Pressure-controlled Mode Research Articles

Bilateral Sequential Lung Transplantation

Bilateral Sequential Lung Transplantation

Maintenance of end-expiratory recruitment with increased respiratory rate after saline-lavage lung injury

Cyclical recruitment of atelectasis with each breath is thought to contribute to ventilator-associated lung injury. Extrinsic positive end-expiratory pressure (PEEPe) can maintain alveolar recruitment at end exhalation, but PEEPe depresses cardiac output and increases overdistension. Short exhalation times can also maintain end-expiratory recruitment, but if the mechanism of this recruitment is generation of intrinsic PEEP (PEEPi), there would be little advantage compared with PEEPe. In seven New Zealand White rabbits, we compared recruitment from increased respiratory rate (RR) to recruitment from increased PEEPe after saline lavage. Rabbits were ventilated in pressure control mode with a fraction of inspired O(2) (Fi(O(2))) of 1.0, inspiratory-to-expiratory ratio of 2:1, and plateau pressure of 28 cmH(2)O, and either 1) high RR (24) and low PEEPe (3.5) or 2) low RR (7) and high PEEPe (14). We assessed cyclical lung recruitment with a fast arterial Po(2) probe, and we assessed average recruitment with blood gas data. We measured PEEPi, cardiac output, and mixed venous saturation at each ventilator setting. Recruitment achieved by increased RR and short exhalation time was nearly equivalent to recruitment achieved by increased PEEPe. The short exhalation time at increased RR, however, did not generate PEEPi. Cardiac output was increased on average 13% in the high RR group compared with the high PEEPe group (P < 0.001), and mixed venous saturation was consistently greater in the high RR group (P < 0.001). Prevention of end-expiratory derecruitment without increased end-expiratory pressure suggests that another mechanism, distinct from intrinsic PEEP, plays a role in the dynamic behavior of atelectasis.

Home mechanical ventilatory support in patients with restrictive ventilatory disorders: A 48-year experience

We performed a retrospective analysis to the effects of negative pressure ventilation (NPV), tracheal intermittent positive pressure ventilation (TIPPV), and nasal intermittent positive pressure ventilation (NIPPV, volume or pressure-controlled ventilatory mode), in 114 patients with restrictive ventilatory disorders instituted in our hospital from 1956 until 2005. The patients were assigned on "ad hoc" basis to NPV, TIPPV, or NIPPV. All patients were subdivided in an idiopathic kyphoscoliosis group (IK, n=64), a post-poliomyelitis syndrome group (PP, n=30), or a miscellaneous group (M, n=20). The patients in the PP group had higher survival rates compared to the IK patients (P<0.05), while the M patients had the lowest survival rates (P<0.01). Both NPV (P<0.01) and TIPPV (P<0.05) lead to a decrease in PaCO2 after 9 months compared to baseline. This decrease in PaCO2 was still present after 5 years NPV (P<0.001) and TIPPV (P<0.05). NIPPV lead to an improvement in pulmonary function (P<0.05) and arterial blood gases (P<0.001) after 9 months compared to baseline. After 5 years NIPPV, the arterial blood gases were still significantly improved compared to baseline (P<0.01). Both volume-controlled and pressure-controlled ventilation improved pulmonary function and arterial blood gases. Long-term home mechanical ventilatory support by both NPV and positive pressure ventilation is effective in patients with IK, PP syndrome, and a M group, even after a period of 5 years.

Recruitment maneuvers attenuate repeated derecruitment-associated lung injury

Repeated derecruitments of previously recruited lungs can exacerbate lung injuries during mechanical ventilation. The aim of this study was to assess lung injury associated with repeated derecruitments and to assess whether this type of injury could be attenuated by recruitment maneuvers. Prospective, randomized, experimental animal study. University laboratory. New Zealand White rabbits. Twenty-one rabbits were ventilated in pressure-controlled mode with constant tidal volume (10 mL/kg). After lung injury was induced by repeated saline lavage, positive end-expiratory pressure (PEEP) at a lower inflection point was applied for 3 hrs. The control group (n = 7) received ventilation with the same PEEP for 3 hrs without derecruitments. In the derecruitment group (n = 7), derecruitment was repeatedly induced by intentional disconnection of the ventilatory circuit for 1 min every 10 mins for 3 hrs. In the recruitment maneuver group (n = 7), continuous positive airway pressure of 30 cm H2O was applied for 30 secs after each derecruitment. After PEEP levels were increased to lower the inflection point value, Pao2 increased to >500 mm Hg in all groups. Increased Pao2 persisted at >450 mm Hg in the control and recruitment maneuver groups, whereas progressive declines in arterial oxygen levels were observed in the derecruitment group (median, 381.1 mm Hg [interquartile range, 350.1-466.7 mm Hg] at 2 hrs and 318.2 mm Hg [214.3-414.9 mm Hg] at 3 hrs, p < .05 compared with other groups). Histologically, there was significantly increased hyaline membrane formation in alveolar ducts in the derecruitment group compared with the control group (p = .005). Also, significantly more membranous and respiratory bronchiolar injuries were observed in the derecruitment group compared with the control and recruitment maneuver group (p < .005). These findings suggest that repeated derecruitments could induce lung injuries during mechanical ventilation, and recruitment maneuvers may attenuate derecruitment-associated lung injuries.

Effects of body temperature on ventilator-induced lung injury

Purpose To evaluate the effects of body temperature on ventilator-induced lung injury. Material and Methods Thirty-four male Sprague-Dawley rats were randomized into 6 groups based on their body temperature (normothermia, 37 ± 1°C; hypothermia, 31 ± 1°C; hyperthermia, 41 ± 1°C). Ventilator-induced lung injury was achieved by ventilating for 1 hour with pressure-controlled ventilation mode set at peak inspiratory pressure (PIP) of 30 cmH 2O (high pressure, or HP) and positive end-expiratory pressure (PEEP) of 0 cmH 2O. In control subjects, PIP was set at 14 cmH 2O (low pressure, or LP) and PEEP set at 0 cmH 2O. Systemic chemokine and cytokine (tumor necrosis factor α, interleukin 1 β, interleukin 6, and monocyte chemoatractant protein 1) levels were measured. The lungs were assessed for histological changes. Results Serum chemokines and cytokines were significantly elevated in the hyperthermia HP group compared with all 3 groups, LP (control), normothermia HP, and hypothermia HP. Oxygenation was better but not statistically significant in hypothermia HP compared with other HP groups. Cumulative mean histology scores were higher in hyperthermia HP and normothermia HP groups compared with control and normothermia HP groups. Conclusions Concomitant hyperthermia increased systemic inflammatory response during HP ventilation. Although hypothermia decreased local inflammation in the lung, it did not completely attenuate systemic inflammatory response associated with HP ventilation.

Effect of inspiratory time on tidal volume delivery in anesthesia and intensive care unit ventilators operating in pressure control mode

Study objective To compare the effect of inspiratory time and lung compliance on tidal volume (V t) delivery in anesthesia and intensive care unit (ICU) ventilators operating in pressure control mode. Setting Respiratory research laboratory of a tertiary care medical center. Design Two anesthesia ventilators with pressure control capability (Narkomed 6000, Dräger Medical, Inc, Telford, Pa, and the Datex-Ohmeda Aestiva 5, Datex-Ohmeda, Inc, Madison, Wis) and one critical care ventilator (Puritan Bennett 7200, Puritan-Bennett, Pleasanton, Calif) were studied under varying inspiratory time and lung compliance conditions using a mechanical lung model. Intervention Each ventilator was set to pressure control mode at a fixed inspiratory/expiratory (I/E) ratio. The respiratory rate (RR) was varied between 6 and 28 breaths per minute. Lung compliance and inspiratory time settings were set to simulate clinical conditions known to affect anesthesia ventilator performance. Measurements Inspiratory flow, V ts, and peak airway pressures were measured using the on-board monitor for each ventilator, and confirmed with the Bicore CP-100 pulmonary mechanics monitor (Bicore Monitoring Systems, Inc, Irvine, Calif). To assess differences in inspiratory flow between ventilators, airway pressures were continuously monitored during inspiration. Main results Increasing RRs caused delivered V ts to decrease for all ventilators. However, decreases in V ts were significantly larger for anesthesia than for ICU ventilators. At a lung compliance of 0.02 L/cm H 2O and set V t of 700 mL, V t delivery for the Puritan Bennett 7200 ventilator remained at 88% of baseline, but decreased to 76% for the Aestiva 5 when RRs were increased from 6 to 28 breaths per minute ( P < .0025). Airway pressure tracings demonstrated a slower increase in inspiratory airway pressure for the Aestiva 5 than for the other ventilators. Conclusion Differences in inspiratory flow delivery between ICU and anesthesia ventilators can cause differences in V t delivery when the pressure control mode is used at high RRs. These differences can significantly impact the perioperative care of critically ill patients requiring ventilatory support.

Inspiratory oscillatory flow with a portable ventilator: a bench study

IntroductionWe observed an oscillatory flow while ventilating critically ill patients with the Dräger Oxylog 3000™ transport ventilator during interhospital transfer. The phenomenon occurred in paediatric patients or in adult patients with severe airway obstruction ventilated in the pressure-regulated or pressure-controlled mode. As this had not been described previously, we conducted a bench study to investigate the phenomenon.MethodsAn Oxylog 3000™ intensive care unit ventilator and a Dräger Medical Evita-4 NeoFlow™ intensive care unit ventilator were connected to a Dräger Medical LS800™ lung simulator. Data were registered by a Datex-S5™ Monitor with a D-fend™ flow and pressure sensor, and were analysed with a laptop using S5-Collect™ software. Clinical conditions were simulated using various ventilatory modes, using various ventilator settings, using different filters and endotracheal tubes, and by changing the resistance and compliance. Data were recorded for 258 combinations of patient factors and respirator settings to detect thresholds for the occurrence of the phenomenon and methods to overcome it.ResultsUnder conditions with high resistance in pressure-regulated ventilation with the Oxylog 3000™, an oscillatory flow during inspiration produced rapid changes of the airway pressure. The phenomenon resulted in a jerky inspiration with high peak airway pressures, higher than those set on the ventilator. Reducing the inspiratory flow velocity was effective to terminate the phenomenon, but resulted in reduced tidal volumes.ConclusionOscillatory flow with potentially harmful effects may occur during ventilation with the Dräger Oxylog 3000™, especially in conditions with high resistance such as small airways in children (endotracheal tube internal diameter <6 mm) or severe obstructive lung diseases or airway diseases in adult patients.

Prediction of fluid responsiveness in patients during cardiac surgery

Left ventricular stroke volume variation (SVV) has been shown to be a predictor of fluid responsiveness in various subsets of patients. However, the accuracy and reliability of SVV are unproven in patients ventilated with low tidal volumes. Fourteen patients were studied immediately after coronary artery bypass grafting (CABG). All patients were mechanically ventilated in pressure-controlled mode [tidal volume 7.5 (1.2) ml kg(-1)]. In addition to standard haemodynamic monitoring, SVV was assessed by arterial pulse contour analysis. Left ventricular end-diastolic area index (LVEDAI) was determined by transoesophageal echocardiography. A transpulmonary thermodilution technique was used for measurement of cardiac index (CI), stroke volume index (SVI) and intrathoracic blood volume index (ITBI). All variables were assessed before and after a volume shift induced by tilting the patients from the anti-Trendelenburg (30 degrees head up) to the Trendelenburg position (30 degrees head down). After the change in the Trendelenburg position, SVV decreased significantly, while CI, SVI, ITBI, LVEDAI, central venous pressure (CVP) and pulmonary artery occlusion pressure (PAOP) increased significantly. Changes in SVI were significantly correlated to changes in SVV (r=0.70; P<0.0001) and to changes in LVEDAI, ITBI, CVP and PAOP. Only prechallenge values of SVV were predictive of changes in SVI after change from the anti-Trendelenburg to the Trendelenburg position. In patients after CABG surgery who were ventilated with low tidal volumes, SVV enabled prediction of fluid responsiveness and assessment of the haemodynamic effects of volume loading.

Post-suction recruitment manoeuvre restores lung function in healthy, anaesthetized pigs.

Endotracheal suction can cause partial lung collapse and hypoxia and alter lung mechanics. We investigated the effects of adding a recruitment manoeuvre directly after endotracheal suction to restore lung volume in volume-controlled ventilation and pressure-controlled ventilation modes. Five anaesthetized pigs were investigated. The effects of endotracheal suction with or without a recruitment manoeuvre were compared in random order. In volume-controlled ventilation, compliance decreased after suction from 33 +/- 5 to 26 +/- 6 ml x cmH2O(-1) (P<0.05), and 30 minutes later it remained decreased at 25 +/- 6 ml x cmH2O(-1). Venous admixture increased after suction from 5 +/- 2 to 8 +/- 4% (P<0.05), but had recovered at 30 minutes. In pressure-controlled ventilation, compliance decreased after suction from 34 +/- 3 to 25 +/- 7 ml x cmH2O(-1) (P<0.05), and 30 minutes later it remained decreased at 25 +/- 7 ml x cmH2O(-1). Venous admixture increased after suction from 5 +/- 2 to 13 +/- 7% (P<0.05), and had not recovered after 30 minutes, 10 +/- 4%. When a recruitment manoeuvre was applied directly after suction, no negative side-effects were registered in volume-controlled ventilation or pressure-controlled ventilation. We conclude that the impairment of lung mechanics and gas exchange induced by endotracheal suction can be prevented by a simple post-suction recruitment manoeuvre. Further studies are needed to identify a suitable suction recruitment manoeuvre in patients with diseased lungs.

Efficacité de la kinésithérapie respiratoire chez des enfants intubés ventilés atteints de bronchiolite aiguë

Objectives. – Despite the lack of clinical studies, chest physiotherapy (CP) is widely used in children with acute bronchiolitis. The main goal of this study was to evaluate its short-term efficacy in children under mechanical ventilation for acute bronchiolitis. Methods. – Twenty children were studied. All were under mechanical ventilation on a pressure-controlled mode. Oxygen saturation, transcutaneous PCO 2 and tidal volume were measured before any intervention, after endotracheal succion, after CP and endotracheal succion and 1 h later. Results. – Thirty-eight analyses were performed. Baseline tidal volume, oxygen saturation and transcutaneous PCO 2 were not modified after endotracheal succion. Immediately and 1 h after CP, SpO 2 (98% vs. 94.5%), and tidal volume (66 vs. 55 ml) significantly increased. Conclusion. – The increase of O 2 saturation and tidal volume may be linked to the improvement of bronchial sputum clearance. Further studies are needed to estimate the long-term efficacy of CP in acute bronchiolitis.

Oxygen tension under hyperbaric conditions in healthy pig brain

To investigate the effect of hyperbaric conditions on brain oxygenation, intracranial pressure and brain glucose/lactate levels in healthy non-brain-traumatized animals. Prospective animal study in a hyperbaric chamber. Twelve adult Landrace/Yorkshire pigs. The animals were normoventilated in a pressure-controlled mode according to the open lung concept first at normobaric pressures (FiO2 of 0.4 and 1.0) and subsequently in the hyperbaric chamber at 1.9 and 2.8 bar (both at an FiO2 of 1.0). Under these conditions brain oxygen tension and intracranial pressure were recorded and brain glucose/lactate levels were measured by microdialysis. At normobaric conditions, increasing the FiO2 from 0.4 (baseline) to 1.0 resulted in a significant increase in brain oxygen tension from 33 +/- 14 to 63 +/- 28 mmHg (P<0.05). Compared with baseline, both hyperbaric conditions (at an FiO2 of 1.0) led to a significant increase in brain oxygen tension to 151 +/- 65 mmHg (P<0.001) at 1.9 bar and to 294 +/- 134 mmHg (P<0.001) at 2.8 bar. If there is a need for increased oxygenation in the brain, then one way to achieve this is to apply hyperbaric conditions at 100% oxygen. Compared with an atmospheric pressure with a FiO2 of 0.4, a nine-fold increase (900%) in PbrO2 values can be reached by increasing the FiO2 to 1.0 and the pressure to 2.8 bar. In this study, hyperbaric oxygen pressure in the brain did not lead to changes in intracranial pressure or in brain glucose/lactate levels.

Modeling the effect of progressive endotracheal tube occlusion on tidal volume in pressure-control mode.

A recognized hazard of prolonged endotracheal intubation is progressive airway occlusion resulting from deposition of secretions on the inner surface of the endotracheal tube (ETT). When volume-controlled ventilation is used, progressive ETT occlusion may be detected by monitoring the difference between peak and plateau airway pressures. In pressure-controlled modes, however, inspiratory airway pressures are preset and thus cannot act as a warning indicator. Instead, changes in delivered tidal volumes may aid the diagnosis of ETT occlusion. To determine whether tidal volume monitoring effectively detects progressive ETT occlusion, we mathematically modeled the response of a ventilator operating in pressure-controlled mode to increasing airway resistance. To corroborate our model, we then bench-tested the Siemens 300 and Puritan-Bennett 7200 ventilators by using a test lung and a series of ETTs ranging in size from 9.0 to 3.5 mm inner diameter to simulate progressive occlusion. We found that when pressure-controlled mode was used, progressive ETT occlusion did not reduce delivered tidal volumes until occlusion was nearly complete. We conclude that prolonged use of pressure-controlled mode may allow significant ETT obstruction to build up undetected, risking complete ETT occlusion and complicating the perioperative care of patients ventilated with this mode. Although increasing airway pressures during volume-controlled ventilation allow early recognition of endotracheal tube (ETT) obstruction, airway pressures with pressure-controlled ventilation are fixed. We found during tests of two intensive care unit ventilators that although ETT obstruction reduces delivered tidal volumes during pressure-controlled ventilation, reductions do not occur until occlusion is advanced.

Evaluation of Parameters of Gas Exchange During Partial Liquid Ventilation in Normal Rabbit Lung

Background: The opitmal ventilator setting during partial liquid ventilation(PLV) is controversial. This study investigated the effects of various gas exchange parameters during PLV in normal rabbit lungs in order to aid in the development of an optimal ventilator setting during PLV. Methods: Seven New-Zealand white rabbits were ventilated in pressure-controlled mode with the following settings; tidal volume() 8 mL/kg, positive end-expiratory pressure(PEEP) 4 , inspiratory-to-expiratory ratio(I:E ratio) 1:2, fraction of inspired oxygen() 1.0. The respiration rate(RR) was adjusted to keep between 35~45 mmHg. The ventilator settings were changed every 30 min in the following sequence : (1) Baseline, as the basal ventilator setting, (2) Inverse ratio, I:E ratio 2:1, (3) high PEEP, adjust PEEP to achieve the same mean inspiratory pressure (MIP) as in the inverse ratio, (4) High , 15 mL/kg, (5) high RR, the same minute ventilation (MV) as in the High . Subsequently, the same protocol was repeated after instilling 18 mL/kg of perfluorodecalin for PLV. The parameters of gas exchange, lung mechanics, and hemodynamics were examined. Results: (1) The gas ventilation(GV) group showed no significant changes in the at all phases. The was lower and the pH was higher at the high and high RR phases(p for the PLV was mmHg. This was significantly lower when decreased compared to the baseline for GV which was mmHg(p=0.001). During PLV, the , was significantly higher at the high PEEP( mmHg) and high ( mmHg) phases compared with the baseline phase. However, it did not change significantly during the inverse I:E ratio or the high RR phases. (3) The was significantly lower at high and RR phases for both the GV and PLV. During the PLV, were significantly higher compared to the GV (p and PEEP are important for optimal oxygenation.

Intracranial pressure, brain PCO2, PO2, and pH during hypo- and hyperventilation at constant mean airway pressure in pigs.

To evaluate in healthy, non-brain-traumatized animals the effects of hypo- and hyperventilation on intracranial pressure (ICP) and brain carbon dioxide, oxygen, and pH during the use of a ventilatory mode at constant mean airway pressure (MAwP). Prospective animal study in a university laboratory. Eight crossbred Landrace/Yorkshire pigs. The animals were ventilated in a pressure-controlled mode according to the open lung concept with an inspired oxygen fraction of 1.0. Starting at normoventilation, a stepwise hypo- and hyperventilation was performed to PaCO2 values of 90.4+/-10.4 and 26.9+/-4.1 mmHg, respectively. The ICP and brain parenchyma values [carbon dioxide (PbrCO2), oxygen (PbrO2), and pH (brpH)] measured by multiparameter sensors were recorded continuously during these maneuvres. During hypoventilation there was a significant increase in PbrCO2 tension, PbrO2 tension, and ICP. During hyperventilation there was a significant decrease in PbrCO2 tension and ICP while the change in PbrO2 was not significant. MAwP was kept stable during the stepwise hypo- and hyperventilation, and this resulted in a constant mean arterial pressure. Controlled hypo- and hyperventilation at constant MAwP in non-brain-traumatized pigs appears to induce changes in ICP and cerebral perfusion pressure which, however, do not necessarily lead to cerebral ischemia. To achieve adequate cerebral perfusion at an increased ICP level due to hypoventilation one must maintain sufficient arterial blood pressure. Hypercapnia resulted in a significant increase in brain oxygenation; however, this does not necessarily mean that permissive hypercapnia is neuroprotective.

Effect of ventilation mode on gas exchange during partial liquid ventilation at different perfluorocarbon doses in surfactant-depleted lung.

Although gas ventilation is an integral part of partial liquid ventilation (PLV), the role of ventilation mode during PLV is not established, especially at a varying perfluorocarbon dose. In 10 surfactant-depleted rabbits, PLV was performed at a low dose (10 ml/kg) and at a functional residual capacity (FRC) dose (30 ml/kg) of perfluorodecalin in pressure-control (PC) and volume-control (VC) modes in balanced sequence. In these four PLV trials, PC mode was adjusted to be identical to VC mode with regard to tidal volume and inspiratory-to-expiratory ratio. PaO2 during PLV in PC mode was higher than in VC mode at the Low dose (159 plus minus 93 mm Hg, 115 plus minus 75 mm Hg, respectively: p = 0.005) and at the FRC dose (228 +/- 114 mm Hg, 164 +/- 104 mm Hg, respectively: p = 0.002). PaCO2 during PLV in PC mode was lower than in VC mode at the Low dose (59 +/- 18 mm Hg, 72 +/- 20 mm Hg, respectively: p = 0.005), whereas PaCO2 at the FRC dose was not different between modes. Curves of inspiratory flow appeared least deformed with PLV in PC mode at the Low dose, whereas they were saw-tooth deformed with PLV in VC mode at both doses. Actual time for inspiratory gas flow during PLV was shorter in PC mode compared with VC mode at both doses. In conclusion, in surfactant-depleted rabbit, gas exchange during PLV was better with PC mode compared with VC mode, especially at a low perfluorocarbon dose. Given the same tidal volume, PC appeared to insufflate the perfluorocarbon-filled lung better than VC at both low and FRC doses of perfluorocarbon.

Dual control modes: combining volume and pressure breaths.

New modes of ventilator operation are often introduced without rhyme or reason. The dual control modes are, however, a response of the manufacturers to clinician desire to provide constant minute volume/tidal volume while operating in the pressure support or pressure control mode. Dual control modes allow the ventilator to control pressure or volume. The ventilator cannot control pressure and volume at the same time, so it is an either/or phenomenon. Dual control modes can operate "within a breath" or on a "breath to breath" basis. Dual control within a breath refers to a technique whereby the ventilator switches from pressure to volume control in the middle of a breath. In the technique of dual control breath to breath, all breaths are pressure control breaths, but the level of pressure varies from breath to breath in an effort to maintain a constant tidal volume.

Ventilator-induced lung injury leads to loss of alveolar and systemic compartmentalization of tumor necrosis factor-alpha.

To determine the effect on compartmentalization of the tumor necrosis factor (TNF)-alpha response in the lung and systemically after ventilation with high peak inspiratory pressure with and without positive end-expiratory pressure (PEEP). Prospective, randomized, animal study in an experimental laboratory of a university. 85 male Sprague-Dawley rats. Lipopolysaccharide was given intratracheally or intraperitoneally to stimulate TNF-alpha production; control animals received a similar amount of saline. Animals were subsequently ventilated for 20 min in a pressure control mode with peak inspiratory pressure/PEEP ratio of either 45/0 or 45/10 (frequency 30 bpm, I/E ratio 1:2, FIO2 = 1). Blood gas tension and arterial pressures were recorded at 1, 10, and 20 min after start of mechanical ventilation. After killing of the animals pressure-volume curves were recorded, and bronchoalveolar lavage (BAL) was performed for assessment of protein content and the small/large surfactant aggregate ratio. TNF-alpha was determined in serum and BAL. TNF-alpha levels were significantly increased after lipopolysaccharide stimulation; furthermore ventilation without PEEP resulted in a significant shift of TNF-alpha to the nonstimulated compartment as opposed to ventilation with a PEEP level of 10 cmH2O. Ventilation strategies which are known to induce ventilation-induced lung injury (VILI) disturb the compartmentalization of the early cytokines response in the lung and systemically. Furthermore, the loss of compartmentalization is a two-way disturbance, with cytokines shifting from the vascular side to the alveolar side and vice versa. A ventilation strategy (PEEP level of 10 cmH2O) which prevents VILI significantly diminished this shift in cytokines.

Analysis of nonlinear volume-dependent respiratory system mechanics in pediatric patients.

Analysis of dynamic respiratory system mechanics is generally based on a resistance-compliance model in which nonlinearities of the respiratory mechanics indices are not considered. The recently developed SLICE method analyzing consecutive volume slices of the tidal volume was used for determination of non-linear volume-dependent respiratory system mechanics. Volume-dependent compliance C(Slice) and resistance R(Slice) were compared with C(MLR) and R(MLR) obtained by standard multiple linear regression analysis (MLR). Prospective observational study. Pediatric intensive care unit in a university hospital. Fifteen pediatric patients, aged 24 days to 9.6 yrs, weighing 3-67.5 kg. None. With respect to their pulmonary status, the patients were grouped into three clinical groups: patients with no lung diseases, patients with restrictive lung diseases, and patients with obstructive lung diseases. All patients were mechanically ventilated via a cuffed endotracheal tube in the pressure-controlled mode. Flow and airway pressure were measured at the proximal end of the tube and tracheal pressure was continuously calculated. Respiratory mechanics were determined either with the SLICE method or, as reference, by using standard MLR. In most patients, the pressure-volume relationship was nonlinear, particularly in patients with restrictive and obstructive lung diseases. In the presence of considerable nonlinearity, the volume-dependent respiratory mechanics indices obtained by the SLICE method showed better agreement between recalculated and original pressure-volume loops compared with the MLR results. Furthermore, signs of overdistension of the patient's lung became obvious when using the SLICE method, whereas they were undetected by MLR. The SLICE method is well suited for the analysis of nonlinear volume-dependent respiratory system mechanics in pediatric patients. The SLICE method may be used as a first step toward an adaptation of ventilator settings with respect to the actual mechanical status of the patient's respiratory system, and, to prevent pulmonary overdistension.

Effects of Fiberoptic Bronchoscopy During Mechanical Ventilation in a Lung Model

To evaluate the effects of fiberoptic bronchoscopy (FOB) on delivered volumes and pressures during mechanical ventilation, utilizing a lung model. Bench study. Laboratory. Using varying-sized endotracheal tubes (ETTs), we ventilated a lung model at two levels of compliance utilizing different modes and parameters of ventilation. After establishing baseline measurements, the bronchoscope was inserted and measurements repeated. During controlled mechanical ventilation (CMV) with a preset high-pressure limit (HPL), tidal volumes (VTs) were reduced from 700 mL to 0 to 500 mL following insertion of the bronchoscope. Increasing the HPL to 120 cm H(2)O resulted in a VT of 40 to 680 mL. Changing from square to decelerating flow waveform resulted in no consistent difference in VT. Auto-positive end-expiratory pressure (auto-PEEP) of 0 to 41 cm H(2)O was present under most conditions. Higher rates and lower peak inspiratory flows were associated with higher levels of auto-PEEP. In the pressure-control (PC) mode, using a preset inspiratory pressure level (IP), VT was reduced from 700 mL to 40 to 280 mL following insertion of the bronchoscope. Maximum IP (100 cm H(2)O) increased VT to 260 to 700 mL. Auto-PEEP was less in the PC mode. Extreme care must be taken when bronchoscopy is performed on a patient receiving mechanical ventilation. Extremely low VT and significant auto-PEEP may develop unless flow, respiratory rate, mode, and ETT size are carefully selected. The PC mode delivered more volume than did the CMV mode. When performing FOB during mechanical ventilation, the inside diameter of the ETT should be > or = 2.0-mm larger than the outside diameter of the bronchoscope to maintain volume delivery and minimize the development of auto-PEEP.

Partial liquid ventilation shows dose-dependent increase in oxygenation with PEEP and decreases lung injury associated with mechanical ventilation

Purpose: The purpose of this article is to evaluate the effect of positive end-expiratory pressure (PEEP) during partial liquid ventilation (PLV) and to investigate if lung damage associated with mechanical ventilation can be reduced by PLV. Materials and Methods: Twenty-two New-Zealand white rabbits were ventilated in pressure-controlled mode maintaining constant tidal volume (10 mL/kg). Lung injury was induced by repeated saline lavage (Pao2 < 100 mm Hg). Two incremental PEEP steps maneuvers (IPSMs) from 2 to 10 cm H2O in 2 cm H2O steps were performed sequentially. The control group received the first IPSM in the supine position and were turned prone for the second IPSM. In the PLV group (n = 7), 12 mL/kg of perfluorodecalin was instilled after lung injury before the two IPSMs. The early prone group (n = 7) received both IPSMs in the prone position. Parameters of gas exchange, lung mechanics, and hemodynamics as well as pathology were examined. Results: During the first IPSM, the PLV group showed a significant increase in Pao2 after instillation of perfluorodecalin (P < .05) and then showed a dose-dependent increase in Pao2 with PEEP. The control and EP groups showed improvement in Pao2 only at higher PEEP, eventually showing no intergroup differences at PEEP of 10 cm H2O. During the second IPSM only the PLV group retained its ability to increase Pao2 to the level obtained during the first IPSM (P < .05 compared with control and EP groups). During the first IPSM all three groups showed increasing trend in static compliance (Cst) with PEEP, peaking at PEEP of 8 cm H2O. During the second IPSM, only the PLV group showed increase in static compliance with PEEP (P < .05 compared with other groups). Lung histology revealed significantly less hyaline membrane formation in the PLV group (P < .05). Conclusion: PLV shows dose-dependent increase in oxygenation with PEEP and may reduce lung damage associated with mechanical ventilation. Copyright © 2000 by W.B. Saunders Company