Benefits from non-invasive ventilation (NIV) and high flow nasal cannula (HFNC) in patients with acute respiratory failure (ARF) can be obtained if close monitoring is undertaken. Indeed, the early detection of worsening signs prevent dangerous delays in endotracheal intubation (ETI). Among the different methods for patient’s monitoring there are clinical, physiological and ventilator parameters as well as ultrasonographic signs [1]. In this context, the quantification and monitoring of inspiratory effort could be a potential predictor of non-invasive respiratory support failure.

One of the methods to assess inspiratory effort during spontaneous breathing is esophageal pressure swings (ΔPes) measurement. Indeed, esophageal manometry allows to estimate pleural pressure (Ppl) and hence dynamic transpulmonary pressure (dynamic PL) as follows: dynamic PL = Paw - Ppl. During non-invasive ventilatory support, dynamic PL can be calculated as the pressure support (PS) set + Pes. Dynamic PL and Pes can be useful to assess patient’s effort when the respiratory muscles are active [2]. A growing body of evidence has shown how an intense inspiratory effort could promote Patient-Self Inflicted Lung Injury (P-SILI). P-SILI is sustained by 1) elevated swing in dynamic PL that causes the inflation of high volumes in the non-dependent compartment; 2) abnormal increases in transpulmonary pressure and trans-vascular pressure in the dependent lung zones with intra-tidal shift of gas (pendelluft) and blood (pendelblut); 3) negative-pressure pulmonary edema; 4) diaphragm injury. [3] Thus, monitoring Pes might play a determinant role in the management of patients with ARF undergoing NIV. In a recent study on 30 patients with ARF, the magnitude of inspiratory effort relief as assessed by ΔPes variation within the first 2 hours of NIV has been shown to be an early and accurate predictor of NIV outcome at 24 hours [4]. However, esophageal manometry is expensive, not easy to implement at bedside and poorly tolerated by many patients.

In this scenario, a recent prospective study by Tonelli and co-workers describes the correlation between ΔPes and nasal pressure swings (ΔPnos) as an additional potential measure of inspiratory effort in spontaneously breathing patients with ARF [5].

Methods

61 patients (83.6% COVID-19) admitted to the Respiratory Intensive Care Unit (RICU) of the University Hospital of Modena were enrolled and received either esophageal and nasal manometry assessment.

Inclusion criteria were the presence of ARF with a peripheral oxygen saturation (SpO2) <90% during conventional oxygen therapy with Venturi mask with an inspiratory oxygen fraction (FiO2) of 0.5 and candidate to treatment escalation to HFNC. The most important exclusion criteria were immediate need for ETI; cardiogenic acute pulmonary edema, concomitant hypercapnia, previous diagnosis of chronic pulmonary diseases, neuromuscular diseases.

ΔPes and ΔPnos were collected at the same time at study inclusion during HFNC (T1) and after 24 h (T2), during HFNC or NIV.

Nasal pressure swings were collected through a self-expanding foam plug that was placed in the nostril and modelled on the shape of the nasogastric tube (for esophageal pressure monitoring) to obtain a sealed tight closure of the external surface of the nostril.

Results

ΔPes and ΔPnos were strongly correlated at T1 and T2. In particular, the ΔPes/ΔPnos ratio was similar at T1 and T2 (2.20 [2.06–2.47] and 2.27 [2.11–2.50] respectively). The ΔPes/ΔPnos ratio at T2 was similar in patients receiving HFNC versus NIV (2.23 [1.89–2.60] and 2.27 [2.15–2.50], respectively. The mean ΔPes/ΔPnos ratio at T1 was 2.27 (standard deviation 0.44), and this value was used as a multiplication factor to compute ΔPes, estimated from ΔPnos (ΔPes = 2.27 x ΔPnos).

Future directions

This study shows that nasal pressure swing during non-assisted and assisted spontaneous breathing is highly correlated with ΔPes in patients with ARF. Should data be confirmed on larger studies, ΔPnos could be an interesting tool to monitor patient’s inspiratory effort. Indeed, nasal manometry is easy to implement and well tolerated by the patients. For this reason it could be extended in different settings of care, enhancing the monitoring of respiratory effort in patients at impending risk of deterioration.

[1] B. Ergan, J. Nasiłowsk and J.C. Winck. How should we monitor patients with acute respiratory failure treated with noninvasive ventilation? Eur Respir Rev. 2018 Apr 13;27(148):170101.

[2] T. Yoshida, L. Brochard. Esophageal pressure monitoring: why, when and how? Curr Opin Crit Care. 2018 Jun;24(3):216-222.

[3] D.L. Grieco, L.S. Menga, D. Eleuteri, M. Antonelli. Patient self-inflicted lung injury: implications for acute hypoxemic respiratory failure and ARDS patients on non-invasive support. Minerva Anestesiol. 2019 Sep;85(9):1014-1023.

[4] R. Tonelli, R. Fantini, L. Tabbì, I. Castaniere, L. Pisani, M. R. Pellegrino, G. Della Casa, R. D'Amico, M. Girardis, S. Nava, E. M. Clini, A. Marchioni. Early Inspiratory Effort Assessment by Esophageal Manometry Predicts Noninvasive Ventilation Outcome in De Novo Respiratory Failure A Pilot Study. Am J Respir Crit Care Med. 2020 Aug 15;202(4):558-567.

[5] R. Tonelli, A. Cortegiani, A. Marchioni, R. Fantini, L. Tabbì, I. Castaniere, E. Biagioni, S. Busani, C. Nani, C. Cerbone, M. Vermi, F. Gozzi, G. Bruzzi, L. Manicardi, M. R. Pellegrino, B. Beghè, M. Girardis, P. Pelosi, C. Gregoretti, L. Ball, E. Clini. Nasal pressure swings as the measure of inspiratory effort in spontaneously breathing patients with de novo acute respiratory failure. Crit Care. 2022 Mar 24;26(1):70.