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PubMed2005

Effects of gas leak on triggering function, humidification, and inspiratory oxygen fraction during noninvasive positive airway pressure ventilation.

OBJECTIVES: During noninvasive positive pressure ventilation (NPPV), the gas leak that commonly occurs around the mask can render NPPV ineffective. We evaluated the effects of gas leak on inspiratory trigger function during NPPV with bilevel pressure and ICU ventilators. In addition, we evaluated the effects of gas leak on fraction of inspired oxygen (Fio(2)) and humidification. METHODS: Air leak was created at the airway opening of a model lung by establishing several different-size holes in the circuit. During simulated spontaneous breathing, we evaluated inspiratory trigger performance of two bilevel pressure ventilators (BiPAP Vision and BiPAP S/T-D; Respironics; Murrysville, PA) and two ICU ventilators (Puritan-Bennett 7200ae and Puritan-Bennett 840; Tyco Healthcare; Mansfield, MA). Inspiratory delay time and inspiratory trigger pressure were analyzed. Fio(2) at the airway opening and inside the model lung were evaluated during BiPAP S/T-D ventilation at supplemental oxygen flows of 3, 6, 9, 12 and 15 L/min. Measured oxygen concentration was compared to mathematically predicted levels. Finally, using two heated humidifiers, we evaluated the effect of gas leak on humidification. RESULTS: The bilevel pressure ventilators triggered properly at all levels of gas leak, and inspiratory triggering was more effective than with the ICU ventilators. Delivered Fio(2) with the BiPAP S/T-D ventilator was affected by gas leak and could be predicted mathematically unless the gas leak was large. With large gas leaks, although relative humidity was maintained, absolute humidity decreased. CONCLUSION: Gas leak affected triggering of ICU ventilators, Fio(2) of the BiPAP S/T-D ventilator, and humidity with both types of humidifiers.

Equipment Design↗
PubMed1989

Diaphragmatic contraction during assisted mechanical ventilation.

Indirect evidence from airway pressure recordings in mechanically ventilated patients suggests that the diaphragm exhibits contractile activity beyond that required to trigger a ventilator-assisted breath. We used the diaphragmatic EMG to provide direct evidence of persistent contractile activity and studied the effects of alterations in ventilator-delivered flow rate and tidal volume on the duration of diaphragmatic contraction. The duration of contraction was expressed in terms of inspired volume. During a single breath, diaphragmatic force generation ceases at the point of peak electromyographic activity; hence, the inspired volume at peak EMG is the volume at the diaphragmatic off-switch (Voff). Ventilator-delivered flow rate and tidal volume were varied during assisted (patient-initiated) and controlled (ventilator-initiated) breaths while diaphragmatic EMG and inspired volume were recorded simultaneously in ten patients with a variety of illnesses requiring mechanical ventilation. Spontaneous ventilator-unassisted breaths were also recorded for comparison. We found that (1) during assisted breaths, diaphragmatic activity continued after the ventilator was triggered, (2) Voff was usually close to spontaneous tidal volume, (3) Voff increased significantly as ventilator-delivered flow rate increased, and (4) controlled breaths may also be associated with phasic electromyographic activity. The data have implications for resting patients on assisted ventilation.

Adult↗
PubMed2004

Duration of mechanical ventilation in life-threatening pediatric asthma: description of an acute asphyxial subgroup.

OBJECTIVE: Acute asphyxial asthma (AAA) is well described in adult patients and is characterized by a sudden onset that may rapidly progress to a near-arrest state. Despite the initial severity of AAA, mechanical ventilation often restores gas exchange promptly, resulting in shorter durations of ventilation. We believe that AAA can occur in children and can lead to respiratory failure that requires mechanical ventilation. Furthermore, children with rapid-onset respiratory failure that requires intubation in the emergency department (ED) are more likely to have AAA and a shorter duration of mechanical ventilation than those intubated in the pediatric intensive care unit (PICU). METHODS: An 11-year retrospective chart review (1991-2002) was conducted of all children who were aged 2 through 18 years and had the primary diagnosis of status asthmaticus and required mechanical ventilation. RESULTS: During the study period, 33 (11.4%) of 290 PICU admissions for status asthmaticus required mechanical ventilation. Thirteen children presented with rapid respiratory failure en route, on arrival, or within 30 minutes of arrival to the ED versus 20 children who progressed to respiratory failure later in their ED course or in the PICU. Mean duration of mechanical ventilation was significantly shorter in the children who presented with rapid respiratory failure versus those with progressive respiratory failure (29 +/- 43 hours vs 88 +/- 72 hours). Children with rapid respiratory failure had greater improvements in ventilation and oxygenation than those with progressive respiratory failure as measured by pre- and postintubation changes in arterial carbon dioxide pressure, arterial oxygen pressure/fraction of inspired oxygen ratio, and alveolar-arterial gradient. According to site of intubation, 23 children required intubation in the ED, whereas 10 were intubated later in the PICU. Mean duration of mechanical ventilation was significantly shorter in the ED group versus the PICU group (42 +/- 63 hours vs 118 +/- 46 hours). There were significantly greater improvements in ventilation and oxygenation in the ED group versus the PICU group as measured by pre- and postintubation changes in arterial carbon dioxide pressure and arterial oxygen pressure/fraction of inspired oxygen ratio. CONCLUSIONS: AAA occurs in children and shares characteristics seen in adult counterparts. Need for early intubation is a marker for AAA and may not represent a failure to maximize preintubation therapies. AAA represents a distinct form of life-threatening asthma and requires additional study in children.

Adolescent↗
PubMed2005

Prediction and analysis model of temperature and its application to a natural ventilation multi-span plastic greenhouse equipped with insect-proof screen.

The natural ventilation widely used in greenhouses has advantages of saving energy and reducing expense. In order to provide information for climate control of greenhouse, a model was developed to predict the variation of air temperature in the naturally ventilated greenhouse equipped with insect-proof screen. Roof ventilation and combined roof and sidewall ventilation were considered in the model. This model was validated against the results of experiments conducted in the greenhouse when the wind was parallel to the gutters. The model parameters were determined by the least squares method. In the used model, effects of wind speed and window opening height on the air temperature variation were analyzed. Comparison between two types of ventilation showed that there existed a necessary ventilation rate which results in air temperature decrease in natural ventilation under special climatic conditions. In our experiments when wind speed was less than 3.2 ms(-1), wind had a more gradual effect on greenhouse temperature for roof ventilation, compared with combined roof and sidewall ventilation, which had greater air temperature decrease than roof ventilation only.

Air Conditioning↗
PubMed2003

Effects of duration of isoflurane anesthesia and mode of ventilation on intracranial and cerebral perfusion pressures in horses.

OBJECTIVE: To test the hypothesis that isoflurane-anesthetized horses during controlled ventilation and spontaneous ventilation exhibit temporal changes in cerebral hemodynamics, as measured by intracranial pressure and cerebral perfusion pressure, that reflect temporal changes in systemic arterial pressure. ANIMALS: 6 healthy adult horses. PROCEDURE: Horses were anesthetized in left lateral recumbency with 1.57% isoflurane in O2 for 5 hours in 2 experiments by use of either controlled ventilation (with normocapnia) or spontaneous ventilation (with hypercapnia) in a randomized crossover design. Intracranial pressure was measured with a subarachnoid strain-gauge transducer. Carotid artery pressure, central venous pressure, airway pressures, blood gases, and minute ventilation also were measured. RESULTS: Intracranial pressure during controlled ventilation significantly increased during constant dose isoflurane anesthesia and thus contributed to decreasing cerebral perfusion pressure. Intracranial pressure was initially higher during spontaneous ventilation than during controlled ventilation, but this difference disappeared over time; no significant differences in cerebral perfusion pressures were observed between horses that had spontaneous or controlled ventilation. CONCLUSIONS AND CLINICAL RELEVANCE: Cerebral hemodynamics and their association with ventilation mode are altered over time in isoflurane-anesthetized horses and could contribute to decreased cerebral perfusion during prolonged anesthesia.

Anesthetics, Inhalation↗
PubMed2004

Excess body weight is not independently associated with outcome in mechanically ventilated patients with acute lung injury.

BACKGROUND: Despite an epidemic of obesity among adults, the effect of excess body weight on outcome from critical illness is not well studied. OBJECTIVE: To examine the association between excess body weight and outcome in mechanically ventilated patients with acute lung injury. DESIGN: Secondary analysis of participants in trials of therapy for acute lung injury. SETTING: 10 U.S. medical centers that participate in the National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome Network. PATIENTS: 902 mechanically ventilated patients who were enrolled in randomized, controlled trials of therapy for acute lung injury. INTERVENTION: Assignment to higher (12 mL/kg of predicted weight) or lower (6 mL/kg of predicted weight) tidal volume ventilation strategies with specified weaning protocols. Some patients also received ketoconazole, lisofylline, or placebo by factorial design. MEASUREMENTS: Mortality rate, rate of unassisted ventilation by day 28, and number of ventilator-free days. RESULTS: Indirect causes of lung injury, including trauma, were more common in obese patients. Overweight and obese patients had higher peak and plateau airway pressures before enrollment because of higher set tidal volumes. After risk adjustment, excess body weight was not associated with death, achievement of unassisted ventilation, or number of ventilator-free days. This lack of effect persisted with categorical or continuous measures of body mass index (BMI). We found no significant interaction between ventilator protocol assignment and BMI category. CONCLUSIONS: After risk adjustment, overweight and obese patients with acute lung injury have outcomes similar to those of patients with normal BMI. The lack of interaction between ventilator protocol assignment and BMI suggests that patients with normal, overweight, or obese BMI benefit from lower tidal volume ventilation for acute lung injury.

Body Mass Index↗
PubMed1999

[Fitness training during nasal ventilation in diseases limited by dyspnea].

METHODS: Five patients with chronic ventilatory failure demonstrated by arterial hyperkapnia and overloaded respiratory muscles under spontaneous ventilation (P01/P01 max) were adapted to passive noninvasive ventilation (ISB). Three of them suffered from severe COPD (FEV1 < 50%), two patients from severe restriction (VC < 30%). These patients had to undergo a bicycle ergometer exercise with and without nasal ventilation until they reached physical exhaustion with standardised incremental increase in external workload. RESULTS: In both settings all patients were able to manage exercise up to their physical exhaustion. The anaerobic limit was exceeded each time. The total ventilation volume had to be increased two- to threefold during exercise with nasal ventilation to maintain the passive ventilation. The reduced load on the respiratory muscles was generally proven by lower pCO2 and higher pH levels. Without ventilation discontinuation of the exercise was caused by dyspnoea, whereas this was due to weakness in the legs under ventilation. In all five cases the achieved level of external workload was higher when supporting the respiratory muscles (43 watts vs. 36 watts) at lower lactate levels. CONCLUSION: On a bicycle ergometer the respiratory muscles can be sufficiently relieved using noninvasive nasal ventilation. A higher level of workload, longer duration and a higher quality of exercise can be achieved thereby. The fact that patients without relief of load of the respiratory muscles complained of dyspnoea, whereas the fact that patients with ventilation complained of weakness in their legs indicates the high efficiency of this method, although the tested patients are severely handicapped individuals who usually do not undergo comparable physical exercise in their daily activities.

Aged↗
PubMed2000

[Non-invasive ventilation in acute respiratory insufficiency].

Non invasive mechanical ventilation represents all the techniques of mechanical ventilation not using endotracheal connection to the respirator. Non invasive mechanical ventilation is essentially represented nowadays by facial (generally used for acute respiratory failure) and nasal ventilation (widely used for long term mechanical ventilation at home). Following in France the first studies of Rideau in the '80 in patients with chronic respiratory failure secondary to muscular dystrophy, Meduri, then Brochard demonstrated the interest of non invasive mechanical ventilation in the management of acute on chronic respiratory failure. A simple algorithm is thus able to recommend in first attempt use of non invasive mechanical ventilation in acute on chronic respiratory failure except if the patient presents in a severe respiratory status imposing in first line endotracheal ventilation. In parallel, more recent studies have demonstrated the interest of that technique in immediate ventilatory link in the spectrum of weaning of endotracheal mechanical ventilation. In hypoxic acute respiratory failure, non invasive mechanical ventilation remains controversial and seems to be better indicated in moderate to severe respiratory status.

Acute Disease↗
PubMed2002

A three year population based survey of paediatric mechanical ventilation in east Denmark.

BACKGROUND: East Denmark has a population of 396,000 children 0-14 years and a yearly birth rate of 30,000, but at present no paediatric intensive care unit (PICU). OBJECTIVE: To perform a population based survey of paediatric mechanical ventilation with the purpose of providing the background for discussions for or against centralization of paediatric intensive care. METHODS: Case records of children 0-14 years treated with mechanical ventilation from January 1996 to December 1998 were retrospectively reviewed and the following data were obtained: Whether or not the child was settled in East Denmark, date of admission, gender, age, underlying chronic condition(s), acute condition(s) leading to mechanical ventilation, duration of positive pressure ventilation, duration of endotracheal intubation, length of stay in ICU, and outcome. Children undergoing mechanical ventilation because of neonatal problems, cardiac surgery or neurosurgery were excluded. RESULTS: Data were obtained from 197 children of which 123 were boys (p < 0.001 for boys vs girls). Median age at admission to ICU was 30 months. Boys were younger than girls (median age 22 vs 41 months, p = 0.01), but as determined by mortality, duration of positive pressure ventilation, intubation and stay in ICU there were no differences between boys and girls with respect to disease course (p > 0.28). Totally, 86 (44%) had at least one underlying chronic condition. The incidence of disease leading to mechanical ventilation in children in East Denmark was estimated to 1.6/10,000/year. An average of 1.1 child was intubated each day. Taking into account the seasonal variation two beds would be required to give coverage for 85% of ICU days needed for paediatric mechanical ventilation while three beds would cover 98%. Children admitted to referral hospital RH more often had underlying chronic conditions and had more severe courses of disease than children admitted to other hospitals (p < 0.001). Mortality did not differ (p = 0.66). CONCLUSION: The number of children requiring mechanical ventilation in East Denmark is too low to provide the background for establishing an independent PICU. However, since paediatric intensive care is a rare and complicated event further centralization of children undergoing mechanical ventilation in East Denmark should be considered.

Adolescent↗
PubMed2003

Ventilating the patient with severe asthma: nonconventional therapy.

Conventional pharmacotherapy of severe asthma and status asthmaticus includes beta2-sympathomimetics, theophylline, corticosteroids and occasionally topical anticholinergics (ipratropium bromide). Since hypoxemia is the most severe phenomenon in status asthmaticus the administration of oxygen is mandatory. However, if the bronchodilating therapy fails and hypoxemia continues, usually respiratory failure develops due to progressive respiratory muscle failure. An increasing PaCO(2) and respiratory acidosis are indications for mechanical ventilatory support to unload the failing respiratory pump. Nowadays, there is increasing consensus that ventilatory support should be administered primarily as non-invasive ventilation (NIV) via a face mask1. However, in a significant number of patients with severe asthma NIV is either contraindicated or insufficient. In this case usually the patient must be endotracheally intubated and mechanically ventilated "invasively". Intubation and ventilation of patients with severe asthma or status asthmaticus is associated with a high incidence of complications compared to patients ventilated for other causes of respiratory failure2,3. Therefore the risks of invasive mechanical ventilation have to be weighted carefully to ongoing conservative therapy and NIV. Cardiopulmonary arrest and severe hypoxemia in spite of O2 supplement and NIV are absolute criteria for intubation and ventilation. Mostly deterioration in mental status and exhaustion are the clinical findings leading to mechanical ventilation. Decision is guided rather by the course of the deterioration (how fast the patient's condition is worsening) than by pathological values alone. An increased PaCO(2) with moderate respiratory acidosis alone is not per se an indication for mechanical ventilation. However, a continuously rising PaCO(2) or the development of a severe metabolic acidosis after 1 hour of NIV is a strong argument for invasive mechanical ventilation. Other criteria are evidence of cardiac failure with fall in pulse volume and dysrhythmias, pneumomediastinum or pneumothorax (which has to be drained before mechanical ventilation!).

Anesthetics, Inhalation↗
PubMed2003

[Evaluation of mechanical ventilation for patients with acute respiratory distress syndrome as a result of interstitial pneumonia after renal transplantation].

OBJECTIVE: To evaluate the clinical value of mechanical ventilation for patients with acute respiratory distress syndrome(ARDS) as a result of interstitial pneumonia after renal transplantation in the intensive care unit (ICU). METHODS: All the clinical data (totally 16 cases) were collected, including the improvement of hypoxemia before and after mechanical ventilation. RESULTS: Different levels of positive end-expiratory pressure (PEEP) 4-15 cm H2O (1 cm H2O=0.098 kPa) were applied in the patients in whom mechanical ventilation was instituted. The time for different mechanical ventilation was different [1-87 days, (15.4+/-21.1) days] and duration of survival was different [1-1 945 days, (154.4+/-497.1) days]. Only one of them was survived (6.7%), and the others died (93.3%). The causes of death were analyzed. Among the patients who received the mechanical ventilation, 3 patients were alive less than 3 days and their dire ct cause of death was not respiratory (circulation and central). Only one of them did not receive artificial ventilation and the cause of death was hypoxemia. The successful experience for one survivor among the patients who received the ventilator was that hypoxemia was improved by the mechanical ventilation, winning the time for the treatment of the original disease. CONCLUSION: The major value of mechanical ventilation was to correct the hypoxemia in order to win the time to cure the interstitial pneumonia and ARDS. The survival rate was still low for such a group of patients because the pathogenesis was not identified, and therefore the disease could not be controlled, even the mechanical ventilation is instituted in time.

Adult↗
PubMed1992

Psychosocial adjustment of post-poliomyelitis ventilator assisted individuals.

The effect of severe disability, tracheostomy, and ventilator use on psychosocial functioning, gainful employment, life satisfaction, and perceived well-being were studied for a population of 395 ventilator assisted post-poliomyelitis individuals (PVAIs). Standard psychosocial survey instruments and other general questioning were used. Two-hundred-seventy-three physically intact health care professionals served as controls. They were surveyed about their own life satisfaction and perceived well-being and were asked to judge how severely disabled ventilator assisted individuals would respond to such questioning. The relative distress associated with ventilator use was also evaluated in a similar manner. Fifty six of 380 responding PVAIs (14.7%) expressed dissatisfaction with their lives in general. This compares with 8.5% of the controls and 7% of a previously studied general population. The controls significantly underestimated the patients' life satisfaction and well-being scores and significantly overestimated the relative hardship associated with ventilator use. The post-polio individuals using noninvasive methods of assisted ventilation were also significantly more satisfied with their lives than were those ventilated via tracheostomy. Fifty-seven of 148 (39%) individuals married and 165 of 395 (42%) individuals were gainfully employed during long-term ventilator use. We conclude that many severely disabled post-poliomyelitis ventilator users lead productive lives. The vast majority have a positive affect and are satisfied with life. Noninvasive ventilatory support alternatives may lend to greater life satisfaction for these individuals than ventilation delivered via an indwelling tracheostomy. Health care professionals may significantly underestimate their patients' satisfaction with life and this may have a bearing on patient management.

Adult↗
PubMed1995

[Practical experiences with home ventilation in childhood].

BACKGROUND: The introduction of portable ventilators independent of compressed air as well as non-invasive devices for assessment of blood gases, helped to facilitate a long-term mechanical ventilation in family environment in the last decade. Home care is of particular interest at the infant age, as the disruption of the mother-child relationship may induce severe developmental disorders, known as syndrome of psychosocial deprivation. PATIENTS AND METHODS: We investigated retrospectively the tendency of the ventilator parameters, the support and the daily practice of 16 families with children of all ages with long-term ventilator assistance. RESULTS: The duration of the ventilation ranged between 5 months and 14 years, on the average at 5.5 years. The average portion of the ventilation at home care was 78%. The respiratory patterns, tidal volume and positive inspiration pressure, exceeded occasionally the physiologic standard of the age group. The common reason is, that the children prefer small sized tubes, having advantages in comfort and speech abilities. Therefore results an increased tube-resistance and air leakage of the tracheostomy tubes. The long-term tendency of the ventilator parameters is stable or improving, excluding the patients with progredient primary diseases. Commonly the motivation of the family members is high, therefore the psychosocial integration of the patients satisfying. Two thirds of the families have no personal support for the domiciliary care of the ventilator assisted child. Mothers tell about an enormous distress. CONCLUSIONS: The long-term mechanical ventilation of children at home care is an adequate therapy for all ages. It combines technical support of the underlying chronic respiratory failure with the chance of an intact psychosocial development of the child. Specialized centres and a national organisation may provide competent information and support for the increasing number of home-ventilated children in Germany.

Adolescent↗
PubMed1994

Noninvasive mechanical ventilation via face mask in patients with acute respiratory failure who refused endotracheal intubation.

OBJECTIVE: To evaluate the response to noninvasive ventilation in a group of terminally ill patients with acute respiratory failure who refused endotracheal intubation. DESIGN: Case series. SETTING: Medical intensive care units (ICUs) in a university health science center. PATIENTS: Eleven patients, nine with hypercapnic and two with hypoxemic acute respiratory failure. Mean age of patients was 64 yrs. INTERVENTION: Mechanical ventilation was delivered via a face mask. The initial ventilatory setting was continuous positive airway pressure mode, with pressure-support ventilation of 10 to 20 cm H2O, titrated to achieve a respiratory rate of < 25 breaths/min and a tidal volume of 5 to 7 mL/kg. Ventilatory settings were adjusted based on results of arterial blood gases. Mean duration of mechanical ventilation was 44 hrs. MEASUREMENTS AND MAIN RESULTS: Mechanical ventilation via face mask was effective in correcting gas exchange abnormalities in seven of 11 patients, all of whom survived and were discharged from the ICU. Four patients with hypercapnic acute respiratory failure died. Mechanical ventilation via face mask was effective in improving respiratory acidosis in three patients and had no effect in one patient. Two of the four patients could not be weaned from mechanical ventilation and opted for discontinuation of this method. Removal of the ventilator while retaining the mask for oxygen supplementation was a nontraumatic experience to the patient and family. Even when respiratory failure did not resolve, mechanical ventilation via face mask was effective in lessening dyspnea and allowed the patient to maintain autonomy and continuous verbal communication. CONCLUSIONS: We conclude that mechanical ventilation via face mask offers an effective, comfortable, and dignified method of supporting patients with end-stage disease and acute respiratory failure.

Acute Disease↗
PubMed1989

Pressure and flow limitations of anesthesia ventilators.

The effect of increasing airway pressure on the mean inspiratory flow and maximum minute ventilation (VE) capabilities of five anesthesia ventilators (Ohio Anesthesia, Airshields Ventimeter, Ohmeda 7000, Draeger AV-E and Siemens 900D) was compared to identify mechanical factor(s) limiting intraoperative ventilation of the lungs of patients with acute respiratory failure. The effect of increasing airway pressure on mean inspiratory flow was determined by cycling each ventilator through increasing restrictors. Maximum VE was measured under three study conditions using a test lung: 1) low compliance (10-30 ml/cmH2O) and minimal airflow resistance; 2) positive end-expiratory pressure (PEEP) of 0, 10, and 20 cmH2O at a compliance of 20 ml/cmH2O with minimal airflow resistance; and 3) increased resistance (19 +/- 11 cmH2O.1(-1).s-1) and compliance of 30 ml/cmH2O. As airway pressure increased from 0 to 80 cmH2O, mean inspiratory flow decreased markedly for all ventilators except the Siemens. The Siemens ventilator delivered the greatest VE under all three conditions and maintained VE when airway pressure increased due to decreased compliance or the application of PEEP; all other ventilators markedly decreased VE under these conditions. The addition of airway resistance reduced maximal VE for all ventilators by limiting the maximal inspiratory duty cycle (T1/TTOT). Thus, mean inspiratory flow of conventional anesthesia ventilators decreases with increasing airway pressure. The decreased inspiratory flow limits maximum VE when airway pressure is elevated because of decreased lung-thorax compliance and/or increased airway resistance, such as that characterizing patients with acute respiratory failure. Significant airway resistance further limits maximum VE by limiting the maximal T1/TTOT that can be used without increasing end-expiratory lung pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1989

Management alternatives for post-polio respiratory insufficiency. Assisted ventilation by nasal or oral-nasal interface.

Post-poliomyelitis patients may develop insidious respiratory failure. Chronic alveolar hypoventilation symptoms are often misdiagnosed and the condition is frequently treated inappropriately by oxygen therapy. Physicians are often at a loss to offer assisted ventilation by noninvasive methods and tracheostomy and long-term tracheostomy intermittent positive pressure ventilation is often refused. We studied the use of two noninvasive positive airway pressure alternatives for the nocturnal ventilatory support of 31 post-poliomyelitis patients. These methods were intermittent positive pressure ventilation via nasal access (NIPPV) and via a strapless oral-nasal interface (SONI IPPV). The use of custom fabricated interfaces was also evaluated. Practical alternatives for assisted daytime ventilation included glossopharyngeal breathing, the pneumobelt ventilator and mouth intermittent positive pressure ventilation. Overnight sleep monitoring was performed on 10 patients breathing autonomously or with body ventilators then repeated on NIPPV and/or SONI IPPV. The mean sleep oxygen saturation (SaO2) increased from 87.5 +/- 9.1% on unassisted breathing or body ventilators to 96.2 +/- 2.0% (P less than 0.01) on NIPPV or SONI IPPV. Of 12 other patients with a mean vital capacity of 472 +/- 480 ml and no significant free time supine, 11 patients also maintained SaO2 greater than 94% during sleep supine on NIPPV and/or SONI IPPV. Twenty-one patients have been on nocturnal NIPPV for an average of 23 (3-70) months. Six have been on nocturnal SONI IPPV for an average of 35 (5-66) months. All patients' hypoventilation symptoms were relieved. In conclusion, NIPPV and SONI IPPV can improve the nocturnal ventilation of post-poliomyelitis patients with chronic alveolar hypoventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Lack of relationship between the true airway pressure and the pressure displayed with an infant ventilator.

OBJECTIVE: To establish if the pressure indicated in the manometer of an infant ventilator (IV 100B, Sechrist, Anaheim, CA) reflects the true pressure delivered to the proximal airway during mechanical ventilation in the neonatal ICU. DESIGN: With approval of our Institutional Research Board, data were collected prospectively. Peak inspiratory pressure and end-expiratory pressure were measured at the "Y" piece of the breathing tubing. Pressure readings from the conventional ventilator's manometer were compared with simultaneously obtained measurements using an electronic monitor. SETTING: This study was conducted in a 45-bed neonatal ICU, admitting 700 to 750 newborns per year. PATIENTS: Twelve neonates who required mechanical ventilation were included in the study. INTERVENTIONS: Specific interventions were not made by study design. Measurements routinely obtained were compared. MEASUREMENTS AND MAIN RESULTS: Two hundred seventy-five simultaneous measurements of peak inspiratory pressure and positive end-expiratory pressure were compared. Peak inspiratory pressure values were higher with the electronic monitor in 273 (99%) of 275 measurements and the mean of the differences between the electronic monitor and ventilator's manometer was statistically significant (p less than .001). For positive end-expiratory pressure measurements, values indicated by the electronic monitor were lower in 152 (55%) of 275 determinations, equal in 65 (23%), and higher in 58 (21%) determinations. Percent variations between methods ranged from 0% to 140% for peak inspiratory pressures and from 0% to 500% for positive end-expiratory pressure. CONCLUSIONS: These data demonstrate that it is impossible to know the true pressure delivered to the proximal airway of a neonate during mechanical ventilation by observing the ventilator pressure manometer. The manometer readings consistently underestimate the true peak inspiratory pressure values and are very unpredictable regarding positive end-expiratory pressure values. These findings support the use of other methods to monitor the proximal airway pressure besides the ventilator's manometer in the neonatal ICU. Furthermore, mean airway pressure should not be calculated from the pressure readings obtained from the tested ventilator's manometer.

Airway Resistance↗
PubMed2003

Effect of ventilatory variables on gas exchange and hemodynamics during total liquid ventilation in a rat model.

OBJECTIVES: To investigate the settings necessary to achieve maximum gas exchange and pulmonary function while minimizing effects on cardiovascular hemodynamics during total liquid ventilation with a pressure-limited, time-cycled ventilator in a rat model. DESIGN: Prospective, randomized controlled animal study. SETTING: A university research laboratory. SUBJECTS: Male Sprague-Dawley rats (n = 48). INTERVENTIONS: All animals had a tracheostomy tube designed for total liquid ventilation placed under anesthesia. The carotid artery was cannulated for blood pressure monitoring and for assessing blood gas data. MEASUREMENTS AND MAIN RESULTS: Forty 492 +/- 33 g rats were assigned to one of four inspiratory/expiratory ratio groups (inspiratory/expiratory ratio of 1:2, 1:2.5, 1:3, and 1:4). Total liquid ventilation was performed with a pressure-limited, time-cycled total liquid ventilator. Outcome measures were evaluated as a function of respiratory rate and included tidal volume, maximal alveolar ventilation, inspiratory and expiratory mean arterial pressures, the difference of mean arterial pressure between the inspiratory and expiratory phase, static end-inspiratory/expiratory pressures, Paco(2), Pao(2), tidal volume + approximate expiratory reserve volume, and lung volume-induced suppression of mean arterial pressure. Maximal alveolar ventilation increased and decreased in parabolic fashion as a function of respiratory rate and was maximal at rates of 4.3-6.8 breaths/min and high inspiratory/expiratory ratios that corroborated with optimal levels of Pao(2) and Paco(2). Lung overdistention occurred at high respiratory rates and high inspiratory/expiratory ratios. Deleterious effects were observed on the difference of mean arterial pressure between the inspiratory and expiratory phase during total liquid ventilation at low respiratory rates, apparently due to increased tidal volume, and on suppression of mean arterial pressure at high inspiratory/expiratory ratios and high respiratory rate apparently due to "auto-positive end-expiratory pressure." These effects were minimized in this model at respiratory rates >/=5.7 and </=6.8 breaths/min and inspiratory/expiratory ratios </=1:2.5. These settings were successfully tested in eight additional animals. CONCLUSION: These data demonstrate the feasibility of performing total liquid ventilation in rodents. A balance must be identified where gas exchange is optimal yet hemodynamics are least affected. In the specific system studied, an inspiratory/expiratory ratio of 1:2.5 and respiratory rate of 6.8 breaths/min appeared to provide optimal gas exchange while minimizing the effects on hemodynamics.

Animals↗