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PubMed2003

Measurement of changes in respiratory mechanics during partial liquid ventilation using jet pulses.

OBJECTIVE: To compare the changes in respiratory mechanics within the breathing cycle in healthy lungs between gas ventilation and partial liquid ventilation using a special forced-oscillation technique. DESIGN: Prospective animal trial. SETTINGS: Animal laboratory in a university setting. SUBJECTS: A total of 12 newborn piglets (age, <12 hrs; mean weight, 725 g). INTERVENTIONS: After intubation and instrumentation, lung mechanics of the anesthetized piglets were measured by forced-oscillation technique at the end of inspiration and the end of expiration. The measurements were performed during gas ventilation and 80 mins after instillation of 30 mL/kg perfluorocarbon PF 5080. MEASUREMENTS AND MAIN RESULTS: Brief flow pulses (width, 10 msec; peak flow, 16 L/min) were generated by a jet generator to measure the end-inspiratory and the end-expiratory respiratory input impedance in the frequency range of 4-32 Hz. The mechanical variables resistance, inertance, and compliance were determined by model fitting, using the method of least squares. At least in the lower frequency range, respiratory mechanics could be described adequately by an RIC single-compartment model in all piglets. During gas ventilation, the respiratory variables resistance and inertance did not differ significantly between end-inspiratory and end-expiratory measurements (mean [sd]: 4.2 [0.7] vs. 4.1 [0.6] kPa x L(-1) x sec, 30.0 [3.2] vs. 30.7 [3.1] Pa x L(-1) x sec2, respectively), whereas compliance decreased during inspiration from 14.8 (2.0) to 10.2 (2.4) mL x kPa(-1) x kg(-1) due to a slight lung overdistension. During partial liquid ventilation, the end-inspiratory respiratory mechanics was not different from the end-inspiratory respiratory mechanics measured during gas ventilation. However, in contrast to gas ventilation during partial liquid ventilation, compliance rose from 8.2 (1.0) to 13.0 (3.0) mL x kPa(-1) x kg(-1) during inspiration. During expiration, when perfluorocarbon came into the upper airways, both resistance and inertance increased considerably (mean with 95% confidence interval) by 34.3% (23.1%-45.8%) and 104.1% (96.0%-112.1%), respectively. CONCLUSIONS: The changes in the respiratory mechanics within the breathing cycle are considerably higher during partial liquid ventilation compared with gas ventilation. This dependence of lung mechanics from the pulmonary gas volume hampers the comparability of dynamic measurements during partial liquid ventilation, and the magnitude of these changes cannot be detected by conventional respiratory-mechanical analysis using time-averaged variables.

Airway Resistance↗
PubMed1997

Cardiopulmonary interactions in healthy children and children after simple cardiac surgery: the effects of positive and negative pressure ventilation.

OBJECTIVE: To investigate the effects of cuirass negative pressure ventilation on the cardiac output of a group of anaesthetised children after occlusion of an asymptomatic persistent arterial duct, and a group of paediatric patients in the early postoperative period following cardiopulmonary bypass. DESIGN: Prospective study. SETTING: The paediatric intensive care unit and catheter laboratory of a tertiary care centre. PATIENTS: 16 mechanically ventilated children were studied: seven had undergone surgery for congenital heart disease, and nine cardiac catheterisation for transcatheter occlusion of an isolated asymptomatic persistent arterial duct. INTERVENTIONS: Cardiac output was measured using the direct Fick method during intermittent positive pressure ventilation and again after a short period of negative pressure ventilation. In five of the postoperative patients a third measurement was made following reinstitution of positive pressure ventilation. RESULTS: Negative pressure ventilation was delivered without complication, with no significant change in systemic arterial oxygen and carbon dioxide tension. The mixed venous saturation increased from 74% to 75.8% in the healthy children, and from 58.9% to 62.3% in the postoperative group. Negative pressure ventilation increased the cardiac index from 4.0 to 4.5 l/min/m2 in the healthy children, and from 2.8 to 3.5 l/min/m2 in the surgical group. The increase was significantly higher in the postoperative patients (28.1%) than the healthy children (10.8%). CONCLUSIONS: While offering similar ventilatory efficiency to positive pressure ventilation, cuirass negative pressure ventilation led to a modest improvement in the cardiac output of healthy children, and to a greater increase in postoperative patients. There are important cardiopulmonary interactions in normal children and in children after cardiopulmonary bypass, and by having beneficial effects on these interactions, negative pressure ventilation has haemodynamic advantages over conventional positive pressure ventilation.

Adolescent↗
PubMed1997

Liquid-assisted ventilation: physiology and clinical application.

Liquid-assisted ventilation, as an alternative ventilation strategy for respiratory distress, is progressing from theory and basic science research to clinical application. Biochemically inert perfluorochemical liquids have low surface tension and high solubility for respiratory gases. From early immersion experiments, two primary techniques for liquid-assisted ventilation have emerged: total liquid ventilation and partial liquid ventilation. While computer-controlled, time-cycled, pressure/volume-limited total liquid ventilators can take maximum advantage of these liquids by completely eliminating the gas phase in the distressed lung, partial liquid ventilation takes advantage of having these liquids in the lung while maintaining gas ventilation. The benefits of both partial and total techniques have been demonstrated in animal models of neonatal and adult respiratory distress syndrome, aspiration syndromes and congenital diaphragmatic hernia and also in combination with other therapeutic modalities including extracorporeal membrane oxygenation, high-frequency ventilation and nitric oxide. Additionally, nonrespiratory applications have expanding potential including pulmonary drug delivery and radiographic imaging. Since its use in neonates in 1989, liquid-assisted ventilation in humans has progressed to a variety of clinical experiences with different aetiologies of respiratory distress. The future holds the opportunity to clarify and optimize the potential of multiple clinical applications for liquid-assisted ventilation.

Adult↗
PubMed1993

Non-invasive mechanical ventilation in the treatment of acute respiratory failure in chronic obstructive pulmonary disease.

Acute respiratory failure is usually managed by means of mechanical ventilation via an endotracheal tube or tracheostomy, when conservative treatment fails. Invasive mechanical ventilation is associated with several complications. The recent development of non-invasive methods of ventilation, has led to an attempt to avoid the complications of invasive mechanical ventilation during episodes of acute respiratory failure, ensuring at the same time a similar degree of efficacy. Both intermittent negative pressure ventilation and positive pressure ventilation by face or nasal mask have recently been used for this purpose. Negative pressure ventilation by means of iron lung, cuirass or poncho-wrap ventilators, has never been used in place of endotracheal intubation, and studies of this kind of ventilation are inconclusive: as a consequence, there is, at the moment, no indication for the generalized use of negative pressure ventilation in acute respiratory failure. Intermittent positive pressure ventilation by facial or nasal masks, has recently been used in the treatment of respiratory failure in place of endotracheal intubation. The results are promising, but remain controversial. It may be attempted in selected patients with obstructive respiratory disorders, but the procedure is very time-consuming for nurses.

Humans↗
PubMed1996

Continuous monitoring of ventilatory mechanics during one-lung ventilation.

OBJECTIVE: The Ultima SV respiratory monitor can be used to monitor the intraoperative effects of the lateral decubitus position and one-lung ventilation on ventilatory mechanics. METHODS: Eight patients with esophageal cancer who required one-lung ventilation for esophagectomy and reconstruction were enrolled in the study. We monitored pressure-volume or flow-rate-volume loops continuously throughout the operation. Respiratory parameters were evaluated closely during five conditions of ventilation: two-lung ventilation in the supine position, two-lung ventilation in the lateral decubitus position, dependent one-lung ventilation in the lateral decubitus position, nondependent one-lung ventilation in the lateral decubitus position, and dependent one-lung ventilation in the lateral decubitus position with the chest opened. Respiratory rate was controlled at 10 breaths/min, and tidal volume was kept constant (10 ml/kg) during surgery. RESULTS: Peak inspiratory pressure increased to 29.0 +/- 9.0 (mean +/- SD) cm H2O in the dependent one-lung in the lateral decubitus position with the chest opened (p < 0.01). Dynamic compliance decreased to 29.4 +/- 4.9 ml/cm H2O in the dependent one-lung in the lateral decubitus position with the chest opened (p < 0.01). The changing configuration of the loops also offered additional and instantaneous information during one-lung ventilation. CONCLUSIONS: One-lung ventilation caused several changes in the whole respiratory system (lung, thorax, and endotracheal tube). Continuous monitoring of flow-rate-volume or pressure-volume loops with in-line spirometry provided comprehensive information regarding parameters in one-lung ventilation.

Aged↗
PubMedDate not supplied

High-frequency ventilation in neonates.

STUDY OBJECTIVE: To provide a brief review of the current status of high-frequency ventilation in neonatal respiratory care. DATA IDENTIFICATION: Publications appearing between 1980 and 1990 were identified by computer searches using the National Library of Medicine's data base, MEDLINE, and by searching bibliographies of identified articles. STUDY SELECTION: Studies related to physiologic background and clinical reports of neonatal application were selected individually. DATA EXTRACTION: Data concerning the physiologic basis, clinical effectiveness and complications, and latest results of a multicenter randomized trial were evaluated and used to develop a current concept. RESULTS OF DATA SYNTHESIS: In early clinical tests of high-frequency ventilation, it was considered beneficial that airway pressure lower than that used in conventional mechanical ventilation might reduce the frequency of pulmonary barotrauma. When high-frequency ventilation was applied to infants with respiratory distress syndrome, the development of chronic pulmonary complications also was expected to decrease. Although several reports supported this hypothesis, a recent controlled trial involving multiple clinical centers did not find significant improvement in the group treated with high-frequency ventilation. Rather, they recognized the frequent occurrence of complications associated with high-frequency ventilation and suggested the prior use of conventional ventilation. However, a possible defect of this study design requires further studies to elucidate the source of these conflicting results. CONCLUSIONS: As a mode of mechanical ventilation, high-frequency ventilation is useful for maintaining ventilation in patients with air leak syndrome or bronchopulmonary fistula or during bronchoscopic examination. But in general, its role as an alternative to conventional ventilation still remains controversial.

High-Frequency Ventilation↗
PubMed2004

Increase in alveolar antioxidant levels in hyperoxic and anoxic ventilated rabbit lungs during ischemia.

Increases in free radicals are believed to play a central role in the development of pulmonary ischemia/reperfusion (I-R) injury, leading to microvascular leakage and deterioration of pulmonary surfactant. Continued ventilation during ischemia offers significant protection against I-R injury, but the impact of alveolar oxygen supply both on lung injury and on radical generation is still unclear. We investigated the influence of hyperoxic (95% O2) and anoxic (0% O2) ventilation during ischemia on alveolar antioxidant status and surfactant properties in isolated rabbit lungs. Normoxic and hyperoxic ventilated, buffer-perfused lungs (n = 5 or 6) and native lungs (n = 6) served as controls. As compared with controls, biophysical and biochemical surfactant properties were not altered in anoxic as well as hyperoxic ventilated ischemic (2, 3, and 4 h) lungs. Assessment of several antioxidants (reduced glutathione (GSH), alpha-tocopherol (vitamin E), retinol (vitamin A), ascorbic acid (vitamin C), uric acid, and plasmalogens (1-O-alkenyl-2-acyl-phospholipids)) in bronchoalveolar lavage fluid (BALF) revealed a significant increase in antioxidant compounds under anoxic and hyperoxic ventilation, with maximum levels occuring after 3 h of ischemia. For example, GSH increased to 5.1 +/- 0.8 microM (mean +/- SE, p <.001) after 3 h of anoxic ventilated ischemia and to 2.7 +/- 0.2 microM (p <.01) after hyperoxic ventilated ischemia compared with native controls (1.3 +/- 0.2 microM), but did not significantly change under anoxic and hyperoxic ventilation alone. In parallel, under ischemic conditions, oxidized glutathione (GSSG) increased during hyperoxic (3 h: 0.81 +/- 0.04 microM, p <.001), but remained unchanged during anoxic (3 h: 0.31 +/- 0.04 microM) ventilation compared with native controls (0.22 +/- 0.02 microM), whereas F2-isoprostanes were elevated under both hyperoxic (3 h: 63 +/- 15 pM, p <.01) and anoxic (3 h: 50 +/- 9 pM, p <.01) ventilation compared with native controls (16 +/- 4 pM). We conclude that oxidative stress is increased in the lung alveolar lining layer during ischemia, during both anoxic and hyperoxic ventilation. This is paralleled by an increase rather than a decrease in alveolar antioxidant levels, suggested to reflect an adaptive response to oxidative stress during ischemia.

Animals↗
PubMed2006

Incidence, risk factors, and outcome of ventilator-associated pneumonia.

OBJECTIVE: The purpose of this study is to determine the incidence, risk factors, and outcome of ventilator-associated pneumonia (VAP). DESIGN: Prospective cohort. SETTING: Three hundred sixty-one intensive care units (ICUs) from 20 countries. PATIENTS AND PARTICIPANTS: Two thousand eight hundred ninety-seven patients mechanically ventilated for more than 12 hours. MEASUREMENTS AND RESULTS: Baseline demographic data, primary indication for mechanical ventilation, daily ventilator settings, multiple organ failure over the course of mechanical ventilation, and outcome were collected. Ventilator-associated pneumonia was present in 439 patients (15%). Patients with VAP were more likely to have chronic pulmonary obstructive disease, aspiration, sepsis, and acute respiratory distress syndrome. Mortality in patients with VAP was 38%. Factors associated with mortality were severity of illness, limited activity before the onset of mechanical ventilation and development of shock, acute renal failure, and worsening of hypoxemia during the period of mechanical ventilation. Case-control analysis showed no increased mortality in patients with VAP (38.1% vs 37.9%, P = .95) but prolonged duration of mechanical ventilation and ICU stay. CONCLUSION: In a large cohort of mechanically ventilated patients, VAP is more likely in patients with underlying lung disease (acute or chronic). Ventilator-associated pneumonia was associated with a significant increase in ICU length of stay but no increase in mortality.

Aged↗
PubMed2005

Survey of operating theatre ventilation facilities for minimally invasive surgery in Great Britain and Northern Ireland: current practice and considerations for the future.

Increasing use of minimally invasive surgery (MIS) and other invasive procedures has raised the question of what ventilation facilities are appropriate for such procedures to prevent infection. The Hospital Infection Society (HIS) Working Party on Infection Control in Operating Theatres undertook a survey of practice in Great Britain and Northern Ireland on the ventilation facilities provided for a variety of MIS and other procedures. Five hundred and fifty questionnaires were forwarded to HIS members, and 186 (39%) replies were received. Fifty-eight percent were from district general hospitals (DGHs). Designated theatres for orthopaedic surgery (although not necessarily ultraclean ventilated theatres) were available in more than 80% of hospitals, with approximately 50% of hospitals having designated theatres for a variety of other surgical subspecialities. Approximately two-thirds of urological procedures were performed in conventionally ventilated operating theatres. Most radiological procedures were performed in non-ventilated theatres or treatment rooms. In around half of the DGHs and university/referral hospitals, orthopaedic MIS procedures such as arthroscopy were performed in ultraclean ventilated theatres. This survey revealed considerable variation in the use of conventionally ventilated theatres and ultraclean ventilated theatres. In particular, many radiological and anaesthetic procedures are performed in treatment rooms or ventilated rooms with less than 20 air changes per hour. Whilst it is not clear whether this is acceptable practice given current knowledge, large-scale clinical trials to determine what standards of ventilation are appropriate to minimize infection for these types of procedures would be difficult to conduct. Research is needed on the relative risk of airborne infection for a variety of procedures, including whether all prosthetic implant procedures should be carried out in ultraclean ventilated theatres, as infection associated with implants is often of airborne origin and of considerable clinical significance.

Air Microbiology↗
PubMed1992

Outcomes of patients admitted to a chronic ventilator-dependent unit in an acute-care hospital.

The outcomes in 61 patients admitted to a chronic ventilator-dependent unit (CVDU) at Saint Marys Hospital in Rochester, Minnesota, during an 18-month period are summarized. This unit was designed for patients who could not be weaned from mechanical ventilators after repeated attempts. Most patients had been ventilator dependent for more than 21 days, but some patients were admitted to the CVDU after briefer periods if special circumstances suggested that weaning from mechanical ventilation would be difficult. The unit was organized to provide a multidisciplinary approach to the general medical and respiratory management of these patients, including a physiologic evaluation of the respiratory system to determine the actual cause of ventilator dependence and complete medical, nursing, and psychosocial assessments to help adopt a plan of care and weaning from the ventilator. Of the numerous causes for ventilator dependence in this study group, chronic obstructive pulmonary disease was the most frequent underlying diagnosis. Of the 61 patients admitted to the CVDU, 58 survived, and 53 were liberated from the mechanical ventilator. Ultimately, 35 patients were dismissed directly home from the CVDU. Five of these patients required nocturnal mechanical ventilation. An additional eight patients were dismissed home after rehabilitation. After being weaned from mechanical ventilation, 11 patients were eventually transferred to nursing homes, and 3 additional patients were transferred to a local hospital or physical medicine unit. One patient remains in the CVDU. Thus, the CVDU has successfully liberated patients from ventilator dependence. In addition, because of a decreased need for nursing care, the unit has been cost-effective.

Adult↗
PubMed1994

Pulmonary mechanics of dogs during transtracheal jet ventilation.

STUDY OBJECTIVE: To quantify the delivered tidal volume and other selected measurements of pulmonary mechanics in an animal model during transtracheal jet ventilation (TTJV), with comparison to positive-pressure mechanical ventilation (PPMV) and spontaneous breathing. DESIGN: Prospective, nonblinded laboratory animal study. INTERVENTIONS: Seven mongrel dogs weighing 24.5 +/- 3.7 kg were anesthetized, paralyzed, and placed within a specially designed volume plethysmograph with the head and neck externalized. Ventilation was performed using TTJV under variable inspiratory time:expiratory time ratios (TI:TE) (1:1, 1:2, 1:3, 1:4, 1.5:2.5, 2:1, 2:2, 3:1, and 4:1) and variable driving air pressures (40, 45, and 50 psi). The dogs then were ventilated with PPMV. Tidal volume, tracheal pressure, transpulmonary pressure, air flow, arterial pressure, central venous pressure, and arterial blood gases were measured during spontaneous ventilation, TTJV, and PPMV. Quasistatic compliance of the lungs was measured after all methods of ventilation. Statistical significance was accepted at P < .05. RESULTS: There was no significant difference between delivered tidal volume during TTJV (446 +/- 69 mL at a TI:TE of 1:3 and 45 psi) and spontaneous breathing (506 +/- 72 mL). TTJV delivered a tidal volume significantly higher than the standard 15 mL/kg volume used for mechanical ventilation in dogs. Tracheal pressure and transpulmonary pressure were not significantly different between TTJV and PPMV. Variations in TI:TE had no significant effect on most of the measured variables, specifically tidal volume or transpulmonary pressure. Minute ventilation increased significantly and PCO2 decreased significantly as frequency increased during TI:TE settings of 1:1, 1:2, and 2:1. Increases in the driving air pressure during TTJV significantly increased the tidal volume as it was raised from 40 psi to 50 psi. There was no change in quasistatic lung compliance during any method of ventilation. CONCLUSION: TTJV delivers an effective tidal volume comparable to both spontaneous breathing and PPMV in a dog model. In the absence of upper-airway obstruction, there was no significant difference in the pulmonary pressures, resistance, and compliance during TTJV, as compared to mechanical ventilation. Variation in TI:TE during TTJV had no major effect on pulmonary mechanics, except to increase minute ventilation and decrease PCO2 as the frequency was increased significantly. Increasing the driving air pressure to the TTJV apparatus significantly augmented delivered tidal volume due to increased air flow.

Animals↗
PubMed1995

A comparison of four methods of weaning patients from mechanical ventilation. Spanish Lung Failure Collaborative Group.

BACKGROUND: Weaning patients from mechanical ventilation is an important problem in intensive care units. Weaning is usually conducted in an empirical manner, and a standardized approach has not been developed. METHODS: We carried out a prospective, randomized, multicenter study involving 546 patients who had received mechanical ventilation for a mean (+/- SD) of 7.5 +/- 6.1 days and who were considered by their physicians to be ready for weaning. One hundred thirty patients had respiratory distress during a two-hour trial of spontaneous breathing. These patients were randomly assigned to undergo one of four weaning techniques: intermittent mandatory ventilation, in which the ventilator rate was initially set at a mean (+/- SD) of 10.0 +/- 2.2 breaths per minute and then decreased, if possible, at least twice a day, usually by 2 to 4 breaths per minute (29 patients); pressure-support ventilation, in which pressure support was initially set at 18.0 +/- 6.1 cm of water and then reduced, if possible, by 2 to 4 cm of water at least twice a day (37 patients); intermittent trials of spontaneous breathing, conducted two or more times a day if possible (33 patients); or a once-daily trail of spontaneous breathing (31 patients). Standardized protocols were followed for each technique. RESULTS: The median duration of weaning was 5 days for intermittent mandatory ventilation (first quartile, 3 days; third quartile, 11 days), 4 days for pressure-support ventilation (2 and 12 days, respectively), 3 days for intermittent (multiple) trials of spontaneous breathing (2 and 6 days, respectively), and 3 days for a once-daily trial of spontaneous breathing (1 and 6 days, respectively). After adjustment for other covariates, the rate of successful weaning was higher with a once-daily trial of spontaneous breathing than with intermittent mandatory ventilation (rate ratio, 2.83; 95 percent confidence interval, 1.36 to 5.89; P < 0.006) or pressure-support ventilation (rate ratio, 2.05; 95 percent confidence interval, 1.04 to 4.04; P < 0.04). There was no significant difference in the rate of success between once-daily trials and multiple trials of spontaneous breathing. CONCLUSIONS: A once-daily trial of spontaneous breathing led to extubation about three times more quickly than intermittent mandatory ventilation and about twice as quickly as pressure-support ventilation. Multiple daily trials of spontaneous breathing were equally successful.

Acute Disease↗
PubMed2004

Noninvasive positive-pressure ventilation for respiratory failure after extubation.

BACKGROUND: The need for reintubation after extubation and discontinuation of mechanical ventilation is not uncommon and is associated with increased mortality. Noninvasive positive-pressure ventilation has been suggested as a promising therapy for patients with respiratory failure after extubation, but a single-center, randomized trial recently found no benefit. We conducted a multicenter, randomized trial to evaluate the effect of noninvasive positive-pressure ventilation on mortality in this clinical setting. METHODS: Patients in 37 centers in eight countries who were electively extubated after at least 48 hours of mechanical ventilation and who had respiratory failure within the subsequent 48 hours were randomly assigned to either noninvasive positive-pressure ventilation by face mask or standard medical therapy. RESULTS: A total of 221 patients with similar baseline characteristics had been randomly assigned to either noninvasive ventilation (114 patients) or standard medical therapy (107 patients) when the trial was stopped early, after an interim analysis. There was no difference between the noninvasive-ventilation group and the standard-therapy group in the need for reintubation (rate of reintubation, 48 percent in both groups; relative risk in the noninvasive-ventilation group, 0.99; 95 percent confidence interval, 0.76 to 1.30). The rate of death in the intensive care unit was higher in the noninvasive-ventilation group than in the standard-therapy group (25 percent vs. 14 percent; relative risk, 1.78; 95 percent confidence interval, 1.03 to 3.20; P=0.048), and the median time from respiratory failure to reintubation was longer in the noninvasive-ventilation group (12 hours vs. 2 hours 30 minutes, P=0.02). CONCLUSIONS: Noninvasive positive-pressure ventilation does not prevent the need for reintubation or reduce mortality in unselected patients who have respiratory failure after extubation.

Aged↗
PubMed2002

E-cylinder-powered mechanical ventilation may adversely impact anesthetic management and efficiency.

UNLABELLED: Anesthesiologists often administer care outside the operating room. These locations may depend on gas cylinders for their oxygen source more than the operating suites supplied by dedicated central pipelines. Using full E-cylinders, we determined the oxygen consumption of two often used, pneumatically driven anesthesia ventilators to answer three questions: How much time is available when mechanically ventilating patients in the setting of absent or malfunctioning central oxygen pipeline? How much oxygen is used by the ventilator to drive the bellows? How does changing the inspiratory to expiratory ratio and the inspiratory flow (Narkomed ventilator only) influence oxygen use? At a ventilation of 5 L/min, we found that mechanical ventilation consumes between 59% and 85% of the available oxygen in an E-cylinder to drive the ventilator at fresh gas flows ranging from 1 to 10 L/min. The time span until the low oxygen alarm sounded ranged from 38 to 99 min. Alteration of the inspiratory flow but not the inspiratory to expiratory ratio had a significant impact. Clinicians must recognize that mechanical ventilation using E-cylinders rapidly depletes this sole oxygen source and could jeopardize patient safety. Conversely, manual or spontaneous ventilation with low fresh gas flows minimizes oxygen depletion. IMPLICATIONS: The time available to ventilate patients with an E-cylinder tank as the sole oxygen source was found to be as short as 38 min. Clinicians must recognize that mechanical ventilation using oxygen cylinders rapidly depletes oxygen and could jeopardize patient safety.

Anesthesia↗
PubMed1998

Partial liquid ventilation reduces pulmonary neutrophil accumulation in an experimental model of systemic endotoxemia and acute lung injury.

OBJECTIVE: To determine whether pulmonary neutrophil sequestration and lung injury are affected by partial liquid ventilation with perfluorocarbon in a model of acute lung injury (ALI). DESIGN: A prospective, controlled, in vivo animal laboratory study. SETTING: An animal research facility of a health sciences university. SUBJECTS: Forty-one New Zealand White rabbits. INTERVENTIONS: Mature New Zealand White rabbits were anesthetized and instrumented with a tracheostomy and vascular catheters. Animals were assigned to receive partial liquid ventilation (PLV, n = 15) with perflubron (18 mL/kg via endotracheal tube), conventional mechanical ventilation (CMV, n = 15) or high-frequency oscillatory ventilation (HFOV, n = 5). Animals were ventilated, using an FIO2 of 1.0, and ventilatory settings were required to achieve a normal PaCO2. Animals were then given 0.9 mg/kg of Escherichia coli endotoxin intravenously over 30 mins. Partial liquid ventilation, conventional mechanical ventilation, or high-frequency oscillatory ventilation was continued for an additional 4 hrs before the animals were killed. A group of animals not challenged with endotoxin underwent conventional ventilation for 4.5 hrs, serving as the control group (control, n = 6). Lungs were removed and samples were frozen at -70 degrees C. Representative samples were stained for histology. A visual count of neutrophils per high-power field (hpf) was performed in five randomly selected fields per sample in a blinded fashion by light microscopy. Lung samples were homogenized in triplicate in phosphate buffer, ultrasonified, freeze-thawed, and clarified by centrifugation. Supernatants were analyzed for myeloperoxidase (MPO) activity by spectrophotometry with o-dianisidine dihydrochloride and hydrogen peroxide at 460 nm. MEASUREMENTS AND MAIN RESULTS: Histologic analysis of lung tissue obtained from control animals showed normal lung architecture. Specimens from the PLV and HFOV groups showed a marked decrease in alveolar proteinaceous fluid, pulmonary vascular congestion, edema, necrotic cell debris, and gross inflammatory infiltration when compared with the CMV group. Light microscopy of lung samples of animals supported with PLV and HFOV had significantly lower neutrophil counts when compared with CMV (PLV, 4 +/- 0.3 neutrophils/hpf; HFOV, 4 +/- 0.5 neutrophils/hpf; CMV, 10 +/- 0.9 neutrophils/hpf; p < .01). In addition, MPO activity from lung extracts of PLV and HFOV animals was significantly lower than that of CMV animals (PLV, 61 +/- 13.3 units of MPO activity/lung/kg; HFOV, 43.3 +/- 6.8 units of MPO activity/lung/kg; CMV, 140 +/- 28.5 units of MPO activity/lung/kg; p < .01). MPO activity from lungs of uninjured control animals was significantly lower than that of animals in the PLV, HFOV, and CMV groups (control, 2.2 +/- 2 units of MPO activity/lung/kg; p < .001). CONCLUSIONS: Partial liquid ventilation decreases pulmonary neutrophil accumulation, as shown by decreased neutrophil counts and MPO activity, in an experimental animal model of ALI induced by systemic endotoxemia. The attenuation in pulmonary leukostasis in animals treated with PLV is equivalent to that obtained by a ventilation strategy that targets lung recruitment, such as HFOV.

Acute Disease↗
PubMed2000

Intratracheal pulmonary ventilation in a rabbit lung injury model: continuous airway pressure monitoring and gas exchange efficacy.

OBJECTIVES: To compare carinal pressures vs. proximal airway pressures, and gas exchange efficacy with a constant minute volume, in lung-injured rabbits during conventional mechanical ventilation (CMV) and intratracheal pulmonary ventilation (ITPV); and to evaluate performance of a prototype ITPV gas delivery and continuous airway pressure monitoring system. DESIGN: Prospective controlled study. SETTING: Animal research laboratory at a teaching hospital. SUBJECTS: Sixteen adult female rabbits. INTERVENTIONS: Anesthetized rabbits were tracheostomized with a multilumen endotracheal tube. Anesthesia and muscle relaxation were maintained continuously throughout the study. Proximal airway pressures and carinal pressures were recorded continuously. The injection port of the multilumen endotracheal tube was used for the carinal pressure monitoring. To prevent obstruction of the port, it was flushed with oxygen at a rate of 11 mL/min. CMV was initiated with a pressure-limited, time-cycled ventilator set at an FiO2 of 1.0 and at a flow of 1.0 L/kg/min. The pressure limit of the ventilator was effectively disabled. A normal baseline for arterial blood gases was achieved by adjusting the inspiratory/expiratory time ratios. ITPV was established using a flow of 1.0 L/kg/min through a reverse thrust catheter, at the same baseline and inspiratory/expiratory ratio. Carinal positive end-expiratory pressure was maintained at a constant value of 2 cm H2O by adjusting the expiratory resistance of the ventilator circuit Lung injury was achieved over a 30-min period by three normal saline lavages of 5 mL/kg each. After lung injury, all animals were consecutively ventilated for 1 hr with CMV, for 1 hr with ITPV, and again for 1 hr with CMV. Six rabbits were ventilated at 30 breaths/min (group 1), and ten rabbits were ventilated at 80 breaths/min (group 2). Four rabbits in group 2 were subjected, 1 hr after return to CMV from ITPV, to another session of ITPV, with positive end-expiratory pressure gradually being increased to 4, 6, and 8 cm H2O for 15 mins each. RESULTS: No significant differences were observed in carinal peak inspiratory pressure between CMV and ITPV modes, at both low and high frequencies of breathing, indicating that the inspired tidal volume remained constant during both modes of ventilation. Significant gradients were noted between proximal airway and carinal peak inspiratory pressure during ITPV but not during CMV. Initiation of ITPV, at a flow of 1.0 L/kg/min, required an increase in the ventilator expiratory resistance to maintain a constant level of positive end-expiratory pressure (2 cm H2O) as measured at the carina. During ITPV, the PaCO2 was significantly reduced by 20% at 30 breaths/min (p < .05) and by 22% at 90 breaths/min (p < .01), compared with CMV. Arterial oxygenation was significantly enhanced with a positive end-expiratory pressure of 6 and 8 cm H2O (p < .05 and .001, respectively), compared with a positive end-expiratory pressure of 2 cm H2O during ITPV. All components of the new prototype gas delivery and airway pressure monitoring system functioned without failure, at least for 3 hrs of the CMV, ITPV, and CMV trials. CONCLUSIONS: ITPV in saline-lavaged, lung-injured rabbits at breathing frequencies of 30 and 80 breaths/min, compared with CMV at the same minute ventilation, can improve CO2 exchange. During ITPV, significant pressure gradients can develop between carinal and proximal airway pressures. Continuous carinal pressure monitoring is therefore necessary for the safe clinical application of ITPV. Reliable carinal pressure monitoring can be achieved by adding a small bias flow through the carinal pressure monitoring port. Although ITPV can remove CO2 from injured lungs efficiently, simultaneous addition of positive end-expiratory pressure can further improve arterial oxygenation.

Animals↗
PubMed2002

Specific compliance and gas exchange during high-frequency oscillatory ventilation.

OBJECTIVES: To evaluate the use of specific compliance (static compliance/functional residual capacity) to adjust mean airway pressure, resulting in optimal gas exchange during high-frequency oscillatory ventilation in a surfactant-deficient newborn piglet. DESIGN: Prospective controlled animal study. SETTING: Laboratory. SUBJECTS: Eight newborn piglets at 5 days of age. BACKGROUND: High-frequency oscillatory ventilation enables the use of relatively high mean airway pressures without the lung damage associated with conventional positive pressure ventilation. Mean airway pressures can be increased, resulting in static lung expansion that approaches total lung capacity with its negative impact on venous return. Therefore, knowledge of lung volume is important for safe patient management. A simple, noninvasive technique to enable the clinician to determine the optimal mean airway pressure likely would improve patient management. INTERVENTIONS: The lungs were lavaged after placement of central catheters and tracheostomy to lower respiratory system compliance and worsen ventilation perfusion matching. The animals were ventilated with high-frequency oscillatory ventilation at the same mean airway pressure as before lung lavage. Mean airway pressures then were increased in a step-wise fashion up to 30 cm H2O or until clinical deterioration occurred. All other ventilator variables, Fio2, frequency, and pressure amplitude were constant throughout the experiment. MEASUREMENTS AND MAIN RESULTS: Before lavage and at each level of mean airway pressure after lung lavage, respiratory system compliance and functional residual capacity were measured. Additionally, central arterial pressure, central venous pressure, heart rate, arterial blood gas, and pulse oximetric saturation were recorded. Lung lavage significantly lowered respiratory system compliance (static as well as specific compliance) and worsened ventilation perfusion matching as evidenced by an increase in Paco2 and a decreased arterial to alveolar oxygen ratio. With increasing mean airway pressures, static/specific compliance improved and then peaked before declining, functional residual capacity increased, and blood gas improved until reaching the flat portion of the pressure-volume relationship of the lung. Optimal gas exchange as reflected by the highest arterial to alveolar oxygen ratio and lowest Paco2 at constant ventilation was found at a mean airway pressure that maintained the functional residual capacity and static respiratory system compliance at the same level as the preinjury levels ("normalized" functional residual capacity and respiratory system compliance). CONCLUSIONS: These results suggest that specific compliance measurement that incorporates static respiratory system compliance and functional residual capacity during high-frequency oscillatory ventilation can be used to adjust mean airway pressure and achieve "normalized" functional residual capacity, static compliance, and gas exchange. These measurements may provide a simple method to optimize lung volume in a surfactant-deficient patient during high-frequency oscillatory ventilation.

Animals↗
PubMed2004

Positive end-expiratory pressure affects regional redistribution of ventilation differently in prone and supine sheep.

OBJECTIVE: To examine interactions between positive end-expiratory pressure (PEEP) and posture on regional distribution of ventilation and to compare measurements of regional ventilation with two aerosols: a wet fluorescent microsphere aerosol (FMS, median mass aerodynamic diameter 1.1 microm) and a dry Tc-labeled carbon particle aerosol (Technegas, TG, median mass aerodynamic diameter approximately 0.1 microm). DESIGN: Experimental study. SETTING: Academic laboratory. SUBJECTS: : Anesthetized and mechanically ventilated sheep (n = 16). INTERVENTIONS: Four conditions were studied: prone or supine posture with or without 10 cm H2O PEEP. MEASUREMENTS AND MAIN RESULTS: Comparisons of FMS and TG were made in five animals. The median correlation coefficient of the two ventilation tracers was .95 (range, .91-.96). The mean ventilation per unit weight of dry lung for horizontal planes was almost identical whether measured with TG or FMS. The distribution of ventilation was assessed by analyzing deposition of aerosol in about 1,000 lung regions per animal. Distribution of ventilation down the vertical axis was linear in prone (the slope indicated a dorsal-to-ventral three-fold difference in ventilation) but unimodal in supine animals with the mode in the center of the lung. Redistribution of ventilation with 10 PEEP differed between posture, shifting the mode in supine toward dependent lung regions while eliminating the dorsal-to-ventral gradient in prone. The regional heterogeneity in ventilation was greater in supine sheep at both levels of PEEP, and this was due mostly to greater isogravitational heterogeneity in supine than in prone position. CONCLUSIONS: The wet fluorescent microsphere aerosol was as reliable as Technegas for high-resolution measurements of regional ventilation. The markedly different effects of 10 PEEP in supine and prone sheep may have important implications for gas exchange both in noninjured and injured lungs.

Administration, Inhalation↗