OPA sizing

Orolpharyngeal Airways (OPA's) are one of the most simple and commonly used supraglottic airways in emergency medicine. OPA's are a semi-rigid tube that maintain the airway patency of unconscious patients by preventing the tongue from relaxing back and occluding the glottis. They have been in use since 1933 (Guedel), yet there is little consensus as to the best method for estimating the correct size.

There are several landmarking methods recommended internationally, with differing bodies suggesting one or more of the following techniques:

         1. Corner of the mouth to the angle of the mandible (MM) - AHA

         2. Corner of the mouth to the tip of the earlobe (ME)- Red Cross

         3. Front of the maxillary incisors to the angle of the mandible (IM) - ERC

These landmarking guides have been in use for quiet some time; although there has been no direct evidence, until now, on how well each measuring method approximates the patients actual airway length.

A group from Yonsei university has helped to shed some light on this dogmatic practice. Their study, recently published a study in the European Journal of Anesthesiology, examined how closely two different OPA sizing techniques estimated a patients overall airway length. The two methods used were: the corner of the mouth to angle of the mandible (MM); and tip of the maxillary incisors to the angle of the mandible (IM). Primary outcome measures were adequacy of ventilation, degree of airway obstruction, trauma to the airway, and distance of the OPA from the epiglottis. This was a prospective randomized crossover study of 113 patients. The population was drawn from a pool of individuals undergoing elective surgery. Patients with any form of functional limitation, airway abnormality, history of difficult intubation, c-spine injury, dental problems, or anticipated difficulty were excluded. The patients were than randomly assigned to have and OPA sized and inserted using either the MM or the IM method of sizing. Prior to surgery all patients had standard monitoring (NIBP, Pulse Oximetry, and ECG) initiated and anesthesia induced. Once paralysis was confirmed a physician blinded to experimental group ventilated each patient without an airway; both manually with a BVM, as well as mechanically, and graded the compliance of the patients airway  (control). OPA's were than inserted in a uniform manner (inverted with 180 degree rotation at the hard palate) and airway compliance was again graded using both manual and mechanical ventilations. Airway placement was than assessed using bronchoscopy to determine the difference between the OPA length and the tip of the epiglottis. The OPA was than removed and the airway was examined for any trauma.

Although both techniques for OPA insertion yielded better ventilation compliance than no airway at all, the IM group tended to have better ventilatory compliance and closer approximation to actual airway size. Because the IM group tended to receive longer airways there were instances of the OPA passing beyond the epiglottis (is this a risk?), although the shorter length airway in the MM group saw ~38% of patients have a fully occluded airway.


This study appears to be the first one that examines the correlation between anatomical measurements and airway length. It is well designed in that it uses patients as their own control. However it has a small sample size, and the patients were all well without airway difficulties. Additionally the sizing method may not fairly represent the commonly held method as airway size was rounded down to the nearest size; whereas, anecdotally at least, I have always been taught to round up to the nearest size, Furthermore the airway obstructions impacted only the mechanically ventilated patients, as all manually provided breaths were successful. These concerns notwithstanding this is the first study to validate how well different OPA sizing methods are. It would seem to suggest that the IM method for estimating OPA size is superior to the MM method, because this an easily disseminated and adopted practice, and there is an absence of foreseeable harm associated with one technique over the other I would suggest that this is a practice change that should be embraced by clinicians across all levels of care.







Deakin, C. D., Nolan, J. P., Soar, J., Sunde, K., Koster, R. W., Smith, G. B., & Perkins, G. D. (2010). European resuscitation council guidelines for resuscitation 2010 section 4. Adult advanced life support. Resuscitation,81(10), 1305-1352.

Guedel, A. E. (1933). A nontraumatic pharyngeal airway. Journal of the American Medical Association, 100(23), 1862-1862.

Kim, H. J., Kim, S. H., Min, N. H., & Park, W. K. (2016). Determination of the appropriate sizes of oropharyngeal airways in adults: correlation with external facial measurements: A randomised crossover study. European journal of anaesthesiology.

Neumar, R. W., Otto, C. W., Link, M. S., Kronick, S. L., Shuster, M., Callaway, C. W., ... & Passman, R. S. (2010). Part 8: Adult advanced cardiovascular life support 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care.Circulation, 122(18 suppl 3), S729-S767.

Red Cross