Changes In Airway Pressure Research Articles

Do atmospheric conditions influence the first episode of primary spontaneous pneumothorax?

Several studies suggest that changes in airway pressure may influence the onset of primary spontaneous pneumothorax (PSP). The aim of this study was to investigate the influence of atmospheric changes on the onset of the first episode of PSP. We retrospectively analysed cases of pneumothorax admitted to our department between 1 January 2009 and 31 October 2013. Patients with recurrent pneumothorax, traumatic pneumothorax, older than 35 years or presenting history of underlying pulmonary disease were excluded. Meteorological data were collected from the Météo-France archives. Variation (Δ) of mean atmospheric pressure, and relative humidity, were calculated for each day between the day at which symptoms began (D-day), the day before first symptoms (D-1), 2 days before the first symptoms (D-2) and 3 days before the first symptoms (D-3). Six hundred and thirty-eight cases of pneumothorax were observed during the period of this study; 106 of them (16.6%) were a first episode of PSP. We did not observe any significant differences between days with or without PSP admission for any of the weather parameters that we tested. We could not find any thresholds in the variation of atmospheric pressure that could be used to determine the probability of PSP occurrence. Variation of atmospheric pressure, relative humidity, rainfall, wind speed and temperature were not significantly related to the onset of the first episode of PSP in healthy patients. These results suggest that the scientific community should focus on other possible aetiological factors than airway pressure modifications.

Mechanisms contributing to the response of upper-airway muscles to changes in airway pressure.

This study assessed the effects of inhaled lignocaine to reduce upper airway surface mechanoreceptor activity on 1) basal genioglossus and tensor palatini EMG, 2) genioglossus reflex responses to large pulses (∼10 cmH2O) of negative airway pressure, and 3) upper airway collapsibility in 15 awake individuals. Genioglossus and tensor palatini muscle EMG and airway pressures were recorded during quiet nasal breathing and during brief pulses (250 ms) of negative upper-airway pressure. Lignocaine reduced peak inspiratory (5.6 ± 1.5 vs. 3.8 ± 1.1% maximum; mean ± SE, P < 0.01) and tonic (2.8 ± 0.8 vs. 2.1 ± 0.7% maximum; P < 0.05) genioglossus EMG during quiet breathing but had no effect on tensor palatini EMG (5.0 ± 0.8 vs. 5.0 ± 0.5% maximum; P = 0.97). Genioglossus reflex excitation to negative pressure pulses decreased after anesthesia (60.9 ± 20.7 vs. 23.6 ± 5.2 μV; P < 0.05), but not when expressed as a percentage of the immediate prestimulus baseline. Reflex excitation was closely related to the change in baseline EMG following lignocaine (r(2) = 0.98). A short-latency genioglossus reflex to rapid increases from negative to atmospheric pressure was also observed. The upper airway collapsibility index (%difference) between nadir choanal and epiglottic pressure increased after lignocaine (17.8 ± 3.7 vs. 28.8 ± 7.5%; P < 0.05). These findings indicate that surface receptors modulate genioglossus but not tensor palatini activity during quiet breathing. However, removal of input from surface mechanoreceptors has minimal effect on genioglossus reflex responses to large (∼10 cmH2O), sudden changes in airway pressure. Changes in pressure rather than negative pressure per se can elicit genioglossus reflex responses. These findings challenge previous views and have important implications for upper airway muscle control.

Influence of inspiration to expiration ratio on cyclic recruitment and derecruitment of atelectasis in a saline lavage model of acute respiratory distress syndrome.

Cyclic recruitment and derecruitment of atelectasis can occur during mechanical ventilation, especially in injured lungs. Experimentally, cyclic recruitment and derecruitment can be quantified by respiration-dependent changes in PaO2 (ΔPaO2), reflecting the varying intrapulmonary shunt fraction within the respiratory cycle. This study investigated the effect of inspiration to expiration ratio upon ΔPaO2 and Horowitz index. Prospective randomized study. Laboratory investigation. Piglets, average weight 30 ± 2 kg. At respiratory rate 6 breaths/min, end-inspiratory pressure (Pendinsp) 40 cm H2O, positive end-expiratory pressure 5 cm H2O, and FIO2 1.0, measurements were performed at randomly set inspiration to expiration ratios during baseline healthy and mild surfactant depletion injury. Lung damage was titrated by repetitive surfactant washout to induce maximal cyclic recruitment and derecruitment as measured by multifrequency phase fluorimetry. Regional ventilation distribution was evaluated by electrical impedance tomography. Step changes in airway pressure from 5 to 40 cm H2O and vice versa were performed after lavage to calculate PO2-based recruitment and derecruitment time constants (TAU). In baseline healthy, cyclic recruitment and derecruitment could not be provoked, whereas in model acute respiratory distress syndrome, the highest ΔPaO2 were routinely detected at an inspiration to expiration ratio of 1:4 (range, 52-277 torr [6.9-36.9 kPa]). Shorter expiration time reduced cyclic recruitment and derecruitment significantly (158 ± 85 torr [21.1 ± 11.3 kPa] [inspiration to expiration ratio, 1:4]; 25 ± 12 torr [3.3 ± 1.6 kPa] [inspiration to expiration ratio, 4:1]; p < 0.0001), whereas the PaO2/FIO2 ratio increased (267 ± 50 [inspiration to expiration ratio, 1:4]; 424 ± 53 [inspiration to expiration ratio, 4:1]; p < 0.0001). Correspondingly, regional ventilation redistributed toward dependent lung regions (p < 0.0001). Recruitment was much faster (TAU: fast 1.6 s [78%]; slow 9.2 s) than derecruitment (TAU: fast 3.1 s [87%]; slow 17.7 s) (p = 0.0078). Inverse ratio ventilation minimizes cyclic recruitment and derecruitment of atelectasis in an experimental model of surfactant-depleted pigs. Time constants for recruitment and derecruitment, and regional ventilation distribution, reflect these findings and highlight the time dependency of cyclic recruitment and derecruitment.

Mechanical ventilation-induced intrathoracic pressure distribution and heart-lung interactions*.

Mechanical ventilation causes cyclic changes in the heart's preload and afterload, thereby influencing the circulation. However, our understanding of the exact physiology of this cardiopulmonary interaction is limited. We aimed to thoroughly determine airway pressure distribution, how this is influenced by tidal volume and chest compliance, and its interaction with the circulation in humans during mechanical ventilation. Intervention study. ICU of a university hospital. Twenty mechanically ventilated patients following coronary artery bypass grafting surgery. Patients were monitored during controlled mechanical ventilation at tidal volumes of 4, 6, 8, and 10 mL/kg with normal and decreased chest compliance (by elastic binding of the thorax). Central venous pressure, airway pressure, pericardial pressure, and pleural pressure; pulse pressure variations, systolic pressure variations, and stroke volume variations; and cardiac output were obtained during controlled mechanical ventilation at tidal volume of 4, 6, 8, and 10 mL/kg with normal and decreased chest compliance. With increasing tidal volume (4, 6, 8, and 10 mL/kg), the change in intrathoracic pressures increased linearly with 0.9 ± 0.2, 0.5 ± 0.3, 0.3 ± 0.1, and 0.3 ± 0.1 mm Hg/mL/kg for airway pressure, pleural pressure, pericardial pressure, and central venous pressure, respectively. At 8 mL/kg, a decrease in chest compliance (from 0.12 ± 0.07 to 0.09 ± 0.03 L/cm H2O) resulted in an increase in change in airway pressure, change in pleural pressure, change in pericardial pressure, and change in central venous pressure of 1.1 ± 0.7, 1.1 ± 0.8, 0.7 ± 0.4, and 0.8 ± 0.4 mm Hg, respectively. Furthermore, increased tidal volume and decreased chest compliance decreased stroke volume and increased arterial pressure variations. Transmural pressure of the superior vena cava decreased during inspiration, whereas the transmural pressure of the right atrium did not change. Increased tidal volume and decreased chest wall compliance both increase the change in intrathoracic pressures and the value of the dynamic indices during mechanical ventilation. Additionally, the transmural pressure of the vena cava is decreased, whereas the transmural pressure of the right atrium is not changed.

Changes in endotracheal tube cuff pressure during laparoscopic surgery in head-up or head-down position.

BackgroundThe abdominal insufflation and surgical positioning in the laparoscopic surgery have been reported to result in an increase of airway pressure. However, associated effects on changes of endotracheal tube cuff pressure are not well established.Methods70 patients undergoing elective laparoscopic colorectal tumor resection (head-down position, n = 38) and laparoscopic cholecystecomy (head-up position, n = 32) were enrolled and were compared to 15 patients undergoing elective open abdominal surgery. Changes of cuff and airway pressures before and after abdominal insufflation in supine position and after head-down or head-up positioning were analysed and compared.ResultsThere was no significant cuff and airway pressure changes during the first fifteen minutes in open abdominal surgery. After insufflation, the cuff pressure increased from 26 ± 3 to 32 ± 6 and 27 ± 3 to 33 ± 5 cmH2O in patients receiving laparoscopic cholecystecomy and laparoscopic colorectal tumor resection respectively (both p < 0.001). The head-down tilt further increased cuff pressure from 33 ± 5 to 35 ± 5 cmH2O (p < 0.001). There six patients undergoing colorectal tumor resection (18.8%) and eight patients undergoing cholecystecomy (21.1%) had a total increase of cuff pressure more than 10 cm H2O (18.8%). There was no significant correlation between increase of cuff pressure and either the patient's body mass index or the common range of intra-abdominal pressure (10-15 mmHg) used in laparoscopic surgery.ConclusionsAn increase of endotracheal tube cuff pressure may occur during laparoscopic surgery especially in the head-down position.

Respiratory motor function in seated and supine positions in individuals with chronic spinal cord injury

This case-controlled clinical study was undertaken to investigate to what extent pulmonary function in individuals with chronic spinal cord injury (SCI) is affected by posture. Forced vital capacity (FVC), forced expiratory volume in one second (FEV1), maximal inspiratory pressure (PImax) and maximal expiratory pressure (PEmax) were obtained from 27 individuals with chronic motor-complete (n=13, complete group) and motor-incomplete (n=14, incomplete group) C2–T12 SCI in both seated and supine positions. Seated-to-supine changes in spirometrical (FVC and FEV1) and airway pressure (PImax and PEmax) outcome measures had different dynamics when compared in complete and incomplete groups. Patients with motor-complete SCI had tendency to increase spirometrical outcomes in supine position showing significant increase in FVC (p=.007), whereas patients in incomplete group exhibited decrease in these values with significant decreases in FEV1 (p=.002). At the same time, the airway pressure values were decreased in supine position in both groups with significant decrease in PEmax (p=.031) in complete group and significant decrease in PImax (p=.042) in incomplete group. In addition, seated-to-supine percent change of PImax was strongly correlated with neurological level of motor-complete SCI (ρ=−.77, p=.002). These results indicate that postural effects on respiratory performance in patients with SCI can depend on severity and neurological level of SCI, and that these effects differ depending on respiratory tasks. Further studies with adequate sample size are needed to investigate these effects in clinically specific groups and to study the mechanisms of such effects on specific respiratory outcome measures.

The assessment of transpulmonary pressure in mechanically ventilated ARDS patients.

The optimal method for estimating transpulmonary pressure (i.e. the fraction of the airway pressure transmitted to the lung) has not yet been established. In this study on 44 patients with acute respiratory distress syndrome (ARDS), we computed the end-inspiratory transpulmonary pressure as the change in airway and esophageal pressure from end-inspiration to atmospheric pressure (i.e. release derived) and as the product of the end-inspiratory airway pressure and the ratio of lung to respiratory system elastance (i.e. elastance derived). The end-expiratory transpulmonary pressure was estimated as the product of positive end-expiratory pressure (PEEP) minus the direct measurement of esophageal pressure and by the release method. The mean elastance- and release-derived transpulmonary pressure were 14.4 ± 3.7 and 14.4 ± 3.8 cmH₂O at 5 cmH₂O of PEEP and 21.8 ± 5.1 and 21.8 ± 4.9 cmH₂O at 15 cmH₂O of PEEP, respectively (P = 0.32, P = 0.98, respectively), indicating that these parameters were significantly related (r(2) = 0.98, P < 0.001 at 5 cmH₂O of PEEP; r(2) = 0.93, P < 0.001 at 15 cmH₂O of PEEP). The percentage error was 5.6 and 12.0 %, respectively. The mean directly measured and release-derived transpulmonary pressure were -8.0 ± 3.8 and 3.9 ± 0.9 cmH₂O at 5 cmH₂O of PEEP and -1.2 ± 3.2 and 10.6 ± 2.2 cmH₂O at 15 cmH₂O of PEEP, respectively, indicating that these parameters were not related (r(2) = 0.07, P = 0.08 at 5 cmH₂O of PEEP; r (2) = 0.10, P = 0.53 at 15 cmH₂O of PEEP). Based on our observations, elastance-derived transpulmonary pressure can be considered to be an adequate surrogate of the release-derived transpulmonary pressure, while the release-derived and directly measured end-expiratory transpulmonary pressure are not related.

Spillover of cytokines and reactive oxygen species in ventilator-induced lung injury associated with inflammation and apoptosis in distal organs.

The mechanism between ventilator-induced lung injury (VILI) and multiple organ injury is unclear. The aim of our study was to investigate the mechanisms of VILI-induced distal organ injury. VILI was induced in rat lungs with high tidal volume (V(T)) ventilation of 40 mL/kg for 6 h. Rats with low V(T) ventilation of 6 mL/kg served as controls. Inflammatory and apoptotic indices in lung and distal organs were assessed. VILI increased lung weight, airway pressure, inflammation, and apoptotic pathologic changes without hemodynamic changes. The white blood cell count and the levels of H2O2, interleukin-1β (IL-1β), tumor necrosis factor alpha, and macrophage inflammatory protein-2 in bronchoalveolar lavage fluid were higher in the VILI group compared with the control group. H2O2, IL-1β, and tumor necrosis factor alpha in blood from the left ventricle were up-regulated. H2O2, IL-1β, tumor necrosis factor alpha, macrophage inflammatory protein-2, c-Jun N-terminal kinase, p38, nuclear factor kappa B, and caspase-3 in lung, heart, liver, and kidney tissues in the VILI group were up-regulated. Furthermore, the apoptotic score for the kidneys was higher than those for other distal organs in the VILI group. High V(T) ventilation induces VILI and is associated with inflammation and apoptosis in distal organs. Up-regulation of reactive oxygen species and cytokines in VILI is associated with systemic inflammatory responses. Kidney tissue appears to be more vulnerable than heart and liver tissues following VILI.

A COMPARATIVE STUDY BETWEEN I-GEL VERSUS CUFFED ENDOTRACHEAL TUBE IN LAPAROSCOPIC SURGERIES IN ADULT PATIENTS

Invention of the endotracheal tube made administration of anesthesia easy. However, laryngoscopic stimulation of oropharyngolaryngeal structures is associated with hemodynamic stress response. Recently, the I-gel has been invented. It is a new 2nd generation supraglottic airway device with a non-inflatable cuff which has several potential advantages including: easier insertion, minimal risk of tissue compression and stability after insertion. Objective: The aim of this study was to compare the I-gel to the cuffed endotracheal tube in laparoscopic surgeries in adult patients. Patients and Methods: A prospective randomized controlled clinical trial among 80 patients who underwent laparoscopic procedures. They were equally divided into two groups: I-gel and cuffed endotracheal tube (ETT) groups. Both the devices were compared as regards insertion characteristics, hemodynamic stability, gas exchange parameters, peak airway pressure changes and the incidence of postoperative complications. Results: No significant statistical difference between the two groups was found regarding heart rate, O2 saturation, end tidal CO2 and peak airway pressure changes. Regarding mean arterial blood pressure, it was more stable after insertion in the I-gel group (P=0.019). There was also significant difference in the insertion time (P=0.0029) and number of insertion attempts (P=0.04) between the two groups. Regarding ease of insertion of gastric tube, it was easier to be inserted in the ETT group (P=0.0001). The postoperative complications were higher in the ETT group; for dysphagia (P=0.0002), dysphonia (P=0.0007), nausea (P=0.0019), vomiting (P=0.00017). However, there was no difference in the presence of blood on the device (P=0.396). Conclusion: I-gel is a safe airway device during the laparoscopic procedures. It was better than the cuffed ETT regarding hemodynamic stability changes after insertion without affecting gas exchange parameters. Although the complications were higher in the ETT group but the gastric tube insertion was more difficult in the I-gel group. Key words: Airway management, I-gel, Laparoscpic surgeries, Endotracheal tube

Sleeping position and responses to a carbon dioxide challenge in convalescent prematurely born infants studied post-term

ObjectivesTo test the hypothesis that the ventilatory response to a carbon dioxide (CO2) challenge would be lower in the prone compared to the supine position in prematurely born infants studied...

Protective strategies for one-lung ventilation.

Hypoxemia and acute lung injury (ALI) are major concerns with one-lung ventilation (OLV) during thoracic surgery. Hypoxemia is usually the result of alveolar hypoventilation and an increasing shunt fraction, whereas ALI is caused by ventilatory stress (volutrauma, atelectrauma, and barotrauma), re-expansion pulmonary injury, and the lung surgery itself. Various protective strategies can be used to overcome the challenges of OLV [1,2]. There is increasing interest in the impact of different ventilator modes on ALI and arterial oxygenation during OLV. Although there is some controversy, many studies report that pressure-controlled ventilation (PCV) has more favorable effects on respiratory function than volume-controlled ventilation (VCV) during thoracic surgery with OLV [3,4,5]. However, the tidal volume (TV) with PCV changes according to lung compliance. Consequently, PCV mode might not achieve the target TV in the case of patient with marked changes in compliance during anesthesia. Recently, new mechanical ventilation modes using a deceleration flow pattern with the Drager (Auto-Flow®) and Datex-Ohmeda (PCV-volume guaranteed [VG] mode) anesthetic machines were introduced. PCV-VG mode adjusts automatically and identifies the minimum inspiratory pressure needed to maintain the desired TV. In this ventilator mode, the TV was delivered consistently regardless of changes in the patient's compliance [6]. In this issue of the Korean Journal of Anesthesiology, Song et al. [7] compare the changes in airway pressure and arterial oxygenation between the VCV and PCV-VG ventilation modes during OLV. They demonstrated that PCV-VG could attenuate airway pressure with a larger exhaled tidal volume rather than VCV during OLV in patients with relatively good pulmonary function. The authors recommend the use of PCV-VG during OLV over VCV in terms of the peak inspiratory pressure and exhaled TV. The beneficial effects of PCV-VG on respiratory function during OLV are based on the enhanced arteriolar oxygenation and reduced lung damage due to pressure [3,5]. The advantages of arterial oxygenation with PCV-VG are explained by the decelerating flow with constant pressure, which reduces atelectasis, and the lowered inspiratory pressure reduces the lung damage and increases the homogenous distribution of the inspired gas [8]. However, PCV-VG mode could not always deliver a consistent TV. When the airway pressure reaches the maximum airway pressure limit preset to avoid barotrauma, the ventilator ends inspiration. Consequently, for a patient with markedly decreased compliance, PCV-VG mode does not provide sufficient TV because it also requires a high peak inspiratory pressure to deliver the desired TV. Therefore, it is important to maintain the compliance within an appropriate range by minimizing and preventing atelectasis during anesthesia, especially in OLV. The alveolar recruitment maneuver (ARM) with 5-10 cmH2O positive end-expiratory pressure (PEEP) is a very useful, simple method for preventing atelectasis and promoting arteriolar oxygenation [9]. Various recruitment maneuvers have been developed, including high pressure-inflation for sustained seconds, intermittent sighs, and stepwise increases in the peak inspiratory pressure with PEEP [9,10]. However, the application of ARM itself is associated with a risk of lung injury and compromised hemodynamics. ARM, PEEP, and PCV-VG must be used meticulously to improve oxygenation based on the patient's lung condition and vital signs.

侵襲的人工呼吸器管理のALS患者におけるベッドアップに伴う気道内圧変化

〔目的〕筋萎縮性側索硬化症患者（ALS）のベッドアップ角度の姿勢の違いによる気道内圧変化を明らかにすることである．〔対象〕侵襲的人工呼吸器管理のALS患者10名とした．〔方法〕ベッドアップ角度0°（0°群），30°（30°群），60°（60°群）における，最高気道内圧を群間で比較した．〔結果〕60°群では，0°群および30°群と比較して最高気道内圧が有意に高かった．〔結語〕筋萎縮性側索硬化症患者の陽圧換気においてベッドアップ座位により気道内圧が増加することから，ベッドアップの際には気道内圧の変動に留意する必要がある．

Volume-controlled versus pressure-controlled ventilation-volume guaranteed mode during one-lung ventilation.

BackgroundThe purpose of this study was to investigate the changes in airway pressure and arterial oxygenation between ventilation modes during one-lung ventilation (OLV) in patients undergoing thoracic surgery.MethodsWe enrolled 27 patients for thoracic surgery with OLV in the lateral decubitus position. The subjects received various modes of ventilation in random sequences during surgery, including volume-controlled ventilation (VCV) and pressure-controlled ventilation-volume guaranteed (PCV-VG) with a tidal volume (TV) of 8 ml/kg of actual body weight. Target-controlled infusion (TCI) with propofol and remifentanil was used for anesthesia induction and maintenance. After double-lumen endobronchial tube (DLT) insertion, the proper positioning of the DLT was assessed using a fiberoptic bronchoscope. Peak inspiratory pressure (Ppeak), exhaled TV, and arterial blood gas were measured 30 min after each ventilation mode.ResultsPpeak was significantly reduced with the PCV-VG mode (19.6 ± 2.5 cmH2O) compared with the VCV mode (23.2 ± 3.1 cmH2O) (P < 0.000). However, no difference in arterial oxygen tension was noted between the groups (PCV-VG, 375.8 ± 145.1 mmHg; VCV, 328.1 ± 123.7 mmHg) (P = 0.063). The exhaled TV was also significantly increased in PCV-VG compared with VCV (451.4 ± 85.4 vs. 443.9 ± 85.9 ml; P = 0.035).ConclusionsDuring OLV in patients with normal lung function, although PCV-VG did not provide significantly improved arterial oxygen tension compared with VCV, PCV-VG provided significantly attenuated airway pressure despite significantly increased exhaled TV compared with VCV.

Comparative evaluation of hemodynamic and respiratory parameters during mechanical ventilation with two tidal volumes calculated by demi-span based height and measured height in normal lungs

Background:Appropriate determination of tidal volume (VT) is important for preventing ventilation induced lung injury. We compared hemodynamic and respiratory parameters in two conditions of receiving VTs calculated by using body weight (BW), which was estimated by measured height (HBW) or demi-span based body weight (DBW).Materials and Methods:This controlled-trial was conducted in St. Alzahra Hospital in 2009 on American Society of Anesthesiologists (ASA) I and II, 18-65-years-old patients. Standing height and weight were measured and then height was calculated using demi-span method. BW and VT were calculated with acute respiratory distress syndrome-net formula. Patients were randomized and then crossed to receive ventilation with both calculated VTs for 20 min. Hemodynamic and respiratory parameters were analyzed with SPSS version 20.0 using univariate and multivariate analyses.Results:Forty nine patients were studied. Demi-span based body weight and thus VT (DTV) were lower than Height based body weight and VT (HTV) (P = 0.028), in male patients (P = 0.005). Difference was observed in peak airway pressure (PAP) and airway resistance (AR) changes with higher PAP and AR at 20 min after receiving HTV compared with DTV.Conclusions:Estimated VT based on measured height is higher than that based on demi-span and this difference exists only in females, and this higher VT results higher airway pressures during mechanical ventilation.

Frequency and intensive care related risk factors of pneumothorax in ventilated neonates.

Objectives. Relationships of mechanical ventilation to pneumothorax in neonates and care procedures in particular are rarely studied. We aimed to evaluate the relationship of selected ventilator variables and risk events to pneumothorax. Methods. Pneumothorax was defined as accumulation of air in pleural cavity as confirmed by chest radiograph. Relationship of ventilator mode, selected settings, and risk procedures prior to detection of pneumothorax was studied using matched controls. Results. Of 540 neonates receiving mechanical ventilation, 10 (1.85%) were found to have pneumothorax. Respiratory distress syndrome, meconium aspiration syndrome, and pneumonia were the underlying lung pathology. Pneumothorax mostly (80%) occurred within 48 hours of life. Among ventilated neonates, significantly higher percentage with pneumothorax received mandatory ventilation than controls (70% versus 20%; P < 0.01). Peak inspiratory pressure >20 cm H2O and overventilation were not significantly associated with pneumothorax. More cases than controls underwent care procedures in the preceding 3 hours of pneumothorax event. Mean airway pressure change (P = 0.052) and endotracheal suctioning (P = 0.05) were not significantly associated with pneumothorax. Reintubation (P = 0.003), and bagging (P = 0.015) were significantly associated with pneumothorax. Conclusion. Pneumothorax among ventilated neonates occurred at low frequency. Mandatory ventilation and selected care procedures in the preceding 3 hours had significant association.

Bench test assessment of mainstream capnography during high frequency oscillatory ventilation

To assess the feasibility, stability and predictability of pCO2 measurement (PETCO2) using a main stream capnograph in a high frequency oscillatory ventilation circuit. A commercially available capnograph was mounted into a high frequency oscillatory ventilator patient circuit, adjustable CO2 flow was introduced into an artificial lung and the output of the CO2 sensor assessed under varying ventilator settings. Influence of oxygen content, pressures, heat and moisture were recorded. A linear relationship between CO2 flow rate and PETCO2 was found. Varying ventilator settings influenced the measurements, but the results for PETCO2 remained within a range of 1.5 mmHg above or under then mean measurement value. Measurements remained stable despite humidification, heat, pressure amplitudes or mean airway pressure changes. From this bench test, we conclude it is feasible to measure PETCO2 using a main stream capnograph during high frequency oscillatory conditions, these measurements were stable during the experiment. Changes in CO2 production or output can be detected. The system may prove to be of clinical value, but further in vivo measurements are warranted.

Increase in Airway Pressure Resulting From Prone Position Patient Placing May Predict Intraoperative Surgical Blood Loss

Prospective study on intraoperative blood loss during lumbar spine surgery. To evaluate the relationship between airway pressure change due to the patient's prone position and intraoperative blood loss during lumbar spine surgery. A prone position may increase abdominal pressure. Changes in abdominal pressure may influence airway pressure and cause intraoperative blood loss as a result of epidural venous congestion. Patients undergoing lumbar spine surgery were placed in a prone position after the administration of general anesthesia. Peak airway pressure, plateau pressure, mean blood pressure, and heart rate were measured 5 minutes after anesthesia induction and 15 minutes after being placed in a prone position. Intraoperative blood loss was measured at the end of surgery. Mean peak airway pressure was 13.7 ± 1.8 mm Hg while in a supine position and increased to 15.1 ± 2.5 mm Hg after placement in the prone position (P = 0.002). Plateau pressure was 12.6 ± 2.5 mm Hg while in a supine position and increased to 14.1 ± 1.9 mm Hg after placement in a prone position (P = 0.0002). Intraoperative blood loss was correlated with peak (R2 = 0.405) and plateau (R2 = 0.489) airway pressure changes. Increase in airway pressure resulting from placement into a prone position may predict intraoperative surgical blood loss.

Change of respiratory mechanics at different intra-abdominal pressures and position change during laparoscopic surgery

Change of respiratory mechanics at different intra-abdominal pressures and position change during laparoscopic surgery

Misdiagnosis of pneumothorax by ultrasonography after central venous catheterization in a patient with pleural adhesion

Misdiagnosis of pneumothorax by ultrasonography after central venous catheterization in a patient with pleural adhesion

Cardiac index and oxygen delivery during low and high tidal volume ventilation strategies in patients with acute respiratory distress syndrome: a crossover randomized clinical trial.

IntroductionThe beneficial effect of low tidal volume (TV) ventilation strategy on mortality in patients with acute respiratory distress syndrome (ARDS) has been attributed to the protective effect on ventilator-induced lung injury, and yet its effect on cardiovascular function might also play an important role. The aim of this study was to assess whether low TV ventilation improves cardiac output and oxygen delivery compared with high TV ventilation strategy in patients with ARDS.MethodsIn this crossover randomized clinical trial 16 ARDS patients were recruited in an intensive care unit at a university-affiliated hospital. Each patient was ventilated for 30 min with low (6 mL/kg) and 30 min with high (12 mL/kg) TV. The two experimental periods, applied in random order and with allocation concealment, were separated by 30 min of basal ventilation. Minute ventilation was constantly maintained by appropriate respiratory rate changes.ResultsCompared with high TV ventilation, low TV ventilation showed decreased pH (7.37 vs. 7.41, P = 0.001) and increased PaCO2 (49 vs. 43 mmHg; P = 0.002). Cardiac index and oxygen delivery index were increased with low compared with high TV ventilation (3.9 vs. 3.5 L.min-1.m-2, P = 0.012, and 521 vs. 463 mL.min-1.m-2, P = 0.002, respectively), while oxygen extraction ratio decreased (0.36 vs. 0.44, P = 0.027). In four patients oxygen extraction ratio was >0.5 during high TV but not during low TV strategy. The magnitude of the change in cardiac index was positively associated with PaCO2 variation (P = 0.004), while it was unrelated to the magnitude of changes in TV and airway pressure. The decrease of cardiac index was predicted by PaCO2 reduction, with and area under ROC curve of 0.72.ConclusionsOur findings suggest that a low TV ventilation strategy increases cardiac index and oxygen delivery, thus supporting the hypothesis that the beneficial effect of low TV ventilation in patients with ARDS could be partially explained by hemodynamic improvement. In other words, low tidal volume ventilation could be protective also for the cardiovascular system and not only for the lung. The slight increase of PaCO2 during low TV ventilation seems to predict the increase of cardiac index.Trial registrationClinicalTrials.gov: NCT00713713