ACID-BASE DISORDERS

ISMAIL M. SIALA

ACID-BASE DISORDERS

Acid-base disorders

Pulse

Haemoglobin

Ca, K, …Temperatur

e

Hydrogen Ion Concentratio

n

Blood Pressure

AbnormalCellularFunction

Acid-base disorders

Pulse

Hemoglobin

Blood Pressure

Tem

perat

ure

ProperCell

Function

Ca, K, …

Physiological

Daily Metabolism

Pathological

DKA

Hydrogen Ion Concentration

Acid-base disorders

Hydrogen Ion Concentration

H+H+

AcidosisAlkalosis

Compensatory Mechanisms

H+ should be normal for normal cellular function.

The body will try to restore the H+ to normal

Compensatory Mechanisms

Complete

H+ returns to normal range

Incomplete

H+ approaches normal range but still abnormal

Compensatory Mechanisms

Kidney

Lung

• CO2-HCO3 System• Hydroxyapatite-Bone• Haemoglobin

Body Buffers

CO2-bicarbonate system

H+ + HCO3 H2CO3 H2O + CO2

Kidney

Lung

pH and H+ concentration

The blood pH represents the H+ concentration pH = - log10 aH+ aH+ = 10 (-pH) )

where aH+ is activity of H+

H+ (nM) 44 40 36

pH 7.36 7.47.44

AlkalosisAcidosis

Acid-base disorders

Hydrogen Ion Concentration

H+H+

AcidosisAlkalosis

pHpH

PH 7.36-7.44 7.4 +.04

PaCO2 35 – 45 mmHg 40 + 5

HCO3 21 – 28 mmol\l 25 +3

PaO2 83 – 108 mmHg

Acid base disturbances

Arterial blood sample Normal values

Heparinized syringe

Radial artery

• A 2 ml syringe• Heparinized• Radial/ femoral artery• Draw 1 ml of blood• Send for analysis

immediately or send in an ice pack

Acid-base disorders

AcidosisAlkalosis

Acid-base disorders

AcidosisMetabolicRespiratory

AlkalosisMetabolicRespiratory

HCO3

Metabolic acidosis

a pH< 7.36 characterized by low plasma HCO3-.

PaCO2 will secondary to

hyperventilation .

Definition:

ACID PaCO2

ALKALI HCO3

H+ + HCO3 H2CO3 H2O + CO2

Mechanisms of Excess H+ in metabolic acidosis

H+ +HCO3 HCO3

Loss of HCO3 more production of H+

Kidney GIT

Small intestine Pancreas

H+ + HCO3 H2CO3 H2O + CO2

H+ + HCO3 H2CO3 H2O + CO2

Anion Gap

ANION GAP

Na+

Anion Gap

HCO3_

Cl-

“Anion gap represents the difference between readily measured anions and cations”

Anion gap = Plasma Na+ - (Cl- + HCO3-)

N= 8 – 14 mmol\l

Unmeasured Anions: albumin, phosphate, sulphate, lactate, ketoacids, others.

Unmeasured Cations: calcium, Mg, globulins, K.

Aetiology of metabolic acidosis

Na+

Anion GapHCO3

_

Cl-

Na+

Anion GapHCO3

_

Cl-

Increased Anion gap acidosis:Lactic acidosisKetoacidosis Diabetic

AlcoholToxins Methanol

Ethylene glycolSalicylate

Uraemia ARF CRF

Normal Anion gap acidosisHyperchloremic acidosis

GIT HCO3- lossDiarrheaPancreatic drainage

Renal tubular acidosisDrugs CA inhibitors

Anion Gap

Metabolic acidosis

Features of primary disease

• Kussmaul’s Breathing• Altered consciousness• Hypotension

Features of Metabolic Acidosis

Clinical Features:

Metabolic acidosis

For primary disease

• Arterial Blood Gas analysis.

For Metaboli

c Acidosis

Investigations:

Arterial blood gas findings

METABOLIC ACIDOSIS

pH

N

PaCO2

/N

HCO3

Compensated

Treatment of Metabolic Acidosis

Treat the underlying cause Correct Acidosis

Correct fluid & electrolyte disturbances

Oral HCO3 replacement in GI loss or RTA .

parentral Na HCO3 in severe acidosis pH <7.1

CO

2

RESPIRATORY ACIDOSIS

Definition:a pH < 7.36 due to retention

of CO2 as a result of alveolar ventilation ACID

PaCO2

ALKALI HCO3

H+ + HCO3 H2CO3 H2O + CO2

Respiratory Physiology

RC

RN

Ms

Ribs

Pl S

Lu

Br

Air

InspirationACTIVE

ExpirationPASSIVE

Acute Chronic

Airway Obstruction

• Foreign body• Laryngospasm• Severe bronchospasm

• COAD

Respiratory Center Depression

• Morphine overdose• CVA• Trauma -

Neuromuscular

• High cervical cord resection

• Myasthenia gravis• Gullian Barre syndrome• Organophosphorus

• MS• Muscular dystrophies• Motor neuron

disease• Diaphragmatic

paralysis

Restriction of chest movements

• Tension Pneumothorax• Flail chest

• Kyphoscolisis• Ankylosing spodylitis

-• Primary alveolar

hypoventilation-Obesity

Aetiology (CO2 Retention)

Respiratory acidosis

Features of primary disease

• CO2 Retention:• Throbbing Headache • Altered level of consciousness(severe)• Myoclonus &hyperreflexia• Astrexis, Flapping tremors• Central cyanosis • Collapsing pulse• Warm periphery• Papilloedema

Features of Respiratory Acidosis

Clinical Features:

Respiratory acidosis

For primary disease

• Arterial Blood Gas analysis.

For Respiratory Acidosis

Investigations:

Arterial blood gas findings

RESPIRATORY ACIDOSIS

pH

N

PaCO2

HCO3

N/

Compensated

Respiratory failure

Type I respiratory

failure

PaO2 < 60 mmHg

N/ PaCO2

Type II respiratory

failure

PaCO2 >50 mmHg

Hypoxia with any value of PaO2

Treatment of Respiratroy Acidosis

Treat the underlying cause Correct CO2 Retention

Naloxone if Narcotic overdose is suspected

Low oxygen concentration

Mechanical ventilation in severe cases

HC

O3

METABOLIC ALKALOSIS

Definition:a pH > 7.44 characterized

by high plasma HCO3

PaCO2 may .In normal renal function it

is rare, why?

ACID PaCO2

ALKALI HCO3

H+ + HCO3 H2CO3 H2O + CO2

Aetiology

• GIT loss• Vomiting• Aspiration of gastric contents

Loss of H+, Cl, & Na (Associated with EC volume depletion)

• Diuretics• penicillinsLoss through kidney

K depletion

• Cushing• OthersMineralocorticoid excess

• In patients with impaired renal functionExogenous alkali

Metabolic Alkalosis

Features of primary disease

• Tetany:• Acute Fall in Ionized Calcium level.

• Manifest:• Carpo-pedal Spasm.• Laryngeal spasm.

• Latent:

• Aletered level of consciousness

Features of Alkalosis

Clinical Features:

Chvostok sign Traussau sign

Metabolic Alkalosis

For primary disease

• Arterial Blood Gas analysis.

For Metaboli

c Alkalosis

Investigations:

Arterial blood gas findings

METABOLIC ALKALOSIS

pH

N

PaCO2

N/

HCO3

Compensated

Treatment of Metabolic Alkalosis

Treat the underlying cause

Mineralo corticoid excess

Hypokalaemia

Improve GFR

Correct EC fluid depletion GFR enhance HCO3 excretion.

CO

2

RESPIRATORY ALKALOSIS

Definition: pH>7.44 due to CO2

washout as a result of hyperventilation

ACID PaCO2

ALKALI HCO3

H+ + HCO3 H2CO3 H2O + CO2

Aetiology

Hypoxia Voluntary CNS Disease

CVA Infections Trauma Tumours

DrugsAspirin Hepatic Failure Gram Negative Septicaemia Heat Exposure Mechanical overventilation

Respiratory Alkalosis

Features of primary disease

• Tetany:• Acute Fall in Ionized Calcium level.

• Manifest:• Parasthesia, numbness around mouth• Carpo-pedal Spasm.• Laryngeal spasm.

• Latent:

• Aletered level of consciousness

Features of Alkalosis

Clinical Features:

Chvostok sign Traussau sign

Respiratory Alkalosis

For primary disease

• Arterial Blood Gas analysis.

For Respiratory Alkalosis

Investigations:

Arterial blood gas findings

RESPIRATORY ALKALOSIS

pH

N

PaCO2

HCO3

/N

Compensated

Treatment of Respiratory Alkalosis

Treat the underlying cause Supportive measures

Rebreathing in a paper bag in Hyperventilation syndrome + sedation

pH PaCO2 HCO3

METABOLIC ACIDOSIS

(OR LOW

NORMAL)

Compensatory

METABOLIC

ALKALOSIS

(OR HIGH NORMAL)

Compensatory

RESPIRATORY ACIDOSIS

(OR LOW

NORMAL)

Compensatory

RESPIRATORY ALKALOSIS

(OR HIGH

NORMAL)

Compensatory

Summary