Surgery – Respiratory method or device – Means for mixing treating agent with respiratory gas
Utility Patent
1998-01-23
2001-01-02
Weiss, John G. (Department: 3761)
Surgery
Respiratory method or device
Means for mixing treating agent with respiratory gas
Utility Patent
active
06167883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related generally to temperature and/or humidity control in a conduit for communicating a gas such as air or oxygen to a medical patient, and more particularly to a tubing with an internal heating element to control the temperature and humidity of the gas therein prior to delivery to a patient.
2. Description of Related Art
Systems are currently in use to aid in the delivery of air or other gases to patients who cannot breathe on their own for various reasons. The human upper airway is a location where inspired air is heated and humidified before passing through the trachea to the lungs. Patients who cannot breathe on their own require the assistance of a ventilator. Air delivered from a ventilator is typically dry, coming from a compressor or liquid oxygen source. When this air is delivered to a patient whose upper airway is bypassed, the mucous layer and sensitive tissues of the lower airway is dried out and an additional metabolic demand is required of the patient to warm the air to body temperature. Patients on long term ventilation without humidification develop mucous plugs in the lower airway, requiring interventional suctioning and may develop damage to the lower airway tissues which may exacerbate drying of the airway. Increased metabolic demand places additional strain on all physiologic systems and threatens patient outcome. Consequently, ventilatory air is often heated and humidified prior to being delivered to patients on ventilatory support where the upper airway is bypassed with an endotracheal or tracheostomy tube.
Conventional ventilator air humidification consists of warming water to an elevated temperature and passing an inspired air flow over or through the warm water to pick up the available humidity and equilibrate the resultant water vapor/air mixture to the humidifier temperature. The inspired air is conducted to the patient through a ventilator circuit hose or tube, typically a corrugated polyethylene hose, which is in communication with the endotracheal or tracheostomy tube. The interconnecting hose is designed to provide a low resistance, lightweight, highly flexible flow channel such that inspiration does not require excessive effort. The hose is adapted to mate with a mask or endotracheal or tracheostomy tube where the air can be delivered to the patient.
Since the ventilator circuit hose typically has a relatively thin wall and a large surface area due to the corrugations, significant heat transfer occurs between the heated flow and the relatively cooler ambient air surrounding the hose. As the heated air travels along the hose, some heat is lost to the air outside of the hose resulting in a temperature drop in the air flow. The drop in temperature in the humidified air flowing through the hose reduces the capacity of the air to suspend the moisture, causing some of the moisture to precipitate out along the length of the tube. This reduction in the humidity of the airstream as the air cools leads to a collection of water in the corrugations of the tube. The condensed water poses a particular hazard to the patient if it accumulates in sufficient quantity to trickle into the endotracheal or tracheostomy tube, where it may be introduced into the lungs. In addition, the water collecting in the warm hose forms a fertile breeding ground for bacteria which can cause airway infections. Lastly, the drop in temperature creates an uncertainty in the temperature of the air being delivered to the patient in addition to the temperature of the air leaving the ventilator.
To reduce the precipitation of water and maintain a suitable air temperature, electrically heated hoses have been used to add additional heat to the flowing air, counteracting the heat lost along the length of the hose. Conventional electrically heated hoses or tubing employ a heating element, in the form of a solid or stranded resistance wire, that is either embedded in the wall or wound around the circumference of the hose. In some cases, the resistance wire is spirally wrapped around a supporting thread before it is wrapped around the hose. These hoses apply heat at the walls, which is communicated to the fluid passing within the hose by convection. Alternatively, the heating element may be loosely strung within the lumen of the hose. In this case, heat is conducted to the fluid passing within the lumen from the heating element through insulation placed over the heating element.
A problem particular to spirally wound heater wire elements is the formation of localized hot spots from variations in power density. The variation in power density is caused by inconsistency of the spiral pitch over a short section of the element. The winding pitch seems to be particularly difficult for manufacturers of this element to maintain and necessitates specialized testing and equipment to detect in a high speed extrusion operation. This localized hot spot can melt through the hose wall and pose a fire threat.
OBJECTS AND SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a heater for a flexible tubing which overcomes the drawbacks of the prior art and improves the delivery of gases at a prescribed temperature and humidity.
It is another object of the present invention to provide a heater which reduces the occurrence of tubing failure due to burn-through.
It is another object of the present invention to provide a heater which is adaptable to currently gas delivery systems.
It is yet another object of the present invention to provide a heater which heats gases more efficiently than prior heating systems.
The objects of the present invention are achieved using a flexible tubing having an elongate flexible plastic ribbon disposed inside the tubing generally along a center region and extending predominantly the length of the tubing, and a heating element carried by the ribbon to heat the air. A preferred embodiment of the present invention uses a temperature gage at the point of delivery which is used to adjust the heater to maintain the temperature of heated and humidified air at the point of delivery to the patient.
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Beran Anthony V.
Minch Morris
Shigezawa Gordon
Price and Gess
Respiratory Support Products Inc.
Srivastava V.
Weiss John G.
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