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- Gudmundsson, Magni
(author)
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Aspects of lung mechanics during mechanical ventilation
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Background: One of the most common diagnoses in the intensive care unit is acute respiratory failure. In its most severe form it is called acute respiratory distress syndrome and often requires mechanical ventilation. The main challenge for physicians is to provide mechanical ventilation that treats the patient´s hypoxia, which can be due to a variety of causes, without damaging the lung. Method: In paper I computed tomography scans were acquired in ten anesthetized surfactant depleted pigs. The volume of gas and atelectasis were correlated with transpulmonary pressure as the pressure support and PEEP were lowered. In paper II a non-invasive method for measuring transpulmonary driving pressure was validated in 31 mechanically ventilated intensive care patients. In paper III external expiratory resistors were added to the expiratory limb of the ventilator while calculating expiratory time constant, respiratory compliance, driving pressure and intrinsic PEEP in 12 anesthetized pigs. In paper IV transpulmonary pressure was calculated from esophageal pressure in supine and prone position in 10 anesthetized lung healthy patients. Results: Gradual decrease in transpulmonary pressure causes a proportional increase in atelectasis and decrease in gas content while the work of breathing increases. There is a good statistical agreement between the conventional and the non-invasive method for measuring transpulmonary driving pressure. Increasing the expiratory resistance increases the expiratory time constant and increases intrinsic PEEP in healthy lungs. There is a great variability in esophageal pressure in the part of the esophagus 22 – 44cm from the nostrils in both supine and prone position. Depending on method the transpulmonary pressure either increases or decreases when patients are turned in prone position. Conclusion: There is no transpulmonary pressure threshold, where atelectasis with desaturation or cyclic collapse suddenly occurs during gradual decrease in the ventilator support. The PEEP-step method is comparable to the traditional esophageal balloon method for measuring transpulmonary driving pressure. The application of expiratory resistors could be useful during weaning from mechanical ventilation. The mean end-expiratory esophageal pressure changes which affect the calculation of transpulmonary pressure but uncertainties about the use of absolute esophageal pressure remains.
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| 2. |
- Gudmundsson, Magni, et al.
(author)
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Atelectasis is inversely proportional to transpulmonary pressure during weaning from ventilator support in a large animal model
- 2018
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In: Acta Anaesthesiologica Scandinavica. - : Wiley. - 0001-5172 .- 1399-6576. ; 62:1, s. 94-104
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Journal article (peer-reviewed)abstract
- BackgroundIn 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 (P-L) during weaning from mechanical ventilation when the spontaneous breathing effort is increased. If the relation between P-L and atelectasis were known, monitoring of P-L might help to avoid formation of atelectasis and cyclic collapse during weaning. The main purpose of this study was to determine the relation between P-L and atelectasis in an experimental model representing weaning from mechanical ventilation. MethodsDynamic 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 P-L obtained using oesophageal pressure recordings. Work of breathing (WOB) was assessed from Campbell diagrams. ResultsGradual decrease in P-L 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. ConclusionWe found a proportional correlation between atelectasis and P-L 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.
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| 3. |
- Gudmundsson, Magni, et al.
(author)
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Transpulmonary driving pressure during mechanical ventilation-validation of a non-invasive measurement method
- 2020
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In: Acta Anaesthesiologica Scandinavica. - : Wiley. - 0001-5172 .- 1399-6576. ; 64:2, s. 211-215
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Journal article (peer-reviewed)abstract
- 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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| 5. |
- Pellegrini, Mariangela, et al.
(author)
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Expiratory Resistances Prevent Expiratory Diaphragm Contraction, Flow Limitation, and Lung Collapse
- 2020
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In: American Journal of Respiratory and Critical Care Medicine. - : AMER THORACIC SOC. - 1073-449X .- 1535-4970. ; 3:7
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Journal article (peer-reviewed)abstract
- Rationale: Tidal expiratory flow limitation (tidal-EFL) is not completely avoidable by applying positive end-expiratory pressure and may cause respiratory and hemodynamic complications in ventilated patients with lungs prone to collapse. During spontaneous breathing, expiratory diaphragmatic contraction counteracts tidal-EFL. We hypothesized that during both spontaneous breathing and controlled mechanical ventilation, external expiratory resistances reduce tidal-EFL.Objectives: To assess whether external expiratory resistances 1) affect expiratory diaphragmatic contraction during spontaneous breathing, 2) reduce expiratory flow and make lung compartments more homogeneous with more similar expiratory time constants, and 3) reduce tidal atelectasis, preventing hyperinflation.Methods: Three positive end-expiratory pressure levels and four external expiratory resistances were tested in 10 pigs after lung lavage. We analyzed expiratory diaphragmatic electric activity and respiratory mechanics. On the basis of computed tomography scans, four lung compartments-not inflated (atelectasis), poorly inflated, normally inflated, and hyperinflated-were defined.Measurements and Main Results: Consequently to additional external expiratory resistances, and mainly in lungs prone to collapse (at low positive end-expiratory pressure), 1) the expiratory transdiaphragmatic pressure decreased during spontaneous breathing by >10%, 2) expiratory flow was reduced and the expiratory time constants became more homogeneous, and 3) the amount of atelectasis at end-expiration decreased from 24% to 16% during spontaneous breathing and from 32% to 18% during controlled mechanical ventilation, without increasing hyperinflation.Conclusions: The expiratory modulation induced by external expiratory resistances preserves the positive effects of the expiratory brake while minimizing expiratory diaphragmatic contraction. External expiratory resistances optimize lung mechanics and limit tidal-EFL and tidal atelectasis, without increasing hyperinflation.
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| 6. |
- Pellegrini, Mariangela, et al.
(author)
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Expiratory Resistances Prevent Expiratory Diaphragm Contraction, Flow Limitation, and Lung Collapse.
- 2020
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In: American journal of respiratory and critical care medicine. - 1535-4970. ; 201:10, s. 1218-1229
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Journal article (peer-reviewed)abstract
- Rationale: Tidal expiratory flow limitation (tidal-EFL) is not completely avoidable by applying positive end-expiratory pressure and may cause respiratory and hemodynamic complications in ventilated patients with lungs prone to collapse. During spontaneous breathing, expiratory diaphragmatic contraction counteracts tidal-EFL. We hypothesized that during both spontaneous breathing and controlled mechanical ventilation, external expiratory resistances reduce tidal-EFL.Objectives: To assess whether external expiratory resistances 1) affect expiratory diaphragmatic contraction during spontaneous breathing, 2) reduce expiratory flow and make lung compartments more homogeneous with more similar expiratory time constants, and 3) reduce tidal atelectasis, preventing hyperinflation.Methods: Three positive end-expiratory pressure levels and four external expiratory resistances were tested in 10 pigs after lung lavage. We analyzed expiratory diaphragmatic electric activity and respiratory mechanics. On the basis of computed tomography scans, four lung compartments-not inflated (atelectasis), poorly inflated, normally inflated, and hyperinflated-were defined.Measurements and Main Results: Consequently to additional external expiratory resistances, and mainly in lungs prone to collapse (at low positive end-expiratory pressure), 1) the expiratory transdiaphragmatic pressure decreased during spontaneous breathing by >10%, 2) expiratory flow was reduced and the expiratory time constants became more homogeneous, and 3) the amount of atelectasis at end-expiration decreased from 24% to 16% during spontaneous breathing and from 32% to 18% during controlled mechanical ventilation, without increasing hyperinflation.Conclusions: The expiratory modulation induced by external expiratory resistances preserves the positive effects of the expiratory brake while minimizing expiratory diaphragmatic contraction. External expiratory resistances optimize lung mechanics and limit tidal-EFL and tidal atelectasis, without increasing hyperinflation.
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| 7. |
- Persson, Per, et al.
(author)
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Detailed measurements of oesophageal pressure during mechanical ventilation with an advanced high-resolution manometry catheter
- 2019
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In: Critical Care. - : BMC. - 1364-8535 .- 1466-609X. ; 23
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Journal article (peer-reviewed)abstract
- Background: Oesophageal pressure (PES) is used for calculation of lung and chest wall mechanics and transpulmonary pressure during mechanical ventilation. Measurements performed with a balloon catheter are suggested as a basis for setting the ventilator; however, measurements are affected by several factors. High-resolution manometry (HRM) simultaneously measures pressures at every centimetre in the whole oesophagus and thereby provides extended information about oesophageal pressure. The aim of the present study was to evaluate the factors affecting oesophageal pressure using HRM.Methods: Oesophageal pressure was measured using a high-resolution manometry catheter in 20 mechanically ventilated patients (15 in the ICU and 5 in the OR). Different PEEP levels and different sizes of tidal volume were applied while pressures were measured continuously. In 10 patients, oesophageal pressure was also measured using a conventional balloon catheter for comparison. A retrospective analysis of oesophageal pressure measured with HRM in supine and sitting positions in 17 awake spontaneously breathing patients is also included.Results: HRM showed large variations in end-expiratory PES (PESEE) and tidal changes in PES (PES) along the oesophagus. Mean intra-individual difference between the minimum and maximum end-expiratory oesophageal pressure (PESEE at baseline PEEP) and tidal variations in oesophageal pressure (PES at tidal volume 6ml/kg) recorded by HRM in the different sections of the oesophagus was 23.7 (7.9) cmH(2)O and 7.6 (3.9) cmH(2)O respectively. Oesophageal pressures were affected by tidal volume, level of PEEP, part of the oesophagus included and patient positioning. HRM identified simultaneous increases and decreases in PES within a majority of individual patients. Compared to sitting position, supine position increased PESEE (mean difference 12.3cmH(2)O), pressure variation within individual patients and cardiac artefacts. The pressure measured with a balloon catheter did not correspond to the average pressure measured with HRM within the same part of the oesophagus.Conclusions: The intra-individual variability in PESEE and PES is substantial, and as a result, the balloon on the conventional catheter is affected by many different pressures along its length. Oesophageal pressures are not only affected by lung and chest wall mechanics but are a complex product of many factors, which is not obvious during conventional measurements. For correct calculations of transpulmonary pressure, factors influencing oesophageal pressures need to be known. HRM, which is available at many hospitals, can be used to increase the knowledge concerning these factors.Trial registration: ClinicalTrials.gov,NCT02901158
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