Cricoid Force Research Articles

The effect of mechanically-induced cricoid force on lower oesophageal sphincter pressure in anaesthetised patients.

In the United Kingdom, cricoid force is central to upper airway management in obstetric and emergency anaesthesia. A reduction in oesophageal barrier pressure (OBP) in these patients may increase regurgitation risk. This study investigated whether the application of cricoid force to anaesthetised patients reduced lower oesophageal sphincter pressure (LOSP) and consequently OBP. Anaesthesia was induced in 29 patients using a standard protocol. An oesophageal balloon catheter was inserted and gastric trace identified. The catheter was withdrawn incrementally and pressure readings recorded at each position before and during the application of 30 N cricoid force, with a sudden rise in pressure indicating lower oesophageal sphincter position. Oesophageal barrier pressure was calculated as the difference between LOSP and gastric pressure. Application of cricoid force significantly reduced OBP without influencing gastric pressure (p < 0.001). The use of cricoid force may increase the risk of gastroesophageal reflux in anaesthetised patients.

Intragastric pressure and its relevance to protective cricoid force.

Cricoid pressure is frequently used to protect the anaesthetised and paralysed patient from passive regurgitation. Although intragastric pressure (Pga) drives regurgitation, its relevance in the setting of protective cricoid force has been largely ignored. We sought to define the likely range of Pga encountered in the population at risk. We studied 100 consecutive patients presenting for surgery requiring mechanical ventilation. We measured respiratory swings in Pga during mechanical ventilation in the paralysed state following rapid sequence induction (n = 24) and routine induction of anaesthesia (n = 76). Pga (mmHg) in the whole group recorded at end-inspiration (Pga-In) and end-expiration (Pga-Ex) was [mean (SD)]: Pga-In 6.48 (2.60) mmHg and Pga-Ex 3.23 (2.24) mmHg. We found no correlation between Pga and body mass index (r2 = 0.018). These findings have implications for the level of cricoid force required to protect a patient during the induction of anaesthesia.

Cricoid yoke: the effect of surface area and applied force on discomfort experienced by conscious volunteers

Background and objective: The application of cricoid force is central to techniques that reduce the risk of gastric regurgitation and the subsequent pulmonary aspiration associated with obstetric and emergency anaesthesia. The discomfort associated with cricoid force in awake preoperative patients increases the incidence of coughing, struggling and pain during induction of anaesthesia. This study determined if increasing the surface area of a cricoid yoke reduced the associated discomfort in volunteers. Methods: Fifty volunteers participated in a randomized single-blinded study. The cricoid yoke was positioned using standard anatomical landmarks and forces of 10, 20, 30 and 40 N were applied in a random order for 20 s, using two different yoke attachments with surface areas of 3 and 10 cm2. A rest of 30 s was allowed between the application of forces. Discomfort was graded by volunteers on a scale from 0 to 10 (0: no discomfort; 10: worse discomfort imaginable). A score of 10 was allocated if the volunteers could not tolerate the applied force for 20 s. Results: Median scores for the small yoke were always higher than those for the large yoke at each force. There were significant differences between the scores for the small and large yokes at 10 and 20 N (P < 0.001) and 30 N (P = 0.0233), but there was no significant difference at 40 N. Conclusions: The larger yoke was tolerated better by volunteers when clinically relevant cricoid forces were applied.

Assessing the Force Generated With Application of Cricoid Pressure

The application of cricoid pressure is a common technique used to decrease the risk of aspiration during anesthetic induction. Research recommends that 3 to 4 kg of cricoid force be applied to achieve effective esophageal occlusion. The purpose of this study was to assess perioperative nurses' knowledge regarding the recommended amount of cricoid force that should be applied to the cricoid cartilage and to assess the amount of force generated when cricoid pressure was applied to a scale-mounted model. A convenience sample of 102 perioperative nurses participated in the study. Five percent of participants identified the correct amount of force necessary. Applied force was significantly less than the recommended amount. Findings of this study suggest perioperative nurses lack both knowledge and clinical skill for generating effective amounts of cricoid force.

Cricoid cartilage pressure decreases lower esophageal sphincter tone.

Cricoid cartilage pressure induced to prevent pulmonary aspiration from regurgitation of gastric contents has been recommended, and its efficacy requires a force greater than 40 Newtons. For regurgitation to occur, both an increase in gastric pressure and relaxation of the lower esophageal sphincter (LES) are necessary. However, the effect of cricoid cartilage pressure on the LES is unknown. This study evaluated the effects of cricoid cartilage pressure on LES in human volunteers. Lower esophageal sphincter and esophageal barrier pressures (which equals LES pressure-gastric pressure) were measured using a manometric method in eight unanesthetized volunteers (4 men, 4 women) classified as American Society of Anesthesiologists physical status 1. The force applied to the cricoid cartilage was measured continuously, and LES pressure was recorded at a cricoid force of 20 and 40 Newtons. Cricoid pressure decreased LES pressure from 24 +/- 3 mmHg to 15 +/- 4 mmHg at a force of 20 Newtons (P < 0.05) and to 12 +/- 4 mmHg with a force of 40 Newtons (P < 0.01). These findings may explain the occurrence of pulmonary aspiration before tracheal intubation despite application of cricoid cartilage pressure.

Use of a mechanical simulator for training in applying cricoid pressure

Using an airway management training model, we have assessed anaesthesia personnel in their use of correct cricoid force and ability to retain this skill after a short training programme. A perspex device, working on a hydraulic principle, was used to measure cricoid pressure when applied to the model. After initial assessment at two levels of cricoid force (20 and 40 N), participants undertook additional training on 3 consecutive days. Thereafter, available participants underwent reassessment at 14-21 days. Forty-nine anaesthetic assistants and anaesthetists underwent initial assessment and 18 completed the full training and reassessment. Untrained, the majority (63%) of participants applied inadequate cricoid force with a wide variation (mean 16.8 (SD 9.3) (range 4.5-43.0) at 20 N and 32.9 (13.3) (14.9-74) at 40 N). After a single training session there was a marked improvement in application of cricoid force. Two additional training sessions did not provide further improvement. After 14-21 days the ability of participants to apply correct cricoid force was retained by 72% of subjects. Those who applied inadequate cricoid force initially were more likely to do so even after training. Most subjects applied too great a cricoid force in the first 5 s of application followed by a progressive loss of force during the next 20 s. This trend improved after training. We conclude that the majority of untrained personnel apply inadequate cricoid force, placing patients at risk of aspiration of gastric contents. While a simple training programme improved application of cricoid force, retained for up to 3 weeks, there was often a substantial decrease in the force applied to the cricoid during a single application, even after training.

Cricoid pressure: teaching the recommended level.

The Sellick maneuver or cricoid pressure is an effective means of preventing passive aspiration of gastric contents. Recent studies recommend a pressure of 20 newtons (N) when the patient is awake, increasing to 30-40 N with unconsciousness. This study was proposed to determine whether with education and practice, anesthesia providers and assistants could be taught a recommended cricoid pressure and retain this skill. Cricoid force was measured using a life-size laryngotracheal model on a calibrated infant scale. Fifty-three participants were divided into six groups: MD faculty; CA-1, 2, and 3 Residents; certified registered nurse anesthetists (CRNA); and Others. Each was asked to apply pressure to the blinded model to simulate application of the Sellick's maneuver to an "awake" and "unconscious" patient on four occasions: before instruction of the recommended pressures (Preinstruction), after being informed of the recommended magnitudes of 20 N/awake and 30-40 N/anesthetized (Postinstruction), after a period of unblinded practice (Postpractice), and 3 mo or longer after practice (Follow-up). Initial attempts revealed inadequate force by all participants, "awake" and "anesthetized". All participants were able to learn the recommended amount of applied pressure and were able to retain this knowledge after 3 mo. This model represents an easy and practical means of teaching the application of the optimal level of force to practitioners and assistants.

Does the laryngeal mask airway compromise cricoid pressure?

The laryngeal mask airway was inserted in 10 cadavers. At postmortem the chest was opened and an infusion set primed with a dilute barium solution was inserted into the oesophagus and ligated in place. A cricoid force of 43 N was then applied and the infusion set was positioned so that when the clamp was opened it generated a pressure of 7.8 kPa within the oesophagus. The cricoid pressure was able to stop the flow of fluid into the oesophagus. This demonstrates that cricoid pressure is effective in preventing reflux at intragastric pressures which are encountered clinically and the presence of the laryngeal mask airway does not compromise this.

Regurgitation and oesophageal rupture with cricoid pressure: a cadaver study.

The efficacy of cricoid pressure was studied in 10 adult cadavers. The oesophageal pressure that would result in regurgitation during measured values of cricoid pressure was determined. Oesophageal pressure, recorded by a 2 mm diameter oesophageal tube, was increased by oesophageal distension with saline, and incremental levels of cricoid force, 20, 30 and 40 Newtons, were applied with a cricoid yoke. With each 10 Newton increment of cricoid force there was a significant rise in the oesophageal pressure required to provoke regurgitation (p < 0.01). Thirty Newtons of cricoid force prevented regurgitation of saline in all cadavers with oesophageal pressures of up to 40 mmHg. Rupture of the oesophagus occurred in three cadavers: one at 30 and two at 40 Newtons of cricoid force, but there was no rupture at 20 Newtons of cricoid force. In the other seven cadavers oesophageal pressures were also studied with a 4.6 mm diameter (14 FG) oesophageal tube, which did not reduce the efficacy of cricoid pressure in preventing regurgitation.

Upper oesophageal sphincter pressure and the effect of cricoid pressure.

Upper oesophageal sphincter pressure has been measured in 24 patients with a sleeve device. The median sphincter pressure when awake was 38 mmHg, and when anaesthetized and paralysed was 6 mmHg. After tracheal intubation, cricoid pressure was applied at measured values between 5 and 50 N using a hand-held cricoid yoke while the sphincter pressure was recorded in two head and neck positions: with and without a standard intubating pillow with neck support. A cricoid force of 40 N increased sphincter pressure to above 38 mmHg in all the patients and the use of the pillow did not alter this effect. With the application of cricoid pressure, operating department assistants raised sphincter pressure to above 38 mmHg in only 50% of patients. Laryngoscopy made little difference to the effect of cricoid pressure except in one patient in whom it reduced the sphincter pressure by 27 mmHg.

Tolerance of cricoid pressure by conscious volunteers

It is recommended that a cricoid pressure (force) of 40 N should be applied to prevent regurgitation. The tolerance of incremental levels of cricoid pressure was assessed in 22 conscious volunteers. Each level of cricoid pressure was applied for 20 s using a cricoid yoke. Only 14 volunteers could tolerate 40 N of cricoid forte for 20 s; all 22 volunteers could tolerate 25 N for that time but 19 of them found it uncomfortable and 1 wanted to retch. Nine subjects complained of breathing difficulties at cricoid forces of 35 N or above; 2 had complete airway obstruction. A, cricoid force of over 20 N is likely to be poorly tolerated by the awake patient. It is recommended that a force of 20 N should be maintained before loss of consciousness and the full force of 40 N be reserved for the onset of general anaesthesia; the assistant can practise these levels on a set of weighing scales.

The determination of an effective cricoid pressure

A study of cricoid pressure was undertaken to relate the applied cricoid force with the resulting intraluminal cricopharyngeal (or oesophageal) pressure. The results indicate that whilst there was a wide range in normal adults a cricoid force of 44 N was judged to be effective in protecting the majority of adult patients from regurgitation.

The determination of an effective cricoid pressure.

A study of cricoid pressure was undertaken to relate the applied cricoid force with the resulting intraluminal cricopharyngeal (or oesophageal) pressure. The results indicate that whilst there was a wide range in normal adults a cricoid force of 44 N was judged to be effective in protecting the majority of adult patients from regurgitation.