SUMMARY
Cricoid pressure is used to reduce the risk of aspiration during rapid sequence induction. The recommended force applied to the cricoid is 10-20 newtons (N; 1.020-1.040 kg) on awake patients and 30-40N (3.060-4.080 kg) on anaesthetised patients. However clinically, it is difficult to estimate the required force. We assessed the effectiveness of 3 recommended teaching methods on the ability to apply the correct force using an airway model that simulated “awake” and “anaesthetised” patients.
Thirty nurses and doctors from two hospitals and with clinical experience applying cricoid pressure were included. Measurements of baseline force for “awake” and “anaesthetised” patients were obtained from all participants using measuring scales. Participants were blinded to the force applied. Participants were taught one of three different techniques: biofeedback, nose and syringe. Post-teaching, blinded force measurements were repeated. Data analysis was performed using a linear mixed model and marginal prediction models of applied force reported.
For “awake” patients, nose method forces were within the recommended range (mean 14.6N, 95%CI 9.7-19.4). The biofeedback method led to predicted forces at the upper limit of recommended (21.6N, 95%CI 16.7-26.4) and the syringe method forces were greater than recommended (29.0N, 95%CI 23.9-34.0). For “anaesthetised” patients, nose method forces were less than recommended (26.3N, 95%CI 21.6-31.1), the biofeedback method led to predicted forces within range (33.4N, 28.4-38.3) and syringe method forces were above those recommended (40.8N, 95%CI 35.8-45.8).
The biofeedback technique is the most effective method for teaching the application of recommended cricoid pressure force for both awake and anaesthetised patients.
Cricoid pressure, first described by Sellick in 1961, is used to reduce the risk of aspiration during induction by posterior displacement of the cricoid cartilage ring and compressing the oesophagus. Sellick recommended that cricoid pressure should be applied “lightly” whilst a patient is awake and “firm” when they are unconscious[1].
Several caveats are relevant to the application of cricoid pressure; one must be able to locate the cricoid cartilage correctly, know when to apply the pressure, know the direction that the pressure is applied and apply the correct force when the patient is awake and anaesthetised[2]. This study focuses on the cricoid pressure force and does not discuss these other aspects further.
Recommended force applied during cricoid pressure varies amongst the literature but is generally 10-20N (1.020-1.040kg) on awake patients and 30-40N (3.060-4.080kg) on anaesthetised patients[3–10]; however, it is difficult for staff to estimate this required force accurately in clinical practice[9,11].
For awake patients, a force greater than 10N is required to prevent aspiration, whilst a force greater than 20N can cause pain and retching. For anaesthetised patients, a force greater than 30N is required to prevent aspiration, whereas a force greater than 40N can cause trauma to the larynx[9]. Studies suggest that most assistants apply less cricoid pressure than is required during intubation[4,12–14].
Multiple methods have been described in the literature to teach the required cricoid pressure force. The most common methods include biofeedback[2,10,15–19], nose[7], and syringe[8,20]. In brief, biofeedback methods include an airway model connected to measuring scales and participants use real-time feedback to apply the recommended force to the model[2,10,15–19]. For the nose method, participants are instructed to use sufficient pressure to cause pain if applied to the bridge of the nose for anaesthetised patients[7]. The syringe method involves pressing the plunger of a 50ml closed syringe to specified depths, which are equivalent to the recommended forces for awake and anaesthetised patients[8,20].
Whilst most studies have reported the biofeedback and syringe methods to be effective in teaching the required force of cricoid pressure[8,17,20], there is limited research evaluating the nose method; albeit Escott et a l.[7] reported that the nose method did not appear useful in teaching cricoid pressure force.
The aim of our study was to evaluate the comparative effectiveness of the biofeedback, nose and syringe methods of teaching the recommended cricoid pressure force on “awake” and “anaesthetised” patients using an airway model.