Veterinary Clinical Medicine-I (General and Systemic)

PRINCIPLES OF RESPIRATORY INSUFFICIENCY

Anoxia

Definition

 It means failure of the tissues to receive an adequate supply of oxygen

Types of anoxia

• Anoxic Anoxia
  • Occurs when there is defective oxygenation of the blood in the pulmonary circulation.
  • It is usually caused by primary disease of the respiratory tract.
• Anemic Anoxia
  • Occurs when there is a deficiency of hemoglobin per unit volume of the blood.
  • The percentage saturation of the available hemoglobin & oxygen tension are normal, but the oxygen carrying capacity of the blood is reduced. It is usually caused by anemia due to any cause.”e.g.”poisoning by nitrites or carbon monoxide .
• Stagnant Anoxia
  • Occurs when the rate of blood flow through the capillaries is reduced.
  • It usually occurs in cases of congestive heart failure, peripheral circulatory failure& venous obstruction.
• Histotoxic Anoxia
  • Occurs when the blood is fully oxygenated, but because of the failure of the “tissue oxidation system,” the tissues can not take up oxygen .
  • It usually occurs as a result of cyanide poisoning.

Special causes of Anoxic Anoxia

• When the oxygen tension of the inspired air is too low, that it can not oxygenate the pulmonary blood.
• Any lesion or dysfunction of the respiratory tract reducing the supply of alveolar air such as :
  • Pneumonia.
  • Pulmonary atelectasis.
  • Pneumothorax.
  • Pulmonary edema &congestion.
  • Any decrease in the chest movement due to pain in the chest wall.
  • Obstruction of air passage by accumulation of the exudates.
• Depression of the respiratory center by drugs or toxins.
• Congenital defects of the heart & large blood vessels, when mixing of arterial & venous blood occurs through shunts between the two circulation.
• Paralysis of respiratory muscles.
• Botulism.
• Tetanus.
• Strychnine poisoning.

Complications of anoxia

• Increase in depth of respiratory movement “hyperpenea” which is mediated by chemoreceptors in the aortic arch & parorecptors in the carotid sinus.
• Stimulation of splenic contraction.
• Erythropoiesis in the bone marrow.
• Increased heart rate.
• Signs of dysfunction of various organs appears, cerebral anoxia, myocardial dysfunction, renal and hepatic dysfunctions as well as reduction in motility and secretory activity of alimentary tract.

Carbon Dioxide Retention “Hypercapnia”

• It means that there is an accumulation of CO2 in the blood and tissues which cannot be eliminated via the lungs and that is due to respiratory insufficiency. This Co2 stimulates the respiratory center.

Respiratory Failure

• Respiratory movements are controlled by respiratory center in the medulla & this center is controlled by afferent impulses from cerebral cortex, heat regulatory center in the hypothalamus, stretch receptors in lungs via the vagus & from chemoreceptors in the carotid body.
• The activity of respiratory center is also regulated by: pH, oxygen & carbon dioxid tensions of the cranial arterial supply. So, stimulation of the above afferent nerves may cause reflex changes in respiration & causing stimulation of the pain fibers.

Definition

• Respiratory failure is the terminal stage of respiratory insufficiency, in which the activity of respiratory center is diminished to the point where the movement of respiratory muscles is completely stopped.

Types & causes

• Respiratory failure may be tachypenic, dyspneic, a sphyxial or paralytic depending on the primary disease.
• A- Asphexial respiratory failure:

Causes

• Pneumonia.
• Pulmonary odema.
• Upper respiratory tract obstruction.

Clinical signs

• Hypercapnia
• Stimulate respiratory center
• Stimulation respiration
• Anoxia.
• Gasping. Apnea 
• Death

Causes

• Poisoning with respiratory center depressants.
• Nervous shock.
• Acute heart failure.
• Hemorrhage.

Clinical signs

• Variable degree of dyspnea & gasping.
• Paralysis of the respiratory center Ø shallow respiration & less frequent then complete stop of respiration .
• Tachypneic respiratory failure

Causes

• Increased pulmonary ventilation "hypoxia " but no carbon dioxide retention "acapnio".

Clinical signs

• Because of the lack of carbon dioxide to stimulate the respiratory movement; Rapid & shallow respiratory & shallow tachypnea are evident.

Treatment of respiratory failure

• In paralytic type - Stimulants of respiratory center are given.
• In asphyxyial type - Oxygen is provided.
• In tachypneic type - Oxygen & CO₂ are provided.