| 1. |
- Engström, Joakim, et al.
(författare)
-
Pharyngeal oxygen administration increases the time to serious desaturation at intubation in acute lung injury : an experimental study
- 2010
-
Ingår i: Critical Care. - 1364-8535. ; 14:3, s. R93
-
Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: Endotracheal intubation in critically ill patients is associated with severe life-threatening complications in about 20%, mainly due to hypoxemia. We hypothesized that apneic oxygenation via a pharyngeal catheter during the endotracheal intubation procedure would prevent or increase the time to life-threatening hypoxemia and tested this hypothesis in an acute lung injury animal model. METHODS: Eight anesthetized piglets with collapse-prone lungs induced by lung lavage were ventilated with a fraction of inspired oxygen of 1.0 and a positive end-expiratory pressure of 5 cmH2O. The shunt fraction was calculated after obtaining arterial and mixed venous blood gases. The trachea was extubated, and in randomized order each animal received either 10 L oxygen per minute or no oxygen via a pharyngeal catheter, and the time to desaturation to pulse oximeter saturation (SpO2) 60% was measured. If SpO2 was maintained at over 60%, the experiment ended when 10 minutes had elapsed. RESULTS: Without pharyngeal oxygen, the animals desaturated after 103 (88-111) seconds (median and interquartile range), whereas with pharyngeal oxygen five animals had a SpO2 > 60% for the 10-minute experimental period, one animal desaturated after 7 minutes, and two animals desaturated within 90 seconds (P < 0.016, Wilcoxon signed rank test). The time to desaturation was related to shunt fraction (R2 = 0.81, P = 0.002, linear regression); the animals that desaturated within 90 seconds had shunt fractions >40%, whereas the others had shunt fractions <25%. CONCLUSIONS: In this experimental acute lung injury model, pharyngeal oxygen administration markedly prolonged the time to severe desaturation during apnea, suggesting that this technique might be useful when intubating critically ill patients with acute respiratory failure.
|
|
| 2. |
- Höstman, Staffan, et al.
(författare)
-
Intensive buffering can keep pH above 7.2 for over 4 h during apnea : an experimental porcine study
- 2013
-
Ingår i: Acta Anaesthesiologica Scandinavica. - 0001-5172. ; 57:1, s. 63-70
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND:Ventilation with low tidal volumes reduces mortality in acute respiratory distress syndrome. A further reduction of tidal volumes might be beneficial, and it is known that apneic oxygenation (no tidal volumes) with arteriovenous CO(2) removal can keep acid-base balance and oxygenation normal for at least 7 h in an acute lung injury model. We hypothesized that adequate buffering might be another approach and tested whether tris-hydroxymethyl aminomethane (THAM) alone could keep pH at a physiological level during apneic oxygenation for 4 h.METHODS:Six pigs were anesthetized, muscle relaxed, and normoventilated. The lungs were recruited, and apneic oxygenation as well as administration of THAM, 20 mmol/kg/h, was initiated. The experiment ended after 270 min, except one that was studied for 6 h.RESULTS:Two animals died before the end of the experiment. Arterial pH and arterial carbon dioxide tension (PaCO(2) ) changed from 7.5 (7.5, 7.5) to 7.3 (7.2, 7.3) kPa, P < 0.001 at 270 min, and from 4.5 (4.3, 4.7) to 25 (22, 28) kPa, P < 0.001, respectively. Base excess increased from 5 (3, 6) to 54 (51, 57) mM, P < 0.001. Cardiac output and arterial pressure were well maintained. The pig, which was studied for 6 h, had pH 7.27 and PaCO(2) 27 kPa at that time.CONCLUSION:With intensive buffering using THAM, pH can be kept in a physiologically acceptable range for 4 h during apnea.
|
|
| 3. |
- Höstman, Staffan, et al.
(författare)
-
Non-toxic alveolar oxygen concentration without hypoxemia during apnoeic oxygenation : an experimental study
- 2011
-
Ingår i: Acta Anaesthesiologica Scandinavica. - 0001-5172. ; 55:9, s. 1078-1084
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Oxygenation without tidal breathing, i.e. apnoeic oxygenation in combination with extracorporeal carbon dioxide removal, might be an option in the treatment of acute respiratory failure. However, ventilation with 100% O(2), which is potentially toxic, is considered a prerequisite to ensure acceptable oxygenation. We hypothesized that trapping nitrogen (N(2)) in the lungs before the start of apnoeic oxygenation would keep the alveolar O(2) at a non-toxic level and still maintain normoxaemia. The aim was to test whether a predicted N(2) concentration would agree with a measured concentration at the end of an apnoeic period. Methods: Seven anaesthetized, muscle relaxed, endotracheally intubated pigs (22-27 kg) were ventilated in a randomized order with an inspired fraction of O(2) 0.6 and 0.8 at two positive end-expiratory pressure levels (5 cm and 10 cm H(2)O) before being connected to continuous positive airway pressure using 100% O(2) for apnoeic oxygenation. N(2) was measured before the start of and at the end of the 10-min apnoeic period. The predicted N(2) concentration was calculated from the initial N(2) concentration, the end-expiratory lung volume, and the anatomical dead space. Results: The mean difference and standard deviation between measured and predicted N(2) concentration was -0.5 +/- 2%, P = 0.587. No significant difference in the agreement between measured and predicted N(2) concentrations was seen in the four settings. Conclusions: This study indicates that it is possible to predict and keep alveolar N(2) concentration at a desired level and, thus, alveolar O(2) concentration at a non-toxic level during apnoeic oxygenation.
|
|
| 4. |
- Kostic, Peter, et al.
(författare)
-
Positive end-expiratory pressure optimization with forced oscillation technique reduces ventilator induced lung injury : a controlled experimental study in pigs with saline lavage lung injury
- 2011
-
Ingår i: Critical Care. - 1364-8535. ; 15:3, s. R126
-
Tidskriftsartikel (refereegranskat)abstract
- Introduction: Protocols using high levels of positive end-expiratory pressure (PEEP) in combination with low tidal volumes have been shown to reduce mortality in patients with severe acute respiratory distress syndrome (ARDS). However, the optimal method for setting PEEP is yet to be defined. It has been shown that respiratory system reactance (Xrs), measured by the forced oscillation technique (FOT) at 5 Hz, may be used to identify the minimal PEEP level required to maintain lung recruitment. The aim of the present study was to evaluate if using Xrs for setting PEEP would improve lung mechanics and reduce lung injury compared to an oxygenation-based approach.Methods: 17 pigs, in which acute lung injury (ALI) was induced by saline lavage, were studied. Animals were randomized into two groups: in the first PEEP was titrated according to Xrs (FOT group), in the control group PEEP was set according to the ARDSNet protocol (ARDSNet group). The duration of the trial was 12 hours. In both groups recruitment maneuvers (RM) were performed every 2 hours, increasing PEEP to 20 cmH(2)O. In the FOT group PEEP was titrated by monitoring Xrs while PEEP was reduced from 20 cmH(2)O in steps of 2 cmH(2)O. PEEP was considered optimal at the step before which Xrs started to decrease. Ventilatory parameters, lung mechanics, blood gases and hemodynamic parameters were recorded hourly. Lung injury was evaluated by histopathological analysis.Results: The PEEP levels set in the FOT group were significantly higher compared to those set in the ARDSNet group during the whole trial. These higher values of PEEP resulted in improved lung mechanics, reduced driving pressure, improved oxygenation, with a trend for higher PaCO(2) and lower systemic and pulmonary pressure. After 12 hours of ventilation, histopathological analysis showed a significantly lower score of lung injury in the FOT group compared to the ARDSNet group.Conclusions: In a lavage model of lung injury a PEEP optimization strategy based on maximizing Xrs attenuated the signs of ventilator induced lung injury. The respiratory system reactance measured by FOT could thus be an important component in a strategy for delivering protective ventilation to patients with ARDS/acute lung injury.
|
|
| 5. |
|
|
| 6. |
- Vimláti, Laszlo, et al.
(författare)
-
Haemodynamic stability and pulmonary shunt during spontaneous breathing and mechanical ventilation in porcine lung collapse
- 2012
-
Ingår i: Acta Anaesthesiologica Scandinavica. - 0001-5172. ; 56:6, s. 748-754
-
Tidskriftsartikel (refereegranskat)abstract
- BackgroundWe 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).MethodsIn 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.ResultsHaemodynamics 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).ConclusionsThis 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.
|
|
| 7. |
- Vimlati, Laszlo, et al.
(författare)
-
Pulmonary shunt is independent of decrease in cardiac output during unsupported spontaneous breathing in the pig
- 2013
-
Ingår i: Anesthesiology. - 0003-3022. ; 118:4, s. 914-923
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 8. |
- Vimlati, Laszlo, et al.
(författare)
-
Spontaneous Breathing Improves Shunt Fraction and Oxygenation in Comparison with Controlled Ventilation at a Similar Amount of Lung Collapse
- 2011
-
Ingår i: Anesthesia and Analgesia. - 0003-2999. ; 113:5, s. 1089-1095
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
