Correlation between the hysteresis of the PV curve and R/I ratio

Artigo

Autor: Marcela Rodriguez Jimenez

Data da primeira publicação: 06.02.2024

Última alteração: 04.04.2024

Removal of linked article on assessing recruitability - no new revision

The authors' point? The normalized maximum distance on a quasi-static PV curve and the recruitment-to-inflation ratio can be used at the bedside as potential indicators of lung recruitability.

Correlation between the hysteresis of the PV curve and R/I ratio

Clinical question

In mechanically ventilated COVID-19 patients, what is the relationship between lung recruitability assessments based on the low-flow quasi-static pressure-volume (PV) curve and the recruitment-to-inflation (R/I) ratio?

Clinical background

Despite the theoretical benefits of lung recruitment and PEEP titration, there is ongoing debate about their use and the optimal ventilator settings for patients with ARDS. These strategies are particularly relevant for patients with moderate to severe ARDS, as indicated by a low PaO2/FiO2 ratio (P/F ratio) of ≤ 200 mmHg.
The response to lung recruitment varies greatly among patients; therefore, lung recruitability should be assessed before performing a lung recruitment maneuver (LRM).
The pressure–volume curve (PV curve) and recruitment-to-inflation ratio (R/I ratio) can be used at the bedside for evaluating lung recruitability and individualizing PEEP.
The correlation between the R/I ratio and CT evaluation has not been validated, whereas hysteresis parameters in PV curves show some correlation with lung-tissue recruitment on CT.

Design and settings

Retrospective, single-center cohort study (Nakayama R, Bunya N, Katayama S, et al. Correlation between the hysteresis of the pressure-volume curve and the recruitment-to-inflation ratio in patients with coronavirus disease 2019. Ann Intensive Care. 2022;12(1):106. Published 2022 Nov 12. doi:10.1186/s13613-022-01081-x1)
Patients with COVID-19 who underwent invasive mechanical ventilation in the intensive care unit of the Department of Emergency Medicine, Sapporo Medical University, Sapporo, Hokkaido, Japan, between January 1, 2021, and September 30, 2021

Patients

Diagnosed with COVID-19
Treated with invasive mechanical ventilation using a HAMILTON-C6 ventilator
Unable to maintain an SpO2 of 93% with noninvasive oxygen therapy (ventilation then initiated following Japanese COVID-19 practice guidelines)

Inclusion criteria	Exclusion criteria
Aged 18 years or older	Under 18 years of age
Diagnosis of COVID-19 confirmed by polymerase chain reaction or quantitative antigen testing of nasal swabs	No recording of respiratory data by Datalogger 5.00
Simultaneous evaluation of the quasi-static PV curve and the R/I ratio using Datalogger 5.00

Interventions
Quasi-static PV curve	R/I ratio (Recruitment-to-inflation ratio)	Recruitability assessment
Inflation from 0–40 cmH2O with a low-flow rate; deflation from 40–0 cmH2O with a constant pressure variation of 2 cmH2O/s Distance at 20 cmH2O, representing the volume difference between the inspiratory and expiratory limbs at 20 cmH2O Normalized distance at 20 cmH2O, representing the distance at 20 cmH2O weighted by the maximal volume (Vmax) Maximal distance, representing the maximal volume difference between the inspiratory and expiratory limbs at the same pressure Normalized maximal distance (NMD), representing the maximal distance weighted by the Vmax AOP, identified as the lower inflection point on the PV curve when compliance was as low as 1.5–2.5 ml/cmH2O above 5 cmH2O	Single-breath method used to reduce PEEP from higher to lower levels (typically from 15 or 18 cmH2O to 5 or 8 cmH2O) and calculate Crs at the lower PEEP level (5 or 8 cmH2O) Measured ΔEELV, representing the recorded change in EELV (end-expiratory lung volume) between the higher and lower PEEP levels Predicted ΔEELV, representing the product of Crs at low PEEP and the change in PEEP Recruited volume (ΔVrec), calculated by subtracting predicted ΔEELV from measured ΔEELV Pressure contributing to recruitment (ΔPrec), defined as the difference between higher and lower PEEP (or AOP if present) Compliance of the recruited lung (Crec), determined by dividing ΔVrec by ΔPrec R/I ratio, can be calculated as a ratio of Crec to Crs at lower PEEP (5 or 8 cmH2O, or above AOP) Compliance ratio (Crs ratio), calculated as the ratio between Crs at higher PEEP (15 or 18 cmH2O) and at lower PEEP (5 or 8 cmH2O)	Patients ventilated for at least 2 min with a high PEEP Single-breath maneuver performed to reduce PEEP (from 15 or 18 to 5 or 8 cmH2O) Plateau pressure measured at least 2 min later Respiratory rate reduced to 8–10 breaths/min before this procedure Recruitability assessment evaluated in the supine flat position

Measurements and main results
Enrollment and baseline characteristics	Correlation between NMD and R/I ratio	Relationship between compliance and recruitability items
Cohort of 87 Japanese COVID-19 patients on mechanical ventilation Recruitability was assessed in 80 patients Both a quasi-static PV curve and R/I ratio assessment were performed on 40 patients Seven patients were excluded due to missing data	NMD of the PV curve showed a significant positive correlation with the R/I ratio (rho = 0.74, p < 0.001) Neither maximal distance nor distance at 20 cmH2O correlated with the R/I ratio Normalized distance at 20 cmH2O showed a moderate correlation with the R/I ratio (rho = 0.70, p < 0.001) In a subgroup with airway pressure at a maximal distance below 20 cm H2O, the correlation between NMD and R/I ratio was strong (rho = 0.80, p < 0.001)	Crs at higher PEEP during the R/I ratio procedure had no significant correlation with NMD (rho = 0.14, p = 0.43) or the R/I ratio (rho = 0.27, p = 0.13) Crs ratio (higher/lower) showed a moderate and positive correlation with NMD (rho = 0.64, p < 0.001) and the R/I ratio (rho = 0.67, p < 0.001)

Primary outcomes

There is a significantly higher correlation between NMD and the R/I ratio than between other parameters like distance at 20 cm H2O and the R/I ratio.
Neither NMD nor the R/I ratio correlated with Crs. Instead, they showed a correlation with the Crs ratio (higher/lower).
The above findings indicate that NMD and R/I ratios may be more informative than other parameters for assessing lung recruitability.

Conclusion

There is a strong correlation between NMD of the quasi-static PV curve and the R/I ratio for recruitability assessment. In addition, NMD and the R/I ratio correlate with the Crs ratio (higher/lower). Therefore, NMD and the R/I ratio could be potential indicators of recruitability that can be performed at the bedside.

Limitations

The study had a relatively small sample size, which may limit the generalizability of its findings to a broader population.
The single-center, retrospective design of the study could introduce bias and also limit the generalizability of the results.
The study acknowledged that it lacked CT data for assessing lung recruitability, which could have provided a more robust reference for validating the findings.
The study highlighted the heterogeneous nature of acute respiratory distress syndrome (ARDS), which may affect the consistency of compliance as an indicator of recruitability.
The study used different methods than previous studies (AOP was identified as the lower inflection point in the PV curve, and plateau pressure was measured at least 2 min later), which may introduce variability in the results.

How to incorporate these findings into my daily work with Hamilton Medical technology?

The response to PEEP or LRMs in ARDS is difficult to predict, as it is dependent on the individual lung’s recruitability and therefore varies greatly between patients. Increasing PEEP or conducting an LRM might be detrimental, especially in patients with low recruitability. Excessive PEEP may cause lung overdistention, resulting in left and/or right cardiac dysfunction.
The strong correlation between NMD and the R/I ratio in patients with airway pressure below 20 cmH2O at maximal distance on the PV curve suggests that NMD is a valuable marker of lung recruitability within a safe range of PEEP. This understanding can help healthcare providers make more informed decisions about PEEP settings in specific patients, ensuring optimal lung recruitment and minimizing the risk of overdistension.
NMD obtained using the P/V Tool technology on Hamilton Medical ventilators has previously been validated in a CT-scan study (Chiumello D, Arnal JM, Umbrello M, et al. Hysteresis and Lung Recruitment in Acute Respiratory Distress Syndrome Patients: A CT Scan Study [published correction appears in Crit Care Med. 2022 Mar 1;50(3):e339]. Crit Care Med. 2020;48(10):1494-1502. doi:10.1097/CCM.00000000000045182), unlike the R/I ratio that has not been directly validated against reference methods like CT scans or hysteresis.
Evidence has shown the P/V Tool to be an adaptable, reliable, and effective means of measuring lung recruitment. It requires no modification to the existing mode, enabling smooth integration into clinical practice.

Resources

Hamilton Medical offers an extensive range of educational material on use of the P/V Tool for assessing recruitability, performing recruitment maneuvers, and setting PEEP. Follow the link below to access articles, videos, e-learning modules, and more.

P/V Tool training

Footnotes

References

1. Nakayama R, Bunya N, Katayama S, et al. Correlation between the hysteresis of the pressure-volume curve and the recruitment-to-inflation ratio in patients with coronavirus disease 2019. Ann Intensive Care. 2022;12(1):106. Published 2022 Nov 12. doi:10.1186/s13613-022-01081-x
2. Chiumello D, Arnal JM, Umbrello M, et al. Hysteresis and Lung Recruitment in Acute Respiratory Distress Syndrome Patients: A CT Scan Study [published correction appears in Crit Care Med. 2022 Mar 1;50(3):e339]. Crit Care Med. 2020;48(10):1494-1502. doi:10.1097/CCM.0000000000004518

Correlation between the hysteresis of the pressure-volume curve and the recruitment-to-inflation ratio in patients with coronavirus disease 2019.

Nakayama R, Bunya N, Katayama S, et al. Correlation between the hysteresis of the pressure-volume curve and the recruitment-to-inflation ratio in patients with coronavirus disease 2019. Ann Intensive Care. 2022;12(1):106. Published 2022 Nov 12. doi:10.1186/s13613-022-01081-x

https://pubmed.ncbi.nlm.nih.gov/36370227/

BACKGROUND Since the response to lung recruitment varies greatly among patients receiving mechanical ventilation, lung recruitability should be assessed before recruitment maneuvers. The pressure-volume curve (PV curve) and recruitment-to-inflation ratio (R/I ratio) can be used bedside for evaluating lung recruitability and individualing positive end-expiratory pressure (PEEP). Lung tissue recruitment on computed tomography has been correlated with normalized maximal distance (NMD) of the quasi-static PV curve. NMD is the maximal distance between the inspiratory and expiratory limb of the PV curve normalized to the maximal volume. However, the relationship between the different parameters of hysteresis of the quasi-static PV curve and R/I ratio for recruitability is unknown. METHODS We analyzed the data of 33 patients with severe coronavirus disease 2019 (COVID-19) who received invasive mechanical ventilation. Respiratory waveform data were collected from the ventilator using proprietary acquisition software. We examined the relationship of the R/I ratio, quasi-static PV curve items such as NMD, and respiratory system compliance (Crs). RESULTS The median R/I ratio was 0.90 [interquartile range (IQR), 0.70-1.15] and median NMD was 41.0 [IQR, 37.1-44.1]. The NMD correlated significantly with the R/I ratio (rho = 0.74, P < 0.001). Sub-analysis showed that the NMD and R/I ratio did not correlate with Crs at lower PEEP (- 0.057, P = 0.75; and rho = 0.15, P = 0.41, respectively). On the contrary, the ratio of Crs at higher PEEP to Crs at lower PEEP (Crs ratio (higher/lower)) moderately correlated with NMD and R/I ratio (rho = 0.64, P < 0.001; and rho = 0.67, P < 0.001, respectively). CONCLUSIONS NMD of the quasi-static PV curve and R/I ratio for recruitability assessment are highly correlated. In addition, NMD and R/I ratio correlated with the Crs ratio (higher/lower). Therefore, NMD and R/I ratio could be potential indicators of recruitability that can be performed at the bedside.

Hysteresis and Lung Recruitment in Acute Respiratory Distress Syndrome Patients: A CT Scan Study.

Chiumello D, Arnal JM, Umbrello M, et al. Hysteresis and Lung Recruitment in Acute Respiratory Distress Syndrome Patients: A CT Scan Study [published correction appears in Crit Care Med. 2022 Mar 1;50(3):e339]. Crit Care Med. 2020;48(10):1494-1502. doi:10.1097/CCM.0000000000004518

https://pubmed.ncbi.nlm.nih.gov/32897667/

OBJECTIVES Hysteresis of the respiratory system pressure-volume curve is related to alveolar surface forces, lung stress relaxation, and tidal reexpansion/collapse. Hysteresis has been suggested as a means of assessing lung recruitment. The objective of this study was to determine the relationship between hysteresis, mechanical characteristics of the respiratory system, and lung recruitment assessed by a CT scan in mechanically ventilated acute respiratory distress syndrome patients. DESIGN Prospective observational study. SETTING General ICU of a university hospital. PATIENTS Twenty-five consecutive sedated and paralyzed patients with acute respiratory distress syndrome (age 64 ± 15 yr, body mass index 26 ± 6 kg/m, PaO2/FIO2 147 ± 42, and positive end-expiratory pressure 9.3 ± 1.4 cm H2O) were enrolled. INTERVENTIONS A low-flow inflation and deflation pressure-volume curve (5-45 cm H2O) and a sustained inflation recruitment maneuver (45 cm H2O for 30 s) were performed. A lung CT scan was performed during breath-holding pressure at 5 cm H2O and during the recruitment maneuver at 45 cm H2O. MEASUREMENTS AND MAIN RESULTS Lung recruitment was computed as the difference in noninflated tissue and in gas volume measured at 5 and at 45 cm H2O. Hysteresis was calculated as the ratio of the area enclosed by the pressure-volume curve and expressed as the hysteresis ratio. Hysteresis was correlated with respiratory system compliance computed at 5 cm H2O and the lung gas volume entering the lung during inflation of the pressure-volume curve (R = 0.749, p < 0.001 and R = 0.851, p < 0.001). The hysteresis ratio was related to both lung tissue and gas recruitment (R = 0.266, p = 0.008, R = 0.357, p = 0.002, respectively). Receiver operating characteristic analysis showed that the optimal cutoff value to predict lung tissue recruitment for the hysteresis ratio was 28% (area under the receiver operating characteristic curve, 0.80; 95% CI, 0.62-0.98), with sensitivity and specificity of 0.75 and 0.77, respectively. CONCLUSIONS Hysteresis of the respiratory system computed by low-flow pressure-volume curve is related to the anatomical lung characteristics and has an acceptable accuracy to predict lung recruitment.

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