Sealing Mechanics Study of Laryngeal Mask Airways via 3D Modeling and Finite Element Analysis

Background: Proper sealing of laryngeal mask airways (LMAs) is critical for airway management in clinical use. A good understanding of the LMA sealing mechanism provides a scientific foundation to improve the sealing of LMAs to reduce the incidence of adverse events. However, no existing methods provide a systematic study on the LMA sealing mechanics. Methods: Computer-aided 3D models are established to visualize LMA – pharynx interactions directly. The finite element analysis (FEA) is adopted to study the LMA sealing mechanics. Results: Two case studies are provided in the paper. The LMA is loaded with a low cuff pressure (CP) (9 mmHg) to investigate the cause of leaking in Case I, and with a high CP (45 mmHg) to detect the critical points of high mucosal pressure in Case II. The established 3D models provide initiative visualization of the sealing situations. The visualization results are verified by pressure distribution along the contacting surface generated from FEA as the quantitative study. Conclusions: Compared with the existing methods, the proposed method does not introduce additional cost, and can provide globe monitoring on the LMA and a comprehensive understanding of sealing mechanics in all areas. The findings on the sealing mechanism and corresponding suggestions for clinic use of LMAs and LMA design have also been presented in the paper.

Relationships Between Oral-Mucosal Pressure Ulcers, Mechanical Conditions, and Individual Susceptibility in Intubated Patients Under Intensive Care: A PCR-Based Observational Study

Purpose: This study was performed to determine the relationship between oral-mucosal pressure ulcer (PU) stage and mechanical conditions and individual susceptibility in intubated patients. Methods: We collected 80 patient-days data from an intensive care unit of a 700-bed hospital in Korea. We analyzed oral-mucosal PUs, medical records, amount of saliva, and oral mucosal swabs. Bacterial abundance was enumerated by real-time polymerase chain reaction. The χ2 or Fisher’s exact test, t-test or Mann-Whitney U test, and Spearman’s rho correlation analysis were performed. Results: The incidence of overall oral-mucosal PUs was 31.3%, and in the maxillary and mandibular sites were 16.3% and 26.3%, respectively. There were significant correlations between the maxillary site PU stage and restraint use (r = .43, p < .001), albumin level (r = −.22, p = .046), and relative abundance of P. aeruginosa (r = .45, p < .001) and S. aureus (r = −.24, p = .033). In the mandibular sites, there were significant correlations between PU stage and restraint use (r = .30, p = .008), level of consciousness (r = .31, p = .005), and relative abundance of P. aeruginosa (r = .25, p = .028) and S. pneumoniae (r = .22, p = .046). Conclusions: Frequent monitoring and repositioning the mechanical pressure on the oral-mucosa could be an effective preventive strategy against the development and advancement of oral-mucosal PUs. Additionally, monitoring the oral microorganisms can prevent advanced stage oral-mucosal PUs in intubated patients.

The incidence and prevalence of medical device-related pressure ulcers in intensive care: a systematic review

Objective: The objective of this review was to synthesise the literature and evaluate the incidence, prevalence and severity of medical device-related pressure ulcers (MDRPU) in adult intensive care patients. Method: Electronic databases and additional grey literature were searched for publications between 2000 and 2017. Outcome measures included cumulative incidence or incidence rate, point prevalence or period prevalence as a primary outcome and the severity and location of the pressure ulcer (PU) as secondary outcome measures. Included studies were assessed for risk of bias using a nine-item checklist for prevalence studies. The heterogeneity was evaluated using 12 statistic. Results: We included 13 studies in this review. Prevalence was reported more frequently than incidence. Pooled data demonstrated a high variation in the incidence and prevalence rates ranging from 0.9% to 41.2% in incidence and 1.4% to 121% in prevalence. Heterogeneity was high. Mucosal pressure injuries were the most common stage reported in the incidence studies whereas category II followed by category I were most commonly reported in the prevalence studies. In the incidence studies, the most common location was the ear and in the prevalence studies it was the nose. Conclusion: While MDRPU are common in intensive care patients, it is an understudied area. Inconsistency in the staging of MDRPU, along with variations in data collection methods, study design and reporting affect the reported incidence and prevalence rates. Standardisation of data reporting and collection method is essential for pooling of future studies.

Comparison of Mucosal Pressures Induced by Cuffs of Different Airway Devices

Background High pressures exerted by balloons and cuffs of conventional endotracheal tubes, the Combitube (Tyco Healthcare Nellcor Mallinckrodt, Pleasanton, CA), the EasyTube (Teleflex Ruesch, Kernen, Germany), the Laryngeal Mask Airway (LMA North America, San Diego, CA), the Intubating Laryngeal Mask Airway (Fastrach; LMA North America), the ProSeal (LMA North America), and the Laryngeal Tube (LT; VBM Medizintechnik, Sulz, Germany) may traumatize the pharyngeal mucosa. The aim of this study was to compare pressures exerted on the pharyngeal, tracheal, and esophageal mucosa by different devices designed for securing the patient's airways. Methods Nineteen fresh cadavers were included. To measure mucosal pressures, microchip sensors were fixed on the anterior, lateral, and posterior surfaces of the proximal balloon and the distal cuff of the investigated devices. Depending on the respective airway device, the cuff volume was increased in 10-ml increments at the proximal balloon starting from 0 to a maximum of 100 ml, and in 2-ml increments at the distal cuff starting from 0 up to 12 ml. Results Tracheal mucosal pressures were significantly higher using the Combitube compared with the endotracheal tube and the EasyTube. Maximal esophageal pressures were significantly higher using the EasyTube compared with the Combitube. Using cuff volumes according to the manufacturers' guidelines, we found the highest pharyngeal pressures with the Intubating Laryngeal Mask Airway versus all other devices. At maximal volumes, the Laryngeal Mask Airway, the Intubating Laryngeal Mask Airway, and the ProSeal induced significantly higher pharyngeal pressures compared with all other devices. Using a pharyngeal cuff volume of 40 ml, the Intubating Laryngeal Mask Airway followed by the Laryngeal Mask Airway exerted significantly higher pressures compared with the other devices. Conclusions Although some devices exhibit a somewhat higher mucosal pressure when compared with others, the authors believe that the observed differences of the cuff pressures do not suggest a clinically relevant danger, because the investigated devices, except the endotracheal tubes, are not intended for prolonged use.

The Influence of Cuff Volume and Anatomic Location on Pharyngeal, Esophageal, and Tracheal Mucosal Pressures with the Esophageal Tracheal Combitube

Background The authors determined the influence of cuff volume and anatomic location on pharyngeal, esophageal, and tracheal mucosal pressures for the esophageal tracheal combitube. Methods Twenty fresh cadavers were studied. Microchip sensors were attached to the anterior, lateral, and posterior surfaces of the distal and proximal cuffs of the small adult esophageal tracheal combitube. Mucosal pressure for the proximal cuff in the pharynx was measured at 0- to 100-ml cuff volume in 10-ml increments, and for the distal cuff in the esophagus and trachea were measured at 0- to 20-ml cuff volume in 2-ml increments. The proximal cuff volume to form an oropharyngeal seal of 30 cm H2O was determined. In addition, mucosal pressures for the proximal cuff in the pharynx were measured in four awake volunteers with topical anesthesia. Results There was an increase in mucosal pressure in the trachea, esophagus, and pharynx at all cuff locations with increasing volume (all: P &lt; 0.001). Pharyngeal mucosal pressures were highest posteriorly (50-ml cuff volume: 99 +/- 62 cm H2O; 100-ml cuff volume: 255 +/- 161 cm H2O). Esophageal mucosal pressures were highest posteriorly (10-ml cuff volume: 108 +/- 55 cm H2O; 20-ml cuff volume: 269 +/- 133 cm H2O). Tracheal mucosal pressures were highest anteriorly (10-ml cuff volume: 98 +/- 53 cm H2O; 20-ml cuff volume: 236 +/- 139 cm H2O). The proximal cuff volume to obtain an oropharyngeal seal of 30 cm H2O was 47 +/- 12 ml. Pharyngeal mucosal pressures were similar for cadavers and awake volunteers. Conclusion We conclude that mucosal pressures for the esophageal tracheal combitube increase with cuff volume, are highest where the cuff is adjacent to rigid anatomic structures, and potentially exceed mucosal perfusion pressure even when cuff volumes are limited to achieving an oropharyngeal seal of 30 cm H2O.