36.3.1 Is This a Difficult Airway?
The term "difficult airway" has been used when conventional direct laryngoscopy reveals a Cormack/Lehane (C/L) Grade 3 (epiglottis only) or Grade 4 (soft palate only) view.9,14-16 Certainly, tracheal intubation can be more difficult in this clinical setting. The ASA Task Force on Management of the Difficult Airway defines difficult airway as "the clinical situation in which a conventionally trained anesthesiologist experiences difficulty with face mask ventilation, endotracheal intubation, or both."17 The other dimensions of airway management (ventilation by extraglottic device and surgical access to the airway) as outlined by Murphy et al must also be considered when estimating the magnitude of airway difficulty.18 DLTs and the Univent tube have been termed "difficult tubes" as they can be more difficult to insert due to their increased outside diameter (OD) and increased overall rigidity which impedes optimal shaping of the tubes.14,16 The criteria for difficult DLT insertion have not been well defined.1,2 However, difficulty can be encountered in the presence of a Cormack/Lehane II (partial glottis) view.9
36.3.2 What Are the Options for Airway Management in This Patient?
Mask ventilation has been demonstrated to be easy but direct laryngoscopy is difficult. The patient's position should have been optimal before induction. If not, then it should be optimized. Head lift and external laryngeal manipulation should be considered part of the best direct laryngoscopy technique. A blade change can be considered if it is anticipated that a specific anatomic problem can be overcome. Placement of a DLT is best accomplished with a curved blade as it leaves more space in the pharynx through which to pass the relatively bulky DLT.9 An Eschmann tracheal introducer (bougie) is unlikely to succeed in the presence of a CL Grade 4 view and may produce trauma.
In the patient who has a difficult direct laryngoscopy and who requires lung separation, the airway management options include placement of a single tube (SLT) and utilization of a bronchial blocker, placement of a Univent tube, or placement of a DLT. The decision to use an SLT as opposed to a Univent or a DLT is based on the degree of difficulty anticipated with the more difficult tube, which is a function of the available airway management equipment (eg, video laryngoscope), the airway anatomy/geometry, and the expertise of the airway practitioner, as well as the anticipated postoperative clinical course. If postoperative ventilation is possible or probable based on the length and extent or type of surgery, anticipated fluid shifts and transfusion requirements, hemodynamic stability, or marginal respiratory reserve, then placement of a DLT may require a tube change at the end of the case.1,2,9 Exchange of a DLT for an SLT at the end of the case is not without risk.2 Edema, secretions, and trauma from the initial intubation1-3,9,16 may make reintubation at the end of surgery more difficult. Optimal positioning for intubation at the end of surgery may also be more difficult to achieve. Reintubation at the end of surgery may be extremely difficult and can be a highly dangerous maneuver3 with potential loss of airway control.1 Aspiration and airway trauma can also occur.1
The decision to proceed with intubation with an SLT, a Univent, or a DLT is a matter of clinical judgment, taking into consideration the technical and airway anatomical issues as well as the anticipated clinical course. The requirement for lung separation must also be evaluated. The absolute indications for lung separation include massive bleeding or abscess in which the nondiseased lung must be protected from contamination, unilateral air leak from bronchopleural or bronchopleural cutaneous fistula, or unilateral pulmonary lavage for alveolar proteinosis or cystic fibrosis.1,3,9,16 Video-assisted thoracoscopic surgery (VATS) has also been included as an absolute indication for lung separation.1,16 Other indications for lung separation are relative and are to improve surgical exposure.3,16 Although many surgical procedures are more easily performed with the lung collapsed, if placement of a DLT or BB is problematic, the need for lung separation as well as the safety of the technique must be considered.9
Intubation techniques that can be used as an alternative to DL include flexible bronchoscopic intubation under general anesthesia, intubation using a video laryngoscope (Glidescope, McGrath, Pentax AirwayScope, Bullard, or Stortz VMAC), or intubation through an LMA or ILMA.
Intubation of the unconscious patient using the flexible bronchoscope is a widely accepted technique. Jaw thrust and tongue traction can be used to open the hypopharynx and facilitate passage of the scope. Minimizing the discrepancy between the OD of the bronchoscope and the internal diameter (ID) of the ensleeved endotracheal tube (ETT) will minimize the risk that the tube will meet obstruction as it is passed through the larynx into the trachea over the scope.
In the setting of predicted difficult DL, awake flexible bronchoscopic intubation has historically been considered to be the safest means to secure the airway9, and in the elective, predicted difficult airway, is still recommended as the preferred technique.3 However, with the introduction of devices that are proving to be useful in the difficult intubation, protocols are changing9 and video laryngoscopes are challenging bronchoscopy as the first choice for accessing the difficult airway.9,19-21
Flexible bronchoscopic intubation using a Univent tube can be more difficult than with a conventional ETT due to the fixed concavity of the Univent as well as its larger OD.1,22 When performing a flexible bronchoscopic intubation with a DLT, the length of the tube relative to the length of the shaft of the scope limits the maneuverability of the scope.16,23 The rigidity of the DLT also makes it harder to advance the tube over the scope.16
Intubation with an SLT utilizing the Glidescope is widely practiced and is associated with a high degree of success.24 Hernandez and Wong have reported the successful placement of a DLT using the Glidescope.25 Shulman and Connelly used the Bullard laryngoscope in a group of 29 patients scheduled for general anesthesia and lung separation.26 A DLT was successfully passed into the trachea in 28 of the 29 patients using the Bullard laryngoscope. Hirabayashi and Norimasa used the Airtraq laryngoscope to place #35 or #37 DLTs in 10 patients.27 Nine of the 10 patients had a CL Grade 1 to 2 view on DL with a Macintosh blade. Suzuki et al reported the successful intubation of a patient with a #39 DLT using the Pentax AirwayScope with a modified blade.28 Poon and Liu used the AirwayScope to place an Airway Exchange Catheter (AEC) into the trachea and then railroaded a #37 DLT over the catheter under visual control using the scope.29 Intubation with a DLT using the Bonfils intubation fiberscope30 and Wu scope31 have also been reported.
Retrograde intubation is an option in the clinical scenario presented here if the equipment and expertise are available.32,33
Intubation with an SLT or AEC through an LMA or ILMA is also an option.34 Intubation by transillumination utilizing a lighted stylet is a nonvisual technique and is not recommended in the presence of pharyngeal masses or anatomic abnormalities of the upper airway.35,36 However, placement of DLTs using a lighted stylet under general anesthesia in patients with predictors of difficult DL but without airway pathology has been reported.22,37,38
In the case presented here, a flexible bronchoscopic intubation under general anesthesia was attempted but the vocal cords could not be visualized. The glottis was visualized with the Glidescope but the larynx was noted to be extremely anterior and neither a bougie nor an ETT could be passed through the glottis because of the acute angle that needed to be negotiated up into the larynx. An ILMA was placed and satisfactory ventilation was achieved. The flexible bronchoscope was passed through the ILMA but the vocal cords could not be identified. The patient was ventilated through the ILMA until the muscle relaxation could be reversed and then awakened.
36.3.3 What Should Be the Next Steps in This Patient's Management?
The patient requires urgent surgery. He was transported to the post anesthesia care unit (PACU) for a period of observation. An explanation of the airway difficulty was provided to the patient, an antisialogogue was administered, and the patient was returned to the OR about 2 hours later for an awake flexible bronchoscopic intubation.
Awake flexible bronchoscopic intubation using an adult bronchoscope and an 8.5-mm ID SLT was performed under topical anesthesia (see Chapter 3). A remifentanil infusion was used to attenuate airway reflexes. The awake intubation was uneventful and was followed by the controlled induction of general anesthesia.
36.3.4 Can Awake Flexible Bronchoscopic Intubation Be Done with a DLT?
Successful awake flexible bronchoscopic intubation with a DLT has been reported by Patane et al.23 The laryngeal and carinal stimulation produced by the DLT requires profound anesthesia of the airway.23 When the DLT has been placed in the trachea, general anesthesia can also be induced before advancing the DLT into the mainstem bronchus under flexible bronchoscopic control.
36.3.5 What Are the Options for Lung Separation in This Case Now that an SLT Has Been Placed?
The options for one lung ventilation include use of a bronchial blocker passed through the SLT or exchange of the SLT for either a Univent tube or a DLT using an AEC and under visual control utilizing a video laryngoscope.2,9,15,39,40
In the case presented here, it was decided to proceed with the placement of a bronchial blocker and not to exchange the SLT for a DLT. This decision was based on the degree of difficulty anticipated with the tube change and the risk associated with this maneuver, as well as the possibility of the requirement for post-op ventilation. An Arndt WEB was chosen and placed uneventfully.
The surgical procedure required 8 hours to complete. The estimated blood loss was 8000 mL. Eleven units of packed red blood cells, 1500 mL of plasma, 8 units of platelets, 6000 mL of crystalloid, and 1500 mL of colloid were administered. At the end of the case, edema of the face and tongue was evident.