Assessing the Effect of Surgery and Related Variables on Perioperative Whole Blood Potassium Levels in Hemodialysis Patients Having Outpatient Vascular Access Procedures

In a prospective randomized study we evaluated the impact of the traditional NPO regime versus a liberalized fluid restriction (NPO for 1 or 2 hours) on residual gastric volume (RGV) and gastric pH prior to Endoscopic Retrograde Cholangiopancreaticography (ERCP) We found no difference in the gastric volume or pH between the study group as a whole and the control group. The group that was given liquids 1 hour prior to the procedure (NPO-1hr) had a lower RGV than the group that was given liquids 2-hours prior to the procedure (NPO-2hr) and the control group. Most previous studies to measure RGV and Ph with liberalized fluid restriction utilized aspiration techniques via blindly passed oral or nasal gastric tubes, usually after the induction of anesthesia and intubation,. This study, using direct vision, demonstrates no difference in RGV in a high-risk group for delayed gastric emptying. It also raises the question of whether there is a benefit of to fluid intake about 60 minutes prior to anesthesia start. Methods After obtaining institutional IRB approval we enrolled 50 patients over a four months period that underwent ERCP’s. The patients were given 240 ml of blue colored liquid between 32 and 162 (mean 85) minutes prior to start of the endoscopy. Our goal was to administer the clear liquid about 60 minutes or about 120 minutes prior to the procedure. Accurate timing of endoscopy after fluid intake was difficult in the clinical setting, so prior to data analysis we decided to split the groups into a 30-89 minute and a 90-120 minute group. Another 50 patients who followed traditional institutional NPO guidelines (NPO after midnight) served as a control group. After the induction of anesthesia in the prone position, the stomach contents were aspirated (routine part of the procedure) through the endoscope and volume and pH as well as absence or presence of blue color were determined. The gastroenterologist was blinded to the fluid management and was unaware if a patient was in the 1or 2-hour or control group. Statistical analysis was done with unpaired t-test. Results In the study group the average fasting time was 85 minutes [32 – 162, SD 34.84]. The average residual gastric volume (RGV) was 20.78 ml [0 – 80, SD 15.19] for the whole group; 15.89 ml [0-32, SD 9.68] for NPO-1hr; 27.0 ml [0-80, SD 18.57] for NPO-2hr. The RGV was statistically significant different for the groups (p=0.0088), with the shorter fasting group having a lower RGV. The pH was 2.88 [0 – 7, SD 2.36] for the whole group; 3.03 [0-7, SD 2.63] for NPO-1hr; 2.67 [1-7, 1.98] for NPO-2hr. The difference in pH was not significant (p=0.596). Blue colored liquid was present in 14 of 50 patients [28%], 8 of 28 in NPO-1hr [28.6%], 6 of 22 in NPO2hr [27.3%]. 1 Brady M, Kinn S, Stuart P. Preoperative fasting for adults to prevent perioperative complications. The Cochrane Library, Volume (4), 2004 The average fasting time in the control group was 704 minutes [455-1200, SD 161.39]. The average RGV was 21.44 minutes [0-110, SD 20.61]. The pH was 2.52 [0-8, SD 2.24] Discussion We conclude that the administration of 240 ml of clear liquid less than 120 minutes prior to an ERCP does not increase RGV or alter the pH significantly. Indeed prolonged fluid restriction may increase gastric volume or lower Ph. The data suggests that fluids administered about 60-90 minutes prior to an ERCP may be more beneficial than prolonged fluid restriction. We propose that more liberal fluid guidelines may increase patient satisfaction and decrease number of case cancellations due to violation of too restrictive guidelines. Poster Presentation 26 Guided Insertion of the LMA ProSeal, a Comparison of Two Single Operator Techniques Allan J. Goldman M.D. Department of Anesthesiology, University of Washington, Seattle, Washington Introduction: The LMA ProSealTM (PS), introduced in 2000, is designed to isolate the respiratory tract from the alimentary tract, and to provide higher inspiratory airway pressure than the LMA Classic (C) during positive pressure ventilation. Besides expanding the use of the LMA into areas where the Classic would be relatively contraindicated, there have been several case reports where the PS has rescued the airway in “cannot intubate/cannot ventilate” patients, for whom the LMA Fastrach and the fiberoptic bronchoscope (FOB) were unsuccessful (1,2). Of note, in both reports the patients were diagnosed with lingual tonsil hyperplasia (LTH) postoperatively. Ovassapian et al reviewed 33 patients with unanticipated failed intubation, all diagnosed afterwards with LTH. Routine physical examination of the airway did not identify its presence (3). Some clinicians have noted that the PS to be slightly more difficult to insert than the C, with a first pass success rates of 82% vs 91% respectively (4). Brimacombe et al reported a Gum Elastic Bougie (GEB)/laryngoscope guided insertion of the PS with a 100% first attempt success (5). Pons et al also reported a 100% success rate preloading the PS with an orogastric (OG) tube (6), and using the standard ‘Brain” insertion technique (without a laryngoscope). Method/Results How does one choose the best guided insertion technique? We have been practicing both techniques this past year on a daily basis, and indeed, they both have close to a 100% first attempt success with an experienced PS user. In contrast, the success rate is quite different in the hands of an inexperienced user. The inexperienced user maintains this high success rate with the GEB, while not with the OG. In a brief series (50 cases) with R2 anesthesiology residents, all with less than 5 previous PS placements, first time placement with the OG was 50%, but 100% with the GEB. We currently perform a single operator version of the Brimacombe GEB technique (see picture). The GEB is placed under direct visualization into the esophagus, the laryngoscope is removed, and the PS is inserted into position over the GEB in a classic Seldinger maneuver, using standard “Brain” insertion with the lubricated cuff flattened against the hard palate. Conclusion: We currently recommend the OG insertion for routine cases, especially when planning to use an OG for the case. The GEB insertion is reserved as a backup technique, and as a first line technique in emergency situations, where rapidly securing the airway is essential. One must never forget the danger of perforating the esophagus, which carries a high degree of morbidity and mortality if not immediately recognized. The OG was designed for use in the esophagus, while the GEB was not. The ideal is to practice and learn the classic “Brain” technique of correct deflation and insertion. We currently feel that the single operator GEB PS technique is an essential airway salvage skill. It is probably a safer option than the LMA Classic in the “cannot intubate or ventilate” patient at risk for aspiration. In these desperate situations, the stomach usually needs decompression. The “Single Operator GEB PS Technique” can be practiced regularly, is easy to learn for those with laryngoscopic skills, and can be mastered by those with poor LMA skills. References: 1. Rosenblatt. The Use of the LMA-ProSeal in Airway Resuscitation. Anesth Analg 2003;97:1773-5 2. Dupanovic. Lingual Tonsil Hyperplasia and Failed Intubation; use of ProSeal LMA. S.A.M. Annual Meeting , Chicago, Ill Sept, 2004 3. Ovassapian et al. The Unexpected Difficult Airway and Lingual Tonsil Hyperplasia. Anesthesiology. 2002 July; 97 124-132 4. Brimacombe et al. A Multicenter Study Comparing the ProSeal and Classic LMA. Anesthesiology, V96, No2, Feb 2002 5. Brimacombe J, Keller C, Judd DV: Gum Elastic Bougie-Guided Insertion of the ProSeal Laryngeal Mask Airway Is Superior to the Digital and Introducer Tool Techniques. Anesthesiology 2004; 100:25-9 6. Pons VM, Madrid V; Ease Placement of the ProSeal with a Gastric Tube Inserted. Anesth Analg 2004;98:1816-17 Poster Presentation 27 The Relationship between Npo Duration and Fasting Blood Glucose: A Preliminary Analysis Jason Greenberg BA, Vivek Moitra MD, Melinda Drum PhD, Bobbi Jean Sweitzer MD Department of Anesthesiology and Critical Care, University of Chicago Hospitals, Chicago, IL