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PubMed1991

The basis and basics of mechanical ventilation.

The development of mechanical ventilators and the procedures for their application began with the simple foot pump developed by Fell O'Dwyer in 1888. Ventilators have progressed through three generations, beginning with intermittent positive pressure breathing units such as the Bird and Bennett device in the 1960s. These were followed by second-generation units--represented by the Bennett MA-2 ventilator--in the 1970s, and the third-generation microprocessor-controlled units of today. During this evolutionary process clinicians recognized Types I and II respiratory failure as being indicators for mechanical ventilatory support. More recently investigators have expanded, clarified, and clinically applied the physiology of the work of breathing (described by Julius Comroe and other pioneers) to muscle fatigue, requiring ventilatory support. A ventilator classification system can help the clinician understand how ventilators function and under what conditions they may fail to operate as desired. Pressure-support ventilation is an example of how industry has responded to a clinical need--that is, to unload the work of breathing. All positive pressure ventilators generate tidal volumes by using power sources such as medical gas cylinders, air compressors, electrically driven turbines, or piston driven motors. Positive end-expiratory pressures, synchronized intermittent mandatory ventilation, pressure support ventilation, pressure release ventilation, and mandatory minute ventilation, are examples of the special functions available on modern ventilators. Modern third-generation ventilators use microprocessors to control operational functions and monitors. Because these units have incorporated the experience learned from earlier ventilators, it is imperative that clinicians understand basic ventilator operation and application in order to most effectively prescribe and assess their use.

Equipment Design↗
PubMed2006

[Pathophysiological basis of mechanical ventilation].

Mechanical ventilation is required if ventilatory insufficiency is present. This is typically indicated by hypercapnea. Hypoxemia occurs secondary to hypoventilation. Usually overload of the respiratory muscles (ventilatory pump) will be the underlying mechanism, for the most part caused by acute or chronic disease. In case of sole hypoxemia mechanical ventilation will only be indicated if the oxygen-content (equals oxygen saturation x haemoglobin x 1.39) drops below a critical threshold or if ventilatory pump failure is imminent on account of the underlying disease (eg. pneumonia). The background of our recommendations is to avoid potential damage caused by mechanical ventilation. Especially high inspiratory pressures and oxygen concentrations can be harmful to the lung. Therefore every case has to evaluated for individual target parameters of ventilation. The use of the oxygen-content instead of the arterial oxygen pressure as the target parameter will usually lead to a more careful ventilation. Cardiogenic pulmonary oedema is an exception to this rule since inspiratory positive pressure and PEEP will result in improved diffusion as well as reduction of preload and work of breathing. In recent years progress has been made on the field of ventilation access especially in severe and acute cases. Non-invasive ventilation is superior to invasive ventilation in patients with exacerbated COPD since it improves outcome effectively. This is being caused by a decline in ventilator associated pneumonias, most likely because non-invasive ventilation allows patients to clear their secretions by coughing, resulting in improved lung clearance. Controlled ventilation allows optimal unloading of the respiratory muscles which have been overloaded by the underlying disease. Application of a controlled ventilation mode in acute disease will usually require some kind of sedation. Assisted ventilation will result in improved gas exchange but only incomplete unloading of respiratory muscles and therefore delayed restitution. Permanent controlled ventilation under sedation for a prolonged period (days) requires intermittent periods of assisted- or spontaneous breathing in order to avoid atrophy of the respiratory muscles. This review summarizes background information on the nature of the derangement, the relation between oxygen supply and consumption under special consideration of respiratory muscle insufficiency and impact of different ventilation modes.

Acute Disease↗
PubMed2003

Noninvasive cardiac output measurement using partial carbon dioxide rebreathing is less accurate at settings of reduced minute ventilation and when spontaneous breathing is present.

BACKGROUND: Although evaluation of cardiac output by the partial carbon dioxide rebreathing technique is as accurate as thermodilution techniques under controlled mechanical ventilation, it is less accurate at low tidal volume. It is not clear whether reduced accuracy is due to low tidal volume or low minute ventilation. The effect of spontaneous breathing on the accuracy of partial carbon dioxide rebreathing measurement has not been fully investigated. The objectives of the current study were to investigate whether tidal volume or minute ventilation is the dominant factor for the accuracy, and the accuracy of the technique when spontaneous breathing effort is present. METHODS: The authors enrolled 25 post-cardiac surgery patients in two serial protocols. First, the authors applied three settings of controlled mechanical ventilation in random order: large tidal volume (12 ml/kg), the same minute ventilation with a small tidal volume (6 ml/kg), and 50% decreased minute ventilation with a small tidal volume (6 ml/kg). Second, when the patient recovered spontaneous breathing, the authors applied three conditions of partial ventilatory support in random order: synchronized intermittent mandatory ventilation-pressure support ventilation, pressure support ventilation with an appropriately adjusted rebreathing loop, and pressure support ventilation with the shortest available loop. After establishing steady state conditions, the authors measured cardiac output using both partial carbon dioxide rebreathing and thermodilution methods. The correlation between the data yielded by the two methods was determined by Bland-Altman analysis and linear regression. RESULTS: Cardiac output with the carbon dioxide rebreathing technique correlated moderately with that measured by thermodilution when minute ventilation was set to maintain normocapnia, regardless of tidal volumes. However, when minute ventilation was set low, the carbon dioxide rebreathing technique underreported cardiac output (y = 0.70x; correlation coefficient, 0.34; bias, -1.73 l/min; precision, 1.27 l/min; limits of agreement, -4.27 to +0.81 l/min). When there was spontaneous breathing, the correlation between the two cardiac output measurements became worse. Carbon dioxide rebreathing increased spontaneous tidal volume and respiratory rate (20% and 30%, respectively, during pressure support ventilation) when the rebreathing loop was adjusted for large tidal volume. CONCLUSIONS: During controlled mechanical ventilation, minute ventilation rather than tidal volume affected the accuracy of cardiac output measurement using the partial carbon dioxide rebreathing technique. When spontaneous breathing is present, the carbon dioxide rebreathing technique is less accurate and increases spontaneous tidal volume and respiratory rate.

Adult↗
PubMed1996

Noninvasive mechanical ventilation in patients with acute respiratory failure.

OBJECTIVES: a) To describe the introduction of noninvasive means to provide positive-pressure ventilation in acute respiratory failure; b) to describe the physiologic response to noninvasive ventilation; c) to review the current published literature on using noninvasive ventilation in patients with acute hypercapnic and/or hypoxemic respiratory failure; d) to describe the technique of applying mask ventilation and current recommendations for using noninvasive ventilation and current recommendations for using noninvasive ventilation in patients with acute respiratory failure; and e) to discuss the advantages and disadvantages of noninvasive ventilation. DATA SOURCES: All relevant articles published in the English medical literature from 1988 through August 1994 were retrieved through a MEDLINE search, as well as from the author's experience. STUDY SELECTION: Studies were selected based on the use of positive-pressure mechanical ventilation delivered, using facial or nasal masks in various acute settings of respiratory failure. DATA EXTRACTION: The authors extracted all applicable data. DATA SYNTHESIS: Studies were analyzed according to the type of respiratory failure (hypercapnic vs. hypoxemic) and underlying conditions where noninvasive ventilation seemed to be a better alternative. The results were evaluated based on types of masks used and modes of ventilation. Outcome measures were compared based on studies that randomized patients with acute respiratory failure to receive noninvasive vs. conventional therapy. Complications of noninvasive ventilation, mainly local, were compared with those complications seen endotracheal intubation in acute respiratory failure patients. CONCLUSIONS: Noninvasive ventilation is a safe and effective means of ventilatory support for many patients with acute respiratory failure. Noninvasive ventilation is well tolerated, principally because it allows the patient to be in control and to continue verbal communication, and should be strongly considered in managing terminally ill patients with potentially reversible causes of respiratory failure. The duration of mechanical ventilation and its associated complications are significantly decreased in hypercapnic respiratory failure with noninvasive ventilation.

Acute Disease↗
PubMed1991

Airway pressure triggered ventilation for preterm neonates.

The usefulness of airway pressure triggered ventilation for the preterm newborn has been assessed using a new patient triggered valveless ventilator, the SLE 2000 infant ventilator (SLE 2000). This ventilator performs well at fast rates with no inadvertent positive end expiratory pressure (PEEP) even at rates of 150 breaths per minute (bpm). The ventilator is triggered by a change in airway pressure equal to or exceeding 0.5 cmH2O. If the infant fails to achieve the change in airway pressure which will trigger the ventilator the infant is ventilated at the back-up rate which is predetermined in conventional mode prior to commencing PTV. Infants were ventilated for one hour on a conventional neonatal ventilator, then for one hour on the SLE 2000 in conventional mode without changing the ventilator settings and finally for one hour on the SLE 2000 in patient triggered mode. Arterial blood gases were checked at the end of each hour. During patient triggered ventilation (PTV) the peak pressure, inspiratory time and inspired oxygen concentration were the same as those used during conventional mode. Simultaneous recordings were made of flow, volume, ventilator and oesophageal pressure change, from this recording the trigger delay during PTV was calculated. The trigger delay, being the time lag from the start of spontaneous inspiration, indicated by the negative deflection in the oesophageal pressure trace, and the onset of the ventilator breath. Thirteen infants were included in the study, median gestational age 32 weeks (range 25-35) and birthweight 1640 g (range 838-3038). All were being ventilated for respiratory distress syndrome (RDS) and were 4 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation Studies as Topic↗
PubMed1997

Ventilation and hypoxic ventilatory response of Tibetan and Aymara high altitude natives.

Newcomers acclimatizing to high altitude and adult male Tibetan high altitude natives have increased ventilation relative to sea level natives at sea level. However, Andean and Rocky Mountain high altitude natives have an intermediate level of ventilation lower than that of newcomers and Tibetan high altitude natives although generally higher than that of sea level natives at sea level. Because the reason for the relative hypoventilation of some high altitude native populations was unknown, a study was designed to describe ventilation from adolescence through old age in samples of Tibetan and Andean high altitude natives and to estimate the relative genetic and environmental influences. This paper compares resting ventilation and hypoxic ventilatory response (HVR) of 320 Tibetans 9-82 years of age and 542 Bolivian Aymara 13-94 years of age, native residents at 3,800-4,065 m. Tibetan resting ventilation was roughly 1.5 times higher and Tibetan HVR was roughly double that of Aymara. Greater duration of hypoxia (older age) was not an important source of variation in resting ventilation or HVR in either sample. That is, contrary to previous studies, neither sample acquired hypoventilation in the age ranges under study. Within populations, greater severity of hypoxia (lower percent of oxygen saturation of arterial hemoglobin) was associated with slightly higher resting ventilation among Tibetans and lower resting ventilation and HVR among Aymara women, although the associations accounted for just 2-7% of the variation. Between populations, the Tibetan sample was more hypoxic and had higher resting ventilation and HVR. Other systematic environmental contrasts did not appear to elevate Tibetan or depress Aymara ventilation. There was more intrapopulation genetic variation in these traits in the Tibetan than the Aymara sample. Thirty-five percent of the Tibetan, but none of the Aymara, resting ventilation variance was due to genetic differences among individuals. Thirty-one percent of the Tibetan HVR, but just 21% of the Aymara, HVR variance was due to genetic differences among individuals. Thus there is greater potential for evolutionary change in these traits in the Tibetans. Presently, there are two different ventilation phenotypes among high altitude natives as compared with sea level populations at sea level: lifelong sustained high resting ventilation and a moderate HVR among Tibetans in contrast with a slightly elevated resting ventilation and a low HVR among Aymara.

Acclimatization↗
PubMed2002

Quality control of mechanical ventilation at the patient's home.

OBJECTIVE: During home mechanical ventilation the prescribed settings are applied without permanent supervision of health professionals. After a long-time period of unattended operation at home the ventilator may not apply the ventilation parameters prescribed. This quality control study of home mechanical ventilation assessed whether tidal volume (V(T)), frequency (f), and minute ventilation (V'(E)) actually applied by the ventilator coincide with the values set on the ventilator control panel and with those prescribed. MEASUREMENTS: Actual V(T), f, and V'(E) applied by the ventilator in 30 patients on nocturnal HMV were measured at the patients' homes. The patients were subjected to volume targeted assist ventilation through nasal mask (n=28) or tracheostomy (n=2). The values of V(T), f, and V'(E) set at the ventilator were recorded. The actual and set V(T), f, and V'(E) values were compared with those prescribed. RESULTS: Considerable differences were found between actual, set and prescribed V(T), f, and V'(E). Actual V'(E) was significantly lower than V'(E) set: mean difference was 0.82 l/min, with considerable individual differences. Differences between actual and prescribed V'(E) were caused both by a poor performance of the ventilator and by a discrepancy between the values prescribed and those set at the ventilator control panel. CONCLUSIONS: Regularly assessing the actual performance of ventilators at the patient's home is a quality control procedure useful for detecting malfunctions which could improve compliance and outcome of home mechanical ventilation.

Adult↗
PubMed2005

The spatial and temporal heterogeneity of regional ventilation: comparison of measurements by two high-resolution methods.

High-resolution estimates of ventilation distribution in normal animals utilizing deposition of fluorescent microsphere aerosol (FMS technique) demonstrate substantial ventilation heterogeneity, but this finding has not been confirmed by an independent method. Five supine anesthetized sheep were used to compare the spatial and temporal heterogeneity of regional ventilation measured by both the FMS technique and by a ventilation model utilizing the data from computed tomography images of xenon gas washin (CT/Xe technique). An aerosol containing 1 microm fluorescent microspheres (FMS) was administered via a mechanical ventilator delivering a 2-s end-inspiration hold during each breath. Following the aerosol administration, sequential CT images of a transverse lung slice were acquired during each end-inspiration hold during washin of a 65% Xenon/35% oxygen gas mixture (CT/Xe technique). Four paired FMS and CT/Xe measurements were done at 30 min intervals, after which the animals were sacrificed. The lungs were extracted, air-dried and sliced in 1cm transverse sections. The lung section corresponding to the CT image was cut into 1 cm3 cubes, with notation of spatial coordinates. The individual cubes were soaked in solvent and the four fluorescent signals were measured with a fluorescence spectrophotometer. The color signals were normalized by the mean signal for all pieces and taken as the FMS estimate of ventilation heterogeneity. The CT images were clustered into 1 cm3 voxels and the rate of increase in voxel density was used to calculate voxel ventilation utilizing the model of . The regional ventilation voxel measurements were normalized by the mean value to give a CT/Xe estimate of ventilation heterogeneity comparable to the normalized FMS measurements. The overall of heterogeneity of ventilation at the 1 cm3 level of resolution was comparable by both techniques, with substantial differences among animals (coefficient of variation ranging from 37% to 74%). The repeated within-animal measurements by both techniques gave consistent values. Both techniques showed comparable large-scale distribution of regional ventilation in the caudal lobes of the supine animals. There were appreciable differences in the temporal variability of ventilation among animals. This study provides an independent confirmation of the scale-dependent heterogeneity of ventilation described by previous FMS aerosol studies of ventilation heterogeneity.

Animals↗
PubMed2000

Respiratory efficacy of subglottic low-frequency, subglottic combined-frequency, and supraglottic combined-frequency jet ventilation during microlaryngeal surgery.

UNLABELLED: We tested the respiratory efficacy of different jet ventilation techniques (subglottic low-frequency versus subglottic combined-frequency and subglottic combined-frequency versus supraglottic combined frequency) in patients undergoing microlaryngeal surgery. The PaCO(2) and the quotient of arterial oxygen tension (PaO(2)) over FIO(2) were measured. After anesthetic induction (propofol, remifentanil, vecuronium), an endotracheal Mon-Jet catheter (Xomed, Jacksonville, FL) for subglottic jet ventilation and a laryngoscope for supraglottic jet ventilation (Carl Reiner G.m.b.H., Vienna, Austria) were inserted. In Group 1 (n = 18), subglottic low-frequency (15 breaths/min), combined-frequency (600 and 15 breaths/min), and low-frequency jet ventilation was subsequently performed (15 min each). In Group 2 (n = 19), the sequence was supraglottic, subglottic, and supraglottic combined-frequency jet ventilation. The driving pressures were initially adjusted to achieve normocapnia and were not changed during the entire study period. The FIO(2) was measured endotracheally. The Wilcoxon's signed rank test was applied. In Group 1, PaCO(2) and PaO(2)/FIO(2) improved significantly after switching from subglottic low-frequency to subglottic combined-frequency jet ventilation (PaCO(2), from 46.6 +/-8.3 to 42.1+/-8.1 mm Hg; PaO(2)/FIO(2), from 311+/-144 to 361+/-141 mm Hg; P<0.05). In Group 2, PaCO(2) increased and PaO(2)/FIO(2) decreased significantly after switching from supraglottic to subglottic combined-frequency jet ventilation (PaCO(2), from 39.4+/-7.1 to 45.9+/-7.5 mm Hg; PaO(2)/FIO(2), from 415+/-114 to 351+/-129 mm Hg; P<0.05). We conclude that subglottic combined-frequency jet ventilation is less effective than supraglottic combined-frequency ventilation, but more effective than subglottic low-frequency jet ventilation. IMPLICATIONS: The combination of high and low respiratory frequencies (600 and 15 breaths/min) improves pulmonary gas exchange during subglottic jet ventilation via an endotracheal catheter. However, subglottic combined-frequency jet ventilation is less effective than supraglottic combined-frequency jet ventilation via a jet ventilation laryngoscope.

Adult↗
PubMed1995

Weekly ventilator circuit changes. A strategy to reduce costs without affecting pneumonia rates.

BACKGROUND: Mechanical ventilator circuits are commonly changed at 48-h intervals. This frequency may be unnecessary because ventilator-associated pneumonia often results from aspiration of pharyngeal secretions and not from the ventilator circuit. We compared the ventilator-associated pneumonia rates and costs associated with 48-h and 7-day circuit changes. METHODS: Ventilator circuits were changed at 48-h intervals during the control period (November 1992 to April 1993) and at 7-day intervals during the study period (June 1993 to November 1993). Nosocomial pneumonias were prospectively identified using the criteria of the Centers for Disease Control and Prevention. The annual cost difference of changing circuits at 48-h and 7-day intervals was calculated using the distribution of ventilator days for the control and study periods. RESULTS: There were 1,708 patients, 9,858 ventilator days, and a pneumonia rate of 9.64 per 1,000 ventilator days in the control group (48-h circuit changes). There were 1,715 patients, 9,160 ventilator days, and 8.62 pneumonias per 1,000 ventilator days when circuits were changed at 1-week intervals (study group). Using a logistic regression model, there were significantly greater odds of developing a ventilator-associated pneumonia in surgical patients (odds ratio 1.77, P = 0.02) and patients in critical care units (odds ratio 1.54, P = 0.05), but no significant risk of ventilator-associated pneumonia in patients in whom circuits were changed at 1-week intervals (odds ratio 0.82, P = 0.22). Changing circuits at 7-day intervals resulted in a 76.6% ($111,530) reduction in the annual cost for materials and salaries. CONCLUSIONS: We found no difference in pneumonia rates with ventilator circuit changes at 48-h and 7-day intervals. Ventilator circuits can be safely changed at weekly intervals, resulting in large cost savings.

Adult↗
PubMed2006

Ventilator-associated pneumonia leading to acute lung injury after trauma: importance of Haemophilus influenzae.

BACKGROUND: Ventilator-associated pneumonia is a clear risk factor for acute lung injury which has been poorly described in trauma patients. This prospective study was undertaken to estimate the incidence of such ventilator-associated pneumonia leading to acute lung injury, the risk factors, and the associated morbidity and mortality in a group of multiple trauma patients. METHODS: Trauma patients who were mechanically ventilated and survived at least 24 h were included. Ventilator-associated pneumonia was confirmed by a bacterial culture of a blind protected telescoping catheter with at least 10 colony-forming units/ml of at least one pathogen. Episodes of acute lung injury were prospectively recorded. RESULTS: Ventilator-associated pneumonia was documented in 78 patients of the 175 included (44%) and led to the development of ventilator-associated pneumonia acute lung injury in 18 patients (23%). The sole independent risk factor for ventilator-associated pneumonia leading to acute lung injury was the presence of Haemophilus influenzae (hazard ratio, 8.8; 95% confidence interval, 2.7-28.6). Eleven (61%) of the 18 patients with ventilator-associated pneumonia leading to acute lung injury had development of a ventilator-associated pneumonia recurrence, as compared with 20 (33%) of the 60 patients with ventilator-associated pneumonia alone (P = 0.03). Seven (39%) of the 18 trauma patients with ventilator-associated pneumonia leading to acute lung injury died, as compared with 9 (15%) of the 60 trauma patients with ventilator-associated pneumonia alone (P = 0.04). CONCLUSION: Acute lung injury complicated the course of 15% of ventilator-associated pneumonia in trauma patients. H. influenzae seemed to be one of the most frequent bacteria involved and the sole risk factor identified. Occurrence of ventilator-associated pneumonia leading to acute lung injury modified the prognosis of trauma patients.

Adult↗
PubMed1997

High-frequency oscillatory ventilation for adult respiratory distress syndrome--a pilot study.

OBJECTIVE: To evaluate the safety and effectiveness of high-frequency oscillatory ventilation using a protocol designed to recruit and maintain optimal lung volume in patients with severe adult respiratory distress syndrome (ARDS). SETTING: Surgical and medical intensive care units in a tertiary care, military teaching hospital. DESIGN: A prospective, clinical study. PATIENTS: Seventeen patients, 17 yrs to 83 yrs of age, with severe ARDS (Lung Injury Score of 3.81 +/- 0.23) failing inverse ratio mechanical conventional ventilation (PaO2/FiO2 ratio of 68.6 +/- 21.6, peak inspiratory pressure of 54.3 +/- 12.7 cm H2O, positive end-expiratory pressure of 18.2 +/- 6.9 cm H2O). INTERVENTIONS: High-frequency oscillatory ventilation was instituted after varying periods of conventional ventilation (5.12 +/- 4.3 days). We employed lung volume recruitment strategy that consisted of incremental increases in mean airway pressure to achieve a PaO2 of > or = 60 torr (> or = 8.0 kPa), with an FiO2 of < or = 0.6. MEASUREMENTS AND MAIN RESULTS: High-frequency oscillator ventilator settings (FiO2, mean airway pressure, pressure amplitude of oscillation [delta P] frequency) and hemodynamic parameters (cardiac output, oxygen delivery [DO2]), mean systemic and pulmonary arterial pressures, and the oxygenation index (oxygenation index = [FiO2 x mean airway pressure x 100]/PaO2) were monitored during the transition to high-frequency oscillatory ventilation and throughout the course of the high-frequency protocol. Thirteen patients demonstrated improved gas exchange and an overall improvement in PaO2/FiO2 ratio (p < .02). Reductions in the oxygenation index (p < .01) and FiO2 (p < .02) at 12, 24, and 48 hrs after starting high-frequency oscillatory ventilation were observed. No significant compromise in cardiac output or DO2 was observed, despite a significant increase in mean airway pressure (31.2 +/- 10.3 to 34.0 +/- 6.7 cm H2O, p < .05) on high-frequency oscillatory ventilation. The overall survival rate at 30 days was 47%. A greater number of pretreatment days on conventional ventilation (p < .009) and an entry oxygenation index of > 47 (sensitivity 100%, specificity 100%) were associated with mortality. CONCLUSIONS: High-frequency oscillatory ventilation is both safe and effective in adult patients with severe ARDS failing conventional ventilation. A lung volume recruitment strategy during high-frequency oscillatory ventilation produced improved gas exchange without a compromise in DO2. These results are encouraging and support the need for a prospective, randomized trial of algorithm-controlled conventional ventilation vs. high-frequency oscillatory ventilation for adults with severe ARDS.

Adolescent↗
PubMed2000

The comfort of breathing: a study with volunteers assessing the influence of various modes of assisted ventilation.

OBJECTIVE: To assess the subjective feeling of comfort of healthy volunteers breathing on various modes of ventilation used in intensive care. DESIGN: A randomized, prospective, double-blinded, crossover trial using volunteers. SETTING: An intensive care unit (ICU) in a teaching hospital. INTERVENTIONS: We compared, by using healthy volunteers, the subjective feeling of comfort of three modes of ventilation used during the weaning phase of critical illness. We used healthy volunteers to avoid other distracting influences of intensive care that may confound the primary feeling of comfort. The modes we compared were synchronized intermittent mandatory ventilation, assisted spontaneous breathing, and biphasic positive airway pressure. The imposed ventilation was comparable with 50% of the volunteers' normal respiratory effort. The volunteers breathed via a mouthpiece through a ventilator circuit, and the modes of ventilation were introduced in a randomized manner. MEASUREMENTS AND MAIN RESULTS: We measured visual analog scores for comfort for the three modes of ventilation and collected a ranking order and open-ended comments. We demonstrated that at the level of support we imposed, assisted spontaneous breathing was the most comfortable mode of ventilation and that synchronized intermittent mandatory ventilation was the most uncomfortable. These results were strongly supported by both the ranking scale and comments of the volunteers. CONCLUSIONS: Assisted spontaneous breathing was the most comfortable mode of ventilation because the pattern was primarily determined by the volunteer. Synchronized intermittent mandatory ventilation was the most uncomfortable because the ventilatory pattern was imposed on the volunteers, leading to ventilator-volunteer dyssynchrony. We also conclude there is wide individual variation in the subjective feeling of comfort. Whereas the mode of ventilation in ICUs is based primarily on the physiologic needs of the patient, the feeling of comfort may be considered when choosing an appropriate mode of ventilation during the weaning phase of critical illness.

Adult↗
PubMed2003

Strategy of antibiotic rotation: long-term effect on incidence and susceptibilities of Gram-negative bacilli responsible for ventilator-associated pneumonia.

OBJECTIVE: To evaluate the long-term effect of a program of rotating antibiotics on the incidence of ventilator-associated pneumonia and the susceptibilities of Gram-negative bacilli responsible for ventilator-associated pneumonia. DESIGN: Prospective program for the surveillance of antibiotic susceptibilities of microorganisms responsible for ventilator-associated pneumonia. SETTING: Academic, university-based, medical intensive care unit (16 beds). SUBJECTS: 2,856 mechanically ventilated patients. INTERVENTIONS: A new program of antibiotic use was introduced at the end of 1996 that involved the rotation of antibiotics in empirical and therapeutic use of the treatment of ventilator-associated pneumonia. The rotation concerned the beta-lactam and aminoglycoside classes, with a rotation interval of 1 month. The use of antibiotics was monitored monthly. No preference was given to any particular antibiotic. In a previous study, the period before the introduction of this protocol (1995-1996) was compared with the period 2 yrs after (1997-1998): The results indicated a decreased incidence of ventilator-associated pneumonia, a lower incidence of potentially resistant Gram-negative bacilli, and increased sensitivities of Gram-negative bacilli, especially Pseudomonas aeruginosa and Burkholderia cepacia. After 1998, we decided to continue a routine for this rotation. The long-term effect of this program was studied by comparing the incidence of Gram-negative bacilli responsible for ventilator-associated pneumonia and their susceptibilities obtained in a third period: 1999-2001. The long-term effect (5 yrs) of such a strategy-2-yr protocol period (1997-1998) and 3-yr routine period (1999-2001)-could be evaluated. MEASUREMENTS AND MAIN RESULTS: During the 7-yr study period, 2,856 patients were mechanically ventilated for >48 hrs. The incidence of ventilator-associated pneumonia remained significantly lower in period 3 (1999-2001): 23% (period 1, 1995-1996) vs. 15.7% (period 2, 1997-1998) vs. 16.3% (period 3, 1999-2001; p =.002). Late-onset ventilator-associated pneumonia occurred in 86.6% and 94% of cases, respectively, in periods 1 and 3 (p =.02). The decrease of the incidence of early-onset ventilator-associated pneumonia was statistically significant during the 7-yr study period: 13% vs. 9% vs. 5.9% (p =.02). Combined with a higher incidence of late-onset ventilator-associated pneumonia, the incidence of potentially resistant Gram-negative bacilli increased in period 3: 42.2% vs. 34.5% vs. 41.7% (nonsignificant), except for B. cepacia: 11.7% vs. 7.4% vs. 3.7% (p =.005). Nevertheless, the potential antibiotic-resistant Gram-negative bacilli were more sensitive to most of the beta-lactams, especially piperacillin-tazobactam and cefepime. CONCLUSIONS: Rotation of antibiotics could help to avoid ventilator-associated pneumonia. It could greatly improve the susceptibilities of the potentially antibiotic-resistant Gram-negative bacilli responsible for late-onset ventilator-associated pneumonia. This program could be applied in routine with good results 5 yrs after its introduction. Further studies, especially multiple-center trials, are necessary to confirm this result and better define the rotation type and intervals.

Aminoglycosides↗
PubMed1998

Systemic oxygen uptake during experimental closed-chest cardiopulmonary resuscitation using air or pure oxygen ventilation.

BACKGROUND: Although clinical cardiopulmonary resuscitation always includes ventilation with pure oxygen, this kind of ventilation has been reported to be associated with worse neurological outcome than ventilation with air in experimental cardiopulmonary resuscitation (CPR). The aim of the present investigation was to compare the systemic oxygen uptake during experimental closed-chest CPR including ventilation with pure oxygen or ambient air and, furthermore, to elucidate possible mechanisms of action in the regulation of pulmonary gas exchange. METHODS: In 24 anesthetized piglets, 2 min of induced ventricular fibrillation and no ventilation was followed by 10 min of closed-chest CPR including i.v. administration of 0.5 mg adrenaline (at 8 min), and in one of the experimental groups alkaline buffer (at 5 min). The piglets were randomly divided into 3 groups: air ventilation during the entire CPR period with saline administration (n=8), air ventilation during the entire CPR period plus tris buffer mixture (n=8), and air ventilation for 3 min followed by 100% oxygen with saline administration (n= 8). RESULTS: In the group ventilated with air and treated with tris buffer mixture, cardiac output was significantly greater than in the group ventilated with pure oxygen. The arterial-mixed venous oxygen content difference was approximately 25% greater with pure oxygen than with air ventilation; however, there was no difference in systemic oxygen uptake. Systemic oxygen uptake increased after administration of tris buffer mixture in the group ventilated with air. CONCLUSIONS: Pulmonary hypoxic vasoconstriction appeared to be abolished during CPR including pure oxygen ventilation. Blood flow, not ventilation or pulmonary gas exchange, is the limiting factor during experimental closed-chest CPR.

Adrenergic Agonists↗
PubMed2006

Ventilation and performance in office work.

Outdoor air ventilation rates vary considerably between and within buildings, and may be too low in some spaces. The purpose of this study was to evaluate the potential work performance benefits of increased ventilation. We analyzed the literature relating work performance with ventilation rate and employed statistical analyses with weighting factors to combine the results of different studies. The studies included in the review assessed performance of various tasks in laboratory experiments and measured performance at work in real buildings. Almost all studies found increases in performance with higher ventilation rates. The studies indicated typically a 1-3% improvement in average performance per 10 l/s-person increase in outdoor air ventilation rate. The performance increase per unit increase in ventilation was bigger with ventilation rates below 20 l/s-person and almost negligible with ventilation rates over 45 l/s-person. The performance increase was statistically significant with increased ventilation rates up to 15 l/s-person with 95% CI and up to 17 l/s-person with 90% CI. Practical Implications We have demonstrated a quantitative relationship between work performance and ventilation within a wide range of ventilation rates. The model shows a continuous increase in performance per unit increase in ventilation rate from 6.5 l/s-person to 65 l/s-person. The increase is statistically significant up to 15 l/s-person. This relationship has a high level of uncertainty; however, use of this relationship in ventilation design and feasibility studies may be preferable to the current practice, which ignores the relationship between ventilation and productivity.

Air Pollution, Indoor↗
PubMed2005

3He MRI-based assessment of posture-dependent regional ventilation gradients in rats.

A recently developed method for quantitative assessment of regional lung ventilation was employed for the study of posture-dependent ventilation differences in rats. The measurement employed hyperpolarized (3)He MRI to detect the build-up of the signal intensity after increasing numbers of (3)He breaths, which allowed for computation of a regional ventilation parameter. A group of six anesthetized rats was studied in both supine and prone postures. Three-dimensional maps of the ventilation parameter were obtained with high spatial resolution (voxel volume approximately 2 mm(3)). Vertical (dorsal-ventral) gradients of the ventilation index, defined as the regional ventilation normalized by the average ventilation within the whole lung, were investigated. Variations in the regional distribution of the ventilation parameter, as well as of the ventilation index, could be detected, depending on the posture of the rats. In supine posture, ventilation was elevated in the dependent parts of the lungs, with a linear gradient of the ventilation index of -0.11 +/- 0.03 cm(-1). In prone posture, the distribution of ventilation was more uniform, with a significantly (P < 0.001) smaller gradient of the ventilation index of -0.01 +/- 0.02 cm(-1). It is concluded that the (3)He MRI-based method can detect and quantify regional ventilation gradients in animals as small as the rat and that these gradients depend on prone or supine posture of the animal.

Administration, Inhalation↗
PubMed2001

Evaluation of inspiratory rise time and inspiration termination criteria in new-generation mechanical ventilators: a lung model study.

INTRODUCTION: Inspiratory rise time adjustment during pressure ventilation and inspiration termination criteria adjustment during pressure support ventilation are available on some of the newest mechanical ventilators. Both are designed to improve patient-ventilator synchrony. However, the function of these adjuncts during pressure ventilation on these ventilators has not been evaluated. METHODS: Three inspiratory rise times (minimum, medium, and maximum) were evaluated in 5 new-generation mechanical ventilators (Hamilton Galileo, Siemens 300A, Puritan Bennett 840, BEAR 1000, and Dräger Evita 4) during pressure support and pressure assist/control. Three inspiration termination criteria settings (minimum, medium, and maximum) were also evaluated in 2 mechanical ventilators (Hamilton Galileo and Puritan Bennett 840) during pressure support. All evaluations were performed with a spontaneous breathing lung model (compliance 50 mL/cm H2O, resistance 8.2 cm H2O/L/s, respiratory rate 12 breaths/min, inspiratory time 1.0 s, and lung model peak inspiratory flow 60 L/min). Throughout the evaluation, inspiratory pressure was set at 15 cm H2O and positive end-expiratory pressure at 5 cm H2O, resulting in a peak airway pressure of 20 cm H2O. RESULTS: Significant (p < 0.05) and important (> 10%) differences were found among the ventilators at similar rise times (minimum, medium, and maximum) and for each ventilator as rise time was varied. Also, significant (p < 0.05) and important (> 10%) differences were observed between ventilators and within each ventilator when inspiration termination criteria were varied. There were significant (p < 0.05) differences between pressure support and pressure assist/control, but most were < 10%, except those associated with expiration. CONCLUSIONS: Major differences exist for each ventilator as rise time or inspiration termination criteria are varied and among ventilators at similar settings. Inspiration termination criteria adjustment markedly affects transition to exhalation in the Puritan Bennett 840.

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