Small Endotracheal Tube Research Articles

Complications of Different Ventilation Strategies in Endoscopic Laryngeal Surgery

Spontaneous ventilation, mechanical controlled ventilation, apneic intermittent ventilation, and jet ventilation are commonly used during interventional suspension microlaryngoscopy. The aim of this study was to investigate specific complications of each technique, with special emphasis on transtracheal and transglottal jet ventilation. The authors performed a retrospective single-institution analysis of a case series of 1,093 microlaryngoscopies performed in 661 patients between January 1994 and January 2004. Data were collected from two separate prospective databases. Feasibility and complications encountered with each technique of ventilation were analyzed as main outcome measures. During 1,093 suspension microlaryngoscopies, ventilation was supplied by mechanical controlled ventilation via small endotracheal tubes (n = 200), intermittent apneic ventilation (n = 159), transtracheal jet ventilation (n = 265), or transglottal jet ventilation (n = 469). Twenty-nine minor and 4 major complications occurred. Seventy-five percent of the patients with major events had an American Society of Anesthesiologists physical status classification of III. Five laryngospasms were observed with apneic intermittent ventilation. All other 24 complications (including 7 barotrauma) occurred during jet ventilation. Transtracheal jet ventilation was associated with a significantly higher complication rate than transglottal jet ventilation (P < 0.0001; odds ratio, 4.3 [95% confidence interval, 1.9-10.0]). All severe complications were related to barotraumas resulting from airway outflow obstruction during jet ventilation, most often laryngospasms. The use of a transtracheal cannula was the major independent risk factor for complications during jet ventilation for interventional microlaryngoscopy. The anesthetist's vigilance in clinically detecting and preventing outflow airway obstruction remains the best prevention of barotrauma during subglottic jet ventilation.

Effect of endotracheal suction on lung dynamics in mechanically-ventilated paediatric patients

Endotracheal suctioning is performed regularly in ventilated infants and children to remove obstructive secretions. The effect of suctioning on respiratory mechanics is not known. This study aimed to determine the immediate effect of endotracheal suctioning on dynamic lung compliance, tidal volume, and airway resistance in mechanically-ventilated paediatric patients by means of a prospective observational clinical study. Lung mechanics were recorded for five minutes before and five minutes after a standardised suctioning procedure in 78 patients intubated with endotracheal tubes < or = 4.0 mm internal diameter. Twenty-four patients with endotracheal tube leaks > or = 20% were excluded from analysis. There was a significant overall decrease in dynamic compliance (p < 0.001) and mechanical expired tidal volume (p = 0.03) following suctioning with no change in the percentage endotracheal tube leak (p = 0.41). The change in dynamic compliance was directly related to both endotracheal tube and catheter sizes. There was no significant change in expiratory or inspiratory airway resistance following suctioning (p > 0.05). Although the majority of patients (68.5%) experienced a drop in dynamic compliance following suctioning, dynamic compliance increased in 31.5% of patients after the procedure. This study demonstrates that endotracheal suctioning frequently causes an immediate drop in dynamic compliance and expired tidal volume in ventilated children with variable lung pathology, intubated with small endotracheal tubes, probably indicating loss of lung volume caused by the suctioning procedure. There is no evidence that suctioning reduces airway resistance.

Pressure drop across neonatal endotracheal tubes during high-frequency ventilation

High-frequency ventilation (HFV) is a concept of mechanical ventilation that is mainly used in therapy of infants. The resistance of the small neonatal endotracheal tubes (ETT) causes a noticeable difference between airway pressure (proximal end of the ETT) and tracheal pressure (distal end of the ETT). The aim of this laboratory study was to evaluate the pressure drop across the ETT during HFV and to investigate whether tracheal pressure can be calculated from airway pressure using conventional methods.

Is the move to the routine use of small endotracheal tubes evidence based?

Traditionally size 9 and 8 endotracheal tubes (ETTs) for men and women respectively have been used for anaesthesia. There is evidence to support this practice, but there is also growing evidence for the use of smaller tubes.

Tracheal Rupture

We previously published a bronchoscopic image of a tracheal tear involving the posterior tracheal wall during an elective surgical procedure.1 We now present a different image in which the entire tracheal was disrupted after emergency endotracheal intubation. A 77-year-old woman presented to an outside institution with atrial fibrillation and respiratory distress requiring urgent intubation. She subsequently developed increasing subcutaneous emphysema prompting x-ray evaluation, which demonstrated pneumomediastinum. Bronchoscopy performed at that time revealed a long membranous tear that extended to the carina. Bilateral chest tubes were placed and the patient was transported to our institution for definitive therapy. On arrival to the intensive-care unit (ICU), a computed tomography (CT) scan was reviewed and revealed extensive disruption of the trachea from above the sternal notch to the carina. The patient was urgently brought to the operating room where a repair was performed after placing the patient on cardiopulmonary bypass for appropriate oxygenation. The bronchoscopic image is presented below in Figure 1.FIGURE 1.: Note the full-thickness tear involving the posterior wall of the midtrachea.Repair was performed through a median sternotomy incision. Postoperatively, the patient was transferred to the thoracic ICU and doing well at the time of this writing. DISCUSSION Although uncommon, tracheal rupture after endotracheal intubation is well described and is said to occur characteristically in elderly females.2–4 Early and emergent repair is imperative to prevent life-threatening complications. Factors predisposing to tracheal laceration are summarized in Table 1.3,4Table 1: Factors Leading to Tracheal Tear or RuptureWomen are more susceptible to iatrogenic tracheobronchial rupture by virtue of their small body size, which puts them at increased risk of placing the tube too far downward in a short and weak membranous trachea.5 The most frequent cause of tracheal injury associated with intubation appears to be excessive cuff to tracheal wall pressure and inadequate tube size.6,7 It is postulated that excessive cuff pressure causes ischemic necrosis with subsequent rupture of the tracheal wall. In most instances, the posterior membranous wall ruptures longitudinally at the junction with the cartilage, and the length of rupture generally corresponds to the length of the cuff. Extensive tearing can be explained by further dissection under positive pressure ventilation.3 Signs of tracheal rupture, commonly subcutaneous emphysema and respiratory distress, appear immediately after intubation. Early radiographic findings include pneumomediastinum, subcutaneous emphysema, and pneumothorax. Pneumothorax occurs only if the tracheobronchial rupture communicates freely with the pleural space. Emergent flexible bronchoscopy is the best means of confirming the diagnosis and determining the exact location and extent of the lesion, which should be performed in the operating room. Aggressive management is essential to avoid life-threatening complications. Immediate complications include tension pneumothorax and anoxia because most of the tidal volume leaks through the tear. Subacute complications include potentially lethal mediastinitis and tracheal stricture.3 Tracheal intubation distal to the lesion or bronchial intubation with a double lumen tube and pleural drainage are of prime importance for control of respiratory distress. A few patients undergoing emergent repair in severe respiratory distress could require cardiopulmonary bypass. In patients with small tears when less than one third of the circumference of the trachea or bronchus is disrupted and in the absence of gross air leak or respiratory embarrassment, conservative management can be opted. However, any patient with a large tear or evidence of respiratory or circulatory compromise, primary surgical repair is the treatment of choice and must be performed at the earliest.3 Authors believe that even if care is applied during intubation, superficial lesions in the transbronchial tree are unavoidable, especially under emergency conditions. Large, iatrogenic disruptions can be avoided by using small endotracheal tubes and double-lumen tubes with carinal spurs should be generally avoided. Continuous monitoring of the cuff pressure is mandatory to overcome the problem of unnoticed cuff distension as a result of diffusion of nitrous oxide.8

Retropharyngeal or cervicomediastinal haematomas following stellate ganglion block

Retropharyngeal or cervicomediastinal haematomas following stellate ganglion block

High-frequency oscillatory ventilation for acute respiratory distress syndrome in adult patients.

High-frequency oscillatory ventilation (HFOV) using an open-lung strategy has been demonstrated to improve oxygenation in neonatal and pediatric respiratory failure, without increasing barotrauma. Animal studies using small (<4 mm) endotracheal tubes have shown reduced histopathologic evidence of lung injury and inflammatory mediator release, suggesting reduced ventilator-induced lung injury. During the last decade, case reports and observational studies of HFOV in patients failing conventional ventilation strategies have suggested improved oxygenation in adult patients with severe acute respiratory distress syndrome. These reports have also suggested that early (2 days) initiation of HFOV is more likely to result in survival than delayed initiation (>7 days). A recently published randomized, controlled trial in acute respiratory distress syndrome patients (n = 148) comparing HFOV with a pressure-control ventilation strategy (Pao(2)/Fio(2) ratio of <or=200 mm Hg on positive end-expiratory pressure of >10 cm H(2)O) demonstrated early (<16 hrs) improvement in Pao(2)/Fio(2) (p =.008) in the HFOV group but no significant difference in oxygenation index between the two groups during the initial 72 hrs of treatment. Thirty-day mortality was 37% in the HFOV group and 52% in the conventional ventilation group (p =.102). There was no significant difference between treatment groups in the prevalence of barotrauma, hemodynamic instability, or mucus plugging. This study suggests that HFOV is as effective and safe as the conventional strategy to which it was compared. For clinical use in adults, a trial of HFOV may be considered when Fio(2) requirements exceed 60% and mean airway pressure is approaching 20 cm H(2)O or higher (or, alternatively, positive end-expiratory pressure of >15 cm H(2)O). It is currently unknown whether initiating HFOV at a lower severity threshold would result in reduced ventilator-associated lung injury or mortality. Future studies should compare different algorithms of applying HFOV to determine the optimal techniques for achieving oxygenation and ventilation, while minimizing ventilator-associated lung injury. The potential role of adjunctive therapies used with HFOV (e.g., prone ventilation, inhaled nitric oxide, aerosolized vasodilators, liquid ventilation) will require further research.

The Effect of Flexible Bronchoscopy on End-Expiratory Lung Volumes in Intubated Patients on Mechanical Ventilatio

PURPOSE: Flexible bronchoscopy (FB) in intubated patients on mechanical ventilation (MV) increases airway resistance. During FB, two ventilatory strategies are possible: maintaining tidal volume (TV) while maintaining baseline PaCO2 or allowing reduction of TV while permitting hypercapnea. Lawson (Chest 2000; 118:824-831) reported significant hyperinflation due to expiratory flow limitation with FB in an intubated lung model particularly with small endotracheal tubes. We studied end expiratory lung volume (EELV) during FB in intubated patients while limiting TV and permitting hypercapnea.

Shearing Of Plastic Coating Of Stylet With Armored Tube: A Case Report

ETT obstruction due to shearing of the plastic sheath of the stylet has been reported in the past with small endotracheal tubes (ETT) (1, 2). We report a similar case of partial obstruction with a 4.5mm armored ETT. To the best of our knowledge, this is the first report of shearing of the plastic-coated stylet that occurred with an armored ETT. We believe that endotracheal tube stylets should be inspected after each use.

Optimization of high-frequency oscillatory ventilation for the treatment of experimental pneumothorax.

To determine the effect of frequency, amplitude, inspiratory time, and mean airway pressure on gas flow through a chest tube in an animal model of pneumothorax treated with high-frequency oscillatory ventilation (HFOV). Observational study. Animal laboratory. Neonatal piglets (n = 12). After saline lavage, a model of experimental pneumothorax was created by selective right mainstem intubation and manual ventilation at high-peak inspiratory pressure. A chest tube was placed, and gas flow through the chest tube was measured with a pneumotachometer during HFOV with the SensorMedics 3100A. The effects of frequency, inspiratory time, amplitude, and mean airway pressure on chest tube gas flow were determined. Gas flow through the chest tube was significantly higher (p <.001) at 5 Hz (601 +/- 23 mL/min) than at 10 Hz (464 +/- 64 mL/min) or 15 Hz (400 +/- 11 mL/min), while mean airway pressure, inspiratory time, and PaCO2 were kept constant. Gas flow was higher at an inspiratory time of 50% compared with one of 30% (645 +/- 49 vs. 436 +/- 36 mL/min, respectively). Gas flow was directly related to amplitude (284 mL/min at an amplitude of 10 cm H2O, increasing to 877 mL/min at an amplitude of 80 cm H2O) when a 3.5-mm endotracheal tube was used; however, gas flow was attenuated at amplitudes of >40 cm H2O when smaller endotracheal tubes were used. Gas flow increased significantly with the increase of mean airway pressure from 92 mL/min at 15 cm H2O to 1433 mL/min at 30 cm H2O. In a neonatal piglet model of pneumothorax treated with HFOV, with amplitude adjusted to maintain constant alveolar ventilation, gas flow through the chest tube was significantly lower at 15 Hz compared with either 10 Hz or 5 Hz. Chest tube gas flow increased with increasing inspiratory time, amplitude, and mean airway pressure. These findings support the use of higher frequencies, short inspiratory times, low amplitudes, and low mean airway pressures for healing air leak with HFOV.

Anaesthesia for the professional singer

EDITOR: We write concerning the anxieties of a 52-year-old female professional singer, who we recently anaesthetized for a laparotomy to remove a hepatic flexure carcinoma. The patient had undergone a previous general anaesthetic requiring tracheal intubation for a laparoscopic procedure over 20 years ago in North America. This resulted, in her opinion, in damage to her vocal cords and led to voice changes postoperatively. In view of our patient's past history, the case was discussed with a consultant otorhinolaryngologist colleague prior to surgery in order establish the best management plan and to protect laryngeal and vocal function. The patient was reassured preoperatively and informed of the efforts that would be made to prevent damage to her voice. After an intravenous induction and paralysis, the following ‘vocal cord friendly’ anaesthetic was administered to minimize laryngeal damage. • The nasogastric tube was inserted under direct vision with a Magill's forceps. • A small endotracheal tube, size 7, was used and the cuff inflated with air until no leak was heard. • The head and neck were immobilized with 1-L plastic bags of intravenous fluid and tape to prevent head movement and consequent cord irritation. • Sevoflurane, in a mixture of nitrous oxide and oxygen, was administered as the least irritant inhalational agent. • Muscle relaxation was monitored to prevent gagging or straining on the endotracheal tube. • Spontaneous ventilation was established at the end of surgery and the endotracheal tube was removed under ‘deep’ anaesthesia. Postoperatively the patient was recommended, after discharge, to return gradually to her normal singing activity over a period of weeks. In a professional singer whose livelihood and identity depend on vocal function and in an age of litigation, a clinical management protocol should be followed to improve the probability of a favourable outcome. Loucks et al. [1] have proposed one such protocol with the aim of avoiding laryngeal trauma from short-term tracheal intubation that may jeopardize the career and psychosocial health of the vocal athlete. The four objectives of this protocol are as follows. To minimize primary damage to the larynx Primary damage refers to any laryngeal trauma caused by intubating the patient, during the intubated period and by extubation. To minimize secondary damage to the larynx Secondary damage refers to possible laryngeal pathology that may result from overuse or misuse of the voice during the recovery period from intubation or because primary trauma has disposed the patient to later laryngeal dysfunction or damage. To promote patient satisfaction Patient satisfaction refers to a series of variables that include: • patient confidence in the protocol; • patient confidence in the healthcare workers; • patient awareness and acceptance of the intubation procedure and associated risks; • patient compliance with the protocol; and • patient acceptance of postextubation vocal status and quality. To quantify vocal function before and after tracheal intubation Quantifying vocal function refers to a careful objective documentation of vocal status both before and after tracheal intubation. The speech language pathologist, the otolaryngologist and a teacher of singing conduct a voice assessment. After exclusion of factors that may hinder vocal recovery – e.g. allergies and asthma – the team undertakes a full assessment of perceptual, acoustic and aerodynamic characteristics of the speaking and singing voice. Vocal performance is documented using objective and subjective measures. After extubation, the speech language pathologist determines the extent of dysphonia related to intubation by means of an abbreviated videolaryngoscopic assessment. This investigation screens for physical trauma or asymmetrical oscillation. A swallowing assessment is conducted to ensure that the patient can swallow fluids safely, thus, enabling the primary vocal hygiene goal to be achieved, i.e. adequate oral hydration. Fortunately, our patient was pleased with her voice after surgery. However, despite these voice box guidelines, like any first-class athlete after an injury, can the patient really expect to return to the same level of vocal fitness?

Down syndrome: analysis of airway size and a guide for appropriate intubation.

The purpose of this study is to prospectively evaluate the airway size of children with Down syndrome (DS). Previous studies have observed an increase in postintubation stridor in children with DS. Anesthetic literature suggests using a smaller endotracheal tube in children with DS, but more specific recommendations are not offered. With this study, recommendations are presented for the appropriate endotracheal tube size to use in children with DS undergoing intubation. A prospective, nonrandomized study was performed on a cohort of 42 children with DS and 32 control subjects. Sizing of the airway was assessed through measurement of an air leak around the endotracheal tube at intubation. The size of the airway was also evaluated through measurements of the tracheal diameter at the "tracheotomy point" on magnetic resonance imagine (MRI) studies of the head and neck which were performed on a group of children with DS. These were compared with normative values of the tracheal diameter in children. The proper size of endotracheal tube in a population of children with DS and in a group of normal controls was determined. The "proper size" of an endotracheal tube was defined as that size of tube which allowed an audible air leak around the tube between 10 and 30 cm of H2O pressure. Anesthetic technique was controlled and identical for all study subjects. Participants had no previous history of airway compromise, stridor, or previous intubation. Weight and age were recorded and evaluated for their influence on the results. A retrospective evaluation was made of MRI studies of the neck that were performed on children with DS. Using measurement techniques described by Reed et al., the tracheal diameters at the "tracheostomy point" were compared with normative values for children. Measurements were both obtained by the author and confirmed by a pediatric radiologist. Using this prescribed method to determine the proper size of endotracheal tube, the control group used endotracheal tubes that were predicted from established anesthesia charts and formulas. However, children with DS required endotracheal tubes at least two sizes smaller. Age was found to be a more reliable factor in predicting the endotracheal tube size. A table of endotracheal tube sizes for intubation in children with DS is presented. Evaluation of the tracheal diameter at the tracheotomy point revealed that children with DS have a smaller trachea when compared with control children. It is not only the subglottis that is smaller; the tracheal diameter as well must be assumed to be of a smaller diameter in children with DS. Children with DS have smaller airways than other children. This is because of an overall decrease in the diameter of the tracheal lumens. Initial intubation of a child with DS should be performed with an endotracheal tube at least two sizes smaller than would be used in a child of the same age without DS, to avert potential trauma to the airway.

Methods for single-lung ventilation in pediatric patients.

Because many children are too small for doublelumen tubes (DLTs), other techniques are often required for single-lung ventilation (SLV) in pediatric patients. This article offers tube selection guidelines for SLV in children.

Anesthesia for Tracheal Resection: A New Technique of Airway Management in a Patient with Severe Stenosis of the Midtrachea

Anesthesia for Tracheal Resection: A New Technique of Airway Management in a Patient with Severe Stenosis of the Midtrachea

Anesthesia for Tracheal Resection: A New Technique of Airway Management in a Patient with Severe Stenosis of the Midtrachea

We report the combined use of a Fogarty catheter (FC), a 3.5-mm fiberoptic bronchoscope (FOB), and a 6.0 endotracheal tube (ETT) to intubate the lower trachea of a patient with a primary upper- and midtracheal tumor causing a 66% stenosis of the tracheal lumen at the level of the thoracic inlet. Initially, the 6.0 ETT, with the FOB and the FC fed to its tip, was placed above the tumor and rotated 90° counterclockwise. The FOB and the FC were advanced through the stenosis, and the FC cuff was inflated just above the carina. The ETT was advanced over the FOB toward the FC cuff, and the ETT cuff was inflated below the tumor and above the FC cuff. After inspection for blood and tumor debris through the FOB’s eyepiece, the FC cuff was deflated, both the FOB and FC were withdrawn, and intermittent positive pressure ventilation (IPPV) was begun.

Prevention of airway complications in thyroplasty patients requiring endotracheal intubation.

Patients who have undergone silicone vocal cord medialization and require additional surgery are at risk for airway complications. There is a narrowed glottic aperture that may be prone to develop postoperative laryngeal edema and prosthesis extrusion. This study was designed to assess the management of this difficult airway and to determine the frequency of postintubation complications. We identified 82 patients who had undergone vocal cord medialization with silicone implants between 1991 and 1995. Seventeen of these patients underwent additional surgical procedures requiring general anesthesia. A retrospective review of these patients' charts was performed to determine the management of the airway and the incidence of postintubation complications. There were no postintubation complications in the 17 patients who were studied. The duration of surgery ranged from 40 minutes to 4 hours 15 minutes. Two patients were ventilated via bronchoscope, and 15 patients were intubated orally. The endotracheal tubes ranged from size 6 to size 9 (median size 8). None of the patients required perioperative steroids. All patients were successfully extubated in the recovery room. No patients required intubation or tracheotomy, and there were no implant extrusions. In this study, the incidence of postintubation airway complications in patients who had undergone previous thyroplasty was minimal. Nevertheless, the potential for airway compromise exists. We recommend preoperative discussion with the anesthesiologist, atraumatic intubation with a small endotracheal tube, and diligent observation for airway compromise.

Endobronchial Intubation in Infants and Small Children

In Response: We appreciate Dr. Gothard's interest in our article [1]. We agree that computer-based literature scanning can miss certain studies. In 1973, Cullum et al. [2] modified the bevel using scissors for right main bronchus intubation. Small endotracheal tubes with Murphy's eye are now available, so this modification is not practiced. Refashioning the tube bevel with scissors can also leave a raw surface, which can damage the mucosa. It can also form a weak point at which the tube can bend, resulting in complete obstruction of the air flow. Ruchi Gupta, MD, DNB S. K. Singhal, MD K. N. Rattan, MCh Balbir Chhabra, DA, MD Departments of Anaesthesiology and Critical Care and Paediatric Surgery; Pt. B. D. Sharma Postgraduate Institute of Medical Sciences; Rohtak 124001, India

Shearing of Plastic Coating of Stylet with Double Lumen Tube

Assistant Professors of Clinical; Anesthesiology; New York Medical College; Valhalla, New YorkIn Reply:-The experience of Sinha and Dubey involving Carlen's double-lumen tube and stylet supports our view that shearing of the sheath over the stylet is likely to occur at the point of angulation. [1]The force exerted at the proximal end of endotracheal tube during the withdrawal of the stylet is linear in direction. This linear force, while overcoming the curvature at the point of angulation, causes contact and friction between the endotracheal tube and the plastic sheath of the stylet. If this frictional force is greater than the tensile strength of the sheath, shearing occurs. Thin plastic sheath (smaller endotracheal tubes and stylets with thin sheaths are likely to be used together) and increased angulation create conditions ideal for shearing. If these conditions are reproduced in a relatively larger inner-diameter tube, as in the case of the double-lumen tube used by Sinha and Dubey, shearing can take place. We agree with the correspondents that the endotracheal tube stylets should be inspected after each use.Mukul Bhargava, M.D.Surya N. M. Pothula, M.D.Suhasini Joshi, M.D.Assistant Professors of Clinical; Anesthesiology; New York Medical College; Valhalla, New York;(Accepted for publication August 31, 1998.)

Spinal Anesthesia for Cesarean Section in a Case of Pemphigus Foliaceous

Spinal Anesthesia for Cesarean Section in a Case of Pemphigus Foliaceous

Influence of gender and endotracheal tube size on preextubation breathing pattern.

An imbalance between work of breathing and respiratory muscle capacity often results in rapid, shallow breathing (increased respiratory rate/tidal volume [f/VT]). Because this imbalance commonly causes unsuccessful weaning from mechanical ventilation, it is not surprising that an elevated f/VT accurately predicts weaning failure. However, while studying extubation outcome, we observed that women and patients with narrow endotracheal tubes are often successfully extubated with an elevated f/VT. We studied 218 medical patients in the intensive care unit who had a f/VT measured through an oral endotracheal tube (off of ventilatory support) during 1 min of spontaneous respiration at the onset of a weaning trial that culminated in extubation. Men and women were comparable at the onset of mechanical ventilation and weaning trials in severity of illness, etiology of respiratory failure, ventilator settings, and gas exchange data. Women were found to have a higher f/VT (79 +/- 5 versus 56 +/- 3 breaths/L, p < 0.001), lower tidal volumes (381 +/- 14 versus 494 +/- 13 ml, p < 0.001), and higher respiratory rate 26 +/- 1 versus 24 +/- 1, p < 0.05). The differences persisted after controlling for extubation outcome. Smaller endotracheal tubes were associated with a higher f/VT, especially for women (< or = 7 mm, 86 +/- 6 versus > 7 mm, 68 +/- 6, p < 0.05). Women were more likely to have a f/VT > or = 100 (19/82 [women] versus 10/136 [men], p < 0.001). Although the overall incidence of extubation failure was similar (11/82 [women] versus 23/136 [men], p = NS), among patients with f/VT > or = 100, men were more likely to require reintubation (3/19 [women] versus 5/10 [men], p = 0.08). We conclude that women, especially when breathing through small endotracheal tubes, have a higher f/VT (including likelihood of f/VT > or = 100) than men, independent of extubation outcome. Consideration of factors that elevate the f/VT, unrelated to physiologic work of breathing and respiratory muscle capacity, should improve application of this index to extubation decision making.