Validating the inspired sinewave technique to measure the volume of the ‘baby lung’ in a porcine lung-injury model

Abstract

Background: Bedside lung volume measurement could personalise ventilation and reduce driving pressure in patients with acute respiratory distress syndrome (ARDS). We investigated a modified gas-dilution method, the inspired sinewave technique (IST), to measure the effective lung volume (ELV) in pigs with uninjured lungs and in an ARDS model. Methods: Anaesthetised mechanically ventilated pigs were studied before and after surfactant depletion by saline lavage. Changes in PEEP were used to change ELV. Paired measurements of absolute ELV were taken with IST (ELV IST) and compared with gold-standard measures (sulphur hexafluoride wash in/washout [ELV SF6 ] and computed tomography (CT) [ELV CT ]). Measured volumes were used to calculate changes in ELV (DELV) between PEEP levels for each method (DELV IST , DELV SF6 , and DELV CT). Results: The coefficient of variation was <5% for repeated ELV IST measurements (n¼13 pigs). There was a strong linear relationship between ELV IST and ELV SF6 in uninjured lungs (r 2 ¼0.97), and with both ELV SF6 and ELV CT in the ARDS model (r 2 ¼0.87 and 0.92, respectively). ELV IST had a mean bias of e12 to 13% (95% limits¼±17 e 25%) compared with ELV SF6 and ELV CT. DELV IST was concordant with DELV SF6 and DELV CT in 98e100% of measurements, and had a mean bias of e73 to e77 ml (95% limits¼±128 e 186 ml) compared with DELV SF6 and e1 ml (95% limits ±333 ml) compared with DELV CT. Conclusions: IST provides a repeatable measure of absolute ELV and shows minimal bias when tracking PEEP-induced changes in lung volume compared with CT in a saline-lavage model of ARDS.

Validating the Inspired Sinewave Technique to Measure Lung Heterogeneity Compared to Atelectasis & Over-Distended Volume in Computed Tomography Images

“…IST can measure accurately the effective lung volume and deadspace volume, which are key parameters to personalise mechanical ventilator [20]. The changes in lung volume due to increased PEEP were reported correctly by the IST [10]. Besides, IST shown its advantages to measure accurate value when the patient breathes stably.…”

“…CT has been used as a standard measurement to quantify the lung and also lung heterogeneity [8], [10]. In this study, we presented a validation of the IST heterogeneity results in CT images.…”

“…However, CT puts patients at risk by necessitating transfer to a scanner and exposure to ionising radiation. On the other hand, lung monitoring using the IST has shown potential to capture lung parameters at the bedside [10].…”

“…IST has the potential to provide bedside measurement of deadspace volume, effective lung volume (ELV), pulmonary blood flow (Qp) and lung heterogeneity. Measurements of the first three parameters have been validated elsewhere [6], [10]- [12]. IST uses available components commonly used in anaesthetic/intensive care practice and has proven efficacy in spontaneously ventilating healthy volunteers [13].…”

Simulation-based optimisation to quantify heterogeneity of specific ventilation and perfusion in the lung by the Inspired Sinewave Test

“…The Inspired Sinewave Test (IST) is a non-invasive method to continuously monitor cardiopulmonary indices by using forced oscillations of nitrous oxide ( ) tracer gas signals 15 – 18 . The IST can measure several lung parameters (E LV —effective lung volume, V D —deadspace volume and Q p —pulmonary blood flow) based on a single, well-mixed compartment model.…”