Positive Intrathoracic Pressure Research Articles

Fluids in ARDS: from onset through recovery.

Early acute respiratory distress syndrome (ARDS) is characterized by protein-rich inflammatory lung edema often associated with a hydrostatic component. Mechanical ventilation with positive intrathoracic pressure further induces salt and water retention, while impairing the pathways designed for edema clearance. In this framework, we will review the recent findings on fluid strategy and edema clearance in ARDS. Consistently, conservative strategies lead to better oxygenation and reduce the length of mechanical ventilation. A possible drawback associated with conservative strategy is the impaired cognitive function. Echography may be used for safer use of furosemide or hemofiltration therapy during edema clearance. Albumin and furosemide techniques may accelerate edema clearance, particularly when pulmonary capillary permeability is restored. Beta-2 agonist therapy does not accelerate edema clearance and is potentially dangerous. Lung edema is likely the single pathogenic factor more relevant for ARDS severity and outcome. Fluid overload must be avoided. Several monitoring techniques are available to reach this target. No specific studies are available to recommend a given fluid composition in ARDS. In our opinion, the general recommendations for fluid composition suggested for severe sepsis and septic shock should be applied to ARDS that may be considered an organ-confined sepsis.

Reliance on end-expiratory wedge pressure leads to misclassification of pulmonary hypertension.

Current guidelines recommend measurement of pulmonary artery wedge pressure (PAWP) at end-expiration. However, this recommendation is not universally followed and may not be physiologically appropriate. We investigated the performance of end-expiratory PAWP in the evaluation of precapillary pulmonary hypertension patients. 329 spontaneously breathing patients undergoing right heart catheterisation were retrospectively classified as having a precapillary, post-capillary or mixed phenotype based on standardised clinical criteria. Tracings were reviewed to compare end-expiratory PAWP with PAWP averaged throughout the respiratory cycle; these values were correlated with the clinical classifications. Predictors of large respirophasic variation in PAWP were determined. Elevated end-expiratory PAWP (>15 mmHg) occurred in 29% of subjects with precapillary phenotype. There were no differences in demographics or clinical history between those with elevated and normal end-expiratory PAWP. Those with elevated end-expiratory PAWP had greater right atrial pressure and respirophasic PAWP variation. Among all subjects, the magnitude of respirophasic variation in PAWP was positively correlated with body mass index and respirophasic variation in left ventricular end-diastolic pressure. A significant proportion of precapillary pulmonary hypertension patients have end-expiratory PAWP >15 mmHg. Spontaneous positive end-expiratory intrathoracic pressure may contribute; in those cases, PAWP averaged throughout respiration may be a more accurate measurement.

Reading Pulmonary Vascular Pressure Tracings. How to Handle the Problems of Zero Leveling and Respiratory Swings

The accuracy of pulmonary vascular pressure measurements is of great diagnostic and prognostic relevance. However, there is variability of zero leveling procedures, and the current recommendation of end-expiratory reading may not always be adequate. A review of physiological and anatomical data, supported by recent imaging, leads to the practical recommendation of zero leveling at the cross-section of three transthoracic planes, which are, respectively midchest frontal, transverse through the fourth intercostal space, and midsagittal. As for the inevitable respiratory pressure swings, end-expiratory reading at functional residual capacity allows for minimal influence of elastic lung recoil on pulmonary pressure reading. However, hyperventilation is associated with changes in end-expiratory lung volume and increased intrathoracic pressure, eventually exacerbated by expiratory muscle contraction and dynamic hyperinflation, all increasing pulmonary vascular pressures. This problem is amplified in patients with obstructed airways. With the exception of dynamic hyperinflation states, it is reasonable to assume that negative inspiratory and positive expiratory intrathoracic pressures cancel each other out, so averaging pulmonary vascular pressures over several respiratory cycles is most often preferable. This recommendation may be generalized for the purpose of consistency and makes sense, as pulmonary blood flow measurements are not corrected for phasic inspiratory and expiratory changes in clinical practice.

The Effects of Trendelenburg Position, Positive Intrathoracic Pressure and Head Rotation on Cross-sectional Area of Internal Jugular Vein

The Effects of Trendelenburg Position, Positive Intrathoracic Pressure and Head Rotation on Cross-sectional Area of Internal Jugular VeinObjective: Central venous catheterization is an interventional procedure which holds an important place in daily practices of many clinicians. Although many routes can be used for this procedure, the most preferred one is internal jugular vein. Many positions and maneuveres have been tried in order to make this procedure easier and with less complications, and in our study, we evaluated the combination of these positions, maneuveres and their effects on the cross-sectional area of right internal jugular vein.Material and Methods: Thirty healthy volunteers were included in the study. By combining supine, 20˚ trendelenburg, manual hepatic compression, simulated Valsalva maneuveres, and 0˚, 15˚, 30˚, 45˚ and maximum head rotations, the cross-sectional area of right internal jugular vein and the overlapping percentage of internal jugular vein on carotid artery were evaluated.Results: Although any significant increases in internal jugular vein cross-sectional area on head rotations of ≥ 30˚ were not detected in any of the groups, the overlapping percentage of internal jugular vein on carotid artery increased significantly for 30˚ and greater head rotation. While simulated Valsalva maneuveres and widest internal jugular vein crosssectional area was obtained in comparing the manoeuvre, a wider internal jugular vein cross-sectional area was detected in 20˚ Trendelenburg position compared to the supine position.Conclusion: We observed that a wider internal jugular vein crosssectional area can be obtained more safely with <30˚ head rotation, valsalva maneuvere and 20˚ tilted trendelenburg position

Negative Pressure Pulmonary Edema Together with Pneumopericardium after General Anesthesia

Negative pressure pulmonary edema is an uncommon complication related to general anesthesia. Its main pathophysiology is excessive negative intrathoracic pressure that is caused by an acute upper airway obstruction. Pneumopericardium, the presence of air within the pericardial sac, is another rare condition. The common pathophysiology of pneumopericardium, except for that caused by blunt or penetrating trauma, is barotrauma-induced alveolar rupture caused by positive intrathoracic pressure. Here, we report the case of a 61-year old female patient with negative pulmonary edema and pneumopericardium after general anesthesia. She recovered after conservative management. (Korean J Med 2014;86:612-617)

The Mechanics of Left Ventricular Filling During the Strain Phase of the Valsalva Maneuver in Healthy Subjects

BackgroundThe aim of this study was to investigate the mechanical changes in left ventricular filling during the strain phase of the Valsalva maneuver in healthy subjects. MethodsThirty healthy volunteers were recruited to undertake the Valsalva maneuver at a load of 40mm Hg for 10seconds. Parameters of left ventricle filling were determined by echocardiography at baseline and at the first and second beats during the strain phase. ResultsCompared with baseline values, the E, E/A ratio, E/esep ratio and E/elat ratio parameters all increased at the first beat (P<0.05). Compared with the first beat values, the E, E/A ratio, E/esep ratio and E/elat ratio parameters all decreased at the second beat (P<0.05). The results demonstrate that left ventricular filling decreases at the second beat during the strain phase of the Valsalva maneuver. Positive intrathoracic pressure decreases left-side heart and pulmonary vessel transmural pressure while increasing blood vessel resistance, which explains the decrease in left ventricular filling. ConclusionsThe results provide a new understanding of the underlying mechanical mechanism of the Valsalva maneuver, indicating that it should be performed clinically at a lower load and shorter strain time to avoid adverse events.

Flying with a Pneumothorax: A Model of Altitude Limitations Due to Gas Expansion

Pneumothorax(PTX) is considered an absolute contraindication to flying. Guidelines for recovery time are arbitrary and fail to acknowledge that some passengers with PTX have flown without incident. One concern is pleural air expansion, causing extrinsic lung compression, increased intrathoracic pressure, and the subsequent risk of tension pneumothorax. We used a model to investigate critical endpoints resulting from PTX expansion at altitude. Pneumothorax expansion was investigated using physiological simulation in the form of a mathematical model comprising elastic lungs, rib cage, hemidiaphragms, mediastinum, and abdomen. Compliance curves were assigned to each compartment based on published data. Cyclical muscle pressures drive normal ventilation. Initial sea-level pleural air volumes were set in the range from 10 to 60% pneumothorax. Pressures, volumes, and mediastinal shift were tracked during ascent to cruising altitude at 8000 ft (2438 m) and during cabin depressurization to 30,000 ft (9144 m). Pleural pressure oscillations during normal breathing became less negative during ascent. Positive pleural pressure was encountered at cabin altitude only if sea-level PTX exceeded 45%. Corresponding peak pressure gradient across the mediastinum did not exceed 5 cm H2O. Our results provide insight into the mechanics of pneumothorax expansion during flight. Sea-level PTX up to 45% would be tolerable in otherwise healthy persons if positive intrathoracic pressure is the dominant mechanism causing respiratory discomfort. Critical limitation in our model is more likely due to hypoxemia caused by altitude and pulmonary shunt from lung collapse. Studies of PTX tolerance to altitude should be conducted with caution.

In silico study of the haemodynamic effects induced by mechanical ventilation and biventricular pacemaker

In silico modeling of the cardiovascular system (CVS) can help both in understanding pharmacological or pathophysiological process and in providing information which could not be obtained by means of traditional clinical research methods due to practical or ethical reasons. In this work the numerical CVS was used to study the effect of interaction between mechanical ventilation and biventricular pacemaker by haemodynamic and energetic point of view. Starting from literature data on patients with intra and/or inter-ventricular activation time delay and treated using biventricular pacemaker, we used in silico simulator to analyse the effects induced by mechanical ventilatory assistance (MVA). After reproducing baseline and CRT conditions, the MVA was simulated changing the mean intrathoracic pressure value. Results show that simultaneous application of CRT and MVA yields a reduction of cardiac output, left ventricular end-diastolic and end-systolic volume when positive mean intrathoracic pressure is applied. In the same conditions, when MVA is applied, left ventricular ejection fraction, mean left (right) atrial and pulmonary arterial pressure increase.

The effects of altered intrathoracic pressure on resting cerebral blood flow and its response to visual stimulation

Investigating how intrathoracic pressure changes affect cerebral blood flow (CBF) is important for a clear interpretation of neuroimaging data in patients with abnormal respiratory physiology, intensive care patients receiving mechanical ventilation and in research paradigms that manipulate intrathoracic pressure. Here, we investigated the effect of experimentally increased and decreased intrathoracic pressures upon CBF and the stimulus-evoked CBF response to visual stimulation.Twenty healthy volunteers received intermittent inspiratory and expiratory loads (plus or minus 9 cmH2O for 270 s) and viewed an intermittent 2 Hz flashing checkerboard, while maintaining stable end-tidal CO2. CBF was recorded with transcranial Doppler sonography (TCD) and whole-brain pseudo-continuous arterial spin labeling magnetic resonance imaging (PCASL MRI).Application of inspiratory loading (negative intrathoracic pressure) showed an increase in TCD-measured CBF of 4% and a PCASL-measured increase in grey matter CBF of 5%, but did not alter mean arterial pressure (MAP). Expiratory loading (positive intrathoracic pressure) did not alter CBF, while MAP increased by 3%. Neither loading condition altered the perfusion response to visual stimulation in the primary visual cortex. In both loading conditions localized CBF increases were observed in the somatosensory and motor cortices, and in the cerebellum.Altered intrathoracic pressures, whether induced experimentally, therapeutically or through a disease process, have possible significant effects on CBF and should be considered as a potential systematic confound in the interpretation of perfusion-based neuroimaging data.

High-frequency oscillatory ventilation after cardiac surgery: a treatment for all ages

In a recent issue of Critical Care, Bojan and colleagues [1] reported their experience with early initiation of highfrequency oscillatory ventilation (HFOV) in pediatric cardiac surgery that demonstrated shorter mechanical ventilation times and intensive care stays. Acute lung injury is common in adult patients undergoing surgery, yet there is scant reporting of the intraoperative utility of HFOV [2]. We initiated HFOV in a 49-year-old morbidly obese (body mass index of 69 kg/m 2 ) man who had aortic stenosis, pulmonary hypertension, and decompensated congestive heart failure and who was undergoing aortic valve replacement. Separation from cardiopulmonary bypass (CPB) with inverse-ratio pressure-control ventilation – fraction of inspired oxygen (FiO 2 ) of 1.0 and positive end-expiratory pressure (PEEP) of 18 cm H 2 O – failed because of hypoxia, defi ned as an arterial partial pressure of oxygen (PaO 2 ) of 64 mm Hg. HFOV was initiated (mean pressure airway of 33 cm H 2 O and FiO 2 of 1.0), yielding a PaO 2 of 74 mm Hg and allowing CPB separation. Th e patient was transitioned to conventional ventilation on postoperative day 3 and was extubated on postoperative day 5. Th is adult patient benefi ted from HFOV, as did the pediatric population of Bojan and colleagues. Continuous positive intrathoracic pressure is a concern as it may impede venous return and thereby limit cardiac output (CO) [3]. However, the transition from ventilation with PEEP to HFOV usually results in signifi cant changes in oxygenation/ventilation but not in CO [4]. In patients with pulmonary hypertension, HFOV has been demonstrated to increase CO and decrease pulmonary vascular resistance [5]. For our patient, HFOV allowed improved oxygenation without aff ecting hemodynamics. HFOV may be a safe and eff ective therapy to improve oxygenation/ventilation in patients undergoing cardiac surgery and possibly is underused because of unfounded hemodynamic concerns. HFOV needs exploration as a rescue tool after CPB for patients with hypoxia.

Repercussão da pressão positiva expiratória final na pressão de perfusão cerebral em pacientes adultos com acidente vascular hemorrágico

Positive intrathoracic pressure may cause hemodynamic changes, which can be transmitted to the cranial compartment, changing intracranial pressure and cerebral perfusion pressure. This can be increased when high positive end-expiratory pressure values are used. To measure the impact of different positive end-expiratory pressure levels on intracranial pressure, cerebral perfusion pressure and mean blood pressure. This study was conducted in a neurological intensive care unit and included 25 adult hemorrhagic stroke patients who were mechanically ventilated on airway pressure control mode. Patients were subjected to various positive end-expiratory values ranging between 0 and 14 cmH2O. The order of these values were randomized, and the variables were assessed five minutes after each new positive end-expiratory pressure level was initiated. Incremental positive end-expiratory pressures led to increased intracranial pressure (p < 0.001), however, no statistically significant changes were observed in mean blood pressure or cerebral perfusion pressure. In this population of patients with hemorrhagic stroke, positive end-expiratory pressure values up to 14 cmH2O did not alter cerebral perfusion pressure or mean blood pressure. Increased intracranial pressures were noted, although these elevations were not clinically significant.

Changes of left ventricular filling during the strain phase of Valsalva maneuver in healthy subjects and its mechanism

Objective To explore changes of left ventricular filling during the strain phase of Valsalva maneuver (VM) and its mechanism. Methods Thirty healthy volunteers were recruited to perform VM with a load of 40 mmHg. Left ventricular filling parameters (E, A, E/A ratio, e and E/e ratio) were determined by echocardiography at baseline,at the first beat and at the second beat during the strain phase of VM,respectively. Results Compared to those at baseline, E, E/A ratio and E/e ratio increased ( P ＜0.05) while A and e did not change ( P＞0.05) at the first beat during the strain phase. Compared to those at the first beat during the strain phase,E, E/A ratio and E/e ratio decreased ( P ＜0.05) while A and e did not change ( P ＞0. 05) at the second beat during the strain phase. Conclusions Left ventricular filling decreased at the second beat during the strain phase of VM, which is different from the present knowledge that left ventricular filling would begin to decrease 4-5 beats later during the strain phase of VM. Positive intrathoracic pressure decreases left-side heart and pulmonary vessel' transmural pressure while increases the blood resistance, which may be the reason that E, E/A ratio and E/e ratio decreased at the second beat during the strain phase of VM. Key words: Echocardiography ; Valsalva maneuver ; Ventricular function, left

Negative-pressure pulmonary edema presented with concomitant spontaneous pneumomediastinum: Moore meets Macklin

Negative-pressure pulmonary edema is an unusual complication mainly associated with general anesthesia. It is caused by excessive negative intrathoracic pressure following a deep inspiration against an acute airway obstruction. The resultant decreased intrathoracic pressure amplifies venous return to the right heart and increases pulmonary capillary wedge pressure that can be further amplified by massive sympathetic discharge due to hypoxia. The combination of increased venous return and pulmonary capillary wedge pressure favours the shift of fluid into the pulmonary interstitium with resultant pulmonary edema. Conversely, spontaneous pneumomediastinum (SP) results from alveolar rupture following an excessive positive intrathoracic pressure. The air leaks out of the alveoli and along the perivascular space toward the mediastinum. We experienced a case of negative pulmonary edema which presented in association with SP. Pneumomediastinum is probably caused by an excessive positive intrathoracic pressure for a subsequent expiration against a closed airway. In the present case, both complications resolved with conservative management.

Breathing strategy to preserve exercising cardiac function in patients with heart failure

The heart and lungs are closely linked as they lie in series, share a common surface area and compete for space within the thoracic cavity. The heart and lungs are exposed to the similar changes in intrathoracic pressure, and reflexes within one organ can influence the other (i.e. vagal influence of lung inflation on heart rate). In patients with heart failure, these cardiopulmonary interactions may be altered due to decreased lung and left ventricular compliance, increased cardiac size, high cardiac filling pressure and altered receptor sensitivity to neural activation. Exercise further affects the cardiopulmonary interactions by stimulating an increase in the depth and frequency of breathing which accentuates the fluctuations in intrathoracic pressure, and by requiring large increases in stroke volume and heart rate in order to respond to the increased metabolic demand. Previous work from our laboratory suggested that patients with heart failure avoid high lung volumes during exercise, often at the expense of unnecessary large positive expiratory intrathoracic pressures resulting in significant wasted effort. Moreover, we also observed that voluntarily increases in lung volume in patients with heart failure induced a mild relative bradycardia, a response not observed in similar aged healthy individuals. Thus, we hypothesized that the rapid shallow low lung volume breathing, in combination with positive expiratory intrathoracic pressure, often adopted by patients with heart failure during exercise is an attempt to preserve, or even enhance, the cardiac response to exercise.

Acute Renal Failure and Mechanical Ventilation: Reality or Myth?

Acute Renal Failure and Mechanical Ventilation: Reality or Myth?

Timing of tracheal intubation in traumatic cardiac tamponade: A word of caution

Airway, breathing, and circulation are top priorities in any resuscitation. However, in cardiac tamponade, the decision to intubate the trachea and initiate positive pressure ventilation (PPV) should only be taken after consideration of the deleterious haemodynamic effects of positive intrathoracic pressure. We suggest that the threshold for intubation and PPV should be raised in tamponade and that intubation and PPV should, if possible, be timed so that relief of tamponade can immediately follow. In the trauma setting, emergency thoracotomy is the best approach. When intubation is unavoidable because of very low oxygen saturation or cardiac arrest, high ventilatory pressures should be avoided.

Technical Notes and Tips: Forced Expiration for Chest Tube Removal – The Other Uses of a Syringe

The incidence of pneumothorax following chest tube removal can be high. The British Thoracic Society recommends that the chest tube should be removed briskly while the patient performs the Valsalva's manoeuvre or during expiration. Sometimes, it can be difficult for patients to comprehend the steps involved in producing this effect. We have devised a novel technique; after taking a deep breath, the patient is asked to blow through the tip of a syringe allowing the plunger to move backwards through the barrel. This technique produces enough positive intrathoracic pressure and decreases the chances of a pneumothorax forming significantly.

Comparaison de deux stratégies d'utilisation de la pression expiratoire positive au cours du syndrome de détresse respiratoire aiguë. Étude ExPress. Présentation du protocole de l'étude

The best strategy for setting positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS) remains controversial. High levels of PEEP could protect the lung by avoiding the opening-closing phenomenon but might, on the other hand, increase the risk of overdistension and the deleterious hemodynamic consequences of positive intrathoracic pressure. The ExPress study is a multicenter randomized controlled trial comparing the effects on mortality of two strategies for setting PEEP in patients with ARDS. The same tidal volume (6 ml/kg) is used in the two strategies. The “maximal alveolar recruitment” strategy is aimed to optimize alveolar recruitment with a high level of PEEP. In this arm, PEEP is set to maintain plateau pressure close to the maximal currently recommended value of 30 cmH 2O. In the “minimal alveolar distension” arm, the goal is to maximally decrease alveolar distension by using low to moderate levels of PEEP (total PEEP between 5 and 9 cm H 2O). The goals for oxygenation and alveolar ventilation are the same in the two arms. Precise guidelines are used to titrate sedation and to conduct weaning. The main efficacy criteria is mortality on day 28. The protocol of the study plans to include 800 patients, recruited in 37 ICU.

Baroreflex control of heart rate during sleep in severe obstructive sleep apnoea: effects of acute CPAP

Baroreflex control of heart rate during sleep (baroreflex sensitivity; BRS) has been shown to be depressed in obstructive sleep apnoea (OSA), and improved after treatment with continuous positive airway pressure (CPAP). Whether CPAP also acutely affects BRS during sleep in uncomplicated severe OSA is still debatable. Blood pressure was monitored during nocturnal polysomnography in 18 patients at baseline and during first-time CPAP application. Spontaneous BRS was analysed by the sequence method, and estimated as the mean sequence slope. CPAP did not acutely affect mean blood pressure or heart rate but decreased cardiovascular variability during sleep. Mean BRS increased slightly during CPAP application (from 6.5+/-2.4 to 7.5+/-2.9 ms x mmHg(-1)), mostly in response to decreasing blood pressure. The change in BRS did not correlate with changes in arterial oxygen saturation or apnoea/hypopnoea index. The small change in baroreflex control of heart rate during sleep at first application of continuous positive airway pressure in severe obstructive sleep apnoea was unrelated to the acute resolution of nocturnal hypoxaemia, and might reflect autonomic adjustments to positive intrathoracic pressure, and/or improved sleep architecture. The small increase in baroreflex control of heart rate during sleep may be of clinical relevance as it was accompanied by reduced cardiovascular variability, which is acknowledged as an independent cardiovascular risk factor.

Antonio Maria Valsalva (1666 - 1723)

Antonio Maria Valsalva (1666 - 1723)