Open Airway Procedural Sedation

Anatomy and Physiology

Practitioners performing OAPS should possess foundational knowledge of the anatomy and physiology of all body systems. Along with this foundational knowledge, intimate knowledge of normal airway anatomy and potential variations is of utmost importance as most severe complications that occur during OAPS, however rare, involve the respiratory system. In a systematic review and meta-analysis examining the incidence of adverse events occurring during the procedural sedation of adults in the emergency department, aspiration and laryngospasm were the 2 most common severe adverse events that required emergent medical intervention.[2] 

As such, all practitioners performing OAPs should be well-versed in the pre-sedation airway assessment to identify patients who may be difficult to ventilate or intubate. Although there is no single best predictor of difficulty in bag-mask ventilation and intubation, one should be familiar with the commonly assessed variables during the pre-sedation airway evaluation, which has proven useful predictors. These variables include the presence of a beard, age >55, history of snoring, obesity, and edentulism.[3] 

For many reasons, patients with restricted mouth openings of less than 2.5 cm are poor candidates for OAPS. These include the potential inability to visualize and suction the oral cavity and oropharynx, the potential inability to insert certain airway adjuncts, and the potential inability to perform direct laryngoscopy for intubation. A thorough history of prior airway procedures or congenital malformations should be obtained. The most commonly utilized scale for pre-anesthetic upper airway anatomy assessment is the Mallampati score, a visual grading scale ranging from I-IV, which looks at the distance/space between the base of the tongue to the soft palate, with scores greater than III/IV being more predictive of a potentially difficult airway and intubation.[4] If there are any concerns for potential airway challenges, practitioners should, at the very minimum, re-evaluate the appropriate clinical setting for OAPS in these patients, with a stronger inclination towards hospital/inpatient settings.

Indications

Although there are no absolute indications for OAPS, it should be considered for diagnostic and therapeutic procedures associated with significant physical or emotional discomfort. According to the parameters outlined by the American Society of Anesthesiologists, the depth of sedation for OAPS ranges from minimal sedation or "anxiolysis" to deep sedation. The depth required for each patient is determined by multiple considerations, including the level of pain anticipated and the need for akinesia.

Contraindications

There are no universally accepted guidelines that outline strict/absolute contraindications for OAPS, as many life-saving procedures need to be performed on patients regardless of their underlying comorbidities. Nonetheless, a thorough and pertinent history and physical exam should be performed on every patient to assess the patient's overall perioperative health. The ASA Physical Status Classification System, created in 1941, is a valuable grading system that is used to evaluate and communicate a patient's level of overall perioperative health before surgery and the administration of anesthesia:

• ASA class I represents normal, healthy patients
• ASA class II represents patients with mild systemic disease(s)
• ASA class III represents patients with severe systemic disease(s)
• ASA class IV represents patients with severe systemic disease(s) that pose a constant threat to life
• ASA class V represents patients who are moribund and not expected to survive without the operation
• ASA class IV represents patients who are declared brain-dead and whose organs are being harvested for donor purposes[5]

Additionally, multiple tools can aid in the perioperative risk stratification of patients before surgery and anesthesia. Examples include the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) calculator and the Revised Cardiac Risk Index (RCRI).[6][7] 

Alternative anesthetic techniques should be considered for patients with significant comorbidities, and careful consideration should be given to the setting where anesthesia is being administered. For example, anesthesia for patients considered ASA III and beyond might be best administered in the hospital/inpatient rather than outpatient clinic setting. Additionally, OAPS should only be performed by those with the appropriate training and certification outlined by their governing bodies.

Equipment

Before performing OAPS, practitioners should have the following equipment and supplies either open or readily available:

• Monitoring equipment and a stethoscope assist in monitoring a patient's blood pressure, heart rate, EKG, end-tidal CO2, pulse oximetry, and temperature. 
• Supplies to establish intravenous access
• A suction device with a Yankauer suction tip
• Airway supplies to include a bag-valve-mask, supraglottic airway, bougie, direct or video-assisted laryngoscope with appropriate blades, oropharyngeal and nasopharyngeal airway adjuncts, and endotracheal tubes of appropriate sizes
• Supplemental oxygen delivery equipment to include a nasal cannula, simple face mask, and high-flow oxygen mask
• Appropriate rescue medications and reversal agents

All equipment/supplies should be routinely checked for expiration, and practitioners and personnel involved in OAPS should regularly review their proper usage.

Personnel

The personnel typically involved in outpatient OAPS include the operator surgeon, anesthesiologist, credentialed anesthetist, nurse, technician, or other support staff. In addition, there should be, at minimum, 2 personnel who are certified in Basic Life Support (BLS), Advanced Cardiac Life Support (ACLS), and, depending on the patient population, Pediatric Advanced Life Support (PALS) as warranted. Local regulatory agencies may have varying requirements, and thus, the regulations set forth by these organizations should be reviewed in detail.

Preparation

In addition to their systematic approach, practitioners should utilize their facility's established Universal Protocol and surgical time-out guidance to prepare for OAPS.[8] A typical pre-operative checklist includes the following:

1. Verification of the patient's identity, the proposed procedure, and documented consent
2. Verification of pertinent past medical history, recent changes, as well as documented allergies
3. Verification of nil per os (NPO status)
4. Marking of the surgical site and laterality as appropriate
5. Ensuring that all appropriate anesthesia-related medications and supplies are present or readily available, functioning, and not expired - this should include rescue medications, reversal agents, and airway supplies
6. Ensuring that all of the appropriate monitoring equipment is properly attached
7. Ensuring that all of the appropriate procedure-related armamentarium and imaging are available
8. Appropriate patient positioning

Technique or Treatment

An ideal anesthetic agent should possess analgesic, sedative, and amnestic properties with a rapid onset and short duration of action, allowing for quick recovery and discharge of patients. Unfortunately, at the time of this writing, no such single agent that possesses all of these properties exists. Therefore, it is common practice to utilize a combination of agents to carry out OAPS, although single-agent OAPS is not uncommon. For example, while there is no standard regimen, most practitioners utilize a combination of a short-acting benzodiazepine such as midazolam and an opioid such as fentanyl for OAPS in adult patients, taking advantage of the anxiolytic, sedative, and amnestic properties of benzodiazepines, and the analgesic properties of opioids. That being said, numerous other medications are often employed, either as sole agents or in combination, like ketofol (ketamine and propofol). Many studies have shown this combination to have fewer adverse effects like respiratory depression compared with single-use agents.[9][10][11]

Benzodiazepines

• One benzodiazepine commonly utilized during the perioperative period is midazolam. It has advantages due to its effects on anterograde amnesia and anxiolysis.
• Midazolam
• DOSE: For healthy adults, an initial dose of 1 to 2 mg IV, followed by further 1 to 2 mg doses every 3 to 5 minutes until the desired effect is achieved. It is uncommon to require greater than 5mg.
• ONSET: When given intravenously, less than 1 minute.
• DURATION: The peak effect occurs at 3 to 5 minutes, and its sedation effects can last 15 to 80 minutes.
• REVERSAL: Flumazenil, 0.2 mg IV over 15 seconds with additional 0.1 mg doses every minute until the desired effect is achieved.[12] It is important to monitor for re-sedation as the duration of flumazenil may be shorter than midazolam.

Opioids

• The most frequently utilized opioid during OAPS at present is fentanyl. It is a synthetic opioid with multiple routes of administration, and although it possesses sedative properties, it is primarily utilized during OAPS for its analgesic properties. One of the benefits of it over other opiates like morphine is that it causes less histamine release and theoretical hypotension and side effects like itching.[13]
• Fentanyl
• DOSE: 1 to 1.5 mcg/kg given as an initial dose, with further doses of 0.5 to 1 mcg/kg given every 10 to 20 minutes.
• ONSET: When given intravenously, less than 1 minute.
• DURATION: Effects can last between 30 to 60 minutes.
• REVERSAL: Fentanyl-related respiratory depression, the most notable potential adverse effects of fentanyl and opioids in general, can be reversed with Narcan (naloxone), a pure opioid antagonist. An initial dose of 0.4 to 2 mg IV can be given, followed by further doses 2 to 3 minutes apart. Although effective for the aforementioned purpose, naloxone can come with unwanted effects such as tachycardia, hypertension, nausea, vomiting, and seizures, to name a few.

Propofol

• A commonly utilized anesthetic for both general anesthesia and OAPS. It has sedative, amnestic, and anti-emetic properties and quick onset and offset times, which are more favorable for OAPS.
• DOSE: A typical sedation dose can range from 25 to 100 mcg/kg/min. It can be administered in boluses or as a continuous infusion.
• ONSET: less than a minute.
• DURATION: 5 to 10 minutes.

Ketamine

• A dissociative anesthetic with sedative, analgesic, and mild amnestic properties. The main factor limiting its use is its association with unpleasant emergence reactions. It is also associated with laryngospasms that are not associated with identifiable risk factors.[14] It also causes increased secretions and acts as an indirect sympathomimetic to increase heart rate and blood pressure. 
• DOSE: 1 to 2 mg/kg IV as an initial dose. Smaller doses can be given if analgesia without dissociation is desired (0.2 to 0.8 mg/kg IV).
• ONSET: less than a minute.
• DURATION: 5 to 15 minutes.

Knowledge of these 4 medications gives any provider a good foundation of OAPS techniques. Many other agents can be utilized during OAPS for specific reasons, but these are beyond the scope of this topic.

Complications

The most commonly encountered complications involve maintaining a patent airway or managing a compromised airway. Examples include respiratory depression-related hypoxia, emesis and aspiration, laryngospasm, bronchospasm, and allergic reactions/anaphylaxis. Other less common but severe complications include seizures, myocardial infarction, cardiac arrest, and stroke. All providers must have the skills, equipment, and knowledge to manage these conditions emergently and transfer to a higher level of care when appropriate. A comprehensive knowledge base in pre-operative assessment/patient selection, airway management, ACLS, PALS, and anesthesia is critical in mitigating and managing the complications of OAPS. In addition, monthly reviews of emergency scenarios and their management can reduce adverse outcomes to airway-related complications. 

For example, one should know the signs and symptoms of laryngospasm, including inspiratory stridor, loss of end-tidal CO2 waveform, and hypoxia. It should be managed algorithmically to ensure the patient maintains adequate oxygenation and recovers ventilation. This is done by delivering continuous positive airway pressure by Bag Valve Mask (BVM), increasing the depth of anesthesia, and finally administering an initial partial dose of succinylcholine (0.1 to 0.5 mg/kg IV) and, ultimately, a full dose (1 to 1.5 mg/kg IV) for attempted intubation.[15]

Clinical Significance

When executed by a well-trained and knowledgeable practitioner, regardless of training background, OAPS can be a safe, efficient, and humane way of performing procedures that would otherwise be intolerable due to pain, discomfort, or emotional stress.

Enhancing Healthcare Team Outcomes

The practice of open-airway procedural sedation is a prime example of the practice of medicine as a team sport, requiring all those involved to be in sync with one another during all phases of care, operating as a cohesive interprofessional team. The individuals performing the procedure and the sedation, if not the same person, should be in regular communication to provide the highest level of care, as various levels of sedation are required during specific stages of each procedure. Additionally, attentiveness from well-trained ancillary support staff leads to improved workflow and identification of potential perioperative issues that may have gone unnoticed. This interprofessional approach leads to improved patient outcomes with open-airway procedural sedation.