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PubMed1993

Apnoea following normocapnic mechanical ventilation in awake mammals: a demonstration of control system inertia.

1. Inhibition of inspiratory muscle activity from volume-related feedback during mechanical ventilation has been shown previously. To determine if this neuromechanical inhibition displays a memory effect, the duration of expiration immediately following cessation of mechanical ventilation was assessed in eight normal subjects. The subjects were passively mechanically ventilated via a nasal mask until the end-tidal CO2 (PET,CO2) was a minimum of 30 mmHg and inspiratory effort was no longer detected, as evidenced by stabilization of mouth pressure and disappearance of surface diaphragm EMG activity. The ventilator output was held constant at a mean tidal volume (VT) of 1.0 l and breath duration of 4.6 s and PET,CO2 was increased 1-1.5 mmHg/min (via increased inspired CO2 fraction, FI,CO2) until inspiratory muscle activity returned. The PET,CO2 at which activation first occurred was defined as the CO2 recruitment threshold (PCO2,RT). The mechanical ventilation protocol was repeated and the PET,CO2 increased 1-1.5 mmHg/min until it was a mean of 1.1 mmHg above spontaneous PET,CO2 and 3.6 mmHg below PCO2,RT. After 4-6 min of mildly hypercapnic mechanical ventilation, the mechanical ventilation was terminated. 2. Following termination of mechanical ventilation, the duration of the subsequent apnoea was 14.6 +/- 2.8 s (mean +/- S.E.M.) or 453 +/- 123% > spontaneous TE and 178 +/- 62% > the TE chosen by the subject during 'assist control' ventilation at VT = 1.0 l. 3. To test the hypothesis that the apnoea following cessation of mechanical ventilation was due to a vagally mediated memory effect, the study was repeated in five double-lung transplant patients with similar PCO2,RT to normal subjects. These pulmonary vagally denervated patients also displayed an apnoea (14.5 +/- 4.0 s) upon cessation of mechanical ventilation (at a PET,CO2 2.0 mmHg > eupnoea and 2.4 mmHg < PCO2,RT), that was 367 +/- 162% > spontaneous TE. 4. We also found significant apnoea in the awake dog immediately following mildly hypercapnic passive mechanical ventilation, and this was similar before and after bilateral vagal blockade (15.7 +/- 1.3 and 19.7 +/- 4.7 s, respectively). 5. We conclude that neuromechanical inhibition of inspiratory muscle activity, produced by passive mechanical ventilation at high VT, exhibits a memory effect reflected in TE prolongation, which persists in the face of substantial increases in chemoreceptor stimuli. This effect is not dependent on vagal feedback from lung receptors. 6. We hypothesize that this persistent apnoea represents an inherent 'inertia', characteristic of the ventilatory control system.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed2003

Sevoflurane anaesthesia in chickens during spontaneous and controlled ventilation.

A crossover study design was used to investigate the dose-related effects of sevoflurane at end-tidal concentrations of 2.2 to 4.4 per cent on the respiratory rate, blood gases, heart rate, arterial blood pressure and ocular signs of chickens during spontaneous and controlled ventilation. The mean (sd) carbon dioxide partial pressure (PaCO2) increased as the concentration of sevoflurane increased, and was 86 (29) mmHg at an end-tidal concentration of 4.4 per cent during spontaneous ventilation, but was maintained between 29 and 42 mmHg during controlled ventilation. The heart rate increased as the concentration of sevoflurane increased during spontaneous ventilation, but did not change during controlled ventilation. Sevoflurane decreased arterial blood pressure during both spontaneous and controlled ventilation, but a dose-dependent decrease in arterial blood pressure was observed only during controlled ventilation. The mean arterial blood pressure at an end-tidal concentration of 4.4 per cent was significantly higher during spontaneous ventilation than during controlled ventilation. Controlled ventilation prevented the increases in PaCO2 and heart rate that were observed during spontaneous ventilation. The decrease in arterial blood pressure during spontaneous ventilation was less than that during controlled ventilation, possibly owing to the effects of hypercapnia.

Administration, Inhalation↗
PubMed1992

Comparison of gas and liquid ventilation: clinical, physiological, and histological correlates.

To differentiate the effects of gas and liquid ventilation on cardiopulmonary function during early development, we compared the clinical, physiological, and histological profiles of gas- and liquid-ventilated preterm lambs (n = 16; 108-116 days gestation). Immediately after cesarean section delivery, ventilation commenced using gas delivered by a volume ventilator (n = 9) or liquid perfluorochemical (n = 7) delivered by a mechanically assisted liquid ventilation system. Pulmonary gas exchange, acid-base status, vital signs, and respiratory compliance were assessed during the 3-h protocol; sections of the lungs were obtained for histological analyses when the animals were killed. Six of nine gas-ventilated lambs expired from respiratory failure before 3 h, with the remaining animals experiencing severe respiratory insufficiency, pneumothoraces, and cardiovascular deterioration. Six of seven liquid-ventilated lambs survived with good gas exchange and cardiovascular stability and without fluorothorax; one experienced ventricular fibrillation before 1 h and expired despite pulmonary stability. Respiratory compliance was significantly greater in the liquid- than in the gas-ventilated lambs. Histological analyses of gas-ventilated lungs demonstrated nonhomogeneous lung expansion, with thick-walled gas exchange spaces containing proteinaceous exudate, hemorrhage, and hyaline membranes. In contrast, liquid-ventilated lungs appeared clear, with thin-walled and uniformly expanded gas exchange spaces that were free of hyaline membranes and luminal debris. Morphometric analyses demonstrated that surface area and gas exchange index were greater in the liquid- than in the gas-ventilated lambs. These results indicate that elimination of surface active forces by liquid ventilation during early development provides more effective gas exchange with less barotrauma compared with gas ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Controlled versus assisted mechanical ventilation effects on respiratory motor output in sleeping humans.

Central apneas occur after cessation of mechanical ventilation despite normocapnic conditions. We asked whether this was due to ventilator-induced increases in respiratory rate or VT. Accordingly, we compared the effects of increased VT (135 to 220% of eupneic VT) with and without increased respiratory rate, using controlled and assist control mechanical ventilation, respectively, upon transdiaphragmatic pressure in sleeping humans. Increasing ventilator frequency +1 per minute and VT to 165-200% of baseline eupnea eliminated transdiaphragmatic pressure during controlled mechanical ventilation and prolonged expiratory time (two to four times control) after mechanical ventilation. During and after assist control mechanical ventilation at 135-220% of eupneic VT, transdiaphragmatic pressure was reduced in proportion to the increase in ventilator volume. However, every ventilator cycle was triggered by an active inspiration, and immediately after mechanical ventilation, expiratory time during spontaneous breathing was prolonged less than 20% of that observed after controlled mechanical ventilation at similar VT. We conclude that both increased frequency and VT during mechanical ventilation significantly inhibited respiratory motor output via nonchemical mechanisms. Controlled mechanical ventilation at increased frequency plus moderate elevations in VT reset respiratory rhythm and inhibited respiratory motor output to a much greater extent than did increased VT alone.

Adult↗
PubMed2004

Trolox attenuates mechanical ventilation-induced diaphragmatic dysfunction and proteolysis.

Prolonged mechanical ventilation results in diaphragmatic oxidative injury, elevated proteolysis, fiber atrophy, and reduced force-generating capacity. We tested the hypothesis that antioxidant infusion during mechanical ventilation would function as an antioxidant to maintain redox balance within diaphragm muscle fibers and therefore prevent oxidative stress and subsequent proteolysis and contractile dysfunction. Sprague-Dawley rats were anesthetized, tracheostomized, and mechanically ventilated with 21% O(2) for 12 hours. The antioxidant Trolox was intravenously infused in a subset of ventilated animals. Compared with acutely anesthetized, nonventilated control animals, mechanical ventilation resulted in a significant reduction (-17%) in diaphragmatic maximal tetanic force. Importantly, Trolox completely attenuated this mechanical ventilation-induced diaphragmatic contractile deficit. Total diaphragmatic proteolysis was increased 105% in mechanical ventilation animals compared with controls. In contrast, diaphragmatic proteolysis did not differ between controls and mechanical ventilation-Trolox animals. Moreover, 20S proteasome activity in the diaphragm was elevated in the mechanical ventilation animals (+76%); Trolox treatment attenuated this mechanical ventilation-induced rise in protease activity. These results are consistent with the hypothesis that mechanical ventilation-induced oxidative stress is an important factor regulating mechanical ventilation-induced diaphragmatic proteolysis and contractile dysfunction. Our findings suggest that antioxidant therapy could be beneficial during prolonged mechanical ventilation.

Animals↗
PubMed2003

Does the tube-compensation function of two modern mechanical ventilators provide effective work of breathing relief?

OBJECTIVE: An endotracheal tube (ETT) imposes work of breathing on mechanically ventilated patients. Using a bellows-in-a-box model lung, we compared the tube compensation (TC) performances of the Nellcor Puritan-Bennett 840 ventilator and of the Dräger Evita 4 ventilator. MEASUREMENTS AND RESULTS: Each ventilator was connected to the model lung. The respiratory rate of the model lung was set at 10 breaths/min with 1 s inspiratory time. Inspiratory flows were 30 or 60 l/min. A full-length 8 mm bore ETT was inserted between the ventilator circuit and the model lung. The TC was set at 0%, 10%, 50%, and 100% for both ventilators. Pressure was monitored at the airway, the trachea, and the pleura, and the data were recorded on a computer for later analysis of the delay time, of the inspiratory trigger pressure, and of the pressure-time product (PTP). The delay time was calculated as the time between the start of inspiration and minimum airway pressure, and the inspiratory trigger pressure was defined as the most negative pressure level. The same measurements were performed under pressure support ventilation of 4 and 8 cmH2O. The PTP increased according to the magnitude of inspiratory flow. Even with 100% TC, neither ventilator could completely compensate for the PTP imposed by the ETT. At 0% TC the PTP tended to be less with the Nellcor Puritan-Bennett 840 ventilator, while at 100% TC the PTP tended to be less with the Dräger Evita 4 ventilator. A small amount of pressure support can be equally effective to reduce the inspiratory effort compared with the TC. CONCLUSION: Although both ventilators provided effective TC, even when set to 100% TC they could not entirely compensate for a ventilator and ETT-imposed work of breathing. The effect of TC is less than that of pressure support ventilation. Physicians should be aware of this when using TC in weaning trials.

Humans↗
PubMed2005

Uneven distribution of ventilation in acute respiratory distress syndrome.

INTRODUCTION: The aim of this study was to assess the volume of gas being poorly ventilated or non-ventilated within the lungs of patients treated with mechanical ventilation and suffering from acute respiratory distress syndrome (ARDS). METHODS: A prospective, descriptive study was performed of 25 sedated and paralysed ARDS patients, mechanically ventilated with a positive end-expiratory pressure (PEEP) of 5 cmH2O in a multidisciplinary intensive care unit of a tertiary university hospital. The volume of poorly ventilated or non-ventilated gas was assumed to correspond to a difference between the ventilated gas volume, determined as the end-expiratory lung volume by rebreathing of sulphur hexafluoride (EELVSF6), and the total gas volume, calculated from computed tomography images in the end-expiratory position (EELVCT). The methods used were validated by similar measurements in 20 healthy subjects in whom no poorly ventilated or non-ventilated gas is expected to be found. RESULTS: EELVSF6 was 66% of EELVCT, corresponding to a mean difference of 0.71 litre. EELVSF6 and EELVCT were significantly correlated (r2 = 0.72; P < 0.001). In the healthy subjects, the two methods yielded almost identical results. CONCLUSION: About one-third of the total pulmonary gas volume seems poorly ventilated or non-ventilated in sedated and paralysed ARDS patients when mechanically ventilated with a PEEP of 5 cmH2O. Uneven distribution of ventilation due to airway closure and/or obstruction is likely to be involved.

Adult↗
PubMed1998

Radiographic assessment of hyperinflation: correlation with objective chest radiographic measurements and mechanical ventilator parameters.

BACKGROUND: Pulmonary barotrauma is a potentially fatal complication of positive pressure ventilation. We previously found that barotrauma occurred in patients with radiographic hyperinflation, but few objective data define the relationships among hyperinflation, objective chest radiograph (CXR) measurements, ventilator parameters, and development of barotrauma. OBJECTIVES: We sought (1) to assess the relationships among hyperinflation, objective CXR findings, mechanical ventilator parameters, and development of barotrauma. (2) To compare radiographic hyperinflation, ventilator parameters, and incidence of barotrauma in a current group of ICU patients with historical control subjects. SETTING: Medical and surgical ICU patients in a university hospital. DESIGN: Prospective blinded observational study; comparison of current series with historical control subjects. METHODS: One hundred two prospectively enrolled mechanically ventilated medical and surgical ICU patients each received portable supine CXRs that were reviewed independently by three radiologists who made objective measurements and subjectively determined the likelihood of hyperinflation. Ventilator parameters were recorded at the bedside at the time each CXR was obtained. CXR measurements and ventilator parameters were then related to the development of barotrauma during the course of ventilation and compared with findings of a prospective study at our institution 1 year earlier. RESULTS: Radiographically recognizable hyperinflation occurred in 18 of 102 mechanically ventilated ICU patients (18%) and correlated with lung length (24.7 vs 19.8 cm; p<0.05) and the anterior rib number that intersects the hemidiaphragm (5.4 vs 4.7; p<0.05). Patients with hyperinflation were ventilated at higher tidal volume per kilogram (VT/kg) (11.0 vs 9.4; p=0.0081), but peak airway pressure, plateau pressure, and positive end-expiratory pressure were similar. There were significant decreases in VT (810 vs 739 mL; p=0.015) and VT/kg (11.0 vs 10.1 mL/kg; p<0.001) in these mechanically ventilated ICU patients in comparison to hospital control subjects evaluated during the previous year. Paralleling these changes was a decrease in the frequency of CXR hyperinflation (p=0.003) and the incidence of ventilator-associated barotrauma (6.5% vs 0.98%; p=0.048). CONCLUSIONS: Ventilation at higher VT/kg is associated with a higher incidence of CXR hyperinflation. Radiographic hyperinflation is associated with lung length > or =24.7 cm and visualization of the sixth anterior rib. Patients with hyperinflation may be at greater risk for developing barotrauma or volutrauma. Ventilatory strategies utilizing lower volumes are associated with a lower incidence of such trauma in the current sample as compared with historical control subjects.

Adolescent↗
PubMed2004

An educational intervention to reduce ventilator-associated pneumonia in an integrated health system: a comparison of effects.

STUDY OBJECTIVES: To determine whether an educational initiative could decrease rates of ventilator-associated pneumonia in a regional health-care system. SETTING: Two teaching hospitals (one adult, one pediatric) and two community hospitals in an integrated health system. DESIGN: Preintervention and postintervention observational study. PATIENTS: Patients admitted to the four participating hospitals between January 1, 1999, and June 30, 2002, who acquired ventilator-associated pneumonia. INTERVENTION: An educational program for respiratory care practitioners and ICU nurses emphasizing correct practices for the prevention of ventilator-associated pneumonia. The program included a self-study module on risk factors for, and strategies to prevent, ventilator-associated pneumonia and education-based in-services. Fact sheets and posters reinforcing the information were posted throughout the ICU and respiratory care departments. MEASUREMENTS AND RESULTS: Completion rates for the module were calculated by job title at each hospital. Rates of ventilator-associated pneumonia per 1,000 ventilator days were calculated for all hospitals combined and for each hospital separately. Overall 635 of 792 ICU nurses (80.1%) and 215 of 239 respiratory therapists (89.9%) completed the study module. There were 874 episodes of ventilator-associated pneumonia at the four hospitals during the 3.5-year study period out of 129,527 ventilator days. Ventilator-associated pneumonia rates for all four hospitals combined dropped by 46%, from 8.75/1,000 ventilator days in the year prior to the intervention to 4.74/1,000 ventilator days in the 18 months following the intervention (p < 0.001). Statistically significant decreased rates were observed at the pediatric hospital and at two of the three adult hospitals. No change in rates was seen at the community hospital with the lowest rate of study module completion among respiratory therapists (56%). CONCLUSIONS: Educational interventions can be associated with decreased rates of ventilator-associated pneumonia in the ICU setting. The involvement of respiratory therapy staff in addition to ICU nurses is important for the success of educational programs aimed at the prevention of ventilator-associated pneumonia.

Adult↗
PubMed1995

Mechanical ventilation with or without 7-day circuit changes. A randomized controlled trial.

OBJECTIVE: To determine whether a practice of not routinely changing ventilator circuits in patients who require prolonged mechanical ventilation is associated with an increased incidence of nosocomial pneumonia. DESIGN: Randomized controlled trial. SETTING: Intensive care units in two university-affiliated teaching hospitals. PATIENTS: 300 patients admitted to an intensive care unit who required mechanical ventilation for more than 5 days. INTERVENTION: Patients were randomly assigned to receive either no routine ventilator circuit changes or circuit changes every 7 days. MEASUREMENTS: The primary outcome measure was the incidence of ventilator-associated pneumonia. Other outcome measures included duration of mechanical ventilation, length of hospital stay, and hospital mortality. RESULTS: 147 patients were randomly assigned to receive no routine ventilator circuit changes, and 153 patients were randomly assigned to receive circuit changes every 7 days. The two groups were similar at the time of randomization with regard to demographic characteristics, intensive care unit admission diagnoses, and severity of illness. Ventilator-associated pneumonia was seen in 36 patients (24.5%) receiving no routine changes and in 44 patients (28.8%) receiving changes every 7 days (relative risk, 0.85 [95% CI, 0.55 to 1.17]). No statistically significant differences for hospital mortality, intensive care unit mortality, death during mechanical ventilation, death in patients with ventilator-associated pneumonia, or mortality directly attributed to ventilator-associated pneumonia were found between the two treatment groups (P > or = 0.11). Patients receiving changes every 7 days had 247 circuit changes costing a total of $7410; patients receiving no routine changes had a total of 11 circuit changes costing $330. CONCLUSION: The elimination of routine ventilator circuit changes can reduce medical care costs without increasing the incidence of nosocomial pneumonia in patients who require prolonged mechanical ventilation.

Adult↗
PubMed2001

[Prevention of infections transmitted by CPAP and noninvasive ventilation].

Nosocomial infections are recognized as a major problem in patients with endotracheal ventilation, but the risk of nosocomial pneumonia is less well known and considered to be lower for patients on noninvasive ventilation. The risk factors for endotrachial ventilation involve the presence of the endoracheal canula and the direct consequences of the reclining position, use of a respirator, sedation, presence of a nosgastric tube, antiulcer treatment, etc. Most of these risk factors are not present in noninvasive ventilation while others, for example the use of a respirator and a ventilation circuit, persist. Several recent studies have demonstrated lower rates of infection in noninvasive compared with endotracheal ventilation. The notion of a specific risk of noninvasive ventilation-related nosocomial infection is less certain although current data do show a risk level no higher than in non-ventilated patients. Noninvasive ventilation should therefore be considered as a preventive measure against nosocomial infection whenever it can replace invasive ventilation. More or less specific preventive measures should however be employed. The principal actions involve taking advantage of the noninvasive nature of the ventilation to reduce the risk factors and other invasive procedures indirectly related with the use of artificial ventilation. Patients should be mobilized as rapidly as possible and oral food intake instituted early. Certain measures concerning humidification of the ventilation circuit remain important as well as other nonspecific measures including hand washing, for the prevention of cross contamination.

Procedural Sedation↗
PubMed2004

[The changes in effective local blood perfusion and compensatory ventilation in different lung areas of acute respiratory distress syndrome rabbits model].

OBJECTIVE: To discuss the mechanism of severe hypoxemia that induced with acute respiratory distress syndrome (ARDS) by way of observing the effective local blood perfusion in different lung areas of ARDS rabbits. METHODS: ARDS rabbit models were established by injecting oleic acid through central vein, and the results of effective local blood perfusion in different areas of rabbit lung (upper area, abdominal area, and dorsal area of right lung)with PIM-II laser perfusion imager and arterial blood gas under different ventilation modes [large tidal volume ventilation, low tidal volume ventilation + positive end-expiratory pressure (PEEP), prone position + large tidal volume ventilation, and prone position + low tidal volume ventilation + PEEP] were measured. RESULTS: The results of oxygenation index were significantly getting worsen after lung injury, and after receiving lung protective ventilation (including low tidal volume + PEEP, prone position + low tidal volume + PEEP), the indexes were taking a turn to the better. After lung injury, the results of effective local lung blood perfusion index (including upper area, abdominal area, and dorsal area) under right lung of ARDS rabbits decreased in the experimental ARDS groups. The results of experimental dorsal area group decreased most significantly, and the results of experimental upper area group changed most lightly. We observed that the effects of receiving low tidal volume + PEEP ventilation were not as good as prone position + low tidal volume + PEEP ventilation in the dorsal area of the rabbit lung compared to the results of effective local area lung blood perfusion index between two ventilation modes, there showed significantly differences in statistics. CONCLUSION: We indicated that the one of the main mechanisms of severe hypoxemia in ARDS might be caught by the shunt between pulmonary artery and pulmonary vein just like physiological right to left shunt, which caused severe ventilation/perfusion disturbance. Both low tidal volume ventilation + PEEP and prone position + low tidal volume ventilation + PEEP had good effects on ameliorating local blood perfusion, and the effects of ventilation mode of prone position + low tidal volume ventilation +PEEP might be better.

Animals↗
PubMed2006

Patient-triggered ventilation.

During patient triggered ventilation, the infant's inspiratory efforts should occur synchronously with ventilator inflations. Such an optimal interaction, however, is dependent on the performance of the triggering device and the ventilator and the infant's lung function. Triggered ventilation (assist control, A/C), synchronous intermittent mandatory ventilation (SIMV), pressure support ventilation (PSV), volume targeted ventilation (VTV) with A/C, SIMV, PSV or proportional assist ventilation (PAV) can be delivered via the endotracheal tube or via nasal prongs. Meta-analysis of randomised trials demonstrated that the only advantage of A/C/SIMV over non-triggered positive pressure ventilation was a shorter duration of ventilation, in particular there was no significant effect on the incidence of chronic lung disease. The reduction in ventilation duration, however, was only seen if triggered ventilation is started in the recovery stage rather than in the acute phase of respiratory distress syndrome. Results from small randomised trials have suggested that A/C rather than SIMV is a better weaning mode, as reduction of the SIMV rate below 20 breaths per minute increases the work of breathing. Other small trials have highlighted triggered ventilation delivered by nasal prongs may reduce extubation failure rate. Physiological studies have demonstrated some advantages of PSV with and without VTV and PAV, whether these translate into improvements in long term clinical outcomes remains to be tested in appropriately designed randomised trials.

Automation↗
PubMed1989

Determinants of tracheobronchial histologic alterations during conventional mechanical ventilation.

It was hypothesized that diverse mechanisms may influence upper airway injury during mechanical ventilation. To assess the roles of several factors in the propagation of such injury, the tracheobronchial histologic changes in 53 newborn piglets were compared following conventional positive pressure ventilation. Eight animals were assigned to each of four positive pressure ventilation groups at "low" settings (an FiO2 of 0.25, a frequency of 10 breaths per minute, a peak inspiratory pressure of 20 cm H2O, a positive end-expiratory pressure of 4 cm H2O, a flow rate of 10 L/min, and an inspiratory time to expiratory time ratio of 1:2): (1) positive pressure ventilation with no hypotension or hypoxemia; (2) positive pressure ventilation with hypotension; (3) positive pressure ventilation with hypoxemia; and (4) positive pressure ventilation with both hypotension and hypoxemia. In addition, eight piglets were assigned to each of two positive pressure ventilation groups at "high" settings (greater frequency [40 breaths per minute], higher peak inspiratory pressure [40 cm H2O], and greater flow rate [17 L/min]): (1) positive pressure ventilation with no hypotension or hypoxemia; and (2) positive pressure ventilation with both hypotension and hypoxemia. The changes were mild and similar among the first three positive pressure groups at low settings. However, the injury scores of the combined hypotension and hypoxemia group (group 4) were greater than those of the former three positive pressure ventilation groups (P less than .004). The piglets receiving positive pressure ventilation at high settings with no hypotension or hypoxemia (group 5) had no more injury than those in the first three groups receiving positive pressure ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

High-frequency oscillatory ventilation for acute respiratory distress syndrome in adults: a randomized, controlled trial.

Observational studies of high-frequency oscillatory ventilation in adults with the acute respiratory distress syndrome have demonstrated improvements in oxygenation. We designed a multicenter, randomized, controlled trial comparing the safety and effectiveness of high-frequency oscillatory ventilation with conventional ventilation in adults with acute respiratory distress syndrome; 148 adults with acute respiratory distress syndrome (Pa(O2)/fraction of inspired oxygen <or= 200 mm Hg on 10 or more cm H2O positive end-expiratory pressure) were randomized to high-frequency oscillatory ventilation (n = 75) or conventional ventilation (n = 73). Applied mean airway pressure was significantly higher in the high-frequency oscillation group compared with the conventional ventilation group throughout the first 72 hours (p = 0.0001). The high-frequency oscillation group showed early (less than 16 hours) improvement in Pa(O2)/fraction of inspired oxygen compared with the conventional ventilation group (p = 0.008); however, this difference did not persist beyond 24 hours. Oxygenation index decreased similarly over the first 72 hours in both groups. Thirty-day mortality was 37% in the high-frequency oscillation group and was 52% in the conventional ventilation group (p = 0.102). The percentage of patients alive without mechanical ventilation at Day 30 was 36% and 31% in the high-frequency oscillation and conventional ventilation groups, respectively (p = 0.686). There were no significant differences in hemodynamic variables, oxygenation failure, ventilation failure, barotraumas, or mucus plugging between treatment groups. We conclude that high-frequency oscillation is a safe and effective mode of ventilation for the treatment of acute respiratory distress syndrome in adults.

APACHE↗
PubMed1995

Outcome of infants with birth weights less than 1000 g with respiratory distress syndrome treated with high-frequency ventilation and surfactant replacement therapy.

OBJECTIVE: To compare outcomes in premature infants with respiratory distress syndrome who received surfactant replacement therapy and were treated with either high-frequency or conventional mechanical ventilation. DESIGN: Retrospective chart review of patient series. SETTING: Tertiary academic medical center. PATIENTS: One hundred fourteen extremely low-birth-weight infants (< 1000 g) with respiratory distress syndrome treated with surfactant replacement therapy, consecutively admitted to the neonatal intensive care unit between September 1989 and August 1992. INTERVENTIONS: Treatment with either high-frequency ventilation (n = 46) or conventional mechanical ventilation (n = 68) after surfactant replacement therapy. MAIN OUTCOME MEASURES: Intraventricular hemorrhage and neurodevelopmental status. RESULTS: Infants who received high-frequency ventilation had significantly lower birth weights and were more premature than infants receiving conventional mechanical ventilation. Despite this, patients ventilated with high frequency had similar incidences of intraventricular hemorrhage and impaired neurodevelopmental outcomes when compared with the conventionally ventilated patients. As expected, the smaller and more premature infants receiving high-frequency ventilation required a longer duration of respiratory support (mechanical ventilation and nasopharyngeal continuous positive airway pressure). Additionally, multiple logistic regression analysis to control for differences in birth weight and gestational age between the two groups revealed a significant association between the combined use of high-frequency ventilation and antenatal corticosteroids and the absence of either intraventricular hemorrhage or pneumothorax. CONCLUSION: We conclude that high-frequency ventilation combined with surfactant therapy is as safe as conventional mechanical ventilation combined with surfactant therapy for treating respiratory distress syndrome in extremely low-birth-weight infants (< 1000 g) and does not increase the risk of either intraventricular hemorrhage or abnormal neurodevelopmental outcome.

Biological Products↗
PubMed2005

Volume-targeted versus pressure-limited ventilation in the neonate.

BACKGROUND: Inflammation caused by lung overdistension (volutrauma) is thought to be important in the pathogenesis of bronchopulmonary dysplasia (BPD). Preterm infants with variable lung compliance are particularly at risk. Volume-targeted neonatal ventilators have been developed as alternatives to traditional pressure-limited ventilators. They deliver consistent, appropriate tidal volumes with the aim of reducing lung damage. It is suggested that these would provide an effective, safer means of ventilating the newborn infant. OBJECTIVES: To determine whether volume-targeted ventilation compared with pressure-limited ventilation leads to reduced rates of death and BPD in newborn infants. Secondary objectives were to determine whether use of volume modes affected clinical outcomes such as incidence of airleak, growth, duration of ventilation or cranial ultrasound findings. SEARCH STRATEGY: The search strategy comprised searches of the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 3, 2004), MEDLINE PubMed 1966 to November 2004, and hand searches of reference lists of relevant articles and conference proceedings. SELECTION CRITERIA: All randomised and quasi-randomised trials comparing the use of volume-targeted versus pressure-limited ventilation in neonates in the first 28 days of life. DATA COLLECTION AND ANALYSIS: Two authors assessed the methodological quality of eligible trials and extracted data independently. When appropriate, meta-analysis was conducted to provide a pooled estimate of effect. For categorical data the relative risk (RR) and risk difference (RD) were calculated with 95% confidence intervals. Number needed to treat was calculated when RD was statistically significant. Continuous data were analysed using weighted mean difference (WMD). MAIN RESULTS: Four randomised trials were identified that addressed the outcomes of this review, recruiting a total of 178 preterm infants. All were recruited during the first 72 hours of life. Caregivers and those evaluating the outcomes of trials were not masked. All trials report high rates of follow-up, although one trial with uneven patient distribution may have had some post-randomisation attrition. No significant difference was found for death by hospital discharge, and no trials reported the combined outcome of death or BPD. When secondary outcomes were examined, pooled analysis of the trials showed that volume-targeted ventilation resulted in significant reductions in duration of ventilation [WMD -2.93 days (-4.28, -1.57)] and rates of pneumothorax [typical RR 0.23 (0.07, 0.76), RD -0.11 (-0.20, -0.03), NNT 9]. There was also a significant difference in rates of severe (Grade 3 or 4) intraventricular haemorrhage favouring the volume-targeted group [typical RR 0.32 (0.11, 0.90), RD -0.16 (-0.29, -0.03), NNT 6]. There was a reduction in the incidence of BPD (supplemental oxygen at 36 weeks) amongst surviving infants, of borderline statistical significance [typical RR 0.34 (0.11, 1.05), RD -0.14 (-0.27, 0.00), NNT=7]. No significant differences were found for failure of mode of ventilation, use of neuromuscular paralysis, patent ductus arteriosus, airleak of any sort or pulmonary interstitial emphysema alone, cranial ultrasound abnormalities or periventricular leucomalacia. None of the trials addressed growth, death after discharge from hospital or neurodevelopmental outcome. AUTHORS' CONCLUSIONS: Although rates of death and BPD were not significantly different between the two ventilator strategies, statistically significant effects favouring volume targeting were shown for some clinically important outcomes. However, the numbers of trials and infants randomised are small and further studies are required to confirm the role of volume targeting in neonatal ventilation.

Bronchopulmonary Dysplasia↗
PubMed1994

[The effect of changes in lung compliance on ventilation in newborns. Results of animal experiments with two different respirators].

In most ventilators used in anaesthesia tidal volume delivered during mechanical ventilation is different from the tidal volume preset at the respirator on the basis of respirator and circuit compliance and gas compression during inspiration. The error in ventilation due to the compressed volume is especially significant clinically when the tidal volume is very small or when the airway pressure is very high. In newborns and neonates in particular, decreasing lung compliance during a surgical procedure may contribute to marked hypoventilation. We therefore investigated ventilation in newborn piglets during decreasing lung compliance induced by tension pneumothorax. We used the anaesthesia ventilator CICERO (Dräger, Lübeck, Germany) and the SERVO 900 C ventilator (Siemens-Elema, Sweden). MATERIALS AND METHODS. Two anaesthesia ventilators, the CICERO (group I, n = 8) and the SERVO ventilators (group II, n = 8) were investigated following randomized selection in a group of 16 newborn piglets (Table 1). After normoventilation for 60 min a tension pneumothorax at +10 mbar was induced. After 15 min the pneumothorax was increased to +20 mbar and maintained at this level for the rest of the study. When hypercapnia (PaCO2 > 45 mmHg) resulted, the respiratory rate was increased by +10/min after 15 min with pneumothorax at +20 mbar. When hypercapnia continued, the respiratory rate was increased again 25 min and if necessary also 35 min after the induction of pneumothorax at +20 mbar. After normoventilation for 60 min (T1) (Table 2), after 15 min with pneumothorax at +10 mbar (T2) and after 15 min (T3), 25 min (T4), 35 min (T5) and 45 min (T6) with pneumothorax at +20 mbar the following parameters were obtained: central venous (CVP) and mean arterial pressure (MAP), heart rate (HR), arterial (PaCO2) and end-tidal CO2 tension (PetCO2), peak inspiratory pressure (PIP), respiratory frequency (RF) and expiratory tidal (Vtex) and minute volume (VE). RESULTS. In group I the pneumothorax resulted in a significantly smaller increase in PaCO2 (43.3 +/- 6.2 mmHg) than in group II (Fig. 1), and hypercapnia was present in only 3 piglets. Vtex (Fig. 2), VE (Fig. 3) and PIP (Fig. 5) increased significantly, with significantly higher values than in group II, while PetCO2 (Fig. 6) decreased significantly. In group II the pneumothorax was attributed to a significant increase in PaCO2 and a marked hypercapnia in all piglets (PaCO2 61.2 +/- 5.9 mmHg) (Fig. 1). Vtex (Fig. 2) and VE (Fig. 3) remained unchanged, while PIP (Fig. 5) and PetCO2 (Fig. 6) increased. Following the increase in RF (Fig. 4) in all piglets, Vtex and VE increased and PaCO2 and PetCO2 decreased. CONCLUSIONS. During ventilation of neonates with the SERVO ventilator a decrease in lung compliance will cause hypoventilation and hypercapnia. This reflected by an increase in peak inspiratory pressure and can be corrected by increasing the respiratory rate. In contrast, the CICERO is able to preserve ventilation by an internal correction for gas compression, but it does not guarantee normoventilation in all cases. In neither group does the end-tidal PCO2 reflect the true ventilation during decreasing lung compliance, so that arterial blood gas analysis seems to be mandatory for the diagnosis of hypercapnia in such situations.

Anesthesia↗