The emetic center is an ill-defined area located in the lateral reticular formation of the medulla. It receives input from the chemoreceptor trigger zone, vestibular apparatus, cerebellum, solitary tract nucleus, and higher cortical center. The receptor types include: dopamine, acetylcholine (muscarine), histamine, and serotonin receptors. Anatomy and Physiology of Vomiting
Incidence The incidence of PONV ranged from 75~80% during the ether era to approximately 9~43% over the past 40 years. Presently, the overall incidence of PONV for all surgeries and patient populations is estimated to be 25~30%. 0.18% of all patients may experience intractable PONV.
Risk Factors for PONV Patient-related factors Factors related to anesthesia Factors related to surgery Factors
Patient-related factors Young age Female gender Body weight History of PONV History of motion sickness Non-smoking Underlying disease: metabolic abnormalities (renal failure, uremia, DM … ), CNS pathology Psychological concerns and preoperative anxiety
Guiedlines for prophylactic antiemetic therapy Post operative nausea and vomiting – can it be eliminated? JAMA, March 13, 2002-Vol 287, No. 10 Patient Factors Female Sex History of PONV or Motion Sickness Nonsmoker Postoperative Opoid Use Surgical Factors Laparoscopy Laparotomy Plastic Surgery Major Breast Surgery Craniotomy Otolaryngologic Procedures Strabismus Surgery Mild to Moderate Risk (20~40%) 1~2 Factors Present Any 1 of the Following: Droperidol, Dexamethasone Scopolamine, Serotonin Antagonist Moderate to High Risk (40~80%) 3~4 Factors Present Droperidol Plus Serotonin Antagonist Or Dexamethasone Plus Serotonin Antagonist Very High Risk (>80%) 4 Factors Present Combination Antiemetics Plus Total IV Anesthesia With Propofol
Lighted Stylet Tracheal Intubation: A Review Anesthesia and analgesia Volume 90(3) March 2000 pp 745-756
The upper “ glow ” shows a well defined circle of light just below the hyoid and above the thyroid cartilage in the midline indicating an ideal position for passing the tip of the endotracheal tube between the vocal cords. From this point, the tube should be advanced easily off the stylet and into the trachea where its position will be confirmed by a cone-shaped light above the suprasternal notch (lower “ glow).
The glow demonstrated just as the lighted stylet passes the vocal cords. The initial circle of light just above the thyroid cartilage may change to a cone of light projecting caudally toward the suprasternal notch.
Learning the techniques (1) Lighted stylet tracheal intubation requires practice, but is easily learned Ellis et al: first 25 attempts: 42 seconds 2 nd 25 attempts: 32 seconds all were successful by the 3 rd attempt
Learning the techniques (2) Fisher and Tunkel : - 125 children (mean age three years) - intubated by anesthesia residents with little or no lighted stylet experience - overall success rate of 83% and a 76% success rate in infants weighing <10 kg - Failures: 1. too large a tracheal tube was chosen 2. persistent vallecular or esophageal entry
Prediction of Ease of Intubation Ainsworth and Howells : 200 patients 87.5% : successfully intubated on the first attempt by using a lighted stylet 99%: tracheally intubated within three attempts Hung et al: 950 patients no correlation between the time to intubate and any of the airway prediction variables, such as the Mallampati score and the circumference of the neck
Sympathetic Stimulation During Intubation Laryngoscopy and endotracheal intubation are both intensely stimulating procedures and are associated with varying degrees of sympathetic activity which may be detrimental in patients with coexisting conditions, such as coronary artery disease, elevated intracranial pressure, and asthma. Results from 3 studies: No significant difference bewteen DL and lightwant lighted stylet tracheal intubation, if performed in the same time as direct laryngoscopy, should not incur greater hemodynamic instability
Complications and Safety Friedman et al. : - The lightwand group had a significantly lower incidence of sore throat, hoarseness, and dysphagia. - Also, hoarseness and sore throat are less severe. Hung et al. ’ s large comparative trial: A significantly lower incidence of traumatic events and fewer postoperative sore throats in the lighted stylet group
The Possibility of Heat Damage Nishiyama et al. : a cat model - Temperature at the tip of the Trachlight ™ : 55° ± 6°C at the time of the first blink 103° ± 10°C after 10 blinks (250 seconds in total.) - No macroscopic signs of burn injuries in any of the cats. - Histologically: moderate neutrophil and lymphocyte infiltration in both the Trachlight ™ and the control specimens, but no significant differences between the two sides. - These findings suggest that there is little risk of burn injury from the clinical use of the Trachlight ™
Lighted Stylet Compared with Direct Laryngoscopy
Indications (1) The difficult airway is possibly the most common indication for the use of the lighted stylet Reasons: (1) the ability of a lighted stylet to negotiate acute oropharynx-tracheal angles, particularly in situations in which neck mobility is limited or contraindicated (2) secretions are not an impedance as they can be in direct or fiberoptic laryngoscopy
Indications (2) Difficult or impossible direct laryngoscopic intubation in cases of: - Congenital abnormalities of upper airway( Treacher-Collins syndrome, Pierre-Robin syndrome, etc) - Acquired abnormalities of the upper airway( trauma, etc) - Limited mandubular protusion - Short thyromental distance - Short neck - High Mallampati grade - secretions or blood in the oropharynx Patients with fixed dental appliances
Adult Difficult Airways Hung et al : 265 patients anticipated difficulty unexpected difficult intubations - In all but two patients, tracheal intubation was successful with the Trachlight ™, the vast majority on the first attempt. - The failures were patients who were grossly obese.
Pediatric Difficult Airways Holzman et al. : 31 patients with either known or anticipated difficult endotracheal intubations 27/31 : aged 5 – 17 years. In all but one case, the trachea was intubated by using a lighted stylet in an average of 30 – 60 seconds
The Emergency Setting (1) Cervical spine injuries present a particular challenge for airway management, for the airway is likely to be obscured with blood and secretions, and the neck cannot be flexed nor the head extended to aid laryngoscopy. Lighted stylets may be useful under these circumstances, but should not be used if there is suspicion of a fracture of the larynx
The Emergency Setting (2) Weis claimed a 100% success rate in securing the airway by using lighted stylet intubation in 28 cervical spine cases the use of lighted stylet intubation: (1) not influenced by blood in the airway (2) allowed administration of cricoid pressure (3) kept the cervical spine in the neutral position
Limitations No visualization of pharyngeal and laryngeal structures Suboptimal transillumination in grossly obese patients or in patients with limited neck extension
Difficulties Difficulties in controlling the tip of the device in case of accidental partial withdrawal of the stylet Unintentional switching off of the light while withdrawing the mental stylet Difficulties in withdrawing the mental stylet Disturbing effects of the blinking light after 30 seconds from switching on
Contraindications few absolute contraindications : the presence of an upper airway foreign body, tumor, polyp, retropharyngeal abscess, or other friable tissue along the intubation course A trauma victim who may have sustained laryngeal injury should have direct visualization rather than blind intubation
Relative contraindications Some consider a known difficult airway and a planned fiberoptic approach to be a relative contraindication, because a blind lightwand intubation attempt might cause bleeding which could make subsequent fiberoptic visualization of the larynx difficult Obesity Short neck Limited neck extension Awake and/or uncooperative patients
Complications there have been very few reported complications two reported incidents of instrument disarticulation Trauma to the upper airway after lighted stylet intubation is generally of a minor nature and includes bleeding, sore throat, hoarseness, and dysphagia two reported cases of arytenoid cartilage dislocation
Conclusion (1) Useful in both oral and nasal intubation fort patients with difficult airways. Also useful in emergency sitautions or when direct laryngoscopy and fiberoptic endoscopy is not effective Can be used in conjunction with other devices (LMA, intubating LMA, DL) Should be avoided in patients with tumors, infections, trauma or foreign body in the upper airway
Conclusion (2) a simple technique that is easily learned valuable if tracheal intubation by using direct laryngoscopy is impossible. At worst, the technique is as good as traditional laryngoscopy; at best and in experienced hands, it is quicker, more reliable, and better tolerated by the patient. With the right choice of stylet, it can be used for all sizes of patients and will not significantly increase department costs. It should be available in all anesthetic departments and taught to all trainees.