Effects of Inspiratory Rise Time on Triggering Work Load During Pressure-Support Ventilation: A Lung Model Study

Abstract

BACKGROUND:

The rise in inspiratory flow is important during patient-triggered ventilation. Many ventilators incorporate a function to control the time to reach the targeted airway pressure (inspiratory rise time). However, it has not been clarified how inspiratory rise time affects inspiratory work load under various ventilator settings. In a bench study we investigated the effect of inspiratory rise time on inspiratory work load during pressure-support ventilation (PSV).

METHODS:

We studied 6 ICU ventilators. We measured flow and pressure at the airway opening (P_ao) at PEEP of 5 cm H₂O, pressure-support of 5 cm H₂O and 10 cm H₂O, 4 triggering sensitivities, and inspiratory drives 300 mL, 500 mL, and 700 mL. The inspiratory-rise-time setting was not consistent between the ventilators, and we chose 3 inspiratory-rise-time levels with each ventilator. The inspiratory delay time (DT) was defined as the time between the onset of inspiration and the return of P_ao to baseline, and was divided into 2 parts at the point of the lowest P_ao: before the lowest P_ao (DT₁), and after the lowest P_ao (DT₂). As an indicator of inspiratory work load we calculated the pressure-time-product (PTP) of the P_ao over the DT. PTP was also divided into PTP₁ and PTP₂, at the point of the lowest P_ao.

RESULTS:

Short inspiratory rise time reduced DT₂, PTP₁, and PTP₂, regardless of the pressure-support level, triggering sensitivity, or inspiratory drive. However, the inspiratory-rise-time setting did not affect DT₁. The PTP₁, PTP₂, and DT₂ values differed significantly among the ventilators. A combination of short inspiratory rise time, high PSV, and sharp triggering sensitivity resulted in the smallest PTP and DT values.

CONCLUSIONS:

Short inspiratory rise time decreased inspiratory work load, regardless of the pressure-support level, triggering sensitivity, or inspiratory drive. Inspiratory work load can be maximally lowered by a combination of a short inspiratory rise time, a sharp triggering sensitivity, and a high inspiratory pressure-support level for a given patient's inspiratory effort.

Keywords

inspiratory rise time pressure-support ventilation pressure-time-product inspiratory delay time

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References

Tobin

, Jubran

, Laghi

. Patient-ventilator interaction. Am J Respir Crit Care Med, 2001; 163(5):1059–1063.

Sassoon

CSH

. Mechanical ventilator design and function: the trigger variable. Respir Care, 1992; 37(9):1056–1069.

MacIntyre

, McConnell

, Cheng

, Sane

. Patient-ventilator flow dyssynchrony: flow-limited versus pressure-limited breaths. Crit Care Med, 1997; 25(10):1671–1677.

Bonmarchand

, Chevron

, Chopin

, Jusserand

, Girault

, Moritz

, et al. Increased initial flow rate reduces inspiratory work of breathing during pressure support ventilation in patients with exacerbation of chronic obstructive pulmonary disease. Intensive Care Med, 1996; 22(11):1147–1154.

Bonmarchand

, Chevron

, Menard

J-F

, Girault

, Moritz-Berthelot

, Pasquis

, et al. Effects of pressure ramp slope values on the work of breathing during pressure support ventilation in restrictive patients. Crit Care Med, 1999; 27(4):715–722.

Uchiyama

, Imanaka

, Taenaka

. Relationship between work of breathing provided by a ventilator and patient's inspiratory drive during pressure support ventilation: effects of inspiratory rise time. Anaesth Intensive Care, 2001; 29(4):349–358.

Chiumello

, Pelosi

, Croci

, Bigatello

, Gattinoni

. The effects of pressurization rate on breathing pattern, work of breathing, gas exchange and patient comfort in pressure support ventilation. Eur Respir J, 2001; 18(1):107–114.

Prinianakis

, Delmastro

, Carlucci

, Ceriana

, Nava

. Effect of varying the pressurization rate during noninvasive pressure support ventilation. Eur Respir J, 2004; 23(2):314–320.

Bunburaphong

, Imanaka

, Nishimura

, Hess

, Kacmarek

. Performance characteristics of bilevel pressure ventilators: a lung model study. Chest, 1997; 111(4):1050–1060.

10.

MacIntyre

, Ho

. Effects of initial flow rate and breath termination criteria on pressure support ventilation. Chest, 1991; 99(1):134–138.

11.

Richard

, Carlucci

, Breton

, Langlais

, Jaber

, Maggoire

, Fougère

, Harf

, Brochard

. Bench testing of pressure support ventilation with three different generations of ventilators. Intensive Care Med, 2002; 28(8):1049–1057.

12.

Thille

, Lyazidi

, Richard

, M , Galia

, Brochard

. A bench study of intensive-care-unit ventilators: new versus old and turbine-based versus compressed gas-based ventilators. Intensive Care Med, 2009; 35(8):1368–1376.

13.

Chiumello

, Pelosi

, Taccone

, Slutsky

, Gattinoni

. Effect of different inspiratory rise time and cycling off criteria during pressure support ventilation in patients recovering from acute lung injury. Crit Care Med, 2003; 31(11):2604–2610.

14.

Chatmongkolchart

, Williams

, Hess

, Kacmarek

. Evaluation of inspiratory rise time and inspiration termination criteria in new-generation mechanical ventilators: a lung model study. Respir Care, 2001; 46(7):666–677.