Manejo de La via Aerea Chest 2007

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DOI 10.1378/chest.06-21202007;131;608-620Chest

J. Matthias Walz, Maksim Zayaruzny and Stephen O. Heard

*Airway Management in Critical Illness

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Airway Management in Critical Illness*

J. Matthias Walz, MD, FCCP; Maksim Zayaruzny, MD; andStephen O. Heard, MD, FCCP

Airway management in the ICU can be complicated due to many factors including the limitedphysiologic reserve of the patient. As a consequence, the likelihood of difficult mask ventilationand intubation increases. The incidence of failed airways and of cardiac arrest related to airwayinstrumentation in the ICU is much higher than that of elective intubations performed in theoperating room. A thorough working knowledge of the devices available for the management ofthe difficult airway and recommended rescue strategies is paramount in avoiding bad patientoutcomes. In this review, we will provide a conceptual framework for airway assessment, with anemphasis on assessment of the patient with limited cervical spine movement or injury and of

morbidly obese patients. Furthermore, we will review the devices that are available for airwaymanagement in the ICU, and discuss controversies surrounding interventions like cricoidpressure and the use of muscle relaxants in the critically ill patient. Finally, strategies for the safeextubation of patients with known difficult airways will be provided.

(CHEST 2007; 131:608 620)

Key words: airway management; critical care; intubation

Abbreviations: AEC airway exchange catheter; ASA American Society of Anesthesiologists; DAA difficultairway algorithm; DI difficult intubation; ETT endotracheal tube; FOI fiberoptic intubation; LMA laryngealmask airway; NIPPV noninvasive positive-pressure ventilation; PDT percutaneous dilatational tracheostomy;RSI rapid sequence intubation

Expertise in airway management is an importantskill for any health-care provider who is caring

for critically ill patients. Due to advances in trainingand technology, elective airway management withinthe confines of the operating room is associated withvery low rates of complications.1 These observationsare in stark contrast to emergent airway managementin the ICU. Complication rates in the ICU environ-ment are much higher due to the limited physiologicreserve and comorbidities of the patient, as well as

the inability, in the majority of cases, to perform athorough evaluation of the patients anatomy prior toairway instrumentation. Furthermore, some of theinduction agents that are suitable for airway manage-ment in the elective setting may be contraindicatedin critically ill patients, further limiting the optionsfor airway instrumentation.

In a systematic study of complications associatedwith airway management in the ICU, Schwartz andcolleagues2 reported major complications in a signif-

icant number of patients. Among the problemsencountered were difficult intubations (DIs) [8%],esophageal intubations (8%), and pulmonary aspira-tion (4%), and an associated mortality rate of 3%.There was a significant correlation between thepresence of hypotension at the time of intubationand cardiac arrest in this study.2 Kollef et al3 re-

viewed retrospectively over a 12-month period 278patients requiring endotracheal intubation in anacute care military hospital. They found that almost10% of patients (22 patients) had at least onesignificant endotracheal tube (ETT) misplacement,

*From the Department of Anesthesiology, Division of CriticalCare Medicine UMass Memorial Medical Center, Worcester,MA.The authors have reported to the ACCP that no significantconflicts of interest exist with any companies/organizations whoseproducts or services may be discussed in this article.Manuscript received August 24, 2006; revision accepted Novem-ber 1, 2006.Reproduction of this article is prohibited without written permissionfrom the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).Correspondence to: J. Matthias Walz, MD, FCCP, Department of

Anesthesiology, UMass Memorial Medical Center, 55 Lake AveNorth, Worcester MA 01655; e-mail: [email protected]: 10.1378/chest.06-2120

CHEST Postgraduate Education CornerCONTEMPORARY REVIEWS IN CRITICALCAREMEDICINE

608 Postgraduate Education Corner

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and 23% of these individuals experienced seriouscomplications.3 A recent prospective, observationalmulticenter study4 performed in French ICUs foundat least one severe complication in 28% of allintubations, with an overall rate of cardiac arrestrelated to endotracheal intubation in the ICU of 2%.The presence of acute respiratory failure and thepresence of shock as the indication for endotracheal

intubation were independent risk factors for compli-cations, whereas supervision by a senior physicianappeared to have a protective effect.4 In a study5 onthe frequency and outcomes of unplanned endotra-cheal extubations in a university trauma-surgicalICU, difficulty with reintubation (multiple or pro-longed attempts) or need for a fiberoptic broncho-scope was a common occurrence (20%). The authorsconcluded that highly skilled airway management isnecessary to avoid adverse outcomes related to rein-tubation.5

The implementation of training programs for ICU

staff, immediate access to advanced airway devices,and knowledge and incorporation of the AmericanSociety of Anesthesiologists (ASA) difficult airwayalgorithm (DAA) [Fig 1] may decrease the incidenceof serious complications related to airway instrumen-tation in the ICU. In a retrospective review of 3,035critically ill patients undergoing emergency airwaymanagement, Mort6 analyzed two time periods, 1990to 1995 and 1995 to 2002, after the implementationof a protocol requiring the availability of advancedairway equipment at the bedside. Cardiac arrestwithin 5 min of intubation occurred in 2% of the

patients overall. However, the rate was reduced by50% between the first and the second time periodanalyzed (1990 to 1995, 2.8%; 1995 to 2002, 1.4%).6

In this review, we assume that the reader has aworking knowledge of airway anatomy and of thetechnique for routine endotracheal intubation. Ac-cordingly, we consider aspects of the use of medica-tions, strategies for airway assessment prior to intu-bation, and some technical approaches to airwaymanagement in critically ill patients. Controversiessurrounding airway management such as rapid se-quence intubation (RSI), the merit of cricoid pres-

sure and the sniffing position, as well as the risksassociated with the use of muscle relaxants will bediscussed. Furthermore, we will provide strategiesfor the safe extubation of the patient with a knowndifficult airway.

Airway Assessment

Assessing a patients airway prior to performing apotentially difficult endotracheal intubation is chal-lenging in the best of circumstances; in the critically

ill patient with severe respiratory distress or failure,it may be virtually impossible. There is some contro-versy as to what assessment tool has the best predic-tive value for DI; however, a focused and briefexamination of the patients airway may substantiallyinfluence the strategy for airway management andthe success of the procedure. An initial step inassessment is to determine the need for invasive vs

noninvasive ventilatory support. If the patient needsinvasive ventilatory support, the individual shouldquickly be assessed for (1) the risk for difficult maskventilation and (2) the risk for DI. Independent riskfactors for difficult mask ventilation in the electivesetting include age of 55 years, body mass index of26 kg/m2, lack of teeth, male gender, Mallampaticlass 4 airway, the presence of a beard, and a historyof snoring.7,8 Whether these factors can be extrapo-lated to critically ill patients is unknown; however, itseems prudent to include them into the analysis inorder to decrease the likelihood of a cannot intu-

bate, cannot ventilate scenario. Several clinical in-dicators for DI have been validated (Table 1). Whilethe positive predictive values of these tests alone orin combination are not particularly high, a straight-forward intubation can be anticipated if the testresults are negative.9 For a recent review on thecommon clinical predictors of DI see the study byReynolds and Heffner.10 Since only about 30% ofairways in the emergency setting can be evaluated inthis fashion, additional evaluation methods havebeen devised. Murphy and Walls11 have introducedthe LEMON (ie, Look, [e]Mallampati class, Ob-

struction, and Neck mobility) airway assessmentmethod to stratify the risk of DI in the emergencydepartment. Furthermore, Reed et al12were able todemonstrate that patients with large incisors, a re-duced mouth opening, and a reduced thyroid-to-floor-of-mouth distance are more likely to have apoor airway grade during laryngoscopy.

Preparation for Endotracheal Intubation

Being prepared for unforeseen complications dur-

ing endotracheal intubation is of prime importancewhen instrumenting airway of a critically ill patient.Furthermore, conditions for intubation should be asclose to ideal as possible in a busy ICU environment,and should include adequate personnel, optimalpatient positioning and lighting, and the necessaryequipment for endotracheal intubation. A supply of100% oxygen, a well-fitting mask with attachedbag-valve device (which should be checked for valvecompetency prior to use), suctioning equipment, aMagill forceps, and oral and nasal airways should beimmediately available. The bed should be positioned

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at the proper height with the wheels locked, and alaryngoscope with blades of various sizes (straightand curved) should be available. The laryngoscopebatteries and light should be checked on a routinebasis.

Traditional teaching recommends placing the pa-tient in the sniffing position, in which the neck is

flexed and the head is slightly extended about theatlantooccipital joint in order to align the oral,pharyngeal, and laryngeal axes.13 An MRI study14 hascalled this concept into question, as the alignment ofthe three axes could not be achieved in any of thethree positions tested (ie, neutral, simple head ex-tension, and the sniffing position). In a randomized

Figure 1. The ASA DAA: practice guidelines for the management of the difficult airway: an updatedreport by the ASA Task Force on Management of the Difficult Airway. Reprinted with permission fromChristie et al.5




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study15 conducted in general surgery patients, simplehead extension was as effective as the sniffing posi-tion in facilitating tracheal intubation. Nonetheless,the sniffing position appears to provide an advantagein obese patients and in patients who have limitedhead extension. The utility of the sniffing position forintubations outside of the operating room is un-known. Preoxygenation prior to airway instrumenta-tion is important and is usually facilitated with theadministration of oxygen via a nonrebreathing facemask and bag-valve mask device. It is important to

note, however, that patients with respiratory failuredue to cardiopulmonary disease may not have anadequate response to conventional preoxygenation.Mort16 was able to demonstrate that only 50% ofpatients in this category have an increase in Pao2 of 5% above baseline values with conventionalpreoxygenation of 4 min duration. To address thisproblem, Baillard and coworkers17 conducted a pro-spective, randomized study in a cohort of medical/surgical ICU patients comparing preoxygenationprior to endotracheal intubation with the use ofnoninvasive positive-pressure ventilation (NIPPV) to

a bag-valve mask device for 3 min duration. Theapplication of NIPPV ensured better pulse oximetricsaturation and Pao2 values during tracheal intuba-tion and up to 5 min into the postintubation periodcompared to the conventional preoxygenation meth-od.17 For a complete checklist of the supplies neededfor endotracheal intubation, see Table 2.

After successful endotracheal intubation, it is ofvital importance to confirm proper tube positioning.Methods to ascertain the position of the tube withinthe trachea include bilateral auscultation of the chestand measurement of end-tidal carbon dioxide by

standard capnography if available, or by means ofcolorimetric chemical detection of end-tidal carbondioxide (eg, Easy Cap II; Nellcor, Inc; Pleasanton,CA). The colorimetric detector is attached to theproximal end of the ETT and changes color onexposure to carbon dioxide. An additional methodfor detecting esophageal intubation uses a bulb thatattaches to the proximal end of the ETT.18 Whensqueezed, the bulb will reexpand if it is in thetrachea, but will remain collapsed with esophagealplacement of the ETT. None of these methods is

absolutely reliable; fiberoptic bronchoscopy is theonly way to document ETT placement with absolutecertainty. Given the potentially serious conse-

Table 1Components of the Preoperative Airway Physical Examination*

Airway Examination Component Nonreassuring Findings

Length of upper incisors Relatively longRelation of maxillary and mandibular incisors during normal jaw

closureProminent overbite (ie, maxillary incisors anterior to mandibular

incisors)Relation of maxillary and mandibular incisors during voluntary

protrusionPatient cannot bring mandibular incisors anterior to (in front of)

maxillary incisorsInterincisor distance 3 cm

Visibility of uvula Not visible when tongue is protruded with patient in sitting position(eg, Mallampati class II)

Shape of palate Highly arched or very narrow Compliance of mandibular space Stiff, indurated, occupied by mass, or nonresilientThyromental distance Less than three ordinary finger breadthsLength of neck ShortThickness of neck ThickRange of motion of head and neck Patient cannot touch tip of chin to chest or cannot extend neck

*This table displays some findings of the airway physical examination that may suggest the presence of a difficult intubation. The decision toexamine some or all of the airway components shown in this table depends on the clinical context and the judgment of the practitioner. The tableis not intended as a mandatory or exhaustive list of the components of an airway examination. The order of presentation in this table follows theline of sight that occurs during conventional oral laryngoscopy. Reprinted with permission from Christie et al.5

Table 2Equipment Needed for Intubation*

Supply of 100% oxygenFace maskBag valve device with PEEP valveEnd-tidal CO2 detectorSuction equipmentSuction catheters

Large-bore tonsil suction apparatus (Yankauer)StyletMagill forcepsOral airwaysNasal airwaysLaryngoscope handle and blades (curved, straight; various sizes)Endotracheal tubes (various sizes)Tongue depressorsSyringe for cuff inflationHeadrestSupplies for vasoconstriction and local anesthesiaTapeTincture of benzoin

*PEEP positive end-expiratory pressure.




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quences of esophageal intubation, auscultation of thechest should always be combined with one additionaltest. Furthermore, a postintubation chest radiographshould always be obtained. Some of the most com-mon complications of endotracheal intubation arelisted in Table 3; for a comprehensive review on thesubject see Hagberg et al.19

The following two patient populations deserve

special mention: the morbidly obese patient; and thecritically ill patient with known or suspected cervicalspine injuries. In a recent review20 of 4,000 patientsin the Australian Incident Monitoring Study, obesityand limited neck mobility were among the mostcommon anatomic factors contributing to DI and/ora failed airway.

Morbid Obesity

Morbidly obese patients are more prone to hypox-emia than individuals of normal weight due to

reductions in expiratory reserve volume, FVC, FEV1,functional residual capacity, and maximum voluntaryventilation.21 Due to body habitus, laryngeal expo-sure may be difficult. In addition, since repositioninga morbidly obese patient may be impossible if diffi-culties during laryngoscopy and/or intubation areencountered, careful patient positioning and choiceof airway management is vitally important. Collinsand coworkers22 compared the difference betweenthe sniff and ramped positions in morbidly obesepatients undergoing elective bariatric surgery withrespect to the quality of the laryngeal view obtained.

They were able to demonstrate significantly betterlaryngeal views when a ramped position wasachieved by arranging blankets underneath the pa-tients body and head until horizontal alignment wasachieved between the external auditory meatus andthe sternal notch.22 It is conceivable that this would

also improve laryngeal exposure in morbidly obesepatients in the ICU setting. If there is concern aboutthe adequacy of the mask airway to maintain oxygen-ation, use of an awake fiberoptic intubation (FOI)technique should always be considered.

C-Spine Injuries and Immobility

Managing the airway of a patient with limited neckmobility or cervical spine injury on an emergent basisrequires careful planning and significant experiencein order to avoid morbidity and mortality. Retrospec-tive studies2327 have suggested that neurologic de-terioration in patients with cervical spine injuries isuncommon after airway management, even in high-risk patients undergoing urgent endotracheal intuba-tion. These studies2327 are limited, however, by theirsmall sample size. While not all cervical spine inju-ries result in clinical instability, the results of initial

radiographic studies in critically ill patients are oftenunknown at the time the airway has to be managed,and cervical spine precautions during airway instru-mentation should be maintained. The reader isreferred to a comprehensive review on airway man-agement after cervical spine injury.28 Manual in-lineimmobilization during endotracheal intubation ap-pears to be safe and effective for the prevention ofmorbidity that is related to airway instrumentation inpatients with cervical spine injuries. Removing theanterior portion of the cervical collar while maintain-ing manual in-line immobilization is associated with

less spinal movement than cervical collar immobili-zation during laryngoscopy and therefore should beroutinely performed.29,30 Furthermore, there is evi-dence suggesting that cricoid pressure does notresult in deleterious cervical movement in a patientwith an injured upper cervical spine.31While there isno evidence in the literature to demonstrate thesuperiority of one mode of endotracheal intubationover the other, the authors of this review believe thatawake FOI techniques should be strongly consideredin the setting of limited neck mobility and cervicalspine injuries. For patients with cervical stabilization

in a halo device, the ability to perform a surgicalairway, should conventional attempts for airwaymanagement fail, may be lifesaving. Conditionsother than trauma that are associated with a de-creased range of motion include any cause of degen-erative disk disease (eg, rheumatoid arthritis, osteo-arthritis, and ankylosing spondylitis) and age 70years. Caution should also be exercised in patientswith previous cervical spine instrumentation thatmay result in unanticipated difficult airway, necessi-tating fiberoptic-guided endotracheal intubation32 orintubation through a laryngeal mask airway (LMA).

Table 3Selected Complications of EndotrachealIntubation

Complications Description

Traumatic complications Corneal abrasionDental damagePerforation or laceration of pharynx,

larynx, trachea, or esophagusVocal cord injuryDislocation of an arytenoid cartilage

Hemodynamic and othercomplications

Mainstem bronchus intubationAspirationHypotensionArrhythmiasHypoxiaHypercarbiaLaryngeal spasmBronchospasm




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RSI and Muscle Relaxants

Since the majority of ICU patients requiring en-dotracheal intubation should be considered to have afull stomach, securing the airway with a rapid-sequence intubation (originally termed rapid se-quence induction in the operating room setting)therefore seems logical. There are, however, several

caveats to consider before embarking on an airwaymanagement strategy that may leave very few op-tions short of surgical airway intervention should theintensivist unexpectedly encounter a cannot intu-bate, cannot ventilate scenario. Furthermore, thereare several contraindications to the use of succinyl-choline in critically ill patients, thus eliminating thefastest and most reliable muscle relaxant that is usedto facilitate rapid sequence endotracheal intubation(see the next section).33 Prior to administering drugsto facilitate airway management in the ICU, a deci-sion should be made about whether spontaneous

breathing should be preserved or ablated duringendotracheal intubation.

Controversies in RSI

The classic teaching of RSI includes the applica-tion of cricoid pressure to avoid the regurgitation ofgastric contents into the lung. Initially described bySellick34 in 1961, this concept has been questionedby an MRI study35 of awake volunteers. Smith et al35

were able to demonstrate that the esophagus waslateral to the larynx in 50% of the subjects.Moreover, cricoid pressure increased the incidence

of an unoccluded esophagus (by 50% and causedairway compression of 1 mm in 81% of thesubjects studied. There are, however, cadaver stud-ies demonstrating the efficacy of cricoid pressure36

and clinical studies showing that gastric insufflationwith air during mask ventilation is reduced whencricoid pressure is applied.37 While cricoid pressuremay or may not decrease the risk of aspiration, thereis evidence that it may worsen the quality of laryn-geal exposure.38,39 In a randomized interventionstudy on human cadavers involving emergency med-icine physicians, a total of 1,530 sets of comparative

laryngoscopies were performed by 104 participants.In this study, bimanual laryngoscopy (external laryn-geal manipulation by the endoscopist with the freehand) improved the view compared to the applica-tion of cricoid pressure, application of back, upward,and right pressure on the thyroid cartilage (alsoreferred to as BURP), or no manipulation. Cricoidpressure and back, upward, and right pressure on thethyroid cartilage frequently worsened the view onlaryngoscopy.40 In a critical appraisal of the availableliterature, including 241 articles on the topic ofcricoid pressure, Butler and Sen41 concluded that

there is little evidence to support the widely heldbelief that the application of cricoid pressure reducesthe incidence of aspiration during RSI. As the appli-cation of cricoid pressure may have adverse effects, acareful analysis of the risks and benefits should beperformed on an individual basis until more system-atic studies are performed.

Choices of Drugs

Emergent airway management in the ICU is fre-quently complicated by the patients limited physio-logic reserve, which will often manifest as hypoten-sion immediately after tracheal intubation. The exactincidence of morbidity and mortality related toairway management facilitated by the use of IVinduction agents in the ICU is unknown; however, itis likely to be underreported. Several comprehensivereviews42 on pharmacologic agents used for airwaymanagement in the ICU have been published; wewill therefore provide a brief overview of commonlyused agents and discuss controversies surroundingtheir use.

Propofol

Propofol is a popular hypnotic agent for severalreasons. It is associated with pleasant emergence andlittle hangover, is readily titratable, and has morerapid onset and offset kinetics than midazolam. Inpatients with cardiac comorbidities and limited phys-

iologic reserve, it can be associated with significanthypotension, thus limiting its use in this patientpopulation. In an analysis of 4,096 patients undergo-ing general anesthesia, Reich and coworkers43 re-ported that ASA physical status class III to V,baseline mean arterial pressure of 70 mm Hg, age 50 years, and the use of propofol were statisticallysignificant multivariate predictors of hypotension. Inthe 2,406 patients with retrievable outcome data,prolonged postoperative hospital stay and/or deathwere more common in the patient group that expe-rienced hypotension.43 While propofol provides su-

perior conditions for endotracheal intubation with-out muscle relaxants compared to sodium pentothal,it induces more hypotension and bradycardia inpatients undergoing elective surgical procedures.44

This adds to previous evidence indicating that propo-fol may not be safe for high-risk patients with knowncardiac dysfunction.45 Whether or not data obtainedin the operating room environment can be extrapo-lated to the ICU setting is unknown; however, theindependent risk factors cited previously certainlyapply to the majority of patients who are in need ofemergent airway management in the ICU.




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Etomidate

Etomidate has onset and offset pharmacokineticcharacteristics that are similar to propofol, and lackssignificant effects on myocardial contractility (evenin the setting of cardiomyopathy), which make it oneof the preferred induction agents for airway manage-ment in critically ill patients. When it was studied46

in a heterogeneous group of patients undergoing RSIin the emergency department, etomidate providedgood intubation conditions with very few hemody-namic derangements, even in those patients with lowBP prior to airway instrumentation. Nevertheless,the role of etomidate in clinical practice is in ques-tion due to its effect on adrenal production ofsteroids. Etomidate inhibits adrenal steroidogenesisthrough the inhibition of mitochondrial hydroxylase,both after a single dose and continuous administra-tion.4749 Based on the available evidence, the use ofetomidate in critically ill patients with sepsis and

septic shock should be discouraged.50

If patients whoare in septic shock receive etomidate, corticosteroidsupplementation to prevent unnecessary deaths isrecommended. Since the adrenal suppression by thedrug lasts longer than previously estimated (up to72 h), some authors51,52 have questioned the use ofetomidate in critically ill patients altogether.

Ketamine

Ketamine is unique among the hypnotic agents inthat it has analgesic, sedative, and amnestic effects. Ithas a slower onset and offset compared to propofol

or etomidate following IV infusion, and stimulatesthe cardiovascular system (ie, raises heart rate andBP by direct stimulation of the CNS). In the usualdosage, ketamine decreases airway resistance.Whether ketamine, when administered as an adjunctduring emergent airway management in the ICU,provides adequate intubation conditions has notbeen studied in a systematic fashion. When com-pared to sodium pentothal in a dose of 5 mg/kg,ketamine (2.5 mg/kg) will provide superior intuba-tion conditions 1 min after the administration ofrocuronium (0.6 mg/kg) in the elective surgery set-

ting.53 These findings are supported by a morerecent prospective, randomized, controlled clinicaltrial54 in which the administration of ketamine re-sulted in excellent intubation conditions in a signif-icantly higher proportion of elective surgery patientswhen compared to the administration of sodiumpentothal. Ketamine also appears to be a usefuladjunct to etomidate when RSI is performed withrocuronium. The combination of ketamine with eto-midate and rocuronium resulted in superior intuba-tion conditions in a prospective, randomized clinicaltrial55 of patients undergoing elective surgery when

compared to the combination of etomidate, fentanyl,and rocuronium, or etomidate with rocuronium,respectively. In the ICU, this combination may beuseful for treating hemodynamically unstable pa-tients with contraindications to the use of succinyl-choline who are in need of emergent airway man-agement facilitated by a neuromuscular blocker. Theuse of ketamine in patients with increased intracra-

nial pressure is controversial; in this setting, it shouldbe administered only after a careful risk-benefitanalysis.56

Dexmedetomidine

Dexmedetomidine is a centrally acting, selective2 receptor agonist that has been approved for use inthe United States for the short-term sedation ofcritically ill patients.57 The drug may be useful forthe awake, fiberoptic management of the airway inthe ICU due to its analgesic, anxiolytic, and sedative

effects without causing clinically significant respira-tory depression.58 There have been case reports59,60

documenting the usefulness of dexmedetomidine forawake FOI in the operating room setting amongpatients undergoing elective surgery; however, nodata are available regarding its use as an adjunct toairway management in the ICU.

Neuromuscular Blocking Agents

Succinylcholine: The use of succinylcholine (1mg/kg IV) will result in excellent intubation condi-

tions in 1 min. Unless there are contraindications,it is the drug of choice when the airway must besecured quickly (ie, in the patient with a full stomachor with symptomatic gastroesophageal reflux). Thedrug may trigger malignant hyperthermia in geneti-cally susceptible persons, and can cause a malignantrise in extracellular potassium concentration in pa-tients with major acute burns, upper or lower motorneuron lesions, prolonged immobility, massive crushinjuries, and various myopathies.61,62 Infrequently,the use of succinylcholine can be associated withprolonged paralysis due to decreased plasma cho-

linesterase activity.63 Caution is also advised con-cerning its use in patients with open globe injuries,renal failure, and serious infections, and in near-drowning victims.42 Patients who are in a state ofprolonged immobility are at a heightened risk ofhyperkalemia when exposed to succinylcholine dueto changes in the regulation and distribution ofacetylcholine receptors during a course of criticalillness, in particular the postsynaptic up-regulation ofnicotinic acetylcholine receptors and the expressionof immature receptors. The up-regulation of recep-tors during periods of immobilization have been




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described as early as 6 to 12 h into the diseaseprocess. Therefore, we recommend avoiding the useof succinylcholine in critically ill patients beyond24 h in those with burns and spinal cord injury, andbeyond 48 to 72 h of immobilization and/or dener-vation. For a comprehensive review on succinylcho-line-induced hyperkalemia, see the article by Martynand Richtsfeld.64

Rocuronium: Of the currently available non-depo-larizing neuromuscular blocking agents, rocuroniumhas the fastest onset of action and represents the onlyalternative to succinylcholine for use during RSI. Ina dose of 0.8 to 1.2 mg/kg, rocuronium will provideexcellent intubation conditions within 60 s. Whencompared to succinylcholine in a randomized, clini-cal trial65,66 on tracheal intubation in emergencycases, the two agents were equivalent with respect toacceptable intubation conditions and the number offailed intubation attempts. Succinylcholine (1 mg/kg)provided superior intubation conditions when com-pared to rocuronium in this trial; however, the doseof rocuronium that was used (0.6 mg/kg) was on thelow end of the dosage range recommended forRSI.65,66 These results were confirmed by a morerecent trial67 demonstrating superior intubation con-ditions for RSI with the use of succinylcholine (1mg/kg) compared to rocuronium (0.6 mg/kg), but nodifference in the rate of adverse airway effects.67 Ametaanalysis68 by the Cochrane Collaborative Groupconcluded that the intubating conditions achievedwith the use of rocuronium are not statisticallydifferent from those achieved with succinylcholinewhen propofol is used as an induction agent.

Ways To Establish the Airway

Three principal modalities are available for thedelivery of mechanical ventilation to a critically illpatient. These are NIPPV via face mask, extraglotticairway devices (eg, various LMAs, an esophageal-tracheal device [Combitube ETC; Tyco-Healthcare-Kendall USA; Mansfield, MA], or a perilaryngeal

airway), or the endotracheal route (eg, ETT ortracheostoma). The most commonly practiced tech-nique for endotracheal intubation is direct laryngos-copy with either a curved blade (Macintosh blade) ora straight blade (Miller blade) of various sizes. Thechoice of blade shape is a matter of personal prefer-ence; however, one study69 has suggested that lessforce and head extension are required when per-forming direct laryngoscopy with a straight blade.With respect to blade material, plastic single-useblades are inexpensive and carry a lower risk ofinfection when compared to metal reusable blades.

Nevertheless, their use in a critical care settingshould be discouraged. In a prospective randomizedtrial70 of 284 adult patients undergoing generalanesthesia requiring RSI, plastic laryngoscope bladeswere less efficient than metal blades, resulting in asignificantly higher rate of failed intubation on thefirst attempt. Several laryngoscope blades to facili-tate DIs have been introduced in the past. These

include, but are not limited to, the McCoy angulatedblade, the Dorges blade, the Viewmax laryngoscopeblade (Rusch; Duluth, GA) with a patented lenssystem, as well as blades augmented by video orfiberoptic capabilities (eg, the Bullard Laryngoscope;ACMI: Southborough, MA; or the GlideScope; Veri-thon; Bothell, WA; or the WuScope; Achi Corp; SanJose, CA). There are no data on the utility of thesetools for airway management in the ICU. In a trialcomparing the alternative blades with standardblades on a human patient simulator, the Dorges andMcCoy blades did not perform any better than the

standard Macintosh blade either in easy or difficulttracheal intubation conditions.71 However, there aredata from patients undergoing elective or emergentintubation in the operating room as well as fromtrials using cadavers and mannequins (some in thesetting of limited neck mobility) suggesting thatbetter glottic visualization is achieved with video-assisted or fiberoptic devices than with conventionalblades.30,7279

Extraglottic airway devices for supralaryngeal ven-tilation can be further divided into cuffed, orallyinserted hypopharyngeal airways (ie, various forms of

LMA) and cuffed orally inserted esophageal airways(esophageal tracheal combitube).80 Of the hypopha-ryngeal devices for ventilation, the LMA-Fasttrach(LMA North America, Inc; San Diego, CA) appearsto be particularly useful for airway management inthe ICU due to its unique design, which allows themask to be used as a conduit for endotrachealintubation. This device was recently modified, and isnow available with an integrated fiberoptic systemand a detachable monitor (LMA Ctrach; LMA NorthAmerica, Inc), allowing for endotracheal intubationunder direct vision without the use of a fiberoptic

bronchoscope. In a study of 254 patients with diffi-cult-to-manage airways, including patients with Cor-mack-Lehane grade 4 views, patients with immobi-lized cervical spines, patients with airways distortedby tumors, surgery, or radiation therapy, and patientswearing stereotactic frames, the insertion of theLMA-Fastrach was accomplished in three or fewerattempts in all patients. The overall success rates forblind and fiberoptically guided intubations throughthe LMA-Fastrach were 96.5% and 100.0%, respec-tively.81 When studied in morbidly obese patientsundergoing elective surgical procedures, the rate of




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successful tracheal intubation with the LMA-Fas-trach was 96.3%.82 Recent data have suggested thatthe new LMA CTrach system has potential advan-tages over the LMA-Fastrach and can be very usefulin the management of the difficult airway.83,84

When a difficult airway is recognized prior to theadministration of induction agents, an awake, FOImay be the best option; however, other modalities of

awake intubation are possible (eg, blind oral or nasalintubation, or retrograde techniques). Fiberopticbronchoscopy may be particularly useful when upperairway anatomy has been distorted by tumors,trauma, endocrinopathies, or congenital anomalies.Furthermore, it is useful in accident victims in whoma question of cervical spine injury exists and thepatients neck cannot be manipulated. If the airwayhas to be secured via FOI in an emergent fashion,the use of a topical anesthesia seems preferable toregional nerve blockade.

Rescue Strategies

Should initial attempts at endotracheal intubationfail, an alternative strategy for providing ventilationto the patient, and ultimately for securing the airway,must be in place. The implementation of the ASADAA in the critical care setting is logical and,according to one analysis,6 may have decreased the

number of failed airways in the ICU environment.Since this airway algorithm was originally developedas a tool for anesthesia providers in the operatingroom, some minor adaptations for the ICU settingshould be considered (Fig 2). While assessments ofthe likelihood of successful intubation and the clin-ical impact of basic management problems remainthe same, critically ill patients in respiratory failurewill almost certainly have less tolerance for periodsof apnea than patients with unanticipated difficultairways in the operating room. The return to spon-

Figure 2. Algorithm for airway management in the ICU. SB spontaneous breathing;NMBA neuromuscular blocking agent; DMV difficult mask ventilation; pt patient.




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taneous ventilation is an important exit strategy forintubation in the operating room during electivesurgery. In the ICU, this is often impossible due tomechanical failure and the limited physiologic re-serves of the patient. Strategies for airway manage-ment in the emergency pathway of the ASA DAAinclude alternative means to provide ventilation (eg,the LMA-Fasttrach described in the previous sec-

tion, as well as the Combitube; Tyco-Healthcare-Kendall USA; Mansfield, MA). The LMA can also beused as an intubation conduit and has been reportedas a successful bridge to percutaneous tracheostomyin a case of failed airway in the ICU.85 The Combi-tube combines the features of an ETT and anesophageal obturator airway, and reduces the risk ofaspiration. The use of these devices can be learnedeasily by personnel who are unskilled in airwaymanagement.86 Other devices that are suitable fornoninvasive rescue strategies include the gum elasticbougie or an airway exchanger catheter (Cook Crit-

ical Care; Bloomington, IN). These devices may beuseful in a situation in which the glottis can be onlypartially visualized and the insertion of the ETT intothe trachea is unsuccessful. In a randomized study38

of 60 patients undergoing elective intubation withthe application of cricoid pressure, the use of a gumelastic bougie was more effective than a regularstylet to facilitate intubation. Another tool includedin the ASA DAA emergency pathway is retrogradeendotracheal intubation, which entails passing a wirethrough the cricothyroid ligament in a cephaladdirection until the tip can be retrieved through the

nose or the mouth. A hollow guiding catheter isinserted in a cephalad direction over the guidewire,the guidewire is removed, and the ETT is thenadvanced antegrade over the guiding catheter intothe trachea. A commercial kit for the procedure isavailable (Cook Critical Care). Success rates for theprocedure vary. In a review87 of 1,368 patientsundergoing endotracheal intubation in the emer-gency department, the authors found that retrogradeendotracheal intubations were attempted in 8 pa-tients, of which only four were successful. Amongthe complications encountered was the inability to

pass the ETT through the vocal cords.87 To over-come this problem, Lenfant and coworkers88 haverecently developed a modification of the techniquein a human cadaver study. Insertion of the hollowguiding catheter antegrade through the ETT into thetrachea prior to removal of the guidewire signifi-cantly increased the success rate from 69%, using theclassic technique, to 89%, using the modified tech-nique.88 It should be noted, however, that eachprovider participating in the study had previouslyperformed at least 10 successful procedures in acadaver, suggesting that this strategy should be

carried out by experienced providers only. Should allalternative and noninvasive strategies to provideventilation fail, a surgical airway has to be estab-lished. The two principal choices are cricothyroid-otomy and tracheostomy, either in a percutaneous oropen surgical fashion. In a study89 comparing surgi-cal cricothyroidotomy (Portex cuffed device; SmithsMedical Ltd; Hythe, UK) and wire-guided cricothy-

roidotomy (cuffed and uncuffed version of Melker-set; Cook Critical Care) in an airway mannequin andartificial lung model, the cuffed devices providedmore effective ventilation and tidal volumes. Fur-thermore, the surgical method was found to bequicker than the wire-guided approach (mean timeto first breath, 44.3 vs 87.2 s, respectively) but mayhave a higher failure rate in inexperienced hands.89

Few data are available on the utility of percutaneousdilatational tracheostomy (PDT) for emergency air-way access. In a case series90 of nine patients whowere in severe respiratory distress, in which intuba-

tion by conventional means had been unsuccessful,all nine patients were successfully intubated usingthe PDT technique. The average time to gain accessto the airway in the authors institution with thistechnique is reportedly 2.8 min, if performed by anexperienced provider.90 Whenever possible, ventila-tion should be provided while access to the airway isbeing established (eg, LMA). While elective PDT inthe critical care setting is safe and effective,91 moredata are needed to establish its utility in emergencyairway management.

Extubation of the Difficult Airway

Extubation of the patient with a known difficultairway requires some planning should respiratoryfailure and the need for reintubation arise. Besidesroutine extubation criteria, the cuff leak test hasbeen advocated as a tool for predicting postextuba-tion respiratory stridor. However, the data on theutility of this test appear equivocal. While someauthors92,93 have suggested that the cuff leak testmight be a useful index of clinically significant

laryngotracheal narrowing, others94,95 have not beenable to confirm this association. In a more recentstudy using real-time laryngeal ultrasonography,Ding et al96 were able to demonstrate a significantrelationship between the air column width duringcuff deflation and the development of postextubationstridor. These data have been confirmed by a secondrecent, prospective randomized trial97 in 128 medi-cal and surgical ICU patients. In this study, areduced cuff leak volume, defined as 24% of tidalvolume, was a reliable indicator for identifying pa-tients with a high risk for developing stridor. Fur-




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thermore, Jaber et al97 were able to show that inpatients who are at risk (eg, traumatic intubation,prolonged intubation, or previous accidental intuba-tion) a leak volume of 130 mL or 12% of the tidalvolume has a sensitivity of 85% and a specificity of95% for the development of postextubation stridor.

Initially described by Benumof,98 extubating thepatient via an airway exchange catheter (AEC) to

retain a conduit for possible reintubation has beendescribed by several authors.99,100 In a prospectivestudy101 of 40 patients who had one or more riskfactors for difficult reintubation, an AEC allowed foruncomplicated reintubation (n 4) without desatu-ration on the first attempt. This was subsequentlyconfirmed in a prospective, observational study102 inpatients who had undergone maxillofacial and majorneck surgery, and were considered to be impossibleto reintubate by direct laryngoscopy. Reintubationwas easily achieved with the AEC up to 18 h afterextubation.102 An advantage of this strategy is the

ability to insufflate oxygen through the catheter toavoid oxygen desaturation while assessing the patientfor evidence of respiratory distress or compromise.

Summary

Managing the airway of a critically ill patient posessome unique challenges for the intensivist. Thecombination of a limited physiologic reserve in thepatient and the potential for difficult mask ventila-tion and intubation mandates careful planning with a

good working knowledge of alternative tools andstrategies, should conventional attempts at securingthe airway fail. If difficulty in managing a patientsairway is anticipated, the use of awake fiberoptictechniques should be strongly considered. Althoughthe use of muscle relaxants may facilitate endotra-cheal intubation, they must be used with extremecaution, and the clinician must have the requisiteskills and alternative equipment to secure the airwayif standard direct laryngoscopy and endotrachealintubation cannot be accomplished. Given the po-tentially high complication rate of endotracheal in-

tubation in an ICU environment, future researchshould be directed at developing protocols to in-crease the safety of airway management in the ICU.Finally, providing adequate ventilation to the patientwho is experiencing respiratory failure takes prece-dence over endotracheal intubation in order to avoidadverse outcomes related to profound hypoxemia.

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DOI 10.1378/chest.06-21202007;131; 608-620Chest

J. Matthias Walz, Maksim Zayaruzny and Stephen O. Heard

*Airway Management in Critical Illness

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Manejo de La via Aerea Chest 2007

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