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PubMed1992

Pressure controlled-inverse ratio ventilation and pulmonary gas exchange during lower abdominal surgery.

Although pressure controlled-inverse ratio ventilation (PC-IRV) has been used successfully in the treatment of respiratory failure, it has not been applied to the treatment of respiratory dysfunction during anaesthesia. With PC-IRV the inspiratory wave form is fundamentally altered so that inspiratory time is prolonged (inverse I:E), inspiratory flow rate is low, and the peak inspiratory pressure is limited. Positive end-expiratory pressure (PEEP) can be applied and the mean airway pressure is higher than with conventional ventilation. To assess the clinical efficacy of this new mode of ventilation we studied ten patients having lower abdominal gynaecologic surgery in the Trendelenburg position under general anaesthesia. Pulmonary O2 exchange was determined during four steady states: awake control (AC), after 30 and 60 min of PC-IRV during surgery, and at the end of surgery. Patients' lungs were ventilated with air/O2 by a Siemens 900C servo ventilator in the PC-IRV mode with an I:E ratio of 2:1 and 5 cm H2O of PEEP. The FIO2 was controlled at 0.5 and arterial blood gases were used to calculate the oxygen tension-based indices of gas exchange. There were significant increases of (A-a) DO2 at 30 and 60 min (41 and 43%). These changes were less than those reported in a previous study using conventional tidal volume ventilation (7.5 ml.kg-1) and were similar to those in patients whose lungs were ventilated with high tidal volumes (12.7 ml.kg-1). Thus, in this clinical model of compromised gas exchange, arterial oxygenation was better with PC-IRV than with conventional ventilation, but not better than with large tidal volume ventilation.

Abdomen↗
PubMed2006

A meta-analysis of noninvasive weaning to facilitate liberation from mechanical ventilation.

PURPOSE: To summarize the evidence comparing noninvasive positive pressure ventilation (NPPV) and invasive positive pressure ventilation (IPPV) weaning on mortality, ventilator associated pneumonia and the total duration of mechanical ventilation among invasively ventilated adults with respiratory failure. SOURCE: Meta-analysis of randomized and quasi-randomized studies comparing early extubation with immediate application of NPPV to IPPV weaning. We selected randomized studies that 1) included adults, with respiratory failure, invasively ventilated for at least 24 hr; 2) compared extubation with immediate application of NPPV to weaning using IPPV; and 3) reported at least one clinically important outcome. PRINCIPAL FINDINGS: We searched MEDLINE (1966 to 2003), EMBASE (1980 to 2003) and the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 2, 2003) for randomized controlled trials comparing NPPV and IPPV weaning. Additional data sources included personal files, conference proceedings and author contact. Two reviewers independently assessed trial quality and abstracted data. Five studies enrolling 171 patients demonstrated that compared to IPPV, noninvasive weaning decreased mortality (relative risk, 0.41 [95% confidence interval [CI] 0.22-0.76]), ventilator associated pneumonia (relative risk, 0.28 [95% CI 0.09-0.85]) and the total duration of mechanical ventilation (weighted mean difference, -7.33 days [95% CI -11.45 to -3.22 days]). CONCLUSIONS: In the absence of a large randomized controlled trial, this meta-analysis demonstrated a consistent positive effect of noninvasive weaning on mortality. Notwithstanding, the use of NPPV to facilitate weaning, in mechanically ventilated patients, with predominantly chronic obstructive pulmonary disease, is associated with promising, but insufficient, evidence of net clinical benefit at present.

Humans↗
PubMed1994

[Jet ventilation superimposed on a special jet laryngoscope for endoluminal stent insertion in the tracheobronchial system].

BACKGROUND: Stenotic processes of the tracheobronchial system may lead to dyspnoea that can become lift-threatening. To restore sufficient function of the blocked airway, a silicone stent can be inserted. The anaesthesia techniques used for this intervention so far have been complicated. The object of this study was to determine whether the super-imposed high-frequency jet ventilation (SHFJV) via the jet laryngoscope originally designed for microlaryngeal surgery can be utilized for endoluminal stent insertion. METHODS: In 12 patients with acute respiratory insufficiency (ASA 3-5) due to stenosis of the tracheobronchial system, an endoluminal silicone stent was inserted through the jet laryngoscope while the patient was ventilated using SHFJV: RESULTS: A significant rise in paO2 readings prior to the jet ventilation and subsequent measurements was observed. The CO2 elimination was good (average paCO2 31.5 +/- 7.5-53.1 +/- 14 mmHg). Variably high paCO2 readings during stent insertion were related to the respective surgical phases. At the end of the surgical manipulation, all patients had sufficient spontaneous ventilation. CONCLUSIONS: First clinical applications of the jet laryngoscope combined with superimposed jet ventilation for stent insertion demonstrated satisfactory results. Not only were the patients ventilated throughout the procedure, but CO2 elimination was also satisfactory. Superimposed jet ventilation provides a sufficient tidal volume with low ventilation pressures, and therefore oxygenation and CO2 elimination are unproblematic. SHFJV enables the anaesthetist to ventilate the patient nearly continuously with minimal phases of apnoea. The only apnoea phases, as with any other method, occur during surgical manipulation while inserting the stent and thus blocking the airway. We believe that the jet laryngoscope with SHFJV presents a distinct advantage for both anaesthetist and surgeon when inserting stents in the tracheobronchial system.

Acute Disease↗
PubMed1996

[Ventilation-perfusion ratio in patients with acute respiratory insufficiency].

UNLABELLED: Acute respiratory failure is characterised by mismatch of ventilation with perfusion (VA/Q). The multiple inert gas elimination technique (MIGET) is a complex method which allows the description of a virtually continuous distribution of VA/Q ratios. We investigated VA/Q relationships in patients admitted to the intensive care unit due to acute respiratory failure and thus requiring for mechanical ventilation. METHOD: Eight patients (mean APACHE 11 = 22 +/- 4) who suffered from acute pneumonia (n = 4), traumatic lung contusion (2), toxic lung failure (1) or massive bilateral atelectasis (1) were investigated by MIGET within 3 days after the begin of mechanical ventilation. A mixture of six inert gases, dissolved in isotonic saline, was infused continuously. Arterial and mixed venous blood samples and expired gas samples were obtained and analysed by gas chromatography. Blood-gas partition coefficients were determined, and the ratios of retention and excretion were calculated. The data were transformed in a 50-compartment model of blood flow and ventilation against VA/Q ratio. We assessed the amount of intrapulmonary shunt (VA/Q = 0), low VA/Q regions (VA/Q = 0.005-0.1), normal VA/Q regions (VA/Q = 0.11-10), high VA/Q regions (VA/Q = 11-100) and dead space ventilation (VA/Q > 100). Furthermore, we calculated the logarithmic standard deviation of pulmonary perfusion distribution (logSDQ). RESULTS: In all patients we found moderate to severe intrapulmonary shunt and VA/Q mismatching. The data are expressed as median values and ranges. Inert-gas-measured shunt was 21% (3-45.5%), whereas low VA/Q regions were little affected. Normal VA/Q regions ranged from 41.5% to 96.0% (median 76.8%). The amount of alveolar dead space ventilation was 28% (19.7-41.8%). Median logSDQ (normal range 0.3-0.6) was calculated to be 0.855 (0.540-1.490). In patients presenting with moderate lung injury (Murray score < 3), a moderate increase in shunt and a moderate VA/Q mismatch were observed. In contrast, patients with severe lung failure and critically decreased oxygenation (Murray score > 3) were characterised by massive shunting and VA/Q mismatching. Additionally, low VA/Q and high VA/Q compartments and an increase in dead space ventilation was found in these patients. CONCLUSIONS: The impairment of oxygenation in patients with acute respiratory failure is due to several pathophysiological mechanisms: increase in intrapulmonary shunt, VA/Q-mismatching and dead space ventilation, according to the severity of lung failure. We conclude from our results that the prevention and/or reduction of non-ventilated lung areas (atelectasis) is an outstanding therapeutic strategy in the treatment of patients with acute respiratory failure. From this point of view, several techniques of systemic changes in body position should be integrated as supportive therapeutic strategies.

APACHE↗
PubMed2004

Infectious and inflammatory dissemination are affected by ventilation strategy in rats with unilateral pneumonia.

OBJECTIVE: To evaluate the effect of V(T) reduction and alveolar recruitment on systemic and contralateral dissemination of bacteria and inflammation during right-side pneumonia. DESIGN: Interventional animal study. SETTING. University hospital research laboratory. SUBJECTS: A total of 54 male Wistar rats. INTERVENTIONS: One day after right lung instillation of 1.4x10(7) Pseudomonas aeruginosa, rats were left unventilated or ventilated for 2 h at low V(T) (6 ml/kg) with different strategies of alveolar recruitment: no PEEP, 8 cm H(2)O PEEP, 8 cm H(2)O PEEP in a left lateral position, 3 cm H(2)O PEEP with partial liquid ventilation, or high V(T) (set such as end-inspiratory pressure was 30 cm H(2)O) without PEEP (ZEEP). After ventilation the lungs, spleen and liver were cultivated for bacterial counts. Global bacterial dissemination was scored considering the percentage of positive spleen, liver and left lung cultures. TNF-alpha was assayed in plasma before and after mechanical ventilation. MEASUREMENTS AND RESULTS: All rats had right-side pneumonia with similar bacterial counts. All mechanical ventilation strategies, with the exception of low V(T)-PEEP 8, promoted contralateral lung dissemination. Overall bacterial dissemination was less in non-ventilated controls (22%) and low V(T)-PEEP 8 (22%) than in high V(T)-ZEEP (67%), low V(T)-PEEP 8 in left lateral position (59%) and low V(T)-ZEEP (56%) ( p<0.05). Partial liquid ventilation prevented systemic bacterial translocation, but at the expense of contralateral bacterial seeding. Plasma TNF-alpha concentration increased significantly after mechanical ventilation with no PEEP at both high and low V(T). CONCLUSIONS: Our results suggest that PEEP might reduce the risk of ventilation-induced bacterial and inflammatory mediator dissemination during pneumonia.

Animals↗
PubMed2002

Prolonged ventilation and intact survival in very low birth weight infants.

UNLABELLED: A requirement for prolonged ventilation (>28 days) has been associated with a poor outcome in infants. We postulated that in the present population of infants who usually receive antenatal steroids and post-natal surfactant, prolonged ventilation in discrete episodes, i.e. discontinuous intermittent positive pressure ventilation (IPPV), would have a better outcome than a requirement for prolonged ventilation continuously from birth (continuous IPPV) and, in addition, that an abnormal ultrasound scan appearance would be a reliable predictor of poor outcome in infants requiring prolonged ventilation. All very low birth weight (VLBW) infants ventilated for at least 28 days (prolonged ventilation) were identified from a prospectively maintained database. At 1 year of age, neurodevelopmental status was assessed and abnormal neurodevelopmental outcome diagnosed if the infant's Griffiths developmental quotient was at least two standard deviations below the mean and/or they had impairment with disability. Of 417 VLBW infants, 41 required prolonged ventilation (30 continuous and 11 discontinuous). In the continuous IPPV group, 18 and one in the discontinuous IPPV group died or had abnormal neurodevelopmental outcome ( P<0.01). All eight infants with major cranial ultrasound abnormalities died or had abnormal outcome ( P<0.01). CONCLUSION: prolonged ventilation can be associated with intact survival, but not in very low birth weight infants with evidence of significant brain injury.

Chi-Square Distribution↗
PubMed2006

Ventilator Y-piece pressure compared with intratracheal airway pressure in healthy intubated children.

OBJECTIVE: Compare airway pressure measurements at the ventilator Y-piece of the breathing circuit (P( Y )) to intratracheal pressure measured at the distal end (P( T )) of the endotracheal tube (ETT) during mechanical ventilation and spontaneous breathing of intubated children. METHODS: Thirty children (age range 29 days to 5 years) receiving general anesthesia were intubated with an ETT incorporating a lumen embedded in its sidewall that opened at the distal end to measure P( T ). Peak inflation pressure (PIP) was measured at P( Y ) and P( T ) during positive pressure ventilation. Just before extubation, all measurements were repeated and imposed resistive work of breathing (WOBi) was calculated at both sites while breathing spontaneously. RESULTS: Average PIP was approximately 25% greater at P( Y ) (19.7 +/- 3.4 cm H(2)O) vs. P( T ) (15.0 +/- 2.9 cm H(2)O), p < 0.01. During spontaneous inhalation P( T ) was 59% lower ({bond}8.5 +/- 4.0 cm H(2)O) vs. P( Y ) ({bond}3.5 +/- 2.0 cm H(2)O), p < 0.01. WOBi measured at P( Y ) (0.10 +/- 0.02 Joule/L) was 86% less than WOBi measured at P( T ) (0.70 +/- 0.40 Joule/L), p < 0.01. CONCLUSIONS: In healthy children P( Y ) significantly overestimates PIP in the trachea during positive pressure ventilation and underestimates the intratracheal airway pressure during spontaneous inhalation. During positive pressure ventilation P( T ) better assesses the pressure generated in the airways and lungs compared to P( Y ) because P( T ) also includes the difference in airway pressure across the ETT tube due to resistance. During spontaneous inhalation, P( T ) reflects the series resistance of the ETT and ventilator circuit, while P( Y ) reflects only the resistance of the ventilator circuit, accounting for the smaller decreases in pressure. Additionally, P( Y ) underestimates the total WOBi load on the respiratory muscles. Thus, P( T ) is a more accurate reflection of pulmonary airway pressures than P( Y ) and suggests that it should be incorporated into ventilator systems to more accurately trigger the ventilator and to reduce work of breathing.

Anesthesia, General↗
PubMed1993

The design and implementation of a ventilator-management advisor.

VentPlan is an implementation of the architecture developed by the qualitative-quantitative (QQ) research group for combining qualitative and quantitative computation in a ventilator-management advisor (VMA). VentPlan calculates recommended settings for four controls of a ventilator by evaluating the predicted effects of alternative ventilator settings. A belief network converts clinical diagnoses to distributions on physiologic parameters. A mathematical-modeling module applies a patient-specific mathematical model of cardiopulmonary physiology to predict the effects of alternative ventilator settings. A decision-theoretic plan evaluator ranks the predicted effects of alternative ventilator settings according to a multiattribute-value model that specifies physician preferences for ventilator treatments. Our architecture allows VentPlan to interpret quantitative observations in light of the clinical context (such as the clinical diagnosis). We report a retrospective study of the ventilator-setting changes encountered in postoperative patients in a surgical intensive-care unit (ICU). We conclude that the QQ architecture allows VentPlan to apply a patient-specific physiologic model to calculate ventilator settings that are optimal with respect to a decision-theoretic value model describing physician preferences for setting the ventilator.

Algorithms↗
PubMed2004

A small animal model of regional alveolar ventilation using HP 3He MRI1.

RATIONALE AND OBJECTIVES: The aim of this study was to establish a standardized procedure for the measurement of regional fractional ventilation in a healthy rat model as a baseline for further studies of pulmonary disorder models. MATERIALS AND METHODS: The lungs of five healthy male Sprague-Dawley rats were imaged using hyperpolarized helium-3 magnetic resonance imaging. From these images, regional fractional ventilation was calculated and maps generated detailing the distribution of fractional ventilation in the lung. The 1.56 mm x 1.56 mm x 4 mm regions of interest were assigned on 5 cm x 5 cm field of view lung maps. Histograms were also generated showing the frequency distribution of fractional ventilation values. To compare fractional ventilation values between animals, the ventilation procedure was standardized to results from individual pulmonary function tests. Each animal's spontaneous tidal volume, respiratory rate, and inspiration percentage (percent of total respiratory cycle in inspiration) were used in their mechanical ventilation settings. RESULTS: Results were similar among all five healthy rats based on examination of ventilation distribution maps and frequency distribution histograms. Mean (0.13) and standard deviation (0.07) were calculated for fractional ventilation in each animal. However, these values were determined to be influenced by slice selection, and therefore the maps and histograms were favored in analysis of results. CONCLUSION: This study shows consistent results in healthy rat lungs and will serve as a baseline study for future measurements in emphysematous rat lungs.

Animals↗
PubMed2004

Weaning from ventilator after cardiac operation using the Ciaglia percutaneous tracheostomy.

OBJECTIVE: To determine the predictors of weaning from mechanical ventilation after cardiac operation with the Ciaglia percutaneous dilatational tracheostomy (PDT) in our preliminary experience in the use of this technique. METHODS: We prospectively analysed 33 consecutive patients (mean age 70.9+/-12.7 years) who underwent PDT in our intensive care unit after cardiac operation. The investigation involved preoperative and postoperative clinical status, operative procedure, indication and timing for PDT. RESULTS: PDT was performed after a mean time of 7.7+/-5.0 consecutive days of translaryngeal intubation. Twenty-four (73%) patients were weaned from ventilator after a mean time of mechanical ventilation of 15.8+/-9.1 days. Time point of PDT was the only predictor of ventilator weaning (P=0.0029): there was significant association between PDT performed before the seventh consecutive day of translaryngeal intubation (early PDT) and successful weaning from ventilator (P=0.01; odds ratio=11.2, 95% confidence interval=1.2-104.3). Among the patients weaned from ventilator, those who underwent early PDT had significantly shorter times of mechanical ventilation, and intensive care unit and hospital stays than patients with later PDT (P=0.035, 0.011 and 0.0073, respectively). Nine (27%) patients died of their underlying disease while still being mechanically ventilated; another six (18%) spontaneously breathing but still incannulated patients died afterward. No major PDT-related complications were observed. Two minor peristomal bleedings and one self-resolving subcutaneous emphysema were recorded. CONCLUSIONS: Early PDT was a safe and effective method to wean from mechanical ventilation the cardiosurgical patients of this series.

Aged↗
PubMed1989

Pulmonary function in preterm infants whose lungs were ventilated conventionally or by high-frequency oscillation.

To test the hypothesis that high-frequency ventilation may reduce the risk of barotrauma and thus the incidence of chronic pulmonary damage in preterm infants who need mechanical ventilation, we measured lung function before discharge in 53 infants who needed mechanical ventilation on the first day after birth and were randomly assigned to receive intermittent mandatory ventilation (n = 26) or to receive high-frequency oscillatory ventilation (n = 27). There were no significant differences between the groups in birth weight (mean +/- SD: 1010 +/- 240 vs 1030 +/- 230 gm), gestational age (29.1 +/- 2.0 vs 28.9 +/- 2.1 weeks), initial ventilatory support (mean airway pressure 7.2 +/- 1.8 vs 8.1 +/- 2.1 cm H2O; FiO2 0.62 +/- 0.24 vs 0.75 +/- 0.22), duration of mechanical ventilation (median (range): 6 (1 to 61) vs 10 (1 to 50) days) and duration of oxygen therapy (13 (1 to 109) vs 27 (4 to 227) days) for the intermittent mandatory ventilation group and the high-frequency oscillatory ventilation group, respectively. At the time of testing, weight was 1830 +/- 340 vs 1830 +/- 290 gm, and age was 68 +/- 24 vs 70 +/- 31 days. Respiratory flows were determined by pneumotachygraphy, esophageal pressure through a water-filled feeding tube, and functional residual capacity by N2 washout. Both groups had abnormal lung function with decreased lung compliance (1.65 +/- 0.51 vs 1.54 +/- 0.36 ml/cm H2O) and elevated pulmonary resistance (102 +/- 24 vs 107 +/- 36 cm H2O/L/sec). Functional residual capacity was in the normal range (30.6 +/- 6.0 vs 28.2 +/- 10.7 ml) in both groups. There were no significant differences in lung function between the two treatment groups. These results do not support the hypothesis that high-frequency oscillatory ventilation reduces the risk of lung damage in preterm infants.

Female↗
PubMed2001

Changes in external ear resonance after ventilation tube (Grommet) insertion in children with otitis media with effusion.

OBJECTIVE: As otitis media with effusion is common in children, the effects of a ventilation tube should be taken into account in the prescription of hearing aids for children. In ears with a ventilation tube, the external auditory canal communicates directly with the middle ear space, and so the impedance of the middle ear may change. Consequently, this will affect external-ear resonance. The aim of this study is to observe the effects of the tympanic membrane perforations caused by the ventilation tube on external-ear resonance. We selected 30 ears with otitis media with effusion to measure external-ear resonance before and after ventilation tube insertion. We compared the external-ear resonance of a control group with that of the otitis media with the effusion group and two types of ventilation-tube groups, respectively. In the subjects who have otitis media with effusion, the average gain of the peak resonance was larger than that in the control group. After ventilation-tube insertion, the amplitude of the gain decreased to the same level as the control group, but a characteristic negative gain appeared around 1000 Hz in about half of all cases. This negative gain was observed more frequently in the ventilation tube with a larger diameter. The raised peak resonance gain in the otitis media with effusion group decreased to a level roughly the same as that of the control group after ventilation-tube insertion. Provision of an additional gain in the low frequencies around 1000 Hz should be considered for patients with a ventilation tube when prescribing hearing aids.

Acoustic Stimulation↗
PubMed1998

Noninvasive ventilation in neuromuscular disease.

The treatment of respiratory failure in patients who have NMD continues to be an evolving process. Negative-pressure ventilation, once prominent in the 1940s and 1950s, gave way to intermittent positive-pressure ventilation with tracheostomy or endotracheal tubes in the 1960s. Now there is a resurgence of noninvasive ventilation, brought about by innovative modes of positive pressure delivered through nasal and facial masks. Although frequently relegated to second-line choices, negative-pressure devices still offer a practical treatment alternative as patient preference still plays a role in selecting a proper mode of ventilation. Studies have shown that noninvasive ventilation can prevent or reverse respiratory failure and improve quality of life and longevity. Despite the seemingly widespread acceptance of noninvasive ventilation in the treatment of respiratory failure, physicians still appear reluctant to use ventilatory assistance in the neuromuscular arena. In 1985, a survey found that respiratory support systems were utilized routinely in only 33% of the 132 responding Muscular Dystrophy Association (MDA) clinics. Bach recently surveyed 273 MDA clinic directors and co-directors from 167 clinics, to evaluate their current use of mechanical ventilation. Ventilatory assistance was recommended and used electively in only 43 (26%) of the 167 clinics. Furthermore, it was the policy in 68 of the clinics to discourage the use of mechanical ventilation. Even more importantly, only 2 physicians who discouraged the use of mechanical ventilation were familiar with the newest noninvasive methods of ventilatory support. Sadly, although our methodologies in the treatment of respiratory failure continue to improve, physician practice has lagged behind. Physicians who treat patients who have NMD need to become cognizant of these new techniques and incorporate them into their present therapeutic armamentarium.

Humans↗
PubMedDate not supplied

Gas-powered and portable ventilators: an evaluation of six models.

INTRODUCTION: Gas-powered resuscitators (ventilators) designed to be used primarily for resuscitation should be basic and simple to use. They offer many advantages over manual methods of ventilation during in-hospital cardiopulmonary resuscitation. Portable ventilators intended for critical care transport require additional, more sophisticated features such as: adjustable pressure limiting valves, air-mixing, airway pressure gauge, independent tidal volume and rate controls, and a Positive End-Expiratory Pressure (PEEP) valve. The performance of six gas-powered resuscitators/portable ventilators (TransPAC, Oxylog, Ambu Matic, ERA 2000, Uni-Vent, and MARS) was evaluated. METHODS: The accuracy of volumes delivered to a test lung at three different compliance and resistance settings, was assessed for each ventilator prior to clinical evaluation during cardio-pulmonary resuscitation (CPR) and patient transport. RESULTS: In each circumstance, measured tidal volumes and level of minute ventilation decreased as resistance was increased and compliance reduced. Much of this loss of measured tidal volume occurred through inspiratory pressure relief valves that tended to start leaking at pressures below the preset level. Increasing levels of back-pressure resulted in further reductions in tidal volume when the ventilators were tested using the air-mix mode (available on three of the devices). In general, each resuscitator functioned well when used during CPR within the hospital. CONCLUSIONS: Each resuscitator tested failed to deliver the preset volumes and this must be considered during their use. Inspiratory pressure relief valves for all but one of the ventilators tested would not permit the delivery of adequate levels of ventilation in patients with low pulmonary compliance and/or high airway resistance.

Electric Power Supplies↗
PubMed1997

Bench test assessment of dosage accuracy and measurement inaccuracy in nitric oxide inhalational therapy during high frequency oscillatory ventilation.

OBJECTIVE: The objective of this study is to determine the accuracy and precision of chemiluminescence and electrochemical nitric oxide (NO) measurements and accuracy of NO dosage with electronic mass flow controllers (MFC) versus rotameters during NO inhalational therapy. METHODS: NO flow was delivered to a high frequency oscillator and mixed with ventilator flow. NO and NO2 concentrations were measured simultaneously with a standard chemiluminescence analyzer and a modified electrochemical analyzer. Dosage accuracy was assessed with gas flows adjusted with either MFC's or rotameters. Accuracy of both analyzers was validated with both NO and ventilator flow regulated with a MFC. RESULTS: In dry air, without pulsatile pressure, MFC controlled NO and ventilator flow resulted in an accuracy expressed as the ratio of calculated concentration to measured concentration (RCM) of 0.995 (CI: 0.983-0.988) when measured with chemiluminescence. When the ventilator rotameter was used instead of a MFC, RCM was 0.856 (CI: 0.835-0.877). With a rotameter for both NO and ventilator flow, RCM increased to 1.175 (CI: 0.793-1.740) with an increase of confidence interval limits. Chemiluminescence was sensitive to humidification of the ventilatory gases (p < 0.05), slightly sensitive to the addition of oxygen and to pulsatile pressure (not significant). RCM obtained with the modified electrochemical analyzer was in close agreement with chemiluminescence RCM, although 95% CI were wider with electrochemical analysis. CONCLUSIONS: During high frequency oscillatory ventilation (HFOV), standard rotameter flow control of both NO and ventilator flow results in unpredictable NO concentrations that would be clinically unacceptable. When one MFC was used for NO flow control, with ventilator flow controlled with a rotameter, this resulted in moderate dosage accuracy. To achieve a still higher accuracy, MFC flow control for both NO and ventilator flow is indicated. During HFOV, standard chemiluminescence analyzers cannot be considered to be the gold standard for determination of the NO concentration delivered. Measurement of NO concentration may not be mandatory for determination of inhaled NO dose during HFOV, but may be used to monitor for unsafe or unwanted events.

Administration, Inhalation↗
PubMed1999

Effects of chemical feedback on respiratory motor and ventilatory output during different modes of assisted mechanical ventilation.

The purpose of the study was to examine the effects of chemical feedback on respiratory motor and ventilatory output in conscious subjects ventilated on various modes of assisted mechanical ventilation. Seven subjects were connected to a ventilator and randomly ventilated on assist-volume control (AVC), pressure support (PS) or proportional assist ventilation (PAV). On each mode, the assist level was set to the highest comfortable level. Airway and oesophageal (Poes) pressures, tidal volume, respiratory frequency (fR) and end-tidal carbon dioxide tension (PET,CO2) were measured breath-by-breath. When the subjects were stable on each mode, the fraction of inspired carbon dioxide (FI,CO2) was increased stepwise, and changes in minute ventilation (V'E) and respiratory motor output, estimated by the pressure-time product of all the respiratory muscles per breath (PTPrm) and per minute (PTPminute), were observed. At zero FI,CO2, PTPminute/PET,CO2 did not differ between modes, while V'E/ PTPminute was significantly lower with PAV than that with PS and AVC. As a result V'E/PET,CO2 was significantly lower with PAV, preventing, unlike AVC and PS, a significant drop in PET,CO2. With PAV, independent of CO2, V'E/PTPminute remained constant, while it decreased significantly with increasing CO2 stimulus with PS and AVC. At high PET,CO2 respiratory effort was significantly lower with PAV than that with PS and AVC. In conclusion, the mode of mechanical ventilation modifies the effects of chemical feedback on respiratory motor and ventilatory output. At all carbon dioxide stimulus levels neuroventilatory coupling was better preserved with proportional assist ventilation than with pressure support and assist-volume control ventilation.

Adult↗
PubMed2000

Weaning from mechanical ventilation.

Patients that require positive pressure ventilation to maintain sufficient alveolar ventilation or pulmonary gas exchange may eventually reach a point in the course of their care wherein mechanical ventilation is no longer necessary. This process of transferring the work of breathing from the ventilator back to the patient is referred to as ventilator weaning. The term "ventilator weaning" may be used to refer to all methods by which this transfer of workload may be accomplished. In many patients, particularly those with short-lasting or readily correctable causes of respiratory insufficiency (e.g., general anesthesia), the discontinuation of positive pressure ventilation may be easily achieved. Indeed, in patients awakening from general anesthesia, the axiom "awake enough to blink, awake enough to breath" may prove to be a sufficient guideline. However, in those patients requiring long-term mechanical ventilatory support, the process can prove to be both frustrating and exceptionally challenging. It is of crucial importance to identify those patients that may be successfully weaned because of both the financial impact of prolonged intensive care unit hospitalization and the risks imposed on the patient by the process of positive pressure ventilation. To be able to predict which patients may be ready to be weaned from the ventilator requires an understanding of the balance between the work of breathing (ventilatory load) and the ability of the patient's respiratory pump to meet those needs (ventilatory capacity). The management of patients experiencing difficulty during the weaning process requires that the clinician recognize imbalances between ventilatory load and capacity and to correct these imbalances once identified.

Algorithms↗
PubMed2002

Effect of ventilator-induced lung injury on the development of reperfusion injury in a rat lung transplant model.

OBJECTIVE: Although mechanical ventilation can potentially worsen preexisting lung injury, its importance in the setting of lung transplantation has not been explored. This study was undertaken to examine the effect of 2 ventilatory strategies on the development of ischemia-reperfusion injury after lung transplantation. METHODS: In a rat lung transplant model animals were randomized into 2 groups defined by the ventilatory strategy during the early reperfusion period. In conventional mechanical ventilation the transplanted lung was ventilated with a tidal volume equal to 50% of the inspiratory capacity of the left lung and a low positive end-expiratory pressure. In minimal mechanical stress ventilation the transplanted lung was ventilated with a tidal volume equal to 20% of the inspiratory capacity of the left lung, and positive end-expiratory pressure was adjusted according to the shape of the pressure-time curve to minimize pulmonary stress. RESULTS: After 3 hours of reperfusion, oxygenation from the transplanted lung was significantly higher with minimal mechanical stress ventilation than with conventional ventilation. In addition, elastance, cytokine levels, and morphologic signs of injury were significantly lower in the group with minimal mechanical stress ventilation. CONCLUSIONS: This study demonstrates that the mode of mechanical ventilation used in the early phase of reperfusion of the transplanted lung can influence ischemia-reperfusion injury, and a protective ventilatory strategy on the basis of minimizing pulmonary mechanical stress can lead to improved lung function after lung transplantation.

Animals↗