1 Small Tubes and Airway Resistance

The physics of laminar gas flow through a conduit are described by the Hagen-Poiseuille equation, which reflects the relationship of resistance varying inversely with the fourth power of tube radius. Despite the fact that gas flow through ETTs is often turbulent rather than laminar, the effect on resistance to gas flow represented by each millimeter decrease in tube size is considerable, ranging from 25% to 100%.³¹ Airway resistance is affected by more than tube diameter: the presence of secretion within the tube, ETT kinking, and positioning of the head and neck can also increase the tendency for turbulent flow.^32,33 The fundamental principle of which to be mindful is that airway resistance induced by an ETT is inversely proportional to the tube size—hence, the mantra that the largest tube is usually the best size.³⁴

Airway resistance increases with decreasing ETT diameter, whether due to internal occlusion, smaller size, or external compression. As airway resistance increases, WOB also increases.³¹ The increase in WOB associated with a 1-mm reduction in ETT diameter varies in accordance with tidal volume and respiratory rate at a given minute ventilation and can range from 34% to 154%.³¹ When ventilation is controlled, the increase in WOB related to ETT resistance is seldom of any consequence, because it is overcome by ventilator adjustments. However, small-diameter tubes create greater difficulty for patients in weaning from ventilatory support due to the higher levels of resistance encountered when attempting to breathe spontaneously.^35,36 It has been suggested that an inability to spontaneously ventilate due to the increased WOB imposed by a 7-mm ETT might indicate that extubation will fail regardless of tube size.^37,38

Increased airway resistance associated with a smaller-diameter ETT may also be associated with inadvertent PEEP. Patients with high oxygen consumption, increased carbon dioxide production, or ventilation-perfusion relationships that produce high dead space ventilation often require higher minute ventilations to achieve appropriate ventilation and oxygenation. The gas flows necessary to maintain such a minute ventilation are also quite high, and the resistance imposed by a smaller-diameter ETT further prohibits the completion of expiratory flow before initiation of the subsequent inspiration. This breath stacking results in air trapping and unwanted PEEP, magnifying the risk of mechanical ventilation because barotrauma and subsequent intrathoracic overpressure could result in circulatory compromise.³⁹

The restriction to gas flow through any ETT increases dramatically when devices such as a suction catheter or bronchoscope are placed in the lumen. The cross-sectional area of the tube is effectively reduced by an amount equal to the cross-sectional area of the device inserted into the tube. The limitation of gas flow has consequences for both the inspiratory and expiratory phases: inspiratory flow may be inadequate to maintain oxygenation and ventilation during the procedure, and retarded expiratory flow may lead to overdistention resulting in barotrauma or circulatory compromise.⁴⁰

2 Large Tubes and Trauma

Whereas smaller-diameter ETTs have disadvantages related to gas flow and airway resistance, larger tubes are more frequently associated with traumatic placements and damage to both the laryngeal structures and the tracheal mucosa.^37,38,41 Larger ETTs are associated with a higher incidence of sore throat after general anesthesia, compared with smaller-diameter tubes, but this difference is relatively negligible with long-term intubation.⁴² With prolonged intubation, laryngeal trauma is more likely. Women, because of the inherently smaller size of their airway, are more susceptible to injury than men.^43,44

Laryngeal structures at particular risk for trauma are the arytenoid cartilages and the cricoid cartilage. Trauma results not only from the shape discrepancy between the round ETT and the angular, wedge-shaped glottic opening but also from direct contact and pressure on these structures and from repetitive tube movement, which leads to ulceration or erosion of the protective mucosa.^44–46 Tracheal mucosal injury can also occur because of the irregular surfaces created by wrinkling and folding of the ETT cuff or the externalized pilot tube used to fill the ETT cuff. If the tracheal lumen is “overcrowded,” airway injury is more likely to occur when large tubes are used and little cuff volume is required to seal the airway.⁴⁷

1 Preformed and Reinforced Tubes

Modifications to the ETT that are made in the operating room setting to accomplish specific surgeries are often developed in response to interference and access issues. The ability to work without disturbing the ETT has led to several variations of the ETT that can be placed safely and remove the risk of inadvertent advancement, dislodgement, kinking, or obstruction. ETTs used in remote locations also have airway access issues associated with tube kinking and partial occlusion, which typically are related to positioning problems and associated comorbidities. In part because of less stringent vigilance, unintended consequences of ETT use outside the operating room may result in more drastic outcomes. In response to these dilemmas, a variety of tubes have been developed to maintain their shape and patency in locations where distortion might cause kinking and occlusion.

Rigid, preformed tubes such as those developed for long-term use in tracheostomy were known to maintain their patency despite the need for angulation. Preformed tubes have been developed for specific application in anesthesia practice as well. The Ring-Adair-Elwyn (RAE) tubes (Mallinckrodt Inc., Pleasanton, CA), both oral and nasal (Fig. 47-4), maintain a fixed contour similar to the average facial profile, allowing for head and neck surgery while minimizing surgical field interference. Their contour also reduces the risk of pressure injury to the posterior pharynx when repositioning is desired. The intra-airway length is tied to the size of the ETT, with a relatively appropriate depth based on the average size of a patient for whom the tube might be selected.^48,49

Figure 47-4 Nasal (left) and oral (right) Ring-Adair-Elwyn (RAE) preformed endotracheal tubes.

(Courtesy Covidien, Mansfield, MA.)

An anode or armored tube with an embedded wire coil is designed to minimize kinking even with quite severe position-induced angulation. Armored tubes are popular for use in head and neck surgery where remote airway access and the potential for kinking of the ETT are concerns. Placement of an armored tube through a tracheostomy for procedures such as laryngectomy is a common practice; it allows placement during surgical procedures such that the tube can be mobilized or the circuit draped away from the field without a high risk of tube kinking. The other common use of a wire-reinforced tube is with the ILMA. These tubes are designed to facilitate placement through the device and to be used for short periods of time. The HPLV cuff and the theoretical possibility of kinking and resultant airway obstruction make the long-term use of ILMAs risky.

The embedded wire concept of the armored ETT has also been developed for long-term tracheostomy use. Although the armored tracheostomy tube is not free of risks, one advantage is that its flexibility allows its length and intratracheal depth to be adjusted, which may be beneficial if tracheomalacia at the level of the cuff develops.⁵⁰ These tracheostomy tubes are also popular for use in morbidly obese patients, in whom, because of the depth of tissue, preformed tracheostomy tubes may not have the shape required to fit an individual patient. One major consequence of this type of reinforced ETT may occur when external pressure is applied to the wire-reinforced component (i.e., by patient biting). Once a compression threshold is reached, the luminal support provided by the wire may be compromised, and a permanent, irreparable dent remains that can significantly endanger ventilation and suctioning capabilities.

2 Laser Tubes

Progress in laser technology has advanced surgical capabilities, particularly for airway surgery. To protect patients and health care providers from laser-induced injury to eyes and airways, special precautions are required. Fire is the most serious danger associated with the use of lasers in the operating room, especially when a laser is used in airway surgery.^30,51–53 A major complication related to the use of lasers for laryngeal surgery is ignition of the ETT.⁵⁴ The laser beam may ignite the tube by direct penetration or indirectly if burning tissue is inhaled into the tube.^30,51,52,55 The ease of ignition is related to the ETT material, the concentration of oxygen in use, and any other adjunctive materials or gases that could support combustion.^30,52,55 Most ETTs are constructed of PVC, which is highly flammable. Ideally, PVC tubes should not be used for airways when a laser is employed.^51,55,56

ETTs can be laser-proofed or protected from the laser beam by wrapping them with either reflective metal tape or muslin. Ideally, they should be constructed from noncombustible materials. In particular, the ETT cuff is vulnerable to puncture by the laser beam and should be filled with saline or water, which allows more energy to be absorbed before disruption.^30,52,55 One trick to enhance appreciation of a penetrated, defective cuff, is to place a dye indicator, such as methylene blue, into the solution that is instilled into the cuff. Any leakage will clearly mark the airway and alert the provider to the potential dangers.⁵⁷ Protecting the tube from the laser beam by wrapping it with a foil tape has proved effective (commercial devices are available) (Fig. 47-5).⁵⁸ Tubes made of materials such as metal and silicone and those with special double cuffs also reduce the risk of airway fires and injury during laser airway surgery.^51,58

Figure 47-5 Rusch Lasertubus laser-safe endotracheal tube.

(Courtesy Teleflex Medical, Durham, NC.)

3 Subglottic Suctioning Evac Endotracheal Tubes

Hospitalized patients who require mechanical ventilation are susceptible to the development of aspiration pneumonia. VAP is known to increase hospital length of stay, health care costs, and mortality.⁵⁹ Organisms that grow in pooled subglottic secretions above the inflated cuff of the ETT, but beneath the glottis, have previously been unmeasurable with any reliability and are now demonstrated to be a major impetus for VAP. Several nursing care measures may be taken to reduce the incidence of VAP caused by this route, including improved oral care, patient positioning by elevating the head of the bed past 30 degrees, frequent suctioning, and ensuring postpyloric tube feedings, but none of these measures completely stops the production.⁶⁰

The presence of these pooled collections has led to the development of specific ETTs that possess a dedicated suction system capable of emptying this area of debris. Drainage of subglottic secretions has been shown to prevent VAP.^61–64 The currently available subglottic drainage ETTs have a suction lumen that opens on the external (posterolateral) surface of the ETT immediately above the cuff (Fig. 47-6). The lumen is attached to constant or intermittent suction for active drainage of the space. Although these ETTs are beneficial, their efficacy is not 100%, and therefore all of the aforementioned nursing care actions remain vital to good hygiene and prevention of VAP. The subglottic drainage tubes have been further developed to include variations in cuff construction (materials, shapes, volumes, locations) that help to prevent aspiration of the subglottic debris.

Figure 47-6 Mallinckrodt Sealguard Evac Endotracheal Tube.

(Courtesy Covidien, Mansfield, MA.)

Subglottic secretions are not the only recognized cause for VAP. Biofilm is an accumulation of debris adhered to the internal circumference of the ETT that is composed of tissue, secretions, mucus, and undetermined bacteria load. Biofilm can be aspirated, leading to a nidus for infection or causing an area of obstruction to airflow. Biofilm removal and reduction by hygiene care are currently better researched than prevention. However, there is a growing interest in the reduction of biofilm through construction of ETTs impregnated with antimicrobial agents.^65–67 The ability of such developments to affect the incidence of VAP has not yet been proved.

4 Double-Lumen Endotracheal Tubes

The uses of a double-lumen endotracheal tube (DLT) (Fig. 47-7) can be separated into relative and absolute indications. The absolute indications are isolation, to avoid soilage or contamination of the contralateral lung tissue when dealing with infections or frank hemoptysis from a unilateral location, bronchoalveolar lavage, and one-lung ventilation (OLV). The most common reason for placement is OLV for surgical exposure, but OLV can also be important in cases of bronchopleural or bronchocutaneous fistula, unilateral pulmonary hemorrhage, giant unilateral bulla or cyst, and severe unilateral ventilation-perfusion mismatch. The relative indications all deal with surgical exposure. Complementing the DLT as another option for lung isolation, particularly if a DLT cannot be placed, are bronchial blocking devices. However, the DLT has an advantage because of the ability to pass suctioning catheters or fiberoptic devices into the area on collapse without drastically jeopardizing OLV or contaminating the contralateral side.

Figure 47-7 Endobronchial blocking devices for lung isolation. Mallinckrodt Endobronchial Tube (top). (Covidien, Mansfield, MA); Fuji TCB Univent Tube (bottom).

(Phycon Products, Tokyo, Japan).

Relative contraindications to the placement of a DLT are fairly minimal. They include patient refusal (likely due to risk of trauma secondary to the large size), a known difficult airway, and the speed with which an isolated airway must be established. In patients with difficult airways, specially designed airway exchange catheters (Cook Medical, Bloomington, IN) (Fig. 47-8) can be used after placement of a conventional ETT to facilitate DLT placement. Additionally, some makers of video laryngoscopic technologies have developed specific DLT devices. The time required for placement is usually the biggest detractor to their use. Situations such as frank hemoptysis may be better served by a rapid-sequence induction and placement of a contralateral, main stem, single-lumen ETT for stabilization.

Figure 47-8 A selection of airway exchange catheters. Double-lumen airway exchange catheter (top), Aintree Intubation Catheter (center) and Portex Single-Use Bougie (bottom).

(Aintree Courtesy Cook Medical, Bloomington, IN; Portex Courtesy Smiths Medical, Carlsbad, CA.)

This technique is not ideal for long-term management. The long-term use of the DLT in the intensive care unit (ICU) setting (>24 to 48 hours) must be approached with caution, because the two smaller-diameter lumens are at significantly increased risk for partial or complete occlusion. Consideration should be given to close monitoring of luminal patency with fiberoptic evaluation on a regular basis and optimization of luminal hygiene to reduce mucus or biofilm accumulation.

5 Supraglottic Airways

Supraglottic devices are continually coming onto the market. Largely designed for shorter surgical procedures to deliver general anesthesia, their use seems to be growing past their original intent. Supraglottic airways (Fig. 47-9) such as the LMA, the esophageal-tracheal Combitube (ETC, Tyco Healthcare, Mansfield, MA), the King LT (King Systems, Noblesville, IN), and other variants have provided valuable means of establishing an (unsecured) airway in an emergency. Equally important is their ability to function as a conduit for endotracheal intubation. For example, the ILMA is a blind passage device that is designed to place an ETT through the LMA. Recently, use of the LMA as a conduit for fiberoptic bronchoscopy and subsequent ETT placement has also been demonstrated in emergency situations.⁶⁸ Although these devices do not provide classically definitive airways, their utility is unsurpassed in helping to manage the difficult airway.

Figure 47-9 Supraglottic devices. LMA Unique (top), (Courtesy USA) King LT Supraglottic Device (bottom).

(LMA Unique courtesy LMA North America Inc., San Diego, CA; King LT courtesy King Systems, Noblesville, IN.)

1 Detection of Esophageal Intubation

Once the clinician has deemed intubation necessary and has performed the intervention, confirmation of proper ET placement must be provided expeditiously. An incorrectly positioned ETT can produce adverse effects, especially in an already apneic patient. Unrecognized esophageal intubation can have disastrous consequences with a reported incidence as high as 8% in critical patients.⁶⁹ Therefore, a brief discussion of verification of ETT placement is warranted.

Once intubation has been accomplished, confirmation of proper placement of the ETT in the trachea needs to be achieved, ideally by the detection of end-tidal carbon dioxide (EtCO₂) in expired gases using capnography or other capnometric (colorimetric) methods.⁷⁰ The detection of EtCO₂ is not fail-safe and does not guarantee that the ETT is positioned within the tracheal lumen (e.g., the tip may lie above the vocal cords). After three to five breaths, the absence of EtCO₂ suggests a nontracheal placement. Blockage or soilage of the EtCO₂ detection device can hamper efforts. EtCO₂ detection should be complemented with indirect maneuvers such as auscultation, ETT misting or fogging, bag compliance, chest wall excursions, lack of phonation, and improved oxygen saturation. The dependence of any EtCO₂ detection device on adequate cardiac output has spurred utilization of an esophageal detector device (Fig. 47-10). It is essentially an air-filled bulb placed on the end of an in situ ETT. After a vacuum has been created by squeezing the bulb, immediate re-expansion should occur when the bulb is placed on an ETT in the trachea (any column of air). If the ETT is esophageal, the suction created by the bulb will draw the pliable esophageal tissue into the distal lumen of the ETT, preventing full expansion of the bulb on top of the ETT (column of soft tissue).^71–73

Figure 47-10 Esophageal bulb detector and a homemade syringe device.

(Courtesy Wolfe-Tory Medical, Inc.)

If intubation is to occur in a patient with cardiac arrest, capnometry may be fallible given the amount of down time and the lack of any life-sustaining cardiac output. If cardiopulmonary resuscitation (CPR) is adequate, this technicality is likely to be moot. However, esophageal bulb detectors can be helpful in this situation, although false-positives and false-negatives do occur and confound ETT verification. Still other methods that are independent of carbon dioxide and cardiac output exist, such as a tracheal whistle to verify correct placement (Box 47-1), but not one is without limitations.^72–77 Ideally, two methods are to be considered fail-safe: direct or indirect visualization of the ETT traversing the vocal cords and fiberoptic verification via the ETT lumen. The limitation of direct laryngoscopy is the operator’s line of sight to the glottic opening. The key is to identify the ETT positioned in the glottis, not simply to see it go in. An indirect method such as video laryngoscopy does improve the validity of ETT passage. Fiberoptic verification is hampered by equipment availability at the bedside, any airway or ETT soilage, time constraints, and operator skill. Chest rise and condensation from expired gas found in the ETT have also been used, but these signs may occur in esophageal intubations as well.⁷⁷ Therefore, the gold standard used today is the presence of EtCO₂ in expired gases as demonstrated by capnography or other colorimetric techniques.⁷⁰

Capnography yields quantifiable measurements of inspired and expired gases in addition to a waveform generated with each tidal volume. Although not without limitations (e.g., lack of portability, need for a power source), capnography reliably identifies initial proper placement of the ETT (nonesophageal) and provides a continuous verification of ETT security. If esophageal intubation has occurred, a gradual reduction in height of the capnograph waveforms is observed with successive breaths. False-positive results during esophageal intubations may occur in situations of ingested CO₂-containing or -liberating substances (e.g., carbonated beverages) before intubation, bag-mask ventilation with inflation of expired air into the stomach, or intubation of the supralaryngeal hypopharynx.⁷⁸ Inappropriate extubations may occur due to misinterpretation of a false-negative situation because an EtCO₂ waveform is lacking despite proper placement. This error may occur with unrecognized circuit disconnections, an obstructed or kinked ETT, a disconnected or contaminated gas sampling line (water, secretions, entrainment of room air), equipment failure, severe bronchospasm, or inadequate cardiac output. Unquestionably, capnography is dependent on pulmonary blood flow. In the absence of perfusion (e.g., cardiac arrest), the utility of capnography can be limited; however, even in very low-flow states (e.g., CPR, separation from cardiopulmonary bypass), it has been shown to provide effective detection. Ornato and colleagues used an animal model to evaluate the relationship between cardiac output (CO) and EtCO₂. Through manipulation of CO, with inotropes or controlled hemorrhage, a logarithmic relationship between CO and EtCO₂ was demonstrated.⁵⁰ This finding shows that capnography is useful in cardiac resuscitation to assist with evaluation of low-flow states and adequacy of perfusion.

To alleviate the logistic concerns with capnography in emergency situations—mainly the lack of portability and the need for a power source—a portable and reliable means of detecting EtCO₂ was developed. Colorimetric EtCO₂ uses a detector impregnated with metacresol purple (Fig. 47-11). This indicator is pH sensitive and changes color, from purple to yellow, in the presence of CO₂. The devices are disposable, attach between the ETT and the circuit or bag, and provide a rapid and reliable indication of CO₂ concentration on a graded scale: A (purple) corresponds to an EtCO₂ level of 0.5%, B (tan) to a level of 0.5% to 2%, and C (yellow) to a level greater than 2%.^70,77 Limitations of this method are that it is ineffective with exposure to humidified gases, vomitus, or secretions and in cases of prolonged cardiac arrest or low-perfusion states. False-positive results can occur as well, just as in capnography. Delays in recognition of esophageal intubation with colorimetric capnometry have been reported far more often than with capnography, particularly in patients with prolonged bag-mask ventilation or ingestion of EtCO₂-containing substances before intubation. Therefore, capnography simply is the best method for detection of esophageal intubation.⁷⁹

Figure 47-11 Example of a colorimetric capnometric device.

(Courtesy Mercury Medical, Clearwater, FL.)

As mentioned previously, the esophageal bulb detector capitalizes on the physical characteristics of the esophagus, which, unlike the trachea, collapses when negative pressure is applied. Commercial devices exist, but a homemade version can be improvised using a syringe that attaches to the end of the ETT. When the plunger is withdrawn, resistance is appreciated if an esophageal intubation has occurred, because the walls of the esophagus collapse around the ETT. Unencumbered aspiration of the plunger occurs with proper tracheal placement.⁷¹ Bulb detector devices are reported to be reliable and effective, with one study demonstrating a sensitivity of 100% and a specificity of 99%.⁷² However, other studies have reported limitations and false-negative results in patients with copious or aspirated secretions, gastric distention, vomitus in the airway, morbid obesity, or reduced functional residual capacity.^71,80–83

A little used but highly effective method of detecting proper ETT location is the passage of a catheter (e.g., bougie) via the ETT to decipher a straight smooth muscle pathway (esophagus without pathology) or a more rigid, angulated tube with reduction in the luminal diameter (tracheobronchial tree). A bougie can be used in this fashion, particularly at the time it is being used as an adjunct to intubation, or later if necessary. Gentle advancement to 28 to 34 cm (in adults) typically results in contact with the carina or a main stem bronchus. Further advancement down a main stem bronchus should be limited by the secondary lobar carina. Gentle unopposed advancement of the bougie beyond 35 cm suggests esophageal placement (assuming no esophageal pathology).

2 Confirmation of Appropriate Depth of Insertion

After correct tracheal placement of the ETT has been verified, it is imperative to identify the correct depth of the ETT to ensure adequate ventilation of each lung.⁴⁹ Before addressing the various methods that assist in confirmation of appropriate ETT depth, a brief discussion of what is considered to be the correct depth is warranted. Malpositioning of ETTs occurs frequently, with unrecognized right main stem intubation occurring in approximately 4% of chest radiographs.^49,69,84 The generally accepted depth of insertion of the ETT is between 2 and 7 cm above the carina, optimally between 4 and 7 cm above the carina with the head and neck in a neutral position.^{49,77,85–87} It is important to realize this, because flexion-extension movements of the neck can displace the ETT upward or downward with resultant extubation or main stem intubation, respectively. Typically the right main stem bronchus is entered, given its straighter trajectory in relation to the trachea. If endobronchial intubation remains undetected, an inadvertent hyperinflation of the ipsilateral lung can occur with subsequent pneumothorax and concomitant atelectasis of the hypoventilated contralateral lung. Indeed, it has been reported that up to 15% of chest radiographs reveal malpositioned ETTs in intubated patients.^84,88,89 This is more frequently seen after difficult airway management.

In the operating room, chest radiographs are not used to confirm proper position; rather, indirect clinical assessment methods are used (i.e., auscultation of bilateral breath sounds, visualization of equal chest expansion, and direct visualization of the ETT tip placed just below the vocal cords). The ETT is also manufactured with distance measurements to aid with the depth of insertion. In orally intubated patients, a depth of 23 cm at the teeth or corner of the mouth has been advocated for men and 21 to 22 cm for women.^90,91 In nasotracheal intubations, a depth of 26 cm at the nares in women and 28 cm in men should be sufficient for proper tracheal position.⁹² Other methods used include direct visualization of the ETT tip in reference to the carina with a fiberoptic scope or catheter,⁶⁹ transtracheal illumination, and ballottement of the ETT cuff in the suprasternal notch.^93–96

3 Cuff Pressure Monitoring

Probably the most often overlooked parameter in daily airway care is cuff pressure.^97,98 Almost universally, this measurement is neglected in operating room intubations. However, it is well documented that excessive forces applied to the tracheal mucosa can cause necrosis and ulceration.^9,99,100 Cuff pressures of 30 cm H₂O for 4 hours have been shown to damage ciliary motility for at least 3 days.^100–102 In addition, animal studies have revealed diminished circulation in the tracheal mucosa with a pressure of just 20 cm H₂O, exaggerated greatly in the presence of hypotension.¹⁰³

Normal occlusive pressures should be between 20 and 30 cm H₂O to avoid complications while maintaining an adequate seal in the tracheal lumen circumferentially around the cuff to prevent microaspiration and ultimately VAP.¹⁰⁰ Depending on the type of cuff used, the same pressure range seems to be effective at accomplishing this task both in vitro and during in vivo animal studies. For example, standardized HVLP cuffs have been demonstrated to be ineffective at preventing microaspiration with pressures as high as 60 cm H₂O,⁷ whereas polyurethane tubes seem to be effective down to 15 cm H₂O.^7,10,104

As was previously discussed, ETTs are not without risks. However, it appears that most of the morbidity is related to either inappropriate inflation of an ETT cuff or a defective ETT cuff.^98–100 An often dreaded scenario that leads to increased morbidity is frequent ETT exchanges for suspected cuff leaks. Trended values for cuff pressure could help to alleviate some of these unnecessary procedures. Most importantly, it has been demonstrated that manual palpation of the cuff or instillation of a standard volume of air often underestimates the actual occlusive pressure delivered, leading to unrecognized complications.^97,98,100 Therefore, it is recommended that frequent examination of the cuff pressure be documented and trended using manometry.

Reusable aneroid manometers can be onerous to calibrate and are often difficult to locate; in addition, they pose a recurring risk of cross-contamination for each patient. The manometers currently in use in most ICUs provide only a single data point at the time of collection. A commercially available disposable, precalibrated device that constantly measures airway cuff pressures is available. The PressureEasy device (Smiths Medical, St. Paul, MN), among others, attaches to the pilot balloon and exhibits a mark in a fixed window when the measured cuff pressure is in the optimal range of 20 and 30 cm H₂O (Fig. 47-12).^97–100

Figure 47-12 Posey Cufflator aneroid manometer (left) and the PressureEasy Pressure Controller Device (right) for monitoring endotracheal tube cuff pressure.

(Cufflator courtesy Posey Company, Arcadia, CA; PressureEasy courtesy Smiths Medical, Dublin, OH.)

4 Evaluation of an Audible Cuff Leak

Although ETT cuff leaks pertain most often to the ICU or postanesthesia care unit (PACU) setting and longer-duration intubations, short-term tracheal intubation in the operating room may also fall prey to an apparent leak. The most relevant question is, When is a cuff leak really a cuff leak? The audible leak implies that air is escaping from the presumably closed ETT system. The leak may be caused by a defective ETT cuff that has failed, ripped, or is microperforated (in which case the pilot balloon deflates spontaneously). Equally possible is a defective pilot balloon–line assembly. The valve on the pilot balloon may be faulty and incompetent, the balloon may have a perforation, the line may be cracked or broken or may become disjointed at the tube end or the valve end. Moreover, the intermittent or continuous audible leak may represent an ETT cuff that fails to seal the airway due to malpositioning, deranged shape, or laxity and deformation of the tracheal wall (e.g., tracheomalacia, tracheitis, tracheal erosion). The ETT cuff (intact pilot balloon) may be subglottic, between the vocal cords, or supraglottic, having been displaced during patient movement, transport, repositioning, “tonguing” (dislodging the ETT by moving it with the tongue) of the ETT, excessive coughing, excessive tension on the ETT by the ventilator circuit, or, commonly, positioning for radiography. Once the ETT is partially displaced upward, an audible leak may prompt further ETT cuff insufflation, leading to further displacement. Head and neck movement by the patient may be all that is required to further displace the ETT into the hypopharyngeal region. This must be diagnosed before disaster strikes.

The various sources of a suspected cuff leak require investigation because each necessitates a different solution. Any one solution, incorrectly applied, may lead to morbidity or mortality. For example, a cuff leak resulting from a herniated cuff above the vocal cords may prompt the team to order a chest radiograph. Further displacement may take place during lifting and repositioning of the patient for the examination. Conversely, if an ETT is malpositioned in the hypopharynx (intact pilot balloon) but is assumed to be a properly positioned ETT with a cuff perforation, an exchange catheter passed via the ETT (presumably into the trachea) may exit the supraglottic ETT and enter the esophagus, leading to airway compromise. Table 47-1 highlights the possible causes and potential solutions, with relevant risk assessments for an apparent cuff leak evaluation.

TABLE 47-1 Causes and Solutions for Apparent ETT Cuff Leaks

ETT, Endotracheal tube.

5 Documentation of Placement

Clinicians who care for patients who are intubated for long periods in the ICU may find it onerous to obtain pertinent airway management details. This can be especially detrimental to future care providers who are faced with a patient with a known or suspected difficult airway. This situation could result for a number of reasons: lack of relevance (routine intubation before the patient’s surgery), lack of continuity (the intubator is no longer involved in the patient’s care), or an incomplete or total lack of documentation.

As an ICU course progresses, the details surrounding the original ETT placement may prove less relevant because the patient’s clinical status and airway are dynamic, not static. A previously easy airway may remain so, but difficulty often increases as edema, trauma, secretion management, and patient status decline to confound an airway intervention. Anatomic abnormalities may be hidden or exaggerated by excessive fluid administration or a capillary leakage phenomenon in the critically ill patient, and examination of the airway may become impossible. Appreciation of the airway adjuncts that have been attempted is imperative for the incoming airway team. Immediate availability of pertinent historical airway management details may prove helpful in delivering better care. Documentation of airway interventions and procedures on a specific sheet (Fig. 47-13) may provide the incoming airway team perspective on what to expect in a single concise location.

Figure 47-13 Example of a detailed airway record for emergency intubations.

1 Taping

The classically described methods are a “barber’s pole” technique for operating room intubations, a simple split tape technique (Fig. 47-14), and a more secure “four-point” technique for intubations anticipated to last for 24 hours or longer. In each of these methods, tape is used to anchor the ETT to the face. Moisture, in the form of sweat, secretions, or vomitus, can jeopardize the integrity of the bond between adhesive and skin, putting the security of the ETT at risk.¹⁰⁵ Additionally, patient comfort is an issue when tape is used for this purpose. Skin breakdown due to allergic reactions, pressure necrosis, or repetitive trauma has been documented as a potential problem from the use of this method. The four-point method is more secure than the barber’s pole technique because the tape encircles the patient’s head and is not as susceptible to moisture because it is anchored to itself as well as to the patient’s skin.

Figure 47-14 The split-tape method of taping the endotracheal tube.

2 Commercially Available Devices

Although several options are available, a proprietary device has been developed to help secure the ETT and provide increased patient comfort while facilitating airway care. This device, the AnchorFast (Hollister Inc., Libertyville, IL) (Fig. 47-15), incorporates an ergonomically designed frame to minimize well-known pressure points, a latex-free adhesive on a pad, and a padded Velcro-style retaining strap that encircles the head. Preliminary studies comparing this device against classic adhesive tapes showed reduced skin breakdown, fewer lip ulcers, and improved patient comfort.^106,112

Figure 47-15 The AnchorFast system for endotracheal tube stabilization.

(Courtesy of Hollister Inc., Libertyville, IL.)

Another commercial device used to secure the ETT has been postulated; it mimics the nasal bridling technique used for nasogastric tubes. This product is still in development.

3 Stapling for Facial Burns

The overall incidence of burn patients in most practices is very small, and this creates an unfamiliarity with their care, particularly as it relates to airway management. The focus of this section is to discuss the unique situation presented by the facial burn. Aside from the obvious difficulties of tube placement initially, replacement of an ETT after a burn resuscitation is far more challenging due to a multitude of unique injuries. The two major problems with securing an ETT for the patient with a facial burn are the increased (and increasing) edema due to ongoing inflammatory processes and continued resuscitation, which makes the face ever expanding, and the actual burned skin, which is constantly weeping and often débrided or sloughing. It should be obvious that adhesive devices, both simple tape and proprietary devices, are ineffective in this situation. A well-documented and accepted method in these patients is to secure the ETT with tape and anchor it to the skin by stapling the tape to the burned areas. This is surprisingly well tolerated, but more importantly it is very reliable to maintain the airway and is easy to care for.

One important airway management caveat should be understood regarding proper ETT position at the gum line or lips in all intubated patients: the ETT marking at these locations only assures the location of the proximal end; it does not guarantee the depth and location of the distal ETT tip. Although this problem pertains most often to the ventilated PACU or ICU patient, an ETT located at 25 cm at the gum line and seemingly secured by tape or a commercial device does not guarantee tracheal intubation (with or without a cuff leak). Typically, a continuous or intermittent apparent cuff leak leads to further insufflation of the pilot balloon to fix the leak. An intact (inflated) pilot balloon, in this clinical situation, should arouse suspicion that the distal tip is abnormally located outside the glottis. The potential for an airway catastrophe is extreme, especially in the patient with a difficult airway, compounded by significant mechanical ventilatory requirements. Proper assessment of the ETT position, preferably with flexible bronchoscopy for diagnostic and therapeutic maneuvers, is indicated.

D Rapid Response Cart for Airway Emergencies

Areas in which care for intubated patients is provided need to have a dedicated set of supplies to establish emergency airways in the event of primary respiratory failure or cardiac arrest to reestablish lost, previously secured airways. The responding airway team must be knowledgeable and competent in advanced management techniques and provided with immediate access to such equipment. Infrequent or casual airway managers should ask for assistance early in the management process or even immediately, before starting. The American Society of Anesthesiologists difficult airway algorithm (Fig. 47-16) should be close at hand to guide less experienced individuals who encounter problems.¹¹³ Supplies on the cart may differ based on personal preference and facility purchase, but there are some items that must be present to help save a life.

Figure 47-16 American Society of Anesthesiologists difficult airway algorithm. LMA, Laryngeal mask airway.

(Courtesy of American Society of Anesthesiologists, Park Ridge, IL.)

Laryngoscopy, ETT exchange, pulmonary toilet, and a “cannot intubate, cannot ventilate” (CICV) scenario must all be covered in the equipment selection. Laryngoscopy includes both conventional (direct) and video laryngoscopy; it is used to assist the team with replacing the ETT after an inadvertent extubation, augmenting the exchange of a damaged ETT over an airway exchange catheter, improving the ability to assess ETT location within the airway, and interrogating the physiologic integrity of an airway slated for extubation.¹¹⁴

An airway exchange catheter, coupled with video laryngoscopy, greatly reduces the complication rates for necessary airway exchanges in ICU patients, thereby earning its place in an airway response cart within the ICU.¹¹⁴ A fiberoptic bronchoscope should be available for confirmation purposes, for awake intubation procedures, and for deeper pulmonary toilet needs to improve ventilation and oxygenation.¹¹⁵ Supraglottic airway devices should be available for situations in which mask ventilation is difficult or as a conduit to facilitate the placement of an endotracheal airway.¹¹⁶ Lastly, equipment for the placement of a surgical airway must be provided. Despite all of the options available, a scalpel may be the only device capable of establishing the airway. In cases of a known or suspected difficult airway, it is helpful to immediately contact someone with the ability to place a surgical airway should other conventional or advanced noninvasive means fail.

Box 47-2 delineates the contents of a proposed difficult airway cart, which should be readily available in case of any airway catastrophe.

1 Mucolytic Agents

Agents used to decrease the viscosity of tracheobronchial secretions and assist with their reduction and clearance have been used for decades. The primary agent in use is N-acetylcysteine (NAC, Mucomyst). NAC is a sulfhydryl-containing compound; therefore, it is classified as a thiol. It has extensive first-pass metabolism in the gastrointestinal tract and liver when administered orally and is almost completely absorbed; only minimal amounts are excreted in the feces. The plasma half-life is approximately 2 hours, with virtually no detectable NAC at approximately 12 hours.¹⁴⁸

Most of NAC’s biochemical effects appear to be related to its sulfhydryl group, which reduces the production hydroxyl radicals.^148,149 This effect has provided many uses for NAC beyond that of a mucolytic agent, including hepatic protection in acetaminophen overdose and renal protection against contrast-induced nephropathy.^52,150 NAC’s effects on mucus viscosity result from its ability to disrupt the disulfide bridges and render them more liquid.^133,148 NAC is usually delivered by nebulizer in combination with a β₂-adrenergic agonist because it can induce bronchospasm.¹⁵¹ Clinically, its effects have been variable in patients with chronic bronchitis, for whom oral NAC is used to assist with exacerbations and symptomatic relief.^152–154 Direct instillation of NAC during bronchoscopy may assist in secretion removal.

Another important factor in mucus viscosity is DNA content. DNA contributes to secretion viscosity because it accumulates from the degradation of bacteria and neutrophils. An agent that is considered mostly a mucokinetic agent, recombinant deoxyribonuclease (DNase, Pulmozyme), has been used in nebulized form in patients with bronchiectasis caused by cystic fibrosis with good results; however, it is expensive, and its use beyond this population of patients is not indicated.^117,155,156

One interesting therapy used in the population of burn patients who have an associated inhalation injury is nebulized heparin. Heparin assists with decreasing and removing bronchial casts that form with inhalation injury. Heparin’s anticoagulant effects assist with removal of casts, and it may act as a free radical scavenger with anti-inflammatory effects. Although studies have not consistently shown a significant change in pulmonary function, cast formation and removal are favorably altered.^157,158

2 Chest Physiotherapy

Chest physiotherapy encompasses a variety of techniques that include position changes, percussion and vibration of the chest wall, and stimulation of a cough response. These are relatively dogmatic approaches that have historically provided poor results. They also tend to be burdensome to both the respiratory therapist and the patient. Newer, alternative techniques show promising results.

1 Pressure Support

Various modalities have been designed to overcome WOB_add imposed by the artificial airway and ventilator.¹⁵⁵ One is pressure support (PS), which is used as either an adjunct or as a mode of ventilation to help the spontaneously breathing patient overcome the WOB_add imposed by an artificial airway.^21,168,172 A preset, flow-triggered inspiratory pressure chosen by the clinician is added to the airway opening pressure when inspiration is triggered by the patient. Because it is flow cycled, the patient can control the duration and depth of inspiration, and the PS ceases when some preset gas flow has diminished, usually about 25% of the maximal peak flow achieved.¹⁷³ PS has been shown to decrease WOB_add even with normal lungs.^173,174 However, in patients with obstructive pulmonary disease and expiratory flow limitation, breath stacking, or auto-PEEP, flow may not decelerate quickly enough, and active exhalation may be necessary to terminate the PS, thereby creating additional WOB.¹⁷⁵ The amount of inspiratory pressure added is usually 4 to 15 cm H₂O. Currently, it is recommended that PS be applied for all spontaneously breathing, intubated patients to assist with overcoming the resistance of the ETT or tracheostomy tube.¹⁷⁶ Additional PS may be necessary if tidal volumes or respiratory rates, or both, are inadequate to support oxygenation. Most patients tolerate PS well, but decreased tolerance in patients susceptible to expiratory flow limitation must be appreciated and accounted for in any management strategy.

2 Continuous Positive Airway Pressure

Continuous positive airway pressure (CPAP) is applied at end-exhalation in spontaneously breathing patients. Much like PEEP, CPAP is designed to offset the degree of atelectasis that occurs inherently in the intubated, supine patient. CPAP ranging from 4 to 10 cm H₂O should be provided for all spontaneously breathing patients in an effort to compensate for the loss of expiratory lung volumes and further promote oxygenation. So-called physiologic PEEP, an amount thought to rectify the aforementioned atelectasis, is theoretical but is estimated to be equivalent to 4 cm H₂O in the normal lung. The reduction in WOB seen with CPAP has been appreciated primarily in the setting of expiratory airflow reductions; in such cases, CPAP offsets the auto-PEEP, thereby reducing the work required to generate the next inspiratory effort.¹⁷⁷ The type of flow-triggered mechanism and the location at which the flow differential is measured (typically at the tracheal end of the ETT) have been shown experimentally to decrease the inspiratory WOB as well.¹⁷⁸ CPAP is usually applied in combination with added PS.

3 Automatic Tube Compensation

As stated previously, the ETT imposes a substantial degree of resistance to inspiration. The modalities described thus far assist with decreasing some of the work needed to overcome this burden. Added PS and PS ventilation help compensate for the resistance primarily encountered during inhalation but not during exhalation, and they are not consistently provided because of the varying flow across the ETT during normal breathing.¹⁷⁹ Much resistance to exhalation is also produced by the presence of an ETT. Indeed, the internal diameter of the ETT greatly affects this phenomenon, as do other factors such as gas flow rates, gas density and viscosity, and luminal secretions adherent to the ETT wall. Automatic tube compensation (ATC) is a feature on some newer ventilators. It is designed to assist with the resistance imposed by the ETT or tracheostomy tube during both the inspiratory and expiratory phases of the respiratory cycle. By altering the PS delivered—raising it during inspiration and lowering it during expiration according to the pressure-flow characteristics of the ETT—ATC adjusts for the resistance and the pressure drop across the ETT during spontaneous breathing. A computer assists by calculating the pressure difference across the ETT (ΔP^ETT) based on ETT size, measuring gas flow and airway pressure, and selecting the resistive properties of the ETT.¹⁷⁹ Unlike PS, ATC cannot be used as a ventilatory mode; it is merely an adjunct component to mechanical ventilation.

One drawback to ATC is the inability to correct for the reductions in airway diameter that can occur with secretions or kinking. This limitation results in an inaccurate measurement of ΔP^ETT such that ATC undercompensates for the pressure difference across the airway. A high index of suspicion is necessary to monitor for this possibility. Clinically, ATC has been shown to decrease the WOB_add encountered with ETTs and tracheostomy tubes.²⁸ When these modalities were used to assist with weaning and extubation of patients in a T-piece trial, there was no difference in the workload encountered with ATC and T-piece alone, whereas adding PS to the T-piece trial at 7 cm H₂O unloaded this additional work.¹⁸⁰

1 Inhalation Drug Delivery

The presence of an ETT does not limit drug delivery to the lungs and may actually enhance it. Many clinicians take advantage of this route of administration. The two predominant methods used to deliver agents are metered-dose inhalers (MDIs) and nebulizers. The drugs delivered by these devices are most commonly bronchodilators, mucolytics, corticosteroids, and antibiotics. For pulmonary ailments, inhaled drugs achieve efficacy comparable to or exceeding that of systemically delivered drugs with a smaller dose.^181–183 Tracheal administration of some traditionally systemic drugs often requires much higher doses to ensure absorption.

Inhalation drug delivery has other advantages over systemic administration. Systemic side effects can be reduced, because systemic absorption is markedly decreased. Variable reports regarding penetration and distribution of an aerosol to the lower respiratory tract range from 0% to 42% with nebulizers and 0.3% to 98% with MDIs. However, when the delivery method was standardized, the amount delivered in either method was similar, about 15%.^184–186

Particle size also plays an important role in delivery. The larger the particle, the less likely it is to be delivered distally to the alveoli. Aerosol particles ranging between 1 and 5 µm are optimal for proper deposition.^{181,182,185,187} The density of the gas carrying the aerosol also influences the delivery in an inverse relationship. Improvement in delivery has been reported when a mixture of helium and oxygen was used in the ventilator circuits of both MDIs and nebulizers.^183,188

2 Inhaled Bronchodilators

Airway reactivity is a ubiquitous consequence of airway manipulation that hinders respiratory function and prolongs the duration of mechanical ventilation. Additional pathophysiologic processes attributed to persistent bronchospastic disease that serve to prolong mechanical ventilation include mucosal inflammation that persists and promotes further mucus production, airway hyperemia and resultant edema, and the consequent narrowing of small airways leading to an increase in closing volume. These processes adversely affect oxygenation as functional residual capacity is decreased and CO₂ elimination, as expiratory flow, is limited. At extremes of expiratory flow limitation, generous amounts of intrinsic PEEP (auto-PEEP) are generated; this can impede cardiac filling by reducing preload, and hypotension and cardiac arrest may result. The physical effects of auto-PEEP are not limited to the cardiovascular system. The obvious effects of alveolar overdistention include an increased physiologic dead space and the potential for barotrauma, especially when controlled positive-pressure mechanical ventilation is instituted. Pneumothorax, pneumomediastinum, and pneumoperitoneum may all occur as a result, as may patient-ventilator dysynchrony.

Many maneuvers are available to reduce the effects of bronchospasm (and higher airway pressures), including decreasing the respiratory rate, prolonging the expiratory time, decreasing the tidal volume, and increasing the inspiratory flow rate. Pharmacologically, the use of β-adrenergic agonists, specifically β₂-agonists such as albuterol, is the mainstay therapy. β₂-receptors on bronchial smooth muscle promote relaxation and dilation of the airway diameter when stimulated. Systemic methylxanthines such as theophylline do not add much benefit in the acute stage of treating bronchospasm or reactive airways. Their narrow therapeutic window and vast side effect profile increase potential toxicity.

β₂-agonists also have a beneficial effect on respiratory cilia in that they cause an increase in ciliary beat frequency.¹⁹⁴ This phenomenon is mediated by β-adrenergic receptors and can be attenuated with nonselective beta-blocking agents. An increase in the frequency of ciliary beating promotes mucus clearance over the respiratory epithelium. Other effects include increased water secretion onto the airway surface, which facilitates mucus clearance.¹⁹⁵ Indeed, the beneficial effects of β-agonists on bronchial reactivity and mucociliary clearance are evident. However, there are data suggesting a more robust effect in healthier airways than in chronically diseased airways such as those seen in patients with chronic bronchitis, possibly due to downregulation and chronic attenuation.¹⁹⁶ Newer formulations of inhaled β-agonists such as levalbuterol may have reduced side effect profiles and possibly improved outcomes.

3 Anticholinergics

Although inhaled β-agonists are pivotal in the reduction of airway reactivity, the use of inhaled anticholinergics such as ipratropium bromide or the newer tiotropium bromide needs to be emphasized, given their obvious synergistic effect with β-agonists. It is well appreciated that many of the mechanisms of airway reactivity and inflammation associated with bronchospastic disease are cholinergically mediated. In patients with chronic obstructive pulmonary disease, the use of these agents alone or in combination with β-agonists is the foundation for rescue therapy and a mainstay in chronic management.¹⁸³

4 Corticosteroids

Inhaled glucocorticoid therapy has become a mainstay of treatment in various obstructive respiratory ailments, including chronic obstructive pulmonary disease and asthma. This class of medicines unquestionably has disease-specific effects at the target organ. Equally interesting is the fact that administration in an aerosol preparation magnifies their effects while markedly reducing their side effect profile, leading to a lower risk-benefit value. Targeted efficacy with minimal adverse effects helps to quantify an appropriate risk-benefit value.^197,198 High lung deposition or targeting, high receptor binding, longer pulmonary retention, and high lipid conjugation are among the pharmacokinetic parameters that lead to improved efficacy of these compounds and should be considered. A low or negligible oral bioavailability, smaller particle size leading to a relatively inactive drug at the oropharynx, higher plasma protein binding, increased metabolism rates, higher clearances, and lower systemic concentrations are associated with lower risks for adverse effects.^197–199

For individuals who require long-term care with inhaled glucocorticoids during ventilator dependency, therapy should be continued to minimize the underlying disease process and thereby decrease the number of new variables, including adrenal insufficiency, in the treatment equation with inhaled or intravenous formulations.²⁰⁰ Despite all of these perceived benefits, inhaled glucocorticoids do not seem to reduce mortality.²⁰¹ Acute exacerbations tend to be treated with intravenous or oral preparations due to the higher doses required.

5 Inhaled Antibiotics

Inhaled antibiotics have been used for decades, falling in and out of favor over the years. They are used primarily for treatment and suppression of chronic airway bacterial colonization. Their theoretical advantages are improved drug delivery and higher concentrations at the site of infection, leading to improved efficacy and better bacterial eradication compared with systemic administration.^90,202–204 The primary concern with this therapy is development of bacterial resistance.

Results differ on efficacy. Inhaled antibiotics, mainly aminoglycosides, have been used extensively in cystic fibrosis patients with good results.^90,202–205 Palmer and colleagues reported a marked reduction in the volume of airway secretions and a decrease in the laboratory markers of inflammation in a prospective study of mechanically ventilated patients with chronic respiratory failure.^90,205 However, their study lacked power and was not randomized.

Other studies have failed to show similar benefits but rather have demonstrated poor, unpredictable drug delivery.²⁰⁶ Unequal ventilation, atelectasis, lobar collapse, and consolidation impair even drug distribution. Bronchospasm with chest tightness has also been reported.¹³⁴ Use of inhaled antibiotics should be limited to selected patients, such as those with cystic fibrosis. Routine use to assist with secretion reduction and clearance in the mechanically ventilated patient is not recommended.