarrhea) Failure to excrete sufficient net acid load
COMPENSATION ICF & ECF Buffers Respiratory Renal
RESPIRATORY COMPENSATION
METABOLIC ACIDOSIS
STIMULATE CENTRAL& PERIPHERAL
CHEMORECEPTORS
INCREASED ALVEOLARVENTILATION
FALL OF pCO2
RAISE pH TOWARDNORMAL
QUESTION 2 Present an algorithm for the diagnosis of
the acid base disorder. Present the table: rule of thumb in bedside interpretation of acid base disorder
STEPS IN ACID-BASE DIAGNOSIS1. Obtain arterial blood gases (ABGs)
and electrolytes (lytes) simultaneously.2. Compare [HCO3] on ABG and lytes to verify accuracy.
3. Calculate anion gap (AG).
4. Know four causes of high AG acidosis (ketoacidosis, lactic acid acidosis, renal failure and toxins).
5. Know two causes of high hyperchloremic or nongap acidosis (bicarbonate loss from GI tract, renal tubular acidosis).
6. Estimate compensatory response.
7. Compare ΔAG and Δ HCO3
8. Compare change in [Cl] with changes in [Na].
STEPS IN ACID-BASE DIAGNOSIS1. Obtain arterial blood gases (ABGs) and electrolytes (lytes)
simultaneously.
2. Compare [HCO3] on ABG and lytes to verify accuracy. * ± 2mmol/L
3. Calculate anion gap (AG).
4. Know four causes of high AG acidosis (ketoacidosis, lactic acid acidosis, renal failure and toxins).
5. Know two causes of high hyperchloremic or nongap acidosis (bicarbonate loss from GI tract, renal tubular acidosis).
6. Estimate compensatory response.
7. Compare ΔAG and Δ HCO3
8. Compare change in [Cl] with changes in [Na].
STEPS IN ACID-BASE DIAGNOSIS1. Obtain arterial blood gases (ABGs) and electrolytes (lytes)
simultaneously.
2. Compare [HCO3] on ABG and lytes to verify accuracy.
3. Calculate anion gap (AG).4. Know four causes of high AG acidosis (ketoacidosis, lactic acid
acidosis, renal failure and toxins).
5. Know two causes of high hyperchloremic or nongap acidosis (bicarbonate loss from GI tract, renal tubular acidosis).
6. Estimate compensatory response.
7. Compare ΔAG and Δ HCO3
8. Compare change in [Cl] with changes in [Na].
STEPS IN ACID-BASE DIAGNOSIS1. Obtain arterial blood gases (ABGs) and electrolytes (lytes)
simultaneously.
2. Compare [HCO3] on ABG and lytes to verify accuracy.
3. Calculate anion gap (AG).
4. Know four causes of high AG acidosis (ketoacidosis, lactic acid acidosis,
renal failure and toxins).5. Know two causes of high hyperchloremic or nongap acidosis
(bicarbonate loss from GI tract, renal tubular acidosis).
6. Estimate compensatory response.
7. Compare ΔAG and Δ HCO3
8. Compare change in [Cl] with changes in [Na].
STEPS IN ACID-BASE DIAGNOSIS1. Obtain arterial blood gases (ABGs) and electrolytes (lytes)
simultaneously.
2. Compare [HCO3] on ABG and lytes to verify accuracy.
3. Calculate anion gap (AG).
4. Know four causes of high AG acidosis (ketoacidosis, lactic acid acidosis, renal failure and toxins).
5. Know two causes of high hyperchloremic or nongap acidosis(bicarbonate loss from GI tract, renal tubular acidosis).
6. Estimate compensatory response.
7. Compare ΔAG and Δ HCO3
8. Compare change in [Cl] with changes in [Na].
STEPS IN ACID-BASE DIAGNOSIS1. Obtain arterial blood gases (ABGs) and electrolytes (lytes)
simultaneously.
2. Compare [HCO3] on ABG and lytes to verify accuracy.
3. Calculate anion gap (AG).
4. Know four causes of high AG acidosis (ketoacidosis, lactic acid acidosis, renal failure and toxins).
5. Know two causes of high hyperchloremic or nongap acidosis (bicarbonate loss from GI tract, renal tubular acidosis).
6. Estimate compensatory response.7. Compare ΔAG and Δ HCO3
8. Compare change in [Cl] with changes in [Na].
Prediction of Compensatory Responses on Simple Acid Base DisturbancesMetabolic Acidosis
PaCO2 = (1.5 x HCO) + 8 or
PaCO2 will 1.25 mmHg per mmol/L in HCO3
Metabolic Alkalosis
PaCO2 will 0.75 mmHg per mmol/L in HCO3 or
PaCO2 = HCO3 + 15
Respiratory Alkalosis
HCO3 will 2-4 most per 10 mmHg in PaCO2
Respiratory Acidosis
HCO3 will 1-4 mmol/L per 10 mmHg in PaCO2
Prediction of Compensatory Responses on Simple Acid Base Disturbances
Metabolic acidosis pH, HCO3 Stimulate medullary chemoreceptors to
ventilation Predict the degree of respiratory compensation:
PaCO2 = (1.5 x HCO3) + 8 = 23 *21-25 mmHg Values <21 & >25 mixed disturbance PaCO2 < 23 = met acidosis & respi alkalosis PaCO2 > 23 = met alkalosis & respi acidosis
Prediction of Compensatory Responses on Simple Acid Base Disturbances
Acid-Base Nomogram Shaded areas show 95% confidence limits for
normal compensation Finding acid-base values within the shaded
areas does not rule out a mixed disturbance Not a substitute for computation
Prediction of Compensatory Responses on Simple Acid Base Disturbances
Acid-Base Nomogram pH 7.39 HCO3 10 mEq/L PCO2 17 mmHg
STEPS IN ACID-BASE DIAGNOSIS1. Obtain arterial blood gases (ABGs) and electrolytes (lytes)
simultaneously.
2. Compare [HCO3] on ABG and lytes to verify accuracy.
3. Calculate anion gap (AG).
4. Know four causes of high AG acidosis (ketoacidosis, lactic acid acidosis, renal failure and toxins).
5. Know two causes of high hyperchloremic or nongap acidosis (bicarbonate loss from GI tract, renal tubular acidosis).
6. Estimate compensatory response.
7. Compare ΔAG and Δ HCO38. Compare change in [Cl] with changes in [Na].
STEPS IN ACID-BASE DIAGNOSIS1. Obtain arterial blood gases (ABGs) and electrolytes (lytes)
simultaneously.
2. Compare [HCO3] on ABG and lytes to verify accuracy.
3. Calculate anion gap (AG).
4. Know four causes of high AG acidosis (ketoacidosis, lactic acid acidosis, renal failure and toxins).
5. Know two causes of high hyperchloremic or nongap acidosis (bicarbonate loss from GI tract, renal tubular acidosis).
6. Estimate compensatory response.
7. Compare ΔAG and Δ HCO3
8. Compare change in [Cl] with changes in [Na].
QUESTION 3 How do you compute for the anion gap?
What is its significance? Compute for the anion gap.
ANION GAP Represents the difference in concentration
between the major plasma cations & the major plasma anions
Cations: Na+
Anions: Cl- & HCO3-
COMPUTING THE ANION GAP
Anion Gap = [Na+] – ([Cl-] + [HCO3-])
Normal range: 8-16 mEq/L
SIGNIFICANCE OF ANION GAP It is a useful way to determine the cause of
metabolic acidosis because changes in the concentration of anions are a result of addition of nonvolatile acids.
Because the condition is diagnosed as metabolic acidosis, nonvolatile acids are added into the body fluids.
ANION GAP If the nonvolatile acid contains Cl- the anion
gap will remain normal (because the decrease in HCO3
- is matched by the increase in Cl-)
If the nonvolatile acid contains another substance, the anion gap will increase (because the Cl- concentration remains unchanged)
COMPUTATION OF ANION GAP
Anion Gap = [Na+] – ([Cl-] + [HCO3-])
Anion Gap = [138.0] – ([108.0] + [10.0])
Anion Gap = (138.0) – (118.0)Anion Gap = 20.0 mEq/L
NR: 8-16 mEq/L** The anion gap is increased
QUESTION 4 What are the causes of high anion gap and
normal anion gap acidosis?
NOMAL VS HIGH NORMAL ANION GAP
Acid gain or bicarbonate loss is accompanied by chloride gain
Anion gap remains unchanged
HIGH ANION GAP Accumulation of acid
anions in ECF Exogenous acid
ingestion Increased endogenous
acid production
DIARRHEA
↑ loss of HCO3 along w/ vol. depletion
Matabolic acidosis and hypokalemia
↑renal synthesis and excretion of NH4
NORMAL ANION GAP
RENAL TUBULAR ACIDOSIS(GFR bet. 20 and 50 mL/min)
↓ # of functioning nephrons
Proximal RTA: ↓ HCO3 tubular reabsorptionOR
Distal RTA: ↓ acid excreation
↑renal synthesis and excretion of NH4
OTHER CAUSES OF NORMAL ANION GAP
Carbonic anhydrase inhibition
Drug-induced hyperkalemia (With renal insufficiency)
HIGH ANION GAP Lactic Acidosis
Increase in plasma lactate Secondary to poor tissue perfusion (Type A) Aerobic disorders (Type B)
Ketoacidosis Increase fatty acid metabolism Accumulation of ketoacids (Acetoacetate & -
hydroxybutyrate) Diabetic ketoacidosis, alcoholic ketoacidosis
↑ ANION GAP Drug and toxin induced
Salicylates: ketones, lactate, salicylate ethylene glycol: glycolate, oxalate Methanol or formaldehyde: Formate
Advanced Renal failure: Sulfate, phosphate, urate
↑ ANION GAP Advanced RF
↓ # of functioning nephrons
Dec. NH4+ prod. and excretion
Failure to balance w/ net acid production
Inc. anion gap
QUESTION 5 How would you treat this patient?
Normal AG acidosis (hyperchloremic acidosis), a slightly elevated AG (mixed hyperchloremic and AG acidosis), or an AG attributable to a nonmetabolizable anion in the face of renal failure: --> Alkali theraphy orally (NaHCO3) or Shohl's solution) IV (NaHCO3), in an amount necesarry to slowly increase the
plasma [HCO3-] into the 20 to 22 mmol/L range. The condition that precipitated the metabolic acidosis in
the patient should also be managed. (Fever and diarrhea ~ Gastroenteritis??)
THANK YOU..