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Cannulae used in laboratory

What is cannulae?

Cannulae is a medical device that is inserted into the patient's trachea and/or bronchus to create a temporary artificial breathing channel for patients, especially those who cannot breathe on their own.

The common cannula head has one or two capsules, which are inflated to hold the cannula in place and seal the airway, or can be used without a capsule. The body of the cannula is usually made of polymeric material with wire coils embedded in the body to improve radial strength and axial flexibility. Some cannula bodies are made of laser-resistant materials or compounded to resist laser exposure. It is a nasal/oral or percutaneous tube inserted into the patient's trachea. One end is connected to the anesthesia ventilator via a breathing line to maintain the patient breathing. Supplied sterile, single-use.

a. The distal end of the catheter has a beveled opening.

b. A cuff-like inflatable cuff is attached to the distal end.

c. The proximal end has an articulating tube for connection to the respirator.

d. The cuff is connected by a thin catheter to a small test balloon, which is used to understand the expansion and contraction of the cuff and its inflation pressure.

e. The side hole is located on the side wall distal to the distal end of the tracheal tube, and its purpose is to allow breathing gas to enter and exit through this side hole when the tracheal tube is affixed to the tracheal wall at an oblique angle.

Types of cannula

Cannulae are divided into two types transoral tracheal catheters and transnasal tracheal catheters according to the site of use.

There is a difference in appearance between the two, the angle of the front bevel of the oral and nasal tracheal catheter is 45° and 30° respectively, and the bevel of the front of the transoral catheter is open to the left direction; the bevel of the transnasal catheter is open to the left or to the right.

Cannulae are divided into catheters with or without a capsule and catheters without a capsule. 5 years and younger or catheters with an internal diameter <5.5 mm are generally used without a capsule; adults and older children 8 years and older use catheters with a capsule.

Clinical use of cannulae

A. Conventional cannulae

Conventional cannulae have good stability, not easy to appear out of the situation, while the fixed way to facilitate oral care and is clinical more common. It is mainly made of PVC, which can cause mucosal damage and bleeding during the use of the catheter, which can have a greater impact on the normal treatment of patients.

B. Reinforced cannulae

Reinforced cannulae have a huge advantage over conventional cannulae in terms of material and composition. The reinforced cannulae, also known as spring tubes, are mainly made of special soft resin and have spiral steel wires inside the walls, which makes the flexibility of the tube body greatly improved. In addition, the reinforced cannulae are softer at the tip and can change with the morphology of the upper airway, resulting in a better fit and less friction with the mucosal tissue, and less damage, which can effectively control complications.

C. Flushable cannulae

In mechanically ventilated patients, due to the weakened or absent swallowing reflex, cough reflex, and cilia movement of the lower airway, oropharyngeal secretions, and colonized bacteria tend to accumulate on the air sac of the catheter, forming a "mucus paste" in this area, which becomes a reservoir of bacteria. Therefore, in order to effectively prevent this phenomenon, it is necessary to effectively remove secretions above the air sac of the tracheal tube in a timely manner. The flushing cannulae, which allow secretions and colonized bacteria accumulated under the voice box to be aspirated with the flushing solution, directly reduce the downward leakage of secretions and migration of colonized bacteria through the oronasopharynx to the lower airway, while the conventional type of tracheal tube is unable to flush the retained material over the air sac, helping to reduce the incidence of postoperative pulmonary complications in the hospital and delaying the development of ventilator-associated pneumonia.

D. Single-lumen bronchial catheter

A single-lumen bronchial catheter is a single-lumen catheter placed in the bronchus. The artificial airway for implementing lung isolation and single-lung ventilation is collectively referred to as an endobronchial tube. Single-lung ventilation refers to the selective detection of lung ventilation during open-heart surgery, where the affected lung is not ventilated and the lung is atrophied. It is characterized by a long, thin tube body and a short sleeve. In order to ensure ventilation of the upper lobe of the right lung, the anterior segment of the right bronchial catheter sleeve is divided into two segments with a side opening in the middle corresponding to the bronchial opening of the upper lobe of the right lung.

E. Double-lumen bronchial catheter

Double-lumen bronchial catheters are widely used in clinical single-lung ventilation. There are three types of double-lumen bronchial catheters, Carlen, White, and Robertshaw. The design principle is basically the same: one tube with two lumens and two openings in two segments, one at the distal end of the catheter and the other at the main bronchus, with balloons installed in the trachea and main bronchus respectively. However, double-lumen tracheal tube intubation is more demanding for the operator, and it is difficult to ensure the correct catheter position due to the anatomical structure of the right main bronchus.

F. Pediatric tracheal tube

Pediatric tracheal tubes are marked with a single or double black circle at 2 cm and 3 cm from the front end, respectively, to guide the length of catheter insertion into the trachea and to prevent over-insertion. Some pediatric catheters are also coated with a longitudinal black line that can be radiographically displayed on an x-ray to understand the position of the catheter in the trachea.

Use of cannula

Nasal cannula

a. After exposing the vocal cords under direct vision with the aid of a laryngoscope, the cannulae are inserted into the trachea through the oral cavity.
a) The patient's head is tilted back and the jaw is held forward and upward with both hands to open the mouth, or the thumb of the right hand is placed against the lower dentition and the index finger against the upper dentition to open the mouth by rotational force.
b) With the laryngoscope handle in the left hand, the laryngeal lens is placed into the mouth from the right corner of the mouth and the tongue body is pushed back to the side and slowly advanced to see the uvula. The lens is lifted vertically and advanced until the epiglottis is revealed. The epiglottis is lifted to reveal the vocal cords.
c) If a curved lens is used, the lens is placed at the junction of the epiglottis and the tongue root (epiglottis valley) and lifted forward and upward, so that the epiglottis ligament of the hyoid bone is tense and the epiglottis is raised against the laryngeal lens, which reveals the vocal fold. If the tube is inserted with a straight lens, the epiglottis should be picked up directly and the vocal folds can be revealed.
d) After intubation is completed, confirm that the cannulae have entered the trachea before fixation.

b. The cannulae are inserted via the nasal cavity into the trachea under non-sighted conditions.
a) Autonomic breathing must be preserved during intubation, and the direction of catheter advancement can be judged by the strength of the exhaled airflow.
b) 1% bupivacaine is used for intranasal surface anesthesia, and 3% ephedrine is dripped to cause vasoconstriction of the nasal mucosa to increase the volume of the nasal cavity and to reduce bleeding.
c) A cannulae of appropriate diameter is selected and inserted into the nasal cavity with the right hand holding the tube. During intubation, listen to the strength of the exhaled airflow in the lateral ear while advancing, while adjusting the patient's head position with the left hand to find the position with the strongest exhaled airflow.
d) The cannulae are rapidly advanced when the vocal cords are opened. the cannulae enter the vocal cords and the resistance to advance is felt to decrease, the exhalation airflow is obvious, sometimes the patient has a cough reflex, and the respiratory bag is seen to stretch with the patient's breathing when connected to the anesthesia machine, indicating that the cannulae are inserted into the trachea.
e) If the exhaled airflow disappears after cannulae advancement, it is a sign of insertion into the esophagus. The cannulae should be backed into the nasopharynx, and the head should be tilted slightly so that the tip of the catheter is cocked upward, which can be aligned with the vocal cords to facilitate insertion.

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