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PubMed1980

Contaminant concentration reduction: general ventilation versus local exhaust ventilation.

General ventilation has often been proposed as a supplement to or replacement of local exhaust ventilation to reduce the concentration of contaminants in the workplace. The use of four air changes and ten air changes per hour of general ventilation to reduce contaminant concentration is studied. The concentration reduction is estimated theoretically. The first cost of general ventilation and the operating costs are estimated for a typical situation. These costs are compared to those of local exhaust ventilation. The general ventilation effect of local exhaust points, in the vicinity of the dust sources, is analyzed in comparison to the effect of general ventilation in an entire plant. The effect of general ventilation on dust counts is presented.

Air Pollutants↗
PubMed1991

Changes in the distribution of ventilation and perfusion associated with separation from mechanical ventilation in patients with obstructive pulmonary disease.

A trial of separation from mechanical ventilation may induce an abnormal respiratory pattern and a maldistribution of ventilation-to-perfusion ratios (VA/Q), especially in patients with chronic obstructive pulmonary disease. This study was designed to assess the effects of three different modes of ventilation on the distribution of global and also regional VA/Q in eight patients with chronic obstructive pulmonary disease recovering from acute respiratory failure who remained dependent on mechanical ventilation after more than 5 days of attempted separation from the ventilator. VA/Q distribution was assessed using the multiple inert gas and isotopic scanning methods after 30 min each of controlled mechanical ventilation (CMV), 10 cmH2O inspiratory pressure support, and spontaneous breathing (SB). Controlled ventilation was provided at a respiratory rate ranging from 12 to 18 breaths per min and a tidal volume of 8 ml.kg-1. In comparison to CMV, SB resulted in a decrease in tidal volume (from 512 +/- 144 to 301 +/- 102 ml, P less than 0.01), and an increase in respiratory rate (from 15.5 +/- 3.2 to 27.3 +/- 15.0 breaths per min, P less than 0.05), which increased dead space (+7.1% of minute ventilation), cardiac output (+36%), and the perfusion to areas of low VA/Q (+8.9% of cardiac output) (P less than 0.05, P less than 0.001, and P less than 0.05, respectively). Isotopic scans revealed a horizontal craniocaudal difference of VA/Q in all modes, with the lowest VA/Q zones at the basal part of the lungs (mean basal VA/Q 0.58 in SB and 1.05 in CMV).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1981

Automatic ventilation with the Ayre's T-piece. A modification of the Nuffield Series 200 ventilator for neonatal and paediatric use.

A simple modification to an existing adult ventilator has been designed to permit mechanical ventilation of neonates and small children with the Ayre's T-piece circuit. The Nuffield Anaesthesia Ventilator Series 200 has been modified by replacing the piston in the patient valve with a fixed leak. This arrangement avoids the problems of critical adjustment commonly encountered with other methods of converting adult ventilators to paediatric use, and allows the ventilator controls to be used normally. The ventilator has been assessed according to the proposed International Standards Organization specifications for the evaluation of the performance of lung ventilators, and the results are described in detail. The modified ventilator is shown to perform as a time-cycled pressure generator capable of delivering tidal volumes between 10 and 300 ml at frequencies from 10 to 85/minute. It is therefore ideally suited to neonatal and paediatric use.

Anesthesia, Inhalation↗
PubMed1989

In what respect does high frequency positive pressure ventilation differ from conventional ventilation?

The original rationale for HFPPV was that under certain conditions adequate alveolar ventilation could be achieved with high ventilatory frequencies and small tidal volumes. It was theorized further that increased ventilatory frequencies and low tidal volumes would decrease the airway pressures, barotrauma, and cardiovascular and other systemic consequences seen with conventional mechanical ventilation. The first clinical applications of HFPPV were in bronchoscopy and laryngoscopy for diagnostic and/or therapeutic purposes. Apart from these endoscopic applications, volume-controlled HFPPV has been compared with conventional ventilation in upper abdominal surgery and coronary artery bypass grafting. The possible advantages of HFPPV over conventional volume-controlled ventilation in the intensive care setting are still unclear. Provided that the mean lung volumes are similar, oxygenation in acute respiratory failure is similar with both ventilation methods. Although the role of HFPPV in the management of pulmonary diseases still remains to be clarified, it does provide effective ventilation in selected types of patients needing ventilatory support. New modes of pressure-controlled ventilation have not resolved all clinical problems in severe ARDS and/or acute respiratory failure. The search for means of optimal ventilatory support with minimal complications must continue, as conventional ventilation does not always offer the best treatment.

Animals↗
PubMed1998

Negative pressure ventilation vs. spontaneous assisted ventilation during rigid bronchoscopy. A controlled randomised trial.

BACKGROUND: Ventilation during interventional rigid bronchoscopy (IRB) under general anaesthesia (jet ventilation, positive pressure ventilation and spontaneous assisted ventilation) may offer some difficulties. This study compares the effectiveness during IRB of intermittent negative pressure ventilation (INPV) and spontaneous assisted ventilation (SAV). METHODS: Thirty-eight patients submitted to IRB were randomised into two groups: SAV or INPV. All patients received a total intravenous anaesthesia; INPV patients were paralysed. Pre- and intra-operative arterial blood gases and O2 flow through a rigid bronchoscope were assessed. The endoscopist applying a subjective score evaluated the operating conditions. RESULTS: Patients of the INPV group, as compared to the SAV group, required a lower dosage of fentanyl (2.6 +/- 1.8 micrograms.kg-1.h-1 vs. 6.6 +/- 4.8 micrograms.kg-1.h-1), a lower O2 supply (3.3 +/- 2.8 l/min vs. 11.6 +/- 3.4 l/min), a shorter recovery time (5.4 +/- 2.9 min vs. 9.8 +/- 7.1 min) and no manually assisted ventilation (0 +/- 0 vs. 1 +/- 1.1 n degree/procedure). Intraoperative PaCO2 was higher in the SAV (8.1 +/- 1.3 kPa) than in the INPV group (5.0 +/- 1.6 kPa) and intraoperative pH differed in the two groups (7.26 +/- 0.05, SAV vs. 7.47 +/- 0.08, INPV). Operating conditions, as assessed by a subjective score, were considered better with INPV than with SAV (4.9 vs. 4.3). CONCLUSIONS: As compared to SAV, INPV in paralysed patients during IRB reduces administration of opioids, shortens recovery time, prevents respiratory acidosis, excludes the need for manually assisted ventilation, reduces O2 need and affords optimal surgical conditions. INPV appears a safe, non-invasive and effective ventilatory management during IRB.

Adult↗
PubMed1987

Ventilation-perfusion inequality during constant-flow ventilation.

Previous work by Lehnert et al. (J. Appl. Physiol. 53:483-489, 1982) has demonstrated that adequate alveolar ventilation can be maintained during apnea in anesthetized dogs by delivering a continuous stream of inspired ventilation through cannulas aimed down the main-stem bronchi. Because an asymmetric distribution of ventilation might introduce ventilation-perfusion (VA/Q) inequality, we compared gas exchange efficiency in nine anesthetized and paralyzed dogs during constant-flow ventilation (CFV) and conventional ventilation (intermittent positive-pressure ventilation, IPPV). Gas exchange was assessed using the multiple inert gas elimination technique. During CFV at 3 l X kg-1 X min-1, lung volume, retention-excretion differences (R-E*) for low- and medium-solubility gases, and the log standard deviation of blood flow (log SD Q) increased, compared with the findings during IPPV. Reducing CFV flow rate to 1 l X kg-1 X min-1 at constant lung volume improved R-E* and log SD Q, but significant VA/Q inequality compared with that at IPPV remained and arterial PCO2 rose. Comparison of IPPV and CFV at the same mean lung volume showed a similar reversible deterioration in gas exchange efficiency during CFV. We conclude that CFV causes significant VA/Q inequality which may be due to nonuniform ventilation distribution and a redistribution of pulmonary blood flow.

Animals↗
PubMed1996

Glottic aperture and effective minute ventilation during nasal two-level positive pressure ventilation in spontaneous mode.

Our goal was to verify glottic behavior and its effects on effective minute ventilation during intermittent positive pressure ventilation applied at increasing inspiratory pressure levels through a nasal mask (nIPPV) using a two-level positive pressure ventilator (two-level IPPV) in spontaneous mode. Ten subjects were studied while awake. The spontaneous mode was used at three levels of inspiratory positive airway pressure (IPAP): 10, 15, and 20 cm H2O. The expiratory pressure was kept at 4 cm H2O. Records of spontaneous breathing without nIPPV were also performed. The glottis was continuously monitored through a fiberoptic bronchoscope. We measured, breath by breath, the widest inspiratory angle formed by the vocal cords at the anterior commissure, the corresponding tidal volume (with respiratory inductive plethysmography), the respiratory frequency and other indices. Our data during wakefulness show that inspiratory pressures of 10 and 15 cm H2O did not result in increases in effective minute ventilation with respect to spontaneous breathing. Only at 20 cm H2O of IPAP did effective minute ventilation increase. This was due essentially to a decrease in respiratory frequency with increasing pressures, offsetting increases in tidal volume at 10 and 15, but not at 20 cm H2O of inspiratory pressure. Changes in end-tidal CO2 suggest that alveolar ventilation increased due to the change in breathing pattern. Contrary to what we observed previously with either two-level IPPV used in the controlled mode, or nIPPV performed with volumetric ventilators, the glottis did not play any noticeable role in the control of effective minute ventilation.

Adult↗
PubMed1997

Determinants of effective ventilation during nasal intermittent positive pressure ventilation.

Our aim was to verify in healthy subjects submitted to nasal intermittent positive pressure ventilation (nIPPV) with a volumetric ventilator on controlled mode, whether changes in ventilator settings (delivered tidal volume (VT), respiratory frequency (fR) and inspiratory flow (V'I) could influence effective minute ventilation (V'E), thus allowing identification of the settings resulting in the highest V'E during nIPPV. We then compared these experimentally obtained "best" settings to those obtained retrospectively in a group of patients submitted to long-term nIPPV for clinical reasons. We studied 10 healthy subjects awake and asleep, and 33 patients with restrictive ventilatory disorders. Changes in delivered V'I (for a constant delivered VT and fR) led to significant changes in V'E. V'E was significantly higher when a given delivered V'E was obtained using higher fR and lower VT than when it was obtained using lower delivered fR and higher VT. Increases in fR generally resulted in increases in V'E. The "best" settings derived from these results were: VT: 13 mL.kg-1 of body weight; fR: 20 breaths.min-1 and V'I: 0.56-0.85 L.s-1. The corresponding average values found in the patient group were: delivered VT: 14 mL.kg-1; fR: 23 breaths.min-1 and delivered V'I: 0.51 L.s-1. Changes in minute ventilation resulting from modifications in ventilator settings can be attributed to the glottic response to mechanical influences. This leads to "ideal" settings quite different from the standard ones in intubated patients. Values derived from nasal intermittent positive pressure ventilation in healthy subjects seem to apply to patients submitted to long-term nasal intermittent positive pressure ventilation.

Adolescent↗
PubMed1998

Negative pressure ventilation versus conventional mechanical ventilation in the treatment of acute respiratory failure in COPD patients.

This case-control study was aimed to evaluate the effectiveness of negative pressure ventilation (NPV) versus conventional mechanical ventilation (CMV) for the treatment of acute respiratory failure (ARF) in patients with chronic obstructive pulmonary disease (COPD) admitted to a respiratory intermediate intensive care unit (RIICU) and four general intensive care units (ICU). Twenty-six COPD patients in ARF admitted in 1994-95 to RIICU and treated with NPV (cases) were matched according to age (+/-5 yrs), sex, causes triggering ARF, Acute Physiology and Chronic Health Evaluation (APACHE) II score (+/- 5 points), pH (+/-0.05) and arterial carbon dioxide tension (Pa,CO2) on admission with 26 patients admitted to ICU and treated with CMV (controls). The primary end points of the study were inhospital death for both groups and the need for endotracheal intubation for cases. The secondary endpoints were length and complications of mechanical ventilation and length of hospital stay. The effectiveness of matching was 91%. Mortality rate was 23% for cases and 27% for controls (NS), five cases needed endotracheal intubation, four of whom subsequently died. The duration of ventilation in survivors was significantly lower in cases than in controls, with a median of 16 h (range 2-111) versus 96 h (range 12-336) (P<0.02), whereas the length of hospital stay was similar in the two groups, with a median of 12 days (range 2-47) for cases vs 12 days (range 3-43) (NS) for controls. No complications were observed in cases, whereas three controls developed infective complications. These results suggest that negative pressure ventilation is as efficacious as conventional mechanical ventilation for the treatment of acute respiratory failure in patients with chronic obstructive pulmonary disease and that it is associated with a shorter duration of ventilation and a similar length of hospital stay compared with conventional mechanical ventilation.

Acute Disease↗
PubMed1998

Intratracheal pulmonary ventilation at low airway pressures in a ventilator-induced model of acute respiratory failure improves lung function and survival.

STUDY OBJECTIVE: The pulmonary parenchyma in patients with acute respiratory failure (ARF) is commonly not involved in a homogenous disease process. Conventional mechanical ventilation (MV) at elevated positive end-expiratory pressure (PEEP) and peak inspiratory pressure (PIP) aims at recruiting collapsed or nonventilated lung units. Invariably, those pressures are also transmitted to the healthiest regions, with possible extension of the disease process (barotrauma). During intratracheal pulmonary ventilation (ITPV), a continuous flow of fresh gas is delivered directly at the carina, bypassing the dead space proximal to the catheter tip. In healthy sheep, it allows lowering tidal volume (VT) to as low as 1.0 mL/kg, at respiratory rates (RR) up to 120 breaths/min, while maintaining normocapnia. In a model of ventilator-induced lung injury, we wished to explore whether ITPV, applied at low VT and low PEEP and tailored to ventilate the healthiest regions of the lungs, could provide adequate oxygenation and alveolar ventilation, without any attempt to recruit lungs. DESIGN: Randomized study in sheep. SETTING: Animal research laboratory. PARTICIPANTS: We induced ARF in 12 sheep following 1 to 2 days of MV at a PIP of 50 cm H2O, except that 5 to 8% of lungs were kept on apneic oxygenation of 5 cm H2O, sparing those regions from the injury process. INTERVENTIONS: Sheep were randomized to volume-controlled MV (control group) (n = 6) with VT of 8 to 12 mL/kg, PEEP of 5 to 10 cm H2O, or to ITPV (n = 6) at PEEP of 3 to 5 cm H2O, VT of 2.5 to 4 mL/kg, PIP of <20 cm H2O, at RRs sufficient to sustain normocapnia. MEASUREMENTS AND RESULTS: Hemodynamic status in the ITPV group progressively improved, and all six sheep were weaned to room air within 83+/-54 h. Sheep in the control group had progressively deteriorating conditions and all animals died after a mean of 50+/-39 h. Barotrauma and postmortem histopathologic changes were more pronounced in the control group. CONCLUSION: In this model of ventilator-induced lung injury, low PEEP-low VT ventilation with ITPV sustained normocapnia and prevented further lung injury, allowing weaning to room air ventilation.

Acute Disease↗
PubMed1998

[The applied value of BiPAP mechanical ventilation via facial of nasal mask before or after ordinary mechanical ventilation].

To expore the applied value of BiPAP ventilator before or after regular ventilation, 44 patients who had indicators of regular mechanical ventilation and 4 patients who had difficulty of getting free from endotracheal intubation mechanical ventilation were ventilated with BiPAP ventilator via facial or nasal mask. The results showed that 13/44 patients had good responses and avoided receiving regular mechanical ventilation with endotracheal intubation or incision. BiPAP ventilation was also effective in patients who were dependent on regular mechanical ventilatin.

Aged↗
PubMed2000

Negative pressure ventilation via chest cuirass to decrease ventilator-associated complications in infants with acute respiratory failure: a case series.

Pulmonary and nonpulmonary complications of invasive positive pressure ventilation are well documented in the medical literature. Many of these complications may be minimized by the use of noninvasive ventilation. During various periods of medical history, negative pressure ventilation, a form of noninvasive ventilation, has been used successfully. We report the use of negative pressure ventilation with a chest cuirass to avoid or decrease the complications of invasive positive pressure ventilation in three critically ill infants at two institutions. In each of these cases, chest cuirass ventilation improved the patient's clinical condition and decreased the requirement for more invasive therapy. These cases illustrate the need for further clinical evaluation of the use of negative pressure ventilation utilizing a chest cuirass.

Acute Disease↗
PubMed2001

Patient-ventilator interactions during volume-support ventilation: asynchrony and tidal volume instability--a report of three cases.

During pressure-support ventilation, tidal volume (V(T)) can vary according to the level of the patient's respiratory effort and modifications of the thoraco-pulmonary mechanics. To keep V(T) as constant as possible, the Siemens Servo 300 ventilator proposes an original modification of pressure-support ventilation, called volume-support ventilation (VSV). VSV is a pressure-limited mode of ventilation that uses V(T) as a feedback control: the pressure support level is continuously adjusted to deliver a preset V(T). Thus, the ventilator adapts the inspiratory pressure level, breath by breath, to changes in the patient's inspiratory effort and the mechanical thoraco-pulmonary properties. The clinician sets V(T) and respiratory frequency, and the ventilator calculates a preset minute volume. It has been shown that ineffective respiratory efforts can occur during pressure-support ventilation.

Female↗
PubMed2005

Ventilator waveforms and the physiology of pressure support ventilation.

Pressure support ventilation (PSV) is a commonly used mode. It is patient-triggered, pressure-limited, and (normally) flow-cycled. Triggering difficulty occurring during PSV is usually due to intrinsic positive end-expiratory pressure. The airway pressure generated at the initiation of inhalation is determined by the pressure support setting and the pressure rise time (pressurization rate) settings on the ventilator. The rise-time setting is clinician-adjustable on many current-generation ventilators. Flow delivery during PSV is determined by the pressure support setting, the pressure generated by the respiratory muscles, and respiratory system mechanics. The delivered tidal volume is determined by the area under the flow-time curve. Patient-ventilator dyssynchrony may occur during PSV if the flow at which the ventilator cycles to exhalation does not coincide with the termination of neural inspiration. The newer generation ventilators offer clinician-adjustable flow-termination during PSV. Ventilator waveforms may be useful to appropriately adjust the ventilator during PSV.

Adult↗
PubMed2005

The ventilator circuit and ventilator-associated pneumonia.

Historically, the relationship between the ventilator circuit and pulmonary infection was accepted as fact, without any scientific evidence. Hence the term, "ventilator"-associated pneumonia. Recent evidence, however, has demonstrated that the major sources of pneumonia in the ventilated patient are colonization of the gastrointestinal tract, with subsequent aspiration around the endotracheal tube cuff, and contamination by caregivers. In recent years, the relationship of respiratory care equipment to ventilator-associated pneumonia has been studied carefully. A number of clinical trials have demonstrated that routine changing of the ventilator circuit fails to impact the incidence of pneumonia in the ventilated patient. Additional studies evaluating the type of humidification device, type of suctioning device, and frequency of change of the devices have resulted in conflicting evidence. This paper reviews the role of the humidifier, ventilator circuit, and airway suctioning equipment on the pathogenesis and prevention of ventilator-associated pneumonia.

Equipment Contamination↗
PubMed1983

High-frequency ventilation. A new concept in mechanical ventilation.

High-frequency ventilation has been shown to provide adequate pulmonary gas exchange in patients who require mechanical ventilation. The advantage of this method of ventilation is that it may allow effective gas transport without high airway pressure or depression of hemodynamic function and thus avoid barotrauma or decreased cardiac output. Currently, three major systems have evolved. (1) High-frequency positive-pressure ventilation uses frequencies of 60 to 120/min, and gas is delivered through a pneumatic valve system. It has been successfully used during surgical procedures, laryngoscopy, and bronchoscopy. (2) High-frequency jet ventilation uses compressed gas delivered through a small-bore cannula at frequencies of up to 400/min. This technique has been used during laryngoscopy and seems to be promising for ventilation of patients with disruption of the airway. (3) High-frequency oscillation uses a wide range of frequencies, up to 40 HZ, and small quasi-sinusoidal volume excursions. It has been reported to provide adequate pulmonary gas exchange in human volunteers and patients in respiratory failure requiring mechanical ventilation. The mechanism of gas transport during high-frequency, low-tidal-volume ventilation is not well understood, but theoretic models suggest that enhanced diffusion, interregional mixing, and intra-airway velocity profiles may be important factors.

Adult↗
PubMed1997

[High frequency ventilation strategies with neonatal conventional ventilator. Assessment of gas exchange, hemodynamic status and lung injury].

Experiments were performed to consider the use of conventional neonatal ventilators with assisted expiratory mechanism using ventilatory high frequency strategies. Gas exchange, hemodynamic state, and lung injury were also assessed. Twenty Albino Wistar rats, undergoing and acute lung lesion through physiological solution wash of the lungs were studied. Afterward, they were distributed into four groups according to the different ventilator strategies, based on the different pressure changes and the tidal volume, the baseline lung volume and the respiratory frequency. Group I, High Frequency Ventilation, with high baseline lung volumes (HFVh); group II, Conventional Mechanical Ventilation, with high baseline lung volume (CMVh), group III, High Frequency Ventilation, with low baseline lung volume (HFV1) and group IV Conventional Mechanical Ventilation, with low baseline lung volume (CMV1). Significant differences were found between group I (HFVh) and groups II (CMVh), III (HFV1) and IV (CMV1) as regards pO2, Artery/Alveolar relation to O2 (a/A), pCO2, arterial blood pressure and histopathologic lung lesion. The hypothesis concerning the decisive role of the baseline lung volume maintainence to minimize progressive damage caused by mechanical ventilation on a previously injured lung while attending ventilatory strategies that generate little pressure and volume cyclical changes was confirmed. We conclude that, high frequency mechanical ventilation is possible through conventional neonatal respirators with assisted expiratory mechanism.

Animals↗
PubMed1996

Nasal two-level positive-pressure ventilation in normal subjects. Effects of the glottis and ventilation.

The purpose of this study was to examine the behavior of the glottis during intermittent positive-pressure ventilation (nIPPV) using a two-level positive-pressure ventilator and to compare the glottic adaptation to this ventilatory mode with the one observed using volumetric ventilators, recently reported by us. Six healthy subjects were studied during both wakefulness and sleep. Their glottis was continuously monitored through a fiberoptic bronchoscope. We measured breath by breath the widest inspiratory angle formed by the vocal cords at the anterior commissure, the corresponding tidal volume, and other indices. We used the controlled ventilatory mode. The expiratory pressure was kept at 4 cm H2O, and the inspiratory pressure was increased by steps from 10 to 15 to 20 cm H2O. Increases in inspiratory pressure did not always lead to increases in effective ventilation reaching the lungs. This was due to a significant narrowing of the glottis by adduction of the vocal cords in all subjects. Periodic breathing with or without apneas were common during wakefulness, but especially during sleep, representing 10.5 +/- 11% (SD) of total sleep time. We conclude that effective ventilation during nIPPV using a two-level positive-pressure ventilator in the controlled mode is less predictable and less stable than during nIPPV using volumetric ventilators.

Adaptation, Physiological↗