FIELD OF THE INVENTION 
     This invention relates to a medical instrument and the use thereof that establishes a “duty channel” for continuous access and control of the airway during bronchoscopy procedures. 
     BACKGROUND OF THE INVENTION 
     The fiber optic bronchoscope is used to access the airway via entry through the nasopharynx or oropharynx with continued passage between the true vocal cords and then advancing caudally into the laryngo-tracheo-bronchial tree. Once airway placement is achieved the fiber optic bronchoscope facilitates the diagnostic and therapeutic collection of glandular secretions and/or tissue specimens, foreign bodies, or tumors using the suction channel for the additional placement of flexible biopsy forceps or flexible brushes or flexible needles under direct vision. The ease and safety with which the procedure is performed can be modified by the presence of unexpected anatomic variations and complications that may arise as the bronchoscope navigates the nasopharynx in search of the laryngeal orifice housing the true vocal cords between which the fiber optic bronchoscope will then enter the larynx. 
     During the procedure a complication or finding may necessitate removal and replacement of the fiber optic bronchoscope and continued control of the airway for rapid reestablishment of patency of the airway or need to be able to mechanically ventilate the lungs while the procedure using a fiber optic bronchoscope ensues to its completion. In order to accomplish these actions it would be necessary to place an endotracheal to able to accept the external diameter of the fiber optic bronchoscope. 
     The current state of the art would force removal of the fiber optic bronchoscope and either orotracheally intubate in the standard manner or precharge the fiber optic bronchoscope with an endotracheal tube over the fiber optic bronchoscope so that after the fiber optic bronchoscope tip has entered the trachea one can slide the endotracheal tube over the fiber optic bronchoscope and so control the airway and use the endotracheal tube as an access channel allowing removal and replacement of the fiber optic bronchoscope as deemed necessary without going through the cumbersome process followed to initiate airway access. Some of the complicating factors include bleeding, encountering foreign bodies of different shapes and anatomic features such as larynx and vocal cord anomalies or polypoid tumors larger than the caliber of the suction channel of the fiber optic bronchoscope. 
     Current options for airway management during such procedures include withdrawal of the bronchoscope and intubation of the patient by endotracheal tube including the use of an obturator (See: U.S. Pat. No. 4,960,122) as a guide. As can be appreciated, time is of the essence to maintain airway control and prevent inadequate ventilation and/or oxygenation. Once the patient is stabilized the fiber optic bronchoscopy would be re-started. However, any trauma that has occurred may result in changes to more poorly identifiable access to the laryngo-tracheo-bronchial tree arising from constriction or edema or cyanosis due to complicating hypoxemia such that insertion may be difficult or impossible because of the presence of inadequate anatomic definition. 
     SUMMARY OF THE INVENTION 
     Given the inadequacies in the present state of the art, a need exists to allow placement of an endotracheal tube to allow rapid and repeated withdrawal and reinsertion of the fiber optic bronchoscope. As a result of the possibility of cumbersome anatomic variations and the importance of time factors involved, the most expeditious manner of emergently placing the endotracheal tube depends on the ability to place the endotracheal tube without being forced to remove the fiber optic bronchoscope prior to the endotracheal tube placement. 
     This invention is a spiral slit endotracheal tube that allows the placement of a “duty channel” that provides continuous access and control of the airway after it is spirally placed over the fiber optic bronchoscope. The spiral slit tube achieves this object without being forced to remove the fiber optic bronchoscope first. The practitioner could then use the “duty channel” to rapidly remove and reinsert the fiber optic bronchoscope as deemed necessary without having to deal with any possible impediments previously described. 
     The duty channel, if necessary, can then be used with the help of an endotracheal tube replacement obturator for the placement of a standard cuffed endotracheal tube or rigid bronchoscope. The spiral slit endotracheal tube has the significant advantage in that it allows continuous maintenance of access and control of the airway. 
     The spiral slit endotracheal tube is made of the same material already used to manufacture standard endotracheal tubes. This is typically a 6-8.5 mm ID plastic tube and a suitable length of about 30 cm or less. In accordance with this invention it has to have a helical slit cut through to the tube lumen at a continuum throughout a substantial portion of its length. The angle of the helix is determined as a function of the wall thickness of the tube and the stiffness of the material to allow ready winding over the bronchoscope to be stable and substantially sealed once mounted. Typically, the helix angle can be in the range of 30-60 degrees angled to the circular base to create a through spiral slit. The edge of the slit preferably has an angled finish so that when the slit edges are coapted it does not leave a grooved surface. When the spiral slit edges are coapted, the cylindrical tube created typically has an internal diameter of 6-8 mm and a length of about 22-30 cm for an adult size. A device for pediatric use would be sized appropriately smaller. 
     In operation, the spiral slit endotracheal tube is placed over the already inserted fiber optic bronchoscope by starting at the start of the angled slit winding the spiral slit over the shaft of the fiber optic bronchoscope until the internal wall is parallel to the axis of the fiber optic bronchoscope. The spiral slit endotracheal tube is secured with surgical tape to the face when the tip of the distal end of the spiral slit endotracheal tube is confirmed by the bronchoscope to be 2 cm rostral to the carina. Once in place a duty channel has been established. The bronchoscope may be removed and subsequently reinserted. 
     This invention will be described in greater detail by referring to the attached drawing and the description of the preferred embodiment that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the spiral slit endotracheal tube according to this invention; and 
         FIG. 2  is a perspective view illustrating how the tube of  FIG. 1  is wound over a bronchoscope. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , the spiral slit endotracheal tube  10  is a flexible plastic tube made from the same material normally used to manufacture conventional endotracheal tubes. Such devices are well known in the art and sold by companies such as Mallinckrodt. See for example, http://www.covidien.com/rms/brands/mallinckrodt 
     The tube is generally made of clear plastic with an internal diameter of 6-8 mm. It will be understood that this size may be varied as a function of patient use. Thus, a device for pediatric use would be sized appropriately smaller. Conventionally, the tube is made with a radiopaque line  12 . It has a distal end  14  which is rounded, tapered or otherwise smoothed to facilitate entry. The distal end may be blunt, as illustrated, or angled. The proximal end has a connector piece  16  that is inserted into the tube and includes a stop plate  18  which also provides surfaces for securing holding the tube. The tube  10  optionally has a side port  22 . 
     In accordance with this invention, the tube  10  has a spiral slit  20  running from the distal end  14  to the zone near the side port  22 . The slit  20  allows the sidewall of the tube to be separated such that the tube can be “wound” onto a bronchoscope. The angle of the helix is chosen to facilitate this mounting of the tube and then close, yet not be so loose that the tube does not remain in position. Typically the angle of the helix is in the range of 30-60 degrees. The walls of the slit may themselves be angled or tapered to allow spreading and then secure closing after mounting over the bronchoscope. 
     Referring now to  FIG. 2 , the operation of the device according to this invention will be described. A bronchoscope  30  has already been inserted either through the nasopharynx or oropharynx and the distal end  32  is advanced caudally into the laryngo-tracheo-bronchial tree. As mentioned, this device is conventionally used for both diagnostic and therapeutic purposes. During such procedures it is sometimes necessary to maintain control of the airway without first removing the bronchoscope. Starting at the distal end  14 , the endotracheal tube  10  is spiral wound over the bronchoscope  30  at a location where the clinician has access to stabilize the scope and by tactile action spread the slit over it. Once the distal end  14  is circumferentially mounted, the rest of the tube  10  is spirally wound on and the tube  10  advances on the bronchoscope  30 . When the tube  10  advances to the side port  22 , mounting is complete and the stop plate  18  is properly located. Thus, the side port  22  is preferably the egress point at the end of the winding process. The bronchoscope  30  may be then withdrawn as the airway is maintained by the tube  10 . 
     In addition, the spiral slit endotracheal tube could provide a channel for completing endotracheal tube placement in cumbersome situations forcing the use of a fiber optic bronchoscope for establishing airway access. In this scenario, after winding on the spiral slit endotracheal tube over the fiber optic bronchoscope the fiber optic bronchoscope is withdrawn and replaced by the endotracheal tube replacement obturator and leaving the endotracheal tube replacement obturator within the laryngo tracheal tree a standard orotracheal tube can be placed over the endotracheal tube replacement obturator followed by removal of the endotracheal tube replacement obturator and leaving the standard endotracheal tube in place within the orotracheal airway. Finally, the endotracheal tube is secured and the cuff of the distal portion of the endotracheal tube is inflated in the standard manner so that the distal tip of the secured endotracheal tube is 2 cm rostral to the carina. 
     This invention is subject to other departures and modifications without departing from the essential scope thereof. For example, while the preferred embodiment has been described with respect to bronchoscope, the device according to this invention may be used with other endotracheal devices. An example is use with a replacement obturator to establish initial airway control for the subsequent placement of instruments and/or a tracheal tube. The rostral end having the connector piece  16  may serve an entry and exit point when using the spiral tube as a channel. The connector could then be fitted with a swiveling punctured rubber capped end (not illustrated). 
     Also, while the angle of the slit is preferably a helix, it is apparent that as a function of length and the material the angle may be adjusted within a wide range.
An endotracheal tube comprising a flexible hollow tube with a spiral slit traversing a substantial length of the tube. The slit has edges that separate to create an opening by which the tube may be spiral wound onto a medical device, such as a fiber optic bronchoscope, that is in use in a pharynx passage. The angle of the slit is preferably in the range of 30-60 degrees.