Increase In Positive End-expiratory Pressure Research Articles

Vital organ blood flow during high-frequency ventilation

We read with interest the article by David and colleagues [1] comparing the effects of high-frequency oscillatory ventilation with pressure controlled ventilation with respect to vital organ blood flow in an animal model of acute lung injury. However, there are some points we wish to comment on. Firstly, the authors state that their study is limited due to the lack of more frequent blood flow measurements, as all parameters were measured only once thirty minutes after switching to a new mean airway pressure (Pmean). Indeed, changes in hemodynamic variables are most pronounced straight after increasing mean airway pressure [2]. It has been shown that cardiac output initially decreased substantially after an increase in positive end-expiratory pressure (PEEP), but that it adapted to the increased PEEP thereafter due to dynamic hemodynamic changes [3]. Consequently, compensatory mechanisms missed by insufficient data sampling could explain the only slightly decreased cardiac output and unchanged organ blood flow seen in the study by David and colleagues [1]. Therefore, it is of paramount importance to investigate parameters of individual organ perfusion more frequently, and obtain variables of tissue oxygenation and metabolism. Furthermore, brain tissue is extremely susceptible to ischemia, and even a few minutes of compromised cerebral perfusion affect the rate of cerebral oxygen metabolism and tissue integrity. To elucidate the impact of mechanical ventilation on brain tissue, the authors should have analyzed cerebral tissue biochemistry [4] or established biomarkers of cerebral ischemia, such as S-100β or neuron-specific enolase. Secondly, cardiac filling pressures have repeatedly been shown to only poorly reflect instantaneous cardiac preload. Right ventricular end-diastolic volume and global end-diastolic volume have been demonstrated to be clearly superior for this than cardiac filling pressures, particularly at high intrathoracic pressures in a model of acute lung injury [5], and would have provided more detailed information regarding interaction of recruitment manoeuvre, preload and organ perfusion.

Acoustic effects of positive end‐expiratory pressure on normal lung sounds in mechanically ventilated pigs

Computerized lung sounds analysis offers a new technique to monitor regional ventilation during spontaneous breathing. The purpose of the present study was to assess the acoustic behaviour of the respiratory system in healthy pigs during mechanical ventilation when a positive end-expiratory pressure (PEEP) is applied. Lung sounds were recorded during mechanical ventilation and different PEEP levels of 0, 5, 10, 15 and 20 cm H(2)O were applied. The increase in end-expiratory lung volume (EELV) related to the PEEP application was also measured and the correlation between changes in EELV (DeltaEELV) and sound amplitude (DeltaA) was examined. The amplitude of normal lung sounds was reduced by application of PEEP >or=10 cm H(2)O (P<0.05). The increase in PEEP from 0 to 20 cm H(2)O reduced the acoustic energy of lung sounds recorded at ZEEP by 0.3 dB (PEEP 5), 2 dB (PEEP 10), 5 dB (PEEP 15) and 7 dB (PEEP 20), which corresponds to 1%, 6%, 14% and 21% in acoustic attenuation, respectively. The variations in DeltaA correlated with changes in lung volume (P<0.05) and with changes in compliance of the respiratory system (P<0.05), but were not correlated with changes of the resistance of respiratory system. The frequency analysis showed a downward shifting of the spectra at frequencies between 150 and 600 Hz for PEEP levels >or=10 cm H(2)O and frequencies between 75 and 600 Hz for PEEP levels >or=15 cm H(2)O. The application of increasing levels of PEEP reduced the amplitude and changed the spectral characteristics of normal lung sounds.

Recruitment maneuver and high positive end-expiratory pressure improve hypoxemia in patients after pulmonary thromboendarterectomy for chronic pulmonary thromboembolism*

To investigate the effects of a recruitment maneuver and high positive end-expiratory pressure (PEEP) on oxygenation and hemodynamics in hypoxemic patients with pulmonary hypertension after pulmonary thromboendarterectomy for chronic pulmonary thromboembolism. Prospective, observational, clinical study. A surgical intensive care unit in a national heart institute. Fourteen consecutively admitted patients who developed acute lung injury (Pa(O2) <300 torr at F(IO2) 1.0) and pulmonary hypertension (mean pulmonary artery pressure >25 mm Hg) after pulmonary thromboendarterectomy for chronic pulmonary thromboembolism. The recruitment maneuver was an increase of PEEP to 30 cm H2O in one step for 1 min at F(IO2) 1.0. The level of pressure control ventilation during the recruitment maneuver was the same as before the maneuver. Subsequently, PEEP was decreased in 15-min intervals from 15 to 10, 5, and 0 cm H2O. Hemodynamics and respiratory variables were analyzed before and during the recruitment maneuver and at each PEEP level. At F(IO2) 1.0, Pa(O2) increased from 240 +/- 62 torr to 470 +/- 83 torr at 15 cm H2O of PEEP and 469 +/- 75 torr at 10 cm H2O of PEEP after the recruitment maneuver (p < .001). At 15 cm H2O of PEEP, cardiac index decreased (from 2.7 +/- 0.6 at baseline to 2.2 +/- 0.3 L.min(-1).m(-2), p < .01) and mean blood pressure decreased (from 86 +/- 8 at baseline to 74 +/- 11 mm Hg, p < .05), but they returned to the baseline levels at 10 cm H2O of PEEP (2.5 +/- 0.4 L.min(-1).m(-2) and 83 +/- 9 mm Hg). There were no differences in mean pulmonary artery pressure at different levels of PEEP. In hypoxemic patients with pulmonary hypertension after pulmonary thromboendarterectomy for chronic pulmonary thromboembolism, oxygenation was improved by the recruitment maneuver followed by high PEEP. However, hemodynamics were transiently suppressed and overall oxygen delivery did not change.

Effects of PEEP on the Intracranial System of Patients With Head Injury and Subarachnoid Hemorrhage: The Role of Respiratory System Compliance

Positive end-expiratory pressure (PEEP) can be effective in improving oxygenation, but it may worsen or induce intracranial hypertension. The authors hypothesized that the intracranial effects of PEEP could be related to the changes in respiratory system compliance (Crs). A prospective study investigated 21 comatose patients with severe head injury or subarachnoid hemorrhage receiving intracranial pressure (ICP) monitoring who required mechanical ventilation and PEEP. The 13 patients with normal Crs were analyzed as group A and the 8 patients with low Crs as group B. During the study, 0, 5, 8, and 12 cm H2O of PEEP were applied in a random sequence. Jugular pressure, central venous pressure (CVP), cerebral perfusion pressure (CPP), intracranial pressure (ICP), cerebral compliance, mean velocity of the middle cerebral arteries, and jugular oxygen saturation were evaluated simultaneously. In the group A patients, the PEEP increase from 0 to 12 cm H2O significantly increased CVP (from 10.6 +/- 3.3 to 13.8 +/- 3.3 mm Hg; p < 0.001) and jugular pressure (from 16.6 +/- 3.1 to 18.8 +/- 3.2 mm Hg; p < 0.001), but reduced mean arterial pressure (from 96.3 +/- 6.7 to 91.3 +/- 6.5 mm Hg; p < 0.01), CPP (from 82.2 +/- 6.9 to 77.0 +/- 6.2 mm Hg; p < 0.01), and mean velocity of the middle cerebral arteries (from 73.1 +/- 27.9 to 67.4 +/- 27.1 cm/sec; F = 7.15; p < 0.001). No significant variation in these parameters was observed in group B patients. After the PEEP increase, ICP and cerebral compliance did not change in either group. Although jugular oxygen saturation decreased slightly, it in no case dropped below 50%. In patients with low Crs, PEEP has no significant effect on cerebral and systemic hemodynamics. Monitoring of Crs may be useful for avoiding deleterious effects of PEEP on the intracranial system of patients with normal Crs.

High-frequency percussive ventilation: an alternative mode of ventilation for head-injured patients with adult respiratory distress syndrome.

Adult respiratory distress syndrome develops in up to 20% of patients with severe head injury. This complicates the treatment of head-injured patients because lung-protective strategies such as high positive end-expiratory pressure (PEEP) and permissive hypercapnia may increase intracranial pressure (ICP) and reduce cerebral perfusion pressure. The use of high-frequency percussive ventilation (HFPV) is an alternate mode of ventilation that may improve oxygenation for head-injured patients while also lowering ICP. Clinical data were collected retrospectively over a 1-year period. Patients were included if they had a severe traumatic brain injury with a Glasgow Coma Score (GCS) of 8 or lower, a ventriculostomy drain for ICP measurement and cerebral spinal fluid drainage, and adult respiratory distress syndrome. Patients were switched from conventional mechanical ventilation to HFPV at the discretion of the attending trauma surgeon. Data for partial pressure of oxygen to fraction of inspired oxygen (PF) ratio, peak inspiratory pressure (PIP), ICP, partial pressure of carbon dioxide level (PCO2), PEEP, and mean airway pressure were compared before and then 4 and 16 hours after institution of HFPV therapy. A total of 10 patients met study criteria. Data were expressed as mean +/- standard error. There was an increase in PF ratio (91.8 +/- 13.2 vs. 269.7 +/- 34.6; p < 0.01), PEEP (14 +/- 2.5 vs. 16 +/- 3.5), and mean airway pressure (20.4 +/- 4.8 vs. 23.6 +/- 6.8) 16 hours after institution of HFPV. There was a decrease in ICP (30.9 +/- 3.4 vs. 17.4 +/- 1.7; p < 0.01), PC02 (37.7 +/- 4.1 vs. 32.7 +/- 1.1; p < 0.05), and PIP (49.4 +/- 10 vs. 41 +/- 7.9; p < 0.05) at 16 hours. Overall mortality was 10%. Therapy with HFPV produced a significant improvement in oxygenation with a concomitant reduction in ICP during the first 16 hours. This therapy may represent an important new method for the management of adult respiratory distress syndrome among head-injured trauma patients, although the long-term outcome of HFPV still needs evaluation.

Bench-to-bedside review: Recruitment and recruiting maneuvers

In patients with acute respiratory distress syndrome (ARDS), the lung comprises areas of aeration and areas of alveolar collapse, the latter producing intrapulmonary shunt and hypoxemia. The currently suggested strategy of ventilation with low lung volumes can aggravate lung collapse and potentially produce lung injury through shear stress at the interface between aerated and collapsed lung, and as a result of repetitive opening and closing of alveoli. An 'open lung strategy' focused on alveolar patency has therefore been recommended. While positive end-expiratory pressure prevents alveolar collapse, recruitment maneuvers can be used to achieve alveolar recruitment. Various recruitment maneuvers exist, including sustained inflation to high pressures, intermittent sighs, and stepwise increases in positive end-expiratory pressure or peak inspiratory pressure. In animal studies, recruitment maneuvers clearly reverse the derecruitment associated with low tidal volume ventilation, improve gas exchange, and reduce lung injury. Data regarding the use of recruitment maneuvers in patients with ARDS show mixed results, with increased efficacy in those with short duration of ARDS, good compliance of the chest wall, and in extrapulmonary ARDS. In this review we discuss the pathophysiologic basis for the use of recruitment maneuvers and recent evidence, as well as the practical application of the technique.

Identification of a Non-Linear Model as a New Method to Detect Expiratory Airflow Limitation in Mechanically Ventilated Patients

Expiratory flow limitation (EFL) can occur in mechanically ventilated patients with chronic obstructive pulmonary disease and other disorders. It leads to dynamic hyperinflation with ensuing deleterious consequences. Detecting EFL is thus clinically relevant. Easily applicable methods however lack this detection being routinely made in intensive care. Using a simple mathematical model, we propose a new method to detect EFL that does not require any intervention or modification of the ongoing therapeutic. The model consists in a monoalveolar representation of the respiratory system, including a collapsible airway that is submitted to periodic changes in pressure at the airway opening: EFL provokes a sharp expiratory increase in the resistance Rc of the collapsible airway. The model parameters were identified via the Levenberg-Marquardt method by fitting simulated data on the airway pressure and the flow signals recorded in 10 mechanically ventilated patients. A sensitivity study demonstrated that only 8/11 parameters needed to be identified, the remaining three being given reasonable physiological values. Flow-volume curves built at different levels of positive expiratory pressure, PEEP, during "PEEP trials" (stepwise increases in positive end-expiratory pressure to optimize ventilator settings) have shown evidence of EFL in three cases. This was concordant with parameter identification (high Rc during expiration for EFL patients). We conclude from these preliminary results that our model is a potential tool for the non-invasive detection of EFL in mechanically ventilated patients.

Lung computed tomography during a lung recruitment maneuver in patients with acute lung injury.

To assess the acute effect of a lung recruitment maneuver (LRM) on lung morphology in patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Ten patients with ALI/ARDS on mechanical ventilation. Prospective clinical study. Computed tomography (CT) scan facility in a teaching hospital. An LRM performed by stepwise increases in positive end-expiratory pressure (PEEP) of up to 30-40 cm H(2)O. Lung basal CT sections were taken at end-expiration (patients 1 to 5), and at end-expiration and end-inspiration (patients 6 to 10). Arterial blood gases and static compliance (C(st)) were measured before, during and after the LRM. Poorly aerated and non-aerated tissue at PEEP 10 cm H(2)O accounted for 60.0+/-29.1% of lung parenchyma, while only 1.1+/-1.8% was hyperinflated. Increasing PEEP to 20 and 30 cm H(2)O, compared to PEEP 10 cm H(2)O, decreased poorly aerated and non-aerated tissue by 16.2+/-28.0% and 33.4+/-13.8%, respectively ( p<0.05). This was associated with an increase in PaO(2) and a decrease in total static compliance. Inspiration increased alveolar recruitment at all PEEP levels. Hyperinflated tissue increased up to 2.9+/-4.0% with PEEP 30 cm H(2)O, and to a lesser degree with inspiration. No barotrauma or severe hypotension occurred. Lung recruitment maneuvers improve oxygenation by expanding collapsed alveoli without inducing too much hyperinflation in ALI/ARDS patients. An LRM during the CT scan gives morphologic and functional information that could be useful in setting ventilatory parameters.

Positive end-expiratory pressure alters intracranial and cerebral perfusion pressure in severe traumatic brain injury.

Optimizing intracranial pressure (ICP) and cerebral perfusion pressure (CPP) is important in the management of severe traumatic brain injury (TBI). In trauma patients with TBI and respiratory dysfunction, positive end-expiratory pressure (PEEP) is often required to support oxygenation. Increases in PEEP may lead to reduced CPP. We hypothesized that increases in PEEP are associated with compromised hemodynamics and altered cerebral perfusion. Twenty patients (mean Injury Severity Score of 28) with TBI (Glasgow Coma Scale score < 8) were examined. All required simultaneous ICP and hemodynamic monitoring. Data were categorized on the basis of PEEP levels. Variables included central venous pressure, pulmonary artery occlusion pressure, cardiac index, oxygen delivery, and oxygen consumption indices. Differences were assessed using Kruskal-Wallis analysis of variance. Data were expressed as mean +/- SE. As PEEP increased from 0 to 5, to 6 to 10 and 11 to 15 cm H O, ICP decreased from 14.7 +/- 0.2 to 13.6 +/- 0.2 and 13.1 +/- 0.3 mm Hg, respectively. Concurrently, CPP improved from 77.5 +/- 0.3 to 80.1 +/- 0.5 and 78.9 +/- 0.7 mm Hg. As central venous pressure (5.9 +/- 0.1, 8.3 +/- 0.2, and 12.0 +/- 0.3 mm Hg) and pulmonary artery occlusion pressure (8.3 +/- 0.2, 11.6 +/- 0.4, and 15.6 +/- 0.4 mm Hg) increased with rising levels of PEEP, cardiac index, oxygen delivery, and oxygen consumption indices remained unaffected. Overall mortality was 30%. In trauma patients with severe TBI, the strategy of increasing PEEP to optimize oxygenation is not associated with reduced cerebral perfusion or compromised oxygen transport.

FiO2 and positive end-expiratory pressure as compensation for altitude-induced hypoxemia in an acute respiratory distress syndrome model: implications for air transportation of critically ill patients.

To determine whether increases in FiO2 or positive end-expiratory pressure will compensate for hypoxemia resulting from exposure to 8000 feet (2440 m) of altitude in a model of acute respiratory distress syndrome. Intervention and crossover design. Military research altitude chamber. Sixteen Yucatan miniature swine (Sus scrofa). Swine initially were placed on mechanical ventilation (zero positive end-expiratory pressure, 21% FiO2). Twelve animals had moderate to severe acute respiratory distress syndrome (50% to 70% FiO2 at sea level to maintain PaO2 of 50-70 torr [6.65-9.31kPa]) induced by intravenous oleic acid. Four animals were controls (no lung injury). The animals were taken to 8000 feet (2440 m) in an altitude chamber, and then stepwise increases of either 5% FiO2 (six animals) or 2.5 cm H2O positive end-expiratory pressure (six animals) were made until PaO2 values exceeded 75 torr (10.0 kPa). If PaO2 did not reach 75 torr (10.0 kPa), and time permitted, the animal was crossed over to the other group. Arterial blood gases were drawn at baseline (sea level and at altitude) and after every change in ventilator settings. Positive end-expiratory pressure increases from 5 to 12.5 cm H2O were required to bring the PaO2 in the injured pigs to 75 torr (10.0 kPa). FiO2 increases did not achieve a PaO2 of 75 torr (10.0 kPa) for three of six animals despite reaching 100% FiO2. One animal crossed over from Fio2 to positive end-expiratory pressure and achieved a PaO2 of 75 torr (10.0 kPa) with 5 cm H2O of positive end-expiratory pressure. Fifty percent of the animals with lung injury had altitude-induced hypoxia that was resistant to increases in FiO2. Increases in positive end-expiratory pressure are more reliable than increases in FiO2 for correcting altitude-induced hypoxia in this model of acute respiratory distress syndrome.

Estimation of end-expiratory lung volume variations by optoelectronic plethysmography.

To test the capability of optoelectronic plethysmography (OEP) to monitor positive end-expiratory pressure (PEEP)-induced changes of end-expiratory lung volume (EELV) changes in mechanically ventilated paralyzed patients. Laboratory and clinical investigation. Intensive care unit of the Ospedale Maggiore Policlinico di Milano. A total of eight patients with respiratory failure of various degrees, sedated and paralyzed. PEEP variations (+/-5 cm H2O) relative to the baseline PEEP of 10 cm H2O. In the model protocol, we tested the reproducibility of the OEP by repeating volume measurements of a plastic torso model over a 21-hr period, every 30 mins. The variations of OEP measurements of the torso model (9337 mL value) were encountered in a range of 16 mL (sd = 4 mL). In the patient protocol, we measured the end-expiratory volume of the chest wall (EEVCW) breath-by-breath by OEP before, during, and after the PEEP increase/decrease and we compared its variations with the corresponding variations of EELV measured by helium dilution technique. The regression line between EELV changes measured by helium and EEVCW changes measured by OEP resulted very close to the identity line (slope 1.06, intercept -0.02 L, r(2) = 0.89) and their difference was not related to their absolute magnitude. After PEEP increase, the new steady state of EEVCW was reached approximately in 15 breaths; and, after PEEP decrease, in 3-4 breaths. The slow increase in EEVCW was mainly because of the abdominal compartment. OEP measurements of EEVCW accurately reflect the changes of EELV. Furthermore, OEP allows a continuous compartmental analysis, even during unsteady conditions.

Influence of tidal volume on alveolar recruitment. Respective role of PEEP and a recruitment maneuver.

Both reduction in tidal volume (VT) and alveolar recruitment may be important to limit ventilator-associated lung injury during mechanical ventilation of patients with the acute respiratory distress syndrome (ARDS). The aim of this study was to assess the risk of alveolar derecruitment associated with VT reduction from 10 to 6 ml/kg. Whether this VT-related derecruitment could be reversed, either by a recruitment maneuver or by an increase in positive end-expiratory pressure (PEEP) level, was also investigated. Fifteen patients with ARDS were successively ventilated using conventional VT (CVT = 10 +/- 1 ml/kg) and low VT (LVT = 6 +/- 1 ml/ kg); total PEEP (PEEPtot) was individually set at the lower inflection point (Plip) of the pressure-volume curve (PEEPtot = 11 +/- 4 cm H(2)O). Pressure-volume curves were recorded from zero PEEP (ZEEP) and from PEEP, and recruited volume (Vrec) was calculated as the volume difference between the two curves for a given pressure. Despite a similar PEEPtot, Vrec was significantly lower with LVT than with CVT, indicating low VT-induced alveolar derecruitment. Reduction in VT was associated with a reduced Sa(O(2)). In 10 patients, Vrec was also measured before and after a recruitment maneuver (two sustained inflations at 45 cm H(2)O), and after an increase in PEEP (by 4 cm H(2)O). Low VT-induced derecruitment was reversed by a recruitment maneuver and by increasing PEEP. We conclude that a reduction in VT could be responsible for alveolar derecruitment, which may be transiently reversed by a reexpansion maneuver or prevented by a PEEP increase above Plip.

High-frequency jet ventilation in life-threatening bilateral pulmonary contusion.

TRAUMA is the leading cause of death among young people in developed countries. 1 Because up to 80% of trauma deaths occur during the first 24 h after trauma, 1 early resuscitation and rapid assessment of trauma lesions are of paramount importance to improving the prognosis. Among traumatic lesions, pulmonary contusion is frequent but has not been recognized as an independent prognosis factor. 2-4 In very few cases, pulmonary contusion may lead to severe hypoxia and hypercarbia, which cannot be adequately controlled using conventional mechanical ventilation. Hypoxia and hypercarbia may have deleterious effects, such as enhancement of brain injury and development of circulatory shock. 5 In the most severe cases, aggressive therapeutic methods, such as extracorporeal membrane oxygenation (ECMO), have been reported. 6 At our institution, high-frequency jet ventilation (HFJV) has been used routinely for many years for the treatment of severe acute respiratory distress syndrome. 7,8 We report a series of severe trauma patients with life-threatening pulmonary contusion successfully treated with HFJV when the conventional mechanical ventilation approach failed to provide appropriate gas exchange. The current data suggest that HFJV can be a life-saving technique in severely hypoxemic patients with bilateral pulmonary contusion.

Positive end-expiratory pressure and response to inhaled nitric oxide: Changing nonresponders to responders

Background: Inhaled nitric oxide (INO) has been shown to improve oxygenation in two thirds of patients with acute respiratory distress syndrome (ARDS). Failure to respond to INO is multifactorial. We hypothesized that the addition of positive end expiratory pressure (PEEP) might modify the response to INO in patients who had previously failed to respond to INO. Methods: Patients with ARDS who failed to respond to INO at 1 ppm (Pa O 2 increase of <20%) were selected. Each patient underwent a PEEP trial using an improvement in static lung compliance as the end point. One hour after the new PEEP level was reached, hemodynamic and blood gas values were obtained. INO was then reinstituted at 1 ppm, and hemodynamic and blood gas variables were obtained 1 hour later. Results: Six of nine patients demonstrated an increase in Pa O 2/F IO 2 (161 ± 27 to 186 ± 29) with a mean increase in PEEP of 3.7 cm H 2O. Each patient responding to PEEP further improved Pa O 2/F IO 2 (186 ± 29 to 223 ± 36) with INO at 1 ppm. The three patients who failed to improve after the PEEP increase also failed to respond to a second trial of INO. There were no changes in cardiac output or systemic vascular resistance. Pulmonary artery pressures decreased slightly (39 ± 5 vs 38 ± 7 vs 35 ± 9 mm Hg). Pulmonary vascular resistance decreased significantly after reintroduction of INO (298 ± 131 vs 310 ± 122 vs 249 ± 105 dynes/sec/cm -5) in patients who responded positively. Conclusions: The response of ARDS patients to INO can be improved if optimum alveolar recruitment is achieved by the addition of PEEP. PEEP and INO have a synergistic effect on Pa O 2/F IO 2. Patients who fail to respond to INO may benefit from an optimum PEEP trial. (Surgery 2000;127:390-4.)

Single-breath CO2 analysis as a predictor of lung volume change in a model of acute lung injury.

To examine the utility of single-breath CO2 analysis as a measure of lung volume change in a model of acute lung injury. Animal laboratory in a university-affiliated medical center. Prospective, animal cohort study comparing 21 variables derived from single-breath CO2 analysis with lung volume measurements determined by nitrogen washout. Seven lambs with saline lavage-induced acute lung injury. Animals were treated with repetitive saline lavage to achieve a uniform degree of acute lung injury (PaO2 < 100 torr [13.32 kPa] on FiO2 of 1.0). Twenty-one derived components of the CO2 expirogram were evaluated as predictors of lung volume change. Lung volume was manipulated by 3-cm H2O incremental increases in positive end-expiratory pressure from 0 to 21 cm H2O and ranged between 90 and 765 mL. Fifty-five measurements of lung volume were available for comparison with derived variables from the CO2 expirogram. Stepwise linear regression identified five variables that were most predictive of lung volume change: a) dynamic lung compliance; b) the slope of phase III; c) the slope of phase II divided by the mixed expired CO2 concentration; d) airway deadspace; and e) PaO2/FIO2 ratio. The multivariate equation was highly statistically significant and explained 94% of the variance (adjusted r2 = .94, p < .0001). The bias and precision of the calculated lung volume were 10.9 and 55.9, respectively. The mean percentage difference for the lung volume estimate derived from the single-breath CO2 analysis station was 3.3%. Our data indicate that analysis of the CO2 expirogram can yield accurate information about lung volume in animals with saline lavage-induced acute lung injury. Specifically, five variables derived from a plot of expired CO2 concentration vs. expired volume predict changes in lung volume in healthy lambs with an adjusted coefficient of determination of 0.94. We hope to further define the utility of this technique by prospective application of this methodology in the clinical setting.

Low-dose surfactant instillation during extracorporeal membrane oxygenation therapy in a patient with adult respiratory distress syndrome and secondary atelectasis after chest contusion

DULT RESPIRATORY DISTRESS SYNDROME (ARDS) is a serious complication in patients with chest contusion. The impaired oxygenation often cannot be improved, either by an increase of respiratory minute volume or by an increase of positive end-expiratory pressure (PEEP). Rather, barotrauma is promoted by these measures, t,2 Frequent postural change can improve the survival rate in patients with ARDS and entails only minor therapeutic interventions) ,4 Previous studies have shown that additional high-dose ambroxol therapy (3 g/24 hr) reliably reduces the incidence of ARDS or improves lung function parameters in patients with existing ARDS.5 Treatment with venovenous extracorporeal membrane oxygenation (ECMO) is an effective extension of therapy. 6 Since its introduction, the survival rate of acute, noninfectious respiratory failure has increased from 56% to 78%. 7 A further step of ARDS treatment is the administration of surfactant. Its successful use has been reported by several authors. TM Costs are extremely high, however, restricting this therapy to highly selected cases. The authors report a patient who developed severe ARDS. Even during ECMO therapy, arterial oxygenation improved only temporarily. To reduce costs and intervention time for therapeutic bronchoscopy in a critical situation, an extremely low dose of surfactant was used.

Expiratory phase and volume-adjusted tracheal gas insufflation: a lung model study.

To evaluate in a lung model the effects of expiratory-phase tracheal gas insufflation (expiratory-phase TGI) with both volume and pressure control ventilation, and tidal volume-adjusted continuous flow TGI (volume-adjusted TGI) on system pressures and volumes. Single-compartment lung model. Research laboratory in a university medical center. Expiratory-phase TGI was established, using a solenoid valve activated by the ventilator. Volume-adjusted TGI was applied by reducing tidal volume (VT) by the product of TGI flow and inspiratory time. Ventilation was provided with pressure control of 20 cm H2O or volume control ventilation with VT similar to that with pressure control ventilation. A rate of 15 breaths/min and positive end-expiratory pressure (PEEP) of 10 cm H2O were used throughout. Inspiratory time periods of 1.0, 1.5, 2.0, and 2.5 secs were used with TGI flows of 0, 4, 8, and 12 L/min. Lung model compliance (mL/cm H2O) and resistance (cm H2O/L/sec) combinations of 20/20, 20/5, and 50/20 were used. In expiratory-phase TGI with pressure control ventilation, peak alveolar pressure remained constant, PEEP increased (p < .01) and VT decreased (p < .01). In expiratory-phase TGI with volume control ventilation and volume-adjusted TGI, there were significant increases in peak alveolar pressure and PEEP (p < .01). Readjustment of VT in volume-adjusted TGI was impossible with longer inspiratory time (> or = 2 secs) and higher TGI flows (> or = 8 L/min). The marked increases in system pressures and volumes observed with continuous-flow TGI can be avoided with expiratory-phase TGI and volume-adjusted TGI.

Manoeuvres to elevate mean airway pressure, effects on blood gases and lung function in children with and without pulmonary pathology.

During mechanical ventilation, mean airway pressure (MAP) can be increased by a variety of manoeuvres, for example increasing inspiratory time or elevating the positive end expiratory pressure (PEEP). It seemed likely that the effect on blood gases and lung function of a particular manoeuvre to increase MAP would be influenced by the presence of respiratory pathology and thus the manoeuvre best at improving respiratory status in children with an abnormal chest radiograph appearance would differ from that most efficacious in children without such a problem. The aim of this study was to test that hypothesis. Twenty-two children, median age 15 months (range 2.5 weeks-10 years) were examined. Group 1 (n = 10) had no chest radiograph abnormalities and group 2 (n = 12) lobar collapse and/or consolidation. The patients were studied at baseline settings and at an elevated MAP resulting from (in random order) an increase in inspiratory time (T1), pressure PEEP or peak inspiratory pressure (PIP). In group 1, elevating PIP improved oxygenation and carbon dioxide elimination (P < 0.01) and prolonging T1 improved oxygenation (P < 0.05). In group 2, only raising PEEP significantly improved oxygenation (P < 0.01), but this was associated with carbon dioxide retention (P < 0.01). The presence of lung pathology does influence which manoeuvre should be used to elevate MAP to improve blood gases in the paediatric population.

Evaluation of Respiratory Inductive Plethysmography in Controlled Ventilation: Measurement of Tidal Volume and PEEP-Induced Changes of End-Expiratory Lung Volume

To determine the accuracy of respiratory inductive plethysmography (RIP) with a respiratory monitor (Respitrace Plus; NIMS Inc., Miami) operating in the DC-mode for the measurement of tidal volumes (VT) and positive end-expiratory pressure (PEEP)-induced changes of end-expiratory lung volume (deltaEELV) in patients with normal pulmonary function, acute lung injury (ALI), and COPD during volume-controlled ventilation. Prospective comparison of RIP with pneumotachography (PT) for assessment of VT and with multibreath nitrogen washout procedure (N2WO) for determination of deltaEELV as reference methods. Mixed ICU at a university hospital. Thirty-one sedated and paralyzed patients: 12 patients with normal pulmonary function mechanically ventilated after major surgery, 10 patients with respiratory failure due to ALI, and 9 patients with a known history of COPD ventilated after surgery or because of respiratory failure due to bronchopulmonary infection. Stepwise increase of PEEP from 0 to 5 to 10 cm H2O and reduction to 0 cm H2O again. On each PEEP level, N2WO was performed. The baseline drift of RIP averaged 25.4+/-29.1 mL/min but changed over a wide range even in single patient measurements. Determination of VT for single minutes revealed that 66.5% and 90.0% of all values were accurate within a range of +/-10% and +/-20%, respectively. The deviation for VT measurements between RIP and PT in patients with COPD was significantly (p<0.05) higher compared to patients with ALI or normal pulmonary function. The difference of deltaEELV between RIP and N2WO was 11.6+/-174.1 mL with correlation coefficients of 0.77 (postoperative and COPD patients) and 0.86 (ALI patients). However, just 25.8% and 46.2% were precise within +/-10% and +/-20%, respectively. deltaEELV determination in COPD patients differed more between RIP and N2WO than in the other groups, but this was not significant. In a mixed group of patients undergoing controlled ventilation, RIP using the Respitrace Plus monitor was not consistently precise enough for quantitative evaluation of VT and EELV when compared to our reference methods. This was most evident in patients with COPD. For long-term volume measurements, a better control of the baseline drift of RIP should be achieved.

Effects of Positive End-Expiratory Pressure on Hepatic Venous Oxygenation in Dogs

Background : Positive end-expiratory pressure(PEEP) ventilation causes reduction in cardiac output and increase of intra-thoracic pressure, hence reduction of hepatic blood flow. The purpose of this study is to evaluate the changes of hepatic venous oxygen saturation, tension and content during increase and removal of PEEP and to evaluate hemodynamic variable which has the greatest effect on hepatic oxygenation. Method : Eight dogs were anethetised with 1.0 vol% isoflurane and 100% oxygen. After 30 minutes of stabilization of vital signs, PEEP were increased from 0 cmH2O to 5 cmH2O and 10 cmH2O and lowered to 0 cmH2O again, and hemodynamic data (heart rate, arterial blood pressure, central venous pressure(CVP), pulmonary arterial pressure, pulmonary arterial occlusion pressure and cardiac output(CO)) and hepatic venous oxygenation data (hepatic venous oxygen saturation(ShvO2), tension(PhvO2) and content(ChvO2)) were measured at each step. Results : CO, ShvO2, PhvO2 and ChvO2 decreased significantly at 10 cmH2O PEEP compared to the baseline and 5 cmH2O PEEP and CO, ShvO2 and ChvO2 increased signicantly with removal of PEEP. CVP increased significantly at 10 cmH2O PEEP and decreased significantly with PEEP removal. PEEP showed close correlationship with CO and CVP considering all steps of PEEP and PEEP removal. ShvO2 and PhvO2 showed most close correlationship with CO considering all steps of PEEP and PEEP removal. Conclusion : ShvO2 with PEEP therapy is dependent upon CO. Therefore cardiac output maintenance is essential during PEEP therapy. For exact evaluation of hepatic oxygenation, it is valuable to monitor ShvO2. (Korean J Anesthesiol 1998; 35: 861∼869)