DISTURBANCE ACID BASE

DR. AKIF AHSAN Assistant Professor

Dept. of Biochemistry JNMC, AMU, Aligarh

A C I D O S I S

A L K A L O S I S

Accumulation of acids or loss of bases

The pH in the arterial blood is < 7.38

Accumulation of bases or loss of acids

The pH in the arterial blood is > 7.42

H2CO3

NaHCO3

NaHCO3

NaHCO3

H2CO3

H2CO3

Metabolic Acidosis

Metabolic Alkalosis

Respiratory Alkalosis

Respiratory Acidosis

OBJECTIVES By the end of this session you should be able to

mention the primary defect, mention the compensatory change and enumerate the

causes of:

Metabolic acidosis 1.

Metabolic alkalosis 2.

Respiratory acidosis 3.

Respiratory alkalosis 4.

Metabolic Acidosis

H2CO3

NaHCO3

< 20

H2CO3

NaHCO3

Primary Defect

Compensation

Secondary Hyperventilation

pH

Clinical Manifestations

Kussmaul Respiration (Deep & Labored breathing)

Lethargy, confusion, headache & weakness.

Nausea & Vomiting

ANION GAP CATIONS ANIONS

ANION GAP (12-16 mEq/L)

ANION GAP = (Na+ + K+) – (HCO3- + Cl -)

Unmeasured Anions

Na+

K+

HCO3-

Cl-

135-145 mEq/L

3.5-5 mEq/L

22-28 mEq/L

96-106 mEq/L

CATIONS ANIONS

Anion Gap (NORMAL)

Unmeasured Anions

Na+

K+

HCO3-

Cl-

NORMAL Anion Gap Metabolic Acidosis

Metabol ic A c ido s i s

CATIONS ANIONS

Anion Gap (HIGH)

Unmeasured Anions

Na+

K+

HCO3-

HIGH Anion Gap Metabolic Acidosis

Metabol ic A c ido s i s

Cl-

↑ Loss of HCO3-

↑ Acid Production

↓ HCO3- reabsorption / ↓ H+ excretion

Causes of Metabolic Acidosis

Diarrhea

Lactic acidosis Diabetic keto-acidosis

Starvation

Renal failure Renal tubular acidosis Acetazolamide therapy

NAGMA (in BLACK) / HAGMA (in RED)

Respiratory Alkalosis

H2CO3

NaHCO3

> 20

H2CO3

NaHCO3

Primary Defect

Compensation

↑ HCO3- excretion

pH

Causes of Respiratory Alkalosis (Hyper-ventilation)

CNS stimulation

Anxiety Psychosis

Fever

Tissue Hypoxia

High altitude Severe Anemia

Miscellaneous causes

Hemothorax (stimulation of J receptors) Mechanical ventilation

Clinical Manifestations

Tachypnea

Chest pain

Light headedness, syncope, seizures

Respiratory Acidosis

H2CO3

NaHCO3

< 20

H2CO3

NaHCO3

Primary Defect

Compensation

Retention of HCO3

- by kidneys

pH

Causes of Respiratory Acidosis (Hypo-ventilation)

Depression of respiratory center

Sedatives Morphine

Obstruction of respiratory tract

COPD Foreign body in upper resp. tract

Miscellaneous causes

Acute asthmatic attack Neuromuscular disorder (Muscular dystrophy)

Clinical Manifestations

Breathlessness & Restlessness

Excess CO2 causes Vasodilation (warm & flushed skin)

Metabolic Alkalosis

H2CO3

NaHCO3

> 20

H2CO3

NaHCO3

Primary Defect

Compensation

Secondary Hypoventilation

pH

↑ HCO3- reabsorption / ↑ H+ excretion

Diuretics Hyper-aldosteronism

↑ Acid loss Vomit ing

Addition of exogenous base

Causes of Metabolic Alkalosis

Antacid Overdose (Magnesium hydroxide)

Electrolyte Shift (compensatory response)

ALKALOSIS

H+ H+

H+

H+

H+

H+ H+

H+ H+ H+

ACIDOSIS H+ is buffered intra-cellularly

Hyper-kalemia

Cells try to correct alkalosis

Hypo-kalemia

K+

K+

H+

H+

H+

H+

H+ K+

K+

Normal ABG Values

PaO2 : 75 to 100 mm Hg

PaCO2 : 38 to 42 mm Hg

HCO3- : 22 to 28 mM/L

Arterial Blood pH : 7.38 to 7.42

MCQ

a) Metabolic acidosis b) Metabolic alkalosis c) Respiratory acidosis d) Respiratory alkalosis

A person was admitted in a coma. Analysis of the arterial blood gave the following values: PCO2 16 mm

Hg; HCO3- 5 mM/L and pH 7.1. What is the

underlying acid-base disorder?

[KEY: a]

MCQ

a) Metabolic acidosis b) Metabolic alkalosis c) Respiratory acidosis d) Respiratory alkalosis

In a man undergoing surgery, it was necessary to aspirate the contents of the upper GI tract. After surgery, the following values were obtained from an arterial blood sample: pH 7.55; PCO2 52 mm Hg and HCO3

- 40 mM/L. What is the underlying disorder?

[KEY: b]

MCQ

a) Uncompensated metabolic acidosis b) Uncompensated respiratory acidosis c) Simultaneous respiratory and metabolic acidosis d) Respiratory acidosis with partial renal

compensation

A young woman is found comatose, having taken an unknown number of sleeping pills an unknown time before. Her ABG report is as follows: pH 6.90;

HCO3- 13 mM/L, PaCO2 68 mm Hg. Her acid-base status is most accurately described as:

[KEY: c]

MCQ

a) ↓ pCO2, normal HCO3- & ↑ pH

b) ↓ pCO2, ↓ HCO3- & ↓ pH

c) ↑ pCO2, normal HCO3- & ↓ p H

d) ↑ pCO2, ↑ HCO3- & ↑ pH

Which of the following laboratory results below indicates compensated metabolic

alkalosis?

[KEY: d]

MCQ

a) Diarrhea b) Vomiting c) Diabetic keto-acidosis d) Starvation

Normal anion gap metabolic acidosis can be seen in:

[KEY: a]

MCQ

a) Mineralocorticoid excess b) Hyperkalemia c) Thiazide diuretic therapy d) Recurrent vomiting

Causes of metabolic alkalosis include all the following except:

[KEY: b]

MCQ

a) Anxiety b) Severe Anemia c) Acute Asthmatic Attack d) Hemothorax

All the following may cause respiratory alkalosis, except:

[KEY: c]

CAN YOU ??? By the end of this session you should be able to

mention the primary defect, mention the compensatory change and enumerate the

causes of:

Metabolic acidosis 1.

Metabolic alkalosis 2.

Respiratory acidosis 3.

Respiratory alkalosis 4.