DIFFICULT AIRWAY
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DIFFICULT AIRWAY
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Difficult airway Vs Compromised airway
Definition of the difficult airway is related solely to tracheal intubation or problems with mask ventilation.
Compromise of the airway implies partial obstruction to airflow and constant threat to the total obstruction if relaxation of the muscles of the upper airway narrows the air passages.
Preoxygenation
Preoxygenation (also commonly termed denitrogenation) should be practiced in all cases when time permits. This procedure entails the replacement of the nitrogen volume of the lung (upward of 69% of the functional residual capacity) with oxygen in order to provide a reservoir for diffusion into the alveolar capillary blood after the onset of apnea. Preoxygenation with 100% O2 via a tight-fitting face mask for 5 minutes in a spontaneously breathing patient can furnish upto 10 minutes of oxygen reserve following apnea (in a patient without significant cardiopulmonary disease and a normal oxygen consumption). The impact of preoxygenation on oxygen reserve is shown in Table 1.11.
Other methods of preoxygenation:
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A series of four vital capacity breaths of 100% O2 over a 30 second period
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Modified vital capacity technique, wherein the patient is asked to take eight deep breaths in a 60 second period
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Pharyngeal insufflation of oxygen has been described to delay the drop in oxyhemoglobin saturation (<90%) sustained during apnea. In this technique, oxygen is insufflated at a rate of 3 liters per minute via a catheter passed through the nares. This technique relies on the phenomenon of apneic oxygenation, a process by which gases are entrained into the alveolar space during apnea, as long as there is a patent airway.
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In the obese patient, bilevel positive airway pressure as well as head-up position (approximately 25°) has been advocated to both reach maximal preinduction arterial oxygenation and to delay oxyhemoglobin desaturation.
NPO status and the Rapid-Sequence Induction (RSI)
Induction of anesthesia in patients who have full stomachs or incompetent gastroesophageal sphincters can result in regurgitation and pulmonary aspiration. Individuals at risk include, pregnant women, diabetics, or others with gastroparesis or intestinal obstruction/ileus/distension, upper gastrointestinal tract hemorrhage, those who require emergency operations, patients presenting from the intensive care unit, patients receiving acute opioid therapy, patients with gastroesophageal reflux disease, and patients who have recently eaten or are experiencing nausea. Individuals experiencing emotional stress have increased gastric acid secretions and are also at an increased risk for aspiration. Obesity by itself, long taught as a risk factor for gastric contents aspiration, may not denote a risk in this regard.
The technique of rapid-sequence induction is performed to gain control of the airway in the shortest amount of time after the ablation of protective airway reflexes with the induction of anesthesia. In the rapid-sequence technique, the administration of a precalculated dose of intravenous anesthetic induction agent is immediately followed by a rapidly acting neuromuscular blocking drug. Laryngoscopy and intubation are performed as soon as muscle relaxation is confirmed. Cricoid pressure (Sellick maneuver) is applied by an assistant from the beginning of induction until confirmation of ETT placement. Cricoid pressure entails the downward displacement of the cricoid cartilage against the vertebral bodies. In this manner, the lumen of the esophagus is ablated, while the completely circular nature of the cricoid cartilage maintains the tracheal lumen. The role of Sellick’s maneuver in rapid sequence induction is widely debated now.
If during rapid-sequence induction, there are difficulties in securing the airway and oxyhemoglobin desaturation occurs, gentle positive pressure ventilation may be used while maintaining cricoid pressure. This positive pressure should require <25 cm H2O pressure. Some authors argue that, because cricoid pressure is of dubious efficacy and may distort the laryngoscopist view, it be released if difficulties are encountered during the intubation attempt.
Methods of verification of tracheal tube placement
Methods of verification of tracheal tube placement (or detection of esophageal intubation) can be classified into nonfailsafe, almost failsafe, and failsafe, depending on their reported reliability and specificity (Table 1.12).
Difficult Airway Algorithm Modified for Trauma
Figure 1.21 depicts the modifications of the ASA difficult airway algorithm for trauma.
Modifications of the ASA DA Algorithm for Trauma
A. Stopping to come back another day is seldom an option with trauma.
B. A surgical airway may be the first/best choice in certain conditions.
C. An awake ETT technique should be chosen in a DA patient providing the patient is cooperative, stable, and spontaneously ventilating.
D. If the patient becomes uncooperative/combative general anesthesia (GA) may need to be administered — but if the airway is difficult, spontaneous ventilation (SV) should be continued (if possible).
E. Awake limb of the ASA Algorithm
An awake intubation technique is recommended for all trauma patients with a recognized difficult airway.... Providing the patient is cooperative, stable, and maintains spontaneous ventilation and adequacy of O2 saturation. The ASA DA Algorithm does not endorse any particular airway technique. However, it does emphasize that the patient must be properly prepared (mentally & physically) for an awake technique.
F. Anesthetized or uncooperative limb of ASA DA Algorithm
There are three common conditions when the need arises to intubate the trachea of an unconscious or anesthetized trauma patient with a DA:
[i] Clinician fails to recognize a difficult airway in preoperative evaluation prior to the induction of anesthesia.
[ii] The DA patient is already unconscious prior to being assessed by the trauma anesthesiologist.
[iii] The patient obviously has a DA, but is hemodynamically unstable (e.g., following trauma) or absolutely refuses to cooperate with an awake intubation (e.g., child, mentally retarded, drugged, or head-injured adult).
Once the patient is anesthetized or is rendered apneic or presents comatose and the trachea cannot be intubated, O2, enriched mask ventilation (MV) is attempted.
If MV adequate, a number of intubation techniques may be employed. Techniques allowing continuous ventilation during airway manipulations are favored over those requiring an interruption of mask ventilation (e.g., FOB, via an LMA or an airway intubating mask, with self-sealing diaphragm).
Alternatively, techniques requiring a cessation of ventilation (at least temporarily) can be employed. These techniques are relatively contraindicated for patients with large right- to-left transpulmonary shunt, or decreased FRC.
G. Confirmation of endotracheal tube (ETT) position.
Immediately after the patient's trachea is intubated, one must confirm ETT position with end-tidal CO2 measurement. If end-tidal CO2 measurement is unavailable, Wee's esophageal detector device (EDD) is reasonably reliable (close to 100% sensitive and specific).
H. Extubation or ETT change of the DA.
If the conditions that caused the airway to be difficult to intubate still exist at the time of extubation, or if new DA conditions exist (e.g., airway edema, halo), then the trachea should be extubated over an AEC and or with the assistance of a FOB.
Difficult airway in ICU/ER
Intubating stylets or Guides
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The Gum elastic bougie (Eschmann Tracheal Tube Introducer):
60 cm long, 15 Fr with a J tip (a 40° angle bend) at the distal end. This “bougie” is most suitable for patients whose laryngeal aperture cannot be seen under direct vision using a laryngoscope. If it is accurately placed, a tactile clicking sensation may be felt as the tip of the bougie slides over the tracheal rings while advancing into the trachea. Furthermore, if the bougie enters the trachea correctly, the bougie is lodged in a distal airway and cannot advance beyond the 30 to 35 cm mark. In contrast, if it is placed in the esophagus, the entire bougie can be advanced without encountering any resistance. After the bougie is placed in the trachea, the ET is advanced distally over the bougie and is guided into the trachea.
2. The flex-guide endotracheal tube introducer:
flexible plastic introducer with a curved distal tip.
3. The Cook airway exchange catheter:
A hollow flexible straight tube designed as a tube exchanger for patients with difficult airways. With an adaptor at the proximal end (Rapi-fit adapter), the device can be used to ventilate patients under difficult circumstances through the inner lumen and the distal ports. However, it does not have a curved tip at the distal end similar to that of the gum elastic bougie.
4. The Sheridan tube exchanger:
Serves a function similar to that of the cook airway exchange catheter with a hollow flexible straight tube.
5. The Schroeder oral/nasal directional stylet:
Disposable articulating stylet that requires no bending prior to intubation. Inserting the stylet into an ET allows the clinician to elevate the tip of the ET by wrapping all four fingers around the proximal ET and using the thumb to depress the proximal end of the stylet.
Lighted stylets (Light wands)
A lighted stylet uses the principle of transillumination of the soft tissues of the anterior neck to guide the tip of the ET into the trachea. It also takes advantage of the anterior (superficial) location of the trachea relative to the esophagus. When the tip of the lighted ET enters the glottic opening, a well-defined circumscribed glow can be readily seen slightly below the thyroid prominence. However, if the tip of the tube is in the esophagus, the transmitted glow is diffuse and cannot be readily detected easily under ambient lighting conditions.
The Trachlight incorporates an improved light source and a more flexible wand portion of the device. This added flexibility broadened the utility of the device for both oral and nasal intubation, made intubation easier, and permitted the evaluation of the position of the tip of the ET after intubation. It consists of three parts: a reusable handle, a flexible wand, and a stiff retractable stylet. The power control circuitry and batteries are encased within the handle.
The combitube: Esophageal-Tracheal Double-Lumen Airway
The Esophageal Tracheal Combitube (Combitube) is a device for emergency intubation that combines the functions of an esophageal obturator airway and a conventional endotracheal tube. The combitube is a double-cuff and double-lumen tube (Fig. 1.22). The so-called oropharyngeal balloon is located at the middle portion of the tube and the so-called tracheoesophageal cuff is located at the distal end. The lumens are separated by a partition wall. Proximally, both lumens are opened and linked by short tubes with universal connectors. Distally, the so-called pharyngeal lumen is blocked and has 8 perforations at the level between the cuffs, and the so-called tracheoesophageal lumen is open. This design allows ventilation both when the combitube is positioned in the esophagus through the perforations of the pharyngeal lumen, and in the trachea, through the opened distal end of the tracheoesophageal lumen. The pharyngeal balloon seals the oral and nasal cavity after inflation. Printed ring marks proximal to the oropharyngeal balloon indicate the limit of insertion.
The combitube is inserted “blindly.” The operator lifts the lower jaw and tongue anteriorly with one hand, and the combitube is inserted with a downward, caudad-curved motion until the proximal depth indicator (two black rings printed on the double-lumen tube) come to rest at the level of the teeth. The oropharyngeal balloon is inflated with 100 ml of air through a blue plastic pilot balloon (85 ml in the small adult size) while the distal cuff is inflated with 5 to 15 ml (via a white pilot balloon). A manual resuscitator or anesthesia circuit is attached to the proximal end of the esophageal lumen (constructed of blue polyvinyl chloride), and ventilation is confirmed by auscultation or other means. Because 90% of Combitube placements result in an esophageal position, ventilation occurs, via this lumen’s hypopharyngeal perforations. If no breath sounds are auscultated and/or gastric inflation is noted, the combitube has been positioned in the trachea. Without repositioning, ventilation is changed to the distal end of tracheal lumen (clear polyvinyl chloride).
Advantages and contraindications for use of the Combitube are given in Table 1.13.
Complications of laryngoscopy and intubation
The common complications are listed in Table 1.14.
Advantages and disadvantages of LMA over face mask or tracheal intubation
The comparative study of LMA versus face mask and tracheal intubation is given in table 1.15.
Different types of Laryngeal Mask Airways
Classic Laryngeal Mask Airway has an inflating cuff and a shaft with connector. The cuff has an inflating tube and pilot balloon. There is an epiglottic bar. Can be reused.
Single use LMA
The ILMA is a modified version of the LMA, which is designed to facilitate blind tracheal intubation with a tracheal tube in an obtunded or anaesthetised patient. It has a soft inflatable laryngeal mask and a rigid, anatomically curved airway tube with a 15 mm connector and is wide enough to accept a cuffed 8 mm ETT. An epiglottic elevator in the mask aperture elevates the epiglottis when an endotracheal tube is passed through the aperture.
Classic Laryngeal Mask Airway has an inflating cuff and a shaft with connector. The cuff has an inflating tube and pilot balloon. There is an epiglottic bar. Can be reused.
Intubation Difficulty Scale (IDS)
N1 : Number of attempts >1
N2 : Number of operators >1
N3 : Number of alternative techniques
N4 : Cormack Grade 1
N5 : Lifting force required (normal 0 or increased 1)
N6 : Laryngeal pressure (not applied 0 or applied 1)
N7 : Vocal cord mobility (abduction 0 or adduction 1)
IDS is used to describe the ease/difficulty of a particular intubation by direct laryngoscope. IDS more than 5 is taken as indicative of difficult intubation and it is essential to include the score of individual parameter. It is an objective method of conveying the difficulty in intubation, if any, to the next caregiver.