Clinical Causes of Hypoxia During Anesthesia
Every doctor should know the answer to the basic question What causes Hypoxia . Factors responsible:
1. Preanaesthesia factors
• Poor physiological status
• Drug intake
• Premedication with narcotics and sedatives depress the respiration
• Decreased compensatory mechanism due to any cause
2. Decreased partial pressure and concentration of the inspired oxygen in anesthesia breathing mixture.
3. Mechanical factors
• Flow meter defects
• Inaccurate reading at low flow rates
• Pressure gauge defects
• Exhausted oxygen cylinders
• Obstruction due to kinking of corrugated tubes
4. Inspired ventilatory inefficiency
• Airway obstruction upper or lower
• Hypoventilation due to any cause
• Decreased effective alveolar ventilation
• Increased shunting
• Obstructive airway diseases
• Types of operative procedure: thoracic operations, 50% shunt; Abdominal operations, 35% shunt
• Poor pattern of ventilation
• Lack of periodic hyperventilation (sigh)
Impaired ventilation
• Increased shunting
• Increased dead space
Deficient oxygen loading
• Metabolic or respiratory acidosis
• Low levels of hemoglobin
• Pulmonary edema
Decreased transport
• Hypovolaemia due to any cause
• Blood loss due to any cause
• Fluid loss due to any cause
5. Cardio circulatory inability
• Pre-existing compensatory disability
• Decreased cardiac output due to any cause
• Myocardial disease
• Metabolic acidosis due to any cause
• Negative iontropic drugs
• Myocardial depression due to drugs or acidosis
• Interference with venous return
• Circulatory depression due to blood loss or due to sympathetic analysis
• Excessive pressure
• Positive pressure ventilation
6. Impaired tissue delivery
• Impaired regional blood flow
• Increased utilization due to acidosis
• Decreased cerebral blood flow
• Excess tissue lactate production and hypocalcaemia
This is a brief discussion of what causes hypoxia, if you have any more questions fell free to ask a doctor.