It is increasingly recognized that extubation of the difficult airway is a situation at risk of life-threatening complications, whereas criteria and guidelines to guide safe practices in airway management at extubation are still based on limited scientific evidence and of unproven effectiveness in improving outcomes.1,2 Several authors suggest that the dissemination of the difficult airway algorithm by the American Society of Anesthesiologists (ASA) in 1993 and 2003 and the increased availability of advanced airway management tools and techniques may have contributed to a reduction in the number of severe outcomes related to tracheal intubation.3 On the contrary, over the same period, the rate of severe airway-related adverse events occurring in the operating room (OR) or in the recovery area after tracheal extubation has not changed.1,2,4,5 The recently published Report of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society (NAP4) identified serious airway complications occurring during anesthesia, in the intensive care unit (ICU), and in the emergency department in the United Kingdom over a 1-year period, and pointed out that one-third of the events occurred at extubation or in the recovery room. Poor airway management strategies, inadequate assessment of risk factors for airway difficulty, and overall failure to plan were frequent contributing factors to adverse events.6,7,a These results confirm the importance of developing preplanned strategies for extubation of the difficult airway to improve patient safety and outcomes, as suggested by the ASA Task Force on Management of the Difficult Airway since 19938,9 and, more recently, by an updated analysis of the ASA Closed Claims database.5 Substantial lack of adequate scientific evidence has prevented the creation of evidence-based tracheal extubation guidelines.
In January 2012, the Difficult Airway Society (DAS) in the United Kingdom, acknowledging the absence of any large randomized controlled trial of extubation practices, released a set of guidelines for the management of tracheal extubation, mainly based on expert opinions. The goal of the society is to provide clinicians with pragmatic guidelines easily applicable in daily practice.10 It will be interesting to see how these guidelines will be received and implemented by clinicians, and whether they will have a measurable impact on patient outcome.
While further studies are needed to support most recommendations concerning airway management11 and evaluate the usefulness of the guidelines issued so far,12 the aim of this narrative review is to identify meaningful information on airway complications after tracheal extubation, and to elucidate epidemiology, outcomes, mechanisms, predictors, and possible preventive strategies of postextubation failure.
On the basis of these findings, a set of practical recommendations is also summarized and presented. These recommendations are in agreement with the criteria for the formulation of a “strategy for extubation of the difficult airway” contained in the 2003 ASA Practice Guidelines for Management of the Difficult Airway.9 Although some of our findings may also apply to the pediatric population, investigating issues related to extubation failure in that population is beyond the scope of this review.
DEFINITIONS
To avoid confusion and ambiguity, it is important to provide the reader with a few commonly used definitions.
Difficult Airway
In the 2003 ASA Practice Guidelines for Management of the Difficult Airway, difficult airway is defined as, “the clinical situation in which a conventionally trained anesthesiologist experiences difficulty with face mask ventilation of the upper airway, difficulty with tracheal intubation, or both.”9
Extubation Failure
Extubation failure has been defined as “the inability to tolerate removal of the translaryngeal tube,”13 and it is generally treated with tracheal reintubation. Su et al.14 suggest that investigating extubation failure requires “to focus on the removal of the artificial airway, rather than on the removal of the mechanical support.” Mechanisms of “extubation failure” include all causes of airway obstruction, such as laryngospasm, upper airway edema, bleeding either leading to hematoma compressing the airway externally or clots internally obstructing the airway, accumulation of respiratory secretions, tracheal collapse due to tracheomalacia, and upper airway soft tissue collapse secondary to the effects of anesthetics, opioids, and muscle relaxants. These mechanisms leading to extubation failure are also frequently described as “extubation-related airway complications”6,7,15 or “airway-related adverse events at extubation.”5–7
Weaning Failure
“Weaning failure is the inability to tolerate spontaneous breathing without ventilatory support,”13 and its treatment includes tracheal reintubation and invasive ventilation or, in selected patients, noninvasive ventilation.16,17 Assessing the adequacy of weaning variables and predictors of airway patency, as well as confirming the integrity of airway reflexes, are important preparatory steps for a successful extubation. This concept is particularly relevant in the ICU setting, where patients may successfully pass a weaning trial but fail extubation due to airway obstruction.18,19 In fact, commonly used weaning trials do not reliably assess “airway patency” or “airway competence,” (the latter being defined as the ability to generate a strong cough and expectorate endotracheal secretions18) and weaning variables do not predict extubation failure.20
“At-Risk” Extubation
“At-risk” extubation is a situation in which the ability of a patient to maintain airway patency and/or oxygenation after tracheal extubation is uncertain.10 This definition was recently proposed and follows a risk stratification process based on airway-related factors and general clinical conditions. Potentially difficult reintubation and/or general risk factors such as “full stomach, unstable cardiovascular physiology, acid-base derangement, or temperature control” characterize this condition.10
Difficult Extubation
A “difficult extubation” in the sense of a “difficult decannulation of the airway” is a rare situation that depends on mechanical factors related to patient, surgery, or anesthesia. For example, patient-related conditions include unrecognized subglottic stenosis or severe edema physically preventing removal of the endotracheal tube (ETT);21 a surgery-related factor might be an erroneously placed surgical stitch anchoring the ETT to the tracheal wall. Incomplete deflation of the ETT cuff, either because of ETT cuff malfunction or negligence, may be considered an anesthesia-related cause.15
EPIDEMIOLOGY AND OUTCOMES OF EXTUBATION FAILURE
Extubation and weaning failure are generally observed within 72 hours of extubation.13,18,22–26 Although some authors consider any intubation within this postoperative time frame as “early,”27 for the purposes of this review, the term “early reintubation” will apply to the immediate postextubation period (within minutes and up to 6 hours after tracheal extubation), whereas the term “late reintubation” will indicate events occurring between 6 and 72 hours after extubation.
Both in the ICU and in postoperative settings, reintubations after extubation failure occur most frequently between 0 and 2 hours postextubation, and seldom after 24 hours.18,25,28–32
This information is relevant to clinicians in deciding how long to monitor patients at risk of extubation failure,13 and, in patients with difficult airway, how long to keep airway exchange catheters (AECs) in place as tools for guiding tracheal reintubation, if required.25
Extubation failure rates vary depending on the population observed. We will review clinical situations and patient conditions most frequently associated with extubation failure.
Emergence and Recovery from Anesthesia
Early reintubation is a relatively rare event in the postoperative period of elective surgeries and after planned extubation, with reported rates of reintubation in the OR and postanesthesia care unit (PACU) between 0.1% and 0.45%. Reasons for early reintubation include respiratory insufficiency, airway obstruction, bronchospasm, prolonged neuromuscular blockade, and side effects of opioids.29,31,33
“Airway obstruction” (all causes) is the most common cause of airway-related events and need for reintubation in the early postoperative setting.3,6,31,34,35 A frequent cause of airway obstruction leading to early extubation failure both in anesthesia and ICU patients is laryngeal edema,36,37 generally observed within 1 hour of extubation and rarely observed after 24 hours.25,28,29,31,32 Fewer data are available on the causes of “late reintubation” in the postoperative setting; patient comorbidities, type of surgery, and postoperative management may all be contributing factors.27
In a retrospective review of >13,000 consecutive PACU admissions published in 1990, Mathew et al.29 observed 26 emergent reintubation events (0.19% rate). In this series, reintubations occurred in a heterogeneous group of patients, more frequently after head and neck surgery, and the main recognized contributing factor was inappropriate medical management. Seventy-seven percent of the reviewed events were classified as “preventable,” as the 2 most common causes of emergent reintubation were found to be persistent sedative and muscle relaxant effect, and inappropriate fluid management. Interestingly, the same investigators reported that “all 26 patients were eventually discharged from the hospital without sequelae of these events,”29 implying a moderately severe impact of extubation failure on patients clinical course.
The 1985 to 1999 ASA Closed Claims database analysis offers a very different perspective on the severity of extubation-related complications. Of the 26 claims from events after tracheal extubation, 21 cases (81%) resulted in either death or brain damage. Notably, the majority of the patients involved were obese (15 of 26). Over the same period, 104 claims related to events at induction of anesthesia were reported, of which 50 (48%) resulted in death or brain damage. Interestingly, although the authors of the analysis were able to detect a significant decrease in severe outcomes after events at anesthesia induction over the years (from 62% in 1985–1992 to 35% in 1993–1999), the same did not hold true for adverse events after extubation.1 We recently surveyed the ASA Closed Claims Project databaseb and were informed that among the 47 claims for difficult intubation on anesthesia induction since 2000, 20 (43%) resulted in death or permanent brain damage. This suggests that the trend toward reduced death/brain damage reported by Peterson et al.1 appears to be continuing. Among claims for failed extubation reported since 2000, death and permanent brain damage occurred in 15 of 16 claims (94%), and there were 8 claims with difficult airway management that occurred postextubation in the recovery period, all (100%) resulting in death/brain damage. In evaluating data from the Closed Claim Project, it is important to remember that only litigated malpractice claims are reported in the database; therefore, failed extubations that resolved uneventfully are not captured, and the rate of events in the population of tracheally intubated patients undergoing general anesthesia cannot be calculated.
The NAP4 study was designed to track only major airway complications as defined by the following outcomes: death, brain damage, need for surgical airway, and unplanned ICU admission, and 38 events that occurred at emergence or during recovery from anesthesia were reported. This corresponds to a rate of severe complications of about 0.001% based on an estimated denominator of 2,872,600 general anesthetics performed yearly in the United Kingdom (1 major airway adverse event postextubation in 75,600 anesthetics).6 In this group of 38 patients whose most common comorbidities were obesity (46%), chronic obstructive pulmonary disease (34 %), and obstructive sleep apnea (OSA; 13%), the mortality rate was 5% (2 deaths), and the cumulative rate of death and severe morbidity (including resuscitated cardiac arrest and brain damage) was 13%.
The percentages of severe outcomes from the ASA Closed Claims database and the NAP4 are not comparable because of the different nature of the data (closed claim versus voluntary report), but in both studies, reviewers considered poor outcomes frequently to be secondary to “less than appropriate care” and/or judgment (often in the presence of head and neck pathologies or postsurgical changes), to incomplete handoff communications, and to lack of adequate postoperative monitoring.6,38
Overall, these data suggest that extubation failure in the early postoperative setting is rare, especially after elective surgery, but it is associated with extremely severe outcomes and litigation, even more frequently than airway-related complications occurring in other phases of anesthesia.1 Airway obstruction is the main cause of extubation failure and need for tracheal reintubation after anesthesia. These serious adverse events are due to a combination of factors that are patient-related (obesity, OSA, chronic obstructive pulmonary disease), surgery-related (head and neck surgery and upper airway manipulation) and, probably more importantly, provider-related (inappropriate or incomplete planning, management, and judgment).1,6,29,38
Tracheal Extubation in the ICU
Reintubation is a fairly common event in critically ill patients (0.4%–25%) after extubation failure and weaning failure,13,25,39 2 frequently intertwined complications in the ICU.
In ICU patients, the impact of extubation or weaning failure and need for reintubation on the overall outcome is often measured in terms of increased ICU and hospital length of stay and mortality. The direct association between the need for reintubation and prolonged ICU and hospital stay and mortality has been demonstrated in a variety of critically ill patients.13,39,40 Of note, a few investigators have found that ICU patients requiring reintubation for respiratory failure have a higher mortality (30%–52.9%) than patients whose tracheas were reintubated because of airway obstruction (7%–17.4%).24,32,41,42 This suggests that “weaning failure” may carry a higher mortality than “extubation failure.”
Certainly, postextubation respiratory failure in critically ill patients may be accompanied by failure of other organs and systems that independently affect mortality.40 On the contrary, upper airway obstruction can occur in less compromised patients and, by itself, does not appear to increase the likelihood of adverse outcomes.41 Another hypothesis to account for this difference in outcome is that patients who fail trials of extubation because of airway obstruction are reintubated earlier than those who fail because of intrinsic respiratory complications,41 and time to reintubation after failure has been found to be an independent predictor of hospital mortality.13,24
Interestingly, in the NAP4 study only 1 of the 36 airway management complications reported in ICU patients occurred at the time of tracheal extubation. It is not possible to calculate the incidence of these events because a reliable estimate of the number of patients managed in ICUs in the same 1-year observation period is missing. This is a limitation of the ICU portion of the study, which is otherwise an extremely interesting and useful source of information on major complications of airway management and clinical practices in anesthesia and intensive care at a national level.43–45 However, other investigations show that tracheal reintubation, either after failed extubation or failed weaning, is a much more common occurrence in the ICU than in the postoperative setting.25 Moreover, unplanned extubation occurs in 5% to 15% of ICU intubated patients and is associated with increased ICU morbidity and mortality.40
CONDITIONS AND PROCEDURES AT INCREASED RISK FOR EXTUBATION FAILURE AND DIFFICULT AIRWAY MANAGEMENT
Conditions such as obesity, OSA,6,46–48 major head/neck and upper airway surgery,6,28,35,49,50 obstetric,51 and cervical spine procedures52–56 carry significantly increased risks of extubation failure and are frequently associated with difficult airway management.
Obesity and OSA
The Centers for Disease Control and Prevention define obese individuals as those with a body mass index >30 kg/m2.57 In the United States, the “heaviest” Western Country, the prevalence of obesity was 34% in 2008.58 OSA is a syndrome characterized by periodic, partial, or complete obstruction of the upper airway during sleep.59 Up to 71% of morbidly obese patients are affected by OSA.60 Expert recommendations and practice guidelines for the perioperative management of the obese and OSA patients largely overlap.46–48,59
Obese patients have a higher incidence of difficult mask ventilation,61–63 increased risk of pulmonary aspiration, airway obstruction, and rapid oxygen desaturation after anesthesia induction.48 Difficult intubation has been reported in 7.5% of morbidly obese patients.64 In reports investigating major airway complications, the prevalence in obese patients is often higher than in the general population. Sixty-five of the 156 (42%) perioperative airway events in the 2005 ASA Closed Claim data analysis (data from 1985 to 1999)1 and 77 of 184 (42%) complications in the NAP4 report6 involved obese patients. In the time periods corresponding to the ASA Closed Claim and NAP4 data collections, prevalence of obesity in the United States ranged between 10% and 25%c (from 1985 to 1999); and in England, the prevalence of obesity was 22% for men and 24% for women (2009 data).d According to recent studies, this relatively high prevalence does not necessarily result in increased hospital stay and higher mortality,65–67 especially for the subgroup of moderately obese patients.68 However, these statistics do suggest that obese patients present a higher risk of airway management-related complications compared with the general population. Important postoperative concerns in the management of both obese and OSA patients include: (1) increased susceptibility to the respiratory-depressant effects of opioids and anesthetics; (2) increased risk of hypoxia that may require the use of continuous positive airway pressure treatment; (3) attention to patient positioning, which should be “nonsupine”; and (4) appropriate monitoring for early detection of respiratory and cardiovascular impairment (such as continuous pulse oximetry, capnography, and telemetry).46–48,59
Of note, in OSA patients undergoing upper airway surgery for the treatment of OSA, the incidence of postoperative airway complications, including obstruction leading to severe oxygen desaturation, may be as high as 5%.46,69
Head and Neck Pathology, Maxillofacial and Major Neck and Upper Airway Surgery
In the presence of head and neck pathology and after maxillofacial and major neck surgery, rates of tracheal reintubation between 0.7% and 11.1% have been reported.29,35 This also applies to endoscopic upper airway surgery, after which 4.2% of the patients whose tracheas were extubated in the OR needed to be reintubated in the PACU.28
In the NAP4 report, 72 of the 184 adverse airway events (39.1%) involved patients with acute or chronic head and neck pathologies. Of these 72, 55 events were anesthesia-related (41.3% of the 133 anesthesia-related events), and the rest occurred in the ICU and emergency department. Of the 55 anesthesia-related events, 13 (23.6%) occurred at the time of tracheal extubation or during the recovery period. These adverse events in patients with head and neck pathologies accounted for 34.2% of all events during emergence or recovery.6
Patients with active head and neck pathology, or who have undergone surgical or radiation treatment for head and neck cancer, are also at an increased risk of adverse airway events when presenting for other types of surgeries. In a 4-year observational study on prediction of impossible mask ventilation and outcomes, Kheterpal et al.63 examined more than 50,000 attempts at mask ventilation over more than 94,000 anesthetics and found that neck radiation changes were the most significant clinical predictor of impossible mask ventilation. Besides critical difficulties with mask ventilation, radiation therapy induces extreme neck rigidity and modification of normal airway anatomy that may cause significant difficulty with tracheal intubation and makes it extremely challenging to perform an emergency tracheostomy. Moreover, postradiation airway edema, that may be worsened by impaired lymphatic drainage after neck dissection, is a contributory risk factor for postextubation laryngeal obstruction in this group of patients.70
Obstetrics
In an analysis of anesthesia-related maternal deaths in Michigan from 1985 to 2003, Mhyre et al.51 found that all anesthesia-related deaths from airway obstruction or hypoventilation (5 events) took place during emergence and recovery and not during the induction of general anesthesia. In contrast, in the NAP4 report, all airway-related adverse events in pregnant women (4 cases) involved emergency cesarean deliveries and occurred at the time of tracheal intubation.6 It is difficult to reconcile the different findings in the 2 reports, especially because of insufficient information about the environment in which the events occurred and the lack of details about the clinical management of these cases. However, the known frequent prevalence of obesity and airway edema among pregnant women71 suggests the necessity of an appropriate strategy to prevent airway-related complications in this group at any stage of the anesthetic management.
Rheumatoid Arthritis
In patients with rheumatoid arthritis (RA), traumatic tracheal intubation due to decreased neck mobility and anatomical abnormalities has been considered a potential contributory cause of postextubation airway obstruction. The prevalence of laryngeal involvement in RA ranges from 13% to 75% in clinical studies and between 45% and 88% in postmortem studies.72 Patients with RA may have deviation of the larynx causing difficulty at intubation;73 arthritis of the cricoarytenoid joints that may present as a life-threatening airway obstruction;72,74–76 and laryngeal rheumatoid nodules that may be worsened by microtrauma and may contribute to airway obstruction.72
In 1994, Wattenmaker et al.77 suggested that fiberoptic intubation should be the method of choice in patients with advanced RA (as defined by the decision to proceed with surgical spine stabilization) to avoid excessive manipulation of the airway during direct laryngoscopy that may have a critical role in the development of postextubation airway obstruction.77 Future studies should compare the safety and facility of video-assisted laryngoscopy techniques in RA patients, because these techniques were not available at the time of the initial study.
Cervical Spine Surgery
Airway obstruction after anterior cervical spine surgery is a known complication that may cause extubation failure. Patients who have undergone anterior cervical spine surgery are at risk of airway compromise both immediately after tracheal extubation at the end of surgery, and for several hours after the surgical procedure (up to 48 hours). Indeed, airway complications after tracheal extubation are particularly insidious in this group of patients, and may occur also in patients who have been kept intubated overnight after surgery, to avoid complications from slow formation of retropharyngeal hematomas.
In 2 different studies, patients experiencing extubation failure after anterior cervical spine surgery required tracheal reintubation between 052 and 24 hours53 after extubation. In a retrospective chart review of 311 anterior cervical procedures, Sagi et al.53 found that airway complications occurred in 6% of cases, a third of which required tracheal reintubation. The authors identified the following as predictors of increased risk of postoperative airway complications: length of surgery >5 hours; surgical exposure of >3 vertebral levels that include C2, C3, or C4; and blood loss ≥300 mL. Considering the potential for the development of delayed respiratory complications, the authors suggested continued close respiratory monitoring of these patients for up to 48 hours postoperatively.53
Overflexion of the cervical spine has been shown to be a possible cause of upper airway obstruction after posterior cervical spine surgery.54–56 The mechanism of this rare but extremely serious complication will be discussed below, in the causes and mechanisms of extubation failure section. RA is an additional risk factor for the development of upper airway obstruction after cervical spine surgery.56
CAUSES AND MECHANISMS OF EXTUBATION FAILURE
Causes of postextubation upper airway obstruction are heterogeneous and can be classified on the basis of the anatomical segment of the airway involved, the predisposing clinical conditions, and the underlying pathophysiologic mechanism.
Pharyngeal Obstructions
Loss of pharyngeal patency is common in obese and OSA patients. This is due to a combination of mechanisms, the main one being the “anatomical mismatch between the craniofacial bony enclosures and the amount of soft tissue.”66 The second mechanism is a reduction in the longitudinal tension of the pharyngeal wall causing collapse of the airway. Pharyngeal wall tension is thought to depend mainly on traction exerted by the trachea moving caudally during inspiration (bigger tidal volumes causing more caudal traction). The decreased traction on the trachea caused by a reduced lung volume expansion in anesthetized obese/OSA patients would then cause upper airway collapse.45,66,78–80 Shallow breathing and lung atelectasis are common contributing factors to upper airway closure in morbidly obese patients after general anesthesia and surgery.
Formation of a retropharyngeal hematoma is a known complication after anterior cervical spine surgery and a life-threatening cause of airway obstruction.53 Accumulation of airway secretions associated with impaired cough reflex or reduced cough strength14,18,81,82 is a common additional cause of pharyngeal obstruction in ICU patients (see below).
Laryngeal Obstructions
Edema of the larynx is a frequent cause of postextubation airway obstruction.6,32,37 Causes include multiple intubation attempts, upper airway and major neck surgery,35,77 upper airway trauma and burns,41 prone or Trendelenburg intraoperative positioning,6 fluid overload,83 prolonged tracheal intubation,32 and long-term effects of neck radiation.70
While edema of the tongue and pharyngeal structures is easily assessed by direct vision or direct laryngoscopy, laryngeal edema may be more difficult to assess and quantify in the presence of an ETT. However, although the presence of an ETT may prevent optimal visualization of the airway,32,36,84 if the tube is small compared with the size of the airway, as frequently indicated in upper airway surgery, examination of the degree and anatomical distribution of edema may be extremely helpful in guiding tracheal extubation.10,34,85 The “degree” of edema is not easily defined as a specific amount of tissue swelling and attempts to develop a “measure of the degree of edema” resulted in moderate levels of agreement among observers.86 Nevertheless, a case-by-case assessment of the disproportion between upper airway diameters, within the finite limits of their bony and cartilaginous enclosures and the swollen mucosa, may predict situations at risk of postextubation upper airway obstruction.87
Flexible laryngoscopy or video-assisted laryngoscopy to detect airway edema before extubation may be useful in selected situations10,87 (Table 3).
;)
Table 3: Evaluation of General Clinical Factors That May Have an Adverse Impact on Ventilation After Tracheal Extubation: Identification of Situations At-Risk
In ICU patients evaluated by fiberoptic endoscopic examination after extubation, edema of the vocal cords but not of the false vocal folds and arytenoids was associated with stridor, impaired vocal cord mobility, and need for reintubation.88
Laryngospasm is caused by contraction of the adductor muscles of the vocal cords, causing complete obstruction of the glottic opening. It is a protective airway reflex, activated by liquids or other substances entering the glottic space. Factors associated with its occurrence in adults are not completely clear, although some risk factors, such as smoking and obesity, have been identified.33,89 In adults, laryngospasm during emergence may occur at a rate of up to 7.5%, and even more frequently in the postextubation phase of procedures on the upper airway.90,91 Use of laryngeal mask airways in adults has been advocated to reduce postextubation respiratory complications such as coughing, desaturation,92 and laryngospasm.93,94 Interestingly, use of a laryngeal mask airway in children has been associated with an increased risk of laryngospasm,95 especially after recent upper respiratory tract infections.96
Laryngospasm may be complicated by negative pressure pulmonary edema (NPPE). Young and healthy male patients appear to be at increased risk for NPPE, and this complication has a prevalence of approximately 0.1% in the postoperative period.97–100 Although relatively rare, NPPE is a very serious complication that may lead to tracheobronchial and alveolar hemorrhage.98 The reported mortality rate due to NPPE ranges between 2% and 40%, with higher mortality rates associated with delayed diagnosis, or underlying ventricular dysfunction or valvular pathology.91,101
Vocal cord paralysis secondary to recurrent laryngeal nerve (RLN) injury is another cause of laryngeal obstruction that frequently follows cervical and intrathoracic surgical procedures. Unilateral paralysis is asymptomatic more than 50% of the time,102 whereas bilateral vocal cord paralysis presents immediately after extubation with stridor and airway obstruction, and may be a life-threatening event. Thyroid surgery is the most common cause of bilateral vocal fold immobility. Nonthyroid surgeries are the main cause of iatrogenic unilateral vocal cord paralysis.102,103 The incidence of temporary RLN palsy after thyroid operations is 9.8%, and the incidence of permanent RLN palsy is 2.3%.104 Reported rates of RLN injury vary greatly in the literature, depending on the method and timing of laryngeal examination. During thyroid surgery, the role of nerve monitoring in identifying the laryngeal nerve, thereby preventing postoperative vocal cord paralysis, is controversial.102,105–107 As a tool to predict postoperative vocal cord function, this technique has been shown to be highly effective at correctly predicting normal nerve function, but it has a low predictive value for nerve injury (positive predictive value 40% and negative predictive value 100%).105
Postoperative Bleeding
Formation of hematoma compressing the upper airways externally or of clots obstructing the airway internally may depend not only on surgical factors, but also on hypocoagulability secondary to medical conditions or to drug effects. Antiplatelet and nonsteroidal anti-inflammatory drugs are associated with increased risk of perioperative bleeding,108 but other commonly prescribed drugs and over-the-counter supplements can also impact surgical bleeding; these side effects may not be adequately known to prescribers. For example, selective serotonin reuptake inhibitors and venlafaxine have been reported to increase the risk of upper gastrointestinal tract bleeding109 and, possibly, the risk of surgical bleeding.110 In at least 1 case reported in the literature, abnormal bleeding after an oral surgical procedure led to airway compromise in a patient taking a selective serotonin reuptake inhibitor combined with nonsteroidal anti-inflammatory drugs.111 In addition, a variety of dietary herbal supplements (such as gingko biloba, saw palmetto, and garlic) have been associated with excessive perioperative bleeding.112
Presence of Masses and Lesions
Masses and lesions obstructing or compressing the airway are well-known causes of difficult airway management. Occasionally, patients with mediastinal masses will undergo procedures for diagnostic purposes or surgery outside of the mediastinum. In such cases, the mass may cause compression on the airway before and after the procedure, requiring special precautions both at anesthesia induction and tracheal extubation, such as maintenance of head-up position as much as possible, the use of short-acting anesthetics, avoidance of muscle relaxants, and preservation of spontaneous ventilation.113 Additionally, substernal and mediastinal masses may be difficult to evaluate and may cause unexpected postdecannulation airway collapse, preventing successful extubation.114
Effects of Drugs Administered in the Perioperative Period
Neuromuscular blocking drugs, anesthetics, and opioids may have deleterious effects on respiratory drive, muscle strength, and airway patency. Consequences of these effects on postoperative respiratory adverse events have been investigated extensively.
In a recent review on the clinical implications of residual neuromuscular block, Murphy and Brull115 report an incidence of this condition that varies widely among studies (2%–64%). In this review, the impact of residual neuromuscular block on pharyngeal and airway muscle function, hypoxic ventilatory drive and subjective weakness is extrapolated from studies in healthy volunteers. In volunteer studies, the effects of neuromuscular blocking drugs may be better separated than in clinical studies from the effects of other drugs that may contribute to respiratory depression and airway obstruction in the postoperative period.
The following effects have been found to correlate with train-of-4 ratios <0.9 (0.7–0.9): impairment of pharyngeal coordination and force of contraction;116,117 increased risk of aspiration;117 reductions in upper airway volumes;118 impairment of upper airway dilator muscle function;118 decreased inspiratory air flow;119 upper airway obstruction;119 impaired hypoxic ventilatory drive;120–122 and profound symptoms of muscle weakness.123
The review also examined large-scale, database-derived investigations assessing risk factors for anesthetic-related adverse outcomes that demonstrated an association between neuromuscular blocking drug use, residual paralysis, and increased perioperative severe morbidity and mortality.124,125 Observational and randomized clinical studies were also considered, confirming that postoperative respiratory events, including airway obstruction, are the most common adverse outcomes associated with residual paralysis.115
In the general surgical patient population, tracheal reintubation due to depressive effects of opioids is uncommon in a monitored postoperative environment. Lee et al.,31 in an analysis of a quality assurance database of 152,939 cases over a 5-year period (107,317 cases performed under general anesthesia), identified 191 reintubations, of which only 9 (4.71%) were classified as secondary to “excessive opioids” administration. However, it is not known how many patients in this population were rescued from opioid overdose with naloxone and/or noninvasive mask ventilation, thereby preventing the need for tracheal reintubation. Identification of all cases of opioid-related respiratory depression would have allowed the assessment of the role of monitoring and timely treatment of respiratory depression in preventing reintubation. It is, in fact, recognized that, in the absence of adequate monitoring of vital variables, in-hospital use of opioids is associated with increased mortality due to undetected upper airway obstruction and central apnea.126,127 For inpatients receiving postoperative opioids, the routine use of pulse oximetry may prevent adverse outcomes from opioid-related respiratory depression. If supplemental oxygen is administered, the use of capnography to detect hypoventilation has been advocated.e
Populations at particularly high risk of respiratory depression and upper airway collapse after anesthesia and administration of opioids are obese/OSA patients46,48,59,128 and patients who have undergone oral and maxillofacial surgery.85,129 In the context of maxillofacial surgery, other factors may further increase the risk of airway obstruction, such as the presence of oral swelling, bleeding inside the airway and/or the use of intermaxillary surgical fixation that may prevent easy access to clear blood and secretions from the upper airway.
Specific Mechanisms of Airway Obstruction After Cervical Spine Surgery
Pharyngeal edema, vocal cord paralysis, and hematoma formation52,53,56 are known causes of airway obstruction after anterior cervical spine surgery. Cerebrospinal fluid leak,130 angioedema,131 and graft or plate dislodgement132,133 are less frequent complications of cervical spine procedures.56
Upper airway obstruction after posterior fusion of the cervical spine in an overflexed position has been described.54–56 In this particular clinical situation, the mechanism of obstruction seems to depend on the narrowing of the pharyngeal space by the overflexion fixation of the cervical spine, rather than the presence of pharyngeal edema. Pharyngeal stenosis and resulting airway obstruction are corrected with surgical revision of the fixation angle.
Cough Strength and Endotracheal Secretions in ICU Patients
Inadequate cough14,81 and excessive airway secretions18 may also lead to loss of airway patency and extubation failure, particularly in ICU patients. In the absence of other causes of airway obstruction, upper airway patency relies on the ability to maintain the airway clear of secretions, owing to a balance between cough strength and amount and thickness of respiratory secretions. Cough strength has been found to be a more reliable predictor of extubation outcome than the amount of endotracheal secretions, also due to the difficulty in standardizing the method to quantify secretions14 (Table 1).
Table 1: Proposed Methods to Evaluate Endotracheal Secretions and Cough Strength
CURRENT RECOMMENDATIONS
A “preformulated strategy for extubation of the difficult airway” has been recommended at least since the publication of the ASA Practice Guidelines for Management of the Difficult Airway in 1993.9 The Practice Guidelines, updated in 2003, suggest that:
“The preformulated extubation strategy should include
- A consideration of the relative merits of awake extubation versus extubation before the return of consciousness.
- An evaluation for general clinical factors that may produce an adverse impact on ventilation after the patient has been extubated.
- The formulation of an airway management plan that can be implemented if the patient is not able to maintain adequate ventilation after extubation.
- A consideration of the short-term use of a device that can serve as a guide for expedited reintubation.”
Of note, with the exception of tube exchangers to guide and expedite reintubation in the presence of a difficult airway,9,10,25,94,134 no other specific tool or procedure to increase safety at extubation has gained wide acceptance or has been routinely adopted in clinical algorithms.
There are reasons why recommendations relative to safe extubation have not been easily translated into clinical practice, as opposed to what occurred in the development of difficult intubation strategies and algorithms. Many reliable anatomical and functional predictors of inability to perform effective mask ventilation and intubation have been identified, and algorithms have been created in which key decision elements are quite easy and quick to assess; for instance, the question “is facemask ventilation adequate?” can be answered easily by a trained anesthesiologist. Advanced airway tools and techniques have been found to be effective in improving success rates of intubation and in the prevention and rescue of airway compromise. Moreover, when intubation and mask ventilation fail, this is immediately recognized as a dangerous clinical situation and can be effectively treated according to a validated difficult airway algorithm.
Evaluating potential risks of airway obstruction after extubation in a patient whose airway is still protected is a more subtle task. Providers may know that their patients’ trachea had been difficult to intubate, and prepare an extubation strategy as the “logical extension of the difficult intubation strategy.”9 However they may fail to recognize situations in which factors related to surgery and anesthesia changed an initial “easy airway” into a difficult one, or created the conditions for postextubation airway obstruction. Moreover, extubation failure may not occur immediately after tracheal extubation and, without appropriate monitoring, may remain undetected until the loss of airway has resulted in a severe adverse outcome.
Our search has confirmed that many predictors of extubation failure can and should be identified before extubation (the statement “extubation … should always be an elective process”10 is true, probably with the sole exception of an airway fire scenario), and that strategies and tools are available to improve extubation outcomes in the presence of difficult airways and/or high risk of postextubation airway obstruction.
In 2006, a panel of experts of the French Society of Anesthesia and Intensive Care (Société Française d’Anesthésie et de Réanimation) gathered in a conference on “Difficult intubation” and formulated a series of criteria for extubation considered “at risk” on the basis of the limited evidence available. In 2008, Francon and other members of the panel published the “Difficult extubation: Extubation criteria and management of risk situations,” a review aimed to expand the issues discussed at the Conference. An “Extubation algorithm for high risk situations” is included, which is mainly based on the use of an AEC that is left in place for up to 1 hour after extubation if oxygen saturation is satisfactory (SpO2 >90%). The AECs may be used as a means of oxygenation, and reintubation or jet ventilation if saturation decreases below 90%.
Leaving the AECs in place for a maximum of 1 hour after extubation and adopting a cutoff SpO2 of 90% for satisfactory oxygenation seem arbitrary choices and definitely not indicated for all types of patients and clinical scenarios. However, recommendations concerning the importance of predicting situations at risk and planning accordingly, optimizing the patients’ medical conditions and demanding the presence of an expert physician when difficulties with extubation are expected, are reasonable, and widely applicable in clinical practice.135
The recently published DAS extubation guidelines10 follow in the same path and provide clinicians with pragmatic algorithms that apply to low-risk and at-risk situations in which difficulty with oxygenation, ventilation, and airway management may be expected.f
The main argument in favor of providing guidelines on the basis of a pragmatic approach and expert opinions is that high quality evidence generated by prospective randomized trials may not always be available, generalizable, or relevant to clinical practice.12 The major weakness of the DAS guidelines is the lack of stringent criteria to diagnose situations and to guide decisions. The key question, “is it safe to remove the tube?” that is central to the at-risk algorithm, can be a difficult one, and the answer is left to the intuition of the individual provider, as is the challenge to make the “appropriate choices” and to select the suitable “advanced techniques” to apply with “meticulous attention to detail.”
Pending further studies evaluating outcomes of specific interventions and strategies leading to the validation of widely accepted guidelines for the extubation of the difficult airway and extubation at risk, the reviewed literature supports the adoption of a series of practices that are consistent with the ASA Practice Guidelines for Management of the Difficult Airway (Tables 2–7).
Table 2: “Awake” Versus “Asleep” Extubation: Pros and Cons
3,10,94Evaluation of General Clinical Factors That May Produce an Adverse Impact on Ventilation After Tracheal Extubation: Optimization of Medical Management
Table 5: Quantitative Methods of Performing the “Cuff-Leak Test” and Proposed Cutoff Values
Table 6: Formulation of an Airway Management Plan That Can Be Implemented if the Patient Is not Able to Maintain Adequate Ventilation After Extubation
Table 7: Use of Airway Exchange Catheters (AECs)
CONCLUSION
Extubation failure may lead to severe outcomes, particularly in the presence of a difficult airway. Situations at risk for postextubation airway complications are frequently recognizable. Patients at risk may be identified by medical history, physical examination, and pre-extubation assessment of variables that predict airway patency and airway competence, but reliable diagnostic tests and predictors are still largely missing. Postextubation complications may be prevented or mitigated by preemptive optimization of the patients’ medical conditions, careful timing and logistics of the extubation process, preparation for urgent or emergent tracheal reintubation (including routine use of AECs in case of extubation of difficult airways), and adequate level of postextubation monitoring and care.
DISCLOSURES
Name: Laura F. Cavallone, MD.
Contribution: This author participated in study design, research and analysis of the literature, and manuscript preparation.
Attestation: Laura F. Cavallone, MD approved the final manuscript.
Name: Andrea Vannucci, MD, DEAA.
Contribution: This author participated in study design, research and analysis of the literature, and manuscript preparation.
Attestation: Andrea Vannucci, MD, DEAA approved the final manuscript.
This manuscript was handled by: Sorin J. Brull, MD, FCARCSI (Hon).
a Available at: http://www.rcoa.ac.uk/nap4. Accessed on April 26, 2012.
Cited Here
b Personal communication from Karen Posner PhD—Laura Cheney Professor in Anesthesia Patient Safety, Department of Anesthesiology, University of Washington on November 10, 2011.
Cited Here
c Available at: http://www.cdc.gov/obesity/data/trends.html. Accessed on November 27, 2011.
Cited Here
d NHS, the Information Centre: Statistics on Obesity, Physical Activity and Diet: England, 2011. Available at: http://www.ic.nhs.uk/statistics-and-data-collections/health-and-lifestyles/obesity. Accessed on November 27, 2011.
Cited Here
e “No Patient Shall Be Harmed By Opioid-Induced Respiratory Depression” in APSF Newsletter Fall 2011. Available at: http://www.apsf.org/newsletters/html/2011/fall/01_opioid.htm. Accessed on December 15, 2011.
Cited Here
f Available at: http://www.das.uk.com/guidelines/guidelineshome.html. Accessed on April 30, 2012.
Cited Here
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