A pilot study has found that patients randomly assigned to cricoid pressure or sham treatment showed no difference in time to lowest peripheral capillary oxygen saturation (SpO2) or lowest SpO2 during anesthesia induction with planned endotracheal intubation.
“Application of 30 N of cricoid pressure was not associated with a significant difference in time to reach lowest SpO2 or lowest SpO2 in preoxygenated patients,” said John Lenart, MD, associate professor of anesthesiology at Loma Linda University School of Medicine, in California. “These results suggest that cricoid pressure at lower forces does not influence oxygen consumption, although its effect on pulmonary aspiration remains to be seen.”
As Dr. Lenart reported at the 2016 annual meeting of the International Anesthesia Research Society (abstract S-11), applying cricoid pressure is believed to decrease a patient’s risk for aspirating gastric contents between the time of anesthesia induction and endotracheal intubation. However, there is evidence that application of cricoid pressure increases heart rate and blood pressure, which may result in faster oxygen consumption (Anesth Analg2001;93:787-790).
“This pilot study was designed to investigate the effect such an increase in oxygen consumption could have on the time to desaturation,” Dr. Lenart said. “We thought that if people have a sympathetic response from cricoid pressure, they should have increased oxygen consumption, which should decrease their time to desaturation.”
While previous studies have indicated a link to sympathetic response, according to Dr. Lenart, these involved the application of cricoid pressure up to 50 N of force.
“With the pressure recommended for prevention of aspiration [i.e., 30 N], we thought that response might be mitigated,” Dr. Lenart said.
Study Design and Results
Dr. Lenart and his colleagues enrolled patients 18 to 65 years of age scheduled for surgery including anesthesia with planned endotracheal intubation. The researchers excluded patients with the following characteristics: suspected difficult mask ventilation or intubation; elevated intracranial pressure; American Society of Anesthesiologists (ASA) class IV physical status or ASA class III physical status with cardiopulmonary disease; planned cardiothoracic surgery; or risk for aspiration of gastric contents.
Enrolled patients were randomly assigned to cricoid pressure or sham treatment, with concealment until after consent. The surgical and anesthetic team and research staff collecting data were blinded to group allocation.
Patients were preoxygenated to a ratio of fraction of oxygen in expired air over fraction of oxygen in inspired air greater than 0.9 before induction, or they were withdrawn for failure to attain this ratio.
After administration of anesthetic and relaxant drugs and before endotracheal intubation, research staff then placed their hands on the patient’s neck, concealed by a drape.
“The staff that applied cricoid pressure were trained and demonstrated ability to reliably reproduce 30 N of force prior to study participation,” said Dr. Lenart, noting that in order to limit variability, two physicians performed 95% of the applications over the course of the study.
“Before cricoid pressure was applied,” he added, “practitioners also practiced on a scale to emphasize the force required.”
Timing started at the onset of apnea, and no mask ventilation or supplemental oxygen was applied after time 0.
Cricoid pressure patients had 30 N of cricoid pressure applied at time 0, which was held until SpO2 no more than 95% or six minutes had elapsed. Cricoid pressure was released before endotracheal intubation, and time to lowest SpO2and intubation were calculated.
The researchers enrolled 40 patients in the study, and two from each group were withdrawn because of preoxygenation failure.
As measured by the difference in time to lowest SpO2 and difference in lowest SpO2, the researchers found no difference in oxygen consumption between groups receiving cricoid pressure and sham treatment (Figure).
Figure. Time (minutes, media; 95% Cl) of apnea to reach lowest recorded SpO2 was not significantly different in patients who had 30 N of cricoid pressure held compared with sham treatment patients.
“Prior reports showed cardiovascular activation using 40-N cricoid pressure,” Dr. Lenart said. “It is possible that excess pressure may cause more sympathetic response than the recommended 30-N cricoid pressure.”
Benefits in Doubt
While the results may indicate a lack of cardiovascular activation at 30 N, Dr. Lenart is unconvinced of the benefits of cricoid pressure in the first place. CT scans of people receiving cricoid pressure have shown that it often doesn’t compress the esophagus, he said, but, in fact, may make it more patent.
“Various studies throughout the years have called into question whether we should even be doing cricoid pressure,” Dr. Lenart observed. “But anesthesiologists have been doing it for such a long time that it’s hard to get anyone to even think about changing practice.”
Given its ambiguous benefits, had cricoid pressure been shown to increase oxygen consumption, certain patient populations might have been excluded.
“If this study had demonstrated that cricoid pressure actually increases oxygen consumption,” he explained, “then perhaps anesthesiologists wouldn’t use it in patients with bad heart disease because it could cause a sympathetic response that would stress the heart.
“But, based on our study, it doesn’t seem to make any difference one way or the other,” he concluded.