Development of the PVC endotracheal tube

The history is outlined of the development from metal through rubber to PVC of the endotracheal tube. The technical advantages of the plastics material both for product performance and for processing are summarized. Design features of the modern product are described. Finally, a view is presented of the need now to combine polymer science and clinical research towards further improvement of intubation anaesthesia.     

Inadvertent migration of guidewire into Murphy's eye of endotracheal tube during percutaneous dilatational tracheostomy

Percutaneous dilatational tracheostomy is a commonly performed bedside procedure in the Intensive Care Unit. Although serious and fatal complications have been reported, the procedure is by and large safe to perform in experienced hands. We report here an innocuous problem encountered twice. After the guidewire insertion and dilatation, subsequent railroading became difficult owing to migration of guidewire into the Murphy''s eye of the endotracheal tube (ETT). Awareness about this possibility can avert inadvertent delays and complications during the procedure. A tug or gentle pulling of ETT after insertion of the guidewire rules out an impaction in the eye or other part of the ETT.     

The endotracheal tube biases the estimates of pulmonary recruitment and overdistension

To assess the impact of the endotracheal tube (ETT) and of different flow waveforms on estimates of alveolar cyclic recruitment (CR) and overdistension (AO). Numerical simulation of the respiratory system plus ETT (inertance L plus a flow-dependent resistance, K (1) and K (2)), with the following non-linear equation of motion [Formula: see text](P (AW) pressure at the airways opening, V volume), under volume-controlled mechanical ventilation. An index %E (2) = 100.(E (2).V (T))/(E (1) + E (2).V (T)) can be calculated where %E (2) > 30% represents AO and %E (2) < 0% represents CR. Parameters were estimated by the least-squares method, either with the complete equation or supressing L, K (2) or both. %E (2) is always underestimated (down to -152 percent points) with incomplete equations of motion. The estimation of %E (2) may be strongly biased in the presence of an ETT excluded from the estimation model.     

Detection of partial endotracheal tube obstruction by forced pressure oscillations

Rapid airway occlusions during mechanical ventilation are followed immediately by high-frequency pressure oscillations. To answer the question if the frequency of forced pressure oscillations is an indicator for partial obstruction of the endotracheal tube (ETT) we performed mathematical simulations and studies in a ventilated physical lung model. Model-derived predictions were evaluated in seven healthy volunteers. Partial ETT obstruction was mimicked by decreasing the inner diameter (ID) of the ETT. In the physical model ETTs of different ID were used. In spontaneously breathing volunteers viscous fluid was applied into the ETT's lumen. According to the predictions derived from mathematical simulations, narrowing of the ETT's ID from 9.0 to 7.0mm decreased the frequency of the pressure oscillations by 11% while changes of the respiratory system's compliance had no effect. In volunteers, a similar reduction (10.9%) was found when 5 ml fluid were applied. We conclude that analysis of pressure oscillations after flow interruption offers a tool for non-invasive detection of partial ETT obstruction.     

Continuous monitoring of tracheal pressure including spot-check of endotracheal tube resistance.

During mechanical ventilation, the resistance of the endotracheal and tracheostomy tube (ETT) highly influences analysis of respiratory system mechanics and imposes additional work of breathing for the spontaneously breathing patient which both can be circumvented by applying the automatic tube compensation (ATC) mode. In the ATC mode, tracheal pressure (ptrach) is continuously calculated on the basis of measured flow and airway pressure using predetermined tube specific coefficients. However, as during long-term ventilation the ETT might become partially obstructed by secretions or tube kinking, the predetermined coefficients are no longer valid rendering calculation of ptrach inaccurate. We propose an easy-to-handle maneuver for the bedside determination of current tube coefficients in the tracheally intubated patient. Based on check-spot measurement of ptrach, current tube coefficients are determined by a least-squares fit procedure valid for the partially obstructed ETT with the indwelling pressure-measuring catheter (PMC). To correct for the removal of the PMC, the relationship between tube coefficients with and those without indwelling PMC has been determined in a laboratory investigation. Accuracy of the procedure was determined during artificial ETT obstruction by comparing calculated with measured ptrach. Correspondence between calculated and measured ptrach has been found excellent. We conclude that by adopting this bedside procedure periodically, accurate calculation of ptrach is guaranteed and the advantages of the ATC mode are ensured even in long-term ventilatory support.     

Reduction of the bacterial load by the silver-coated endotracheal tube (SCET), a laboratory investigation.

Microaspiration enabled by high-volume-low-pressure cuffed endotracheal tubes is the most likely explanation for ventilator-associated pneumonia. To decontaminate the secretion at the proximal end of the cuff we developed a silver-coated endotracheal tube (SCET). In an in vitro model we investigated the efficacy of SCET to lower the bacterial load of secretion and aspirate. We developed a continuously contaminated and mechanically ventilated oropharynx-larynx-lung model to investigate the reduction of the bacterial count by SCET compared to controls. The model was continuously contaminated via the oropharynx-larynx with Pseudomonas aeruginosa ATCC 27853. During the investigation period of 50 hours the bacterial count of oropharynx-larynx and lung was measured as colony-forming-units/ml. In addition, the characteristic curve of silver ion release of SCET was determined. SCET significantly reduced the bacterial count in oropharynx-larynx at all timepoints (p < 0.05). In lung the bacterial count was significantly lower beginning with the 36th hour of recording (p < 0.05). A reduction of greater than 2 log was found from 28 hours on in oropharynx-larynx and from 50 hours on in lung. The release of silver ions was very rapid and was described by a mono-exponential function with a time-constant tau of about 60 minutes and a saturation concentration of 200 +/- 80 microg/l. SCET showed a significant inhibition of growth of P. aeruginosa in the continuously contaminated and mechanically ventilated oropharynx-larynx-lung model. SCET by thus might be helpful in reducing ventilator-associated pneumonia.     

Changes in the lung surfactant of rabbits during endotracheal halothane anesthesia

Endotracheal halothane anesthesia without any attendant operation in rabbits for 3.5 h causes changes in the surface-active properties of the surfactant, with an increase in the surface tension of lung washings as measured on Wilhelmy scales. A study of phospholipid fractions in lung washings by thin-layer chromatography on silica gel showed a decrease in phosphatidylcholine, one of the principal structures of the surface-active lipoprotein, and a simultaneous increase in the lysolecithin fraction. Determination of the content of free fatty acids in lung washings after halothane anesthesia showed a significant increase over the control. The possible mechanism of the harmful action of halothane anesthesia on the lung surfactant is discussed.Central Research Laboratory, Department of Normal Physiology, Tadjik Medical Institute, Dushanbe. (Presented by Academician V. N. Chernigovskii.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 84, No. 10, pp. 423–425, October, 1977     

复方利多卡因乳膏涂抹气管导管表面预防甲状腺手术全麻拔管期呛咳躁动

目的评价复方利多卡因乳膏涂抹于气管导管表面,用于全麻甲状腺手术气管黏膜表面麻醉的有效性。方法前瞻随机双盲对照研究,连续纳入北京协和医院42例甲状腺部分或全切手术患者,随机分为对照组(C组)和试验组(L组)。将L组气管导管前1/2和套囊表面均匀涂布复方利多卡因乳膏(约2 g),C组导管表面涂抹石蜡油。研究终点为拔管期自发或诱发的(人为套囊放气充气)呛咳躁动事件。记录血流动力学指标,随访患者在麻醉恢复室(PACU)和住院期间并发症。结果拔管前的自发呛咳躁动率L组低于C组(15%和65%)(P0.01);套囊放气充气试验阳性率L组低于C组(35%和90%)(P0.001)。带管期间发生血压或心率增加超过基线20%的发生率,L组有低于C组的趋势(1.65±1.26和5.57±2.06次/例);拔管后1 min两组间收缩压与心率乘积,L组(12 867±2 169)低于C组(16 385±2 242)(P0.05)。结论对于全麻下甲状腺手术,气管导管表面涂抹复方利多卡因乳膏进行气管黏膜表面麻醉,能够有效减少全麻拔管期患者的呛咳和躁动,降低心血管应激。     

颏下动脉穿支皮瓣的数字解剖学研究

目的为颏下动脉穿支皮瓣的设计和安全切取提供解剖学基础。方法应用红色乳胶灌注新鲜尸体标本2具;使用改良了的明胶--氧化铅血管造影技术,灌注新鲜尸体标本8具。后者中的2具尸体,使用螺旋CT进行扫描并通过相应的软件存储扫描得到的图像,并三维重建。然后,对10具尸体层次解剖追踪颏下区外径≥0.5 mm的穿支,测量其走行、分支、分布情况并拍摄X线片。同时应用ScionImage软件对颏下动脉营养区域的表面积进行计算。结果颈前区和下颌前区皮肤和肌肉的营养主要通过:甲状腺上动脉、舌动脉、颏下动脉、颏动脉、面动脉等几个主要动脉的穿支供应。颏下动脉从面动脉起始处的直径为(1.7±0.4)mm,沿途发出(1.8±0.6)支穿支营养颏下区的皮肤。颏下动脉营养皮肤的范围为(45±10.2)cm2。其最大的一个穿支出现于二腹肌前腹内侧缘的后面。同时,面动脉、颏下动脉、舌下动脉的穿支之间存在丰富的吻合。结论本文阐述了颏下皮瓣的解剖学基础,并结合重建的三维可视化模型对皮瓣血供和皮瓣设计提供了依据。     

Brr2p-mediated conformational rearrangements in the spliceosome during activation and substrate repositioning

Brr2p is one of eight RNA helicases involved in pre-mRNA splicing. Detailed understanding of the functions of Brr2p and other spliceosomal helicases has been limited by lack of knowledge of their in vivo substrates. To address this, sites of direct Brr2p–RNA interaction were identified by in vivo UV cross-linking in budding yeast. Cross-links identified in the U4 and U6 small nuclear RNAs (snRNAs) suggest U4/U6 stem I as a Brr2p substrate during spliceosome activation. Further Brr2p cross-links were identified in loop 1 of the U5 snRNA and near splice sites and 3′ ends of introns, suggesting the possibility of a previously uncharacterized function for Brr2p in the catalytic center of the spliceosome. Consistent with this, mutant brr2-G858R reduced second-step splicing efficiency and enhanced cross-linking to 3′ ends of introns. Furthermore, RNA sequencing indicated preferential inhibition of splicing of introns with structured 3′ ends. The Brr2-G858Rp cross-linking pattern in U6 was consistent with an open conformation for the catalytic center of the spliceosome during first-to-second-step transition. We propose a previously unsuspected function for Brr2p in driving conformational rearrangements that lead to competence for the second step of splicing.     

Correction of compliance and resistance altered by endotracheal tube leaks and non-linear pressure/volume-relationships

Measurements of lung compliance (C) and resistance (R) are influenced by endotracheal tube leaks (ETTL) as well as non-linear pressure/volume relationships (P/V relationship). To keep C and R reliable, we developed an algorithm to mathematically correct inspiratory and expiratory volume (V) and flow. In this study, a ventilated lung model for non-linear P/V relationship with adjustment of an increasing ETTL was studied. In addition, the recordings (airway pressure, flow, and volume) of 21 infants (median weight: 1,220 g, range: 640-2,160 g, with a median leak size of 32%, range: 24-56%) were investigated. C and R were calculated continuously from the recordings of flow, volume, and airway pressure over time according to the changing volume. A method especially developed for the analysis of non-linear pressure-volume-relationship (APVNL) was employed. C and R affected by leaks were corrected applying the newly developed mathematical algorithm and compared with measurements without leakage. C could be corrected up to a leak of 80% and R up to 55% leak at half tidal V for the model with non-linear P/V-R. C and R without leak and after leak correction did not differ significantly in all infants where the APVNL method was applied (P > 0.05).     

Theoretical estimation of retinal oxygenation during retinal detachment

The aim of the present work was to simulate the oxygenation of the whole retina during different degrees of retinal detachment. A differential equation describing the oxygenation of the whole retina, at different degrees of detachment, was set up and solved numerically. The results show that the choroid can supply the outer retina with a fairly large amount of oxygen as long as the detachment height is lower than about 1mm. This study thus supports the view that hyperoxia may well prove to be clinically beneficial.     

Electromyography as a new means of navigation during endotracheal intubation

Abstract

This study tested a method of using rapid analysis of electromyographic response patterns to electrical stimulation to enable real-time navigation during endotracheal intubation. An electromyographic response detection device was constructed and integrated into a standard endotracheal tube. The rebound rates of the response voltages were measured in the trachea and oesophagus after stimulation in an acute study performed in three freshly euthanized male Suffolk sheep. In a blind study, a physician attempted to identify the tissue type solely from the electrical response signals. In the acute study, the observed rebound rate was found to be significantly faster in tracheal tissue (2.21?×?10^?3 V s^?1) than in oesophageal tissue (3.45?×?10^?2 V s^?1; p?=?0.000 05). In the blind study, the physician correctly determined the oesophagus response rate seven out of eight times and the tracheal rate eight out of nine times. These results suggest that electromyographic responses can be used to accurately differentiate tracheal from oesophageal tissue during ETT insertion, thus offering a valuable new means of enhancing patient safety.     

Uterine thermal balloon therapy under local anaesthesia for the treatment of menorrhagia: a pilot study

This study evaluates the use of local anaesthesia in a subset of patients undergoing uterine thermal balloon endometrial ablation for the treatment of menorrhagia. Out of 51 patients with dysfunctional uterine bleeding, 18 were included for uterine balloon therapy under local anaesthesia. Inclusion criteria were dysfunctional bleeding with absence of organic lesions in the uterine cavity, adequate relaxation and pain control during physical examination and diagnostic hysteroscopy, and patient desire to avoid a general anaesthetic. Paracervical block was performed with 20 ml of dilute 1% lignocaine HCl with epinephrine 1:200,000. Success of the procedure was defined as amenorrhoea, hypomenorrhoea, or eumenorrhoea. The median follow-up period was 13.9 +/- 5 months and 11 patients (61%) had follow-up of >1 year. Treatment led to a significant decrease in menstrual flow, duration, and pad count in all patients (P < 0.0001). No intra- operative complications occurred. A pain scale (level 1-10) was used to evaluate the patients' tolerance of the procedure (mean 3.8 +/- 1.3). In light of these successful and well tolerated procedures, thermal balloon endometrial ablation, utilizing local anaesthesia, appears practical as an office-based therapy.