Detailed measurements of oesophageal pressure during mechanical ventilation with an advanced high-resolution manometry catheter.

BACKGROUND: Oesophageal pressure (PES) is used for calculation of lung and chest wall mechanics and transpulmonary pressure during mechanical ventilation. Measurements performed with a balloon catheter are suggested as a basis for setting the ventilator; however, measurements are affected by several factors. High-resolution manometry (HRM) simultaneously measures pressures at every centimetre in the whole oesophagus and thereby provides extended information about oesophageal pressure. The aim of the present study was to evaluate the factors affecting oesophageal pressure using HRM. METHODS: Oesophageal pressure was measured using a high-resolution manometry catheter in 20 mechanically ventilated patients (15 in the ICU and 5 in the OR). Different PEEP levels and different sizes of tidal volume were applied while pressures were measured continuously. In 10 patients, oesophageal pressure was also measured using a conventional balloon catheter for comparison. A retrospective analysis of oesophageal pressure measured with HRM in supine and sitting positions in 17 awake spontaneously breathing patients is also included. RESULTS: HRM showed large variations in end-expiratory PES (PESEE) and tidal changes in PES (ΔPES) along the oesophagus. Mean intra-individual difference between the minimum and maximum end-expiratory oesophageal pressure (PESEE at baseline PEEP) and tidal variations in oesophageal pressure (ΔPES at tidal volume 6 ml/kg) recorded by HRM in the different sections of the oesophagus was 23.7 (7.9) cmH2O and 7.6 (3.9) cmH2O respectively. Oesophageal pressures were affected by tidal volume, level of PEEP, part of the oesophagus included and patient positioning. HRM identified simultaneous increases and decreases in PES within a majority of individual patients. Compared to sitting position, supine position increased PESEE (mean difference 12.3 cmH2O), pressure variation within individual patients and cardiac artefacts. The pressure measured with a balloon catheter did not correspond to the average pressure measured with HRM within the same part of the oesophagus. CONCLUSIONS: The intra-individual variability in PESEE and ΔPES is substantial, and as a result, the balloon on the conventional catheter is affected by many different pressures along its length. Oesophageal pressures are not only affected by lung and chest wall mechanics but are a complex product of many factors, which is not obvious during conventional measurements. For correct calculations of transpulmonary pressure, factors influencing oesophageal pressures need to be known. HRM, which is available at many hospitals, can be used to increase the knowledge concerning these factors. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02901158.

Effect of positive end-expiratory pressure on gastric insufflation during induction of anaesthesia when using pressure-controlled ventilation via a face mask: A randomised controlled trial.

BACKGROUND: Face mask ventilation (FMV) during induction of anaesthesia is associated with risk of gastric insufflation that may lead to gastric regurgitation and pulmonary aspiration. A continuous positive airway pressure (CPAP) has been shown to reduce gastric regurgitation. We therefore hypothesised that CPAP followed by FMV with positive end-expiratory pressure (PEEP) during induction of anaesthesia would reduce the risk of gastric insufflation. OBJECTIVE: The primary aim was to compare the incidence of gastric insufflation during FMV with a fixed PEEP level or zero PEEP (ZEEP) after anaesthesia induction. A secondary aim was to investigate the effects of FMV with or without PEEP on upper oesophageal sphincter (UES), oesophageal body and lower oesophageal sphincter (LES) pressures. DESIGN: A randomised controlled trial. SETTING: Single centre, Department of Anaesthesia and Intensive Care, Örebro University Hospital, Sweden. PARTICIPANTS: Thirty healthy volunteers. INTERVENTIONS: Pre-oxygenation without or with CPAP 10 cmH2O, followed by pressure-controlled FMV with either ZEEP or PEEP 10 cmH2O after anaesthesia induction. MAIN OUTCOME MEASURES: A combined impedance/manometry catheter was used to detect the presence of gas and to measure oesophageal pressures. The primary outcome measure was the cumulative incidence of gastric insufflation, defined as a sudden anterograde increase in impedance of more than 1 kΩ over the LES. Secondary outcome measures were UES, oesophageal body and LES pressures. RESULTS: The cumulative incidence of gastric insufflation related to peak inspiratory pressure (PIP), was significantly higher in the PEEP group compared with the ZEEP group (log-rank test P < 0.01). When PIP reached 30 cmH2O, 13 out of 15 in the PEEP group compared with five out of 15 had shown gastric insufflation. There was a significant reduction of oesophageal sphincter pressures within groups comparing pre-oxygenation to after anaesthesia induction, but there were no significant differences in oesophageal sphincter pressures related to the level of PEEP. CONCLUSION: Contrary to the primary hypothesis, with increasing PIP the tested PEEP level did not protect against but facilitated gastric insufflation during FMV. This result suggests that PEEP should be used with caution after anaesthesia induction during FMV, whereas CPAP during pre-oxygenation seems to be safe. TRIAL REGISTRATION: ClinicalTrials.gov, identifier: NCT02238691.

Does the ß-receptor antagonist esmolol have analgesic effects?: A randomised placebo-controlled cross-over study on healthy volunteers undergoing the cold pressor test.

BACKGROUND: Esmolol may attenuate the sympathetic response to pain and reduce postoperative opioid consumption. It is not clear whether esmolol has an analgesic effect per se. OBJECTIVES: The aim of this study was to evaluate the analgesic effect of esmolol in the absence of anaesthetics and opioids. We tested the hypothesis that esmolol would reduce the maximum pain intensity perceived during the cold pressor test (CPT) by 2 points on a 0 to 10 numeric pain rating scale (NRS) compared to placebo. DESIGN: Randomised, placebo-controlled cross-over study. SETTING: Postoperative recovery area, Örebro University Hospital. Study period, November 2013 to February 2014. PARTICIPANTS: Fourteen healthy volunteers. Exclusion criteria included ongoing medication, pregnancy and breastfeeding and participation in other medical trials. INTERVENTIONS: At separate study sessions, participants received interventions: esmolol (0.7 mg kg bolus over 1 min followed by infusion at 10 µg kg min); 0.9% normal saline bolus then remifentanil infusion at 0.2 µg kg min and 0.9% normal saline bolus and infusion according to a random sequence. All infusions were administered over 30 min. MAIN OUTCOME MEASURES: Perceived maximum pain intensity score, pain tolerance and haemodynamic changes during CPT, and occurrence of side-effects to interventions compared to placebo, respectively. RESULTS: Esmolol did not reduce perceived pain intensity or pain tolerance during the CPT. The NRS-max score was similar for esmolol, 8.5 (±1.4) and placebo, 8.4 (±1.3). The mean difference was 0.1 [95% confidence interval (-1.2 to 1.4)], P value equal to 0.83. Remifentanil significantly reduced NRS-max scores, 5.4 (±2.1) compared to placebo, [mean difference -3.1 (95% confidence interval (-4.4 to -1.8)), P < 0.001]. Side-effects were seen with remifentanil but not with esmolol. CONCLUSION: No direct analgesic effect of esmolol could be demonstrated in the present study. The postoperative opioid-sparing effect demonstrated in previous studies, could therefore be secondary to other factors such as avoidance of opioid-induced hyperalgesia, synergy with coadministered opioids or altered pharmacokinetics of those drugs. TRIAL REGISTRATION: European clinical trials database, https://eudract.ema.europa.eu/, EudraCT no. 2011-005780-24.

Effects of Esmolol on the Esophagogastric Junction: A Double-Blind, Randomized, Crossover Study on 14 Healthy Volunteers.

BACKGROUND: Passive regurgitation may occur throughout the perioperative period, increasing the risk for pulmonary aspiration and postoperative pulmonary complications. Hypnotics and opioids, especially remifentanil, that are used during anesthesia have been shown to decrease the pressure in the esophagogastric junction (EGJ), that otherwise acts as a barrier against passive regurgitation of gastric contents. Esmolol, usually used to counteract tachycardia and hypertension, has been shown to possess properties useful during general anesthesia. Like remifentanil, the ß-1-adrenoreceptor antagonist may be used to attenuate the stress reaction to tracheal intubation and to modify perioperative anesthetic requirements. It may also reduce the need for opioids in the postoperative period. Its action on the EGJ is however unknown.The aim of this trial was to compare the effects of esmolol and remifentanil on EGJ pressures in healthy volunteers, when administrated as single drugs. METHODS: Measurements of EGJ pressures were made in 14 healthy volunteers using high-resolution solid-state manometry. Interventions were administered in a randomized sequence and consisted of esmolol that was given IV as a bolus dose of 1 mg/kg followed by an infusion of 10 µg·kg·minute over 15 minutes, and remifentanil with target-controlled infusion of 4 ng/mL over 15 minutes. Interventions were separated by a 20-minute washout period. Analyses of EGJ pressures were performed at baseline, and during drug administration at 2 (T2) and 15 minutes (T15). The primary outcome was the inspiratory EGJ augmentation, while the inspiratory and expiratory EGJ pressures were secondary outcomes. RESULTS: There was no effect on inspiratory EGJ augmentation when comparing remifentanil and esmolol (mean difference -4.0 mm Hg [-9.7 to 1.7]; P= .15). In contrast, remifentanil significantly decreased both inspiratory and expiratory pressures compared to esmolol (-12.2 [-18.6 to -5.7]; P= .003 and -8.0 [-13.3 to -2.8]; P= .006). CONCLUSIONS: Esmolol, compared with remifentanil, does not affect EGJ function. This may be an advantage regarding passive regurgitation and esmolol may thus have a role to play in anesthesia where maintenance of EGJ barrier function is of outmost importance.

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

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.

The aging digestive tract: what should anesthesiologists know about it?

At present, elderly individuals represent approximately 18.5% of the European population and account for about 23% of surgical procedures performed. This patient population is at a higher risk for perioperative complications and adverse postoperative outcome. This narrative review highlights our current knowledge about physiological changes in the aging gut and the implications for anesthesiologists. The reduced response to stimuli in the pharynx, and reduction of the cough reflex that occurs in many older individuals, probably explains the increased incidence of aspiration pneumonia that occurs in the elderly. These changes also increase the risk for aspiration during anesthesia. Aging affects the clearance of fluids and solids in the esophagus, associated with a higher incidence of gastro-esophageal reflux disease. Healthy aging appears to be associated with modest slowing of gastric emptying, but this does not demand prolonged preoperative fasting. The physiological changes associated with polypharmacy also make elderly patients a risk group for pulmonary aspiration during anesthesia. Further research is needed to determine the effects of commonly used anesthetic agents on the pharyngo-gastrointestinal tract in elderly patients.

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.

High-resolution solid-state manometry of the upper and lower esophageal sphincters during anesthesia induction: a comparison between obese and non-obese patients.

BACKGROUND: The prevalence of obesity has increased dramatically in recent decades. The gastrointestinal changes associated with obesity have clinical significance for the anesthesiologist in the perioperative period. The lower esophageal sphincter and the upper esophageal sphincter play a central role in preventing regurgitation and aspiration. The effects of increased intra-abdominal pressure during anesthesia on the lower esophageal sphincter and the upper esophageal sphincter in obese patients are unknown. In the present study we evaluated, with high-resolution solid-state manometry, the upper esophageal sphincter, lower esophageal sphincter, and barrier pressure (BrP) (lower esophageal pressure--gastric pressure) in obese patients during anesthesia induction and compared them with pressures in non-obese patients. METHODS: We studied 28 patients, ages 18 to 72 years, 14 with a body mass index > or = 35 kg/m(2), who were undergoing laparoscopic gastric bypass, and 14 with a body mass index < or = 30 kg/m(2), who were undergoing laparoscopic cholecystectomy, using high-resolution solid-state manometry. RESULTS: Upper esophageal sphincter pressure decreased during anesthesia induction in both groups. Lower esophageal sphincter pressure decreased in both groups during anesthesia induction, and it was significantly lower in obese patients than in non-obese patients. The BrP decreased in both groups and was significantly lower in the obese group than in the non-obese group. The BrP remained positive at all times in both groups. CONCLUSION: Lower esophageal sphincter and BrPs decreased in both obese and non-obese patients during anesthesia induction, but were significantly lower in obese patients. Although the BrP was significantly lower, it remained positive in all patients.

Comparison of stereoscopic digital imaging and slide film photography in the identification of macular degeneration.

BACKGROUND: This study compared the sensitivity and specificity of stereoscopic digital photography of the retina through a dilated pupil with a 45 degrees nonmydriatic camera and Joint Photographic Experts Group (JPEG) compression of the images with the sensitivity and specificity of 35-mm slide film photography in the identification of age-related macular degeneration (AMD). METHODS: Consecutive patients with a diagnosis of AMD were enrolled. Stereoscopic retinal images of the disc, macula and temporal macula were captured with a digital 45 degrees nonmydriatic camera (then compressed into JPEG format) and with a standard fundus camera and slide film. A single retinal specialist graded both image formats in masked fashion, at least 1 month apart, using a modified Age-Related Eye Disease Study (AREDS) severity scale. The digital images were displayed on a monitor and viewed with the use of liquid crystal display shutter glasses and stereo imaging software. The film images were mounted on a light box and graded with the use of a stereoviewer. Primary outcome measures included the presence or absence of AMD pathological features. Positive and negative predictive values (PPVs and NPVs), sensitivity, specificity and weighted kappaw statistics were calculated. RESULTS: We photographed 203 eyes (of 103 patients) with both digital and slide film cameras. Correlation of the 2 image formats was substantial in identifying AREDS level 3a or greater (kappaw=0.64, standard error=0.08, PPV=0.95, NPV=0.66, sensitivity=0.93, specificity=0.74) and excellent in identifying level 4b or greater (kappaw=0.83, standard error=0.05, PPV=0.81, NPV=0.98, sensitivity=0.94, specificity=0.94). INTERPRETATION: High-resolution stereoscopic, mydriatic, 45 degrees digital images captured with a nonmydriatic camera and JPEG compressed correlate well with stereoscopic slide film photographs in the identification of moderate to advanced AMD (AREDS level 3a or greater).