Dataset Information

Bedside monitoring of lung volume available for gas exchange.

ABSTRACT:

Background

Bedside measurement of lung volume may provide guidance in the personalised setting of respiratory support, especially in patients with the acute respiratory distress syndrome at risk of ventilator-induced lung injury. We propose here a novel operator-independent technique, enabled by a fibre optic oxygen sensor, to quantify the lung volume available for gas exchange. We hypothesised that the continuous measurement of arterial partial pressure of oxygen (PaO₂) decline during a breath-holding manoeuvre could be used to estimate lung volume in a single-compartment physiological model of the respiratory system.

Methods

Thirteen pigs with a saline lavage lung injury model and six control pigs were studied under general anaesthesia during mechanical ventilation. Lung volumes were measured by simultaneous PaO₂ rate of decline (V_PaO2) and whole-lung computed tomography scan (V_CT) during apnoea at different positive end-expiratory and end-inspiratory pressures.

Results

A total of 146 volume measurements was completed (range 134 to 1869 mL). A linear correlation between V_CT and V_PaO2 was found both in control (slope = 0.9, R² = 0.88) and in saline-lavaged pigs (slope = 0.64, R² = 0.70). The bias from Bland-Altman analysis for the agreement between the V_CT and V_PaO2 was - 84 mL (limits of agreement ± 301 mL) in control and + 2 mL (LoA ± 406 mL) in saline-lavaged pigs. The concordance for changes in lung volume, quantified with polar plot analysis, was - 4º (LoA ± 19°) in control and - 9° (LoA ± 33°) in saline-lavaged pigs.

Conclusion

Bedside measurement of PaO₂ rate of decline during apnoea is a potential approach for estimation of lung volume changes associated with different levels of airway pressure.

SUBMITTER: Tran MC

PROVIDER: S-EPMC7835652 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundThe ARDS is characterized by different degrees of impairment in oxygenation and distribution of the lung disease. Two radiological patterns have been described: a focal and a diffuse one. These two patterns could present significant differences both in gas exchange and in the response to a recruitment maneuver. At the present time, it is not known if the focal and the diffuse pattern could be characterized by a difference in the lung and chest wall mechanical characteristics. Our aims were to investigate, at two levels of PEEP, if focal vs. diffuse ARDS patterns could be characterized by different lung CT characteristics, partitioned respiratory mechanics and lung recruitability.MethodsCT patterns were analyzed by two radiologists and were classified as focal or diffuse. The changes from 5 to 15 cmH2O in blood gas analysis and partitioned respiratory mechanics were analyzed. Lung CT scan was performed at 5 and 45 cmH2O of PEEP to evaluate lung recruitability.ResultsOne-hundred and ten patients showed a diffuse pattern, while 58 showed a focal pattern. At 5 cmH2O of PEEP, the driving pressure and the elastance, both the respiratory system and of the lung, were significantly higher in the diffuse pattern compared to the focal (14 [11-16] vs 11 [9-15 cmH2O; 28 [23-34] vs 21 [17-27] cmH2O/L; 22 [17-28] vs 14 [12-19] cmH2O/L). By increasing PEEP, the driving pressure and the respiratory system elastance significantly decreased in diffuse pattern, while they increased or did not change in the focal pattern (Δ15-5: - 1 [- 2 to 1] vs 0 [- 1 to 2]; - 1 [- 4 to 2] vs 1 [- 2 to 5]). At 5 cmH2O of PEEP, the diffuse pattern had a lower lung gas (743 [537-984] vs 1222 [918-1974] mL) and higher lung weight (1618 [1388-2001] vs 1222 [1059-1394] g) compared to focal pattern. The lung recruitability was significantly higher in diffuse compared to focal pattern 21% [13-29] vs 11% [6-16]. Considering the median of lung recruitability of the whole population (16.1%), the recruiters were 65% and 22% in the diffuse and focal pattern, respectively.ConclusionsAn early identification of lung morphology can be useful to choose the ventilatory setting. A diffuse pattern has a better response to the increase of PEEP and to the recruitment maneuver.