Reflux/Regurgitation

Written by admin on December 22, 2015. Posted in Other Documents.

Reflux/Regurgitation

Historically, the publications show that Laryngeal Masks have a higher incidence of methylene blue dye regurgitation than Guedel airways when used with Facemasks in live patients. This seems counter-intuitive but when a capsule of blue dye is ingested by the patient 10 minutes before induction and the airway is visualized after the end of surgery in patients at no known risk of regurgitation Barker P states “Dye was observed within the Laryngeal Mask in 7 of 28 patients (25%). No patients in the Facemask-Guedel airway group regurgitated dye (p=0.005)”. This result is supported by the measurement of lower oesophageal sphincter (LOS) tone for both the Laryngeal Mask and the Guedel when used with a Facemask, Rabey PG states that in a cohort of randomly allocated patients, the Laryngeal Mask group demonstrated a “mean (SEM) decrease in barrier pressure (LOS minus gastric pressure) of 3.6 (1.4) cmH2O, compared with a mean increase of 2.2 (1.2) cmH2O in the (Guedel +) Facemask group (p<0.005)”. Further evidence shows that placement of a Laryngeal Mask in a cadaver, without sphincter tone, reduces regurgitation of fluid from the Oesophagus into the Pharynx (Ref; Keller C, Brimacombe J, Radler C, Puhringer F. Do laryngeal mask airway devices attenuate liquid flow between the oesophagus and pharynx? A randomized, controlled cadaver study. Anaesth Analg. 1999; 88(4): 904-7) but in the living Human, with an active sphincter, such placement may open the Oesophagus and reduce LOS (Lower Oesophageal Sphincter) tone, thus increasing the regurgitation of trace dye. The Tulip study bronchoscopies showed a fully closed Oesophagus and no evidence of reflux or regurgitation.

The direct bronchoscopies of Tulips in-situ during this study demonstrated that the Tulips all sat in the correct anatomical position, which is 1-3cm deeper into the Oropharynx than an equivalent Guedel airway but 2-5cm higher than an equivalent Laryngeal Mask whose tip lies within the opening of the Oesophagus. The multiple visualizations showed that the Tulips sat entirely within the Oropharynx and did not enter the Larynx or Oesophagus in any way. The bronchoscopies through the Tulip breathing tube offered good glottic views of the Vocal Cords such that intubation would have been possible and showed that the Oesophagus was fully closed, making gastric insufflation unlikely at normal ventilation pressures.

The published evidence shows that gastric insufflation begins to increase at approximately 20cmH2O of ventilation pressure, with greater increases at ventilation pressures >25cmH2O for the Guedel + Facemask technique so it is unlikely that gastric inflation will occur with the Tulip at normal ventilation pressures with a similar anatomical position to the Guedel airway and a demonstrably closed Oesophagus. Schmidbauer W et al. (Schmidbauer W, Genzwurker H, Ahlers O, Proquitte H, Kerner T. Cadaver study of oesophageal insufflation with supraglottic airway devices during positive pressure ventilation in an obstructed airway. Br J Anaesth. 2012; 109(3): 454-8) found that “no oesophageal insufflation could be detected at a ventilation pressure of 20 mbar in any (supraglottic) device. Using inspiratory pressures of 40 and 60 mbar, oesophageal insufflation occurred in all devices”. They concluded that “the use of SADs with inspiratory pressures of 20 mbar appears to be safe regarding the risk of intra-gastric insufflation” but that “higher inspiratory pressures should be strictly avoided”. The role of high ventilation pressures in gastric insufflation was further described by Ho-Tai LM, who showed showed that if “after induction of anaesthesia, two airway management techniques (Facemask/Guedel or Laryngeal Mask) and three peak pressures (20, 25 and 30 cm H2O) were randomly applied during controlled ventilation in 60 patients. The frequency of gastro-oesophageal insufflation was 1.6%, 5% and 5% for the LMA and 5%, 15% and 26 internet viagra india.6% for the FM for ventilation pressures of 20, 25 and 30 cm H2O respectively”. These published findings show that all supraglottic airways are susceptible to the phenomena of gastric insufflation with Helmy AM et al. finding that “the incidence of gastric insufflation was significantly more with LMA group 9 (22.5%) vs. I-gel group (5%) (P=0.016)”. Thus with an increased LOS barrier pressure in live patients, a reduced incidence of regurgitation with Guedel type airways in some studies and the role of ventilation pressures in minimizing gastric insufflation, 20cmH2O is considered a safe maximum for Tulip use in routine scenarios.

The definitive management in potential regurgitation and aspiration risk remains the Endotracheal tube as any regurgitated gastric contents may contain solids as well as fluids and those solids will not pass through the gastric drain tubes of either a Laryngeal Mask or an iGEL. Additionally, either device may be misplaced e.g. into the Larynx itself, may fit incorrectly through either incorrect selection of size or through under/over-inflation of the cuff (Brimacombe J., et al. Aspiration of gastric contents during use of a ProSeal laryngeal mask airway secondary to unidentified foldover Malposition. Anaesth Analg. 2003; 97(4): 1192-4.), so aspiration protection cannot be assured. The tracheal protection that is afforded by the Endotracheal tube is not only from the design and anatomical location of the tube and the inflated cuff within the Trachea, but also from the fact that the Endotracheal tube is visualized during placement through laryngoscopy (direct or indirect) and its anatomical placement verified every time. Supraglottic airway devices are placed blind, every time.

The gastric drain tube diameter of a Laryngeal Mask Supreme is not listed in the IFU’s (Instructions For Use) but the largest recommended gastric tube for use through the gastric drain lumen of a size 4 is 14G, which corresponds to a 4.7mm external diameter (French Gauge = Diameter in mm x 3), suggesting that the gastric drain lumen has a minimum diameter of approximately 5mm. The iGEL size 4 has a gastric drain lumen which is also 5mm. The internal diameters of the United Kingdom’s wall mounted Yankauer suction catheters are I.D. (Internal Diameter) 6mm which may also not cope with gastric regurgitated contents due to the presence of the solids that are contained within partially digested contents of the Stomach.
Supraglottic airway devices cannot provide aspiration protection even when they are equipped with gastric drain lumens as aspiration is still possible, but still they are used safely every day when such risk has been assessed as being low, especially if they are used judiciously and with low ventilation pressures that avoid gastric insufflation.Reflux/Regurgitation

The published evidence shows that gastric insufflation begins to increase at approximately 20cmH2O of ventilation pressure, with greater increases at ventilation pressures >25cmH2O for the Guedel + Facemask technique so it is unlikely that gastric inflation will occur with the Tulip at normal ventilation pressures with a similar anatomical position to the Guedel airway and a demonstrably closed Oesophagus. Schmidbauer W et al. (Schmidbauer W, Genzwurker H, Ahlers O, Proquitte H, Kerner T. Cadaver study of oesophageal insufflation with supraglottic airway devices during positive pressure ventilation in an obstructed airway. Br J Anaesth. 2012; 109(3): 454-8) found that “no oesophageal insufflation could be detected at a ventilation pressure of 20 mbar in any (supraglottic) device. Using inspiratory pressures of 40 and 60 mbar, oesophageal insufflation occurred in all devices”. They concluded that “the use of SADs with inspiratory pressures of 20 mbar appears to be safe regarding the risk of intra-gastric insufflation” but that “higher inspiratory pressures should be strictly avoided”. The role of high ventilation pressures in gastric insufflation was further described by Ho-Tai LM, who showed showed that if “after induction of anaesthesia, two airway management techniques (Facemask/Guedel or Laryngeal Mask) and three peak pressures (20, 25 and 30 cm H2O) were randomly applied during controlled ventilation in 60 patients. The frequency of gastro-oesophageal insufflation was 1.6%, 5% and 5% for the LMA and 5%, 15% and 26.6% for the FM for ventilation pressures of 20, 25 and 30 cm H2O respectively”. These published findings show that all supraglottic airways are susceptible to the phenomena of gastric insufflation with Helmy AM et al. finding that “the incidence of gastric insufflation was significantly more with LMA group 9 (22.5%) vs. I-gel group (5%) (P=0.016)”. Thus with an increased LOS barrier pressure in live patients, a reduced incidence of regurgitation with Guedel type airways in some studies and the role of ventilation pressures in minimizing gastric insufflation, 20cmH2O is considered a safe maximum for Tulip use in routine scenarios.