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.