Changes In Airway Pressure Research Articles

Pressure-controlled ventilation could decrease intraoperative blood loss and improve airway pressure measures during lumbar discectomy in the prone position: A comparison with volume-controlled ventilation mode.

Background and Aims:Prone positioning may induce alterations of hemodynamic and airway pressure parameters that may affect intraoperative (IO) blood loss. Pressure-controlled ventilation (PCV) may modify these alterations. To observe the relation between ventilation mode and hemodynamic, airway pressure changes, and blood loss during lumbar discectomy performed in the prone position.Material and Methods:Volume-controlled ventilation (VCV) patients were using tidal volume (TV) of 8–10 ml/Kg, but for pressure-controlled ventilation (PCV) patients peak inspiratory pressure (PIP) was adjusted to provide the same TV according to ideal body weight. Respiratory and hemodynamic parameters were recorded in supine (T1), on turning to prone (T2), and on returning to the supine position (T3). Primary outcome included amount of IO blood loss; Secondary outcome included need for blood transfusion, IO hemodynamics, and airway pressure changes.Results:IO blood loss and central venous pressure (CVP) were significantly higher with VCV than PCV patients. Heart rate and blood pressure were significantly reduced in the prone position with little impact of ventilation mode. Prone positioning resulted in significant increase of P-peak and non-significant decrease of P-mean pressure with VCV, while with PCV resulted in a significantly increased airway pressures. P-peak pressure was significantly lower with PCV in supine and prone positions than VCV. P-mean pressure was significantly lower in supine but significantly higher in the prone position with PCV than VCV.Conclusions:Prone positioning and VCV were associated with increased CVP and IO blood loss, while PCV could lessen these effects and significantly improve airway pressures.

Invasive Mechanical Ventilation.

Invasive mechanical ventilation is a potentially lifesaving intervention for acutely ill patients. The goal of this review is to provide a concise, clinically focused overview of basic invasive mechanical ventilation for the many clinicians who care for mechanically ventilated patients. Attention is given to how common ventilator modes differ in delivering a mechanical breath, evaluation of respiratory system mechanics, how to approach acute changes in airway pressure, and the diagnosis of auto-positive end-expiratory pressure. Waveform interpretation is emphasized throughout the review.

Ex Vivo Assessment of Porcine Donation After Circulatory Death Lungs That Undergo Increasing Warm Ischemia Times.

BackgroundIncreased utilization of donation after circulatory death (DCD) lungs may help alleviate the supply/demand mismatch between available donor organs and lung transplant candidates. Using an established porcine DCD model, we sought to determine the effect of increasing warm ischemia time (WIT) after circulatory arrest on lung function during ex vivo lung perfusion (EVLP).MethodsPorcine donors (n = 15) underwent hypoxic cardiac arrest, followed by 60, 90, or 120 minutes of WIT before procurement and 4 hours of normothermic EVLP. Oxygenation, pulmonary artery pressure, airway pressure, and compliance were measured hourly. Lung injury scores were assessed histologically after 4 hours of EVLP.ResultsAfter EVLP, all 3 groups met all the criteria for transplantation, except for 90-minute WIT lungs, which had a mean pulmonary artery pressure increase greater than 15%. There were no significant differences between groups as assessed by final oxygenation capacity, as well as changes in pulmonary artery pressure, airway pressure, or lung compliance. Histologic lung injury scores as well as lung wet-to-dry weight ratios did not significantly differ between groups.ConclusionsThese results suggest that longer WIT alone (up to 120 minutes) does not predict worse lung function at the conclusion of EVLP. Expanding acceptable WIT after circulatory death may eventually allow for increased utilization of DCD lungs in procurement protocols.

Effects of Prone Positioning on Transpulmonary Pressures and End-expiratory Volumes in Patients without Lung Disease

The effects of prone positioning on esophageal pressures have not been investigated in mechanically ventilated patients. Our objective was to characterize effects of prone positioning on esophageal pressures, transpulmonary pressure, and lung volume, thereby assessing the potential utility of esophageal pressure measurements in setting positive end-expiratory pressure (PEEP) in prone patients. We studied 16 patients undergoing spine surgery during general anesthesia and neuromuscular blockade. We measured airway pressure, esophageal pressures, airflow, and volume, and calculated the expiratory reserve volume and the elastances of the lung and chest wall in supine and prone positions. Esophageal pressures at end expiration with 0 cm H2O PEEP decreased from supine to prone by 5.64 cm H2O (95% CI, 3.37 to 7.90; P < 0.0001). Expiratory reserve volume measured at relaxation volume increased from supine to prone by 0.15 l (interquartile range, 0.25, 0.10; P = 0.003). Chest wall elastance increased from supine to prone by 7.32 (95% CI, 4.77 to 9.87) cm H2O/l at PEEP 0 (P < 0.0001) and 6.66 cm H2O/l (95% CI, 3.91 to 9.41) at PEEP 7 (P = 0.0002). Median driving pressure, the change in airway pressure from end expiration to end-inspiratory plateau, increased in the prone position at PEEP 0 (3.70 cm H2O; 95% CI, 1.74 to 5.66; P = 0.001) and PEEP 7 (3.90 cm H2O; 95% CI, 2.72 to 5.09; P < 0.0001). End-expiratory esophageal pressure decreases, and end-expiratory transpulmonary pressure and expiratory reserve volume increase, when patients are moved from supine to prone position. Mean respiratory system driving pressure increases in the prone position due to increased chest wall elastance. The increase in end-expiratory transpulmonary pressure and expiratory reserve volume may be one mechanism for the observed clinical benefit with prone positioning.

Genioglossus reflex responses to negative upper airway pressure are altered in people with tetraplegia and obstructive sleep apnoea.

Protective reflexes in the throat area (upper airway) are crucial for breathing. Impairment of these reflexes can cause breathing problems during sleep such as obstructive sleep apnoea (OSA). OSA is very common in people with spinal cord injury for unknown reasons. This study shows major changes in protective reflexes that serve to keep the upper airway open in response to suction pressures in people with tetraplegia and OSA. These results help us understand why OSA is so common in people with tetraplegia and provide new insight into how protective upper airway reflexes work more broadly. More than 60% of people with tetraplegia have obstructive sleep apnoea (OSA). However, the specific causes are unknown. Genioglossus, the largest upper-airway dilator muscle, is important in maintaining upper-airway patency. Impaired genioglossus muscle function following spinal cord injury may contribute to OSA. This study aimed to determine if genioglossus reflex responses to negative upper-airway pressure are altered in people with OSA and tetraplegia compared to non-neurologically impaired able-bodied individuals with OSA. Genioglossus reflex responses measured via intramuscular electrodes to ∼60 brief (250ms) pulses of negative upper-airway pressure (∼-15cmH2 O at the mask) were compared between 13 participants (2 females) with tetraplegia plus OSA and 9 able-bodied controls (2 females) matched for age and OSA severity. The initial short-latency excitatory reflex response was absent in 6/13 people with tetraplegia and 1/9 controls. Genioglossus reflex inhibition in the absence of excitation was observed in three people with tetraplegia and none of the controls. When the excitatory response was present, it was significantly delayed in the tetraplegia group compared to able-bodied controls: excitation onset latency (mean±SD) was 32±16vs. 18±9ms, P=0.045; peak excitation latency was 48±17vs. 33±8ms, P=0.038. However, when present, amplitude of the excitation response was not different between groups, 195±26vs. 219±98% at baseline, P=0.55. There are major differences in genioglossus reflex morphology and timing in response to rapid changes in airway pressure in people with tetraplegia and OSA. Altered genioglossus function may contribute to the increased risk of OSA in people with tetraplegia. The precise mechanisms mediating these differences are unknown.

Mask pressure effects on the nasal bridge during short-term noninvasive ventilation.

The aim of this study was to assess the influence of different masks, ventilator settings and body positions on the pressure exerted on the nasal bridge by the mask and subjective comfort during noninvasive ventilation (NIV).We measured the pressure over the nasal bridge in 20 healthy participants receiving NIV via four different NIV masks (three oronasal masks, one nasal mask) at three different ventilator settings and in the seated or supine position. Objective pressure measurements were obtained with an I-Scan pressure-mapping system. Subjective comfort of the mask fit was assessed with a visual analogue scale.The masks exerted mean pressures between 47.6±29 mmHg and 91.9±42.4 mmHg on the nasal bridge. In the supine position, the pressure was lower in all masks (57.1±31.9 mmHg supine, 63.9±37.3 mmHg seated; p<0.001). With oronasal masks, a change of inspiratory positive airway pressure (IPAP) did not influence the objective pressure over the nasal bridge. Subjective discomfort was associated with higher IPAP and positively correlated with the pressure on the skin.Objective measurement of pressure on the skin during mask fitting might be helpful for mask selection. Mask fitting in the supine position should be considered in the clinical routine.

A Modified Definition for Obstructive Sleep Apnea in Home Sleep Apnea Testing after Stroke or Transient Ischemic Attack

Home sleep apnea testing (HSAT) underestimates obstructive sleep apnea (OSA) severity. Overnight oxygen desaturation has been shown to be a strong predictor of incident stroke, and may be helpful in determining which patients with lower apnea-hypopnea indices (AHIs) should be offered treatment. To examine whether a modified definition for OSA that uses oxygen desaturation (i.e., AHI 5-14.9 per hour and lowest O2 desaturation ≤88%), as compared to an AHI ≥ 15 per hour, would impact: (1) changes in Epworth Sleepiness Scale scores post-continuous positive airway pressure (CPAP) initiation; (2) CPAP compliance rates; and (3) the accuracy of automated versus manual scoring of HSAT. One hundred and six patients with a prior stroke or transient ischemic attack (TIA) underwent HSAT. Epworth Sleepiness Scale and CPAP compliance were measured at baseline and 3-6 months. Median age was 67.5 years, 57.5% male, and 76.4% presented with stroke. Fifty-nine patients were diagnosed with OSA; of these 54.2% met criteria for the "modified definition" for OSA (AHI 5-14.9 per hour with oxygen desaturation) and 45.8% met criteria for the "classic definition" for OSA (AHI ≥15). The modified (versus classic) definition had: (1) a greater decrease in ESS (P = .05) post-CPAP initiation; (2) comparable CPAP compliance rates; and (3) comparable automatically versus manually scored AHIs (Spearman's rho = .96, Cohen's Kappa ≥ .75 for both definitions, P < .001). Using a modified definition of OSA that uses a lower AHI cutoff and includes an oxygen desaturation cutoff in the setting of HSAT for stroke or transient ischemic attack (TIA) patients may improve daytime sleepiness post-CPAP initiation, while not significantly affecting CPAP compliance rates nor the accuracy of automated scoring.

Chest wall effect on the monitoring of respiratory mechanics in acute respiratory distress syndrome.

The respiratory system mechanics depend on the characteristics of the lung and chest wall and their interaction. In patients with acute respiratory distress syndrome under mechanical ventilation, the monitoring of airway plateau pressure is fundamental given its prognostic value and its capacity to assess pulmonary stress. However, its validity can be affected by changes in mechanical characteristics of the chest wall, and it provides no data to correctly titrate positive end-expiratory pressure by restoring lung volume. The chest wall effect on respiratory mechanics in acute respiratory distress syndrome has not been completely described, and it has likely been overestimated, which may lead to erroneous decision making. The load imposed by the chest wall is negligible when the respiratory system is insufflated with positive end-expiratory pressure. Under dynamic conditions, moving this structure demands a pressure change whose magnitude is related to its mechanical characteristics, and this load remains constant regardless of the volume from which it is insufflated. Thus, changes in airway pressure reflect changes in the lung mechanical conditions. Advanced monitoring could be reserved for patients with increased intra-abdominal pressure in whom a protective mechanical ventilation strategy cannot be implemented. The estimates of alveolar recruitment based on respiratory system mechanics could reflect differences in chest wall response to insufflation and not actual alveolar recruitment.

Hemodynamic, Airway Pressure, and Capnometric Changes and Perioperative Outcome in Pediatric Laparoscopic Inguinal Herniorrhaphy: A Comparison with Open Inguinal Herniorrhaphy.

Background:Laparoscopic procedures which are now established in pediatric population as well exposes the child to supplemental cardiorespiratory changes due to increase in intraabdominal pressure (IAP) and hypercarbia.Aims:This study aims to analyze the effects of pneumoperitoneum and postural modifications on cardiorespiratory system (primary outcome) during pediatric laparoscopic herniorrhaphy (LH) and its comparison with open herniorrhaphy (OH) and assessment of overall perioperative outcome (secondary outcome).Settings and Design:A prospective, observational study conducted in a tertiary care hospital.Materials and Methods:Fifty children undergoing either LH (n = 25) or OH (n = 25) were included in the study. Anesthetic procedure was standardized. Parameters monitored were heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressures (MAP), electrocardiogram lead-II, end-tidal CO2 (ETCO2), airway pressures PPeak, PPlateau, PMean, pulse oximetry, IAP, minute ventilation/respiratory rate alterations.Statistical Analysis Used:Student's t-test and Chi-square test were applied to compare different variables between the two groups. Intragroup analysis was done using the analysis of variance test.Results:The HR was comparable in both groups. The rise in SBP, DBP, and MAP was 9% (102.88 ± 6.91–121.32 ± 6.63), 19% (60.88 ± 4.94–77.00 ± 9.75), and 14.8% (73.92 ± 4.65–90.40 ± 8.42), respectively, in group LH. The rise in peak, plateau, and mean airway pressures was 19.4% (14.20 ± 2.00–18.00 ± 2.54), 20.1% (13.32 ± 1.89–16.89 ± 2.60), and 16.1% (6.20 ± 1.00–7.47 ± 0.96), respectively, in group LH. ETCO2 showed a maximum rise of 19.4% (34.52 ± 3.61–41.21 ± 3.99) in group LH. In laparoscopic group, recurrence was seen in 3 patients.Conclusions:We found significant hemodynamic, airway pressure, and capnometric changes during pediatric LH with comparable perioperative outcome among the two groups.

α1-Anti-trypsin improves function of porcine donor lungs during ex-vivo lung perfusion

Ex-vivo lung perfusion (EVLP), a technique for donor lung assessment, also represents a platform for donor lung repair and immunomodulation. α1-Anti-trypsin (A1AT), a medication used to treat emphysema in A1AT-deficient patients, has anti-inflammatory properties and has been shown to attenuate ischemia-reperfusion injury in rat and pig lung transplants. The objective of this study was to determine whether administration of A1AT during EVLP can improve donor lung quality after prolonged hypothermic preservation. Pig donor lungs were retrieved, preserved at 4°C for 24 hours, and then subjected to normothermic EVLP for 12 hours using the Toronto protocol. The treatment group (n = 6) received 3 mg/ml A1AT (Zemaira) in the EVLP perfusate, acellular Steen solution. The control group (n = 6) was perfused with Steen solution only. Physiologic functions and gas exchange were measured hourly. Pulmonary edema, lung injury, apoptosis and inflammatory mediators were evaluated in lung tissues and perfusate. A1AT treatment significantly reduced pulmonary arterial pressure, pulmonary vascular resistance and airway pressure changes from the baseline when compared with controls. A1AT treatment significantly improved both dynamic and static pulmonary compliance, and change in partial pressure of oxygen (ΔPO2) between the left atrium and the pulmonary artery. Furthermore, A1AT treatment also significantly reduced pulmonary edema (wet-to-dry ratio), pulmonary cell apoptosis and pro-inflammatory cytokine levels (interleukin-1α and -8) in the perfusate. Treatment of 24-hour-preserved pig donor lungs with A1AT during EVLP resulted in improved physiologic function, reduced pulmonary edema and inflammation and decreased cell death. Our findings suggest that treatment of donor lungs during EVLP with A1AT is a promising strategy to attenuate early lung injury and improve donor lung function before lung transplantation.

An automated and reliable method for breath detection during variable mask pressures in awake and sleeping humans.

Accurate breath detection is crucial in sleep and respiratory physiology research and in several clinical settings. However, this process is technically challenging due to measurement and physiological artifacts and other factors such as variable leaks in the breathing circuit. Recently developed techniques to quantify the multiple causes of obstructive sleep apnea, require intermittent changes in airway pressure applied to a breathing mask. This presents an additional unique challenge for breath detection. Traditional algorithms often require drift correction. However, this is an empirical operation potentially prone to human error. This paper presents a new algorithm for breath detection during variable mask pressures in awake and sleeping humans based on physiological landmarks detected in the airflow or epiglottic pressure signal (Pepi). The algorithms were validated using simulated data from a mathematical model and against the standard visual detection approach in 4 healthy individuals and 6 patients with sleep apnea during variable mask pressure conditions. Using the flow signal, the algorithm correctly identified 97.6% of breaths with a mean difference±SD in the onsets of respiratory phase compared to expert visual detection of 23±89ms for inspiration and 6±56ms for expiration during wakefulness and 10±74ms for inspiration and 3±28 ms for expiration with variable mask pressures during sleep. Using the Pepi signal, the algorithm correctly identified 89% of the breaths with accuracy of 31±156ms for inspiration and 9±147ms for expiration compared to expert visual detection during variable mask pressures asleep. The algorithm had excellent performance in response to baseline drifts and noise during variable mask pressure conditions. This new algorithm can be used for accurate breath detection including during variable mask pressure conditions which represents a major advance over existing time-consuming manual approaches.

Comparison of Propofol with Desflurane for Laparoscopic Sleeve Gastrectomy in Morbidly Obese patients: A Prospective Randomized Trial

Background: Laparoscopic sleeve gastrectomy has become one of the most effective treatment options for adults with severe obesity. However, optimal anesthetic management for laparoscopic sleeve gastrectomy has not been described yet. Methods: In this prospective randomized study, we compared the effects of propofol anesthesia (Group 1) with desflurane anesthesia (Group II) in morbid obese patients for laparoscopic sleeve gastrectomy. We compared postoperative recovery and hemodynamic parameters of the patients. We also investigated the changes in tracheal cuff pressure and peak airway pressure of these obese patients during orogastric tube insertion and peritoneal CO2 insufflation. Results: Eye opening and extubation time were longer in the propofol group than in the desflurane group (p 0.05). Six patients in Group I and eight patients in Group II had sore throat (p > 0.05). Eight patients in Group I a...

Equine Welfare during Exercise: An Evaluation of Breathing, Breathlessness and Bridles.

Simple SummaryHorses have superior athletic capabilities due largely to their exceptional cardiorespiratory responses during exercise. This has particular relevance to horses’ potential to experience breathlessness, especially when their athletic performance is reduced by impaired respiratory function. Breathlessness, incorporating three types of unpleasant experiences, has been noted as of significant animal welfare concern in other mammals. However, the potential for breathlessness to occur in horses as usually ridden wearing bitted bridles has not yet been evaluated in detail. Accordingly, key physiological responses to exercise and the consequences of impaired respiratory function are outlined. Then the physiological control of breathing and the generation of the aversive experiences of breathlessness are explained. Finally, the potential for horses with unimpaired and impaired respiratory function to experience the different types of breathlessness is evaluated. This information provides a basis for considering the circumstances in which breathlessness may have significant negative welfare impacts on horses as currently ridden wearing bitted bridles. Potential beneficial impacts on respiratory function of using bitless bridles are then discussed with emphasis on the underlying mechanisms and their relevance to breathlessness. It is noted that direct comparisons of cardiorespiratory responses to exercise in horses wearing bitless and bitted bridles are not available and it is recommended that such studies be undertaken.Horses engaged in strenuous exercise display physiological responses that approach the upper functional limits of key organ systems, in particular their cardiorespiratory systems. Maximum athletic performance is therefore vulnerable to factors that diminish these functional capacities, and such impairment might also lead to horses experiencing unpleasant respiratory sensations, i.e., breathlessness. The aim of this review is to use existing literature on equine cardiorespiratory physiology and athletic performance to evaluate the potential for various types of breathlessness to occur in exercising horses. In addition, we investigate the influence of management factors such as rein and bit use and of respiratory pathology on the likelihood and intensity of equine breathlessness occurring during exercise. In ridden horses, rein use that reduces the jowl angle, sometimes markedly, and conditions that partially obstruct the nasopharynx and/or larynx, impair airflow in the upper respiratory tract and lead to increased flow resistance. The associated upper airway pressure changes, transmitted to the lower airways, may have pathophysiological sequelae in the alveolae, which, in their turn, may increase airflow resistance in the lower airways and impede respiratory gas exchange. Other sequelae include decreases in respiratory minute volume and worsening of the hypoxaemia, hypercapnia and acidaemia commonly observed in healthy horses during strenuous exercise. These and other factors are implicated in the potential for ridden horses to experience three forms of breathlessness—”unpleasant respiratory effort”, “air hunger” and “chest tightness”—which arise when there is a mismatch between a heightened ventilatory drive and the adequacy of the respiratory response. It is not known to what extent, if at all, such mismatches would occur in strenuously exercising horses unhampered by low jowl angles or by pathophysiological changes at any level of the respiratory tract. However, different combinations of the three types of breathlessness seem much more likely to occur when pathophysiological conditions significantly reduce maximal athletic performance. Finally, most horses exhibit clear behavioural evidence of aversion to a bit in their mouths, varying from the bit being a mild irritant to very painful. This in itself is a significant animal welfare issue that should be addressed. A further major point is the potential for bits to disrupt the maintenance of negative pressure in the oropharynx, which apparently acts to prevent the soft palate from rising and obstructing the nasopharynx. The untoward respiratory outcomes and poor athletic performance due to this and other obstructions are well established, and suggest the potential for affected animals to experience significant intensities of breathlessness. Bitless bridle use may reduce or eliminate such effects. However, direct comparisons of the cardiorespiratory dynamics and the extent of any respiratory pathophysiology in horses wearing bitted and bitless bridles have not been conducted. Such studies would be helpful in confirming, or otherwise, the claimed potential benefits of bitless bridle use.

Relationships and CPAP adherence among women with obstructive sleep apnea

BackgroundObstructive sleep apnea contributes to daytime sleepiness, poor quality of life and increased risk for heart disease and hypertension among women. Continuous positive airway pressure improves sleepiness and quality of life and may reduce health risks but few studies have evaluated predictors of adherence among women. The goal of this study was to evaluate the role of relationship factors in women’s continuous positive airway pressure (CPAP) adherence and change in relationship quality among married/partnered women.MethodsWomen recently diagnosed with obstructive sleep apnea completed relationship quality, social support questionnaires and spousal involvement interviews. CPAP adherence was collected at 12 weeks.ResultsData were available for 16 women. Average CPAP adherence was 3.6 SD = 2.7 h per night. Women with higher reports of social support had higher adherence. None of the unmarried/partnered participants were adherent to the recommendation of CPAP use ≥ 4 h per night at 12 week follow-up. Marital status was not associated with demographic, disease severity or social support measures. Relationship conflict among married/partnered participants was associated with lower adherence. In qualitative surveys, encouragement and support were the two most commonly reported types of partner involvement. Relationship quality did not change between baseline and 3 months.ConclusionResults suggest relationship factors are robust predictors of CPAP adherence among women with obstructive sleep apnea.

Mechanisms of the deep, slow-wave, sleep-related increase of upper airway muscle tone in healthy humans

Upper airway muscle activity is reportedly elevated during slow-wave sleep (SWS) when compared with lighter sleep stages. To uncover the possible mechanisms underlying this elevation, we explored the correlation between different indices of central and reflex inspiratory drive, such as the changes in airway pressure and end-expiratory CO2 and the changes in the genioglossus (GG) and tensor palatini (TP) muscle activity accompanying transitions from the lighter N2 to the deeper N3 stage of non-rapid eye movement (NREM) sleep in healthy young adult men. Forty-six GG and 38 TP continuous electromyographic recordings were obtained from 16 men [age: 20 ± 2.5 (SD) yr; body mass index: 22.5 ± 1.8 kg/m2] during 32 transitions from NREM stages N2 to N3. GG but not TP activity increased following transition into N3 sleep, and the increase was positively correlated with more negative airway pressure, increased end-tidal CO2, increased peak inspiratory flow, and increased minute ventilation. None of these correlations was statistically significant for TP. Complementary GG and TP single motor unit analysis revealed a mild recruitment of GG units and derecruitment of TP units during the N2 to N3 transitions. These findings suggest that, in healthy individuals, the increased GG activity during SWS is driven primarily by reflex stimulation of airway mechanoreceptors and central chemoreceptors.NEW & NOTEWORTHY The characteristic increase in the activity of the upper airway dilator muscle genioglossus during slow-wave sleep (SWS) in young healthy individuals was found to be related to increased stimulation of airway mechanoreceptors and central chemoreceptors. No evidence was found for the presence of a central SWS-specific drive stimulating genioglossus activity in young healthy individuals. However, it remains to be determined whether a central drive exists in obstructive sleep apnea patients.

Airway driving pressure and lung stress in ARDS patients.

BackgroundLung-protective ventilation strategy suggests the use of low tidal volume, depending on ideal body weight, and adequate levels of PEEP. However, reducing tidal volume according to ideal body weight does not always prevent overstress and overstrain. On the contrary, titrating mechanical ventilation on airway driving pressure, computed as airway pressure changes from PEEP to end-inspiratory plateau pressure, equivalent to the ratio between the tidal volume and compliance of respiratory system, should better reflect lung injury. However, possible changes in chest wall elastance could affect the reliability of airway driving pressure. The aim of this study was to evaluate if airway driving pressure could accurately predict lung stress (the pressure generated into the lung due to PEEP and tidal volume).MethodsOne hundred and fifty ARDS patients were enrolled. At 5 and 15 cmH2O of PEEP, lung stress, driving pressure, lung and chest wall elastance were measured.ResultsThe applied tidal volume (mL/kg of ideal body weight) was not related to lung gas volume (r2 = 0.0005 p = 0.772). Patients were divided according to an airway driving pressure lower and equal/higher than 15 cmH2O (the lower and higher airway driving pressure groups). At both PEEP levels, the higher airway driving pressure group had a significantly higher lung stress, respiratory system and lung elastance compared to the lower airway driving pressure group. Airway driving pressure was significantly related to lung stress (r2 = 0.581 p < 0.0001 and r2 = 0.353 p < 0.0001 at 5 and 15 cmH2O of PEEP). For a lung stress of 24 and 26 cmH2O, the optimal cutoff value for the airway driving pressure were 15.0 cmH2O (ROC AUC 0.85, 95 % CI = 0.782–0.922); and 16.7 (ROC AUC 0.84, 95 % CI = 0.742–0.936).ConclusionsAirway driving pressure can detect lung overstress with an acceptable accuracy. However, further studies are needed to establish if these limits could be used for ventilator settings.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-016-1446-7) contains supplementary material, which is available to authorized users.

Simulation Research on a New Spot-First-Aid of Foreign Body Asphyxia in the Hypopharynx

Airway suffocation is a kind of unexpected emergency. The author's research group proposed a new spot-first-aid method of foreign body asphyxia in the hypopharynx, and compares it with traditional “Heimlich Maneuver” first aid method by simulation comparative study. This article mainly introduced the main contents and methods of the research, primarily on: the processing of CT Imaging data, including: Visual C++ program is used to realize the contour extraction algorithm processing based on CT images pre-processing, and restore the respiratory organs in asphyxia status in the processing of image morphology. Compare the two spot first aid methods by simulation. The Main research steps including: establishing simulated equivalent circuit simulation to compare two different spot first aid methods influence on the change of respiratory airway pressure and the animals steps of the experiments.

The occlusion tests and end-expiratory esophageal pressure: measurements and comparison in controlled and assisted ventilation.

Background Esophageal pressure is used as a reliable surrogate of the pleural pressure. It is conventionally measured by an esophageal balloon placed in the lower part of the esophagus. To validate the correct position of the balloon, a positive pressure occlusion test by compressing the thorax during an end-expiratory pause or a Baydur test obtained by occluding the airway during an inspiratory effort is used. An acceptable catheter position is defined when the ratio between the changes in esophageal and airway pressure (∆Pes/∆Paw) is close to unity. Sedation and paralysis could affect the accuracy of esophageal pressure measurements. The aim of this study was to evaluate, in mechanically ventilated patients, the effects of paralysis, two different esophageal balloon positions and two PEEP levels on the ∆Pes/∆Paw ratio measured by the positive pressure occlusion and the Baydur tests and on the end-expiratory esophageal pressure and respiratory mechanics (lung and chest wall).MethodsTwenty-one intubated and mechanically ventilated patients (mean age 64.8 ± 14.0 years, body mass index 24.2 ± 4.3 kg/m2, PaO2/FiO2 319.4 ± 117.3 mmHg) were enrolled. In step 1, patients were sedated and paralyzed during volume-controlled ventilation, and in step 2, they were only sedated during pressure support ventilation. In each step, two esophageal balloon positions (middle and low, between 25–30 cm and 40–45 cm from the mouth) and two levels of PEEP (0 and 10 cmH2O) were applied. The ∆Pes/∆Paw ratio and end-expiratory esophageal pressure were evaluated.ResultsThe ∆Pes/∆Paw ratio was slightly higher (+0.11) with positive occlusion test compared with Baydur’s test. The level of PEEP and the esophageal balloon position did not affect this ratio. The ∆Pes and ∆Paw were significantly related to a correlation coefficient of r = 0.984 during the Baydur test and r = 0.909 in the positive occlusion test. End-expiratory esophageal pressure was significantly higher in sedated and paralyzed patients compared with sedated patients (+2.47 cmH2O) and when esophageal balloon was positioned in the low position (+2.26 cmH2O). The esophageal balloon position slightly influenced the lung elastance, while the PEEP reduced the chest wall elastance without affecting the lung and total respiratory system elastance.ConclusionsParalysis and balloon position did not clinically affect the measurement of the ∆Pes/∆Paw ratio, while they significantly increased the end-expiratory esophageal pressure.

Quantifying the Amount of Bleeding and Associated Changes in Intra-Abdominal Pressure and Mean Airway Pressure in Patients Undergoing Lumbar Fixation Surgeries: A Comparison of Three Positioning Systems.

Study DesignProspective, randomised controlled, single centre study of 45 patients posted for two level lumbar fixation surgery in the prone position.PurposeTo compare intra-abdominal pressure (IAP), mean airway pressure mean airway pressure and blood loss during the spine surgery in prone position using three different positioning systems.Overview of LiteratureStudies have correlated IAP with the amount of perioperative bleeding. However, IAP and airway pressures while assessing the bleeding comparing two or more prone positioning systems are unclear.MethodsThis prospective study was conducted on a cohort of 45 patients scheduled for two-level lumbar fixation. Patients were randomly allocated to a spine table, Wilson's frame, and thermomodulated pads. Bladder pressure as an indicator of IAP, mean and peak airway pressures, and blood loss were monitored.ResultsIAP increased whenever patient position was changed to prone .The increase in pressure was more in the Wilson's frame group but was statistically significant only on prolonged positioning. Adopting the prone position always increased the mean airway pressure, but the increased was significant only in the Wilson's frame group. Mean airway pressure decreased in the spine table group and was statistically significant. The blood loss in the spine table group was significantly less as compared to the other groups.ConclusionsPositioning on a spine table results in less blood loss and low mean airway pressure. The Wilson's frame results in high IAP, increased mean airway pressure, and more blood loss. The thermomodulated frame increases mean airway pressure and produces a moderate increase in IAP and airway pressure.

Effect of regulating airway pressure on intrathoracic pressure and vital organ perfusion pressure during cardiopulmonary resuscitation: a non-randomized interventional cross-over study.

BackgroundThe objective of this investigation was to evaluate changes in intrathoracic pressure (Ppl), airway pressure (Paw) and vital organ perfusion pressures during standard and intrathoracic pressure regulation (IPR)-assisted cardiopulmonary resuscitation (CPR).MethodsMultiple CPR interventions were assessed, including newer ones based upon IPR, a therapy that enhances negative intrathoracic pressure after each positive pressure breath. Eight anesthetized pigs underwent 4 min of untreated ventricular fibrillation followed by 2 min each of sequential interventions: (1) conventional standard CPR (STD), (2) automated active compression decompression (ACD) CPR, (3) ACD+ an impedance threshold device (ITD) CPR or (4) ACD+ an intrathoracic pressure regulator (ITPR) CPR, the latter two representing IPR-based CPR therapies. Intrapleural (Ppl), airway (Paw), right atrial, intracranial, and aortic pressures, along with carotid blood flow and end tidal CO2, were measured and compared during each CPR intervention.ResultsThe lowest mean and decompression phase Ppl were observed with IPR-based therapies [Ppl mean (mean ± SE): STD (0.8 ± 1.1 mmHg); ACD (−1.6 ± 1.6); ACD-ITD (−3.7 ± 1.5, p < 0.05 vs. both STD and ACD); ACD-ITPR (−7.0 ± 1.9, p < 0.05 vs. both STD and ACD)] [Ppl decompression (mean ± SE): STD (−6.3 ± 2.2); ACD (−13.0 ± 3.8); ACD-ITD −16.9 ± 3.6, p < 0.05 vs. both STD and ACD); ACD-ITPR −18.7 ± 3.5, p < 0.05 vs. both STD and ACD)]. Interventions with the lower mean or decompression phase Ppl also demonstrated lower Paw and were associated with higher vital organ perfusion pressures.ConclusionsIPR-based CPR methods, specifically ACD-ITPR, yielded the most pronounced reduction in both Ppl and Paw and resulted in the most favorable augmentation of hemodynamics during CPR.Electronic supplementary materialThe online version of this article (doi:10.1186/s13049-015-0164-5) contains supplementary material, which is available to authorized users.