OXYGEN TOXICITY (POISONING)

OXYGEN TOXICITY (POISONING)

Oxygen toxicity is the increased oxygen content in tissues, beyond certain critical level. It is also called oxygen poisoning. It occurs because of breathing pure oxygen with a high pressure of 2 to 3 atmosphere (hyperbaric oxygen). In this condition, an excess amount of oxygen is transported in plasma as dissolved form because oxygen carrying capacity of hemoglobin is limited to 1.34 mL/g.

EFFECTS OF OXYGEN TOXICITY

1. Lung tissues are affected first with tracheobronchial irritation and pulmonary edema

2. Metabolic rate increases in all the body tissues andthe tissues are burnt out by excess heat. Heat also

destroys cytochrome system, leading to damage of tissues.

3. When brain is affected, first hyperirritability occurs. Later, it is followed by increased muscular twitching,

ringing in ears and dizziness.

4. Finally, the toxicity results in convulsions, coma and death.

HYPERCAPNEA

Hypercapnea is the increased carbon dioxide content of blood.

CONDITIONS WHEN HYPERCAPNEA OCCURS

Hypercapnea occurs in conditions, which leads to blockage of respiratory pathway, as in case of asphyxia. It also occurs while breathing the air containing excess carbon dioxide content.

EFFECTS OF HYPERCAPNEA

1. Effects on Respiration

During hypercapnea, the respiratory centers are stimulated excessively. It leads to dyspnea.

2. Effects on Blood

The pH of blood reduces and blood becomes acidic.

3. Effects on Cardiovascular System

Hypercapnea is associated with tachycardia and increased blood pressure. There is flushing of skin due

to peripheral vasodilatation.

4. Effects on Central Nervous System

During hypercapnea, the nervous system is also affected, resulting in headache, depression and laziness. These symptoms are followed by muscular rigidity, fine tremors and generalized convulsions. Finally, giddiness and loss of consciousness occur.

HYPOCAPNEA

Hypocapnea is the decreased carbon dioxide content in blood.

CONDITIONS WHEN HYPOCAPNEA OCCURS

Hypocapnea occurs in conditions associated with hypoventilation. It also occurs after prolonged hyperventilation, because of washing out of excess carbon dioxide.

EFFECTS OF HYPOCAPNEA

1. Effects on Respiration

Respiratory centers are depressed, leading to decreased rate and force of respiration.

2. Effects on Blood

The pH of blood increases, leading to respiratory alkalosis. Calcium concentration decreases. It causes

tetany, which is characterized by neuromuscular hyperexcitability and carpopedal spasm.

3. Effects on Central Nervous System

Dizziness, mental confusion, muscular twitching and loss of consciousness are the common features of

hypocapnea.

ASPHYXIA

Asphyxia is the condition characterized by combination of hypoxia and hypercapnea, due to obstruction of air passage.

CONDITIONS WHEN ASPHYXIA OCCURS

Axphyxia develops in conditions characterized by

acute obstruction of air passage such as:

1. Strangulation

2. Hanging

3. Drowning, etc.

EFFECTS OF ASPHYXIA

Effects of asphyxia develop in three stages:

1. Stage of hyperpnea

2. Stage of convulsions

3. Stage of collapse.

1. Stage of Hyperpnea

Hyperpnea is the first stage of asphyxia. It extends for about 1 minute. In this stage, breathing becomes

deep and rapid. It is due to the powerful stimulation of respiratory centers by excess of carbon dioxide.

Hyperpnea is followed by dyspnea and cyanosis. Eyes become more prominent.

2. Stage of Convulsions

Stage of convulsions is characterized mainly by convulsions (uncontrolled involuntary muscular contractions). Duration of this stage is less than 1 minute. Hypercapnea acts on brain and produces the following effects:

i. Violent expiratory efforts

ii. Generalized convulsions

iii. Increase in heart rate

iv. Increase in arterial blood pressure

v. Loss of consciousness.

3. Stage of Collapse

Stage of collapse lasts for about 3 minutes. Severe hypoxia produces the following effects during this

stage:

i. Depression of centers in brain and disappearance of convulsions

ii. Development of respiratory gasping occurs.During respiratory gasping, there is stretching of the body with opening of mouth, as if gasping for breath.

iii. Dilatation of pupils

iv. Decrease in heart rate

v. Loss of all reflexes.

Duration between the gasps is gradually increased and finally death occurs.

All together, asphyxia extends only for 5 minutes. The person can survive only by timely help such as

relieving the respiratory obstruction, good aeration, etc.

DYSPNEA

Dyspnea means difficulty in breathing. It is otherwise called the air hunger. Normally, the breathing goes on without consciousness. When breathing enters the consciousness and produces discomfort, it is called

dyspnea. Dyspnea is also defined ‘as a consciousness of necessity for increased respiratory effort’.

DYSPNEA POINT

Dyspnea point is the level at which there is increased ventilation with severe breathing discomfort. The normal person is not aware of any increase in breathing until the pulmonary ventilation is doubled. The real discomfort develops when ventilation increases by 4 or 5 times.

CONDITIONS WHEN DYSPNEA OCCURS

Physiologically, dyspnea occurs during severe muscular exercise. The pathological conditions when

dyspnea occurs are:

1. Respiratory Disorders

Dyspnea occurs in the respiratory disorders, characterized by mechanical or nervous hindrance to respiratory movements and obstruction in any part of respiratory tract. Thus, dyspnea occurs in:

i. Pneumonia

ii. Pulmonary edema

iii. Pulmonary effusion

iv. Poliomyelitis

v. Pneumothorax

vi. Severe asthma, etc.

2. Cardiac Disorders

Dyspnea is common in left ventricular failure and decompensated mitral stenosis.

3. Metabolic Disorders

Metabolic disorders, which cause dyspnea are diabetic acidosis, uremia and increased hydrogen ion

concentration.