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  • 1.
    Buehler, Sarah
    et al.
    Univ Med Ctr Freiburg, Dept Anesthesiol & Intens Care Med, Div Expt Anesthesiol, Freiburg, Germany..
    Schumann, Stefan
    Univ Med Ctr Freiburg, Dept Anesthesiol & Intens Care Med, Div Expt Anesthesiol, Freiburg, Germany..
    Vimlati, Laszlo
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Lichtwarck-Aschoff, Michael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Guttmann, Josef
    Univ Med Ctr Freiburg, Dept Anesthesiol & Intens Care Med, Div Expt Anesthesiol, Freiburg, Germany..
    Simultaneous monitoring of intratidal compliance and resistance in mechanically ventilated piglets: A feasibility study in two different study groups2015In: Respiratory Physiology & Neurobiology, ISSN 1569-9048, E-ISSN 1878-1519, Vol. 219, p. 36-42Article in journal (Refereed)
    Abstract [en]

    Compliance measures the force counteracting parenchymal lung distension. In mechanical ventilation, intratidal compliance-volume (C(V))-profiles therefore change depending on PEEP, tidal volume (V-T), and underlying mechanical lung properties. Resistance counteracts gas flow through the airways. Due to anatomical linking between parenchyma and airways, intratidal resistance-volume (R(V))-profiles are hypothesised to change in a non-linear way as well. We analysed respiratory system mechanics in fifteen piglets with lavage-induced lung injury and nine healthy piglets ventilated at different PEEP/V-T-settings. In healthy lungs, R(V)-profiles remained mostly constant and linear at all PEEP-settings whereas the shape of the C(V)-profiles showed an increase toward a maximum followed by a decrease (small PEEP) or volume-dependent decrease (large PEEP). In the lavage group, a large drop in resistance at small volumes and slow decrease toward larger volumes was found for small PEEP/V-T-settings where C(V)-profiles revealed a volume-dependent increase (small PEEP) or a decrease (large PEEP and large VT). R(V)-profiles depend characteristically on PEEP, V-T, and possibly whether lungs are healthy or not. Curved R(V)-profiles might indicate pathological changes in the underlying mechanical lung properties and/or might be a sign of derecruitment.

  • 2.
    Kawati, Rafael
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Vimlati, Laszlo
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Sjöstrand, Ulf
    Hedenstierna, Göran
    Guttmann, Josef
    Lichtwarck-Aschoff, Michael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Change in expiratory flow can early detect partial endotracheal tube obstruction in pressure controlled ventilationArticle in journal (Refereed)
  • 3. Schumann, S.
    et al.
    Goebel, U.
    Haberstroh, J.
    Vimlati, Laszlo
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Schneider, M.
    Lichtwarck-Aschoff, Michael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Guttmann, J.
    Determination of respiratory system mechanics during inspiration and expiration by FLow-controlled EXpiration (FLEX): a pilot study in anesthetized pigs2014In: Minerva Anestesiologica, ISSN 0375-9393, E-ISSN 1827-1596, Vol. 80, no 1, p. 19-28Article in journal (Refereed)
    Abstract [en]

    Background. Differences between inspiratory and expiratory lung mechanics result in the hysteresis of the pressure volume-loop. While hysteresis area is a global parameter describing the difference between inspiration and expiration in mechanics under quasi-static conditions, a detailed analysis of this difference under the dynamic conditions of mechanical ventilation is feasible once inspiratory and expiratory compliance (C-in/C-ex) are determined separately. This requires uncoupling of expiratory flow rate and volume (V). Methods. Five piglets were mechanically ventilated at positive end-expiratory pressure (PEEP) levels ranging from 0 to 15 cmH(2)O. Expiratory flow rate was linearized by a computer-controlled resistor (flow-controlled expiration). The volume-dependent C-in(V) and C-ex(V) profiles were calculated from the tracheal pressure volume-loops. Results. The intratidal curve-progression of C-ex(V) was altogether higher with a steeper slope compared to C-in(V). With increasing positive end-expiratory pressure (PEEP) dynamic hysteresis area decreased and C-ex(V) tended to run more parallel to C-in(V), Conclusion. The relation between inspiratory and expiratory compliance profiles is associated with the hysteresis area and behaves PEEP dependent. Analysing the C-in-C-ex-relation might therefore potentially offer a new approach to titrate PEEP and tidal volume.

  • 4.
    Schumann, S.
    et al.
    Univ Freiburg, Fac Med, Med Ctr, Dept Anesthesiol & Crit Care, Freiburg, Germany.
    Vimlati, Laszlo
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Kawati, Rafael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Guttmann, J.
    Univ Freiburg, Fac Med, Med Ctr, Dept Anesthesiol & Crit Care, Freiburg, Germany.
    Lichtwarck-Aschoff, Michael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Cardiogenic oscillations to detect intratidal derecruitment and overdistension in a porcine model of healthy and atelectatic lungs2018In: British Journal of Anaesthesia, ISSN 0007-0912, E-ISSN 1471-6771, Vol. 121, no 4, p. 928-935Article in journal (Refereed)
    Abstract [en]

    Background: Low positive end-expiratory pressure (PEEP) can result in alveolar derecruitment, and high PEEP or high tidal volume (V-T) in lung overdistension. We investigated cardiogenic oscillations (COS) in the airway pressure signal to investigate whether these oscillations can assess unfavourable intratidal events. COS induce short instantaneous compliance increases within the pressure-volume curve, and consequently in the compliance-volume curve. We hypothesised that increases in COS-induced compliance reflect non-linear intratidal respiratory system mechanics. Methods: In mechanically ventilated anaesthetised pigs with healthy (n = 13) or atelectatic (n = 12) lungs, pressure-volume relationships and the ECG were acquired at a PEEP of 0, 5, 10, and 15 cm H2O. During inspiration, the peak compliance of successive COS (C-COS) was compared with intratidal respiratory system compliance (C-RS) within incremental volume steps up to the full V-T of 12 ml kg(-1). We analysed whether C-COS variation corresponded with systolic arterial pressure variation. Results: C-COS-volume curves showed characteristic intratidal patterns depending on the PEEP level and on atelectasis. Increasing C-RS- or C-COS-volume patterns were associated with intratidal derecruitment with low PEEP, and decreasing patterns above 6 ml kg(-1) and high PEEP showed overdistension. C-COS was not associated with systolic arterial pressure variations. Conclusions: Heartbeat-induced oscillations within the course of the inspiratory pressure-volume curve reflect nonlinear intratidal respiratory system mechanics. The analysis of these cardiogenic oscillations can be used to detect intratidal derecruitment and overdistension and, hence, to guide PEEP and V-T settings that are optimal for respiratory system mechanics.

  • 5. Schumann, S.
    et al.
    Vimlati, Laszlo
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Lichtwarck-Aschoff, Michael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Guttmann, J.
    Dynamic Hysteresis Behaviour of Respiratory System Mechanics2013In: Biomedizinische Technik (Berlin. Zeitschrift), ISSN 1862-278X, E-ISSN 0013-5585, Vol. 58Article in journal (Refereed)
    Abstract [en]

    The static pressure-volume (PV) curve of the respiratory system is characterized by hysteresis behaviour. Determination of separate inspiratory and expiratory compliance is required to analyse this phenomenon during the dynamic situation of mechanical ventilation. In five piglets expiratory flow was linearized (flow-controlled expiration, FLEX) to allow for compliance estimation separately for inspiration and expiration. Expiratory compliance was higher than inspiratory compliance along the entire intratidal course, converging at higher volumes. At higher PEEP levels expiratory and inspiratory compliance tended to run more in parallel. We conclude that the analysis of the separate inspiratory and expiratory compliance profiles allows for indicating unfavourable mechanical ventilation settings.

  • 6. Schumann, Stefan
    et al.
    Vimlati, Laszlo
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Kawati, Rafael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Guttmann, Josef
    Lichtwarck-Aschoff, Michael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Analysis of Dynamic Intratidal Compliance in a Lung Collapse Model2011In: Anesthesiology, ISSN 0003-3022, E-ISSN 1528-1175, Vol. 114, no 5, p. 1111-1117Article in journal (Refereed)
    Abstract [en]

    Background: For mechanical ventilation to be lung-protective, an accepted suggestion is to place the tidal volume (V-T) between the lower and upper inflection point of the airway pressure-volume relation. The drawback of this approach is, however, that the pressure-volume relation is assessed under quasistatic, no-flow conditions, which the lungs never experience during ventilation. Intratidal nonlinearity must be assessed under real (i.e., dynamic) conditions. With the dynamic gliding-SLICE technique that generates a high-resolution description of intratidal mechanics, the current study analyzed the profile of the compliance of the respiratory system (C-RS).

    Methods: In 12 anesthetized piglets with lung collapse, the pressure-volume relation was acquired at different levels of positive end-expiratory pressure (PEEP: 0, 5, 10, and 15 cm H2O). Lung collapse was assessed by computed tomography and the intratidal course of C-RS using the gliding-SLICE method.

    Results: Depending on PEEP, C-RS showed characteristic profiles. With low PEEP, C-RS increased up to 20% above the compliance at early inspiration, suggesting intratidal recruitment; whereas a profile of decreasing C-RS, signaling overdistension, occurred with V-T > 5 ml/kg and high PEEP levels. At the highest volume range, C-RS was up to 60% less than the maximum. With PEEP 10 cm H2O, C-RS was high and did not decrease before 5 ml/kg V-T was delivered.

    Conclusions: The profile of dynamic C-RS reflects nonlinear intratidal mechanics of the respiratory system. The SLICE analysis has the potential to detect intratidal recruitment and overdistension. This might help in finding a combination of PEEP and V-T level that is protective from a lung-mechanics perspective.

  • 7.
    Vimlati, Laszlo
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Kawati, Rafael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Hedenstierna, Göran
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Physiology.
    Larsson, Anders
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Lichtwarck-Aschoff, Michael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Spontaneous Breathing Improves Shunt Fraction and Oxygenation in Comparison with Controlled Ventilation at a Similar Amount of Lung Collapse2011In: Anesthesia and Analgesia, ISSN 0003-2999, E-ISSN 1526-7598, Vol. 113, no 5, p. 1089-1095Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: Spontaneous breathing (SB), when allowed during mechanical ventilation (MV), improves oxygenation in different models of acute lung injury. However, it is not known whether oxygenation is improved during mechanically unsupported SB. Therefore, we compared SB without any support with controlled MV at identical tidal volume (V(T)) and respiratory rate (RR) without positive end-expiratory pressure in a porcine lung collapse model.

    METHODS: In 25 anesthetized piglets, stable lung collapse was induced by application of negative pressure, and animals were randomized to either resume SB or to be kept on MV at identical VT (5 mL/kg; 95% confidence interval: 3.8 to 6.4) and RR (65 per minute [57 to 73]) as had been measured during an initial SB period. Oxygenation was assessed by blood gas analysis (n = 15) completed by multiple inert gas elimination technique (n = 8 of the 15) for shunt measurement. In addition, possible lung recruitment was studied with computed tomography of the chest (n = 10).

    RESULTS: After induction of lung collapse, PaO(2)/FIO(2) decreased to 90 mm Hg (76 to 103). With SB, PaO(2)/FIO(2) increased to 235 mm Hg (177 to 293) within 15 minutes, whereas MV at identical VT and RR did not cause any improvement in oxygenation. Intrapulmonary shunt by 45 minutes after induction of lung collapse was lower during SB (SB: 27% [24 to 30] versus MV: 41% [28 to 55]; P = 0.017). Neither SB nor MV reduced collapsed lung areas on computed tomography.

    CONCLUSIONS: SB without any support improves oxygenation and reduces shunt in comparison with MV at identical settings. This seems to be achieved without any major signs of recruitment of collapsed lung regions.

  • 8.
    Vimlati, Laszlo
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Larsson, Anders
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Hedenstierna, Göran
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Physiology.
    Lichtwarck-Aschoff, Michael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Pulmonary shunt is independent of decrease in cardiac output during unsupported spontaneous breathing in the pig2013In: Anesthesiology, ISSN 0003-3022, E-ISSN 1528-1175, Vol. 118, no 4, p. 914-923Article in journal (Refereed)
    Abstract [en]

    Background: During mechanical ventilation (MV), pulmonary shunt is cardiac output (CO) dependent; however, whether this relationship is valid during unsupported spontaneous breathing (SB) is unknown. The CO dependency of the calculated venous admixture was investigated, with both minor and major shunt, during unsupported SB, MV, and SB with continuous positive airway pressure (CPAP). Methods: In seven anesthetized supine piglets breathing 100% oxygen, unsupported SB, MV (with tidal volume and respiratory rate corresponding to SB), and 8 cm H2O CPAP (airway pressure corresponding to MV) were applied at random. Venous return and CO were reduced by partial balloon occlusion of the inferior vena cava. Measurements were repeated with the left main bronchus blocked, creating a nonrecruitable pulmonary shunt. Results: CO decreased from 4.2 l/min (95% CI, 3.9-4.5) to 2.5 l/min (95% CI, 2.2-2.7) with partially occluded venous return. Irrespective of whether shunt was minor or major, during unsupported SB, venous admixture was independent of CO (slope: minor shunt, 0.5; major shunt, 1.1%.min(-1).l(-1)) and mixed venous oxygen tension. During both MV and CPAP, venous admixture was dependent on CO (slope MV: minor shunt, 1.9; major shunt, 3.5; CPAP: minor shunt, 1.3; major shunt, 2.9% .min(-1).l(-1)) and mixed-venous oxygen tension (coefficient of determination 0.61-0.86 for all regressions). Conclusions: In contrast to MV and CPAP, venous admixture was independent of CO during unsupported SB, and was unaffected by mixed-venous oxygen tension, casting doubt on the role of hypoxic pulmonary vasoconstriction in pulmonary blood flow redistribution during unsupported SB.

  • 9.
    Vimlati, Laszlo
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Larsson, Anders
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Hedenstierna, Göran
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Physiology.
    Lichtwarck-Aschoff, Michael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Spontaneous breathing reduces pulmonary shunt independent of hypoxic vasoconstriction in the lung collapse modelManuscript (preprint) (Other academic)
    Abstract [en]

    Background: Compared with mechanical ventilation (MV), spontaneous breathing (SB) improves oxygenation even without recruiting atelectatic lung areas, probably by redistributing perfusion to well ventilated areas whose alveolar vessels are not compressed by the higher alveolar pressures of MV. We assumed that regional vasoconstriction, presumably hypoxic vasoconstriction (HPV), causes a redistribution of perfusion, and when the vasoconstriction is blocked by sodium nitroprusside (SNP) infusion, pulmonary shunt in the porcine lung collapse model is similar during SB and MV.

    Methods: Lung collapse was induced in 8 piglets by negative pressure application. The animals were allowed both to breathe spontaneously or set to MV at settings matched to SB, in random order. Calculated venous admixture (Qva/Qt), a proxy for pulmonary shunt, was measured, and any vasoconstriction was blocked by SNP infusion. For determining vascular tone, venous return was gradually reduced and cardiac output (CO) over pulmonary perfusion pressure (Pppulm) plots were recorded.

    Results: With SNP, Qva/Qt increased both during MV (from 7.7 to 20.2%, P=0.009) and SB (from 3.5 to 9%, P=0.013) with similar slopes of the Pppulm over CO plot (~1.5 mmHg*min/L), indicating a similar hypoxic response during both conditions.

    Conclusion: Despite attenuating any vasoconstriction, unexpectedly, pulmonary shunt was lower during spontaneous breathing than during MV. This suggests a mechanism active during SB, favorably redistributing pulmonary blood flow and not silenced by SNP.

  • 10.
    Vimláti, Laszlo
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Larsson, Anders
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Hedenstierna, Göran
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Physiology.
    Lichtwarck-Aschoff, Michael
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Haemodynamic stability and pulmonary shunt during spontaneous breathing and mechanical ventilation in porcine lung collapse2012In: Acta Anaesthesiologica Scandinavica, ISSN 0001-5172, E-ISSN 1399-6576, Vol. 56, no 6, p. 748-754Article in journal (Refereed)
    Abstract [en]

    Background

    We investigated the haemodynamic stability of a novel porcine model of lung collapse induced by negative pressure application (NPA). A secondary aim was to study whether pulmonary shunt correlates with cardiac output (CO).

    Methods

    In 12 anaesthetized and relaxed supine piglets, lung collapse was induced by NPA (−50 kPa). Six animals resumed spontaneous breathing (SB) after 15 min; the other six animals were kept on mechanical ventilation (MV) at respiratory rate and tidal volume (VT) that corresponded to SB. All animals were followed for 135 min with blood gas analysis and detailed haemodynamic monitoring.

    Results

    Haemodynamics and gas exchange were stable in both groups during the experiment with arterial oxygen tension (PaO2)/inspired fraction of oxygen (FiO2) and pulmonary artery occlusion pressure being higher, venous admixture (Qva/Qt) and pulmonary perfusion pressure being lower in the SB group. CO was similar in both groups, showing slight decrease over time in the SB group. During MV, Qva/Qt increased with CO (slope: 4.3 %min/l; P < 0.001), but not so during SB (slope: 0.55 %min/l; P = 0.16).

    Conclusions

    This porcine lung collapse model is reasonably stable in terms of haemodynamics for at least 2 h irrespective of the mode of ventilation. SB achieves higher PaO2/FiO2 and lower Qva/Qt compared with MV. During SB, Qva/Qt seems to be less, if at all, affected by CO compared with MV.

  • 11.
    Vimláti, László
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
    Benefits of Spontaneous Breathing: Compared with Mechanical Ventilation2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    When spontaneous breathing (SB) is allowed during mechanical ventilation (MV), atelectatic lung areas are recruited and oxygenation improves thereby. Whether unsupported SB at its natural pattern (without PEEP and at low pressure/small tidal volume) equally recruits and improves oxygenation, and if so by which mechanism, has not been studied.

    A porcine lung collapse model was designed to study this question. The cardiac output dependency of the pulmonary shunt was investigated with healthy lungs and with major shunt (during one-lung ventilation) and with SB, MV and continuous positive airway pressure (CPAP). The hypoxic pulmonary vasoconstriction (HPV) was blocked with sodium nitroprusside (SNP) to see whether HPV is the only mechanism available for ventilation/perfusion (VA/Q) matching during MV and SB. In all experiments, respiratory rate and tidal volume during MV were matched to SB. Oxygenation was assessed by serial blood gas measurements, recruitment by thoracic CTs; pulmonary shunt was assessed by multiple inert gas elimination or venous admixture.

    SB attained better oxygenation and lower pulmonary shunt compared with MV, although it did not recruit collapsed lung. Pulmonary shunt did not correlate with cardiac output during SB, whereas a correlation was found during MV and CPAP. With blocked HPV, pulmonary shunt was considerably lower during SB than MV.

    In conclusion, SB improves VA/Q matching as compared with MV, even when no recruitment occurs. In contrast to MV and CPAP, cardiac output has no major effect on pulmonary shunt during SB. The improved VA/Q matching during SB despite a blocked HPV might indicate the presence of a SB-specific mechanism that improves pulmonary blood flow redistribution towards ventilated lung regions independent of or supplementary to HPV.

    List of papers
    1. Spontaneous Breathing Improves Shunt Fraction and Oxygenation in Comparison with Controlled Ventilation at a Similar Amount of Lung Collapse
    Open this publication in new window or tab >>Spontaneous Breathing Improves Shunt Fraction and Oxygenation in Comparison with Controlled Ventilation at a Similar Amount of Lung Collapse
    Show others...
    2011 (English)In: Anesthesia and Analgesia, ISSN 0003-2999, E-ISSN 1526-7598, Vol. 113, no 5, p. 1089-1095Article in journal (Refereed) Published
    Abstract [en]

    BACKGROUND: Spontaneous breathing (SB), when allowed during mechanical ventilation (MV), improves oxygenation in different models of acute lung injury. However, it is not known whether oxygenation is improved during mechanically unsupported SB. Therefore, we compared SB without any support with controlled MV at identical tidal volume (V(T)) and respiratory rate (RR) without positive end-expiratory pressure in a porcine lung collapse model.

    METHODS: In 25 anesthetized piglets, stable lung collapse was induced by application of negative pressure, and animals were randomized to either resume SB or to be kept on MV at identical VT (5 mL/kg; 95% confidence interval: 3.8 to 6.4) and RR (65 per minute [57 to 73]) as had been measured during an initial SB period. Oxygenation was assessed by blood gas analysis (n = 15) completed by multiple inert gas elimination technique (n = 8 of the 15) for shunt measurement. In addition, possible lung recruitment was studied with computed tomography of the chest (n = 10).

    RESULTS: After induction of lung collapse, PaO(2)/FIO(2) decreased to 90 mm Hg (76 to 103). With SB, PaO(2)/FIO(2) increased to 235 mm Hg (177 to 293) within 15 minutes, whereas MV at identical VT and RR did not cause any improvement in oxygenation. Intrapulmonary shunt by 45 minutes after induction of lung collapse was lower during SB (SB: 27% [24 to 30] versus MV: 41% [28 to 55]; P = 0.017). Neither SB nor MV reduced collapsed lung areas on computed tomography.

    CONCLUSIONS: SB without any support improves oxygenation and reduces shunt in comparison with MV at identical settings. This seems to be achieved without any major signs of recruitment of collapsed lung regions.

    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:uu:diva-161927 (URN)10.1213/ANE.0b013e31822ceef8 (DOI)000296236200025 ()
    Available from: 2011-11-23 Created: 2011-11-21 Last updated: 2017-12-08Bibliographically approved
    2. Haemodynamic stability and pulmonary shunt during spontaneous breathing and mechanical ventilation in porcine lung collapse
    Open this publication in new window or tab >>Haemodynamic stability and pulmonary shunt during spontaneous breathing and mechanical ventilation in porcine lung collapse
    2012 (English)In: Acta Anaesthesiologica Scandinavica, ISSN 0001-5172, E-ISSN 1399-6576, Vol. 56, no 6, p. 748-754Article in journal (Refereed) Published
    Abstract [en]

    Background

    We investigated the haemodynamic stability of a novel porcine model of lung collapse induced by negative pressure application (NPA). A secondary aim was to study whether pulmonary shunt correlates with cardiac output (CO).

    Methods

    In 12 anaesthetized and relaxed supine piglets, lung collapse was induced by NPA (−50 kPa). Six animals resumed spontaneous breathing (SB) after 15 min; the other six animals were kept on mechanical ventilation (MV) at respiratory rate and tidal volume (VT) that corresponded to SB. All animals were followed for 135 min with blood gas analysis and detailed haemodynamic monitoring.

    Results

    Haemodynamics and gas exchange were stable in both groups during the experiment with arterial oxygen tension (PaO2)/inspired fraction of oxygen (FiO2) and pulmonary artery occlusion pressure being higher, venous admixture (Qva/Qt) and pulmonary perfusion pressure being lower in the SB group. CO was similar in both groups, showing slight decrease over time in the SB group. During MV, Qva/Qt increased with CO (slope: 4.3 %min/l; P < 0.001), but not so during SB (slope: 0.55 %min/l; P = 0.16).

    Conclusions

    This porcine lung collapse model is reasonably stable in terms of haemodynamics for at least 2 h irrespective of the mode of ventilation. SB achieves higher PaO2/FiO2 and lower Qva/Qt compared with MV. During SB, Qva/Qt seems to be less, if at all, affected by CO compared with MV.

    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:uu:diva-175676 (URN)10.1111/j.1399-6576.2012.02700.x (DOI)000305070400012 ()22524589 (PubMedID)
    Available from: 2012-06-11 Created: 2012-06-11 Last updated: 2017-12-07Bibliographically approved
    3. Pulmonary shunt is independent of decrease in cardiac output during unsupported spontaneous breathing in the pig
    Open this publication in new window or tab >>Pulmonary shunt is independent of decrease in cardiac output during unsupported spontaneous breathing in the pig
    2013 (English)In: Anesthesiology, ISSN 0003-3022, E-ISSN 1528-1175, Vol. 118, no 4, p. 914-923Article in journal (Refereed) Published
    Abstract [en]

    Background: During mechanical ventilation (MV), pulmonary shunt is cardiac output (CO) dependent; however, whether this relationship is valid during unsupported spontaneous breathing (SB) is unknown. The CO dependency of the calculated venous admixture was investigated, with both minor and major shunt, during unsupported SB, MV, and SB with continuous positive airway pressure (CPAP). Methods: In seven anesthetized supine piglets breathing 100% oxygen, unsupported SB, MV (with tidal volume and respiratory rate corresponding to SB), and 8 cm H2O CPAP (airway pressure corresponding to MV) were applied at random. Venous return and CO were reduced by partial balloon occlusion of the inferior vena cava. Measurements were repeated with the left main bronchus blocked, creating a nonrecruitable pulmonary shunt. Results: CO decreased from 4.2 l/min (95% CI, 3.9-4.5) to 2.5 l/min (95% CI, 2.2-2.7) with partially occluded venous return. Irrespective of whether shunt was minor or major, during unsupported SB, venous admixture was independent of CO (slope: minor shunt, 0.5; major shunt, 1.1%.min(-1).l(-1)) and mixed venous oxygen tension. During both MV and CPAP, venous admixture was dependent on CO (slope MV: minor shunt, 1.9; major shunt, 3.5; CPAP: minor shunt, 1.3; major shunt, 2.9% .min(-1).l(-1)) and mixed-venous oxygen tension (coefficient of determination 0.61-0.86 for all regressions). Conclusions: In contrast to MV and CPAP, venous admixture was independent of CO during unsupported SB, and was unaffected by mixed-venous oxygen tension, casting doubt on the role of hypoxic pulmonary vasoconstriction in pulmonary blood flow redistribution during unsupported SB.

    Keywords
    pulmonary shunt, cardiac output, mechanical ventilation, spontaneous breathing
    National Category
    Anesthesiology and Intensive Care
    Research subject
    Physiology
    Identifiers
    urn:nbn:se:uu:diva-182302 (URN)10.1097/ALN.0b013e318283c81f (DOI)000316355000021 ()
    Available from: 2012-10-11 Created: 2012-10-09 Last updated: 2017-12-07Bibliographically approved
    4. Spontaneous breathing reduces pulmonary shunt independent of hypoxic vasoconstriction in the lung collapse model
    Open this publication in new window or tab >>Spontaneous breathing reduces pulmonary shunt independent of hypoxic vasoconstriction in the lung collapse model
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Background: Compared with mechanical ventilation (MV), spontaneous breathing (SB) improves oxygenation even without recruiting atelectatic lung areas, probably by redistributing perfusion to well ventilated areas whose alveolar vessels are not compressed by the higher alveolar pressures of MV. We assumed that regional vasoconstriction, presumably hypoxic vasoconstriction (HPV), causes a redistribution of perfusion, and when the vasoconstriction is blocked by sodium nitroprusside (SNP) infusion, pulmonary shunt in the porcine lung collapse model is similar during SB and MV.

    Methods: Lung collapse was induced in 8 piglets by negative pressure application. The animals were allowed both to breathe spontaneously or set to MV at settings matched to SB, in random order. Calculated venous admixture (Qva/Qt), a proxy for pulmonary shunt, was measured, and any vasoconstriction was blocked by SNP infusion. For determining vascular tone, venous return was gradually reduced and cardiac output (CO) over pulmonary perfusion pressure (Pppulm) plots were recorded.

    Results: With SNP, Qva/Qt increased both during MV (from 7.7 to 20.2%, P=0.009) and SB (from 3.5 to 9%, P=0.013) with similar slopes of the Pppulm over CO plot (~1.5 mmHg*min/L), indicating a similar hypoxic response during both conditions.

    Conclusion: Despite attenuating any vasoconstriction, unexpectedly, pulmonary shunt was lower during spontaneous breathing than during MV. This suggests a mechanism active during SB, favorably redistributing pulmonary blood flow and not silenced by SNP.

    Keywords
    pulmonary shunt, pulmonary hypoxic vasoconstriction, sodium nitroprusside, mechanical ventilation, spontaneous breathing
    National Category
    Anesthesiology and Intensive Care
    Research subject
    Physiology
    Identifiers
    urn:nbn:se:uu:diva-182303 (URN)
    Available from: 2012-10-09 Created: 2012-10-09 Last updated: 2013-01-23Bibliographically approved
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