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High-frequency ventilation in rabbits with respiratory insufficiency.

Treatment of respiratory insufficiency using continuous positive pressure ventilation (CPPV) with positive end-expiratory pressure (PEEP) is often associated with high airway pressures and large tidal volumes resulting in parenchymal damage and an exacerbation of ventilation/perfusion mismatch. High-frequency jet ventilation and high-frequency oscillation purportedly provide adequate ventilation and might preclude these harmful side effects. Few data exist comparing these methods in a model of respiratory insufficiency. Respiratory insufficiency was produced in three groups of six rabbits by 15 pulmonary lavages with saline (35 ml kg-1) to remove surfactant, following which ventilation for the subsequent 5 hr was as follows: group I, CPPV with a frequency of 60 bpm, and a minute volume of 400 ml min-1 kg-1; group II, oscillatory ventilation with a loudspeaker system delivering a tidal volume of 6-8 ml at a frequency of 5 Hz; and group III, jet ventilation with volumes of 6-8 ml at a frequency of 5 Hz. All groups were ventilated with a PEEP of 10 cm H2O and a FiO2 of 1.0. Arterial blood samples were taken every hour. All three methods provided adequate oxygenation without important differences. The arterial pCO2 rose in all three groups owing to the seriousness of the respiratory insufficiency created. This rise was the highest with oscillatory ventilation. Three of the six rabbits deteriorated after 3 hr of jet ventilation and died with elevated pCO2S with pO2S with bloody edema coming out of the trachea. Because of this apparent damaging effect of jet ventilation and because oscillatory ventilation achieved the same gas exchange but at lower airway pressures as compared to jet ventilation and CPPV, it is thought that oscillatory ventilation is superior over both jet ventilation and CPPV for application in respiratory insufficiency.

Airway Resistance↗

Risk factors for and economic implications of prolonged ventilation after cardiac surgery.

OBJECTIVE: The study's objective was to identify predictors of prolonged ventilation and assess clinical and cost implications in patients undergoing cardiac surgery. METHODS: Patients undergoing cardiac surgery were classified as (1) ventilated less than 96 hours or (2) ventilated 96 hours or more. Multivariate modeling was used to identify predictors of prolonged ventilation and to ascertain the impact of prolonged ventilation on in-hospital mortality and bed occupancy costs and 5-year survival. RESULTS: A total of 7553 patients were studied; 197 (2.6%) had prolonged ventilation. Median ventilation times were 8 and 192 hours, and in-hospital mortality was 1.0% and 22.2% in the control and prolonged ventilation groups, respectively (P < .001). In-hospital mortality remained higher in the prolonged ventilation group after adjustment and when comparing propensity-matched patients (odds ratio 8.06; 95% confidence interval [CI] 4.27-15.2; P < .001 for propensity-matched groups). Independent predictors of prolonged ventilation were as follows: older age, New York Heart Association class, ejection fraction less than 50%, creatinine greater than 200 micromol/L, multiple valve replacements, aortic procedures, operative priority, reoperation for bleeding, inotropes, and preoperative intra-aortic balloon pump. Five-year survival was lower in the prolonged ventilation group (56.1% [95% CI 46.6%-64.6%] vs 88.8% [95% CI 87.9%-89.6%]) also after adjustment for imbalances and when comparing propensity-matched patients (hazard ratio 2.39; 95% CI 1.75-3.27; P < .001 for propensity-matched groups). Mean bed occupancy costs were 14,286 dollars (95% CI 12,731 dollars-15,690 dollars) and 2761 dollars (95% CI 2705 dollars-2814 dollars) in the prolonged ventilation and control groups, respectively (P < .001). CONCLUSION: Prolonged ventilation is associated with high in-hospital mortality and costs, and poor 5-year survival. Identified predictors of prolonged ventilation might help to optimize the clinical management of these patients.

Aged↗

Partial liquid ventilation with perflubron in premature infants with severe respiratory distress syndrome. The LiquiVent Study Group.

BACKGROUND: The intratracheal administration of a perfluorocarbon liquid during continuous positive-pressure ventilation (partial liquid ventilation) improves lung function in animals with surfactant deficiency. Whether partial liquid ventilation is effective in the treatment of infants with severe respiratory distress syndrome is not known. METHODS: We studied the efficacy of partial liquid ventilation with perflubron in 13 premature infants with severe respiratory distress syndrome in whom conventional treatment, including surfactant therapy, had failed. Partial liquid ventilation was initiated by instilling perflubron during conventional mechanical ventilation to a volume approximating the functional residual capacity. Infants were considered to have completed the study if they received partial liquid ventilation for at least 24 hours. RESULTS: Ten infants received partial liquid ventilation for 24 to 76 hours. In the other three infants, partial liquid ventilation was discontinued within four hours in favor of high-frequency ventilation, which was not permitted by the protocol, and the data from these infants were excluded from the analysis. Within one hour after the instillation of perflubron, the arterial oxygen tension increased by 138 percent and the dynamic compliance increased by 61 percent; the mean (+/- SD) oxygenation index was reduced from 49 +/- 60 to 17 +/- 16. Chest radiographs showed symmetric filling, with patchy clearing during the return from partial liquid to gas ventilation. There were no adverse events clearly attributable to partial liquid ventilation. Infants were weaned from partial liquid to gas ventilation without complications. Eight infants survived to 36 weeks' corrected gestational age. CONCLUSIONS: Partial liquid ventilation leads to clinical improvement and survival in some infants with severe respiratory distress syndrome who are not predicted to survive.

Fluorocarbons↗

Imposed work and oxygen delivery during spontaneous breathing with adult disposable manual ventilators.

BACKGROUND: Manual ventilators (resuscitators) are used primarily to ventilate the lungs of patients lacking spontaneous ventilatory effort. However, in many settings patients are allowed to breathe through the manual ventilator. Although many aspects of manual ventilator function have been studied, very little has been reported on the use of manual ventilators during spontaneous breathing. The purpose of this study was to evaluate inspiratory and expiratory imposed work of breathing and oxygen delivery during spontaneous breathing through disposable manual ventilators. METHODS: Simulated spontaneous breathing was established with a two-chambered test lung, with one chamber serving as the test chamber and the other as the driving chamber. Imposed work of breathing was evaluated with decelerating inspiratory flow at a rate of 20 breaths/min at tidal volume (VT) 0.25 1 and peak flow 40 l/min, at VT 0.5 l and peak flow 80 l/min, and VT 0.81 and peak flow 120 l/min. Flow (integrated to volume) and pressure were measured between the manual ventilator and test lung, and inspiratory and expiratory imposed work of breathing were calculated by integration of the volume-pressure curve. Oxygen concentration was measured with an oxygen analyzer placed between the manual ventilator and the test lung at 20 breaths/min, VT 0.5 l, and flow 45 l/min. An oxygen flow of 15 l/min was added to the device for all evaluations. Two of the manual ventilators had built-in positive end-expiratory pressure valves, and imposed work was evaluated at 10 cmH2O with these. RESULTS: There were significant differences in imposed work between inspiration and expiration (P < 0.001) and among the three levels of ventilatory demand (P < 0.001). For each ventilatory demand, there was a significant difference in work between manual ventilator brands for inspiratory work and expiratory work (P < 0.001). At a VT of 0.5 l and peak flow of 80 l/min, the pooled inspiratory imposed work for all manual ventilators was 0.44 +/- 0.12 J/l, and the pooled expiratory imposed work was 0.29 +/- 0.05 J/l. With 10 cmH2O positive end-expiratory pressure, the inspiratory imposed work was very high (> 1 J/l). Four of the devices were unable to deliver more than 0.85 oxygen concentration at the spontaneous ventilatory pattern evaluated. CONCLUSIONS: Adult disposable manual ventilators produce a substantial imposed work of spontaneous breathing, which is increased with the addition of positive end-expiratory pressure. With some manual ventilators, a high oxygen concentration may not be delivered during spontaneous breathing. We recommend that patients not be allowed to spontaneously breathe through disposable manual ventilators.

Adult↗

Different ventilation strategies affect lung function but do not increase tumor necrosis factor-alpha and prostacyclin production in lavaged rat lungs in vivo.

BACKGROUND: Using an in vivo animal model of surfactant deficiency, the authors compared the effect of different ventilation strategies on oxygenation and inflammatory mediator release from the lung parenchyma. METHODS: In adult rats that were mechanically ventilated with 100% oxygen, acute lung injury was induced by repeated lung lavage to obtain an arterial oxygen partial pressure < 85 mmHg (peak pressure/positive end-expiratory pressure [PEEP] = 26/6 cm H2O). Animals were then randomly assigned to receive either exogenous surfactant therapy, partial liquid ventilation, ventilation with high PEEP (16 cm H2O), ventilation with low PEEP (8 cm H2O), or ventilation with an increase in peak inspiratory pressure (to 32 cm H2O; PEEP = 6 cm H2O). Two groups of healthy nonlavaged rats were ventilated at a peak pressure/PEEP of 32/6 and 32/0 cm H2O, respectively. Blood gases were measured. Prostacyclin (PGI2) and tumor necrosis factor-alpha (TNF-alpha) concentrations in serum and bronchoalveolar lavage fluid (BALF) as well as protein concentration in BALF were determined after 90 and 240 min and compared with mechanically ventilated and spontaneously breathing controls. RESULTS: Surfactant, partial liquid ventilation, and high PEEP improved oxygenation and reduced BALF protein levels. Ventilation with high PEEP at high mean airway pressure levels increased BALF PGI2 levels, whereas there was no difference in BALF TNF-alpha levels between groups. Serum PGI2 and TNF-alpha levels did not increase as a result of mechanical ventilation when compared with those of spontaneously breathing controls. CONCLUSIONS: Although alveolar protein concentration and oxygenation markedly differed with different ventilation strategies in this model of acute lung injury, there were no indications of ventilation-induced systemic PGI2 and TNF-alpha release, nor of pulmonary TNF-alpha release. Mechanical ventilation at high mean airway pressure levels increased PGI2 levels in the bronchoalveolar lavage-accessible space.

6-Ketoprostaglandin F1 alpha↗

Pressure-support ventilation in children with severe asthma.

OBJECTIVE: To review the efficacy of pressure-support ventilation in the management of children with status asthmaticus requiring mechanical ventilation. DESIGN: A case series. SETTING: A university hospital. SUBJECTS: Children requiring mechanical ventilation due to respiratory failure despite medical therapy during an episode of acute asthma. INTERVENTIONS: Mechanical ventilation with pressure-support ventilation. MEASUREMENTS AND MAIN RESULTS: Respiratory parameters (ventilatory settings, minute ventilation, respiratory rate, airway pressures) and blood gases were determined before, on initiation, and for 6 hrs after pressure-support ventilation. Spontaneous ventilation with an initial respiratory rate of 45 breaths/min (range 31 to 46) and an inspiration/expiration ratio (I/E) of 1:1.2 (range 1:1.1 to 1:2) was readily established in each patient. Arterial pH normalized (7.41, range 7.39 to 7.43) within 6 hrs (4.25, range 2 to 6) of the time at which ventilation was begun and the Paco2 decreased (p < .02) to 44 torr (range 39 to 47) (5.9 kPa, range 5.2 to 6.3) during pressure support ventilation. CONCLUSION: Pressure-support ventilation permitted patient-cycled spontaneous ventilation in children with asthma. The ability of patients to determine their own respiratory pattern and to maintain forced exhalation during pressure-support ventilation may have important advantages in children with severe asthma who require mechanical ventilation.

Child↗

Mechanical ventilation exacerbates alveolar macrophage dysfunction in the lungs of ethanol-fed rats.

BACKGROUND: Patients with alcohol abuse have a two- to three-fold increased risk of acute lung injury and respiratory failure after sepsis or trauma but are also at increased risk of nosocomial pneumonia. Mechanical ventilation exacerbates lung injury during critical illnesses. In this study we tested whether mechanical ventilation of the alcoholic lung promotes on balance a proinflammatory phenotype favoring ventilator-induced lung injury or an immunosuppressive phenotype favoring ventilator-associated pneumonia. METHODS: Lungs from rats fed an isocaloric diet with or without ethanol (six weeks) were isolated and ventilated ex vivo with a low-volume (protective) or high-volume (injurious) strategy for two hours with or without prior endotoxemia (two hours). In other experiments, rats were subjected to high-volume ventilation in vivo. Airway levels of the proinflammatory cytokines tumor necrosis factor-alpha, macrophage inflammatory protein-2, and interleukin-1beta were determined after mechanical ventilation ex vivo and compared with edematous lung injury after high-volume ventilation in vivo. In parallel, alveolar macrophage phagocytosis of bacteria and secretion of interleukin-12 during ventilation ex vivo and endotoxin-stimulated alveolar macrophage phagocytosis and tumor necrosis factor-alpha secretion in vitro were determined. RESULTS: Ethanol ingestion suppressed the proinflammatory response to injurious mechanical ventilation and did not increase experimental ventilator-induced lung injury. In parallel, ethanol ingestion blunted the innate immune response of alveolar macrophages during injurious ventilation ex vivo and after endotoxin stimulation in vitro. CONCLUSIONS: Ethanol ingestion dampens ventilator-induced inflammation but exacerbates macrophage immune dysfunction. These findings could explain at least in part why alcoholic patients are at increased risk of ventilator-associated pneumonia.

Alcoholism↗

Work of breathing and airway occlusion pressure during assist-mode mechanical ventilation.

We determined the effect of varying ventilator tidal volume (VT) and inspiratory flow (V) on the inspiratory muscle work (WI) during assist-mode mechanical ventilation (AMV) in four healthy subjects. In another four subjects, under constant chemoreceptor input, we determined the responses of neuromuscular output as assessed by the mouth occlusion pressure (P0.1) to alteration in WI. During AMV, the inspiratory external work of breathing is partitioned between WI and ventilator work. With a constant ventilator trigger sensitivity, we calculated WI (joules/L of volume) as the difference between the area subtended by the airway pressure-inspiratory volume curves and the ordinate of the assisted breaths subtracted from that of the controlled breaths at ventilator V of 40, 60 and 80 L/min and ventilator VT of 100, 125 and 150 percent spontaneous breathing VT. At all ventilator settings, WI was less than inspiratory muscle work of spontaneous breathing (SB) and was a function of both ventilator VT and V (p less than 0.05), but ventilator V has more effect on WI. Under isocapnia and hyperoxia, we measured P0.1 and WI during AMV at ventilator VT of 125 percent of spontaneous breathing VT and ventilator V of 60, 80 and 100 L/min. End-expiratory lung volume remained constant. P0.1 during AMV was similar to that of the SB. Although WI decreased with increasing ventilator V, P0.1 did not decrease significantly. We conclude that during AMV, both ventilator V and to a less extent ventilator VT determine W. In healthy subjects changes in WI do not affect P0.1.

Airway Resistance↗

Daily living with distress and enrichment: the moral experience of families with ventilator-assisted children at home.

OBJECTIVE: The growing shift toward home care services assumes that "being home is good" and that this is the most desirable option. Although ethical issues in medical decision-making have been examined in numerous contexts, home care decisions for technology-dependent children and the moral dilemmas that this population confronts remain virtually unknown. This study explored the moral dimension of family experience through detailed accounts of life with a child who requires assisted ventilation at home. This study involved an examination of moral phenomena inherent in (1) the individual experiences of the ventilator-assisted child, siblings, and parents and (2) everyday family life as a whole. METHODS: A qualitative method based on Richard Zaner's interpretive framework was selected for this study. The population of interest for this study was the families of children who are supported by a ventilator or a positive-pressure device at home. Twelve families (38 family members) were recruited through the Quebec Program for Home Ventilatory Assistance. Children in the study population fell into 4 diagnostic groups: (1) abnormal ventilatory control (eg, central hypoventilation syndrome), (2) neuromuscular disorders, (3) spina bifida, and (4) craniofacial or airway abnormalities resulting in upper airway obstruction. All 4 of these diagnostic groups were included in this study. Among the 12 children recruited, 4 received ventilation via tracheostomies, and 8 received ventilation with face masks. All of the latter received ventilation only at night, except for 1 child, who received ventilation 24 hours a day. Family moral experiences were investigated using semistructured interviews and fieldwork observations conducted in the families' homes. RESULTS: Data analysis identified 6 principal themes. The themes raised by families whose children received ventilation invasively via a tracheostomy were not systematically different or more distressed than were families of children with face masks. The principal themes were (1) confronting parental responsibility: parental responsibility was described as stressful and sometimes overwhelming. Parents needed to devote extraordinary care and attention to their children's needs. They struggled with the significant emotional strain, physical and psychological dependence of the child, impact on family relationships, living with the daily threat of death, and feeling that there was "no free choice" in the matter: they could not have chosen to let their child die. (2) Seeking normality: all of the families devoted significant efforts toward normalizing their experiences. They created common routines so that their lives could resemble those of "normal" families. These efforts seemed motivated by a fundamental striving for a stable family and home life. This "striving for stability" was sometimes undermined by limitations in family finances, family cohesion, and unpredictability of the child's condition. (3) Conflicting social values: families were offended by the reactions that they faced in their everyday community. They believe that the child's life is devalued, frequently referred to as a life not worth maintaining. They felt like strangers in their own communities, sometimes needing to seclude themselves within their homes. (4) Living in isolation: families reported a deep sense of isolation. In light of the complex medical needs of these children, neither the extended families nor the medical system could support the families' respite needs. (5) What about the voice of the child? The children in this study (patients and siblings) were generally silent when asked to talk about their experience. Some children described their ventilators as good things. They helped them breathe and feel better. Some siblings expressed resentment toward the increased attention that their ventilated sibling was receiving. (6) Questioning the moral order: most families questioned the "moral order" of their lives. They contemplated how "good things" and "bad things" are determined in their world. Parents described their life as a very unfair situation, yet there was nothing that they could do about it. Finally, an overarching phenomenon that best characterizes these families' experiences was identified: daily living with distress and enrichment. Virtually every aspect of the lives of these families was highly complicated and frequently overwhelming. An immediate interpretation of these findings is that families should be fully informed of the demands and hardships that would await them, encouraging parents perhaps to decide otherwise. This would be but a partial reading of the findings, because despite the enormous difficulties described by these families, they also reported deep enrichments and rewarding experiences that they could not imagine living without. Life with a child who requires assisted ventilation at home involves living every day with a complex tension between the distresses and enrichments that arise out of this experience. The conundrum inherent in this situation is that there are no simple means for reconciling this tension. This irreconcilability is particularly stressful for these families. Having their child permanently institutionalized or "disconnected" from ventilation (and life) would eliminate both the distresses and the enrichments. These options are outside the realm of what these families could live with, aside from the 1 family whose child is now permanently hospitalized, at a tremendous cost of guilt to the family. CONCLUSIONS: These findings make important contributions by (1) advancing our understanding of the moral experiences of this group of families; (2) speaking to the larger context of other technology-dependent children who require home care; (3) relating home care experiences to neonatal, critical care, and other hospital services, suggesting that these settings examine their approaches to this population that may impose preventable burdens on the lives of these children and their families; and (4) examining a moral problem with an empirical method. Such problems are typically investigated through conceptual analyses, without directly examining lived experience. These findings advance our thinking about how we ought to care for these children, through a better understanding of what it is like to care for them and the corresponding major distresses and rewarding enrichments. These findings call for an increased sensitization to the needs of this population among staff in critical care, acute, and community settings. Integrated community support services are required to help counter the significant distress endured by these families. Additional research is required to examine the experience of other families who have decided either not to bring home their child who requires ventilation or withdraw ventilation and let the child die.

Caregivers↗

Pressure support and pressure assist/control: are there differences? An evaluation of the newest intensive care unit ventilators.

BACKGROUND: Pressure support (PS) has been widely studied in both patients and lung models, but there is little data available evaluating pressure assist/control (P A/C, frequently referred to as PCV) and no data comparing the operational capabilities of these two modes on the newest generation of ICU ventilators. We used a spontaneously breathing lung model to evaluate the response of the following new generation ventilators to varying inspiratory demand in both PS and P A/C: Bear 1000, Dräger Evita 4, Hamilton Galileo, Nellcor Puritan-Bennett 840 and 740, Siemens Servo 300A, TBird AVS. METHODS: A bellows-in-a-box lung model was set at a respiratory rate of 12 breaths/min, inspiratory time of 1.0 second, and peak inspiratory flows (modified square wave) of 40, 60, and 80 L/min. Each ventilator was set at three levels of PS and P A/C: 10, 15, and 20 cm H(2)O. On all ventilators, flow-triggering was set as sensitive as possible without causing self-triggering. RESULTS: Trigger pressure, trigger pressure-time product, inspiratory trigger time delay, ventilator-delivered peak flow, inspiratory area as a percent of the ideal inspiratory area, expiratory time delay, supraplateau expiratory pressure change, and expiratory area all varied among ventilators and at different lung model peak flows (p < 0.01 and >/= 10% difference). However, PS and P A/C on a given ventilator only differed with regard to expiratory variables (p < 0. 01 and >/= 10% difference). CONCLUSION: In a given ventilator little difference exists in gas delivery and response variables between PS and P A/C, but performance differences do exist among the ventilators evaluated. Ventilator performance is diminished at high lung model peak flows and low pressure settings. (I)), whereas PS gives control over ending inspiration to the patient. What has not been clearly defined is the gas delivery and ventilator response differences, if any, between these two (PS and P A/C) pressure targeted assist modes. Most new generation intensive care unit (ICU) ventilators provide both pressure support (PS) and pressure assist/control (P A/C) ventilation.19,20 The specific operational difference between these two modes is the mechanism that transitions inspiration to expiration. With pressure support the primary mechanism is a decrease in peak inspiratory flow to a predetermined level, whereas with P A/C mechanical T(I) is preset.19,20 We compared the operation of seven of the newest generation ICU ventilators in a spontaneously breathing lung model in both PS and P A/C. We hypothesized that there would be no difference in variables assessed between PS and P A/C except for the transition to expiration and that there would be no difference in response among ventilators evaluated.

Equipment Safety↗

Pulmonary functional MRI: an animal model study of oxygen-enhanced ventilation combined with Gd-DTPA-enhanced perfusion.

BACKGROUND: The assessment of regional pulmonary ventilation and perfusion is essential for the evaluation of a variety of lung disorders. Pulmonary ventilation MRI using inhaled oxygen as a contrast medium can be obtained with a clinical MR scanner, without additional equipment, and has been demonstrated to be a feasible means of assessing ventilation in animal models and some clinical patients. However, few studies have reported on MR ventilation-perfusion imaging. In this study, we evaluated the usefulness of oxygen-enhanced ventilation in combination with first-pass Gd-DTPA-enhanced perfusion MRI in a canine model of pulmonary embolism and airway obstruction. METHODS: Peripheral pulmonary embolisms were produced in eight dogs by intravenous injection of gelfoam strips at the pulmonary segmental arterial level, and airway obstructions were created in five of the dogs by inserting a self-designed balloon catheter into a secondary bronchus. Oxygen-enhanced MR ventilation images were produced by subtracting images from before and after inhalation of pure oxygen. Pulmonary perfusion MR images were acquired with a dynamic three-dimensional fast gradient-echo sequence. MR ventilation and perfusion images were read and contrasted with results from general examinations of pathological anatomy, ventilation-perfusion scintigraphy, and pulmonary angiography. RESULTS: Regions identified as having airway obstructions matched using both MR ventilation and perfusion imaging, but regions of pulmonary embolisms were mismatched. The area of airway obstruction defects was smaller using MR ventilation imagery than that using ventilation scintigraphy. Abnormal perfusion regions due to pulmonary embolisms were divided into defective regions and reduced regions based on the time course of signal intensity changes. In the diagnosis of pulmonary embolisms with the technique of ventilation and perfusion MRI, sensitivity and specificity were 75.0% and 98.1%, respectively, and the diagnostic results of this MRI technique were in agreement with the results of ventilation-perfusion scintigraphy and pulmonary angiography (K: 0.899, 0.743). CONCLUSIONS: Oxygen-enhanced ventilation in combination with pulmonary perfusion MRI can be used to diagnose abnormalities of airways and blood vessels in the lungs, and can provide regional functional information with high spatial and temporal resolution. This method possesses great potential value for clinical applications.

Airway Obstruction↗

Perioperative pulmonary function in acute respiratory failure: effect of ventilator type and gas mixture.

Whether maintaining pulmonary nitrogenation and/or a stable ventilatory pattern during surgery would minimize changes in perioperative pulmonary function in two groups of patients with acute respiratory failure (ARF) whose lungs were being mechanically ventilated was examined. Group 1 (n = 39 cases) (inspired oxygen fraction [FIO2] less than or equal to 0.5, minute ventilation less than or equal to 15 l/min, peak inspiratory pressure less than or equal to 50 cmH2O, positive end-expiratory pressure [PEEP] less than or equal to 10 cmH2O) were assigned randomly to one of four intraoperative ventilator-gas mixture (FIO2 approximately 0.5) combinations: 1) Siemens 900C ventilator, N2/O2; 2) Siemens 900C ventilator, N2O/O2; 3) Ohio anesthesia ventilator, N2/O2; or 4) Ohio anesthesia ventilator, N2O/O2. Group 2 (n = 15 cases) (ventilatory requirements exceeding any of those in Group 1) had their lungs ventilated intraoperatively with the Siemens 900C ventilator and a gas mixture determined by their anesthesiologist (FIO2 approximately 0.6-1.0). In patients whose lungs were ventilated with the Ohio N2O/O2 combination, PaO2/FIO2 decreased significantly (P less than 0.05) from 358 +/- 93 mmHg (mean +/- SD) preoperatively to 282 +/- 77 mmHg intraoperatively. The level of PEEP increased significantly from 5 +/- 3 cmH2O preoperatively to 9 +/- 4 cmH2O intraoperatively (P less than 0.05). In patients whose lungs were ventilated with the Ohio N2/O2 combination, PaO2/FIO2 decreased significantly from 270 +/- 86 mmHg preoperatively to 174 +/- 74 mmHg intraoperatively. These variables did not change significantly in patients ventilated with the Siemens ventilator (groups 1 and 2). Pulmonary oxygen gas exchange returned to preoperative values by the first hour postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗

Response to exogenous surfactant is different during open lung and conventional ventilation.

OBJECTIVE: Previous studies have shown that the efficacy of exogenous surfactant is dose-dependent during conventional positive pressure ventilation (PPVCON). The present study aimed to determine whether this dose-dependent relationship is also present during open lung (OLC) ventilation. We also explored the effect of exogenous surfactant on the ventilation pressures applied during ventilation. DESIGN: Animal study. SETTING: University-affiliated research laboratory. SUBJECTS: Seventy-two newborn piglets. INTERVENTIONS: After repeated whole lung lavage, animals were randomly allocated to two surfactant groups receiving either 100 mg/kg surfactant (S100) or 25 mg/kg surfactant (S25) or to a control group receiving a bolus of air. Within each group, animals were randomly assigned to either PPVCON, open lung PPV (PPVOLC), or open lung high-frequency oscillatory ventilation (HFOVOLC) and ventilated for 5 hrs. MEASUREMENTS AND MAIN RESULTS: The ventilation pressures decreased in a dose-dependent way, showing the largest reduction in the S100 group. In both OLC groups, oxygenation, lung mechanics, and polymorphonuclear neutrophils analyzed in bronchoalveolar lavage were independent of the surfactant dose. In the PPVCON group, however, there was a clear dose-dependency, resulting in a deterioration of oxygenation and lung mechanics and an increase in polymorphonuclear neutrophils as the surfactant dose decreased. Although comparable between the three ventilation groups, bronchoalveolar lavage interleukin-8 concentrations significantly increased in all ventilation groups as the surfactant dose increased. Alveolar protein influx and conversion of large to small aggregate surfactant were higher during PPVCON compared with both OLC groups. There were no differences in the surfactant treatment response between PPVOLC and HFOVOLC. CONCLUSION: Exogenous surfactant enables a reduction in ventilation pressures. Compared with PPVCON, the efficacy of surfactant treatment is less dose-dependent during open lung ventilation. Surfactant conversion during open lung ventilation is reduced compared with PPVCON. Exogenous surfactant seems to up-regulate bronchoalveolar lavage interleukin-8 concentrations, independent of the ventilation strategy.

Analysis of Variance↗

Characteristics and outcomes in adult patients receiving mechanical ventilation: a 28-day international study.

CONTEXT: The outcome of patients receiving mechanical ventilation for particular indications has been studied, but the outcome in a large number of unselected, heterogeneous patients has not been reported. OBJECTIVE: To determine the survival of patients receiving mechanical ventilation and the relative importance of factors influencing survival. DESIGN, SETTING, AND SUBJECTS: Prospective cohort of consecutive adult patients admitted to 361 intensive care units who received mechanical ventilation for more than 12 hours between March 1, 1998, and March 31, 1998. Data were collected on each patient at initiation of mechanical ventilation and daily throughout the course of mechanical ventilation for up to 28 days. MAIN OUTCOME MEASURE: All-cause mortality during intensive care unit stay. RESULTS: Of the 15 757 patients admitted, a total of 5183 (33%) received mechanical ventilation for a mean (SD) duration of 5.9 (7.2) days. The mean (SD) length of stay in the intensive care unit was 11.2 (13.7) days. Overall mortality rate in the intensive care unit was 30.7% (1590 patients) for the entire population, 52% (120) in patients who received ventilation because of acute respiratory distress syndrome, and 22% (115) in patients who received ventilation for an exacerbation of chronic obstructive pulmonary disease. Survival of unselected patients receiving mechanical ventilation for more than 12 hours was 69%. The main conditions independently associated with increased mortality were (1) factors present at the start of mechanical ventilation (odds ratio [OR], 2.98; 95% confidence interval [CI], 2.44-3.63; P<.001 for coma), (2) factors related to patient management (OR, 3.67; 95% CI, 2.02-6.66; P<.001 for plateau airway pressure >35 cm H(2)O), and (3) developments occurring over the course of mechanical ventilation (OR, 8.71; 95% CI, 5.44-13.94; P<.001 for ratio of PaO(2) to fraction of inspired oxygen <100). CONCLUSION: Survival among mechanically ventilated patients depends not only on the factors present at the start of mechanical ventilation, but also on the development of complications and patient management in the intensive care unit.

Adult↗

Comparison of total resistive work of breathing in two generations of ventilators in an animal model.

Spontaneous breathing through an endotracheal tube and ventilator circuit is associated with an increased work of breathing (WOB). Recently, pediatric ventilators have introduced improved features to optimize patient-ventilator interactions. We performed an experiment utilizing an animal model to compare total resistive WOB of two widely used ventilators, the Siemens Servo Ventilator 300 (SV300) with patient-optimized features, such as flow-triggering and rapid response time, and the Siemens 900C (S900C) without those features. A total of 120 experiments of 10 minutes duration each were performed in 6 anesthetized, intubated lambs. In each experiment, the animal was randomized to either pressure support ventilation (PSV) of 5 cm H2O, or continuous positive airway pressure (CPAP) with 0 cmH2O end expiratory pressure (ZEEP) while supported by the SV300 or the S900C. Each animal was used as its own control. WOB was measured with a Bicore monitoring device as WOB of the animal (WOBp), WOB of the ventilator (WOBv), and the pressure time product (PTP) for each breath during the experiment. Oxygen consumption (Vo2) of the animal was measured using breath-by-breath gas analysis with a customized metabolic monitoring system. A Wilcoxon signed rank sum test was used for analysis. All comparisons between the ventilators for both CPAP and PSV showed a statistically significant difference (p < 0.001). WOBp was reduced by 47% during pressure support ventilation (PSV) and by 47% during CPAP when the SV300 was used compared to the S900C. We conclude that WOB is significantly lower in animals ventilated with the SV300 than with the S900C ventilator, and we speculate that ventilators with the features of the SV300 may offer advantages in ventilating pediatric patients.

Airway Resistance↗

Occupational exposure to nitrous oxide - the role of scavenging and ventilation systems in reducing the exposure level in operating rooms.

OBJECTIVES: The aim of this study was to assess the level of occupational exposure to nitrous oxide (N(2)O) in operating rooms (ORs), as related to different ventilation and scavenging systems used to remove waste anaesthetic gases from the work environment. METHODS: The monitoring of N(2)O in the air covered 35 ORs in 10 hospitals equipped with different systems for ventilation and anaesthetic scavenging. The examined systems included: natural ventilation with supplementary fresh air provided by a pressure ventilation system (up to 6 air changes/h); pressure and exhaust ventilation systems equipped with ventilation units supplying fresh air to and discharging contaminated air outside the working area (more than 10 air changes/h); complete air-conditioning system with laminar air flow (more than 15 air changes/h). The measurements were carried out during surgical procedures (general anaesthesia induced intravenously and maintained with inhaled N(2)O and sevofluran delivered through cuffed endotracheal tubes) with connected or disconnected air scavenging. Air was collected from the breathing zone of operating personnel continuously through the whole time of anaesthesia to Tedlar((R)) bags, and N(2)O concentrations in air samples were analyzed by adsorption gas chromatography/mass spectrometry. RESULTS: N(2)O levels in excess of the occupational exposure limit (OEL) value of 180mg/m(3) were registered in all ORs equipped with ventilation systems alone. The OEL value was exceeded several times in rooms with natural ventilation plus supplementary pressure ventilations and twice or less in those with pressure/exhaust ventilation systems or air conditioning. N(2)O levels below or within the OEL value were observed in rooms where the system of air conditioning or pressure/exhaust ventilation was combined with scavenging systems. Systems combining natural/pressure ventilation with scavenging were inadequate to maintain N(2)O concentration below the OEL value. CONCLUSION: Air conditioning and an efficient pressure/exhaust ventilation (above 12 air exchanges/h) together with efficient active scavenging systems are sufficient to sustain N(2)O exposure in ORs at levels below or within the OEL value of 180mg/m(3).

Air Pollutants, Occupational↗

Extracranial radiosurgery: immobilizing liver motion in dogs using high-frequency jet ventilation and total intravenous anesthesia.

PURPOSE: Extracranial radiosurgery requires control of organ motion. The purpose of this study is to quantitatively determine the extent of liver motion in anesthetized dogs with continuous i.v. propofol infusion with or without muscle relaxants and high-frequency jet ventilation. METHODS AND MATERIALS: Five dogs were used in the experiment. Each dog was restrained while anesthetized in the supine position using an alpha cradle. Surgical metal clips were implanted around the liver periphery so that its motion could be visualized using a fluoroscopic imaging device in a conventional simulator. Initially, two orthogonal simulation films were taken to correlate locations of implanted clips. Two orthogonal views of fluoroscopic images for each anesthetized dog were recorded on a magnetic tape and analyzed from the post-imaging data. Liver motion was documented under the following three conditions: 1) ventilated with a conventional mechanical ventilator, 2) ventilated with a high-frequency jet ventilator, and 3) ventilated with a high-frequency jet ventilator and total muscle paralysis (with vecuronium injection). The maximum liver motion for each dog was analyzed in three orthogonal directions: the inferior-to-superior direction, the anterior-to-posterior direction, and the right-to-left direction. RESULTS: When the anesthetized dogs were ventilated with a conventional mechanical ventilator, the average liver motions were 1.2 cm in the inferior-to-superior direction, 0.4 cm in the anterior-to-posterior direction, and 0.2 cm in the right-to-left direction, respectively. After the introduction of high-frequency jet ventilation, the average liver motions were reduced to 0.2 cm in the inferior-to-superior direction, 0.2 cm in the anterior-to-posterior direction, and 0.1 cm in the right-to-left direction. The maximum liver motion was dependent on ventilator settings. There was no additional measurable motion reduction with the addition of the muscle relaxant. CONCLUSION: The liver motion in each anesthetized dog was controlled under 3.0 mm in all directions with the use of high-frequency jet ventilation. No detectable advantage was identified by the injection of muscle relaxant in terms of further reducing the liver motion. The preclinical animal study indicated that the use of high-frequency jet ventilation (HFJV) would be able to limit the liver motion to an extent acceptable for the application of extracranial radiosurgery in humans. Radiosurgery for localized liver tumors warrants further investigation.

Anesthesia, Intravenous↗

High-frequency oscillatory ventilation for the prevention of chronic lung disease of prematurity.

BACKGROUND: There remains uncertainty concerning the safety and efficacy of high-frequency oscillatory ventilation as compared with those of conventional ventilation for the respiratory support of very preterm infants. We conducted a multicenter trial to determine whether early intervention with high-frequency oscillatory ventilation reduced mortality and the incidence of chronic lung disease among newborns with a gestational age of 28 weeks or less. METHODS: We randomly assigned preterm infants with a gestational age of 23 to 28 weeks to either conventional ventilation or high-frequency oscillatory ventilation within one hour after birth. Randomization was stratified according to center and gestational age (23 to 25 weeks or 26 to 28 weeks). RESULTS: A total of 400 infants were assigned to high-frequency oscillatory ventilation, and 397 were assigned to conventional ventilation. The composite primary outcome (death or chronic lung disease, diagnosed at 36 weeks of postmenstrual age) occurred in 66 percent of the infants assigned to receive high-frequency oscillatory ventilation and 68 percent of those in the conventional-ventilation group (relative risk in the group assigned to high-frequency oscillatory ventilation, 0.98; 95 percent confidence interval, 0.89 to 1.08). Similar proportions of infants died or had chronic lung disease in each gestational-age group. In both treatment groups treatment failure occurred in 10 percent of infants (relative risk in the group assigned to high-frequency oscillatory ventilation, 0.99; 95 percent confidence interval, 0.66 to 1.50). There were no significant differences between the groups in a range of other secondary outcome measures, including serious brain injury and air leak. CONCLUSIONS: The results obtained with high-frequency oscillatory ventilation and conventional ventilation do not differ significantly in the early treatment of respiratory disease in very preterm infants. Assessment of long-term effects will require additional follow-up.

Bronchopulmonary Dysplasia↗