Inverse Kinematics of Concentric Tube Robots in the Presence of Environmental Constraints

Inverse kinematics (IK) of concentric tube continuum robots (CTRs) is associated with two main problems. First, the robot model (e.g., the relationship between the configuration space parameters and the robot end-effector) is not linear. Second, multiple solutions for the IK are available. This paper presents a general approach to solve the IK of CTRs in the presence of constrained environments. It is assumed that the distal tube of the CTR is inserted into a cavity while its proximal end is placed inside a tube resembling the vessel enabling the entry to the organ cavity. The robot-tissue interaction at the beginning of the organ-cavity imposed displacement and force constraints to the IK problem to secure a safe interaction between the robot and tissue. The IK in CTRs has been carried out by treating the problem as an optimization problem. To find the optimized IK of the CTR, the cost function is defined to be the minimization of input force into the body cavity and the occupied area by the robot shaft body. The optimization results show that CTRs can keep the safe force range in interaction with tissue for the specified trajectories of the distal tube. Various simulation scenarios are conducted to validate the approach. Using the IK obtained from the presented approach, the tracking accuracy is achieved as 0.01 mm which is acceptable for the application.

Fluoroscopy-guided removal of a bitten endotracheal tube in an adult sheep

SummaryA 60 kg female white alpine sheep accidentally bit its endotracheal tube during the recovery phase after an experimental surgical intervention. The distal tube portion had slipped down the trachea and was no longer visible in the laryngeal opening. The distal tube part could be recovered rapidly under fluoroscopic guidance using endoscopic forceps. The remaining recovery time was uneventful and the animal was able to complete the study with no complications.

Obstruction of the Tube/Valve

Tube shunt obstruction is a relatively common complication, with reported rates up to 15%. Tube obstructions can be divided into 2 basic types: 1) distal tube obstruction in the anterior chamber, ciliary sulcus, or pars plana; and 2) proximal tube obstruction at the tubeplate junction. Occasionally tube obstruction may lead the surgeon and patient to believe that the tube shunt was never successful at controlling intraocular pressure (IOP) postoperatively. This complication generally has a high impact on the patient’s postoperative course. Preoperative planning and careful surgical technique can avoid many cases of obstruction. Distal tube obstruction is typically a serious postoperative complication, with a sudden elevation in IOP resulting in pain, inflammation, and worsened vision. The distal end of the tube may be obstructed by blood, fibrin, iris, vitreous, lens material, silicone oil, and/ or viscoelastic. Treatment is tailored to the immediate cause. No matter what the cause of obstruction, if tube repositioning becomes necessary, the use of tube extenders, available either commercially or created with readily available 22-gauge angiocatheter sleeves and silicone tubing (used for nasolacrimal duct intubation), facilitate this procedure if the tube is too short to reposition (see Chapter 30). If a blood clot or fibrin is present, observation with use of ocular hypotensive agents and frequent (every 1–2 hours) application of topical prednisolone acetate, 1% may be sufficient. Tissue plasminogen activator (tPA) also may be injected into the anterior chamber to rapidly resolve the clot. The usual dose of tPA is 12.5 μg in 0.1 cc (0.1 mL) and is readily available from most hospital pharmacies. Multiple injections may be required, but concerns about cost have lessened with the advent of a recombinant form of tPA. In one series of 36 patients treated with tPA after tube shunt surgery, severe hyphema, flat anterior chamber, and profound hypotony were seen after 11% (6 of 55) tPA injections. Blood in the tube may be flushed out with balanced saline solution, using a 27-gauge cannula inserted into the eye through a paracentesis wound. If the tube is buried in the iris, pilocarpine may pull the iris out of the tube.

Intraoperative herniation of a tracheostomy tube cuff

A case of intraoperative tracheostomy tube obstruction is reported. The clinical features and the chain of events leading to the diagnosis of cuff herniation are presented. The different mechanisms of herniation are discussed. In the present case we speculate that a manufacturing defect together with nitrous oxide diffusion into the cuff caused dilatation and herniation of the latter which led to obstruction of the distal tube lumen. We draw attention to this rare but life-threatening complication.