Making the Switch to LMAs

Anesthesia

By: Wanda Wilson

Published: 10/10/2007

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What you need to know before using these devices in your center.


Why has the laryngeal mask airway found favor in same-day surgery? In large part because the device facilitates the fast-track approach to rapid post-anesthesia recovery. After all, we all want minimal residual effects and fast induction and emergence characteristics for the general anesthetic agents delivered in our ORs. I'm going to discuss how LMAs can minimize room turnover time, increase case efficiency and offer the possibility of safely adding more patients to your already busy day.

For the uninitiated, the LMA is lubricated on the posterior surface of the device and inserted blindly into the hypopharynx so that, once the cuff is inflated, the LMA forms a low-pressure seal around the entrance to the larynx. Use of a bite block (rolled 4x4 gauze or dental bite guard) and correct taping stabilizes the LMA and prevents potential occlusion of the tube.

When the LMA is correctly positioned, the anterior margin of the LMA lies at the base of the hypo-pharynx, with the tip at the esophageal opening against the upper esophageal sphincter. The cuff's lateral edges lie in the piriform fossae and the upper border lies at the base of the tongue below the tonsils.

Since its introduction in the 1980s, LMA use has increased in a wide variety of patients and clinical settings, despite the disadvantage of possible aspiration. The U.S. Food and Drug Administration approved the LMA in 1991. LMA North America, the first company to market the device, is now joined by several competitors producing many variations of the device.

Some LMAs are designed to minimize obstruction and allow passage of the fiberoptic scope or endotracheal tube. Others feature dual tubes to separate the respiratory and gastrointestinal tracts. Choice of LMA can be based on provider preference or a specific indication. After carefully assessing the airway, the anesthesia provider selects the optimal size based on a patient's weight and anatomical features to ensure safe, effective use. The devices range in size, classified from 1 to 6. Use of an oversized LMA is associated with a degree of throat soreness and hoarseness, while an undersized LMA predisposes patients to anesthetic gas leakage.

Pluses, minuses
LMA technique has improved anesthetic delivery for the patient and the provider. The technique is easy to teach and learn compared with endotracheal intubation. Advantages of anesthetic delivery via the LMA include decreased airway resistance, minimized dead space, minimal neurocirculatory response to insertion, less stimulation of the airway receptors and reflexes, and lower anesthetic requirement for tolerance of the airway device.

My Second Look at LMAs

I started my anesthesia training in the 1980s, when the laryngeal mask airway didn't exist. As I began to focus my practice on ASC and office-based anesthesia services, I became an expert at various levels of sedation and performed less and less general anesthesia. Occasionally I'd find myself in an ASC where the LMA was an emerging tool, but I was reluctant to use it. Plus, my initial use of the LMA was unsatisfactory because I hadn't trained on the device during school or my early years in practice. Every sonorous breath, every fleck of heme noted after insertion of the slightly mal-positioned device caused me great anxiety, even though my patients were never compromised.

One of my ASC practice settings recently added a general plastic surgeon. While much of our caseload (blepharoplasties, facelift, browlifts) could be satisfactorily and safely anesthetized with varying degrees of sedation, and other cases (liposuction with the patient needing to be both prone and supine) were predisposed to general endotracheal techniques, other cases made me seriously reconsider use of the LMA.

I spoke to many colleagues about their techniques and experiences and I devised a reasonable care plan specifically designed for patients undergoing abdominoplasty, breast augmentation or reduction mammoplasty.

My technique includes careful screening of patients for airway anatomy and reflux, pre-op sedation with 2mg of midazolam, pre-induction xylocaine 70mg to 100mg, fentanyl 50mcg and induction with 150mg to 200mg of propofol. The slightly inflated, well-lubricated LMA is inserted using a tongue blade to assist placement. I find that most adult patients are well served by a #3 LMA for both ease of insertion and quality of airway patency. All patients resumed spontaneous respiration within several minutes of induction.

Anesthesia is maintained with 60 percent nitrous oxide, propofol drip at 100 mcg/kg/min to 120mcg/kg/min and fentanyl titrated to respiratory rate. During abdominal muscle plication or creation of the sub muscular pocket and breast implant insertion when more profound relaxation is desired, I merely give a propofol bolus and increase my ventilatory assistance. I tend to remove the LMA from patients in deep sedation to avoid coughing and bucking in the newly plicated abdomen.

With increased experience, I've become adept at using the LMA. I've had the occasional difficult insertion, but I'm impressed with the short LMA learning curve and the minimal narcotic needed when titrating to respiratory rate. With the inclusion of 30mg ketorolac in my care plan, I have comfortable, awake and alert patients ready for timely post-op discharge.

- Jay Horowitz, CRNA

Mr. Horowitz ("[email protected]")), a nurse anesthetist in Sarasota, Fla., is a member of the Outpatient Surgery editorial board.

Anesthesia providers benefit from improved maintenance, support and partial seal of the airway; freeing of the provider's hands in the surgical field and reduced fatigue; avoidance of facial nerve injury and eye injuries among patients due to face masks; and no requirement for muscle relaxation or laryngoscopy for placement.

Additionally, providers see a lower incidence, severity and duration of sore throat when compared to endotracheal intubation and less air pollution in the operating room. Other advantages may include lower incidence of patient coughing and improved oxygen saturation during emergence.

LMAs are most useful in solving emergencies resulting from difficult or failed intubations. The device plays a significant role in the difficult airway algorithm of the American Society of Anesthesiologists, either as an airway ventilation device or conduit for a fiberoptic scope.1 It also became part of the American Heart Association's guidelines for CPR and emergency care and is used as an airway management tool in cardiac arrest.2

LMA use does have disadvantages, including possible gastric distention, aspiration of gastric contents, coughing, laryngospasm and trauma to the airway if difficult to place. Knowing that the LMA has potential risks and cautions, the anesthesia provider should fully understand the proper use and selection of appropriate patients.

Contraindications of LMA use include

  • the inability of the patient to extend his neck or open his mouth >5cm;
  • pharyngeal pathology such as anatomical abnormalities or tumors in the airway;
  • airway obstruction at or below the larynx;
  • low pulmonary compliance and high airway resistance;
  • inadequate depth of anesthesia;
  • increased risk of regurgitation (incompetent lower esophageal sphincter)
  • morbid obesity; and
  • one-lung ventilation.

Clinical studies document a low incidence of clinically detectable regurgitation with the LMA.3,4 Still, anesthesia providers should take precautions to minimize or prevent regurgitation and aspiration. Steps to minimize risks include selecting appropriate patients while considering the surgical procedure, having an adequate depth of anesthesia for insertion of the LMA and maintenance during surgery, avoiding gastric distension and ensuring return of protective airway reflexes before you remove the LMA.

Anesthetic agents
Propofol is the recommended induction agent for the LMA technique. Insertion of the LMA is usually achieved within 30 seconds of induction, provided the level of anesthesia is adequate.5 Propofol appears to obtund the upper airway reflexes and produces appropriate relaxation, facilitating LMA insertion.5 Other induction agents, like thiopental, don't appear to create the ideal condition for insertion. Propofol has a shorter half-life and offers antiemetic, anxiolytic and euphoric effects.

The most common problem encountered with the insertion and tolerance of the LMA is directly related to inadequate depth of anesthesia, regardless of the anesthetic agent used. The propofol induction technique can be improved with the titrated addition of intravenous agents such as midazolam, fentanyl and lidocaine. These pharmacological drugs as well as inhaled anesthetic agents suppress the response to noxious stimuli, enhance the conditions for LMA insertion and maintenance of an appropriate level of anesthesia for outpatient surgery.

The LMA has achieved an important role in anesthesia practice worldwide. It is easy and atraumatic to insert with minimal responses from the patient's neurocirculatory systems. The minimally invasive LMA technique reduces the need for muscle relaxants and total anesthetic sedation. As a suitable alternative to the facemask and endotracheal tube in a variety of surgeries, the LMA technique is safe and efficient for airway management and for the delivery and maintenance of anesthesia in the outpatient setting. Most importantly, the LMA can be a life-saving airway device during difficult or failed intubations.

References
1. American Society of Anesthesiologists Task Force on Management of the Difficult Airway. ASA practice guidelines for management of the difficult airway. Anesthesiology. 2003; 98:1269-1277.
2. American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2005; 112:IV51-IV57.
3. Brimacombe JR, Berry A. The incidence of aspiration associated with the laryngeal mask airway: a meta-analysis of published literature. J Clin Anesth. 1995; 7:297-305.
4. Owens TM, Robertson P, Twomey C, Doyle M, McDonald N, McShane AJ. The incidence of gastroesophageal reflux with the laryngeal mask airway: a comparison with the face mask using esophageal lumen pH electrodes. Anesth Analg. 1995; 80:980-984.
5. Brain AIJ, Denman WT, Goudsouzian NG. LMA Instructional Manual. 1998. San Diego: LMA North America, Inc.

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