Rebecca Ahlstrand

Aspiration Induced by Remifentanil : A Double-blind, Randomized, Crossover Study in Healthy Volunteers

Background:Remifentanil is widely used for monitored anesthesia care in spontaneously breathing patients. However, the authors’ previous studies have shown that remifentanil induces subjective swallowing difficulties, which may increase the risk of aspiration. Methods:Twenty-five healthy volunteers participated in a double-blind, randomized, crossover trial at the University Hospital in Örebro, Örebro, Sweden. The volunteers were studied on two different occasions during which they received either remifentanil with an effect-site target concentration of 3 ng/ml or saline over 1 h. A radionuclide tracer was infused simultaneously into the nasopharynx at a rate of 0.1 ml/min. Aspiration was determined by lung scans, and subjective swallowing difficulties and grip strength were evaluated. The primary outcome was the difference in occurrence of aspiration between remifentanil and placebo treatments. The secondary outcomes were differences in swallowing difficulty and grip strength and the association between aspiration and swallowing difficulty. Results:During remifentanil and placebo infusion, 48 and 12% of the volunteers aspirated, respectively, difference: 36% (95% CI, 10 to 62%). A similar significant difference was found for swallowing difficulties but not for the association between aspiration and swallowing. No difference was found in grip strength between the two treatments. Conclusions:Remifentanil infusion at concentrations used in monitored anesthesia care increases the incidence of aspiration. However, the subjective swallowing difficulty induced by remifentanil is not indicative of the aspiration risk.

Effects of remifentanil on the esophagogastric junction and swallowing

A recent study demonstrated that reflux is associated with impaired pressure augmentation in the esophagogastric junction (EGJ), caused by diaphragmal contractions during inspiration. It is unknown whether this augmentation is influenced by opioids. Swallowing difficulties can be a poorly recognised side effect of remifentanil. Here, we investigated whether remifentanil influences inspiratory EGJ augmentation and evaluated subjective swallowing difficulties induced by remifentanil. We also used the peripheral opioid receptor antagonist methylnaltrexone to evaluate whether these effects are centrally or peripherally mediated.

Effects of cricoid pressure and remifentanil on the esophageal sphincters using high-resolution solid-state manometry.

Background: Cricoid pressure has been shown to decrease the pressure in the lower esophageal sphincter (LES), increasing the risk of aspiration. Whether this reaction is due to pain associated with the application of cricoid pressure has not been studied. The aim of this study was to compare the effects of cricoid pressure with those of peripheral pain on pressures in the LES, and to study whether remifentanil influences these effects. Data from the upper esophageal sphincter (UES) are also described.

Effects of propofol on oesophageal sphincters: a study on young and elderly volunteers using high-resolution solid-state manometry.

Background and objective The oesophageal sphincters play an important role in protecting the airway. During manometric studies, administration of an anxiolytic agent is often required to make insertion of the catheter acceptable for the patient. The anxiolytic should not affect the results of the measurements. This study evaluates the effects of two different doses of propofol on the pressures in the oesophageal sphincters. The effect of increased abdominal pressure was also studied. Methods Twenty healthy volunteers, 10 young (mean age 25 years) and 10 elderly (mean age 71 years), were recruited. The effects of a low dose of propofol [0.3 mg kg−1 intravenously (i.v.)] and a high dose of propofol (young group 0.9 mg kg−1 i.v. and elderly group 0.6 mg kg−1 i.v.) were studied with and without external abdominal pressure. Results There were no statistically significant changes in lower oesophageal sphincter (LOS) pressure after the low dose of propofol. After the high dose, there was an increase in LOS pressure, which was statistically significant in the young group (P < 0.05). The upper oesophageal sphincter (UOS) pressure decreased after both doses of propofol (P < 0.01 for the higher dose and P < 0.05 for the lower dose). Conclusion A low dose of propofol (0.3 mg kg−1 i.v.) leaves the LOS unaffected in young and elderly volunteers and can be used safely as an anxiolytic agent during studies of the LOS without influencing the results. However, the UOS is more sensitive to the effects of propofol and we do not recommend the use of propofol as an anxiolytic agent during manometric studies of the UOS.

Effects of remifentanil on pharyngeal swallowing: A double blind randomised cross-over study in healthy volunteers.

BACKGROUND Exposure to remifentanil increases the incidence of pulmonary aspiration in healthy volunteers. This effect may be explained by impairment of airway defence mechanisms and/or altered swallowing function. Pressure-flow analysis is a technique that allows objective assessment of swallowing based on pressure-impedance patterns recorded during bolus swallowing. OBJECTIVES The aim of this study was to use pressure-flow analysis to quantify the effect of remifentanil on healthy pharyngeal swallowing and to compare these effects with morphine. DESIGN A double-blind, randomised, cross-over study. SETTING A tertiary care teaching hospital. VOLUNTEERS Eleven young volunteers (mean age, 23 years) and seven older volunteers (mean age, 73 years). INTERVENTIONS Volunteers were studied twice and received either a target-controlled remifentanil infusion (target concentrations: young, 3 ng ml−1; old, 2 ng ml−1) or a bolus injection of morphine (dose: young, 0.1 mg kg−1; old, 0.07 mg kg−1). Pharyngeal pressure and impedance were recorded with an indwelling catheter while swallowing 10 boluses of liquid during each measuring phase. Variables defining swallowing function were calculated and compared to determine drug effects. MAIN OUTCOME MEASURES Pharyngeal pressure-flow variables following remifentanil exposure. RESULTS Changes produced by remifentanil in the measured variables were consistent with greater dysfunction of swallowing. Both the strength of the pharyngeal contractions and pharyngeal bolus propulsion were reduced, whereas flow resistance was increased. The swallow risk index, a global index of swallowing dysfunction, increased overall. At the experimental doses tested, morphine produced similar, but less extensive effects on swallowing. CONCLUSION Remifentanil induced dysfunction of the pharyngeal swallowing mechanism. This may contribute to an increased risk of aspiration. TRIAL REGISTRATION NCT01924234 (www.clinicaltrials.gov).

Effects of remifentanil on esophageal motility: a double‐blind, randomized, cross‐over study in healthy volunteers

Recent studies have shown that remifentanil increases the risk of aspiration and induces subjective swallowing difficulties. The mechanisms are not completely understood. Here, we investigated whether remifentanil impairs esophageal motility and hypothesized that this is one possible underlying mechanism. Naloxone was used to evaluate whether the effects of remifentanil are mediated through opioid receptors. We also examined subjective swallowing difficulties and the influence of metoclopramide on remifentanil‐induced effects.

High-resolution solid-state manometry of the effect of rocuronium on barrierpressure.

The pressure in the lower esophageal sphincter (LES) is partly dependent on striated muscles derived from the crural portion of the diaphragm. The effect of neuromuscular blockade on the integrity of the esophagogastric junction is not well studied. We conducted a prospective interventional study to determine the effect of rocuronium on the barrier pressure (LES pressure – intragastric pressure) of the esophagogastric junction. We also studied the effect of positive pressure ventilation on the barrier pressure after neuromuscular blockade with rocuronium.

Time-to-intubation in obese patients : A randomized study comparing direct laryngoscopy and videolaryngoscopy in experienced anaesthetists

BACKGROUND Airway management may be difficult in obese patients. Moreover, during prolonged intubation, oxygen desaturation develops rapidly. Videolaryngoscopy improves the view of the larynx, and the Storz® C-MAC™ has been shown to be superior to other videolaryngoscopes in terms of intubation time in obese patients. However, no effort has been made to compare the Storz® C-MAC™ with direct laryngoscopy. The aim of the study was to evaluate if the use of Storz® C-MAC™ may reduce intubation time when compared to direct laryngoscopy (classic Macintosh® blade). METHODS Eighty patients with Body Mass Index >35 kg/m2 were randomized to orotracheal intubation using either Macintosh® laryngoscope, or the Storz® C-MAC™ with the standard Macintosh blade. Patients had no previous history of a difficult airway. Time-to-intubation (TTI) was defined as the time from the moment anesthetist took the laryngoscope until end-tidal carbon dioxide was detected. RESULTS No significant difference in TTI could be demonstrated between the two devices tested (mean difference -1.7 s (95% CI:-6.9 to 3.5 s). All patients in the videolaryngoscopy group were successfully intubated with the allocated device, whereas five patients in the direct laryngoscopy group required an alternative device for successful intubation. No significant difference regarding the subjective difficulty of intubation and postoperative sore throat between groups was demonstrated. CONCLUSIONS In obese patients the airway may be secured equally fast using direct laryngoscopy (Macintosh®) and with videolaryngoscopy using the Stortz® C-MAC™. The risk for failed intubation, however, appears to be greater with direct laryngoscopy, especially in male obese patients.

Barrier pressure of the oesophagogastric junction during propofol induction with and without alfentanil: a double-blind, randomised, crossover study in volunteers.

Context Practice varies regarding the use of opioids during rapid sequence induction. Controversy exists as to whether opioids may increase the risk of pulmonary aspiration by decreasing the barrier pressure (lower oesophageal sphincter–intragastric pressure). Objectives To evaluate the effects of adding alfentanil during anaesthesia induction with propofol with respect to the barrier pressure in the oesophagogastric junction. Participants and setting Seventeen healthy volunteers (11 men and six women) participated in a double-blind, randomised, crossover trial at the University Hospital in Orebro, Sweden. Interventions and outcome measures The volunteers were anaesthetised on two different occasions, randomly assigned to receive either alfentanil 20 &mgr;g kg−1 or an equivalent amount of isotonic saline, administered intravenously, 1 min before induction with propofol 2 mg kg−1. One minute after propofol administration, a cricoid pressure of 30 N was applied. The primary outcome was the difference in the change in barrier pressure between the alfentanil and the placebo occasion 1 min after propofol administration. The secondary outcomes were differences in the changes in barrier pressure 1 min after alfentanil or placebo administration and during ongoing cricoid pressure application. Results There were no statistically significant differences in barrier pressure, at any time point, between anaesthesia induction with alfentanil and propofol compared with induction with placebo and propofol. The barrier pressure never decreased to less than 2.4 mmHg in any volunteer. Conclusion Our study showed no increased risk regarding the integrity of the gastro-oesophageal junction when alfentanil is added during an induction with propofol in volunteers. This supports the practice of adding opioids as adjuvants during rapid sequence induction.

Pressure measurement in the upper esophagus during cricoid pressure: A high‐resolution solid‐state manometry study

The use of cricoid pressure is controversial, and its ability to occlude the esophagus has been questioned. In this study, high‐resolution solid‐state manometry was used to analyze pressure changes in the upper esophagus from cricoid pressure during modified rapid sequence induction. This is a secondary analysis of data from a previous study.