End-expiratory Pressure Research Articles

A new expiratory support system for resolving air trapping in lungs during mechanical ventilation: A lung model study

The aim of the study was to assess a new expiratory support (ES) system in resolving air trapping in the lungs during mechanical ventilation. The ES system consisted of a cylinder and two valves that were connected to the ventilatory circuit. The movements of them were synchronized with the ventilator. The cylinder aspirated gas during expiration. We compared the effects of the ES on air trapping between a narrower and an ordinary size endotracheal tube (ETT) (internal diameter (ID): 5 and 8 mm). In addition, we compared the effects of the ES on air trapping between normal and high airway resistance of the lungs (5 and 20 cm H(2)O/L/s). The ventilatory settings were as follows: volume controlled ventilation with constant inspiratory flow rate; tidal volume, 0.5 L; inspiratory time, 1.0 s; expiratory time, 1.0, 1.5, or 2.0 s; and PEEP, 0 cm H(2)O. The ES normalized the end-expiratory alveolar pressure of the 5 mm ID ETT at a level similar to that of the 8 mm ID ETT. The ES also resolved the air trapping induced by the high airway resistance of the lungs. In conclusion, the ES system resolved the air trapping associated with a narrow endotracheal tube and high airway resistance of the lungs.

GABAergic Pump Cells of Solitary Tract Nucleus Innervate Retrotrapezoid Nucleus Chemoreceptors

The retrotrapezoid nucleus (RTN) contains central respiratory chemoreceptors that are inhibited by activation of slowly adapting pulmonary stretch receptors (SARs). Here we examine whether RTN inhibition by lung inflation could be mediated by a direct projection from SAR second-order neurons (pump cells). Pump cells (n = 56 neurons, 13 rats) were recorded in the nucleus of solitary tract (NTS) of halothane-anesthetized rats with intact vagus nerves. Pump cells had discharges that coincided with lung inflation as monitored by the tracheal pressure. Their activity increased when end-expiratory pressure was raised and stopped instantly when ventilation was interrupted in expiration. Many pump cells could be antidromically activated from RTN (12/36). Nine of those were labeled with biotinamide. Of these nine cells, eight contained glutamic acid decarboxylase 67 (GAD67) mRNA and seven were found to reside in the lower half of the interstitial subnucleus of NTS (iNTS). Using the retrograde tracer cholera toxin-B, we confirmed that neurons located in or close to iNTS innervate RTN (two rats). Many such neurons contained GAD67 mRNA and a few contained glycine transporter2 (GLYT2) mRNA. Anterograde tract tracing with biotinylated dextranamide (four rats) applied to iNTS also confirmed that this region innervates RTN by a predominantly GABAergic projection. This work confirms that many rat NTS pump cells are located in and around the interstitial subnucleus at area postrema level. We demonstrate that a GABAergic subset of these pump cells innervates the RTN region. We conclude that these inhibitory neurons probably contact RTN chemoreceptors and mediate their inhibition by lung inflation.

Crocodiles and neonatal resuscitation

Crocodiles and neonatal resuscitation

Inhibition of respiratory‐related activity of the facial nerve by pulmonary vagal C‐fiber activation in the rat

We have previously reported that respiratory-related facial nerve activity can be modulated by hypercapnia, lung inflation, and positive end-expired pressure (PEEP). Whether respiratory-related rhythmic activities of the facial nerve could be modulated by pulmonary C-fiber activation is unclear. Activity of the facial and phrenic nerve was recorded simultaneously in the anesthetized and ventilated adult rat. Activation pulmonary C-fiber by intra-jugular injection of capsaicin produced a dose-dependent reduction of amplitude and onset of the facial nerve activity. Furthermore, uncoupled facial activity (persistent rhythmic activity during phrenic cessation) evoked by increasing PEEP could be also suppressed by capsaicin injection. Single fiber recording from the facial nerve revealed that capsaicin treatment produced inhibition on activity of expiratory-inspiratory (EI) motoneuron during expiration such that became inspiratory motoneurons and of pre-inspiratory motoneurons. In addition, capsaicin injection could attenuate the uncoupled activity of EI from the phrenic burst caused by PEEP manipulation. These results implied that capsaicin might differentially inhibit pre-inspiratory than inspiratory facial activity.

Pulmonary Responses to Overventilation in Late Multiple Organ Failure

Patients with multiple organ failure (MOF) require mechanical ventilation for several days. The enormous significance of the ventilation strategy for the outcome of these patients is well appreciated. However, most studies have focused on the onset and the early phase of MOF. It was the aim of the current study to investigate the effect of ventilation in the course of MOF. Using a model where mice develop MOF 7-14 days after intraperitoneal injection of zymosan, the authors analyzed lung functions, signaling pathways, and mediator release in response to protective ventilation (end-expiratory pressure -3 cm H2O; end-inspiratory pressure -10 cm H2O) and overventilation (-22.5 cm H2O) in isolated lungs ex vivo. On day 7, pulmonary compliance, pulmonary resistance, and tidal volume were normal, but vascular resistance was elevated compared with untreated animals. During ex vivo ventilation, these lungs showed enhanced nuclear factor-kappaB activation, Akt kinase phosphorylation, and cytokine release, and this was further aggravated by overventilation. After 14 days, zymosan-treated animals were characterized by pulmonary hypertension, reduced tidal volume, elevated pulmonary resistance, and increased mediator production. However, in these lungs, neither nuclear factor-kappaB activation nor cytokine production where enhanced by overventilation. The zymosan model is characterized by pulmonary inflammation, diminished lung functions, and chronic hypertension. Mechanical ventilation with high distending pressures further augmented cytokine production in this chronic model of MOF only if it significantly augmented tidal volume. The authors speculate that these findings may be explained on the basis of different degrees of lung stretch.

Uncoupling of upper airway motor activity from phrenic bursting by positive end-expired pressure in the rat

Phasic bursting in the hypoglossal nerve can be uncoupled from phrenic bursting by application of positive end-expired pressure (PEEP). We wished to determine whether similar uncoupling can also be induced in other respiratory-modulated upper airway (UAW) motor outputs. Discharge of the facial, hypoglossal, superior laryngeal, recurrent laryngeal, and phrenic nerves was recorded in anesthetized, ventilated rats during stepwise changes in PEEP with a normocapnic, hyperoxic background. Application of 3- to 6-cmH(2)O PEEP caused the onset inspiratory (I) UAW nerve bursting to precede the phrenic burst but did not uncouple bursting. In contrast, application of 9- to 12-cmH(2)O PEEP uncoupled UAW neurograms such that rhythmic bursting occurred during periods of phrenic quiescence. Single-fiber recording experiments were conducted to determine whether a specific population of UAW motoneurons is recruited during uncoupled bursting. The data indicate that expiratory-inspiratory (EI) motoneurons remained active, while I motoneurons did not fire during uncoupled UAW bursting. Finally, we examined the relationship between motoneuron discharge rate and PEEP during coupled UAW and phrenic bursting. EI discharge rate was linearly related to PEEP during preinspiration, but showed no relationship to PEEP during inspiration. Our results demonstrate that multiple UAW motor outputs can be uncoupled from phrenic bursting, and this response is associated with bursting of EI nerve fibers. The relationship between PEEP and EI motoneuron discharge rate differs during preinspiratory and I periods; this may indicate that bursting during these phases of the respiratory cycle is controlled by distinct neuronal outputs.

Positional Pressure Changes of the Gastroesophageal Junction Antireflux Barrier Detected with High Resolution Esophageal Manometry

Purpose: The gastroesophageal junction (GEJ) antireflux barrier consists of end-expiratory lower esophageal sphincter (LES) tone with superimposed phasic respiratory pressure changes representing the crural diaphragm. Esophageal manometry is usually performed with water swallows with the subject supine, an unnatural position for eating meals. The aim of this study was to establish normal values for high resolution manometry for swallowing water and viscous boluses in the supine and upright positions. Methods: 15 normal volunteers (ages 19 to 45 years; 8 males, 7 females) underwent esophageal manometry using a high resolution manometry catheter with 36 solid state circumferential pressure sensors spaced 1 cm apart (Sierra Scientific Instruments). The catheter was placed transnasally with sensors spanning the pharynx, esophagus, LES, and proximal stomach. Each subject performed twelve 5 ml water swallows in the supine position, six 5 ml water swallows upright and six 5 ml viscous swallows (Jello) upright. Results are expressed as mean ± SEM. Results: The esophageal length was 25.5 ± 1.4 cm; the GEJ high pressure zone was 4.2 ± 0.2 cm. There were no double high pressure zones suggestive of hiatal hernia. The end-expiratory basal LES pressure was lower in the upright position (3.4 ± 0.9 mmHg) than supine (16.9 ± 1.8 mm Hg; p < 0.01). The mid-respiratory LES pressure was lower upright (8.8 ± 1.1 mmHg) than supine (27.1 ± 1.5 mm Hg; p < 0.01). The crural diaphragm component, represented by the difference of mid-respiratory and end-expiratory pressures, was also less upright (8.6 ± 0.9) than supine (10.8 ± 1.3; p= 0.056). Swallow-induced esophageal contractions were reduced in amplitude upright (62 ± 9 mm Hg 5 cm above LES) compared to supine (74 ± 7 mm Hg; p= 0.036). Swallows using jello in the upright position had an increase in esophageal contraction pressures (73 ± 10 mmHg) compared to water swallows upright (62 ± 9 mm Hg; p= 0.051) without change in peristaltic velocity. Conclusions: This study demonstrates positional pressure changes in the GEJ high pressure zone of both the intrinsic LES and extrinsic crural components. The reduction of the GEJ high pressure zone in the upright position may be due to the additional presence of gravitational forces preventing reflux as well as anatomic changes. The decrease in the antireflux barrier upright might explain, in part, postprandial gastroesophageal reflux that occurs in normal subjects.

Ventilação mecânica no Brasil: aspectos epidemiológicos

There are few epidemiological studies in mechanical ventilation, and the aim of the study is to show how this procedure is being used in Brazil. A 1-day point prevalence study was performed in 40 ICUs, with 390 patients; 217 of these patients were in mechanical ventilation. The results evaluated were the characteristics of ventilated patients, their distribution in Brazil, the mechanical ventilation's causes, the main ventilatory modes, the more important ventilators settings, and the weaning stage of mechanical ventilation. The median age of the ventilated patients was 66 years old. The median APACHE II was 20, while the median time of mechanical ventilation was 11 days. Acute respiratory failure occurred in 71% of the patients, coma in 21.2%, acute exacerbation of chronic respiratory failure in 5.5%, and the neuromuscular disease in 2.3%. The volume-controlled ventilation (VCV) (30%), the pressure support ventilation (PSV) (29.5%), and the pressure-controlled ventilation (PCV) (18%) were the ventilatory modes most used; the PSV had been the main mode in weaning (63.5%). The median of tidal volume (8 mL/kg) was higher in VCV. The median of maximal inspiratory pression (30 cmH2O) and the median of positive end-expiration pressure (PEEP) (8 cmH2O) were higher in PCV. The predominance of ventilated patients in ICUs was marked by clinical severity of them, and a longer hospital stay time; acute respiratory failure was the principal mechanical ventilation cause; VCV and PSV ventilated more patients, with PSV being more used in weaning patients.

Efficiency of Use of the «Lung Opening» Maneuver Under Artificial Ventilation in Patients With Acute Respiratory Distress Syndrome

The paper provides the results of use of the «lung opening» maneuver under artificial ventilation (AV) in adult patients with acute respiratory distress syndrome of various genesis. It shows it possible to improve gas exchange by this method in severe acute respiratory failure of the parynchematous type. It has been found that there is a more effective recovery of lung function, less AV timing, and a shorter length of stay in a intensive care unit in patients with acute respiratory distress syndrome in whom the «lung opening» maneuver is regularly (4—6 times daily) used under AV than in those undergoing a traditional support in accordance with the principles of safe AV. The paper shows it possible to select the optimum end-expiratory positive pressure during this maneuver. The authors also describe the «lung opening» maneuver protocol used by them, indications for and contraindications to the maneuver.

The Relationship of Pleural Pressure to Symptom Development During Therapeutic Thoracentesis

To describe the relationship of patients' symptoms during therapeutic thoracentesis to pleural pressure (Ppl). Review of prospectively collected data during 169 therapeutic thoracentesis procedures. University Hospital in Boston, MA. One hundred sixty-nine patients who had Ppl measured during therapeutic thoracentesis were included in this study. End-expiratory pressures were measured after the withdrawal of 5 mL of fluid and every 240 mL thereafter until the pressure was lower than -20 cm H(2)O, chest discomfort developed in the patient, or no more fluid could be removed. Patients' symptoms, including chest pain, chest discomfort, and cough were recorded simultaneously. There was no correlation between the amount of pleural fluid removed and the development of symptoms. The closing pressures and the total change in Ppl (see the "Materials and Methods" section for definitions), however, were significantly lower in the group of patients who experienced chest discomfort compared to patients who developed cough or were asymptomatic. There was also a trend toward a significantly lower pleural elastance in patients who developed cough compared to that in the other two groups. Additionally, only 22% of patients in whom chest discomfort developed, and 8.6% of patients in whom symptoms did not develop, had potentially dangerous Ppl values (ie, lower than -20 cm H(2)O). The development of chest discomfort is associated with a potentially unsafe drop in Ppl values and should be a sign to terminate thoracentesis. It is not necessary to terminate thoracentesis solely because of the development of cough. Without attention to pleural manometry, a significant percentage of patients may develop potentially dangerous Ppl. Although we recommend pleural manometry with all thoracenteses, when it is not used attention to symptoms remains a valuable surrogate.

A New Equal Area Method to Calculate and Represent Physiologic, Anatomical, and Alveolar Dead Spaces

Physiologic dead space is usually estimated by the Bohr-Enghoff equation or the Fletcher method. Alveolar dead space is calculated as the difference between anatomical dead space estimated by the Fowler equal area method and physiologic dead space. This study introduces a graphical method that uses similar principles for measuring and displaying anatomical, physiologic, and alveolar dead spaces. A new graphical equal area method for estimating physiologic dead space is derived. Physiologic dead spaces of 1,200 carbon dioxide expirograms obtained from 10 ventilated patients were calculated by the Bohr-Enghoff equation, the Fletcher area method, and the new graphical equal area method and were compared by Bland-Altman analysis. Dead space was varied by varying tidal volume, end-expiratory pressure, inspiratory-to-expiratory ratio, and inspiratory hold in each patient. The new graphical equal area method for calculating physiologic dead space is shown analytically to be identical to the Bohr-Enghoff calculation. The mean difference (limits of agreement) between the physiologic dead spaces calculated by the new equal area method and Bohr-Enghoff equation was -0.07 ml (-1.27 to 1.13 ml). The mean difference between new equal area method and the Fletcher area method was -0.09 ml (-1.52 to 1.34 ml). The authors' equal area method for calculating, displaying, and visualizing physiologic dead space is easy to understand and yields the same results as the classic Bohr-Enghoff equation and Fletcher area method. All three dead spaces--physiologic, anatomical, and alveolar--together with their relations to expired volume, can be displayed conveniently on the x-axis of a carbon dioxide expirogram.

Maintained inspiratory activity during proportional assist ventilation in surfactant-depleted cats early after surfactant instillation: phrenic nerve and pulmonary stretch receptor activity

BackgroundInspiratory activity is a prerequisite for successful application of patient triggered ventilation such as proportional assist ventilation (PAV). It has recently been reported that surfactant instillation increases the activity of slowly adapting pulmonary stretch receptors (PSRs) followed by a shorter inspiratory time (Sindelar et al, J Appl Physiol, 2005 [Epub ahead of print]). Changes in lung mechanics, as observed in preterm infants with respiratory distress syndrome and after surfactant treatment, might therefore influence the inspiratory activity when applying PAV early after surfactant treatment.ObjectiveTo investigate the regulation of breathing and ventilatory response in surfactant-depleted young cats during PAV and during continuous positive airway pressure (CPAP) early after surfactant instillation in relation to phrenic nerve activity (PNA) and the activity of PSRs.MethodsSeven anesthetized, endotracheally intubated young cats were exposed to periods of CPAP and PAV with the same end-expiratory pressure (0.2–0.5 kPa) before and after lung lavage and after surfactant instillation. PAV was set to compensate for 75% of the lung elastic recoil.ResultsTidal volume and respiratory rate were higher with lower PaCO2 and higher PaO2 during PAV than during CPAP both before and after surfactant instillation (p < 0.05; both conditions). As an indicator of breathing effort, esophageal deflection pressure and PNA were lower during PAV than during CPAP in both conditions (p < 0.02). Peak PSR activity was higher and occurred earlier during PAV than during CPAP (p < 0.01), and correlated linearly with PNA duration in all conditions studied (p < 0.001). The inspiratory time decreased as tidal volume increased when CPAP was changed to PAV, with the highest correlation observed after surfactant instillation (r = -0.769). No apneic periods could be observed.ConclusionPSR activity and the control of breathing are maintained during PAV in surfactant-depleted cats early after surfactant instillation, with a higher ventilatory response and a lower breathing effort than during CPAP.

Characteristics of pre‐inspiratory and decoupled activities of the upper airway motoneurons in the rat

Inspiratory activities of the upper airway motor nerves (UAWMN) commence before phrenic burst. These pre-inspiratory (Pre-I) activities of the UAWMN may play an important role in the stabilization of UAW patency. To get insight into the mechanism for this preceding onset of the UAW motoneurons, we investigated influence of different level of positive end-expired pressure (PEEP) on pre-I activities of UAWMN in the first part of the current study. Activities of UAWMN, including the facial, hypoglossal, and superior laryngeal nerves, and the phrenic nerve were recorded simultaneously in anesthetized and artificially ventilated rats. Our results showed that Pre-I activities of UAWMN were all increased and even decoupled from phrenic burst (a response activity during phrenic cessation) by the increase of PEEP to a level between 6–12 cmH2O. Further increased PEEP to a level of 15 cmH2O produced, however, an inhibition on Pre-I and decoupled activities. In the second part, we monitored single fiber activities on each of the UAWMN and found that decoupled activity was primarily due to the persistence of activities of expiratory-inspiratory (EI) motoneurons during phrenic burst cessation. Our data suggest that signals from changes in PEEP might induce either excitation or inhibition on Pre-I and decoupled activities of UAWMN. They might also indicate that rhythmic activities of UAWMN could be uncoupled from the phrenic nerve burst by increasing PEEP.

Effect of Laparoscopic Gastric Banding on Esophageal Motility

Alterations in esophageal motility may occur after placement of an adjustable gastric band as treatment for morbid obesity, near the gastro-esophageal junction. It causes an outlet obstruction, especially during follow-up after the band is filled. 29 morbidly obese patients underwent conventional manometry preoperatively, 6 weeks postoperatively before and after filling the band and at 6 months postoperatively. A questionnaire was used to assess upper gastrointestinal symptoms during follow-up. After band placement, there was a significant increase in lower esophageal sphincter (LES) end-expiratory pressure at 6 weeks with an empty band: 1.3 (0.9-1.9) kPa (median (interquartile range) (P=0.003), 6 weeks with a filled band: 2.1 (1.5-2.8) kPa (P=0.0001), and at 6 months: 1.5 (1.3-1.9) kPa (P=0.001), compared to the preoperative pressure: 0.8 (0.6-1.3) kPa. Also after band placement, the high pressure zone length increased (preop 5.0 (4.3-6.0) cm vs 6 weeks 6.0 (5.0-6.5) cm (P=0.003). The propagation of peristaltic contractions was not significantly altered after band placement. Heartburn decreased 6 weeks postoperatively (P=0.04) but increased at 6 months. Heartburn at 6 months was correlated with pouch formation (0.667; P<0.01). Adjustable gastric band placement causes an increase in LES pressure and length of the high pressure zone. It decreases reflux symptoms in the short-term, but this effect appears not to be related to an effect on LES pressure or length. Pouch formation increases reflux symptoms without having any relationship to LES pressure and length. Band placement in the short-term does not disturb propagation of esophageal contractions.

Arterial to end-tidal carbon dioxide pressure difference and correlation of the difference with end-expiratory pressure in critically ill patients with severe lung injury

Arterial to end-tidal carbon dioxide pressure difference and correlation of the difference with end-expiratory pressure in critically ill patients with severe lung injury

Effects of helium on high frequency jet ventilation in model of airway stenosis

The addition of helium to the inspired gas may facilitate ventilation in the presence of clinically evident upper airway obstruction. However, there are no data on the effects of using a helium-oxygen mixture during high frequency jet ventilation (HFJV) in upper airway obstruction. HFJV at a frequency of 150 min(-1) (driving pressure 2 bar, inspiratory time 30%) was applied to a trachea-lung model to simulate ventilation through varying degrees of fixed laryngotracheal stenosis (2.5-8.5 mm). HFJV was delivered from above, through and below the level of stenosis to simulate supraglottic, transglottic and infraglottic administration. Measurements of distal tracheal pressures were repeated for each route at steady state for each stenosis diameter using both 100% oxygen and helium-oxygen (50% oxygen, 50% helium). The output of the ventilator was measured during operation on oxygen and helium-oxygen. Peak, mean and end-expiratory pressures were greater during simulated supraglottic HFJV than during transglottic and infraglottic HFJV, and pressures increased markedly as the diameter of the stenosis decreased for all routes of ventilation (P<0.001). Generated pressures during HFJV using helium-oxygen and 100% oxygen were very similar overall, although reductions in pressures were observed during ventilation with helium-oxygen via the transglottic and transtracheal routes at stenosis diameters <4 mm (P<0.05). However, HFJV with the helium-oxygen mixture increased the delivered gas volumes by approximately 18%. Using 50% helium-oxygen during HFJV in the presence of airway stenosis allows an 18% increase in minute volume at generated airway pressures which are the same as or lower than those when using 100% oxygen.

277 Correlation Between Cytokines, BDP and Modality of Ventilation in Preterm Newborns: Improvement with Melatonin

Background: Ventilator-associated lung injury traditionally has been believed to result from the use of high pressures and multiple ventilation strategies have been tried to reduce injury and improve outcomes. Inflammatory cytokines are present in the lungs of newborns with BPD, oxidant injury may be another serious cause of lung injury and melatonin is known act as radical scavenger.Aims: The aim of current study was to evaluate lung inflammatory response in preterm infants with respiratory distress syndrome (RDS), mechanically ventilated with and without VG, as measured by proinflammatory cytokines (IL-6, IL-8, and TNFa) in tracheobronchial aspirate and by clinical outcome in a group of 55 newborns treated with melatonin. And 55 newborns without melatonin treatmentResults: Considering ventilator parameters and clinical outcome of the studied population, the two groups (treated and untreated) differed statistically significantly in maximal O2 concentration used, PIP (peak inspiratory pressure), PEEP (end expiratory pressure) as well as in the ventilatory modes used and in the oxygenation index (Median airway presure x O2 concentration / PaO2). Higher values were in untreated group. In both groups (treated and untreated) the values were higher in patients ventilated in the A/C mode and were lower in HFVO patients and in PSV with VG. Il-6 at time 0 presents values similar in treated and untreated nfants and equivalent in the six groups of ventilation modes; at 24 hr and at 71 hr IL-6 is higher all groups without a correlation with ventilation mode or treatment. At 7 days, IL-6 levels is significantly reduced in treated-newborns relative to those that received diluent and those ventilated in PSV and in GV had lower levels of IL-6. IL-8 values at 0 hr did not differ in the groups; at 24 hr there was a significant rise in the six groups; at 72 hr the melatonin treated newborns had a significant reduction in IL-8 serum levels that remain also at 7 days. TNFa levels did not differ? at 0 time. At 24 hr there were no differences from the from basal values in melatonin or untreated newborns. At 72 hr the melatonin-groups showed a statistical significant reduction compared to those in the diluent treated newborns which increased at 7 days, when higher TNFa levels were seen in untreated in relation to the group and to the ventilation mode. There were no differences in serum levels of any cytokines prior to the onset of treatment.Conclusion: Compared with the melatonin treated RDS newborns, the concentrations of inflammatory cytokines were significantly higher in the newborns given only the diluent. The current study suggests that reducing volutrauma will also reduced biotrauma as expressed by a reduction of inflammatory cytokines and an improved outcome; clearly, melatonin treatment provides benefits in this regard.

High-frequency percussive ventilation

To review the technique and clinical application of high-frequency percussive ventilation in critically ill patients. Literature search and descriptive review. High-frequency percussive ventilation is a time-cycled, pressure-limited mode of ventilation that delivers subphysiologic tidal volumes at rates that can exceed 500 breaths/min. It offers the potential advantage over conventional ventilation of providing equal or improved oxygenation and ventilation at lower peak and end-expiratory pressures. This modality has been used to manage severe lung disease in the neonatal and pediatric population, treat inhalation injury in pediatric and adult patients, and as salvage therapy in adult patients with acute respiratory distress syndrome. High-frequency percussive ventilation has been shown to provide favorable gas exchange in several well-defined patient populations. It reliably improves oxygenation and provides adequate ventilation at lower peak pressures than conventional ventilation. Adequately powered, randomized, prospective studies demonstrating significant mortality benefit have not yet been performed.

Effects of continuous negative extra-abdominal pressure on cardiorespiratory function during abdominal hypertension: an experimental study

To investigate whether negative extra-abdominal pressure (NEXAP) improves respiratory function and induces a blood shift from the intrathoracic compartment and to assess whether these effects are influenced by abdominal pressure. Prospective, randomized, controlled trial in the animal laboratory of a university hospital. Eight sedated and paralyzed pigs (19.6+/-3.4 kg). Application of NEXAP (-20 cmH(2)O). Airway, esophageal, gastric and central venous pressures were recorded simultaneously. Intrathoracic blood volume was assessed by PiCCO. The effects of NEXAP were assessed with and without abdominal hypertension by intraperitoneal insufflation of helium. NEXAP caused a lasting drop of gastric (1.97+/-2.26 mmHg) and esophageal (1.21+/-0.67 mmHg) pressures, while end-expiratory airway pressure was similar, hence transpulmonary pressure increased. Intrathoracic blood volume dropped from 358+/-47 to 314+/-47 ml. The fall was associated with a decrease in central venous pressure (R(2)=0.820). When peritoneal pressure was raised (24.7+/-5.5 mmHg), the effects were less marked. However, the difference between negative pressure around the abdomen and the pressure inside the abdomen (effective NEXAP) was correlated with the proportional changes in intrathoracic blood volume (R(2)=0.648), being greater with more negative effective NEXAP. NEXAP improved chest wall elastance during abdominal hypertension (from 0.067+/-0.023 to 0.056+/-0.021 cmH(2)O/ml). NEXAP increases lung volume and causes a shift of blood from the intrathoracic compartment. It needs to be tailored against abdominal pressure to be effective.

Measurement of Forced Expiratory Flows and Lung Volumes

After completing this article, readers should be able to: 1. Describe the information that measurements of forced expiratory flow can provide in spontaneously breathing and mechanically ventilated infants. 2. Delineate how lung volume can be measured. The measurements of forced expiratory flows and lung volumes are important to the evaluation of patients who have respiratory symptoms. Until recently, measurements have been restricted to adults and children old enough to cooperate with testing maneuvers. Newer techniques have enabled such measurements to be made in infants and led to improved understanding of normal lung and airway growth during infancy and early childhood, when dramatic changes occur. The measurements have had important clinical uses in the evaluation and treatment of infants who have respiratory disease, but their use has been limited because they require specialized equipment and expertise as well as sedation of the infant. In this article, we discuss the techniques required for measurement of forced expiratory flows and lung volumes, their limitations, and applications in clinical practice. Detection of airflow obstruction, by physical examination or by quantitative measurement techniques, is facilitated by increasing expiratory flow rates. Measurement of forced expiratory flows is useful because flow rates are inversely proportional to the fourth power of the radius of the airway and, therefore, are indicative of airway size when flow is limited. Disease states affecting the airways, including asthma, bronchopulmonary dysplasia (BPD), or congenital lesions such as pulmonary hypoplasia or vascular airway compression, are expected to decrease expiratory flow. Infants typically are sedated for testing to maintain relaxed breathing with a face mask placed over the mouth and nose. This sedation often is perceived by parents and physicians as one of the barriers to such testing. (1) However, sedation can be achieved safely using oral chloral hydrate at a dose of 80 to 100 mg/kg. …