Relationship between Work of Breathing Provided by a Ventilator and Patients’ Inspiratory Drive during Pressure Support Ventilation;Effects of Inspiratory Rise Time

Abstract

Inspiratory drive and work of breathing provided by a ventilator (WOBv) during pressure support ventilation (PSV) were examined in 15 patients. At PSV 10 and 15 cm H ₂ O during CPAP 5 cm H ₂ O, patients with low P _0.1 (<4.2 cm H ₂ O, n=9) showed WOBv 0.57 and 0.92 J/l, those with high P _0.1 (>4.2 cm H ₂ O, n=6) showed 0.31 and 0.62 J/l respectively. WOBv was smaller and pressure-time product of oesophageal pressure (PTP) was significantly larger in high P _0.1 patients. Peak inspiratory flow for low P _0.1 patients increased as PSV level increased but high P _0.1 patients showed no significant change. In a lung model, effects of inspiratory rise time (IRT) and PSV were studied at high and low inspiratory drives by using ventilators with (Servo 300) and without (Mallinckrodt 7200a) adjustable IRT. With 7200a, PSV 10 cm H ₂ O during low drive was compared with PSV 10 and 15 cm H ₂ O during high drive. In Servo 300, PSV 10 cm H ₂ 2O (IRT 0.6 and 0.0 sec) during low drive was compared with PSV 10 cm H ₂ O (IRT 0.6 and 0.0 sec) and PSV 15 cm H ₂ O (IRT 0.6 sec) during high drive. Raising PSV and shortening IRT both increased peak inspiratory flow. Initial inspiratory flow increased in inverse proportion to IRT, but higher PSV had a little effect. WOBv with high drive was less than with low drive. Higher PSV preserved WOBv by increasing tidal volume. Shortening IRT recruited WOBv by increasing initial inspiratory flow without changing airway pressure and tidal volume. Compared with higher PSV, shorter IRT reduced PTP more. In conclusion, WOBv decreased as inspiratory drive increased due to inability to increase inspiratory flow. Increasing initial inspiratory flow was more effective than raising PSV to preserve inspiratory assistance of PSV at high inspiratory drive.

Keywords

VENTILATION: pressure support work of breathing pressure time product inspiratory drive rise time

References

MacIntyre

N.R.

Respiratory function during pressure support ventilation.

Chest 1985; 89: 677–683.

Brochard

, Harf

, Lorino

, Lemaire

Inspiratory pressure support prevents diaphragmatic fatigue during weaning from mechanical ventilation.

Am Rev Respir Dis 1989; 139: 513–521.

Branson

R.D.

, Campbell

R.S.

, Davis

K.J.

, Johannigman

J.A.

, Johnson

D.J.

, Hurst

J.M.

Altering flow rate during maximum pressure support ventilation (PSVmax): effects on cardio-respiratory function.

Resp Care 1990; 35: 1056–1064.

Amato

M.B.P.

, Barbus

C.S.V.

, Bonassa

, Saldiva

P.H.

, Zin

W.A.

, de Carvalho

C.R.

Volume-assured pressure support ventilation: A new approach for reducing muscle workload during acute respiratory failure.

Chest 1992; 102: 1225–1234.

MacIntyre

N.R.

, Ho

Effects of initial flow rate and breath termination criteria on pressure support ventilation.

Chest 1991; 99: 134–138.

Baydur

, Behrakis

P.K.

, Zin

W.A.

, Jaeger

, Milic-Emili

A simple method for assessing the validity of the esophageal balloon technique.

Am Rev Respir Dis 1982; 126: 788–791.

Marini

J.J.

Monitoring during mechanical ventilation.

Clinics in Chest Med 1988; 9: 73–100.

Herrera

, Blasco

, Venegas

, Barba

, Doblas

, Marquez

Mouth occlusion pressure (P_0.1) in acute respiratory failure.

Intensive Care Med 1985; 11: 134–139.

Takahashi

, Takezawa

, Kimura

, Nishiwaki

, Shimada

Comparison of inspiratory work of breathing in T-piece breathing, PSV, and pleural pressure support ventilation.

Chest 1991; 100: 1030–1034.

10.

Yamazaki

, Yamakage

, Ujike

, Namiki

Change in work of breathing during continuous positive airway pressure with increased airway resistance.

Chest 1994; 105: 860–867.

11.

Lofaso

, Brochard

, Hang

, Lorino

, Harf

, Isabey

Home versus intensive care pressure support devices: Experimental and clinical comparison.

Am J Respir Crit Care Med 1996; 153: 1591–1599.

12.

Tobin

M.J.

, Van de Graaff

W.B.

Monitoring of lung mechanics and work of breathing. In: Tobin

M.J.

ed. Principles and practice of mechanical ventilation. McGraw-Hill, New York 1994; 967–1003.

13.

Bergman

N.A.

, Waltemath

C.L.

A comparison of some methods for measuring total respiratory resistance.

J Appl Physiol 1974; 36: 131–134.

14.

Mancebo

, Amaro

, Mollo

J.L.

, Lorino

, Lemaire

, Brochard

Comparison of the effects of pressure support ventilation delivered by three different ventilators during weaning from mechanical ventilation.

Intensive Care Med 1995; 21: 913–919.

15.

Kacmarek

R.M.

: The role of pressure support ventilation in reducing of work of breathing. Respir Care 1988; 33: 99–120.

16.

Giannouli

, Webster

, Roberts

, Younes

Response of ventilator-dependent patients to different levels of pressure support and proportional assist.

Am J Respir Crit Care Med 1999; 159: 1716–1725.

17.

Bonmarchand

, Chevron

, Chopin

. 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: 1147–1154.

18.

Bonmarchand

, Chevron

, Ménard

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

19.

Jubran

Inspiratory flow rate: More may not be better.

Crit Care Med 1999; 27: 670–671.

20.

Manning

H.L.

, Molinary

E.J.

, Leiter

J.C.

Effect of inspiratory flow rate on respiratory sensation and pattern of breathing.

Am J Respir Crit Care Med 1995; 151: 751–757.

21.

Corne

, Gillespie

, Roberts

, Younes

Effects of inspira-tory flow rate on respiratory rate in intubated ventilated patients.

Am J Respir Crit Care Med 1997; 156: 304–308.

22.

Cohen

I.L.

, Bilen

, Krishnamurthy

The effects of ventilator working pressure during pressure support ventilation.

Chest 1993; 103: 588–592.