Surgery – Respiratory method or device – Respiratory gas supply means enters mouth or tracheotomy...
Patent
1996-08-30
1998-10-13
Millin, V.
Surgery
Respiratory method or device
Respiratory gas supply means enters mouth or tracheotomy...
12820715, 12820222, 604 97, A61M 1600
Patent
active
058197230
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to tracheal tubes, and more specifically, relates to methods and apparatus for controlling the conditions of the intubation.
BACKGROUND OF THE INVENTION
Tracheal intubation is used in respiratory medicine to deliver or remove a fluid to the airways of a patient. Tracheal intubation with an endotracheal tube is commonly used during general anesthesia and when critically ill patients require airway protection and mechanical ventilation. Tracheal tubes include those used in tracheostomies as well as endotracheal tubes. Under certain conditions of long term ventilation, a tracheostomy tube is inserted through a surgical opening through the neck. An endotracheal tube is inserted into the trachea through either the mouth or nose (nasotracheal tube). Tracheal tubes are used for ventilation, and removal of secretions. Typically, endotracheal tubes are disposable plastic tubes, easily placed through the mouth or nose, that guarantee a patent conduit for the delivery of respiratory gases. A seal between the outer wall of the tracheal tube and the inner lining of the trachea (the tracheal mucosa) must be formed. Most endotracheal tubes (except those for small children) provide a very compliant, thin walled inflatable cuff that forms a seal with the proximal tracheal rings. This seal allows for positive pressure ventilation at normal airway pressures with minimal leakage. The seal thus provides a closed circuit for ventilation and also prevents aspiration of pharyngeal contents into the respiratory tract. This seal is usually formed by inflating a pressurized cuff that surrounds the tracheal tube. The pressure in the cuff must be adequate to form a seal, but it is known that over-pressurization will cause tracheal trauma including hemorrhage, ulcers, perforation and strictures. The main cause of trauma is the loss of blood flow (ischemia) and resultant necrosis of the tracheal lining.
Cuff pressures are typically set between 10-50 mm Hg. This range of pressures is relatively wide and for any particular patient the formation of a seal without creating an ischemia will require holding the pressure in a much narrower range. Moreover, because tracheal tubes are used in a dynamic environment, the pressure required to maintain an adequate seal will vary. Finally, cuff pressure will vary due to the diffusion of nitrous oxide into the cuff. Thus, establishing a correct cuff pressure and correctly regulating the cuff to this pressure are both important. For example, during mechanical ventilation, the intracuff pressure must be low enough to allow tracheal capillary perfusion, thus reducing the risk of ischemia, while being high enough to prevent either loss of tidal volume or significant aspiration.
The use of high volume, low pressure endotracheal tube cuffs starting in 1973 reduced the incidence of complications from prolonged tracheal intubation. This more compliant cuff design provides a satisfactory tracheal seal for positive pressure ventilation associated with significantly lower cuff-tracheal mucosa contact pressure. Unfortunately, when lung compliance significantly decreases--as often occurs in critically ill ICU patients--high airway pressures are transmitted through the distal cuff surface during inspiration. Cuff-tracheal mucosal contact pressures approach peak airway pressures as high as 50 mm Hg during each inspiration. This contact pressure far exceeds tracheal mucosal perfusion pressure of 15 mm Hg and significant ischemic damage can occur, and in fact mucosal ischemic damage commonly occurs in observed patient populations. Endoscopic and biopsy studies suggest a high incidence of mucosal ulceration, cartilage infiltration with bacteria, and ultimately, scar formation with the development of clinically significant airway narrowing. Local mucosal defense mechanisms are inhibited during tissue ischemia, allowing bacteria to multiple and invade deeper structures.
An additional cause of cuff pressures that exceed mucosal perfusion pressure is brought about during nitrous oxide gener
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Deane, Jr. William J.
Millin V.
Thomas Jefferson University
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