Tracheostomy Inner Cannula Collapsible Struts
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Solution Overview
Problem
Existing inner cannulae for tracheostomy tubes face challenges in being thin-walled yet stiff enough to prevent buckling, while also being easily removable without applying excessive force, and require innovative engagement mechanisms to securely lock and unlock within the tracheostomy tube hub.
Innovation Solution
The inner cannula features a machine end region with cooperating engagement formations on the outer surface and hub that allow secure retention and easy removal through a twisting mechanism, utilizing collapsible struts and a grip system to disengage the cannula from the hub, enabling angular displacement and flexible sections for enhanced removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the inner cannula is made thin-walled to provide a large bore and reduce flow resistance, then the flow resistance is reduced, but the cannula becomes insufficiently stiff and may buckle or kink during insertion
Solution Approach 1:
The inner cannula is divided into multiple functional segments: a thin-walled shaft portion for low flow resistance, a machine end region with engagement formations for secure retention, and a collapsible region with struts for controlled deformation during removal. This segmentation allows each portion to be optimized independently - the shaft remains thin for airflow while the machine end region provides structural support and engagement capability
Solution Approach 2:
Different regions of the inner cannula are given different wall thicknesses and structural properties. The shaft portion has thin walls to minimize flow resistance, while the machine end region has thicker walls and structural reinforcements (engagement formations) to provide stiffness and secure engagement with the hub. The collapsible region has intermediate properties allowing controlled deformation
2Strength
If the inner cannula is made sufficiently stiff to prevent buckling, then structural integrity is maintained, but excessive force is required to remove the cannula from the tracheostomy tube
Solution Approach 1:
The engagement mechanism transitions from a static rigid connection to a dynamic system that changes state with twisting motion. The collapsible region with struts allows the machine end region to deform angularly when twisted, converting the engagement formations from an engaged state (providing secure retention) to a disengaged state (allowing easy removal). This dynamic behavior allows the same structure to provide both stiffness during normal use and ease of removal when needed
Solution Approach 2:
The cannula is segmented into a stiff shaft portion and a more compliant machine end region with collapsible struts. This segmentation allows the shaft to maintain structural integrity while the machine end region can deform during removal, reducing the force required to extract the cannula from the hub
3Reliability
If the inner cannula is retained securely in the hub against axial withdrawal force, then secure locking is achieved, but the engagement mechanism becomes complex requiring additional components
Solution Approach 1:
The engagement and locking functions are merged into a single integrated mechanism. The engagement formations on the inner cannula and hub work together to provide both secure retention against axial withdrawal and controlled disengagement through twisting. The collapsible struts serve dual purposes: providing structural support and enabling the twisting motion that releases the engagement formations. This merging eliminates the need for separate locking components while maintaining secure retention
Solution Approach 2:
The engagement mechanism is designed to be self-locking through the geometry of the engagement formations and the elastic properties of the collapsible region. Once inserted, the engagement formations automatically lock into position without requiring additional locking actions. For removal, the user simply applies twisting motion which automatically releases the engagement formations through the collapsible struts, eliminating the need for separate unlocking mechanisms
Data Source
AI summary
A tracheostomy tube assembly comprises an outer tracheostomy tube (1) and an inner cannula (20) fitted in the tube. The machine end of the inner cannula has a collapsible region (22) formed by a plurality of curved or bent struts (26) extending parallel with one another between a machine end collar (28) and a patient end collar (27). The struts (26) carry outwardly-projecting catches (23) arranged to engage a rib (24) extending around the inside of a hub (16) at the machine end of the tube and thereby resist removal of the cannula from the tube. The inner cannula (20) is removed by twisting the machine end collar (28) so that the struts (26) collapse inwardly and thereby disengage the catches (23) from the rib (24).