The Effects of Cricoid Pressure, Remifentanil, and Propofol
on Esophageal Motility and the Lower Esophageal Sphincter
Kristian Thorn, MD, Sven-Egron Thorn, MD, PhD, and Magnus Wattwil, MD, PhD
Department of Anesthesiology and Intensive Care, Orebro University Hospital, Sweden
tion of anesthesia when there is a risk of aspiration of
to investigate the effects of cricoid pressure, remifen-
and esophageal motility. We recorded LES pressure
gastric pressure) in 10 healthy volunteers using a Dent
sleeve device. There was a significant decrease in LESP
was not seen during the infusion of remifentanil 0.2
?g · kg?1· min?1.Remifentanilperseortogetherwitha
bolus dose of propofol 1 mg/kg IV did not induce any
statistical change in LESP or BrP. Remifentanil abol-
coid pressure. In conclusion, cricoid pressure of 30 N
induced a decrease of LESP and BrP in awake volun-
teers. These effects were not seen during the remifen-
tanil infusion. This shows the importance of when
to apply cricoid pressure during rapid-sequence
(Anesth Analg 2005;100:1200–3)
aspiration. By occluding the esophagus, regurgitation
of gastric contents is prevented from reaching the
respiratory tract. Complete occlusion occurs only at a
force of at least 40 N (2). In 1997, Tournadre et al. (3)
showed that cricoid pressure in awake volunteers in-
duced a relaxation in the lower esophageal sphincter
(LES) at a force of only 20 N. This was even more
profound at 40 N. However, the effect of cricoid pres-
sure during the different steps of complete anesthesia
induction has not been studied. Many anesthesiolo-
gists include both opioids and propofol in rapid-
sequence induction (RSI). The purpose of this study in
volunteers was to investigate the effects of cricoid
pressure, remifentanil, and propofol on the LES and
esophageal motility during an anesthesia induction.
he use of cricoid pressure, described by Sellick
(1) in 1961, is the gold standard during the in-
duction of anesthesia when there is a risk of
After receiving approval from the institutional human
investigation committee and informed written con-
sent, we enrolled 10 healthy nonsmoking volunteers (5
men and 5 women: mean age, 22.5 [21–25] yr; mean
weight, 68.5 [50–98] kg) with no diseases involving the
respiratory, cardiac, or digestive systems. None of the
participants was taking any medication, and all had
fasted for at least 8 h.
Electrocardiogram, noninvasive arterial blood pres-
sure, Spo2, and respiratory rate were monitored in
each volunteer and recorded every 5 min. Bispectral
index (BIS) monitoring was used for registration of
anesthesia depth. All volunteers received oxygen 2
L/min through a nasal catheter.
LES pressure (LESP) and gastric pressure were re-
corded, and then the barrier pressure (BrP) was calcu-
lated (BrP ? LESP ? gastric pressure). We did this
using a Dent sleeve device, which consists of a 5-cm-
long thin-walled silicon sleeve glued along a catheter
(4). After inserting the catheter through the nose and
into the esophagus and stomach, without using any
local or topical anesthesia, the LES was identified us-
ing a pull-through technique, as described by Mittal et
al. (5). Simultaneously, esophageal pressure (1 and 6
cm) and proximal and gastric pressure (1 cm) distal to
the sleeve were measured with side holes. The cathe-
ter was constantly perfused with water at 0.5 mL/min
Accepted for publication September 22, 2004.
Address correspondence and reprint requests to Kristian Thorn,
MD, Department of Anesthesiology and Intensive Care, Orebro
University Hospital, 701 85 Orebro, Sweden. Address e-mail to
©2005 by the International Anesthesia Research Society
Anesth Analg 2005;100:1200–30003-2999/05
per channel using a low compliance system, and the
transducers were set to zero at the mid chest position
and calibrated before each measurement. Pressure
tracings were recorded continuously using a multiple-
channel recording system.
Cricoid cartilage pressure was applied using a
model of the right thumb and the two first index
fingers (Fig. 1), which is in agreement with the appli-
cation in clinical practice. This model applies a con-
stant cricoid pressure of 30 N and has been developed
in cooperation with the medical engineers at our
After a stable period of 15 min of rest, we confirmed
the positioning of the sleeve by letting the volunteers
swallow 5 mL of water. Five minutes later, cricoid
pressure was applied three times, 30 s each time, at
5-min intervals. The pressure was applied at least 30 s
after any voluntary swallowing. After each applica-
tion of cricoid pressure, the experience of discomfort
because of the procedure was assessed using a visual
analog scale (VAS; 0–10 cm). After another 5-min
period of rest, an IV infusion of remifentanil 0.2
?g · kg?1· min?1was started. When this had infused
for 20 min, the sequence of cricoid pressure applica-
tions was repeated as above. Finally, the volunteers
received a bolus dose of propofol 1 mg/kg IV. Two
minutes later, one last cricoid pressure was applied.
This time it was only performed once because of the
short time of deep anesthesia. Then the infusion of
remifentanil was stopped. After another 5–10 min, the
participants had awakened.
The baseline values were calculated as the average
pressure during 30 s at the end of the rest period. The
results during cricoid pressure are the average pressures
during the periods when it was applied. The results
during the infusion of remifentanil alone or together
with a bolus dose of propofol are the average pressures
30 s before each sequence of cricoid pressure.
Analysis of variance followed by the Fisher Pro-
tected Least Significant Test was used for statistical
analysis of the results. P ? 0.05 was considered statis-
There was a small but significant decrease in LESP and
BrP during cricoid pressure in the awake volunteers
(Fig. 2). LESP decreased from 22.2 ? 9.0 to 18.0 ? 7.5
mm Hg (mean ? sd) and BrP decreased from 13.1 ?
10.8 to 10.4 ? 10.5 mm Hg (P ? 0.05). The decrease
occurred in 9 of 10 volunteers. Neither remifentanil
nor propofol had any significant influence on either
LESP or BrP compared with basal levels, and there
was no significant change when cricoid pressure was
applied (Fig. 2). BIS levels were 51.3 ? 8.4 (mean ? sd)
when cricoid pressure was applied after the bolus
dose of propofol.
The cricoid pressure did not induce esophageal pro-
pulsive motility, e.g., swallowing, either when awake or
during remifentanil or propofol anesthesia. Remifentanil
completely abolished esophageal motility, and 6 of 10
volunteers even complained of great difficulty in induc-
ing swallowing. The discomfort from cricoid pressure
measured with a VAS was 4 (3–7) during the control
state and 0 (0–1) (P ? 0.01) during remifentanil infusion.
Respiratory rate decreased with remifentanil, as ex-
pected, and some of the volunteers had to be re-
minded to continue breathing. They were all well
oxygenated, and their arterial blood pressure and elec-
trocardiogram were normal.
In this study, cricoid pressure significantly decreased
LESP and BrP in awake volunteers. This is in accordance
Figure 1. The model of the right thumb and the two first index
fingers applying a constant cricoid pressure of 30 N.
Figure 2. The x-axis shows the different stages of the study: baseline
value, during cricoid pressure (CCP), remifentanil infusion (R), and
remifentanil together with a bolus dose of propofol (RP). The y-axis
shows the pressure in mm Hg (mean ? sem). There was a significant
decrease (*P ? 0.05) of lower esophageal sphincter pressure (LESP)
and barrier pressure (BrP) when cricoid pressure was performed in
the awake volunteers.
THORN ET AL.
CRICOID PRESSURE, REMIFENTANIL–ESOPHAGEAL SPHINCTER
with the findings of Chassard et al. (6) and Tournadre et
al. (3) who reported a decrease in LESP and BrP after
cricoid pressure in anesthetized pigs and in awake vol-
cricoid pressure during complete anesthesia induction
with drugs frequently used today. The results showed
that there was no effect of cricoid pressure on LESP or
BrP during the infusion of remifentanil. Furthermore,
adding a bolus dose of propofol 1 mg/kg IV to complete
the anesthesia induction did not change LESP or BrP.
LESP and BrP were monitored with a Dent sleeve
catheter. The sleeve has an advantage over side-hole
manometry because it takes the axial movement of the
LES during breathing into account. The catheter also
makes it possible to study esophageal propulsive con-
tractions, e.g., swallowing, and it is the method used
for continuous-pressure monitoring (5).
In the present study, cricoid pressure did not induce
swallowing. Our data also show that remifentanil
abolished spontaneous esophageal motility, and some
of the volunteers even experienced great difficulty in
inducing swallowing. This is in accord with the stud-
ies of Noordzij et al. (7) and Mittal et al. (8) who have
shown that mechanical stimulation of the laryngo-
pharynx induces relaxation of LES without swallow-
ing. However, our results show that remifentanil can
counteract this effect. A different point of view is that
remifentanil completely eliminated the experience of
discomfort induced by cricoid pressure. This might be
of clinical interest because anesthesiologists have
varying opinions concerning when to start applying
the pressure and what force to use (9). Many patients
apparently experience cricoid pressure when they are
still more or less awake, resulting in a decrease in BrP.
Therefore, LES relaxation is probably induced by me-
chanical stimulation related to pain or discomfort, and
these effects can be blocked by opioids.
Although uncommon, with an incidence of approx-
imately 3–5 per 10,000 general anesthesia inductions,
aspiration of gastric contents is still considered one of
the major complications of anesthesia (10). The use of
cricoid pressure, also known as “Sellick’s maneuver”
(1), has become the gold standard for preventing this.
Studies by Vanner et al. (11,12) have shown that a
cricoid pressure of 30–40 N is capable of preventing
regurgitation. In our study, we used a pressure of 30 N
because the use of 40 N may cause laryngeal distortion
and thereby complicate intubation (13).
There is a correlation between LESP and reflux
(14,15), but it is not possible to define LESP or BrP
values below which reflux will occur (16,17). Even so,
it seems logical to avoid, if possible, any anesthesio-
logic procedure or medication that would decrease
LESP or BrP. The effects of some different drugs on
LES have been studied (16,18). The opioids, morphine
and pethidine, decrease LESP when given IV (19,20),
but in one study, there was a slight increase in LESP
when morphine was given subcutaneously (21). Fur-
ther, Penagini and Bianchi (22) found that morphine
decreased the number of spontaneous LES relaxations
and thereby might be able to prevent reflux. We found
no studies concerning remifentanil.
Because of the effects of opioids on LESP reviewed
above, opioids have been used with caution when there
has been an increased risk of regurgitation. That is par-
ticularly true regarding anesthesia in obstetrics (23).
However, Morris and Cook (9) reported, from a national
survey in the United Kingdom, that opioids were in-
cluded in 76% of RSI, where fentanyl was the most
widely used opioid. They believe the rationale for this is
the reduction of cardiovascular stimulation and the as-
sumption of reducing the risk of awareness (9). Conse-
quently, we believe that studies of the effects of short-
acting opioids on LESP and BrP are of clinical interest
widely used drug during RSI (24). It could be reasonably
argued that we used rather small doses of remifentanil
and propofol. Nevertheless, BIS-monitoring to evaluate
the depth of anesthesia showed acceptable values, and
deeper anesthesia would probably have augmented the
effects of remifentanil and propofol. Further dose-
response studies of the effects of remifentanil and propo-
fol on LESP and BrP might therefore be of interest,
particularly studies in humans with a full stomach.
In conclusion, cricoid pressure significantly decreased
LESP and BrP when performed in awake volunteers (P
? 0.05). However, this effect could not be seen during
the infusion of remifentanil 0.2 ?g · kg?1· min?1.
Remifentanil per se, or together with a bolus dose of
LESP and BrP. Remifentanil abolished spontaneous
esophageal motility and completely eliminated the ex-
perience of discomfort induced by cricoid pressure. This
shows the importance of when to apply cricoid pressure
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THORN ET AL.
CRICOID PRESSURE, REMIFENTANIL–ESOPHAGEAL SPHINCTER