LECTURE SCRIPT

MANAGEMENT OF THE AIRWAY
MAJ Alan Storrow, MD, USAF
Wilford Hall Medical Center
San Antonio, Texas
GS ACEP

Managing the compromised airway is one of the most challenging aspects of emergency medicine. It is the first priority in patient care; the “A” of the ABC’s. Complete airway obstruction leads to irreversible brain damage in 3-5 minutes and cardiac arrest in as little as 4 minutes. The physician who understands the pathophysiologic processes that lead to airway compromise and is skillful in airway management techniques is well prepared to intervene successfully in this situation.

There are many etiologies of airway compromise. Trauma to the face and neck can lead to airway obstruction through accumulation of blood and secretions, airway compression by an expanding hematoma, or physical transection of the airway. A number of infectious processes can affect various structures within or adjacent to the airway and lead to airway compromise secondary to swelling or abscess formation. Other non-infectious causes of airway edema include inhalation injury, allergic reactions and angioneurotic edema. Physical obstruction by tumor or foreign body must also be considered. Congenital anomalies, subglottic stenosis and vocal chord dysfunction are other causes of airway compromise.

The patient who presents with acute airway obstruction is in obvious distress. If obstruction is complete, the patient cannot cough, speak or breathe; and is noted to have increased heart rate, blood pressure and paradoxical respirations with no air movement . Within minutes the patient becomes cyanotic, loses consciousness and becomes apneic. Cardiac arrest quickly follows respiratory arrest, occurring 4-10 minutes after airway obstruction.

Initial management of the airway utilizes basic maneuvers to open the airway and enhance oxygenation. Supplemental oxygen should be provided to any seriously ill or injured patient. The concentration of oxygen provided is dependent on the flow rate and type of device used. Any critically ill patient should initially receive 100% oxygen delivered by a non-rebreather mask. Pre-oxygenation of the adult patient with 100% oxygen for 2-3 minutes prior to intubation provides 4-5 L of oxygen reserve.

At the same time the patient is being provided with oxygen, basic maneuvers to open the airway are performed. Patients not suspected of having a cervical spine injury can most effectively have their airway opened by a head tilt in combination with chin lift or jaw thrust. This maneuver is usually effective in lifting the tongue off the posterior pharynx. If cervical spine injury is suspected, a chin lift or jaw thrust alone is utilized to open the airway. Patients presenting with airway obstruction due to foreign body aspiration may be treated with other techniques. Abdominal thrusts (Heimlich maneuver) are used on the conscious patient with complete upper airway obstruction or partial obstruction with poor air exchange. This technique has been credited with saving approximately 50,000 lives; it should, however, be avoided in infants, and pregnant or obese patients. Foreign body removal in the unconscious patient is best managed by direct laryngoscopy and removal with Magill forceps. Finally, use a suction device to clear blood, secretions, and particulate matter from the upper airway.

Airway adjuncts are used to provide continued airway patency once the airway has been opened or cleared. Oropharyngeal and nasopharyngeal airways both maintain airway patency by providing a passage between the tongue and posterior pharynx. The oropharyngeal airway is used only in the unconscious patient; the nasopharyngeal airway may be used in a semi-conscious or unconscious patient. While both devices are effective in maintaining airway patency, they do not provide protection from aspiration. Thus, they should only be used until a more definitive airway can be provided in patients at risk for aspiration or when endotracheal intubation is otherwise indicated.

Indications for orotracheal intubation include apnea, upper airway obstruction, airway protection, respiratory insufficiency, controlled hyperventilation, and administration of drugs if IV access is unobtainable. There are no absolute contraindications to orotracheal intubation; however, caution and proper technique must be exercised in patients with suspected cervical spine injury.
The first step when preparing for intubation is equipment preparation. The appropriate size tube and an additional tube 0.5-1.0 mm smaller should be selected and the cuff checked for leaks. Approximate tube size for an adult female is 7.0-8.0 , 8.0-9.0 for males. A stylet should then be inserted into the tube. Next, select the type and size of laryngoscope blade and check the light source of the laryngoscope. There are two basic blade designs-straight (Miller) and curved(McIntosh). The tip of the straight blade lifts the epiglottis directly,
whereas the curved blade fits into the vallecula and lifts the epiglottis passively by moving the larynx. The straight blade is usually better in children and in patients with a very anterior larynx. Finally, turn on the suction device and place the tip at the head of the bed. Pre-oxygenate the patient with 100% oxygen and ventilate as needed to provide the patient with an oxygen reserve in preparation for intubation. Cricoid pressure is recommended if the patient requires active ventilation.

The patient is placed in a supine position, with the head at the level of the intubators lower sternum. The head is in the “sniffing” position, with the head extended on the neck and the neck slightly flexed in relation to the trunk. A small towel placed under the occiput may facilitate this position. With the laryngoscope in the left hand, place the blade into the right side of the patient’s mouth, sweeping the entire tongue all the way to the left. Lifting the
laryngoscope along the line of the handle, attempt to visualize the vocal cords. Suctioning and cricoid pressure may be performed at this point as needed to enhance visualization. Once the cords are visualized, the tube is inserted into the far right side of the mouth and advanced through the cords. The balloon is inflated and tube placement is verified.

Inability to intubate is usually due to a few common mistakes. These include improper positioning, incorrect use of the laryngoscope ( not sweeping tongue far enough to left, leveraging against teeth, using incorrect size and type of blade), obscuring line of vision when passing tube, and equipment malfunction. Complications of orotracheal intubation include esophageal intubation, right mainstem intubation, aspiration, dental trauma, and vocal cord injury.

The other route for endotracheal intubation is nasotracheal intubation.
Nasotracheal intubation is indicated when it is difficult or impossible to perform direct laryngoscopy. This may occur when there is an anatomic abnormality
or pathologic condition affecting the upper airway. It may also be used as an alternative to orotracheal intubation in patients who require intubation and are awake, have spontaneous respirations or have a potential c-spine injury. Contraindications to nasotracheal intubation include apnea, basilar skull fracture, anticoagulant use or coagulopathy, severe midface injuries, or upper airway foreign body, abscess or tumor.

Nasotracheal intubation is technically more difficult than orotracheal intubation. An awake patient may be placed in the sitting position; otherwise, the supine position is used. The larger nostril is selected for tube placement. The nasal mucosa is constricted with phenylephrine and anesthetized with lidocaine spray. Select a cuffed tube 1 mm in size smaller than would be used for orotracheal intubation.

Lubricate the tube then insert it with the bevel toward the septum, advancing slowly. Listen at the end of the tube; when airway sounds are at maximum gently but swiftly advance through cords when patient inspires. Confirm tube placement by auscultation, looking for mist in tube, and ultimately with an x-ray.
Nasotracheal intubation can be difficult, but a few helpful techniques may prove useful. To better hear airway sounds occlude the opposite nostril or attach a
plastic “whistling” cap to the end of the ET tube. If airway sounds decrease or the “whistling” stops as the tube is advanced the tube is in the esophagus and needs to be pulled back. Cricoid pressure may also facilitate correct tube placement. Some prefer to guide the tube into the glottis with Magill forceps under direct visualization. Complications of nasotracheal intubation include esophageal intubation, aspiration, nasal trauma / epistaxis, posterior pharyngeal wall perforation, and vocal cord injury.

Rapid sequence induction is a technique for inducing rapid onset of sedation and paralysis for controlled orotracheal intubation. This technique allows immediate control of the airway while minimizing the risk of aspiration. It also decreases the potentially adverse physiologic responses that often accompany intubation. Rapid sequence induction is indicated in patients requiring emergent intubation who would be difficult to intubate without paralysis. It is also indicated in patients who have increased intracranial pressure or an open eye injury. Contraindications include the inability to perform orotracheal intubation due to a fixed airway obstruction or distortion of airway anatomy, or not being prepared to obtain surgical control of the airway if rapid sequence intubation is unsuccessful.

Equipment preparation, patient positioning and pre-oxygenation are all performed in the same manner as oral intubation without rapid sequence induction.

The rapid induction of sedation and paralysis begins with premedication. Non- depolarizing paralytic agents are given in sub-paralytic doses to prevent succinylcholine induced fasciculations which cause increased intragastric, intracranial, and intraocular pressure. Either pancuronium or vecuronium may be used, both at a dose of 0.01 mg/kg IV push. These medications are most effective when given 3 minutes prior to paralysis with succinylcholine. Atropine 0.01 mg/kg IV push (minimum dose of 0.1 mg) is recommended in children to prevent the bradycardia that can occur in response to succinylcholine. It is also recommended for adults prior to a second dose of succinylcholine. Lidocaine 1.5 mg/kg given IV over 30-60 seconds is used to suppress the cough reflex and increased intracranial pressure response in patients with head trauma. When indicated, these medications may be given in rapid succession at the onset of rapid sequence induction. Administering lidocaine and waiting for the
non-depolarizing agents to take effect can add minutes to the intubation sequence. These steps may need to be avoided if immediate intubation is required.

The next step is the induction of sedation/unconsciousness, which can be achieved with a variety of different medications. Thiopental, fentanyl, and midazolam are among the agents most commonly used. Thiopental is a barbiturate which provides rapid and brief sedation. It is the drug of choice in patients with head trauma who are hemodynamically stable. It reduces cerebral metabolism and oxygen consumption which secondarily reduces cerebral blood flow and intracranial pressure. Adverse effects include hypotension, respiratory depression, and bronchospasm in asthmatics. The dose is 3-5 mg/kg IV push. Fentanyl is a potent narcotic analgesic with rapid onset and short duration. Adverse effects include respiratory depression and potential chest wall rigidity if >10 ug/kg is given rapidly. The dose is 2-3 ug/kg IV at a rate of I-2 ug/kg/min, titrating to effect. Midazolam is a benzodiazepine which provides a rapid onset of sedation with a lesser potential for cardiorespiratory depression than other drugs in its class. Other advantages are its amnestic effect and short duration of action. Adverse effects include respiratory depression and hypotension. The dose is 0.02-0.04 mg/kg given in 1 mg boluses, not to exceed 2.5 mg over 2 minutes. Midazolam and thiopental may be combined with fentanyl to obtain effective sedation and analgesia; however, decreased doses may be needed to avoid adverse effects enhanced by using more than one of these medications. Cricoid pressure is initiated at the onset of sedation prior to inducing paralysis.

Paralysis is achieved with the depolarizing agent succinylcholine. Many of its adverse side effects can be prevented with appropriate premedication as discussed above. Succinylcholine can induce hyperkalemia in patients at risk and should be avoided in patients with pre-existing hyperkalemia or previous disease states which may make them hypersensitive to succinylcholine. These include previous burns, neuromuscular or primary muscle disease, head or spinal cord injury, or stroke. Once succinylcholine has been given, allow 45-90 seconds for relaxation and then orally intubate the patient. Cricoid pressure should be maintained until a cuffed ET tube is in place.

Indications for cricothyrotomy include failure of oral or nasal endotracheal intubation, upper airway obstruction not relieved with other measures, and traumatic injuries making oral or nasal intubation difficult or hazardous.
Contraindications include patients who can be successfully intubated by the oral or nasal route, patients with severe trauma to the larynx, cricoid cartilage or trachea (transection), or children less than 10-12 years.
The first step in performing a cricothyrotomy is locating the cricothyroid membrane. It is found in the notch located between the laryngeal prominence and the cricoid cartilage. If time permits, prepare the skin in sterile fashion and provide local anesthesia (lidocaine with epinephrine). Incise the skin over the cricothyroid membrane with a 3-4 cm vertical midline incision. Next, the larynx is stabilized with the thumb and forefinger of the non-dominant hand and the membrane is incised with a 1 cm horizontal stab, allowing only the tip of the scalpel to penetrate the membrane. The incision is dilated by inserting curved Mayo scissors next to the scalpel blade and spreading. The scalpel handle can also be used to dilate the incision by placing through the incised membrane and rotating 90 degrees. Insert a tracheal dilator and open. Pass a #4 Shiley tracheostomy tube or modified endotracheal tube between dilator and into trachea.

The more common complications of cricothyrotomy include bleeding, injury to adjacent structures, incorrect tube placement, infection, and subglottic stenosis.

The indications for this procedure are the same as for surgical cricothyrotomy.
It is the surgical airway of choice for children less than 12 years old. Contraindications are the same as for surgical cricothyrotomy. As in surgical cricothyrotomy, locate the cricothyroid membrane and anesthetize the skin overlying it. Using a 14 gauge or larger catheter over needle attached to a 5cc syringe puncture the skin aiming caudally at 30-45 degree angle. Puncture the
membrane and aspirate air to insure correct placement. Advance the catheter and withdrawal the needle. Attach catheter to high pressure oxygen source (50 psi) with tubing that has side port or “Y” connector to allow for jet ventilation. Failure to use a high pressure oxygen source will not adequately ventilate the patient resulting in hypercarbia. Recently commercial percutaneous catheter kits have become available that utilize a similar technique but provide a larger catheter. Most kits use a 6mm or 7mm tube which provides for adequate ventilation using bag-valve oxygen source.

Complications of percutaneous transtracheal ventilation include subcutaneous emphysema, kinking or blocking of catheter, bleeding, infection, incorrect placement and damage to surrounding structures.

It is important to remember that most pediatric cardiac arrests are due to respiratory insufficiency or failure. Successful airway management and ventilation will often result in successful cardiac resuscitation.

When managing the pediatric airway, it is important to consider anatomical differences that may influence methods or equipment used. These differences include a relatively larger head and occiput, a smaller airway, and a larger tongue to oropharynx ratio. The larynx is higher and more anterior than in the adult, and the narrowest portion of the airway in children is at the level of the cricoid ring.

The basic maneuvers of airway management in pediatric patients are similar to those in adults. The indications for supplemental oxygen and the use of airway adjuncts are the same. There are some important differences to keep in mind when opening the airway. Due to the larger head and occiput size found in infants and small children, the neck is naturally flexed with a relative alignment of the pharyngeal and tracheal axes when the child is in the supine position. Further flexion of the neck, as might occur if a pillow is placed under the head, may make visualization of the glottis more difficult. It is equally important not to hyperextend the neck of the small child or infant, as this may actually lead to airway obstruction. The patient should be placed in the “sniffing position” to open the airway; care must be taken not to hyperflex or extend as discussed. Management of airway obstruction is similar to adults except 4 back blows and 4 chest thrusts are used in an infant < 1yr old instead of abdominal thrusts.

Pediatric patients without effective respiratory effort or inadequate ventilation
should be supported with assisted respirations. This is most effectively done with a bag-valve-mask device. This technique is extremely useful in pediatric airway management, frequently allowing the rescuer to overcome upper airway obstruction and adequately ventilate the patient. It is important not to overinflate the lungs of the pediatric patient, remembering the appropriate tidal volume is 10-15 cc/kg. Bag-valve-mask ventilation should always be used with 100% oxygen and cricoid pressure to avoid gastric distention.

The technique for pediatric orotracheal intubation is similar to that of the adult.
The equipment will vary depending on the child’s size. A straight laryngoscope blade is recommended for children up to age 4-5 years due to the anterior larynx and relatively long epiglottis. Uncuffed endotracheal tubes are used in children less than 8 years old due to the narrowing of the airway at the cricoid ring. While this narrowing of the airway provides an adequate seal around the uncuffed tube, an air leak of 15-20 cm H2O should be expected in the properly intubated child. There are many methods to estimate the correct tube size in children. The size of the little finger approximates the external tube diameter; or the following formula can be used to estimate the internal tube diameter : age + 16 4

Reference tables are also available to check appropriate tube and blade sizes.
The key to successful intubation in the pediatric patient is familiarity with the different equipment and airway anatomy.

REFERENCES

1. Roberts & Hedges: Clinical Procedures in Emergency Medicine
second edition, W.B. Saunders Company, 1991

2. Rosen & Barkin: Emergency Medicine “Concepts and Clinical Practice”,
third edition, Mosby Year Book Inc., 1992

3. Bushore, Seidel, Fleisher, Wagner: Advanced Pediatric Life Support,
American Academy of Pediatrics/American College of Emergency Physicians
revised 1991

4. Tintinalli, Krome, Ruiz: Emergency Medicine “A Comprehensive Study
Guide”, McGraw-Hill Book Company 1988