Regional anesthesia in difficult airway: The quest for a solution continues.

Difficult airway, a scenario with potentially life threatening outcome, is routinely encountered by an anesthesiologist leaving him with the dilemma of whether to use regional anesthesia (RA) or general anesthesia. Our study aims to look into this problem. The literature search was performed in the Google, PubMed, and Medscape using key words "regional anesthesia, difficult airway, pregnancy, ventilation, intubation, epidural anesthesia, nerve blocks." More than 38 free full articles and books published from the year 1987 to 2014 were retrieved and studied. At first sight, RA may appear to offer an ideal solution as it helps to avoid the problem of difficult airway. However, the possibility of a total spinal block, failed or incomplete RA, local anesthetic toxicity or unforeseen surgical complication may make it imperative that the airway is secured. The correct decision can only be made by the anesthetist when all the relevant clinical information is taken into account. It is also important to ensure that before considering RA in a patient of difficult airway, an anesthesiologist must have a preformulated strategy for intubation.

INTRODUCTION

Difficult airway remains the greatest challenge faced during the administration of anesthesia on a day to day basis. Maintaining a patent airway is essential for adequate oxygenation and ventilation and failure to do so, even for a brief period of time can be life threatening. We, as anesthesiologists, are sometimes caught in a dilemma of choice of anesthesia in difficult airway patients and feel very comfortable by giving regional anesthesia (RA), thus saving ourselves from having to manage a difficult airway. However, one can't be lucky every time. We, therefore, undertook this study to know the pros and cons of RA versus general anesthesia (GA) in a difficult airway scenario. The literature search was performed in the Google, PubMed, and Medscape using key words “regional anesthesia, difficult airway, pregnancy, ventilation, intubation, epidural anesthesia, nerve blocks.” More than 38 free full articles and books published from the year 1987 to 2014 were retrieved and studied. The American Society of Anesthesiologists (ASA) task force defined a difficult airway as “the clinical situation in which a conventionally trained anesthesiologist experiences difficulty with mask ventilation, difficulty with tracheal intubation, or both.“[1] The task force further noted that the “difficult airway represented a complex interaction between patient factors, the clinical setting, and the skills and preferences of the practitioner.”

Successful mask ventilation would imply the ability to adequately ventilate and oxygenate a patient using a mask, circuit, and supply of oxygen. The ASA task force defined difficult mask ventilation as occurring when:

It is not possible for the unassisted anesthesiologist to maintain the SpO2>90% using 100% oxygen and positive pressure mask ventilation in a patient whose SpO2 was >90% before anesthetic intervention; and/or

It is not possible for the unassisted anesthesiologist to prevent or reverse signs of inadequate ventilation during positive pressure mask ventilation.

The incidence of failed intubation in the parturients has been estimated between 1.3 and 3/1000 and of difficult endotracheal intubation, of 64/1000.[23] Therefore, the most crucial, part of the physical examination is the assessment of airway to avoid disaster associated with airway problems. Mallampati classification used alone is imprecise. If combined with other predictors of difficult airway criteria (thyromental distances, neck extension, interincisor space, submandibular compliance), the specificity and sensitivity of the preoperative assessment are improved.[4] If all the above tests are positive, the anesthesiologist should have a high index of suspicion that airway maintenance would be difficult in anaesthetized patient.

Difficult airway is routinely encountered while administering anesthesia to obstetric cases, in cases of morbid obesity and in surgeries on elderly population. Difficult airway in obstetric cases is mostly due to airway edema, friability of mucosal tissues caused by hormonally induced fluid retention as well as the weight gain associated with pregnancy. In addition, evaluation of the airway may need to be repeated, since changes may occur throughout the pregnancy as well as during the course of labor.[5] Difficult endotracheal intubation is also seen in elderly patients due to degenerative changes such as dental loss and head and neck joint changes.[6789] Difficult airway situation may arise when access to the oral cavity is impeded by unfavorable anatomy such as a small mouth, receding jaw as well as by a reduced mouth opening due to radiation therapy, jaw fracture, or previous head and neck surgery. Tumor infiltration, scarring from radiation, burns, surgery may affect visualization of the larynx.[10] Difficulty in neck extension may be seen in patients due to prior cervical fusion or advanced osteoarthritis or in cases of short neck or dwarfism. In addition, neck extension is contraindicated in patients with unstable cervical spines due to fractures, rheumatoid arthritis, Down's syndrome, etc. Difficulty in mask ventilation may occur in patients with a large tongue, heavily bearded individuals, edentulous patients or those who are morbidly obese. Finally, there is a group of patients who cannot be intubated using direct laryngoscopy due to anatomical variations even though their airway appears to be normal.[11]

When facing a scenario of a difficult airway, the anesthetist has to choose between either RA or GA. In such situations RA may appear to be an ideal option considering the problems that might arise in establishing an airway. However, as stated by Benumof.[12] “Use of RA in patient with a recognised difficult airway does not solve the problem of the difficult airway; it is still there.” In RA techniques, situations may arise which necessitate the conversion of the RA to a GA. Major concerns are:

What if the RA fails or the effect is partial or incomplete?

The likelihood of the failure of regional technique cannot be predicted because it depends upon the skill and experience and sometimes, the luck of the anesthesiologist performing the nerve block

What if there is a high or total spinal anesthesia?

The fall in oxygen saturation, apnea, and the cardiovascular compromise that may ensue will necessitate a conversion to GA

What if there is a sudden deterioration of patient's condition during surgery?

There may be blood loss leading to hypotension, hypothermia, myocardial ischemia or infarction, hypoglycemia, bronchospasm/laryngospasm, anaphylaxis, transfusion reactions, or seizures. In such circumstances, an immediate and sometimes unplanned endotracheal intubation is required

What if there is a toxicity of local anesthetics?

As in RA, we are using local anesthetic drugs, there is always a possibility of an allergic reaction or local anesthetic systemic toxicity (LAST). LAST may be diagnosed in a patient having altered mental status, neurological symptoms or cardiovascular instability after a RA. Management protocol involves immediate focus on airway management, intubation, and ventilation with 100% oxygen

What if there is an unforeseen or accidental prolongation of surgery?

RA generally should not be elected for a patient with a known difficult airway if the surgery cannot be terminated rapidly (in case of failed or inadequate block) or access to the patient airway is compromised. Important questions are:

Will surgery require the patient to be in a position on the operating table which compromises the anaesthetic or maintenance of the airway?

Is endotracheal intubation necessary?

Is muscle relaxation necessary? For example abdominal surgery will require use of muscle relaxants

Will hypotension or blood loss be a particular risk? What kind of venous access is required? Is a central line required?

What sort of monitoring is required? Will arterial access be required?

Although uncommon, such complications may arise where a conversion to GA may be required urgently, with the patient sometimes in very awkward surgical postures that may trap an unprepared anesthetist off guard. This conversion may be required at time when the patient's airway is relatively less accessible to the anesthesiologists as well as at a time when deteriorating patient condition mandates hastening the ventilation and intubation process.

Two cases are presented here that highlight the importance of having a definitive airway management plan in patients even if there is a high chance of successful RA.

A 26-year-old primigravida presented at 38-week gestation for an urgent cesarean section delivery due to fetal bradycardia. On examination of her airway, she had prominent, loose incisors, a prominent over-bite, a high-arched palate, and a Mallampati Class IV visibility of oro-pharyngeal structures. A spinal anesthetic was offered to the patient, surgery was started and a live male baby was delivered. During closure, an injury to the patient's left ureter required a urologist to be called in. More than an hour had passed since the spinal anesthetic and with the block height receded to about T7-8 dermatomal level, the patient started complaining of discomfort. A GA was planned with pre-oxygenation followed by a rapid sequence induction. Laryngoscopic attempts failed to reveal any glottic structures (Cormack–Lehane grade 4 view). Oxygenation was maintained, using a face mask and gentle mask ventilation, while senior help was called for. The senior anesthesiologist attempted laryngoscopy with standard Macintosh and McCoy blades without any success. Patient's spontaneous respiration returned, and, considering the futility of any further attempts at laryngoscopy, a size 3 ProSeal™ laryngeal mask airway (LMA) was inserted. The procedure lasted for another hour, and at the end of surgery, as the patient regained consciousness, she spat the LMA out.[13]

An 82-year-old man with controlled hypertension and mild ischemic heart disease presented with a hip fracture and was anesthetized for a hemiarthroplasty. He was edentulous and also undergoing regular tracheal dilatations for tracheal stenosis (computed tomography scan showing the diameter of the narrowest part to be just under 7 mm). Spinal anesthetic was administered. Two hours into the surgery, there was a surgical complication and the implanted prosthesis broke. With the spinal anesthetic wearing off, the patient was informed about the need for a GA. Induction with sevoflurane and intravenous fentanyl was performed. The plan was to maintain spontaneous ventilation at all stages to avoid any dynamic loss of tracheal tone complicating the tracheal stenosis. A classic LMA was inserted, however resulted in an inadequate seal and partial airway obstruction. A fibreoptic bronchoscope was then used to intubate with a size 5 endotracheal tube. Surgery lasted for another 45 min, following which, the trachea was extubated after the return of adequate spontaneous respiration.[13]

A spinal anesthetic, if not contraindicated, is our routine anesthetic for surgeries in these two cases. Techniques of prolonging regional blocks such as combined spinal and epidural (CSE) (over single shot spinal) or other catheter techniques have been advocated in cases where the duration of procedure is uncertain. Both these cases could have been managed with an epidural alone or a CSE, thus allowing continued management of the complications. A successful spinal component of a CSE, however does not guarantee a successful epidural as well. It may be argued that considering a fetal emergency a spinal anesthetic was the correct choice in the first case as it would have saved the additional time taken to place an epidural catheter of a CSE. In the second case, a CSE would have offered more assurance. Therefore, it is prudent to consider catheter techniques in all complicated cases where a GA is best avoided. Both the cases were successfully managed due to the presence of a backup airway management plan. These cases reiterate the notion that, although a regional anesthetic technique helps avoid a difficult airway situation, it does not “manage” the problem, and so an airway management plan should always be discussed with the patient and planned in advance.

Obstetric cases are usually complicated by the presence of morbid obesity as well as the difficult airway scenario associated. RA appears to be the best choice in such a situation. Neuraxial blockade, besides the advantages of an awake patient who is able to protect her airway and is alert to any distress during the operation helps to circumvent the whole difficult airway scenario. Some degree of preoperative preparation is required before GA can be administered to a patient and the comparative ease of administering RA finds favor with most anesthetists. The literature regarding maternal morbidity and mortality strongly emphasizes the increased safety of RA versus GA for obstetrical patients.[1415]

Single shot spinal anesthesia remains the most common type of anesthesia employed. Concerns about the inadequate block associated with epidural anesthesia as well as the relative ease of the procedure of subarachnoid block have led to an increased acceptance worldwide. Generally, a T4-S5 sensory block is needed for adequate anesthesia during cesarean section.[16] Subarachnoid block in such situations provides a dense reliable block of rapid onset. However, it has its own set of limitations. If spinal anesthesia is chosen, the chances of a high spinal blockade occurring remains a potential threat. This is due to the decreased cerebrospinal fluid volume caused by engorged epidural venous plexus, exaggerated curvature of lumbar spine, pelvic fat and hormonal changes of pregnancy. Another significant limitation is the inability to extend the block if anesthesia is inadequate. Many abdominal deliveries are repeat surgeries. They may be associated with potentially greater surgical difficulty, such as the increased risk of placenta previa and a more prolonged surgical time, thus needing an extensive block.

Continuous spinal anesthesia (CSA) technique offers several advantages over single shot spinal anesthesia such as fewer hemodynamic alterations and side effects by enabling the reduction and fractionation of the induction dose through a catheter. The slow onset block of the sympathetic system with this technique allows the cardiovascular system to adapt more easily than when the block is more abrupt as in 1single dose spinal anesthesia. Coker[17] used CSA for cesarean section for a morbidly obese parturient patient with epidural needle and catheter. The development of postdural puncture headache (PDPH) after a dural puncture with an epidural needle can occur; however, the incidence of PDPH in the morbidly obese patient is far less likely.[18] The role of CSA in obstetrics is debatable. Technique failure remains an important issue in the patients of morbid obesity for lower-segment cesarean section. If CSA is chosen with micro catheters then side effects such as inadequate anesthesia and neurolytic effects such as cauda equina syndrome may occur.[19] The importance of avoiding an excessively high block in obese patient who has multiple medical problems including potentially difficult airway cannot be more emphasized.[20]

Another option that appears viable in such a scenario is the use of epidural anesthesia. Epidural anesthesia offers several advantages such as the ability to titrate the dose to achieve the desired level of analgesia, ability to extend the block for prolonged surgery, a decreased incidence and slow speed of developing hypotension, and utilization for postoperative analgesia. Technical problems may be encountered with RA in morbidly obese parturients including difficulty in patient positioning and identification of anatomical landmarks. Locating the midline and the intervertebral space can be difficult due to obliteration of usually palpable bony landmarks such as spinous process by large amount of adipose tissue, requiring repeated attempts at needle placement. Incomplete motor block and shivering sufficient to stimulate myotonic contractions with epidural anesthesia has been reported in patients with myotonic dystrophy. In addition, there is a concern about inadequate sensory block with epidural anesthesia. Because of the difficulty associated with blocking sacral nerve roots, epidural block may be inadequate in up to 25% patients.[21] In addition, there is an increased risk of intravenous placement of epidural catheter due to engorged epidural veins and decrease in epidural space in addition to dislodgement of epidural catheter.

When an obstetric patient with an anticipated difficult airway presents for an urgent surgical intervention, anesthetists must provide safe anesthesia for both mother and child by maintaining adequate maternal oxygenation to avoid fetal asphyxia. Regional procedures are the options of choice in these patients. A 34-year-old pregnant woman at 23 weeks of gestation who was involved in an automobile accident and sustained blunt and penetrating trauma to the left forearm with subsidiary tendon and vascular injuries, required urgent intervention. She was managed successfully with ultrasonography guided infraclavicular brachial plexus nerve block which avoided the need for GA in mother, at the same time avoiding the exposure of fetus to anesthetic drugs.[22]

An alternative approach to a difficult airway scenario involves the use of both RA and GA simultaneously. RA in the form of nerve blocks is used to facilitate fiber optic intubation (FOI) in a patient while keeping him in an awake state till the point where an airway is secured.[23] FOI is regarded as a safe way of managing some airway problems, particularly anticipated difficulty with direct laryngoscopy.[242526] Several authors have reported that FOI can be achieved with considerable hemodynamic stability[272829] under local anesthetic when combined with sedation while producing minimal patient discomfort. Overall, providing topical anesthesia to the nasal and/or oral mucosa in combination with a method to anesthetize the laryngeal/tracheal structures is the most effective and the most commonly chosen plan. However not all anesthesiologists are trained enough and equipment is not available at all centers in addition to technical difficulties one may encounter.

Administering RA in an airway, especially the nerve blocks, does require some degree of practice before the clinician can become proficient in their use. Trying to perform an unfamiliar procedure in an emergent situation is at the very least inadvisable and may even be dangerous. In addition, while it might be attractive to use a combination of several of these techniques at the same time to provide as much anesthesia as possible, this temptation must be tempered with the knowledge that local anesthetics are absorbed very rapidly from the respiratory mucosa and toxic levels may be approached. The patient may be simply unwilling to remain awake during the process of intubation or he may not give consent to the procedures like nerve blocks to administer RA. Laryngobronchoscopy in an awake, unprepared patient can lead to undesirable elevations in the patient's sympathetic and parasympathetic outflow causing excessive salivation and gag and cough reflexes making intubation difficult. Similarly, problems will be encountered in pediatric patients, patients with learning disabilities and patients who are uncooperative due to head injury, intoxication, etc.

Technical difficulties may be encountered while performing these blocks. In a case of enlarged goiter,[30] FOI has been recommended for the airway management. However difficulty in identifying landmarks due to enlarged goiter remains a problem. Another concern is the availability of FOI except for in tertiary centers.

There may be situations where both RA and GA fail to provide a solution to a difficult airway. A classical example of limitation of any type of anesthetic approach can be seen in the patients suffering from achondroplasia. A general recommendation regarding the ideal anaesthetic regime cannot be given in these cases, as both GA and RA present potential problems.[15] Difficult mask ventilation, difficult intubation,[31] risk for cervico-medullary compression, eight-fold higher obesity rate, increased incidence of sleep apnea, restrictive lung diseases at an early age;[32] all these offer limitation to GA. Despite the altered respiratory system, GA is frequently regarded as the method of choice.[33] Due to the anatomical changes in the spine and the craniocervical junction as well as due to an increased incidence of hydrocephalus, neuraxial anesthetics are relatively contraindicated.

Ankylosing spondylitis is another condition which presents a unique set of circumstances creating a dilemma for the anesthetist. The patient presents with an unusual combination of a rigidly fused spine and focal exuberant cervical osteophytosis. As the cervical spine involvement progresses, the decreasing neck extension can progress to a “chin on chest” deformity.[34] Therefore, on one hand, there is a difficult airway scenario, while simultaneously the chances of success of RA are limited by a rigid spine. Majority of studies preferred RA over GA[3536] in patients with diagnosed ankylosing spondylitis. RA is also expected to be difficult but still subarachnoid block through paramedian approach can always be advocated and recommended as first line anaesthetic technique for lower limb orthopedic surgeries.[37]

LIMITATIONS

Our study was limited by the fact that not much has been mentioned in the literature about this topic. We have basically referred to experiences of people who shared them in the form of challenges faced after having given RA in difficult airway scenario. In addition, we have included anticipated difficult airway and have not discussed emergent situations where we suddenly come across difficult airway as it would have been beyond the scope of this article.

CONCLUSION

With all the above information and discussion, we conclude that before considering RA in a patient of difficult airway, an anesthesiologist must have a preformulated strategy for intubation. At first sight RA may appear to offer an ideal solution. However, technical difficulties, procedural complications, longer duration of surgery, unforeseen surgical complication, inexperience of the anesthetist performing the block, psychological mindset of patient who may be unwilling to remain awake during the procedure or of the surgeon who may find it stressful to operate on an awake patient may make it imperative that the airway is secured. The correct decision can only be made by the anesthetist when all the relevant clinical information is taken into account. There is a place for RA in the patient with the difficult airway when it is used by a clinician who has a clear understanding of the risks involved and a clear definition of the type and likelihood of difficulty which may be experienced with intubation or ventilation.[38]

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Conflicts of interest

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