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PubMed1998

Effects of partial liquid ventilation on lung injury in a model of acute respiratory failure: a histologic and morphometric analysis.

OBJECTIVE: To compare the histopathologic changes observed in a sheep model of oleic acid-induced acute respiratory failure during partial liquid ventilation with perflubron with gas ventilation. DESIGN: Randomized, controlled study. SETTING: Animal laboratory and pathology laboratories of a university hospital. SUBJECTS: Fourteen healthy adult sheep, weighing 64.9 +/- 6.4 kg. INTERVENTIONS: Lung injury was induced with oleic acid (0.15 mL/kg). A tracheostomy tube was inserted, along with systemic and pulmonary artery monitoring catheters. Animals were randomized to undergo either partial liquid ventilation (n = 7) or gas ventilation (n = 7). Animals underwent euthanasia at the end of the 90-min study period, after which the endotracheal tube was clamped with the lungs in expiratory hold at a positive end-expiratory pressure of 5 cm H2O. En bloc excision of the heart and lungs was performed by thoracotomy. Perfusion of the isolated lung vasculature with 2.5% paraformaldehyde and 0.25% glutaraldehyde in a 0.1-M phosphate buffer was performed. Histologic analysis followed. MEASUREMENTS AND MAIN RESULTS: Gas exchange increased markedly in the animals that underwent partial liquid ventilation compared with the gas-ventilated animals (PaO2 at 90 mins: gas ventilation-treatment group, 40 +/- 8 torr [5.3 +/- 1.1 kPa]; partial liquid ventilation-treatment group, 108 +/- 60 torr [14.4 +/- 8.0 kPa]; p = .004). Lung histologic analysis demonstrated a better overall diffuse alveolar damage score (partial liquid ventilation-treatment group, 12.4 +/- 1.4; gas ventilation-treatment group, 15.0 +/- 1.7; p = .01). In the partial liquid ventilation-treatment group, we observed an increase in mean alveolar diameter (partial liquid ventilation-treatment group, 82.4 +/- 2.9 microm; gas ventilation-treatment group, 67.7 x 3.9 microm; p = .0022) and a decrease in the number of alveoli per high-power field (partial liquid ventilation-treatment group, 25.7 +/- 0.9, gas ventilation-treatment group, 31.4 +/- 2.5; p = .0022), in septal wall thickness (partial liquid ventilation-treatment group, 6.0 +/- 0.6 microm; gas ventilation-treatment group, 8.3 +/- 1.0 microm; p = .0033), and in mean capillary diameter (partial liquid ventilation-treatment group, 13.0 +/- 0.8 microm; gas ventilation-treatment group, 19.9 +/- 1.4 microm; p = .0022). CONCLUSIONS: Partial liquid ventilation is associated with notable improvement in gas exchange and with a reduction in the histologic and morphologic changes observed in an oleic acid model of acute lung injury.

Animals↗
PubMed1998

Monitoring perioperative changes in distribution of pulmonary ventilation by functional electrical impedance tomography.

BACKGROUND: Electrical impedance tomography (EIT) is a noninvasive technique providing cross-sectional images of the thorax. We have tested an extended evaluation procedure, the functional EIT (f-EIT), to identify the local shifts of ventilation known to occur during the transition between spontaneous, controlled and assisted ventilation modes. METHODS: Ten patients scheduled for elective laparotomy were studied in the surgical ward, operating theatre and ICU during spontaneous and different modes of mechanical ventilation. Sixteen ECG electrodes were placed on the circumference of the thorax and connected with an EIT device (APT System Mark I, IBEES, Sheffield, UK). Measurements lasting 180 s were performed and f-EIT images of regional ventilation computed. The geometrical centre of ventilation was determined to quantify the regional distribution of lung ventilation during individual modes of ventilation. RESULTS: F-EIT confirmed the differences in the distribution of ventilation associated with various modes of artificial ventilation. Accentuated ventilation of the dependent lung regions was observed during spontaneous breathing, whereas a shift of the centre of ventilation to the nondependent regions was found during controlled ventilation. In the course of assisted ventilation a continuous displacement of the centre of ventilation back towards the dependent lung regions, consistent with an increased proportion of spontaneous breathing, was detected. Unassisted spontaneous breathing after weaning from mechanical ventilation resulted in a similar ventilation distribution as during tidal breathing prior to surgery. CONCLUSION: F-EIT determined the redistribution of lung ventilation during different modes of mechanical ventilation. We expect that f-EIT will become a useful noninvasive bedside monitoring technique for imaging regional ventilation in pulmonary diseased patients during mechanical ventilation.

Abdomen↗
PubMed1975

A comparative study of the effects of dry vs. humidified ventilation on canine lungs.

To compare the effects on canine ciliary and bronchial mucosal function of varying periods of ventilation with dry vs. humidified gas mixtures, 29 anesthetized dogs underwent 2, 4, and 6 hours of ventilation through a Carlen's double-lumen tube. Six dogs were evaluated by clearance studies, nine by differential bronchospirometry, six by surfactant studies, six by electron microscopy, and two by ventilation scanning. By means of two separate respiratory systems, dry gas (DG) was used to ventilate the right lung, and humidified gas (HG) ventilated the left lung in each dog. Serial chest roentgenograms showed more rapid clearance of inspired tantalum dust from the HG-ventilated lung in each of the six dogs, the disparity in clearance between the two lungs being more pronounced after longer periods of ventilation. The surface tension in DG-ventilated lungs increased fourfold, whereas in HG-ventilated lungs it increased only twofold as compared to preoperative values. Longer periods of ventilation did not change the surface tension appreciably in either DG- or HG-ventilated lungs. Scanning electron micrographs of bronchial mucosa from DG-ventilated lungs showed tangling and matting of cilia with a granular and stringy material attached to most cilia; these changes were much less pronounced in HG-ventilated lungs. Bronchospirometric studies showed an increase in ventilatory function in each of the lungs ventilated with the HG mixture (percent Vo2 on 100 percent oxygen increased 27.7 percent) to compensate for the decreased gas exchange provided by the contralateral DG-ventilated lung. Function in each of the lungs returned to normal within 24 hours. Ventilation scans with Xenon133 showed no apparent change in isotope uptake in the HG-ventilated lungs as compared to the DG lungs during the first 24 hours after ventilation. The observations from the present study suggest that ventilation of canine lungs with DG for 4 or more hours dries mucus and transiently retards mucociliary clearance and gas exchange. These changes may be minimized by ventilation with a humidified gas mixture. Application of these findings to patients undergoing prolonged general anesthesia and to lung preservation studies is suggested.

Animals↗
PubMedDate not supplied

[The impact of mechanical ventilation strategies that minimize atelectrauma in an experimental model of acute lung injury].

OBJECTIVE: To evaluate whether ventilation strategies that target alveolar stabilization and prevention of atelectrauma would be associated with more favorable physiologic outcomes in a combined model of acute lung injury. METHODS: Thirty-nine rabbits were instrumented and ventilated with FiO(2) of 1.0. Combined lung injury was induced by an infusion of lipopolysaccharide and tracheal saline lavage. Animals were randomized to receive conventional ventilation with tidal volume of 10 ml/kg, PEEP of 4 cm H(2)O; conventional ventilation with surfactant (Infasurf, 3 mg/kg IT); partial liquid ventilation (18 ml/kg of perflubron IT); or high-frequency oscillatory ventilation with mean airway pressure of 14 cm H(2)O and frequency of 4 Hz. Uninjured ventilated animals served as controls. Conventional ventilation with surfactant, partial liquid ventilation and control groups were ventilated with settings identical to the conventional ventilation group. Animals were studied for 4 hours, during which serial blood gas measurements were obtained. After sacrifice, lungs were harvested for injury grading by a microscopic lung injury score and measurement of 4-hydroxy-nonenal, a marker of lipid peroxidation. RESULTS: Conventional ventilation resulted in hypoxia and greater evidence of lung injury. Animals treated with partial liquid ventilation, high-frequency oscillatory ventilation or conventional ventilation with surfactant had adequate oxygenation, but conventional ventilation with surfactant resulted in higher lung injury scores and increased pulmonary oxidative damage. CONCLUSION: Strategies that minimize atelectrauma (partial liquid ventilation and high-frequency oscillatory ventilation) are associated with adequate oxygenation and attenuated lung injury. Surfactant improves oxygenation in comparison to conventional ventilation alone but resulted in increased injury, presumably because the inadequately low PEEP was insufficient to stabilize the alveoli during expiration.

Analysis of Variance↗
PubMed2006

Clinical manifestations and risk factors of children receiving triple ventilating tube insertions for treatment of recurrent otitis media with effusion.

OBJECTIVE: Our goal was to determine risk factors for children receiving additional ventilating tube insertions after initial tube insertion and to determine the changes of clinical manifestations in children who have undergone 3 ventilating tube insertion procedures. STUDY DESIGN: We retrospectively analyzed medical and operation records of 423 young patients who had ventilating tube insertion because of chronic otitis media with effusion from January 1993 to December 1998. The single-operation group included patients who had 1 ventilating tube insertion only, and the triple-operation group included patients who received ventilating tube insertion 3 times because of recurring chronic otitis media with effusion. RESULTS: At the first operation, there were significant differences between the single- and triple-operation groups in mean age, the proportion who received a concurrent adenoidectomy, the mean indwelling period of the first ventilating tube, the proportion who developed postoperative otorrhea within 1 month, and the proportion who had early extrusion of the ventilating tube within 3 months of surgery. In the triple-operation group, the accumulated number of adenoidectomies, the indwelling period of the ventilating tube, and the time interval before subsequent ventilating tube insertion after ventilating tube extrusion significantly increased as ventilating tube insertion procedures were performed repeatedly. Although there was no difference when compared with the single-operation group, the proportion of glue-like effusion significantly decreased as ventilating tube insertion procedures were performed repeatedly. There were no significant differences between the single- and triple-operation groups in male/female ratio, site of ventilating tube insertion, and the proportion of patients with glue-like effusion at the first ventilating tube insertion. CONCLUSIONS: The probability of receiving additional ventilating tube insertion because of recurrent otitis media with effusion significantly increased in younger patients at the time of first ventilating tube insertion. The concurrent adenoidectomy, duration of the ventilating tube, postoperative otorrhea within 1 month, and early extrusion of the ventilating tube also influenced the probability of additional ventilating tube insertion.

Child, Preschool↗
PubMed1986

High-frequency ventilation and tracheal injuries.

Recent reports linking serious tracheal injuries to various forms of high-frequency ventilation prompted this study. We compared the tracheal histopathology seen following standard-frequency, conventional mechanical ventilation with that seen following high-frequency, conventional mechanical ventilation, and two different forms of high-frequency jet ventilation. Twenty-six adult cats were examined. Each was mechanically ventilated for 16 hours. Seven received standard-frequency, conventional mechanical ventilation at 20 breaths per minute. Seven received high-frequency, conventional mechanical ventilation at 150 breaths per minute. Six received high-frequency jet ventilation at 250 breaths per minute via the Instrument Development Corporation VS600 jet ventilator (IDC). Six received high-frequency jet ventilation at 400 breaths per minute via the Bunnell Life Pulse jet ventilator (BLP). A semiquantitative histopathologic scoring system graded tracheal tissue changes. All forms of high-frequency ventilation produced significant inflammation (erosion, necrosis, and polymorphonuclear leukocyte infiltration) in the trachea in the region of the endotracheal tube tip. Conventional mechanical ventilation produced less histopathology than any form of high-frequency ventilation. Of all of the ventilators examined, the BLP, the ventilator operating at the fastest rate, produced the greatest loss of surface cilia and depletion of intracellular mucus. IDC high-frequency jet ventilation and high-frequency, conventional mechanical ventilation produced nearly identical histologic injuries. In this study, significant tracheal damage occurred with all forms of high-frequency ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2000

Improved flow and pressure capabilities of the Datex-Ohmeda SmartVent anesthesia ventilator.

STUDY OBJECTIVE: To compare the flow and pressure capabilities of the Datex-Ohmeda SmartVent (Ohmeda 7900, Datex-Ohmeda, Madison, WI) to previous Ohmeda (7810 and 7000, Datex-Ohmeda, Madison, WI) anesthesia ventilators. To determine airway pressure and minute ventilation thresholds for intraoperative use of a critical care ventilator. DESIGN: Three anesthesia ventilators and one critical care ventilator (Siemens Servo 900C, Siemens, Solna, Sweden) were studied in a lung model. Retrospective medical record review. SETTING: Research Laboratory and Critical Care Unit of a Level I Trauma Center. PATIENTS: 145 mechanically ventilated patients treated for acute respiratory failure who underwent 200 surgical procedures. INTERVENTIONS: The effect of increasing pressure on mean inspiratory flow was determined by cycling each ventilator through increasing restrictors. Maximum minute ventilation was measured at low compliance (10-30 mL/cm H2O), positive end-expiratory pressure (PEEP) (0-20 cm H2O), and increased airway resistance (approximately 19 and approximately 36 cm H2O/L/sec) in a mechanical lung model. MEASUREMENTS AND MAIN RESULTS: Flow, volume, and pressure were measured with a pulmonary mechanics monitor (BICORE CP-100, Thermo Respiratory Group, Yorba Linda, CA). Preoperative peak airway pressure and minute ventilation (VE) were extracted from the medical record. Mean inspiratory flow declined with increasing pressure in all anesthesia ventilators. The SmartVent and the 7810 produced greater mean inspiratory flow than did the 7000 ventilator. As compliance progressively decreased, the Siemens, the SmartVent, and the 7810 ventilators maintained VE compared to the 7000 ventilator. The Siemens and the SmartVent maintained VE with PEEP, compared to the 7810 and 7000 ventilators. During increased airway resistance, maximal VE was lower for all ventilators. The SmartVent met the ventilation requirements in 90% of the patients compared to 67% of patients with the 7000 ventilator. CONCLUSION: The improved pressure and flow capabilities of the SmartVent increase the threshold for using a critical care ventilator intraoperatively to a peak airway pressure > 65 cm H2O and/or VE > 18 L/min.

Acute Disease↗
PubMed1995

Airway leak size in neonates and autocycling of three flow-triggered ventilators.

OBJECTIVES: To define the spectrum of airway leak in the neonatal population and examine the occurrence rate of autocycling of three flow-triggered ventilators within the defined spectrum of airleak. DESIGN: Prospective study of pulmonary function tests of intubated infants and performance of ventilators on a mechanical lung model under simulated clinical conditions. SETTING: An intensive care nursery and research laboratory at a university medical center. INTERVENTIONS: Analysis of pulmonary function tests of 50 infants from our intensive care nursery, selected at random, to determine size of airleak around the endotracheal tube. The rate of autocycling of ventilators due to airleak of variable size, while connected to a test lung was subsequently studied. Ventilators were set on the assist-control mode with the control rate set at 0 breath/min. Each ventilator was studied at the maximum sensitivity setting, which was 1, 2.5, and 3.3 mL/sec for each ventilator, respectively, and also at decreased sensitivity settings to 10 mL/sec. Airleak size was varied (10% to 45%) by increasing the orifice size within the endotracheal tube adapter/connector sideport and/or the positive end-expiratory pressure level (2 to 8 cm H2O). MEASUREMENTS AND MAIN RESULTS: In the infants, airleak size was calculated during synchronous ventilator breaths as (inspiratory minus expiratory) tidal volume/expiratory tidal volume x 100% (n = 25 +/- 11 breaths/patient). Mean +/- SD leak size in the infants was 15.6 +/- 11%. A minimal leak size of 0 to 10% was present in 15 (30%) infants, leak size of 10% to 20% in 24 (48%), leak size of 20% to 30% in seven (14%), and leak size > 30% in four (8%) infants. The relative tendency of the three ventilators to autocycle is a function of the maximum sensitivity setting, which varies with each ventilator. The ventilator with the maximum sensitivity set at 1 mL/sec autocycled rapidly (> or = 40 breaths/min) at leak size of > 10%; the ventilator set at 2.5 mL/sec autocycled rapidly at leak size of > or = 20%; and the ventilator set at 3.3 mL/sec autocycled rapidly at leak size of > or = 30%. In all ventilators, the rate of autocycling increased with increased leak size, and decreased with decreased sensitivity setting. CONCLUSIONS: Flow-triggered ventilators are susceptible to autocycling due to flow compensation to maintain positive end-expiratory pressure levels in the presence of an airway leak. The difference in autocycling is due to the maximum sensitivity setting of each ventilator, and not to intrinsic ventilator flowsensing or other software mechanisms. The 3.3-mL/sec setting was the least prone to autocycling and seems appropriate. The ventilator set at 2.5 mL/sec at the time of this study has been released instead at 4 mL/sec, due to these findings. The ventilator with the maximum setting at 1 mL/sec autocycled readily at leak size of > or = 10%. Since such a leak size was present in 70% of infants, this setting should be used with caution. Using these guidelines, autocycling of all three ventilators is likely to occur mainly in 8% of infants with leak size of > 30%. In these cases, lowering the sensitivity setting and/or positive end-expiratory pressure level may decrease autocycling, or may necessitate reintubation with a larger endotracheal tube.

Equipment Failure↗
PubMed2006

[Clinical study of mechanical ventilation in acute cardiogenic pulmonary edema patients].

OBJECTIVE: To study the application of mechanical ventilation in acute cardiogenic pulmonary edema (ACPE), and compare the changes in hemodynamics between continuous positive airway pressure proportional pressure support (CPAP-PPS) with continuous positive airway pressure-pressure support ventilation (CPAP-PSV). METHODS: Non-invasive and invasive ventilation were performed in 77 ACPE patients. At the initiation of invasive ventilation and the phase of low assist ventilation in 61 patients who were treated with mechanical ventilation longer than 24 hours, hemodynamics was monitored by partial CO(2) rebreathing method (non-invasive cardiac output, NICO) cardiopulmonary management system, and then compared the changes in the two kinds of ventilation under medicinal intervention. RESULTS: Among 33 of 61 ACPE patients underwent non-invasive ventilation, 24 were successful, and the ratio was 72.7%. Among 33 patients with invasive ventilation (including 5 in whom ventilation was switched to non-invasive mode), 11 failed. Biphasic positive airway pressure/pressure support ventilation (BIPAP/PSV) was used in pressure controlled ventilation, with high pressure (Phigh) 16-24 cm H(2)O (1 cm H(2)O=0.098 kPa), time of high pressure (Thigh) 1.5 seconds, positive end expiratory pressure (PEEP) 6-15 cm H(2)O, fractional concentration of inspired oxygen (FiO(2)) 0.5, cardiac output (CO)/cardiac index (CI) was significantly improved compared with those of initial ventilation in successful ones in invasive group, and the improvement was more significant in PPS compared with PSV in low assist ventilation (all P<0.001). Those in whom invasive ventilation was failed had a low CI (<1.5 L.min(-1).m(-2)) even under drug intervention. CONCLUSION: Hemodynamic monitoring should be performed when medicinal intervention and non-invasive/invasive ventilation are given to ACPE patients. Pressure controlled ventilation is recommended, and PEEP should be individualized (normally 6-15 cm H(2)O). Spontaneous ventilation should be restored as soon as possible, CPAP-PPS mode is practicable in patients in whom weaning of mechanical ventilation is difficult.

Acute Disease↗
PubMed2006

Complications of different ventilation strategies in endoscopic laryngeal surgery: a 10-year review.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Adolescent↗
PubMed1991

Tracheal damage following conventional and high-frequency ventilation at low and high humidity.

OBJECTIVES: To compare the degree of tracheobronchial damage in newborn lambs ventilated for 6 hrs with relative humidities of 30% or 90% and continuous positive airway pressure breathing, conventional mechanical ventilation of 25 and 60 breaths/min, or high frequency flow-interrupted ventilation at 600 breaths/min. BACKGROUND AND METHODS: Tracheobronchial damage secondary to mechanical ventilation remains a major iatrogenic lesion of the newborn despite substantial advances in both mechanical design and ventilatory techniques. A histologic scoring system was used to compare the damage noted in the tracheobronchial epithelium of newborn lambs after 6 hrs of conventional mechanical ventilation or high-frequency flow-interrupted ventilation at two relative humidities. Three groups of animals were ventilated for 6 hrs with an FIO2 of 0.21 at 36.0 degrees C and relative humidity of 90%. The first group received continuous positive airway pressure of 4 cm H2O, the second group received slow rate, conventional mechanical ventilation at 25 breaths/min, and the third group received fast rate, conventional mechanical ventilation at 60 breaths/min. Two other groups of animals were ventilated for 6 hrs with an FIO2 of 0.21 at 36.0 degrees C and relative humidity of 30%. The first group was ventilated with high-frequency flow-interrupted ventilation at 600 breaths/min and the second group with slow rate, conventional mechanical ventilation at 25 breaths/min. Two additional groups served as nonintubated controls; one group was killed immediately after sedation and the other group was killed after 6 hrs of sedation. RESULTS: The damage was mild but significantly different from controls when 90% humidity was used and there was no difference in the histology score between continuous positive airway pressure breathing and conventional mechanical ventilation at 25 or 60 breaths/min. Significant inflammation, erosion, necrosis, and blistering occurred with both conventional mechanical ventilation at 25 breaths/min and high-frequency flow-interrupted ventilation at 600 breaths/min when 30% humidity was used. The damage was only found 5 mm below the tip of the endotracheal tube and not at 3.5 cm beyond the endotrachea tube in the trachea nor in the right main bronchus. CONCLUSION: These data indicate that endotracheal intubation and mechanical ventilation, regardless of the method of ventilation, cause damage to the tracheal mucosa, but that poorly humidified inspired gases cause significantly greater damage.

Animals↗
PubMed1998

Frequency, causes, and outcome of home ventilator failure.

STUDY OBJECTIVES: The safety of home ventilators has been questioned. We collected data to study the following: frequency of home ventilator failure, apparent causes for the failure or malfunction, and adverse consequences following the failure. STUDY DESIGN: Information on all requests to correct home ventilator failures reported to a home respiratory equipment vendor was collected prospectively between November 1991, and November 1992. PATIENTS: There were 150 ventilator-assisted patients aged 2 to 77 years; 44 were < or = 18 years. They received 841,234 h of home mechanical ventilation (average, 15.4 h/d per ventilator-assisted patient). RESULTS: There were 189 reports of home ventilator failure. Defective equipment or mechanical failure was found in only 39% (73 reports), equivalent to one home ventilator failure for every 1.25 years of continuous use. Other causes of ventilator failure included the following: improper care, damage, or tampering with the ventilator by caregivers (13%), functional equipment improperly used by caregivers (30%), and equipment functional but the patient's condition changed, mimicking ventilator failure (3%). No problem could be identified in 16%. The following actions were required: ventilator replacement (44%), repair of a defective part (6%), replacement of a functioning ventilator for psychological comfort (14%), ventilator adjustments made (21%), caregiver reeducation (7%), caregiver anxiety or distress reduced (3%), and no action required (4%). Hospitalization was required only in two cases (1%). No adverse outcomes, deaths, or serious injuries were associated with home ventilator failure. CONCLUSIONS: We conclude that in 150 patients requiring home mechanical ventilation, ventilator failure occurred relatively infrequently, and there were no adverse outcomes as a result of equipment failure at home. We speculate that equipment failure is not a frequent or serious problem for ventilator-assisted patients treated at home.

Adolescent↗
PubMed1998

Noninvasive mechanical ventilation in the weaning of patients with respiratory failure due to chronic obstructive pulmonary disease. A randomized, controlled trial.

BACKGROUND: In patients with acute exacerbations of chronic obstructive pulmonary disease, mechanical ventilation is often needed. The rate of weaning failure is high in these patients, and prolonged mechanical ventilation increases intubation-associated complications. OBJECTIVE: To determine whether noninvasive ventilation improves the outcome of weaning from invasive mechanical ventilation. DESIGN: Multicenter, randomized trial. SETTING: Three respiratory intensive care units. PATIENTS: Intubated patients with chronic obstructive pulmonary disease and acute hypercapnic respiratory failure. INTERVENTION: A T-piece weaning trial was attempted 48 hours after intubation. If this failed, two methods of weaning were compared: 1) extubation and application of noninvasive pressure support ventilation by face mask and 2) invasive pressure support ventilation by an endotracheal tube. MEASUREMENTS: Arterial blood gases, duration of mechanical ventilation, time in the intensive care unit, occurrence of nosocomial pneumonia, and survival at 60 days. RESULTS: At admission, all patients had severe hypercapnic respiratory failure (mean pH, 7.18+/-0.06; mean PaCO2, 94.2+/-24.2 mm Hg), sensory impairment, and similar clinical characteristics. At 60 days, 22 of 25 patients (88%) who were ventilated noninvasively were successfully weaned compared with 17 of 25 patients (68%) who were ventilated invasively. The mean duration of mechanical ventilation was 16.6+/-11.8 days for the invasive ventilation group and 10.2+/-6.8 days for the noninvasive ventilation group (P = 0.021). Among patients who received noninvasive ventilation, the probability of survival and weaning during ventilation was higher (P = 0.002) and time in the intensive care unit was shorter (15.1+/-5.4 days compared with 24.0+/-13.7 days for patients who received invasive ventilation; P = 0.005). Survival rates at 60 days differed (92% for patients who received noninvasive ventilation and 72% for patients who received invasive ventilation; P = 0.009). None of the patients weaned noninvasively developed nosocomial pneumonia, whereas 7 patients weaned invasively did. CONCLUSIONS: Noninvasive pressure support ventilation during weaning reduces weaning time, shortens the time in the intensive care unit, decreases the incidence of nosocomial pneumonia, and improves 60-day survival rates.

Aged↗
PubMed1990

Theoretical analysis of factors influencing recovery of ventilation distributions from inert gas washout data.

A method is presented that allows to calculate distributions of ventilation from measured time courses of inert gas washout. In the mathematical description of the washout process a discontinuous algorithm is applied: For each individual breath inspiratory and expiratory tidal volumes, endexpiratory alveolar volume, and dead space inspiration are taken into account. Furthermore, volume reduction of the alveolar gas according to the gas exchange ratio is considered. Commonly in ventilation analysis, the specific ventilation serves as abscissa of the density of the ventilation distribution. As at a given location the specific ventilation changes with varying tidal volumes even if the distribution pattern of the ventilation amongst the lung remains unchanged, the normalized specific ventilation is newly introduced instead. This quantity is defined to be the ratio of regional alveolar ventilation and regional endexpiratory alveolar volume divided by the total alveolar ventilation. The normalized specific ventilation reflects the distribution of the ventilation independently of variations in tidal volume and respiratory frequency. Furthermore, it allows direct comparison of ventilation distributions that are determined at varying alveolar ventilations. Ventilation distributions are approximated by the transformed beta distribution which is parameterized by its mean, variance, and skewness. In order to evaluate simplifications introduced in former studies and to quantify their effects on the resulting ventilation distributions, washout time courses are generated in a computer simulation from the comprehensive discontinuous algorithm and are used to recover ventilation distributions by means of accordingly simplified algorithms. Furthermore, the influence of errors that may occur in the measurement of tidal volumes are assessed. The results of these studies are summarized as follows: Serious errors are introduced in the recovered distributions if ventilation is modelled as a continuous process and if physiological variations in tidal volumes or endexpiratory alveolar volumes or dead space inspiration are neglected. Modelling the entire dead space as common dead space or as local dead space only, entails significant errors as well. Statistical errors of 2% in the measured volumes practically do not have any impacts on the recovered distributions whereas systematic errors significantly deteriorate the results. In conclusion, in ventilation analysis it is essential to apply a discontinuous description of the inert gas washout process that accounts for dead space inspiration and variations in the above mentioned quantities. In addition it is important to obtain all measured values with the highest achievable precision.

Computer Simulation↗
PubMed1994

The laryngeal mask airway and positive-pressure ventilation.

BACKGROUND: The utility of the laryngeal mask airway during positive-pressure ventilation has yet to be determined. Our study was designed to assess whether significant leaks occurred with positive-pressure ventilation and if leaks were associated with gastroesophageal insufflation. METHODS: Forty-eight patients undergoing elective surgery were studied. After induction of anesthesia and paralysis, controlled ventilation was used with four different peak pressure settings in each patient (15, 20, 25, and 30 cmH2O). The order of ventilator pressure settings was assigned from a randomized block schedule. Data collected included inspiratory and expiratory volumes, qualitative assessments of gastroesophageal insufflation, and leak at the neck. After data collection during laryngeal mask use, the anesthesiologist intubated the trachea and measurements were repeated for tracheal tube ventilation. Leak was calculated by subtracting the expiratory from the inspiratory volume and expressed as a fraction of the inspiratory volume. RESULTS: Ventilation with the laryngeal mask airway was adequate at all ventilation pressures and comparable with tracheal tube ventilation. Leak fraction (mean +/- SD) at 15, 20, 25, and 30 cmH2O for laryngeal mask ventilation were 0.13 +/- 0.15, 0.21 +/- 0.18, 0.25 +/- 0.16 and 0.27 +/- 0.17, respectively, and 0.03 +/- 0.03, 0.05 +/- 0.03, 0.05 +/- 0.03 and 0.04 +/- 0.03, respectively, for tracheal tube ventilation. Leak fractions for ventilation with the laryngeal mask were consistently greater than those measured for tracheal tube ventilation at similar ventilation pressures. Leak fraction with laryngeal mask ventilation increased with increasing airway pressures, whereas leak with tracheal tube ventilation remained unchanged. The frequency of gastroesophageal insufflation ranged from 2.1% at a ventilation pressure of 15 cmH2O to 35.4% at 30 cmH2O. CONCLUSIONS: Ventilation using the laryngeal mask appears to be adequate if airway resistance and pulmonary compliance are normal. Gastroesophageal insufflation of air will become a problem in the presence increased ventilation pressure.

Adolescent↗
PubMed1996

Comparison of volume control and pressure control ventilation: is flow waveform the difference?

OBJECTIVE: To examine the hypothesis that a decelerating inspiratory flow waveform is responsible for improvements in gas exchange during pressure control ventilation for acute lung injury. DESIGN: Prospective, controlled, crossover study. MEASUREMENTS AND MAIN RESULTS: Twenty-five patients with acute lung injury requiring mechanical ventilation with a positive-end expiratory pressure > or = 10 cm H2O, ventilator frequency of > or = 8 bpm, inspired oxygen concentration of > or = 0.50, peak inspiratory pressure > or = 40 cm H2O, and requiring sedation and paralysis were studied. Patients were ventilated at a tidal volume of 10 mliters/kg, respiratory frequency was set to maintain a pH > 7.30 and PaCO2 < 50 mm Hg, and positive end-expiratory pressure (PEEP) set to maintain Pao2 > 70 mm Hg or Sao2 > 93% with an Fio2 < or = 0.50. In random sequence, ventilator mode was changed from volume control with a square flow waveform, pressure control ventilation with a decelerating flow waveform, or volume control ventilation with a decelerating flow waveform. Tidal volume, minute ventilation, and airway pressures were continuously measured at the proximal airway. After 2 hours of ventilation in each mode, arterial and mixed venous blood gases were drawn and cardiac output determined by thermodilution. Dead space to tidal volume ratio was determined from mixed expired gas concentrations and Paco2. During volume control ventilation with a square flow waveform, Pao2 was decreased (75 +/- 11 mm Hg vs. 85 +/- 9 mm Hg and 89 +/- 12 mm Hg), p < 0.05, and peak inspiratory pressure was increased (50 +/- 9 cm H2O vs. 42 +/- 7 cm H2O and 39 +/- 9 cm H2O) p < 0.05 compared to volume control with a decelerating flow waveform and pressure control ventilation. Mean airway pressure was also lower with volume control with a square flow waveform (17 +/- 4 cm H2O vs. 20 +/- 4 cm H2O and 21 +/- 3 cm H2O) compared to volume control with a decelerating flow waveform and pressure control ventilation. There were no differences in hemodynamic parameters. CONCLUSIONS: Both pressure control ventilation and volume control ventilation with a decelerating flow waveform provided better oxygenation at a lower peak inspiratory pressure and higher mean airway pressure compared to volume control ventilation with a square flow waveform. The results of our study suggest that the reported advantages of pressure control ventilation over volume control ventilation with a square flow waveform can be accomplished with volume control ventilation with a decelerating flow waveform.

Adult↗
PubMed2005

Daily cost of an intensive care unit day: the contribution of mechanical ventilation.

OBJECTIVE: To quantify the mean daily cost of intensive care, identify key factors associated with increased cost, and determine the incremental cost of mechanical ventilation during a day in the intensive care unit. DESIGN: Retrospective cohort analysis using data from NDCHealth's Hospital Patient Level Database. SETTING: A total of 253 geographically diverse U.S. hospitals. PATIENTS: The study included 51,009 patients >/=18 yrs of age admitted to an intensive care unit between October 1, 2002, and December 31, 2002. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Days of intensive care and mechanical ventilation were identified using billing data, and daily costs were calculated as the sum of daily charges multiplied by hospital-specific cost-to-charge ratios. Cost data are presented as mean (+/-sd). Incremental daily cost of mechanical ventilation was calculated using log-linear regression, adjusting for patient and hospital characteristics. Approximately 36% of identified patients were mechanically ventilated at some point during their intensive care unit stay. Mechanically ventilated patients were older (63.5 yrs vs. 61.7 yrs, p < .0001) and more likely to be male (56.1% vs. 51.8%, p < 0.0001), compared with patients who were not mechanically ventilated, and required mechanical ventilation for a mean duration of 5.6 days +/- 9.6. Mean intensive care unit cost and length of stay were 31,574 +/- 42,570 dollars and 14.4 days +/- 15.8 for patients requiring mechanical ventilation and 12,931 +/- 20,569 dollars and 8.5 days +/- 10.5 for those not requiring mechanical ventilation. Daily costs were greatest on intensive care unit day 1 (mechanical ventilation, 10,794 dollars; no mechanical ventilation, 6,667 dollars), decreased on day 2 (mechanical ventilation:, 4,796 dollars; no mechanical ventilation, 3,496 dollars), and became stable after day 3 (mechanical ventilation, 3,968 dollars; no mechanical ventilation, 3,184 dollars). Adjusting for patient and hospital characteristics, the mean incremental cost of mechanical ventilation in intensive care unit patients was 1,522 dollars per day (p < .001). CONCLUSIONS: Intensive care unit costs are highest during the first 2 days of admission, stabilizing at a lower level thereafter. Mechanical ventilation is associated with significantly higher daily costs for patients receiving treatment in the intensive care unit throughout their entire intensive care unit stay. Interventions that result in reduced intensive care unit length of stay and/or duration of mechanical ventilation could lead to substantial reductions in total inpatient cost.

Adult↗
PubMed1986

Effect of mechanical ventilation on hepatic drug pharmacokinetics.

Mechanical ventilation was able to induce a decrease in cardiac output and regional blood flow, especially hepatic flow. Thus, hepatic elimination of drugs with a high hepatic-extraction ratio, which was linked to alteration in hepatic blood flow, could be reduced during mechanical ventilation. The aim of this work was to determine the effect of mechanical ventilation on pharmacokinetic parameters of lidocaine, which is a well-known nonrestrictive elimination drug at the hepatic level. Five patients (mean age, 58 years) with normal hepatic function and quite similar gasometric parameters before and after weaning from mechanical ventilation were studied. With a washout period of 48 hours between mechanical ventilation and spontaneous ventilation, each patient was submitted to the following protocol: lidocaine in a bolus (1.5 mg/kg intravenously), followed by infusion (1.0 to 1.7 mg/min for 120 minutes). The results were that the peak plasma concentration after the bolus during mechanical ventilation was 3.22 +/- 0.37 mg/L (mean +/- SE) vs 2.40 +/- 0.35 mg/L during spontaneous ventilation (p less than 0.02). Steady-state plasma concentration during mechanical ventilation was 2.10 +/- 0.20 mg/L vs 1.64 +/- 0.16 mg/L during spontaneous ventilation (p less than 0.01). Total clearance was 604.2 +/- 87.0 ml/min during mechanical ventilation vs 775.0 +/- 112.1 ml/min during spontaneous ventilation (p less than 0.01). Elimination half-life was 245.2 +/- 50.6 minutes during mechanical ventilation vs 160.0 +/- 40.6 minutes during spontaneous ventilation (p less than 0.05). Distribution volume was 188.6 +/- 50.2 L during mechanical ventilation and 183.0 +/- 50.8 L during spontaneous ventilation (not significant). These preliminary data clearly demonstrated a decrease in lidocaine elimination in patients submitted to mechanical ventilation, but the magnitude of dosage adjustment of such a highly hepatic-extracted drug in patients submitted to mechanical ventilation remains to be investigated.

Adult↗