Skip to main content

Volume 3 Supplement 1


Comparing two different modes of mechanical ventilation by the least square fitting method: nava versus PSV


The Least Square Fitting (LSF) method is a statistical approach used for evaluating respiratory mechanics [1]. It allows measurement of respiratory mechanics continuously at the bedside, even in presence of flow limitation [23], without the need for constant inspiratory flow rate, end-inspiratory hold and end-expiratory occlusion. These features allow the application of the LSF method to assisted ventilation modes, such as pressure support ventilation (PSV) [3] and neurally-adjusted ventilatory assist (NAVA).


We compared the LSF performance during PSV and NAVA. Our hypothesis was that the LSF works better during NAVA than during PSV, since NAVA algorithm allows a more accurate neuro-ventilatory coupling.


15 patients undergoing mechanical ventilation for acute respiratory failure were ventilated using randomly either PSV or NAVA. Data of resistance (Rrs), elastance (Ers) and total positive end expiratory pressure (PEEPtot) were obtained by fitting the equation Paw = Rrs x V´ + VT/Crs + PEEPtot during inspiration. The coefficient of determination (CD) of the applied equation was used to compare data obtained during NAVA and PSV, the higher being the CD, the better the quality of the data. These data were obtained at the beginning of mechanical ventilation (T0), and after 12 (T12), 24 (T24), 36 (T36), 48 (T48), 60 (T60) and 72 (T72) hours of mechanical ventilation.


Data obtained with LSF were statistically more reliable during NAVA than during PSV (Chi-squared test: p < 0.001). The CD level showed a higher value during NAVA (T0 median 0.9855), that was maintained constantly higher in time, than during PSV (T0 median 0.9288), in which the value of the CD progressively worsened by the hours of mechanical ventilation.


The LSF method of the LSF performs better during NAVA then during PSV. By the hours of mechanical ventilation the performance of the LSF method further worsens during PSV while remains constant during NAVA. Our data indirectly confirm more physiological patient-ventilation interactions during NAVA than during PSV.


Figure 1


Figure 2

Table 1
Table 2


  1. 1.

    Gillard C, Flemale A, Dierckx JP, et al: Measurement of elffective elastance of the total respiratory system in ventilated patients by a computed method. Intensive Care Med. 1990, 16: 189-195. 10.1007/BF01724801.

    PubMed  CAS  Article  Google Scholar 

  2. 2.

    Volta CA, Marangoni E, Alvisi V, et al: Respiratory mechanics by least square fitting in mechanically ventilated patients: applications on flow-limited COPD patients. Intensive Care Med. 2002, 28: 48-5. 10.1007/s00134-001-1147-8.

    PubMed  Article  Google Scholar 

  3. 3.

    Iotti GA, Braschi A, Brunner JX, et al: Respiratory mechanics by least square fitting in mechanically ventilated patients: applications during paralysis and during pressure support ventilation. Intensive Care Med. 1995, 21: 406-413. 10.1007/BF01707409.

    PubMed  CAS  Article  Google Scholar 

Download references

Author information



Corresponding author

Correspondence to V Cricca.

Rights and permissions

Open Access  This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.

The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

To view a copy of this licence, visit

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Spadaro, S., Grasso, S., Cricca, V. et al. Comparing two different modes of mechanical ventilation by the least square fitting method: nava versus PSV. ICMx 3, A319 (2015).

Download citation


  • Mechanical Ventilation
  • Acute Respiratory Failure
  • Little Square Fitting
  • Respiratory Mechanic
  • Pressure Support Ventilation