Hypoxia

HYPOXIA Definition: Lack of oxygen at tissue levels. Types of hypoxia: 1. HYPOXIC 2. ANEMIC 3. STAGNANT 4. HISTOTOXIC

POINTS TO REMEMBER: 1. Hypoxic hypoxia is the most common cause of hypoxia. 2. Peripheral chemoreceptors are stimulated by all types of hypoxia except histotoxic hypoxia. HYPOXIC HYPOXIA Characterized by 1. Low arterial pO2. 2. Low arterial % O2 saturation of Hb. 3. Amount of Hb is normal. 4. Rate of blood flow is normal. Causes: 1. High altitude: low pO2 IN inspired air 2. Decreased alveolar ventilation: 1) airway obstruction. 2) Respiratory centre pO2 by drugs. 3) Weakness of respiratory muscles. 3. Gas exchange failure. 1) All factors altering ventilation Perfusion ratio.(V/P ratio) 4. Venous arterial shunt. (Congenital heart disease.).

PATHOPHYSIOLOGY: HYPOXIC HYPOXIA ↓ RESPIRATORY CENTRE ↓ HYPERVENTILATION ↓ DECREASED pCO2 ↓ O2 HB curve shifts to left ↓ Less release of O2 from Hb. ↓ Tissue hypoxia.

ANAEMIC HYPOXIA

CHARACTERISTIC FEATURES: 1. Arterial pO2 is normal. 2. Arterial O2 content is decreased 3. Hb is reduced. 4. Arterial % O2 saturation of Hb decreased 5. Blood flow is normal. CAUSES: 1. 2. 3. 4.

Anemia. Bleeding Methemoglobinemia. Presence of carboxy hemoglobin.

STAGNANT HYPOXIA DEFINITION: Blood flow to the tissue is low leading to decreased O2 delivery to tissues. Characteristic features: 1. Blood flow to the tissues is decreased 2. Normal arterial O2 content. 3. Normal arterial PO2. 4. Normal arterial % O2 saturation of Hb. 5. Normal Hb. Causes: 1. Circulatory failure 2. Bleeding 3. Heart failure.

HISTOTOXIC HYPOXIA DEFINITION: Oxygen delivery to the tissues is normal but due to action of toxic agents, tissues cannot make use of O2 delivered to them. Characteristic features: 1. Normal arterial pO2. 2. Normal arterial % O2 SATURATION OF Hb. 3. Normal Hb. 4. BLOOD FLOW IS NORMAL. 5. Hb content is normal. Causes: 1. Toxic agents: cyanide poisoning .

Hypoxic hypoxia

Stagnant hypoxia.

Anemic hypoxia

Histotoxic hypoxia.

1.Hb Normal 2.Arterial decreases PO2 normal 3. Blood flow to tissues.

Normal normal decreased

Decreased normal normal

Normal normal normal

Circulatory collapse. Bleeding Heart failure

Cyanide poisoning Anemia Bleeding Methemoglob inemia Presence of carboxy hemoglobin.

O2 Decreases.

normal

Significantly reduced.

normal

Decreased

Normal

Normal

Normal

Arterial %O2 Decreased saturation of Hb

Normal

Decreased

Normal

Characteristic features

Low PO2 in inspired air. Decreased pulmonary ventilation. Altered V/P Ratio.

Causes

Arterial content

Arterial PO2