Summary

In study session III you have learnt

• The ability to achieve good mouth opening is important for many airway procedures. The jaw-thrust maneuver moves the mandible and attached relaxed soft tissue structures anteriorly which helps to make airway patent.
• The nose warms, filters, and humidifies incoming air and is the organ of smell. An endotracheal or tracheostomy tube which bypassed the upper respiratory tract would result in cold dry gases reaching the trachea
• Pharyngeal obstruction is a common problem under anesthesia and in the recovery period. The commonest cause is the tongue falling back in the unconscious patient.
• The larynx is situated at the upper end of the respiratory tract, where it extends from the epiglottis to the lower end of the cricoid cartilage opposite to the 4th, 5th and 6th cervical vertebrae.
• In adults the narrowest portion of the larynx is the opening between the vocal cords. In children below the age of 10 years the narrowest portion is at the level of the cricoid cartilage.
• The vallecula is depressions between the median and lateral glossoepiglottic folds that connect the lateral edges of the epiglottis to the base of the tongue. The tip of Macintosh laryngoscope inserted to vallecula to achieve indirect elevation of the epiglottis.
• The superior and recurrent laryngeal nerves supply the larynx.
• Trachea extends from the lower edge of the cricoid cartilage to the carina. An endotracheal tube or a tracheostomy tube which is too long will pass from the trachea into the right main bronchus.
• The goals of respiration are to provide oxygen to the tissues and to remove carbon dioxide. Normal lung function requires a balanced interrelationship between the respiratory (the upper and lower airway), nervous, and cardiovascular systems.
• Mechanisms to achieve the goal of respiration are pulmonary ventilation, diffusion of oxygen and carbon dioxide between the alveoli and the blood, transport of oxygen and carbon dioxide in the blood and body fluid to and from the body's tissue cells; and regulation of ventilation and other facets of respiration by the respiratory centre.
• Normal quiet breathing is accomplished almost entirely by movement of the diaphragm.
• The venous blood arrives in the lung (from the tissues) with an O2 pressure of 40 mmHg. Because of the difference in pressure (103 - 40 mmHg), O2 passes from the alveoli into the blood stream. This transfer occurs by the process of diffusion.
• The venous blood arriving in the lung is rich in CO2. The pressure of CO2 in the venous blood is 46 mmHg. The alveolar pressure is 40 mmHg. The CO2 diffuses from the venous blood to the alveoli. The arterial blood leaves the lung with an oxygen tension of 100 mmHg and a CO2 tension of 40 mmHg.
• The gases in the alveoli pass into the blood in the capillaries by the process of diffusion. Diffusion of oxygen from the alveolus into the red blood cell and diffusion of carbon dioxide in the opposite direction occur in the respiratory membrane. The overall thickness of the respiratory membrane in some areas is as little as 0.2 micrometer, and it averages about 0.6 micrometer.
• The respiratory unit is composed of a respiratory bronchiole, alveolar ducts, atria, and alveoli.
• Oxygen is carried in combination with the hemoglobin in the red blood cells (1 gm of hemoglobin can carry 1.34 ml of O2) and carried in solution (0.3 ml of oxygen per 100ml of blood).
• The respiratory center is composed of several groups of neurons located bilaterally in the medulla oblongata and pons of the brain stem.
• Compliance is a measure of distensibility of the lung by change in pressure. Airway resistance denotes the measure of obstruction to the flow of gas in the air passages.