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PubMed2001

[Time for extubation and sequential noninvasive mechanical ventilation in COPD patients with exacerbated respiratory failure who received invasive ventilation].

OBJECTIVE: To discuss the optimal time for extubation and sequential non-invasive mechanical ventilation in COPD patients with exacerbated respiratory failure who received invasive ventilation. METHODS: 24 patients received invasive ventilation for 3 days were randomly assigned to receive noninvasive ventilation (study group) or to continue the weaning process with invasive ventilation (control group). The incidence of ventilator-associated pneumonia (VAP), the incidence of death, the duration of ventilation, the hospitalization were analyzed in two groups. RESULTS: Between study group and control group, the incidence of VAP was 0/12 vs 7/12, P = 0.027; the incidence of death was 0/12 vs 3/12, P = 0.217; the continued duration of ventilation after invasive ventilation for 3 days was (7 +/- 5) days vs (15 +/- 12) days, P < 0.05; the hospitalization was (16 +/- 6) days vs (25 +/- 12) days, P < 0.05, respectively. CONCLUSIONS: In COPD patients with exacerbated respiratory failure who received invasive ventilation, invasive ventilation for 3 days followed by noninvasive ventilation may decrease the incidence of VAP, shorten the duration of ventilation and hospitalization.

Aged↗
PubMed2001

[Comparison of volume preset and pressure preset ventilators during daytime nasal ventilation in chronic respiratory failure].

Both volume preset and pressure preset ventilators are available for domiciliary nasal ventilation. Owing to their technical characteristics, it has been suggested that impaired ventilatory mechanics might cause a drop in the tidal volume (Vt) delivered by pressure preset devices, thereby placing mechanical ventilation at risk of inefficacy. We have assessed two ventilator systems (one pressure preset and one volume preset) with regard to the tidal volume and end-tidal carbon dioxide tension (PetCO(2)) changes that may be achieved in a group of awake patients with stable chronic respiratory failure (CRF). Eleven patients with stable CRF were ventilated in the assist/control mode for two consecutive one-hour periods. One ventilator was tested each hour, in random order. The VIGIL'AIR(R) system was used to record Vt, Respiratory Rate (RR), and Inspiratory/Expiratory ratio (I/E). The deviation E (E=preset value - measured value) was calculated for each measurement. Changes in PetCO(2) and arterial oxygen saturation were determined respectively by a capnometer and a pulse oximeter. Comparison of the mean deviation of Vt calculated for the two ventilators revealed a difference in patients with chronic obstructive pulmonary disease (COPD). The deviation was greatest with the pressure preset ventilator (PPV), which gave mean measured values higher than the mean preset values. The same comparison failed to reveal any difference in restrictive CRF. Comparison of the volume preset and pressure preset ventilators for RR, I/E and PetCO(2) did not reveal any difference. Compared to the volume preset ventilator, the efficacy of PPV to ventilate is not affected by the restrictive or obstructive nature of CRF. Our results show that pressure-preset ventilator is an adequate alternative to the volume-preset device for daytime non invasive ventilation in chronic respiratory insufficiency.

Aged↗
PubMed2006

Preferences for mechanical ventilation among survivors of prolonged mechanical ventilation and tracheostomy.

BACKGROUND: Among survivors of prolonged mechanical ventilation, preferences for this treatment have rarely been explored. OBJECTIVES: To elicit preferences of survivors of prolonged mechanical ventilation (>or=7 days) and factors influencing these preferences. METHODS: A descriptive, cross-sectional survey design was used. Subjects were recruited from intensive care units in a tertiary care hospital and from long-term care facilities. Each subject (n = 30) was asked to reflect on the decision to use mechanical ventilation; rate current health, pain/discomfort in the intensive care unit and from mechanical ventilation, perceived family financial burden, and emotional/physical stress related to mechanical ventilation; identify changes that would influence preference for mechanical ventilation; and answer questions about quality of life, functional status, depressive symptoms, and communication. RESULTS: Most subjects (75.9%) would have chosen mechanical ventilation. Median days of mechanical ventilation and tracheostomy were greater for subjects who would have chosen mechanical ventilation (98.5 vs 70), as were median days of tracheostomy (102 vs 64). Patients who would not have chosen mechanical ventilation had more depressive symptoms and were more likely to be insured by Medicare. No other variables differed between groups. Patients who preferred mechanical ventilation would change their preference on the basis of their families' emotional/physical stress and financial burden. Patients who did not prefer mechanical ventilation would change their preference if the family financial burden and emotional/physical stress were reduced and current health improved. CONCLUSIONS: Most patients would have chosen mechanical ventilation. Survivors' preferences were influenced by their current health and families' financial burden and stress.

Adult↗
PubMed2003

Use of high-frequency jet ventilation in neonates with hypoxemia refractory to high-frequency oscillatory ventilation.

OBJECTIVE: To describe the response to high-frequency jet ventilation in infants with hypoxemic respiratory failure unresponsive to high-frequency oscillatory ventilation. METHODS: This was a retrospective analysis of chart records on demographics, ventilator settings, blood gas analysis and calculated oxygenation index prior to and during the first 7 days of high-frequency jet ventilation in ten consecutive infants. RESULTS: Before the initiation of high-frequency jet ventilation, the ventilatory mean airway pressure (MAP; cmH2O), fraction of inspired oxygen (FiO2) and oxygenation index on high-frequency oscillatory ventilation were 14.3 +/- 1.3, 0.97 +/- 0.02 and 29 +/- 5, respectively. Three hours after the initiation of high-frequency jet ventilation, the oxygenation index improved to 18 +/- 4 (p < 0.001) and the improvement was sustained during the study period. By 6 h of high-frequency jet ventilation, the FiO2 decreased to 0.62 +/- 0.09 (p < 0.01) and, by 1-3 h of ventilation, the MAP decreased to 10.9 +/- 1.3 (p < 0.01). The improvement in FiO2 persisted for 7 days while, although the MAP remained lower throughout the study, the improvement in MAP failed to reach statistical significance after 72 h. No significant changes in pH, pCO2, or pO2 before or during high-frequency jet ventilation were noted. CONCLUSION: High-frequency jet ventilation improves hypoxemic respiratory failure unresponsive to high-frequency oscillatory ventilation in infants. These findings suggest that not all high-frequency ventilatory devices yield the same clinical results.

Airway Resistance↗
PubMed1998

Respiratory muscle performance, pulmonary mechanics, and gas exchange between the BiPAP S/T-D system and the Servo Ventilator 900C with bilevel positive airway pressure ventilation following gradual pressure support weaning.

STUDY OBJECTIVE: Our objective was to compare respiratory muscle performance, pulmonary mechanics, and gas exchange between the BiPAP S/T-D ventilation system (Respironics Inc; Murrysville, PA) and the Servo Ventilator 900C (Siemens-Elma AB; Sweden) with similar inspiratory and expiratory airway pressure in patients who are recovering from acute respiratory failure. STUDY DESIGN: A prospective, randomized, clinical trial. SETTING: Medical ICU. PATIENTS AND METHODS: We studied 27 medical patients on mechanical ventilators following gradual pressure support weaning. Each patient breathed while in the following equivalent modes: (a) an inspiratory pressure preset (pressure support mode) of 5 cm H2O with an external positive end-expiratory pressure (PEEP) of 5 cm H2O on the Servo Ventilator 900C and (b) an inspiratory pressure preset of 10 cm H2O with an expiratory pressure preset of 5 cm H2O on the BiPAP S/T-D. Using the CP-100 pulmonary monitor, we compared the total work of breathing (WOB), the pressure-time index (PTP), and other pulmonary mechanics and gas exchange parameters between the two modes. RESULTS: The WOB injoules per liter (mean +/- SE) (0.76+/-0.08 vs 0.73+/-0.08, p = 0.70), the WOB in joules per minute (8.62+/-1.06 vs 8.11+/-0.96, p = 0.60), and the PTP in cm H2O/s/min (187+/-18 vs 167+/-18, p = 0.21) between the BiPAP S/T-D and the Servo Ventilator 900C were not statistically different. There were statistically significant differences between the two ventilators in auto-PEEP (1.34+/-0.37 vs 0.88+/-0.30 cm H2O, p = 0.03), duty cycle (0.44+/-0.01 vs 0.37+/-0.01, p < 0.001), and expiratory airway resistance (11.81+/-1.53 vs 8.75+/-1.22 cm H2O/L/s, p < 0.001), but not in respiratory rate (27.48+/-1.54 vs 28.06+/-1.61 breaths/min, p = 0.40) or in minute ventilation (10.43+/-0.59 vs 10.27+/-0.37 L/min, p = 0.66). There was a statistically significant difference in the ratio of Pa(O2) to the fraction of inspired oxygen (F(IO2)) (333+/-21 vs 300+/-22, p < 0.03) but not in Pa(CO2) (48+/-2 vs 47+/-2 mm Hg, p = 0.59) between the BiPAP S/T-D and the Servo Ventilator 900C. CONCLUSIONS: Despite differences in initiating and maintaining the inspiratory and expiratory phases, in breathing circuits, and in ventilator circuits between the two ventilators, the performance of the BiPAP S/T-D is equally efficacious to that of a conventional mechanical ventilator in supporting respiratory muscles. Thus, the BiPAP S/T-D is safe and effective when used in mechanically ventilated patients recovering from acute respiratory failure who do not require total ventilatory support.

Adult↗
PubMed1994

Mechanical ventilators optimized for pediatric use decrease work of breathing and oxygen consumption during pressure-support ventilation.

OBJECTIVES: a) To investigate whether the patient work of breathing needed to trigger inspiration is affected by the type of ventilator delivering pressure-support ventilation for mechanically ventilated pediatric patients. b) To determine whether changes in oxygen consumption (VO2) trend with changes in work of breathing and would thus be helpful in tracking work of breathing. DESIGN: Prospective study. SETTING: Pediatric intensive care unit at a university hospital. PATIENTS: Nine mechanically ventilated patients (2 to 75 months of age). INTERVENTIONS: While maintaining a constant pressure-support ventilation level, patients were alternately supported with the Siemens Servo 900C, the Bird VIP, and the Newport Wave E200 ventilators in random order. MEASUREMENTS AND MAIN RESULTS: Work of breathing, defined as the integral of the pressure-volume curve corresponding to negative pressure, was calculated with a pulmonary monitoring system. VO2 was measured with a metabolic cart. Patient distress levels were assessed using the COMFORT scale, a behavioral scoring system. Mean values (20 breaths/patient) for measured variables with each ventilator were compared using analysis of variance and Scheffé tests, with p < .05 indicating statistical significance. The lowest VO2 (103 +/- 35 mL/min/m2) and work of breathing (24 +/- 15 g.cm/m2) were achieved with the Bird VIP ventilator and were significantly (p < .05) lower than those values obtained with either the Siemens Servo 900C (VO2 147 +/- 33 mL/min/m2; work of breathing 49 +/- 18 g.cm/m2) or the Newport Wave E200 (VO2 122 +/- 33 mL/min/m2; work of breathing 35 +/- 15 g.cm/m2). Also, the values of work of breathing and VO2 obtained using the Newport Wave E200 were significantly (p < .05) lower than those values obtained using the Servo 900C. No change in behavioral distress occurred when the ventilators were changed. In all patients, there was a clear similarity in the trends of VO2 and work of breathing. CONCLUSIONS: We conclude that VO2 and work of breathing may be reduced significantly using the latest generation of mechanical ventilators optimized for infant and pediatric use. Because work of breathing is less with the Bird VIP than the other two ventilators tested, leading to a corresponding decrease in VO2, we suggest that the Bird VIP better adapts the patient to the ventilator and may facilitate weaning from ventilatory support. We also suggest that changes in VO2 might be helpful in tracking changes in work of breathing.

Analysis of Variance↗
PubMed2000

Elective high frequency jet ventilation versus conventional ventilation for respiratory distress syndrome in preterm infants.

BACKGROUND: This section is under preparation and will be included in the next issue. OBJECTIVES: The objective of this review was to determine whether the elective (commencing soon after initiation of mechanical ventilation) use of high frequency jet ventilation (HFJV), as compared to conventional ventilation (CV) in preterm infants with respiratory distress syndrome (RDS), would decrease the incidence of chronic lung disease (CLD) without adverse effects. SEARCH STRATEGY: Randomized trials from MEDLINE were identified by means of MeSH and text words 'high frequency ventilation', 'high frequency jet ventilation', 'jet ventilation' from the years 1980 to 1997. The EMBASE database, the Oxford Database of Perinatal Trials, the Neonatal Trials Register of the Neonatal Review Group of the Cochrane Collaboration and the Cochrane library were also accessed. Proceedings of recent SPR/APS meetings were hand searched. Information was obtained from experts in the field, and cross references were checked. SELECTION CRITERIA: All randomized controlled trials of elective high frequency jet ventilation versus conventional ventilation in preterm infants born at less than 35 weeks GA or with a birth weight less than 2000 gms with respiratory distress were included in the systematic review. Trials which used HFJV to 'rescue' preterm infants due to severe respiratory distress usually beyond 24 hours, and trials that used HFJV for a mandatory time period and then switched back to CV, were not included in this review. DATA COLLECTION AND ANALYSIS: The standard methods of the Neonatal Cochrane Review Group were used, including independent trial assessment and data extraction. Data were analysed using relative risk (RR) and risk difference (RD). From 1/RD the number needed to treat (NNT) for benefits and number needed to harm (NNH) for adverse outcomes were calculated. MAIN RESULTS: Overall analysis of the three trials showed that HFJV is associated with a reduction in CLD at 36 weeks postmenstrual age in survivors [RR 0.58 (0.34, 0. 98), RD -0.138 (-0.268, -0.007), NNT 7 (4, 90)]. The use of home oxygen therapy was evaluated in only one study (Keszler 1997) and a lower rate was found in the HFJV group [RR 0.24 (0.07, 0.79), RD -0. 176 (-0.306, -0.047), NNT 5 (3, 21)]. Overall there was a trend towards an increase in the risk of PVL in the HFJV group, which was not significant. Subgroup analyses shows a significant increase in risk of PVL in the trial by Wiswell 1996 [RR 5.0 (1.19, 21.04), RD 0.250 (0.069, 0.431), NNH 4.0 (2.3,14.5)] where a 'low volume strategy' was the standard protocol for HFJV. In the other trial by Keszler 1997, where the intention was to use a 'high volume strategy', there was no significant difference in the incidence of PVL, RR 0.42 (0.14, 1.30). In the overall analysis, there were no significant differences in the incidence of neonatal mortality, IVH all grades or in grades 3 or 4 IVH. In the subgroup where 'low volume strategy' was used there was a non-significant trend toward an increase in risk of IVH all grades and grades 3 or 4 IVH. REVIEWER'S CONCLUSIONS: The overall analysis shows a benefit in pulmonary outcomes in the group electively ventilated with HFJV. Of concern is the significant increase in acute brain injury in one trial which used lower mean airway pressures when ventilating with HFJV. There are as yet no long term pulmonary or neurodevelopmental outcomes from any of the trials. Until further studies ascertain the most appropriate strategy to routinely ventilate premature infants with HFJV safely, ventilation with HFJV cannot be recommended for preterm infants with RDS.

High-Frequency Ventilation↗
PubMed2005

Dead-space washout by split-flow ventilation. A new method to reduce ventilation needs in premature infants.

OBJECTIVE: Chronic lung disease caused by volutrauma is one of the most important consequences of preterm delivery. In this pilot study a new method is presented that consists of flushing part of the dead space with fresh gas in order to reduce high tidal volumes, the chief cause of volutrauma. The aim of the study was to evaluate if the new method could reduce ventilatory effort in preterm infants by diminishing dead space. DESIGN AND SETTING: In split-flow ventilation, gas required for dead-space washout is split off from the regular ventilation circuit. The split flow bypasses the apparatus dead space and fills it retrogradely with fresh breathing gas, mainly in the pause between exhalation and inspiration. The mean per-minute ventilation and ventilation index after 12 h of conventional ventilation were compared with corresponding mean values after 12 h of split-flow ventilation in 17 preterm infants weighing <2,000 g. Statistical analysis was performed using the T -test for matched pairs. RESULTS: After switching from conventional ventilation to split-flow ventilation, the mean per-minute ventilation per kilogram of body weight decreased significantly from a mean value of 0.314+/-0.097 l/kg/min to 0.190+/-0.043 l/kg/min ( p <0.001), while the ventilation index decreased significantly from 28.47+/-7.48 to 16.10+/-4.13 ( p <0.001). CONCLUSION: Split-flow ventilation significantly reduces apparatus dead space during ventilation in preterm infants. This leads to reduced ventilatory effort.

Bronchopulmonary Dysplasia↗
PubMed1981

Measurements of regional ventilation using nitrogen-13 and krypton-81m in mechanically ventilated dogs.

13N2 and 81Krm were used to measure changes in upper/lower (U/L) ratios of regional ventilation in supine anaesthetised dogs mechanically ventilated at different tidal volumes and the results compared. Analysis of the slopes of the 13N2 washout curves indicated that U/L specific ventilation was less than unity at low tidal volumes and decreased as tidal volume increased. U/L total ventilation, measured using the specific ventilation results and estimations of relative lung using 13N2, also decreased with increase in tidal volume. Preferential distribution of ventilation to dependent lung regions thus increased with tidal volume despite the opposing hydrostatic forces from the abdomen. Regional count density distributions in 81Krm images of the lungs were analysed. At high specific ventilation rates, correction of 81Krm count density is required in order to obtain correct regional ventilation information. The specific ventilation rates in this series were such that the uncorrected U/L count ratios of 81Krm increased as tidal volume increased in contrast to the decrease in U/L total ventilation recorded by the 13N2 method. When corrections using the 13N2 specific ventilation results were applied, the changes in U/L 81Krm count ratios with tidal volume showed a similar trend to the changes in total ventilation measured with 13N2. Sources of error in the two techniques are briefly discussed.

Animals↗
PubMed1999

Comparison of exogenous surfactant therapy, mechanical ventilation with high end-expiratory pressure and partial liquid ventilation in a model of acute lung injury.

We have compared three treatment strategies, that aim to prevent repetitive alveolar collapse, for their effect on gas exchange, lung mechanics, lung injury, protein transfer into the alveoli and surfactant system, in a model of acute lung injury. In adult rats, the lungs were ventilated mechanically with 100% oxygen and a PEEP of 6 cm H2O, and acute lung injury was induced by repeated lung lavage to obtain a PaO2 value < 13 kPa. Animals were then allocated randomly (n = 12 in each group) to receive exogenous surfactant therapy, ventilation with high PEEP (18 cm H2O), partial liquid ventilation or ventilation with low PEEP (8 cm H2O) (ventilated controls). Blood-gas values were measured hourly. At the end of the 4-h study, in six animals per group, pressure-volume curves were constructed and bronchoalveolar lavage (BAL) was performed, whereas in the remaining animals lung injury was assessed. In the ventilated control group, arterial oxygenation did not improve and protein concentration of BAL and conversion of active to non-active surfactant components increased significantly. In the three treatment groups, PaO2 increased rapidly to > 50 kPa and remained stable over the next 4 h. The protein concentration of BAL fluid increased significantly only in the partial liquid ventilation group. Conversion of active to non-active surfactant components increased significantly in the partial liquid ventilation group and in the group ventilated with high PEEP. In the surfactant group and partial liquid ventilation groups, less lung injury was found compared with the ventilated control group and the group ventilated with high PEEP. We conclude that although all three strategies improved PaO2 to > 50 kPa, the impact on protein transfer into the alveoli, surfactant system and lung injury differed markedly.

Animals↗
PubMed2001

In vivo physiologic comparison of two ventilators used for domiciliary ventilation in children with cystic fibrosis.

OBJECTIVE: Home noninvasive mechanical ventilation (NIMV) is used with increasing frequency for the treatment of patients with respiratory failure caused by cystic fibrosis, yet the optimal mode of ventilation in such children is unknown. We compared the physiologic short-term effects of two ventilators with different modes (one pressure support and the other assist control/volume-targeted [AC/VT]) commonly used for domiciliary ventilation. DESIGN: Prospective, randomized, crossover comparison of two ventilators with different modes. SETTING: Tertiary pediatric university hospital. PATIENTS: Eight children with cystic fibrosis (age, 11-17 yrs) and chronic respiratory failure (pH 7.4 +/- 0.0; PaO2, 57.5 +/- 7.5 torr; PaCO2, 46.1 +/- 2.5 torr), naive to NIMV. INTERVENTIONS: Two 20-min runs of pressure support and AC/VT ventilation were performed in random order, each run being preceded and followed by 20 mins of spontaneous breathing. MEASUREMENTS: Flow and airway pressure and esophageal and gastric pressures were measured to calculate esophageal (PTPes) and diaphragmatic pressure-time product (PTPdi) and the work of breathing. RESULTS: The two NIMV sessions significantly improved blood gas variables and increased tidal volume with no change in respiratory rate. Indexes of respiratory effort decreased significantly during the two modes of NIMV compared with spontaneous breathing, with PTPdi/min decreasing from 497.8 +/- 115.4 cm H2O x sec x min(-1) during spontaneous breathing to 127.8 +/- 98.3 cm H2O x sec x min(-1) and 184.3 +/- 79.8 cm H2O x sec x min(-1), during AC/VT and pressure support, respectively (p <.0001), and the work of breathing decreasing from 1.83 +/- 0.12 J.L-1 during spontaneous breathing to 0.48 +/- 0.32 J.L-1 and 0.75 +/- 0.30 J.L-1, during AC/VT and pressure support, respectively (p <.0001). In addition, the effect of AC/VT ventilation was significantly superior to pressure support judged by PTPes and the work of breathing, but this result was explained by three patients who adapted extremely well to the AC/VT ventilation, with the disappearance of ventilator triggering, in effect adopting a controlled mode. There was a correlation between the improvement in PTPdi/min or the work of breathing and patient's subjective impression of comfort during the AC/VT ventilation. CONCLUSIONS: In awake, stable children with cystic fibrosis, both AC/VT and pressure support unloaded the respiratory muscles. The disappearance of ventilator triggering occurred in a subgroup of patients during AC/VT ventilation, and this explained the good tolerance and the superiority of this mode in the present study.

Adolescent↗
PubMed1995

Out-of-hospital ventilation: bag--valve device vs transport ventilator.

OBJECTIVE: To examine the patterns of out-of-hospital airway management and to compare the efficacy of bag-valve ventilation with that of the use of a transport ventilator for intubated patients. METHODS: A prospective, nonrandomized, convenience sample of 160 patients requiring airway management in the out-of-hospital urban setting was analyzed. A survey inquiring about airway and ventilatory management was completed by emergency medical services (EMS) personnel, and arterial blood gas (ABG) samples were obtained within 5 minutes of patient arrival in the ED. The ABG parameters were compared for patients grouped by different airway techniques and presence or absence of cardiac arrest (systolic blood pressure < 50 mm Hg) upon ED presentation. RESULTS: Over a one-year period, 160 surveys were returned. The majority (62%) of the patients were men; the population mean age was 61 +/- 19 years. Presenting ABGs were obtained for 76 patients; 17% (13/76) had systemic perfusion and 83% (63/76) were in cardiac arrest. There was no difference in ABG parameters between the intubated cardiac arrest patients ventilated with a transport ventilator (pH 7.17 +/- 0.17, PaCO2 37 +/- 20 torr, and PaO2 257 +/- 142 torr) and those ventilated with a bag-valve device (pH 7.20 +/- 0.16, PaCO2 42 +/- 21 torr, and PaO2 217 +/- 138 torr). The patients ventilated via an esophageal obturator airway (EOA) device had impaired gas exchange, compared with the groups who had endotracheal (ET) intubation (pH 7.09 +/- 0.13, PaCO2 76 +/- 30 torr, and PaO2 75 +/- 35 torr). The intubated patients not in cardiac arrest had similar ABG parameters whether ventilated manually with a bag-valve device or with a transport ventilator. Endotracheal intubation was successfully accomplished in 93% (123/132) of attempted cases. CONCLUSIONS: In this sample, ET intubation was the most frequently used airway by EMS providers. When ET intubation was accomplished, adequate ventilation could be achieved using either bag-valve ventilation or a transport ventilator. Ventilation via the EOA proved inadequate.

Adult↗
PubMedDate not supplied

Rapid assessment of ventilation by measurement of carbon dioxide elimination during high-frequency ventilation of kittens.

Monitoring of the effectiveness of ventilation is a significant problem during high-frequency ventilation (HFV). The time necessary to achieve equilibrium of the arterial tension of carbon dioxide (Paco2) following step changes in ventilation is appreciable, because of large body stores of CO2. Waiting for Paco2 to reach equilibrium is not only time-consuming but a potentially dangerous means of monitoring ventilator adjustments during HFV. Five kittens of mean +/- SD 1,082 +/- 383 gm weight were studied during HFV, both with normal lungs and lungs injured by saline lavage-induced surfactant depletion. The transcutaneous tension of carbon dioxide (Ptcco2) was monitored continuously to determine the time required to achieve equilibrium of Paco2 following a step change in ventilation. The rate of pulmonary CO2 elimination (VECO2) was measured immediately before and immediately after (less than 12 sec) step changes in ventilation and was used to predict the change in Paco2 achieved once equilibrium was reestablished. With normal lungs, equilibration time following step changes in ventilation was found to be approximately 20 minutes. After step decreases in ventilation of the injured lung, achieving equilibrium state took significantly longer, approximately 30 minutes. The Paco2 predicted was significantly related to the change in Paco2 achieved at equilibrium for both normal and injured lung studies. We concluded that direct monitoring of VECO2 during HFV may be a useful clinical monitoring technique, allowing rapid and accurate assessment of the efficiency of ventilation following step changes in ventilation and potentially assisting in optimizing ventilator settings.

Animals↗
PubMed2002

Bench testing of pressure support ventilation with three different generations of ventilators.

OBJECTIVE: The new generations of intensive care ventilators tend to be more innovative and sophisticated than previous ones, but little is known about their respective performance for delivering pressure support ventilation (PSV) and how they compare to previous generations. DESIGN: Active lung model bench test. APPARATUS: Twenty-two commercially available ventilators classified into three categories: new generation ventilators (after 1993, n=7), previous generation (before 1993, n=6), and recent piston or turbine-based ventilators ( n=9). MEASUREMENTS AND RESULTS: During PSV, the unloading efficacy of the assistance depends on the ventilator's ability to meet inspiratory flow demand. Three levels of flow (0.1 l/s, 0.6 l/s, and 1.2 l/s) were used to simulate inspiratory demand and the net area of the inspiratory airway pressure-time trace was calculated over the first 0.3 s, 0.5 s, and 1 s (Area (0.3), Area (0.5), and Area (tot)) with three levels of PSV (5 cmH(2)O, 10 cmH(2)O, and 15 cmH(2)O). To assess the respective role of pressure support delivery and triggering function, triggering sensitivity was assessed independently by measuring the time delay ( TD (tg)) and the pressure fall (Delta Paw (tg)) with two levels of inspiratory drive. All the new generation ventilators exhibited significantly better results than most of the previous generation ventilators regarding Area (0.3) and TD (tg), indicating large improvements in terms of triggering and pressurisation. CONCLUSION: Regarding PSV and trigger performance, the new generation ventilators - but also some piston and turbine-based ventilators - outperform most of previous generation ventilators.

Benchmarking↗
PubMed2003

Gentamicin pharmacokinetics in term newborn infants receiving high-frequency oscillatory ventilation or conventional mechanical ventilation: a case-controlled study.

OBJECTIVE: To compare the pharmacokinetics of gentamicin in infants receiving high-frequency oscillatory ventilation (HFOV) with infants receiving conventional mechanical ventilation. DESIGN: A case-controlled study design was used to compare the pharmacokinetics of gentamicin in critically ill infants receiving HFOV and conventional mechanical ventilation. Medical records of all full-term newborn infants (> or =37 weeks gestational age) who received either high-frequency mechanical ventilation or conventional mechanical ventilation between 1991 and 2001 were reviewed and relevant patient demographics, renal function tests and gentamicin administration and plasma concentration data collected. Elimination rate constant, half-life, volume of distribution and clearance for both groups were calculated using standard kinetics equations. SETTING: A tertiary care children's hospital. PATIENTS: Newborn infants, > or =37 weeks gestational age, receiving gentamicin and high-frequency mechanical ventilation or conventional mechanical ventilation. MEASUREMENTS AND MAIN RESULTS: In total, 18 patients were included in the conventional mechanical ventilation group and 15 in the HFOV group. The mean gentamicin dose for conventional mechanical ventilation and HFOV groups infants were 2.52+/-0.07 and 2.5+/-0.07 mg/kg/dose, respectively. Initial dosing interval was 12 hours in all of the conventional mechanical ventilation infants and 13 of the 15 HFOV infants. The dosing interval for the remaining two HFOV infants was 18 hours. No patient in either group demonstrated oliguria. Statistical analysis using the Student t-test for unequal variances yielded significant differences between the two groups with regard to elimination rate constant, half-life, volume of distribution and clearance, with a p value of <0.05 for all the observations. The mean of the highest P(aw) received by each patient in the HFOV group (19.2+/-4.05) was considerably higher than in the conventional mechanical ventilation group (13.4+2.23) (p>0.05). CONCLUSION: Infants receiving HFOV had reduced gentamicin clearance. Full-term infants receiving HFOV should be initiated at gentamicin dosing intervals of 18 hours rather than the traditional 12 hours recommended for this age group.

Anti-Bacterial Agents↗
PubMed1984

Ventilation and perfusion of each lung during differential ventilation with selective PEEP.

Lung perfusion was studied in 10 patients (mean age 58 yr) in the lateral position during enflurane anesthesia. They were ventilated through a double-lumen endotracheal catheter: 1) by one ventilator with free distribution of ventilation between the lungs, with no (zero) end-respiratory pressure (ZEEP); 2) as above but with a general positive end-expiratory pressure (PEEP) of 9 cmH2O; or 3) by two ventilators with equal distribution of ventilation between the lungs and with a selective PEEP of 8 cmH2O to the dependent lung only. Total ventilation was on average 8 l/min (BTPS) throughout the study. During the first method, 34% of ventilation was distributed to the dependent and 66% to the nondependent lung. Cardiac output (thermodilution) was 4.5 l/min, 57% being distributed to the dependent lung as assessed by iv boli of Xenon 133. During the second method, ventilation was assumed to be distributed equally between the lungs. Cardiac output was decreased to 3.8 l/min, and the dependent lung received 81% of lung blood flow. During the third method, cardiac output was significantly greater than during the second method (4.1 l/min), 51% passing to the dependent lung. Peak and end-inspiratory airway pressures were 5-18 cm H2O lower during selective than during general PEEP. Arterial oxygen tension was significantly greater during the third method than during either of the other ventilator settings and the alveolar-arterial oxygen tension difference was almost halved compared with the first method. It is concluded that differential ventilation with selective PEEP improves ventilation-perfusion matching and thus oxygenation.

Adult↗
PubMed2005

Pressure support ventilation combined with volume guarantee versus synchronized intermittent mandatory ventilation: a pilot crossover trial in premature infants in their weaning phase.

OBJECTIVE: To compare pressure support ventilation combined with volume guarantee (PSV-VG) to synchronized intermittent mandatory ventilation (SIMV) regarding safety, course of blood gases, and infant-ventilator interaction in premature infants. DESIGN: Prospective, two-treatment, crossover pilot study. SETTING: Tertiary care neonatal unit. PATIENTS: Twenty-five ventilated premature infants: median (range) gestational age 26.1 wks (23.1-35.7), birth weight 765 g (450-3170), age at study 5 days (2-27), in their weaning phase. INTERVENTIONS: Infants were studied for three 30-min periods, starting from SIMV, followed by PSV-VG, and back again to SIMV. After concluding the last period, all infants were switched back to PSV-VG. On the next day, infants were studied in the opposite direction. During each period, vital parameters, ventilation parameters, degree of physical activity, duration of rhythmic breathing, and the number of vital signs monitor alarms were recorded. MEASUREMENTS AND MAIN RESULTS: Nineteen infants (84%) could be successfully ventilated with PSV-VG till the next day. PSV-VG achieved a similar oxygenation level as SIMV but with significantly lower ventilation pressures. Comparable ventilation was achieved, but infants with strong respiratory drive were more liable to hyperventilation episodes during PSV-VG. Although infants breathed more rhythmically during PSV-VG, suggesting better infant-ventilator synchrony, the infants' behavioral state and the fluctuations in blood gases did not differ. CONCLUSIONS: The potentials of PSV-VG to improve infant-ventilator synchrony and to decrease pressure needed to ventilate premature lungs are promising, even though the changes were small. However, its benefits during acute illness and on the final outcome remain to be proven.

Cross-Over Studies↗
PubMed1994

The effect of insufflation leaks upon ventilation. A quantified comparison of ventilators.

Some ventilator-dependent patients use uncuffed tracheostomy tubes, resulting in fluctuations in the minute volume of ventilation. Bedside measurement of ventilation is difficult because of the insufflation and exsufflation leaks. This laboratory study of five different ventilators measured the tidal volumes achieved with three insufflation leaks introduced in an increasing order of magnitude and at three levels of compliance. The largest leak reduced the peak inflation pressure from 26 to 14 cmH2O in two pressure-limited ventilators with a 35% loss of the initial tidal volume of 800 ml. The turbine-driven pressure-limited ventilator retained a peak pressure of 20.5 cmH2O and lost only 14% of the volume, whereas the volume ventilators lost 65% of the tidal volume. The loss of volume was 3% for every cmH2O decrease in airway pressure due to a leak, regardless of the ventilator or compliance. Using the Friedman test, the differences between the volume ventilators and the pressure ventilators were significant whilst the three pressure-limited ventilators did not perform significantly differently from each other.

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