Comparison of mouth-to-mouth resuscitation and Combitube ventilation in a bench model

CONTEXT: In addition to heart massage, the primary goal of cardiopulmonary resuscitation is efficient oxygenation and ventilation. OBJECTIVE: To compare the ease of learning and handling of standard mouth-to-mouth resuscitation with the Combitube (Tyco Healthcare Nellcor, Pleasanton, CA) ventilation. METHODS: After a 30 minute theoretical introduction and demonstration of mouth-to-mouth resuscitation and use of the Combitube in mannequins, following American Heart Association guidelines, 26 adolescent school children (15 of them 14 years old, 11 of them 10 years old) undertook two ventilation trials, each consisting of five single ventilations, with each technique. Only the second trial with each technique was evaluated. Qualitative implementation (grades: very good, good, failed) was evaluated, several procedure-related time points were recorded, and tidal volumes (ml) were measured. RESULTS: With mouth-to-mouth resuscitation, the time interval until start of first ventilation was 36.5 seconds shorter than with the Combitube (P < 0.001). With the Combitube, the time needed for five single ventilations was 6.4 seconds less than with mouth-to-mouth resuscitation (P < 0.001) and mean tidal volumes were higher (mouth-to-mouth resuscitation, 450 +/- 384 ml, versus Combitube, 735 +/- 358 ml; P < 0.05). CONCLUSION: Most of the school children performed both techniques to a high qualitative level. The study shows that mouth-to-mouth resuscitation and use of the Combitube have equal ease of learning, a precondition for proficient retention of skills. Tidal volumes were significantly higher with the Combitube and, not surprisingly, the time interval until the start of first ventilation was significantly shorter with mouth-to-mouth resuscitation. Regardless of the ventilation technique or device, we believe that subsequent retraining of ventilation skills is very important.     

Effectiveness of various airway management techniques in a bench model simulating a cardiac arrest patient

The purpose of this study was to assess the levels of lung and gastric tidal volumes paramedics achieve when performing ventilation with bag-valve-mask, laryngeal mask, and Combitube. Twenty paramedics performed ventilation with a bag-valve mask, laryngeal mask, and Combitube in a bench model simulating an unintubated cardiorespiratory arrest patient. Lung and gastric tidal volumes and lung and gastric peak airway pressures were subsequently measured. The results showed that mean +/- SEM lung tidal volumes were significantly higher with the laryngeal mask and Combitube compared to the bag-valve-mask (701 +/- 264 vs. 742 +/- 311 vs. 353 +/- 110 mL, respectively). No gastric inflation occurred with the Combitube; gastric inflation was significantly lower with the laryngeal mask compared to the bag-valve-mask (25 +/- 15 vs. 230 +/- 25 mL, respectively). Both the laryngeal mask and Combitube proved to be valid alternatives for bag-valve-mask ventilation in our bench model simulating an unintubated patient with cardiorespiratory arrest.     

Airway management by paramedics using endotracheal intubation with a laryngoscope versus the oesophageal tracheal Combitube and EasyTube on manikins: a randomised experimental trial

INTRODUCTION: The EasyTube, which is constructed in a similar way to the Combitube, is a recently introduced alternative to tracheal intubation for airway management in emergency medicine. OBJECTIVE: To determine if there is a difference in rate of, and time to, successful airway placement and ventilation using tracheal intubation, Combitube and EasyTube. METHODS: Twenty-six paramedics, trained in tracheal intubation received additional training in the use of the Combitube and the EasyTube. Each participant performed all three methods twice in random order on a manikin. Time to successful ventilation (presented as mean and standard deviation) and success rate were recorded. RESULTS: Mean time to successful ventilation was significantly longer for tracheal intubation (45.2 s (S.D.=15.8)) than for the Combitube (36.0 s (S.D. = 8.6)) p = 0.002 and the EasyTube (38.0 s (S.D.=15.3)) p = 0.023 with no difference between the latter (p = 1.000). Success rate for the Combitube and EasyTube combined (103/104) was significantly higher than for tracheal intubation (45/52) with odds ratio 16.0 (95% CI: 1.9-134); p = 0.002. CONCLUSION: For paramedics tested on manikins placement success rate was higher with less time required for the Combitube and Easytube than for tracheal intubation with no differences between the Combitube and EasyTube.     

Piriform Sinus Perforation During Esophageal-Tracheal Combitube Placement

The Esophageal-Tracheal Combitube is a new alternative airway device. Few complications of its use have been reported. This article reports a case of a 71-year-old female with angioedema of the tongue and airway obstruction who suffered piriform sinus rupture during Combitube placement by prehospital personnel, resulting in massive subcutaneous emphysema. Caution is required when using this device in all but the most controlled situations.     

Comparison of different airway management strategies to ventilate apneic,nonpreoxygenated patients

OBJECTIVE: Endotracheal intubation is the gold standard for providing emergency ventilation, but acquiring and maintaining intubation skills may be difficult. Recent reports indicate that even in urban emergency medical services with a high call volume, esophageal intubations were observed, requiring either perfect intubation skills or development of alternatives for emergency ventilation. DESIGN: Simulated emergency ventilation in apneic patients employing four different airway devices that used small tidal volumes. SETTING: University hospital operating room. SUBJECTS: Forty-eight ASA I/II patients who signed written informed consent before being enrolled into the study. INTERVENTIONS: In healthy adult patients without underlying respiratory or cardiac disease who were breathing room air before undergoing routine induction of surgery, 12 experienced professional paramedics inserted either a laryngeal mask airway (n = 12), Combitube (n = 12), or cuffed oropharyngeal airway (n = 12) or placed a face mask (n = 12) before providing ventilation with a pediatric (maximum volume, 700 mL) self-inflating bag with 100% oxygen for 3 mins. MEASUREMENTS AND MAIN RESULTS: In three of 12 cuffed oropharyngeal airway patients, two of 12 laryngeal mask airway patients, and one of 12 Combitube patients, oxygen saturation fell below 90% during airway device insertion, and the experiment was terminated; no oxygenation failures occurred with the bag-valve-mask. Oxygen saturation decreased significantly (p <.05) during insertion of the Combitube and laryngeal mask but not with the bag-valve-mask and cuffed oropharyngeal airway; however, oxygen saturation increased after 1 min of ventilation with 100% oxygen. No differences in tidal lung volumes were observed between airway devices. CONCLUSIONS: Paramedics were able to employ the laryngeal mask airway, Combitube, and cuffed oropharyngeal airway in apneic patients with normal lung compliance and airways. In this population, bag-valve-mask ventilation was the most simple and successful strategy. Small tidal volumes applied with a pediatric self-inflating bag and 100% oxygen resulted in adequate oxygenation and ventilation.     

Evaluation of the oesophageal-tracheal double-lumen tube (Combitube) during general anaesthesia

OBJECTIVES: Evaluation of safety and effectiveness of the Combitube during general anaesthesia. PATIENTS AND METHODS: 250 patients undergoing general anaesthesia were enrolled in the study. The respective types and duration of surgery, ease of insertion of the Combitube, and potential complications were recorded. Maximum ventilatory pressures and leak fraction were also evaluated in this study. RESULTS: Duration of surgery varied between 20 and 410 min. More than 96% of the blind Combitube insertions were successful at the first attempt, with a mean time of less than 18 +/- 5 seconds (range 12-24 seconds). In 99% of patients the Combitube worked well, and adequate oxygenation and ventilation was possible. All patients were haemodynamically stable during the entire duration of surgery. In all patients, pulse oximetry showed an oxygen saturation of 97 +/- 2% and an end-tidal carbon dioxide of 38 +/- 6 mmHg. Leak fraction, calculated as a fraction of the inspired volume, did not increase to more than 5% up to a ventilation pressure of 40 cm H2O. Superficial laceration occurred in 18 patients (7.2%) without further sequelae. No severe injuries were observed during the study period. CONCLUSION: Ventilation via the Combitube appears to be safe and effective during general anaesthesia. Practice in elective cases is a requirement for successful use in an emergency situation.     

Combined use of the esophageal-tracheal Combitube with a colorimetric carbon dioxide detector for emergency intubation/ventilation

Objective. The esophageal-tracheal Combitube (Sheridan, Inc., Argyle, NY) is a unique double lumen tube that has been introduced as an emergency intubation device. Since it is placed blindly, proper use requires determination of which lumen can be successfully used for ventilation. The Easycap (Nellcor, Inc., Pleasanton, CA) is a colorimetric carbon dioxide detector that reacts with exhaled gas to indicate proper tracheal tube location. The purpose of this study was to determine if the Easycap can be used to identify which Combitube lumen is patent to the trachea after blind placement in dogs.Methods and Results. The study was conducted using 8 anesthetized dogs. In each of 15 blind insertions of the Combitube, the Easycap device responded appropriately by changing color from purple to yellow when connected to the lumen communicating with the trachea. When the Easycap device was connected to the alternate lumen, no color change was appropriately observed in 9 out of 15 cases (60%) after 6 breaths; in 4 of the remaining 6 (87%, total), no color change was noted after 12 breaths. In the 2 remaining cases, the color change indicated the need for further verification of the tube location. In separate experiments, 10 direct tracheal and esophageal insertions of the Combitube were correctly verified by the appropriate Easycap color change.Conclusions. Our results suggest that the Easycap device may be useful with the Combitube, although human data are required.     

Airway management with the Combitube during anaesthesia and in an emergency.

The oesophageal-tracheal Combitube (Kendall-Sheridan Catheter Corp., Argyle, NY) is a device designed for difficult airways and emergency intubation. The manufacturer recommends that the Combitube size 37F SA be used in patients with a height of between 122 and 152 cm. The aim of this study was to evaluate whether ventilation is effective and reliable in anaesthetized patients taller than 152 cm using the size 37F SA in the oesophageal position. We also evaluated whether airway protection is adequate and whether direct intubation of the trachea with the Combitube inserted in the oesophagus is possible. We studied 15 adult patients undergoing routine general anaesthesia and 20 patients who required emergency intubation following trauma. They were between 150 and 180 cm in height. Under direct vision, a size 37F SA Combitube was inserted into the oesophagus of all the patients undergoing routine general anaesthesia (control group). Blind insertion was performed in the emergency patients (emergency group). The pharyngeal balloon was inflated with a volume titrated to air leak and cuff pressures were measured. During surgery, a laryngoscope was inserted into the pharynx with the pharyngeal balloon deflated and the laryngoscopic view was evaluated using the Cormack-Lehane scale. Ventilation was effective and reliable in all 35 patients who were between 150 and 180 cm in height. In addition, a direct relationship between the pharyngeal balloon volume and patient height was established (P<0.05), using linear regression models. The laryngoscopic view of the glottis was adequate to allow direct tracheal intubation in patients in the control group, so that the Combitube size 37F SA may be used in patients from 122 to 185 cm in height. The trachea could be directly intubated with the Combitube in the oesophageal position in patients with normal airways and in patients involved in trauma. In all patients in the emergency group, blind insertion of the Combitube resulted in the device being placed in the oesophagus. The airway protection appears to be adequate.     

Alternative ventilation strategies in cardiopulmonary resuscitation

The introduction of the 2000 Guidelines for Cardiopulmonary Resuscitation emphasizes a new, evidence-based approach to the science of ventilation during cardiopulmonary resuscitation (CPR). New laboratory and clinical science underemphasizes the role of ventilation immediately after a dysrhythmic cardiac arrest (arrest primarily resulting from a cardiovascular event, such as ventricular defibrillation or asystole). However, the classic airway patency, breathing, and circulation (ABC) CPR sequence remains a fundamental factor for the immediate survival and neurologic outcome of patients after asphyxial cardiac arrest (cardiac arrest primarily resulting from respiratory arrest). The hidden danger of ventilation of the unprotected airway during cardiac arrest either by mouth-to-mouth or by mask can be minimized by applying ventilation techniques that decrease stomach gas insufflation. This goal can be achieved by decreasing peak inspiratory flow rate, increasing inspiratory time, and decreasing tidal volume to approximately 5 to 7 mL/kg, if oxygen is available. Laboratory and clinical evidence recently supported the important role of alternative airway devices to mask ventilation and endotracheal intubation in the chain of survival. In particular, the laryngeal mask airway and esophageal Combitube proved to be effective alternatives in providing oxygenation and ventilation to the patient in cardiac arrest in the prehospital arena in North America. Prompt recognition of supraglottic obstruction of the airway is fundamental for the management of patients in cardiac arrest when ventilation and oxygenation cannot be provided by conventional methods. "Minimally invasive" cricothyroidotomy devices are now available for the professional health care provider who is not proficient or comfortable with performing an emergency surgical tracheotomy or cricothyroidotomy. Finally, a recent device that affects the relative influence of positive pressure ventilation on the hemodynamics during cardiac arrest has been introduced, the inspiratory impedance threshold valve, with the goal of maximizing coronary and cerebral perfusion while performing CPR. Although the role of this alternative ventilatory methodology in CPR is rapidly being established, we cannot overemphasize the need for proper training to minimize complications and maximize the efficacy of these new devices.     

Advances in airway management

Emergency ventilation is an essential component of basic life support. Respiratory emergencies occur far more frequently than cardiac arrest and, if not treated promptly and effectively, may lead to cardiac arrest. Many respiratory emergencies require assisted ventilation to prevent the occurrence of hypoxemia, hypercarbia, and cardiac decompensation. Emergency assisted ventilation is often difficult to perform and is associated with several adverse complications, such as gastric inflation, regurgitation, and pulmonary aspiration. The American Heart Association sponsored conferences in 1999 and 2000 to review and revise guidelines for cardiopulmonary resuscitation. This article reviews the science behind guideline changes related to pulmonary resuscitation and discusses recent advances in emergency airway management, focusing on noninvasive techniques for ventilation (mouth-to-mouth ventilation, bag-mask ventilation) and alternative airway devices (laryngeal mask airway, the Combitube).     

S UCCESSFUL P REHOSPITAL A IRWAY M ANAGEMENT BY EMT-D S U SING THE C OMBITUBE

Objective. To evaluate the ability to train emergency medical technicians-defibrillation (EMT-Ds) to effectively use the Combitube for intubations in the prehospital environment. Methods. This was an 18-month prospective field study in which EMT-Ds were trained how and in what situations to use the Combitube. Data were then obtained for all patients in whom Combitube insertion was attempted. Indications for use of the Combitube included: unconsciousness without a purposeful response, absence of the gag reflex, apnea or respiratory rate less than 6 breaths/min, age more than 16 years, and height at least 5 feet tall. Contraindications were: obvious signs of death, intact gag reflex, inability to advance the device due to resistance, or known esophageal pathology. Data were entered prospectively from the San Diego County EMS QANet database for prehospital providers. Results. Twenty-two EMT-D provider agencies, involving approximately 500 EMT-Ds, were included as study participants. Combitube insertions were attempted in 195 prehospital patients in cardiorespiratory arrest, with appropriate indication for Combitube use. An overall successful intubation rate (defined as the ability to successfully ventilate) of 79% was observed. Identical success rates for medical and trauma patients were noted. The device was placed in the esophagus 91% of the time. Resistance during insertion was the major reason for unsuccessful Combitube intubations. An overall hospital admission rate of 19% was observed. No complications were reported. Conclusion. EMT-Ds can be trained to use the Combitube as a means of establishing an airway in the pre-hospital setting. Future studies will need to further evaluate its effect on patient outcome.     

Comparison of isocapnic hyperventilation and treadmill exercise in children with exercise-induced asthma

The degree of post-exercise airway obstruction (Exercise-Induced Asthma (EIA] in 14 children was compared to the degree of airway obstruction following isocapnic hyperventilation. EIA was provoked by 6 min of treadmill running. Isocapnic hyperventilation was performed sitting during 6 min. The total ventilation (Vtot) during the two provocations was identical. The temperature of the inspired air was also identical during the two provocations, and the relative humidity was 40% during treadmill-running and 15% during hyperventilation. The decrease in peak expiratory flow after treadmill-running was 29%. After hyperventilation a fall on 19% was seen. These figures are statistically different. It is concluded that although there is a significant difference in airway obstruction after the two provocations the ventilation is greater importance for EIA than is the work load.     

Cyclic appearance of left ventricular outflow tract dynamic obstruction during mechanical ventilation: evidence for a preload dependent phenomenon

The cyclic appearance of dynamic left ventricular outflow tract obstruction during mechanical ventilation, according to the phasic changes in preload, is described in this article. Hemodialysis-induced fluid removal resulted in preload dependence as evidenced by the pulse pressure variation in a 56-year-old critically ill patient. The clinical picture was suggestive of myocardial failure. Transthoracic echocardiography disclosed dynamic left ventricular outflow tract obstruction associated with systolic anterior motion of the mitral valve. Progressive fluid restitution resulted in a parallel decrease in both the degree of dynamic obstruction and pulse pressure variation. During fluid loading, dynamic obstruction disappeared at first during the inspiratory phase of intermittent positive pressure ventilation corresponding to the phasic increase in left ventricular preload. Further fluid loading resulted in the disappearance of dynamic obstruction during both inspiratory and expiratory phase of intermittent positive pressure ventilation. This is the first reported case clearly relating left ventricular outflow tract dynamic obstruction to preload dependence during mechanical ventilation in a critically ill patient without predisposing anatomical factor.     

Necrotizing tracheobronchitis: complication of mechanical ventilation in an adult

A 51-year-old woman had localized interstitial pneumonia that rapidly progressed to involve all lung fields. After 9 days of conventional mechanical ventilation, pneumothorax developed in the presence of an obstruction of the right main bronchus. Bronchoscopy and endobronchial biopsies revealed NTB involving the tracheobronchial tree distal to the tip of the endotracheal tube, with complete obstruction of the right main bronchus by hard, eschar-like material. Tracheal mucosa proximal to the tip of the endotracheal tube was normal. Subsequent bronchoscopy, 20 days later, showed marked resolution of NTB. Though a frequent complication of mechanical ventilation in the neonate, NTB as a complication of conventional mechanical ventilation has not previously been recognized in an adult. Necrotizing tracheobronchitis should be suspected in adults who have had mechanical ventilation and who are experiencing ventilatory difficulties, after routine problems have been treated or excluded.     

The critical airway, rescue ventilation, and the combitube: Part 1

Emergency and unexpected difficult airway management can rapidly deteriorate into a critical airway event such as "cannot ventilate, cannot intubate" (CVCI). A critical airway event (i.e., inadequate mask ventilation, failed intubation, and CVCI) can be resolved by rescue ventilation, thus avoiding potential neurological disability or death. Recommended options include use of the larygeal mask airway, the esophageal-tracheal Combitube (ETC; Tyco-Healthcare-Nellcor, Pleasanton, Calif), transtracheal jet ventilation, or a surgical airway. This article reviews proper use of the ETC in combination with the self-inflating bulb (SIB) and/or portable carbon dioxide detector to resolve critical airway situations. The combined use of these 3 devices provides on ideal integrated system for airway control and ventilation. In addition, critical airway events and rescue ventilation options; ETC design, technical aspects, training, insertion, and ventilation; determining ETC location (i.e., esophagus vs trachea); and monitoring ETC lung ventilation are reviewed. The SIB primarily assesses ETC location within the esophagus or the trachea; the carbon dioxide detector also permits monitoring lung ventilation. Use of the ETC in prehospital, emergency medicine, and anesthesia settings, including ETC advantages, contraindications, and reported complications will be reviewed in Part 2. How to safely exchange the ETC for a definitive airway also will be reviewed.     

Sound level analysis in endotracheal tube obstruction in spontaneous breathing and mechanical ventilation—an animal model study

Endotracheal tube (ETT) obstruction, either complete or partial, is a serious life threatening complication in intubated patients. Therefore, implementing a practical method to diagnose this condition is vital. Alteration in respiratory sound signals caused by ETT occlusion can be used for early detection of obstruction. This study is aimed to assess changes in respiratory sound signals after creation of different types of tubal obstruction in an animal model experiment. Artificial internal obstructions were created in three different sizes and three different locations by stitching pieces of smaller tubes in ETTs with internal diameter of 8 mm. A microphone was used to record respiratory sounds during both spontaneous breathing and mechanical ventilation in seven anesthetized dogs. The sound intensity levels produced by different grades and degrees of obstructions were measured and compared with those in non-obstructed tubes. During spontaneous breathing, significant decrease in sound intensity level was detected even with the lowest grades of obstruction (p?=?0.003, 0.001, and 0.002, proximal, middle and distal obstructions, respectively). However, in mechanical ventilation, significant decrease in sound intensity was observed only in distal tubal obstruction (p?=?0.037). The difference among levels of sound intensity produced by different obstruction locations of occlusion was not statistically significant (p?≥?0.090). Data analysis revealed that sound intensity level decreased significantly when the degree of obstruction increased. In addition, this change in sound level was not related to the location of obstruction. The decrease in sound intensity changes can be used to detect ETT obstruction. However, further studies are needed for clinical application.     

Helium-oxygen and conventional mechanical ventilation in the treatment of large airway obstruction and respiratory failure in an infant

The application of 70% helium-30% oxygen mixtures by tight-fitting face mask in the emergency management of large airway obstruction is well known. We present the case of an infant with severe large airway obstruction and respiratory failure that was unresponsive to the more traditional approaches of airway management, including the delivery of He-O2 by face mask, endotracheal intubation, and conventional mechanical ventilation with oxygen alone. This case was successfully managed with He-O2, when concentrations of O2 were lower than those previously reported in association with conventional mechanical ventilation, until the obstruction could be surgically corrected. We suggest using a new combination of the low-density helium-oxygen gas mixtures and conventional mechanical ventilation, both of which are readily available in most intensive care units.     

COPA as an aid for tracheal intubation

The purpose of this study is to verify the usefulness of the cuffed oropharyngeal airway (COPA) as a device to guide a tracheal tube using a semiblind technique with a lightwand. Ten anaesthetised patients (ASA I-II, aged 35-67) undergoing to an elective surgery were analysed. We selected and positioned a correct size of COPA for each patient. A lightwand (Trachlight) was then inserted into the COPA to confirm correct placement of this device. The lightwand was then removed and the first portion of a tube exchanger (TE) was inserted and connected by a 15-mm connector with the breathing circuit and its position was confirmed by End Tidal CO(2) values during ventilation. The patients were then paralysed and ventilation through the first portion of the TE reconfirmed. The COPA was removed, and the second portion of the TE was connected and used as a guide for a tracheal intubation. This combined technique had a success rate of six out of ten patients and could be used for airway management if a fibre optic scope or other devices such as a Combitube, LMA or LMA Fastrach were not available. The preliminary data from this study are not indicative of the statistical validity of this technique. Further studies should be performed to verify the statistical reliability of the technique.     

An assessment of protection of the airway from aspiration of oropharyngeal contents using the Combitube airway.

A Combitube airway was inserted blindly into 27 American Society of Anaesthesiologist (ASA) grade 1 and 2 patients undergoing general anaesthesia. All had Cormack and Lehane grade 1 direct views of the larynx. Ten ml of 0.1% methylene blue dye was instilled into each patients mouth for the duration of surgery. The oropharynx was then aspirated and dried at completion of surgery and the Combitube removed. The laryngeal inlet and trachea were examined for dye staining. In 25/27 patients (93%) no tracheal soiling was seen. In 2/27 patients (7%) tracheal soiling was seen (95% confidence interval 0.9-24.3%). The Combitube protects the airway in the majority of patients from aspiration of dye within the oral cavity, but the failure rate means it cannot be relied upon absolutely to do so. This has implications for management of the trauma patient.     

Lung collapse during low tidal volume ventilation in acute respiratory distress syndrome

BACKGROUND: Current ventilator management for acute respiratory distress syndrome (ARDS) incorporates low tidal volume (V(T)) ventilation in order to limit ventilator-induced lung injury. Low V(T) ventilation in supine patients, without the use of intermittent hyperinflations, may cause small airway closure, progressive atelectasis, and secretion retention. Use of high positive end-expiratory pressure (PEEP) levels with low V(T) ventilation may not counter this effect, because regional differences in intra-abdominal hydrostatic pressure may diminish the volume-stabilizing effects of PEEP. CASE SUMMARY: A 35-year-old man with abdominal compartment syndrome (intra-abdominal pressure > 48 cm H2O developed ARDS and was treated with V(T) of 4.5 mL/kg and PEEP of 20 cm H2O. Despite aggressive fluid therapy, appropriate airway humidification and tracheal suctioning, the patient developed complete bronchial obstruction, involving the entire right lung and left upper lobe. After bronchoscopy the patient was placed on a higher V(T) (7.0 mL/kg). Intermittent PEEP was instituted at 30 cm H2O for 2 breaths every 3 minutes. This intermittently raised the end-inspiratory plateau pressure from 38 cm H2O to 50 cm H2O. With the same airway humidity and tracheal suctioning practices bronchial obstruction did not reoccur. CONCLUSION: Low V(T) ventilation in ARDS may increase the risk of small airway closure and retained secretions. This adverse effect highlights the importance of pulmonary hygiene measures in ARDS during lung-protective ventilation.