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PubMed1992

[A study of the parameters of the delivered tidal volume. Ventilation on a lung model using the CICERO anesthetic ventilator].

In many anaesthesia ventilators in common use, the tidal volume delivered is different from the tidal volume preset on the respirator. Tidal volume delivered by mechanical ventilation during anaesthesia may be influenced by fresh gas flow (FGF), the respiratory rate (RR) or the inspiratory: expiratory ratio (I:E). This may cause inadequate hypo- or hyperventilation in small children, especially in newborns and neonates. Using small tidal volumes from 20 to 100 ml preset on the respirator, we investigated in a lung model the tidal volumes delivered by the anaesthesia ventilator CICERO (Dräger, FRG) with variations of FGF, RR and I:E. MATERIAL AND METHODS. The anaesthesia ventilator CICERO (software version 4.16) was equipped with the low-compliance tubes of the "Ulmer Kinder-Set" (Rüsch Co.) and the regular CO2 canister (1500 ml) of the machine. The circuit was connected to a lung model consisting of a glass clyinder filled with copper wool with a compliance of 3.3 ml/mbar. To create a pressure-volume correlation of the entire system, i.e. the lung model, the anaesthesia circuit and the ventilator, calibrated glass syringes were used and the pressure increase in the test lung was measured. This pressure-volume correlation was linear. The pressure increase in the lung model caused by the tidal volume during ventilation therefore reflected the actual tidal volume delivered. The study was performed with small tidal volumes from 20 to 100 ml that could be adjusted exactly on the ventilator. Delivered tidal volumes were studied by varying the FGF from 1 to 6 l/min and the RR from 20 to 60/min (with I:E = 1:1.5) and by varying the RR from 20 to 60/min and the I:E from 2:1 to 1:3 (with FGF = 21/min). RESULTS. By varying FGF, RR and I:E no changes in delivered tidal volumes were noted. In all settings of the ventilator studied, the delivered tidal volume was similar to the desired tidal volume preset on the ventilator. The highest deviation from the delivered tidal volume to the tidal volume preset was 17.5% with a tidal volume of 20 ml. In preset tidal volumes 30-100 ml this deviation was lower than 10%. An intermittent "auto-PEEP" up to 5 mbar was noted during high respiratory rates (50 and 60/min) combined with an I:E at 2:1 and 1:1 or with a FGF at 4 or 6 l/min. The compliance of the ventilator equipped with the circuit was 4.2 ml/mbar. CONCLUSION. The findings in this study prove that with tidal volumes ranging from 20 to 100 ml the actual tidal volume delivered by the anaesthesia ventilator CICERO is equivalent to the tidal volume set on the machine regardless of the variation of FGF, RR and I:E. These findings are mainly based on two circumstances. Firstly, fresh gas flow is fed into a reservoir and not added to the volume delivered by the bellow during inspiration as in many other respirators. Secondly, the CICERO works with a compliance correction function integrated into the machine. Computed compressible volume from the circuit and the ventilator is added to the tidal volume preset on the ventilator; therefore, the volume delivered by the bellow consists of the volume set on the ventilator plus the compressible volume. With these characteristics the anaesthesia ventilator CICERO meets important requirements for a ventilator in paediatric anaesthesia. However, for final assessment further clinical studies are required.

Anesthesiology↗

PubMed1999

Prospective, randomized, controlled clinical trial comparing traditional versus reduced tidal volume ventilation in acute respiratory distress syndrome patients.

OBJECTIVE: To assess the safety and potential efficacy of a mechanical ventilation strategy designed to reduce stretch-induced lung injury in acute respiratory distress syndrome. DESIGN: Prospective, randomized, controlled clinical trial. SETTING: Eight intensive care units in four teaching hospitals. PATIENTS: Fifty-two patients with acute respiratory distress syndrome. INTERVENTIONS: Traditional tidal volume patients: tidal volume 10-12 mL/kg ideal body weight, reduced if inspiratory plateau pressure was > 55 cm H2O (7.3 kPa). Small tidal volume patients: tidal volume 5-8 mL/kg ideal body weight, to keep plateau pressure < 30 cm H2O (4.0 kPa). MEASUREMENTS AND MAIN RESULTS: Mean tidal volumes during the first 5 days in traditional and small tidal volume patients were 10.2 and 7.3 mL/kg, respectively (p < .001), with mean plateau pressure = 30.6 and 24.9 cm H2O (3.3 kPa), respectively (p < .001). There were no significant differences in requirements for positive end-expiratory pressure or FIO2, fluid intakes/outputs, requirements for vasopressors, sedatives, or neuromuscular blocking agents, percentage of patients that achieved unassisted breathing, ventilator days, or mortality. CONCLUSIONS: The reduced tidal volume strategy used in this study was safe. Failure to observe beneficial effects of small tidal volume ventilation treatment in important clinical outcome variables may have occurred because a) the sample size was too small to discern small treatment effects; b) the differences in tidal volumes and plateau pressures were modest; or c) reduced tidal volume ventilation is not beneficial.

Adult↗

PubMed1999

Thoracic electrical impedance tomographic measurements during volume controlled ventilation-effects of tidal volume and positive end-expiratory pressure.

The aim of the study was to analyze thoracic electrical impedance tomographic (EIT) measurements accomplished under conditions comparable with clinical situations during artificial ventilation. Multiple EIT measurements were performed in pigs in three transverse thoracic planes during the volume controlled mode of mechanical ventilation at various tidal volumes (V(T)) and positive end-expiratory pressures (PEEP). The protocol comprised following ventilatory patterns: 1) V(T)(400, 500, 600, 700 ml) was varied in a random order at various constant PEEP levels and 2) PEEP (2, 5, 8, 11, 14 cm H2O) was randomly modified during ventilation with a constant V(T). The EIT technique was used to generate cross-sectional images of 1) regional lung ventilation and 2) regional shifts in lung volume with PEEP. The quantitative analysis was performed in terms of the tidal amplitude of the impedance change, reflecting the volume of delivered gas at various preset V(T) and the end-expiratory impedance change, revealing the variation of the lung volume at various PEEP levels. The results showed: 1) an increase in the tidal amplitude of the impedance change, proportional to the delivered V(T) at all constant PEEP levels, 2) a rising end-expiratory impedance change, with PEEP reflecting an increase in gas volume, and 3) a PEEP-dependent redistribution of the ventilated gas between the planes. The generated images and the quantitative results indicate the ability of EIT to identify regional changes in V(T) and lung volume during mechanical ventilation.

Animals↗

PubMed1995

Volume delivery during positive pressure inflation--relationship to spontaneous tidal volume of neonates.

Volume delivery by positive pressure inflation was determined in 20 premature infants and 10 infants born at term on days 1 and 2. The spontaneous tidal volume, respiratory rate and inspiratory to expiratory (I:E) ratio were measured daily in the first week of life in an additional group of 20 infants born prematurely. Measurements were made using a pneumotachograph only when the infants were stable and had acceptable blood gases for at least 2 h. There was variability between individuals but the median delivered volume by positive pressure ventilation ranged between 4.9 and 6.1 ml/kg on days 1 and 2 and within the groups of different maturity. There was no significant difference in the results of infants born prematurely or at term or when studied on days 1 or 2. The median spontaneous tidal volume during the first week of life varied between 5.4 and 6.7 ml/kg; respiratory rate between 72 and 80 breaths/min and I:E ratio from 0.67 to 0.77. Postnatal age had no significant effect on the results. These results suggest volume delivery by positive pressure inflation during a stable period of ventilation is similar to the spontaneous tidal volume.

Forced Expiratory Flow Rates↗

PubMed2006

Effect of humidifying devices on the measurement of tidal volume by mechanical ventilators.

PURPOSE: We hypothesized that expiratory tidal volume was underestimated, because a heat-moisture exchanger traps the expired vapor. We, therefore, designed patient and bench studies to investigate the accuracy of tidal volume monitoring. METHODS: In a patient study, applying two humidifying systems (a heat-moisture exchanger and a heated humidifier) and two tidal volumes (12 and 6 ml x kg(-1)) with a Servo ventilator 300, we recorded the displayed expiratory tidal volume and thoracic volume displacement, measured by respiratory inductive plethysmography. Temperature, relative humidity, and absolute humidity were measured at the airway opening and at the end of the expiratory limb. Using a model lung, we also tested three different ventilators (Puritan-Bennett 7200ae, Evita 4, and Servo ventilator 300) to investigate whether the effects of the heat-moisture exchanger and the heated humidifier on monitored tidal volume varied according to the brand of ventilator. RESULTS: With the use of the heat-moisture exchanger, the displayed expiratory tidal volume was significantly smaller, by 12%-14%, than that with the heated humidifier, although thoracic volume displacement was identical in the two systems. The temperature and absolute humidity at the end of the expiratory limb were significantly lower with the heat-moisture exchanger than with the heated humidifier. In the model lung study, we investigated the effects of different brands of ventilator on the expiratory tidal volume. A similar degree (8%-14%) of underestimation of tidal volume was observed with the heat-moisture exchanger, regardless of ventilator brand. CONCLUSION: Monitored expiratory tidal volume was underestimated by approximately 10%, when using a heat-moisture exchanger.

Adolescent↗

PubMed2003

High tidal volume ventilation induces NOS2 and impairs cAMP- dependent air space fluid clearance.

Tidal volume reduction during mechanical ventilation reduces mortality in patients with acute lung injury and the acute respiratory distress syndrome. To determine the mechanisms underlying the protective effect of low tidal volume ventilation, we studied the time course and reversibility of ventilator-induced changes in permeability and distal air space edema fluid clearance in a rat model of ventilator-induced lung injury. Anesthetized rats were ventilated with a high tidal volume (30 ml/kg) or with a high tidal volume followed by ventilation with a low tidal volume of 6 ml/kg. Endothelial and epithelial protein permeability were significantly increased after high tidal volume ventilation but returned to baseline levels when tidal volume was reduced. The basal distal air space fluid clearance (AFC) rate decreased by 43% (P < 0.05) after 1 h of high tidal volume but returned to the preventilation rate 2 h after tidal volume was reduced. Not all of the effects of high tidal volume ventilation were reversible. The cAMP-dependent AFC rate after 1 h of 30 ml/kg ventilation was significantly reduced and was not restored when tidal volume was reduced. High tidal volume ventilation also increased lung inducible nitric oxide synthase (NOS2) expression and air space total nitrite at 3 h. Inhibition of NOS2 activity preserved cAMP-dependent AFC. Because air space edema fluid inactivates surfactant and reduces ventilated lung volume, the reduction of cAMP-dependent AFC by reactive nitrogen species may be an important mechanism of clinical ventilator-associated lung injury.

Acute Disease↗

PubMed1985

Neonatal endotracheal flowmeter for tidal volume, airway pressure, and end-tidal gas.

We have designed a new endotracheal flowmeter to measure tidal volume, phasic and mean airway pressures, inspiratory time, and end-tidal PCO2 and PO2 in intubated infants. The flowmeter is light (11 g) and adds minimal dead space (1.0 ml) and resistance (2 cmH2O X 100 ml- X s) to the infant's airway. The volume signal (less than or equal to 10 ml) is linear to 7 Hz, and end-tidal gases can be measured at respiratory rates of 90 breaths/min. This flowmeter is particularly valuable for evaluation of rapid mechanical ventilation of very low birth weight infants.

Airway Resistance↗

PubMed2000

The effect of perfluorocarbon vapour on the measurement of respiratory tidal volume during partial liquid ventilation.

During partial liquid ventilation perfluorocarbon vapour is present in the exhaled gases. The volumes of these gases are measured by pneumotachometers. Error in measuring tidal volumes will give erroneous measurement of lung compliance during partial liquid ventilation. We aim to compare measured tidal volumes with and without perfluorocarbon vapour using tidal volumes suitable for use in neonates. Tidal volumes were produced with a 100 ml calibration syringe from 20 to 100 ml and with a calibrated Harvard rodent ventilator from 2.5 to 20 ml. Control tidal volumes were drawn from a humidifier chamber containing water vapour and the PFC tidal volumes were drawn from a humidifier chamber containing water and perfluorocarbon (FC-77) vapour. Tidal volumes were measured by a fixed orifice, target, differential pressure flowmeter (VenTrak) or a hot-wire anenometer (Bear Cub) placed between the calibration syringe or ventilator and the humidifier chamber. All tidal volumes measured with perfluorocarbon vapour were increased compared with control (ANOVA p < 0.001 and post t-test p < 0.0001). Measured tidal volume increased from 7 to 16% with the fixed orifice type flow-meter, and from 35 to 41% with the hot-wire type. In conclusion, perfluorocarbon vapour flowing through pneumotachometers gives falsely high tidal volume measurements. Calculation of lung compliance must take into account the effect of perfluorocarbon vapour on the measurement of tidal volume.

Animals↗

PubMed1986

Measurement of tidal volume during high-frequency jet ventilation.

The measurement of tidal volume during high-frequency jet ventilation is difficult due to the high-frequency components of the inspiratory flow. To validate tidal volume measured with a screen pneumotachograph placed on the expiratory limb, we simultaneously determined tidal volume with a body plethysmograph in seven anesthetized normal adult New Zealand rabbits before and after saline lung lavage. Four to six comparisons of tidal volume were obtained by varying peak inspiratory pressures at each combination of frequency (120, 240, and 480/min) and inspiratory to expiratory time ratio (1:1, 1:3, 1:5, 1:9). Overall, 90% of the tidal volumes measured with the pneumotachograph were within 10% of 1 ml of the volumes determined with the plethysmograph, independent of frequency, inspiratory to expiratory time ratio, and lung compliance. There was unidirectional outward flow at the pneumotachograph during inspiration when both normal and saline lavaged lungs were being ventilated, suggesting a lack of gas entrainment. We conclude that a pneumotachograph on the expiratory limb may be used to measure tidal volume and gas entrainment in vivo during high-frequency jet ventilation. Determination of tidal volume may serve to optimize ventilator settings during high-frequency jet ventilations and facilitate an understanding of the mechanism involved in gas exchange.

Animals↗

PubMed1999

Preoxygenation: comparison of maximal breathing and tidal volume breathing techniques.

BACKGROUND: Preoxygenation with tidal volume breathing for 3-5 min is recommended by Hamilton and Eastwood. This report compares tidal volume preoxygenation technique with deep breathing techniques for 30-60 s. METHODS: The study was conducted in two parts on patients undergoing elective coronary bypass grafting. In the first group (n = 32), each patient underwent all of the following preoxygenation techniques: the traditional technique consisting of 3 min of tidal volume breathing at an oxygen flow of 5 l/min; four deep breaths within 30 s at oxygen flows of 5 l/min, 10 l/min, and 20 l/min; and eight deep breaths within 60 s at an oxygen flow of 10 l/min. The mean arterial oxygen tensions after each technique were measured and compared. In the second group (n = 24), patients underwent one of the following techniques of preoxygenation: the traditional technique (n = 8), four deep breaths (n = 8), and eight deep breaths (n = 8). Apnea was then induced, and the mean times of hemoglobin desaturation from 100 to 99, 98, 97, 96, and 95% were determined. RESULTS: In the first group of patients, the mean arterial oxygen tension following the tidal breathing technique was 392+/-72 mm Hg. This was significantly higher (P<0.05) than the values obtained following the four deep breath technique at oxygen flows of 5 l/min (256+/-73 mm Hg), 10 l/min (286+/-69 mm Hg), and 20 l/min (316+/-67 mm Hg). In contrast, the technique of eight deep breaths resulted in a mean arterial oxygen tension of 369+/-69 mm Hg, which was not significantly different from the value achieved by the traditional technique. In the second group of patients, apnea following different techniques of preoxygenation was associated with a slower hemoglobin desaturation in the eight-deep-breaths technique as compared with both the traditional and the four-deep-breaths techniques. CONCLUSION: Rapid preoxygenation with the eight deep breaths within 60 s can be used as an alternative to the traditional 3-min technique.

Anesthesia↗

PubMed1989

Partitioning of pulmonary resistance in dogs: effect of tidal volume and frequency.

To determine the sensitivity of pulmonary resistance (RL) to changes in breathing frequency and tidal volume, we measured RL in intact anesthetized dogs over a range of breathing frequencies and tidal volumes centering around those encountered during quiet breathing. To investigate mechanisms responsible for changes in RL, the relative contribution of airway resistance (Raw) and tissue resistance (Rti) to RL at similar breathing frequencies and tidal volumes was studied in six excised, exsanguinated canine left lungs. Lung volume was sinusoidally varied, with tidal volumes of 10, 20, and 40% of vital capacity. Pressures were measured at three alveolar sites (PA) with alveolar capsules and at the airway opening (Pao). Measurements were made during oscillation at five frequencies between 5 and 45 min-1 at each tidal volume. Resistances were calculated by assuming a linear equation of motion and submitting lung volume, flow, Pao, and PA to a multiple linear regression. RL decreased with increasing frequency and decreased with increasing tidal volume in both isolated and intact lungs. In isolated lungs, Rti decreased with increasing frequency but was independent of tidal volume. Raw was independent of frequency but decreased with tidal volume. The contribution of Rti to RL ranged from 93 +/- 4% (SD) with low frequency and large tidal volume to 41 +/- 24% at high frequency and small tidal volume. We conclude that the RL is highly dependent on breathing frequency and less dependent on tidal volume during conditions similar to quiet breathing and that these findings are explained by changes in the relative contributions of Raw and Rti to RL.

Airway Resistance↗

PubMed2001

The effects of different mouth-to-mouth ventilation tidal volumes on gas exchange during simulated rescue breathing.

UNLABELLED: The American Heart Association recommends tidal volumes of 700 to 1000 mL during mouth-to-mouth ventilation, but smaller tidal volumes of 500 mL may be of advantage to decrease the likelihood of stomach inflation. Because mouth-to-mouth ventilation gas contains only 17% oxygen, but 4% carbon dioxide, it is unknown whether 500-mL tidal volumes given during rescue breathing may result in insufficient oxygenation and inadequate carbon dioxide elimination. In a university hospital research laboratory, 20 fully conscious volunteer health care professionals were randomly assigned to breathe tidal volumes of 500 or 1000 mL of mouth-to-mouth ventilation gas (17% oxygen, 4% carbon dioxide, 79% nitrogen), or room air control (21% oxygen, 79% nitrogen) for 5 min. Arterial blood gases were taken immediately before, and after breathing 5 min of the experimental gas composition. When comparing 500 versus 1000 mL of mouth-to-mouth ventilation tidal volumes with 500 mL of room air, 500 mL of mouth-to-mouth ventilation tidal volume resulted in significantly (P < 0.05) lower mean +/- SEM arterial oxygen partial pressure (70 +/- 1 versus 85 +/- 2 versus 92 +/- 3 mm Hg, respectively), and lower oxygen saturation (94 +/- 0.4 versus 97 +/- 0.2 versus 98 +/- 0.2%), but increased arterial carbon dioxide partial pressure (46 +/- 1 versus 40 +/- 1 versus 39 +/- 1 mm Hg, respectively). Sixteen of 20 volunteers had to be excluded from the experiment with 500 mL of mouth-to-mouth ventilation gas after about 3 min instead of after 5 minutes as planned because of severe nervousness, sweating, and air hunger. We conclude that during simulated mouth-to-mouth ventilation, only large (approximately 1000 mL), but not small (approximately 500 mL) tidal volumes were able to maintain both sufficient oxygenation and adequate carbon dioxide elimination. IMPLICATIONS: To provide efficient mouth-to-mouth ventilation, it is important to administer tidal volumes of 1000 mL; tidal volumes of 500 mL were not adequate.

Adult↗

PubMed2006

Lung inflammation in preterm infants with respiratory distress syndrome: effects of ventilation with different tidal volumes.

Ventilation with an inappropriate tidal volume (Vt) triggers lung inflammation, an important predisposing factor of bronchopulmonary dysplasia. It still remains uncertain what the appropriate starting target Vt should be during the acute phase of respiratory distress syndrome (RDS). Our aim was to evaluate lung inflammation in preterm infants undergoing synchronized intermittent positive-pressure ventilation (SIPPV) with two different tidal volumes Vt during the acute phase of RDS. Thirty preterm infants (gestational age, 25-32 weeks) with acute RDS were randomly assigned to be ventilated with Vt = 5 ml/kg (n = 15) or Vt = 3 ml/kg (n = 15). Proinflammatory cytokines (interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor (TNF)-alpha) were determined in the tracheal aspirate on days 1, 3, and 7 of life. IL-8 and TNF-alpha levels collected on day 7 were significantly higher (P < 0.05), and mechanical ventilation lasted longer in the group with Vt = 3 ml/kg (16.8 +/- 4 vs. 9.2 +/- 4 days; P = 0.05). In conclusion, our data show significantly higher lung inflammation in preterm infants ventilated with Vt = 3 ml/kg, suggesting a role for Vt = 5 ml/kg in reducing both inflammatory response during the acute phase of RDS and the length of ventilation. Whether the use of this starting Vt prevents bronchopulmonary dysplasia requires further study.

Humans↗

PubMed2004

Exhaled tidal volume overestimation in mechanically ventilated patients with large cardiogenic oscillation.

OBJECTIVES: In postcardiac surgery patients, we often noticed that monitored tidal volumes exceeded the ventilator settings. We investigated whether cardiogenic oscillation causes overestimation of tidal volume. DESIGN: Prospective, observational, clinical study. SETTING: Surgical intensive care unit in a national heart institute. PATIENTS: Eight postcardiac surgery patients (age 13-70). INTERVENTIONS: Patients were paralyzed and received flow-triggered volume-controlled ventilation with a tidal volume of 10 mL/kg. In random order, two types of ventilator (Bird 8400 STi and Servo-300) and two respiratory rates (5 and 10 breaths/min) were applied to each patient via a disposal ventilatory circuit and heat-and-moisture exchanger. For each ventilator, we adjusted the flow-triggering sensitivity to prevent autotriggering due to cardiogenic oscillation: 10 L/min for the Bird 8400 STi and green zone for the Servo-300. MEASUREMENTS AND MAIN RESULTS: The magnitude of cardiogenic oscillation during mechanical ventilation was defined as peak expiratory flow fluctuation at end-expiration. We recorded tidal volume using the monitoring devices on the ventilators and calculated the discrepancy from the set tidal volume. Cardiogenic oscillation was significantly greater with the Bird 8400STi (4.0 +/- 1.8 L/min) than with the Servo-300 (1.7 +/- 0.8 L/min). With the Bird 8400 STi, the discrepancy between monitored tidal volume and set tidal volume ranged from 15 to 260 mL when the respiratory rate was 5 breaths/min and from -9 to 75 mL at 10 breaths/min; there was a linear correlation between the overestimation of tidal volume and the magnitude of cardiogenic oscillation. In contrast, with the Servo-300, the discrepancy was relatively small (-36 to 14 mL). CONCLUSIONS: In mechanically ventilated patients with large cardiogenic oscillation, exhaled tidal volume is overestimated on at least one model of ventilator.

Adolescent↗

PubMed2006

Tidal hyperinflation during low tidal volume ventilation in acute respiratory distress syndrome.

RATIONALE: Tidal volume and plateau pressure limitation decreases mortality in acute respiratory distress syndrome. Computed tomography demonstrated a small, normally aerated compartment on the top of poorly aerated and nonaerated compartments that may be hyperinflated by tidal inflation. OBJECTIVES: We hypothesized that despite tidal volume and plateau pressure limitation, patients with a larger nonaerated compartment are exposed to tidal hyperinflation of the normally aerated compartment. MEASUREMENTS AND MAIN RESULTS: Pulmonary computed tomography at end-expiration and end-inspiration was obtained in 30 patients ventilated with a low tidal volume (6 ml/kg predicted body weight). Cluster analysis identified 20 patients in whom tidal inflation occurred largely in the normally aerated compartment (69.9 +/- 6.9%; "more protected"), and 10 patients in whom tidal inflation occurred largely within the hyperinflated compartments (63.0 +/- 12.7%; "less protected"). The nonaerated compartment was smaller and the normally aerated compartment was larger in the more protected patients than in the less protected patients (p = 0.01). Pulmonary cytokines were lower in the more protected patients than in the less protected patients (p < 0.05). Ventilator-free days were 7 +/- 8 and 1 +/- 2 d in the more protected and less protected patients, respectively (p = 0.01). Plateau pressure ranged between 25 and 26 cm H(2)O in the more protected patients and between 28 and 30 cm H(2)O in the less protected patients (p = 0.006). CONCLUSIONS: Limiting tidal volume to 6 ml/kg predicted body weight and plateau pressure to 30 cm H(2)O may not be sufficient in patients characterized by a larger nonaerated compartment.

Aged↗

PubMed2006

Hyperoxia and tidal volume: Independent and combined effects on neonatal pulmonary inflammation.

BACKGROUND: Hyperoxia and tidal volume mechanical ventilation are independent factors in the genesis of lung injury, but it remains unclear the extent to which each is responsible or contributes to this process in newborns. OBJECTIVES: To study the independent and combined effects of hyperoxia and tidal volume mechanical ventilation on the induction of lung inflammation in a newborn piglet model of ventilator-induced lung injury. METHODS: Following exposure to either ambient air or F(I)O2 = 1.0 for a period of 3 days, newborn piglets were randomized to receive mechanical ventilation with either high tidal volume (20 ml/kg) or low tidal volume (6 ml/kg) for 4 h while controlling for pH. RESULTS: Monocyte chemoattractant protein-1 level in the lungs of animals randomized to hyperoxia with high tidal volume ventilation was significantly elevated, compared to all other groups (p < 0.05). Myeloperoxidase assayed in lung homogenate was found to be significantly higher in nonventilated animals exposed to hyperoxia (p < 0.01). Only in animals previously exposed to hyperoxia did the addition of high tidal volume ventilation further increase the level of myeloperoxidase present (p < 0.05). Pulmonary vascular resistance was significantly elevated after 4 h of mechanical ventilation compared to 1 h (p < 0.001). CONCLUSIONS: We conclude that in neonatal piglets undergoing hyperoxic stress, superimposition of high tidal volume ventilation exacerbates the lung inflammation as assessed by lung monocyte chemoattractant protein-1 and level of myeloperoxidase.

Animals↗

PubMed2000

Arterial blood-gases with 500- versus 1000-ml tidal volumes during out-of-hospital CPR.

The correct tidal volume during cardiopulmonary resuscitation (CPR) is presently debated. While the European Resuscitation Council (ERC) and American Heart Association (AHA) previously recommended a tidal volume of 800-1200 ml, the ERC has recently reduced this to 400-600 ml. In a prospective, randomised study of 17 non-traumatic out-of-hospital cardiac arrest patients intubated and mechanically ventilated 12 min(-1) with 100% oxygen, we have therefore compared arterial blood gases generated with tidal volumes of 500 and 1000 ml. Mean time from cardiac arrest to arrival of the ambulance was 13+/-8 and 14+/-8 min in the two groups, respectively. Arterial blood samples were taken percutaneously 5 and 10-15 min after onset of the mechanical ventilation and analysed instantly. Pa(CO(2)) was significantly higher for a tidal volume of 500 than 1000 ml at both 5 and 10-15 min, 7.48+/-2.23 versus 3.70+/-0.83 kPa (P=0.002) and 7. 45+/-1.19 versus 3.98+/-1.58 kPa (P<0.001). The pH was lower for 500 than 1000 ml at 10-15 min, 7.01+/-0.10 versus 7.20+/-0.17 (P=0.034), with a strong trend in the same direction at 5 min (P=0.06). There was adequate oxygenation with no differences in Pa(O(2)) or BE at any time between the two groups, and no significant differences in any blood gas variables between the 5- and 10-15-min samples. We conclude that arterial normocapnia is not achieved with either tidal volume during advanced life support with non-rebreathing ventilation at 12 min(-1). What ventilation volume is required for CO(2) removal and oxygenation during basic life support with mouth-to-mouth ventilation cannot be extrapolated from the present data. In that situation the risk of gastric inflation, regurgitation and aspiration must also be taken into account.

Aged↗

PubMed2002

Mechanical ventilation in acute lung injury and ARDS. Tidal volume reduction.

Traditional mechanical ventilation practices used generous tidal volumes in patients with acute lung injury and acute respiratory distress syndrome (ALI/ARDS). This approach may have caused overdistention of aerated lung units, thus exacerbating lung injury in some patients. Several recent clinical trials of traditional versus lower tidal volume strategies in ALI/ARDS yielded disparate results. In the largest study, the lower tidal volume approach was associated with lower mortality and more ventilator-free days. This article reviews the rationale for tidal volume reduction in ALI/ARDS and the differences between the studies. Several different interpretations of the recent clinical trial results are addressed.

Adult↗