A 34-year-old woman was scheduled for a hysteroscopy under general anesthesia. She was morbidly obese but otherwise healthy. The morning gynecology surgery list was overbooked with five cases, a mixture of ambulatory cases and inpatient cases. On arrival at the patient's cubicle, the anesthesiologist found the curtain was drawn around the patient's bed, and she was donning a hospital gown. The anesthesiologist waited for 5 minutes, but as he had other patients to see, he left without performing the preoperative assessment. Once she was taken to the operating room, the anesthesiologist discovered from chart review that the patient had a history of gastroesophageal reflux. After induction of general anesthesia, the patient could be ventilated but her trachea could not be intubated. A supraglottic airway was successfully placed, and surgery proceeded uneventfully under general inhalation anesthesia. The patient had a bruised upper airway, which caused her some discomfort, but she otherwise recovered and was discharged home later that day.
A 76-year-old man with recurrent lymphoma and an oral tumor mass at the base of the tongue was booked for a biopsy of this mass under general anesthesia. The patient had a history of hypertension treated with amlodipine. He had not been seen in a preanesthetic assessment clinic. On the day of the surgery, the patient was conscious, alert, and oriented without any stridor or breathlessness. An anesthesiologist came to examine the patient and could not see much of the mass with the patient sitting in a chair, opening his mouth maximally, and sticking out his tongue. The anesthesiologist was unable to locate the patient's head and neck CT scan to further evaluate the mass. The surgeon arrived late and did not communicate about the patient with the anesthesiologist. The anesthesiologist induced general anesthesia, but laryngoscopy and intubation proved extremely difficult as the posterior tongue mass, the size of a small lemon, obscured the view of the larynx. The anesthesiologist kept the patient oxygenated and asleep while attempting to use a fiberoptic bronchoscope to intubate the patient. Another anesthesiologist was called, and together they were able to intubate him with the fiberoptic bronchoscope. The biopsy of the tongue mass was obtained, and the patient was extubated and discharged home later that day.
Commentary by Jeanna Blitz, MD
The preanesthetic evaluation is a critical element of providing care to a patient who requires anesthesia for surgery or a procedure. The components of this clinical process include patient evaluation, history taking, and chart review. The goals of the evaluation are to formulate a patient-specific anesthetic plan, educate the patient, and organize all of the necessary resources for the patient's care.(1)
The primary responsibility for ensuring the adequacy of the patient's oxygenation and ventilation during the surgical procedure lies with the anesthesiologist. Anesthetic medications may depress or stop the patient's breathing altogether, and the anesthesiologist must establish successful oxygenation either by manual ventilation by face mask, supraglottic airway device, or tracheal intubation. Failure to establish successful oxygenation in a patient who is not breathing spontaneously may result in brain damage or death within minutes. Brain damage and death attributed to difficulty with airway management is the most common cause of anesthesia malpractice claims.(2)
Difficulty with airway management may be due to one or more causes: failed intubation, inability to manually ventilate the patient by mask, premature extubation, or the sequelae of the aspiration of gastric contents. Assessing the patient preoperatively for risk factors associated with difficulties related to any of the above reasons is crucial in order to formulate an appropriate anesthetic plan. Unfortunately, in neither case example above did such preoperative preanesthetic evaluation seem to occur.
While no preoperative screening test exists that definitively confirms ease of intubation or mask ventilation, specific clinical conditions have been demonstrated to increase the risk of difficulty with either mask ventilation or intubation. Risk factors associated with difficult mask ventilation include obesity, history of snoring, limitations of the cervical spine, and neck abnormalities (Table 1).(3) A separate but related set of clinical factors predict the degree of potential difficulty with placing an endotracheal tube (Table 2).(4,5)
In these two cases, both patients had risk factors for difficulty in establishing successful mask ventilation, as well as for difficulty with intubation. Knowing that the patient's airway may prove challenging allows the anesthesiologist to plan for the anesthetic and to gather necessary resources or additional help prior to starting the case. The patient in the first case may have a thick neck or a high Mallampati score, given her morbid obesity. The patient in the second case is noted to have a pharyngeal tumor for which he has likely undergone radiation therapy to his head and neck. He may have limited range of motion in his neck and lack the ability to protrude his mandible because of prior neck radiation therapy, in addition to the pharyngeal mass, which will likely obscure the view of his glottic opening during laryngoscopy.
Overall, rates of difficult and failed intubations have declined fourfold in the last decade. Prior to 2006, 6.6/1000 intubation attempts were described as difficult, and 0.2 failure to intubate scenarios occurred in every 1000 intubations.(4) By 2010, those rates had declined to 1.6/1000 difficult intubations and 0.06/1000 failed intubations.(4) This decline is thought to be related to a combination of technical and systems advances in safety, such as better access to advanced airway devices, greater participation in simulation sessions, and increased use of an algorithm for the management of the difficult airway.(6) The American Society of Anesthesiologists Difficult Airway Algorithm was created to guide clinician decision-making in a time of increased stress and urgency, when critical decision-making and cognitive processing may lead to a shift toward a shortcut heuristic mental model.(6,7) This emergency airway algorithm has been shown to improve success and patient outcomes.
In a recent study, the incidence of difficult mask ventilation combined with difficult laryngoscopy was found to be 0.4% of 176,679 adult cases.(8) The Difficult Airway Algorithm emphasizes the safety advantage of performing an awake intubation in specific patients at high risk for difficulty with both mask ventilation and intubation.(6) This awake intubation is accomplished by using fiberoptic or video laryngoscopy, but it has limitations related to patient comfort and cooperation. Moreover, it requires additional time and planning to successfully numb the patient's oropharynx with local anesthetic. When an awake intubation is planned, a careful discussion about this technique and the process involved is needed to set expectations with the patient. This conversation should take place during the preanesthetic evaluation and consultation.
Although the patient in the second case likely would have benefitted from securing his airway while he was awake, the cognitive barriers associated with discussing this unpleasant procedure with the patient, the perceived increase in time that it would take to prepare the patient and the equipment for the procedure, and the potential concern about appearing incompetent in front of the surgeon and other operating room staff may have prevented the anesthesiologist from making this decision. Furthermore, because the anesthesiologist was ultimately able to intubate the patient despite difficulty, the clinical decision to induce general anesthesia prior to intubation may be positively reinforced in the provider's mind since "all's well that ends well," despite the clear risk associated with selecting an asleep intubation technique.
A careful evaluation of the patient's airway and plan for airway management is only one component of the preanesthetic evaluation. A complete evaluation also includes consideration of any preexisting medical conditions that may increase the patient's risk for a significant complication related to the anesthetic. The ability to reduce that risk by optimizing the patient's medical status often exists, but may require several days, weeks, or months to fully enact. Furthermore, perceived time pressure when assessing the patient on the day of surgery may lead to the clinician taking decision-making shortcuts, such as in the first case by assuming everything was fine without the examination since the patient was "healthy," or as in the second case by feeling reassured by the presence of additional help and availability of rescue equipment if an emergency arose.
The patient safety benefit of performing the evaluation prior to the day of surgery has resulted in the creation of many different, yet successful models of preanesthetic patient review and evaluation. For example, preoperative evaluation clinics have been associated with a reduction in in-hospital mortality at several institutions.(9,10) However, robust preoperative evaluation clinics may not be feasible for all hospitals due to cost or staffing constraints. In hospital systems without a preoperative evaluation clinic, the preanesthetic evaluation may be initiated by review of the patient's medical records in the days immediately prior to surgery and completed through a patient history and physical examination on the day of surgery. Patient information and risk assessment may also be gathered via screening assessments, patient-entered data via an interface within the electronic health record, and review of prior anesthetic records. This chart review process may be performed by the anesthesiologist assigned to the case, or other designated staff members including anesthesiologists, resident anesthesiologists in training, or advanced practice providers who have been specifically trained in the preanesthetic assessment. In the second case, the anesthesiologist was unable to locate the patient's head and neck CT scan preoperatively to further evaluate the mass. On top of that, the patient was not seen in a preanesthesia clinic for evaluation and review of his records. The ability to review the CT scan may have influenced the anesthetic plan and potentially avoided the adverse event. Team-based models of care may lend "another pair of eyes" and reduce the time constraints associated with performing the preanesthetic evaluation in the timeframe immediately before surgery. However, this model may also lead to the false comfort that someone else has already evaluated the patient and communicated any pertinent details. All patients must be reevaluated immediately prior to administering anesthesia as a condition of participation with the Centers for Medicare and Medicaid Services.(11)
In larger hospital systems, an additional challenge may arise due to their many surgeons and anesthesiologists. Clinicians may not know each other well or work together frequently. Mechanisms to address this challenge include standard practices such as implementing a required preoperative discussion between the anesthesiologist, surgeon, operating room nursing staff, and the patient to ensure that a shared mental model exists. A specific communication tool with prompts and a delineated chain of command to be followed during emergencies in the operating room has also been associated with improved patient safety outcomes.(12)
- Difficult mask ventilation and intubation are critical safety events; loss of control of the patient's airway will lead to hypoxia and brain damage and death within minutes.
- Clinical factors exist to identify patients who are at higher risk of potentially difficult ventilation and intubation.
- A complete evaluation of the airway and knowledge of difficult airway predictors can alert the anesthesiologist to the potential for difficulty with airway management and allow for appropriate planning.
- It is not possible to definitively predict difficulty with airway management. Therefore, the American Society of Anesthesiologists Difficult Airway Algorithm should be used to guide the management of these emergency situations, helping to avoid cognitive processing that may shift toward a shortcut heuristic method of decision making.
- Whenever possible, a standardized, preanesthetic evaluation process should be established and should include review of available information in the electronic health record, screening assessment, and an in-person visit at a preoperative evaluation clinic, if available. None of these processes obviate the need for an in-person patient evaluation by the anesthesiologist on the day of surgery.
Jeanna Blitz, MD
Medical Director, Pre Admission Testing
Department of Anesthesiology, Perioperative Care and Pain Medicine
NYU Langone Health
NYU School of Medicine
New York, NY
Table 1. Predictors of Difficult Mask Ventilation.(3,5)
|Obstructive sleep apnea or history of snoring
|Age older than 55 years
|Body mass index of 30 kg/m2 or greater
|Mallampati classification III or IV
|Lack of teeth
|Cervical spine: limited flexion or extension or unstable
|Abnormal neck anatomy: laryngeal mass, radiation changes, thick neck, tracheal deviation
|Short thyromental distance
|Limited mouth opening
|History of asthma, chronic obstructive pulmonary disease, or recent respiratory illness
Table 2. Predictors of Difficult Intubation.(4-6)
|Long upper incisors, protuberant teeth
|Inability to protrude mandible
|Small mouth opening
|Large tongue or small pharynx
|Mallampati classification III or IV
|High, arched palate
|Short thyromental distance
|Short, thick neck
|Limited cervical mobility
|Previous neck radiation
|History of sleep apnea
|Abnormal head and neck anatomy related to congenital or acquired disease state
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