Work of breathing through different sized endotracheal tubes

The ability to breathe spontaneously through an endotracheal tube is a usual prerequisite before an intubated patient can have it removed. Other researchers have measured air flow resistance through endotracheal tubes. In this study, we evaluated work of breathing in joules per min and tension-time index while three normal volunteers breathed through different sized endotracheal tubes. Four 27.5-cm endotracheal tubes were used. Subjects breathed with a constant tidal volume of 500 ml. By increasing respiratory frequency, minute ventilation was increased from 5 to 30 L/min. As tube diameter decreased, work and the tension-time index increased. Changes were magnified at higher minute ventilations through the 6- and 7-mm endotracheal tubes, and the tension-time index critical fatigue level of 0.15 was approached or exceeded.     

Additional work of breathing imposed by endotracheal tubes, breathing circuits, and intensive care ventilators

A disadvantage of spontaneous breathing through an endotracheal tube (ETT) and connector attached to a breathing circuit and/or ventilator (breathing device) is an increase in the work of breathing. The work of breathing associated with ETT of 6 to 9-mm diameter and eight breathing devices was determined, using a lung simulator to mimic spontaneous inspiration at flow rates of 20 to 100 L/min and a tidal volume of 500 ml, at both zero end-expiratory pressure (ZEEP) and 10 cm H2O continuous positive airway pressure (CPAP). Work associated with the breathing devices alone (WCIR) ranged from -0.002 kg.m/L (Servo 900-C ventilator, 7-mm ETT, 20 L/min, ZEEP) to 0.1 kg.m/L (continuous flow circuit, 7-mm ETT, 100 L/min, CPAP), the latter representing 196% of the work of normal breathing. When the devices were attached to ETT, total apparatus work (WAPP) ranged from 0.009 kg.m/L (Mapleson-D circuit, 9-mm ETT, 20 L/min, ZEEP) to 0.25 kg.m/L (Drager EV-A, 6-mm ETT, 100 L/min, ZEEP), the latter representing 490% of the work of normal breathing. This additional work imposed by the ETT varied considerably among devices. Spontaneous breathing through modern ventilators, circuits and ETT imposes a burden of increased work, most of which is associated with the presence of the ETT and connector. Whether this burden represents an impediment to the weaning patient, or has training value for the ultimate resumption of unassisted spontaneous ventilation, remains to be determined.     

Flow resistance, work of breathing of humidifiers, and endotracheal tubes in the hyperbaric chamber

Humidification of inspired gas is critical in ventilated patients, usually achieved by heat and moisture exchange devices (HMEs). HME and the endotracheal tube (ETT) add airflow resistance. Ventilated patients are sometimes treated in hyperbaric chambers. Increased gas density may increase total airway resistance, peak pressures (PPs), and mechanical work of breathing (WOB). We tested the added WOB imposed by HMEs and various sizes of ETT under hyperbaric conditions. We mechanically ventilated 4 types of HMEs and 3 ETTs at 6 minute ventilation volumes (7-19.5 L/min) in a hyperbaric chamber at pressures of 1 to 6 atmospheres absolute (ATA). Peak pressure increased with increasing chamber pressure with an HME alone, from 2 cm H₂O at 1 ATA to 6 cm H₂O at 6 ATA. Work of breathing was low at 1 ATA (0.2 J/L) and increased to 1.2 J/L at 6 ATA at minute ventilation = 19.5 L/min. Connecting the HME to an ETT increased PP as a function of peak flow and chamber pressure. Reduction of the ETT diameter (9 > 8 > 7.5 mm) and increase in chamber pressure increased the PP up to 27.7 cm H₂O, resistance to 33.2 cmH₂O*s/L, and WOB to 3.76 J/L at 6 ATA with a 7.5-mm EET. These are much greater than the usually accepted critical peak pressures of 25 cm H₂O and WOB of 1.5 to 2.0 J/L. Endotracheal tubes less than 8 mm produce significant added WOB and airway pressure swings under hyperbaric conditions. The hyperbaric critical care clinician is advised to use the largest possible ETT. The tested HMEs add negligible resistance and WOB in the chamber.     

Insertion of difficult nasogastric tubes through a nasoesophageally placed endotracheal tube

A technique is described to facilitate the insertion of NG tubes with the aid of nasoesophageal insertion of an endotracheal tube. This technique is particularly useful in comatose and anesthetized patients. The equipment utilized is easily assembled and readily available. We have found this method to be easier and more successful than those previously described.     

Effect of inspiratory flow waveform on work on endotracheal tubes: a model analysis

Objective: This model analysis aimed to predict the impact of different inspiratory flow waveforms, i. e., constant, sinusoidal, and two linearly decreasing flows, on the resistive work (Wres) performed on endotracheal tubes. Design: Model analysis. Results: Model analysis predicts that: (i) minimal Wres is obtained with the constant flow; (ii) for any given tidal volume/inspiratory duration (Vt/Ti, mean inspiratory flow), Wres increases with decreasing tube size; (iii) for any given inspiratory flow waveform, Wres increases with increasing Vt/Ti, being lowest with constant flow. Conclusions: These findings have major clinical implications: at any given ventilator setting, not only the size of the endotracheal tube but also the inspiratory flow waveform must be taken into account to interpret the values of Wres and hence of the total work of breathing. Received: 23 July 1998 Final revision received: 4 December 1998 Accepted: 18 February 1999     

Unrecognized esophageal placement of endotracheal tubes

Unrecognized esophageal placement of endotracheal tubes during general anesthesia or in apneic unanesthetized patients is not an uncommon occurrence. Allowing this mishap to proceed to asphyxia and catastrophe is inexcusable. If one is uncertain, proper placement can be quickly verified by mouth-to-tube insufflation of a subject's lungs with one's own expired air immediately after intubation. This method of verification may be useful in areas other than the operating room, where intubations are performed for resuscitation or airway control.     

Effect of inner cannula removal on the work of breathing imposed by tracheostomy tubes: a bench study

BACKGROUND: Tracheotomy has been used to assist in weaning patients from mechanical ventilation. Some patients fail to be weaned from the ventilator despite tracheostomy. We hypothesized that removing the inner cannula from the tracheostomy tube would decrease the tube's imposed work of breathing (WOB(IMP)). METHODS: The hypothesis was tested using a lung model, by measuring the change in WOB(IMP) when the inner cannula was removed. A mechanical lung model was developed using a test lung to simulate a spontaneously breathing patient. WOB(IMP) was measured with a commercially available lung mechanics monitor. Shiley size 6, 8, and 10 nonfenestrated tracheostomy tubes were tested with the inner cannula in and out. Breathing conditions were simulated using tidal volumes (V(T)) of 300 and 500 mL matched with breathing frequencies of 12, 24, and 32 breaths per minute, by using a ventilator to simulate spontaneous breathing through one side of the test lung. RESULTS: Under all the tested breathing conditions, WOB(IMP) for each of the 3 tracheostomy tubes was significantly reduced (p < 0.05) when the inner cannula was removed. Also, as simulated spontaneous inspiratory flow demand increased (ie, as V(T) and/or frequency were increased), WOB(IMP) also increased, and vice versa. With the cannula removed, WOB(IMP) was not significantly different between the size 6 and 8 tubes nor between the size 8 and 10 tubes when V(T) was 300 mL and frequency was 12 breaths per minute. CONCLUSIONS: There was a significant decrease in WOB(IMP) with each tube when the inner cannula was removed. WOB(IMP) increased with an increase in inspiratory flow demand (ie, increase in V(T) and/or frequency), as well as when tube size decreased. In weaning a tracheostomized patient from mechanical ventilation, increasing the internal diameter of the tube by removing the inner cannula may be beneficial. Further study is needed to determine if these findings are clinically important.     

气管插管固定的护理进展

气管插管术是急救工作中经常采用的抢救措施之一，用于缓解上呼吸道梗阻、气管内给药及进行机械通气，是呼吸肌麻痹和手术麻醉开放气道的最常见方法和不可缺少的手段“J。在救治过程中，有效地保护和固定气管插管，防止其移位和脱管，是抢救成功的有力保障。气管插管的移位或脱管，不但会造成非计划拔管，影响救治效果，还有可能威胁患者生命，严重者成为医疗事故。现将近年来对气管插管固定方法和进展综述如下。     

Complications from unrecognized defects in endotracheal tubes

Considerable effort has been made to improve endotracheal tubes and make them safer than they have been in the past; yet complications continue to occur, due, in most instances, to inherent defects in the tube. It is not possible to identify these defects in a routine preoperative examination. Three cases are presented illustrating how defects in anode endotracheal tubes almost caused fatalities during anesthesia. Other possible complications and contributing factors causing obstruction of endotracheal tubes are also reviewed. Until some way is devised for the automatic compensation of the increases in volumes and pressures in endotracheal tube cuffs, hourly deflation is recommended to prevent complications.     

Antimicrobial-coated endotracheal tubes: an experimental study

OBJECTIVE: Antibiotic-resistant bacterial biofilm may quickly form on endotracheal tubes (ETTs) and can enter the lungs, potentially causing pneumonia. In an attempt to prevent bacterial colonization, we developed and tested in an in-vitro study and animal study several antibacterial-coated ETTs (silver sulfadiazine with and without carbon in polyurethane, silver sulfadiazine and chlorhexidine with and without carbon in polyurethane, silver-platinum with and without carbon in polyurethane, chlorhexidine in polyurethane, and rose bengal for UV light). DESIGN, SETTING, ANIMALS, INTERVENTIONS: After preliminary studies, silver sulfadiazine in polyurethane (SSD-ETT) was selected among the coatings to be challenged every 24 h with 10(4)-10(6) Pseudomonas aeruginosa/ml and evaluated at 6 h, 24 h, and 72 h with standard microbiological studies, scanning electron microscopy, and confocal scanning microscopy. Subsequently, eight sheep were randomized to receive either a SSD-ETT or a standard ETT (St-ETT). After 24 h of mechanical ventilation, standard microbiological studies were performed together with scanning electron microscopy and confocal microscopy. MEASUREMENTS AND RESULTS: In the in-vitro study SSD-ETT remained bacteria-free for up to 72 h, whereas St-ETT showed heavy P. aeruginosa growth and biofilm formation (p < 0.01). In sheep, the SSD-ETT group showed no bacterial growth in the ETT, ventilator tubing, and lower respiratory tract, while heavy colonization was found in the St-ETT (p < 0.01), ventilator tubing (p=0.03), and lower respiratory tract (p < 0.01). CONCLUSION: This study describes several effective and durable antibacterial coatings for ETTs. Particularly, SSD-ETT showed prevention against P. aeruginosa biofilm formation in a 72-h in-vitro study and lower respiratory tract colonization in sheep mechanically ventilated for 24 h.     

4种方法消毒气管内套管效果比较研究

目的比较3%双氧水、2%戊二醛、硼砂酚醛浸泡和煮沸消毒方法对气管内套管的消毒效果。方法在实验观察的基础上,分别采用上述方法对同期气管切开病人使用中的气管内套管进行消毒,并对每种方法消毒前后、4种方法消毒前、4种方法消毒后内套管染菌情况进行比较。结果4种方法消毒前内套管染菌情况均较严重,各组间比较无显著性差异(P>0.05);每种方法消毒前后内套管染菌情况显示显著性差异(P<0.01或P<0.001);4种方法消毒后内套管染菌量比较,除双氧水组与其它各组间有显著性差异外(P<0.01),其余各组间均无显著性差异(P>0.05)。结论4种方法用于气管内套管消毒均有效,其中尤以煮沸法、戊二醛浸泡法、硼砂酚醛浸泡法为佳,双氧水浸泡法稍差。2%戊二醛及硼砂酚醛浸泡可以取代传统的煮沸法用于气管内套管的消毒。     

Minimizing work of breathing with continuous positive airway pressure and intermittent mandatory ventilation: an improved continuous low-flow system

Minimizing work of breathing (WOB) during intermittent mandatory ventilation (IMV) and continuous positive airway pressure (CPAP) is important as it facilitates weaning from mechanical ventilation. To minimize WOB, we devised a simple, continuous-flow CPAP-IMV system that uses a weighted, partially filled reservoir bag and operates efficiently at low fresh gas flow (FGF). We compared both the pattern and WOB of our system (FGF at 15 L/min) with a conventional continuous-flow CPAP/IMV system (FGF at 15 and 30 L/min) as well as with two relatively efficient demand-value systems, the Servo 900 B and 900 C. Six healthy male subjects were studied; tidal volumes (VT), flow, mouth pressure, and pleural pressure (Ppl) were measured. Ten breaths, matched for VT, from each subject on each system were selected for analysis. Mechanical WOB was estimated by integrating Ppl with respect to VT. The conventional continuous-flow system was associated with a high work/breath relative to the other systems (p less than .001). The weighted reservoir system was associated with a significantly lower work/breath (p less than .001), its performance approaching that of the Servo 900B. Work/breath was least with the Servo 900C (p less than .001). As breathing frequency was higher with the demand valve than continuous-flow systems (p less than .001), the difference in work/time was minimal between the weighted reservoir bag and demand-valve systems. These systems were all associated with significantly (p less than .001) lower work/time than the conventional system at both FGF.(ABSTRACT TRUNCATED AT 250 WORDS)     

Additional inspiratory work of breathing imposed by tracheostomy tubes and non-ideal ventilator properties in critically ill patients

Objective: To determine the tracheostomy tube-related additional work of breathing (WOB_add) in critically ill patients and to show its reduction by different ventilatory modes. Design: Prospective, clinical study. Setting: Medical ICU of a university teaching hospital. Intervention: Standard tracheostomy due to prolonged respiratory failure. Measurements and results: Ten tracheostomized, spontaneously breathing patients were investigated. As the tube resistance depends on gas flow, patients were subdivided according to minute ventilation into a low ventilation group ( = 10 l/min; n = 5) and a high ventilation group ( > 10 l/min; n = 5). The WOB_add due to tube resistance and non-ideal ventilator properties was calculated on the basis of the tracheal pressure measured. Ventilatory modes investigated were: continuous positive airway pressure (CPAP), inspiratory pressure support (IPS) of 5, 10, and 15 cm H₂O above PEEP, and automatic tube compensation (ATC). In the low ventilation group, WOB_add during CPAP was 0.382 ± 0.106 J/l. It was reduced to below 15 % of that value by ATC or IPS more than 5 cm H₂O. In the high ventilation group WOB_add during CPAP increased to 0.908 ± 0.142 J/l. In this group, however, only ATC was able to reduce WOB_add below 15 % of the value observed in the CPAP mode. Conclusions: The results indicate that, depending on respiratory flow rate, (1) tracheostomy tubes can cause a considerable amount of WOB_add, and (2) ATC, in contrast to IPS, is a suitable mode to compensate for WOB_add at any ventilatory effort of the patient. Received: 12 August 1998 Final revision received: 22 February 1999 Accepted: 24 February 1999     

气管插管固定方法的应用进展

气管插管在临床危重症抢救中应用率较高,是抢救危重症患者的重要手段。意外拔管是气管插管的常见并发症,未妥善固定是气管插管意外拔管的重要原因之一。通过介绍气管插管固定方法,包括医用胶布固定法、Duropore胶布固定法、寸带固定法、别针固定法、气管插管固定器等方法,提出针对不同人群选择最适合的材料及固定方法,使气管插管固定更加牢固。