In acute respiratory distress syndrome (ARDS) damaged alveolar epithelium, leakage of plasma proteins into the alveolar space and inactivation of pulmonary surfactant lead to respiratory dysfunction. ...Lung function could potentially be restored with exogenous surfactant therapy, but clinical trials have so far been disappointing. These negative results may be explained by inactivation and/or too low doses of the administered surfactant. Surfactant based on a recombinant surfactant protein C analogue (rSP-C33Leu) is easy to produce and in this study we compared its effects on lung function and inflammation with a commercial surfactant preparation in an adult rabbit model of ARDS.
ARDS was induced in adult New Zealand rabbits by mild lung-lavages followed by injurious ventilation (V
20 m/kg body weight) until P/F ratio < 26.7 kPa. The animals were treated with two intratracheal boluses of 2.5 mL/kg of 2% rSP-C33Leu in DPPC/egg PC/POPG, 50:40:10 or poractant alfa (Curosurf®), both surfactants containing 80 mg phospholipids/mL, or air as control. The animals were subsequently ventilated (V
8-9 m/kg body weight) for an additional 3 h and lung function parameters were recorded. Histological appearance of the lungs, degree of lung oedema and levels of the cytokines TNFα IL-6 and IL-8 in lung homogenates were evaluated.
Both surfactant preparations improved lung function vs. the control group and also reduced inflammation scores, production of pro-inflammatory cytokines, and formation of lung oedema to similar degrees. Poractant alfa improved compliance at 1 h, P/F ratio and PaO
at 1.5 h compared to rSP-C33Leu surfactant.
This study indicates that treatment of experimental ARDS with synthetic lung surfactant based on rSP-C33Leu improves lung function and attenuates inflammation.
Background
In a previous study, we found a rebound of arterial carbon dioxide tension (PaCO2) after stopping THAM buffer administration. We hypothesized that this was due to reduced pulmonary CO2 ...elimination during THAM administration. The aim of this study was to investigate this hypothesis in an experimental porcine hypercapnic model.
Methods
In seven, initially normoventilated, anesthetized pigs (22–27 kg) minute ventilation was reduced by 66% for 7 h. Two hours after commencing hypoventilation, THAM was infused IV for 3 h in a dose targeting a pH of 7.35 followed by a 2 h observation period. Acid‐base status, blood‐gas content and exhaled CO2 were measured.
Results
THAM raised pH (7.07 ± 0.04 to 7.41 ± 0.04, P < 0.05) and lowered PaCO2 (15.2 ± 1.4 to 12.2 ± 1.1 kPa, P < 0.05). After the infusion, pH decreased and PaCO2 increased again. At the end of the observation period, pH and PaCO2 were 7.24 ± 0.03 and 16.6 ± 1.2 kPa, respectively (P < 0.05). Pulmonary CO2 excretion decreased from 109 ± 12 to 74 ± 12 ml/min (P < 0.05) during the THAM infusion but returned at the end of the observation period to 111 ± 15 ml/min (P < 0.05). The estimated reduction of pulmonary CO2 elimination during the infusion was 5800 ml.
Conclusions
In this respiratory acidosis model, THAM reduced PaCO2, but seemed not to increase the total CO2 elimination due to decreased pulmonary CO2 excretion, suggesting only cautious use of THAM in hypercapnic acidosis.
This paper reviews 28 papers or commentaries published in Journal of Clinical Monitoring and Computing in 2018 and 2019, within the field of respiration. Papers were published covering endotracheal ...tube cuff pressure monitoring, ventilation and respiratory rate monitoring, lung mechanics monitoring, gas exchange monitoring, CO
2
monitoring, lung imaging, and technologies and strategies for ventilation management.
Background
In mechanically ventilated, lung injured, patients without spontaneous breathing effort, atelectasis with shunt and desaturation may appear suddenly when ventilator pressures are ...decreased. It is not known how such a formation of atelectasis is related to transpulmonary pressure (PL) during weaning from mechanical ventilation when the spontaneous breathing effort is increased. If the relation between PL and atelectasis were known, monitoring of PL might help to avoid formation of atelectasis and cyclic collapse during weaning. The main purpose of this study was to determine the relation between PL and atelectasis in an experimental model representing weaning from mechanical ventilation.
Methods
Dynamic transverse computed tomography scans were acquired in ten anaesthetized, surfactant‐depleted pigs with preserved spontaneous breathing, as ventilator support was lowered by sequentially reducing inspiratory pressure and positive end expiratory pressure in steps. The volumes of gas and atelectasis in the lungs were correlated with PL obtained using oesophageal pressure recordings. Work of breathing (WOB) was assessed from Campbell diagrams.
Results
Gradual decrease in PL in both end‐expiration and end‐inspiration caused a proportional increase in atelectasis and decrease in the gas content (linear mixed model with an autoregressive correlation matrix; P < 0.001) as the WOB increased. However, cyclic alveolar collapse during tidal ventilation did not increase significantly.
Conclusion
We found a proportional correlation between atelectasis and PL during the ‘weaning process’ in experimental mild lung injury. If confirmed in the clinical setting, a gradual tapering of ventilator support can be recommended for weaning without risk of sudden formation of atelectasis.
This paper reviews 32 papers or commentaries published in Journal of Clinical Monitoring and Computing in 2016, within the field of respiration. Papers were published covering airway management, ...ventilation and respiratory rate monitoring, lung mechanics and gas exchange monitoring, in vitro monitoring of lung mechanics, CO
2
monitoring, and respiratory and metabolic monitoring techniques.
Background
It is not well known what is the main mechanism causing lung heterogeneity in healthy lungs under mechanical ventilation. We aimed to investigate the mechanisms causing heterogeneity of ...regional ventilation and parenchymal densities in healthy lungs under anesthesia and mechanical ventilation.
Methods
In a small animal model, synchrotron imaging was used to measure lung aeration and regional‐specific ventilation (sV̇). Heterogeneity of ventilation was calculated as the coefficient of variation in sV̇ (CVsV̇). The coefficient of variation in lung densities (CVD) was calculated for all lung tissue, and within hyperinflated, normally and poorly aerated areas. Three conditions were studied: zero end‐expiratory pressure (ZEEP) and FIO2 0.21; ZEEP and FIO2 1.0; PEEP 12 cmH2O and FIO21.0 (Open Lung‐PEEP = OLP).
Results
The mean tissue density at OLP was lower than ZEEP‐1.0 and ZEEP‐0.21. There were larger subregions with low sV̇ and poor aeration at ZEEP‐0.21 than at OLP: 12.9 ± 9.0 vs. 0.6 ± 0.4% in the non‐dependent level, and 17.5 ± 8.2 vs. 0.4 ± 0.1% in the dependent one (P = 0.041). The CVsV̇ of the total imaged lung at PEEP 12 cmH2O was significantly lower than on ZEEP, regardless of FIO2, indicating more heterogeneity of ventilation during ZEEP (0.23 ± 0.03 vs. 0.54 ± 0.37, P = 0.049). CVD changed over the different mechanical ventilation settings (P = 0.011); predominantly, CVD increased during ZEEP. The spatial distribution of the CVD calculated for the poorly aerated density category changed with the mechanical ventilation settings, increasing in the dependent level during ZEEP.
Conclusion
ZEEP together with low FIO2 promoted heterogeneity of ventilation and lung tissue densities, fostering a greater amount of airway closure and ventilation inhomogeneities in poorly aerated regions.
High frequency jet ventilation (HFJV) can be used to minimise sub-diaphragmal organ displacements. Treated patients are in a supine position, under general anaesthesia and fully muscle relaxed. These ...are factors that are known to contribute to the formation of atelectasis. The HFJV-catheter is inserted freely inside the endotracheal tube and the system is therefore open to atmospheric pressure.
The aim of this study was to assess the formation of atelectasis over time during HFJV in patients undergoing liver tumour ablation under general anaesthesia.
In this observational study twenty-five patients were studied. Repeated computed tomography (CT) scans were taken at the start of HFJV and every 15 minutes thereafter up until 45 minutes. From the CT images, four lung compartments were defined: hyperinflated, normoinflated, poorly inflated and atelectatic areas. The extension of each lung compartment was expressed as a percentage of the total lung area.
Atelectasis at 30 minutes, 7.9% (SD 3.5, p = 0.002) and at 45 minutes 8,1% (SD 5.2, p = 0.024), was significantly higher compared to baseline 5.6% (SD 2.5). The amount of normoinflated lung volumes were unchanged over the period studied. Only a few minor perioperative respiratory adverse events were noted.
Atelectasis during HFJV in stereotactic liver tumour ablation increased over the first 45 minutes but tended to stabilise with no impact on normoinflated lung volume. Using HFJV during stereotactic liver ablation is safe regarding formation of atelectasis.
Background
Transpulmonary driving pressure plays an important role in today's understanding of ventilator induced lung injury. We have previously validated a novel non‐invasive method based on ...stepwise increments of PEEP to assess transpulmonary driving pressure in anaesthetised patients with healthy lungs. The aim of this study was to validate the method in patients who were mechanically ventilated for different diagnoses requiring intensive care.
Methods
We measured transpulmonary pressure (Ptp) and calculated transpulmonary driving pressure (ΔPtp) in 31 patients undergoing mechanical ventilation in an intensive care unit. Parallel triplicate measurements were performed with the PEEP step method (PtpPSM) and the conventional oesophageal balloon method (Ptpconv). Their agreement was compared using the intraclass correlation coefficient (ICC) and the Bland Altman plot.
Result
The coefficient of variation for the repeated measurements was 4,3 for ΔPtpPSM and 9,2 for ΔPtpconv. The ICC of 0,864 and the Bland Altman plot indicate good agreement between the two methods.
Conclusion
The non‐invasive method can be applied in mechanically ventilated patients to measure transpulmonary driving pressure with good repeatability and accuracy comparable to the traditional oesophageal balloon method.
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