Response Time of Four Pressure Support Ventilators: Effect of Triggering Method and Bias Flow

Abstract

BACKGROUND: Patient-ventilator dyssynchrony due to an unresponsive ventilator demand-flow system can result in fatigue and failure to wean from mechanical ventilation. PURPOSE: We sought to evaluate the response times (T_r) of several ventilators to weak inspiratory efforts at various pressure support (PS) ventilation levels and to gauge the effects of bias flow (BF, intended to be used as a system leak compensator and to reduce the subjective sense of delay in breathing against a closed system) on T_r when sensitivity is maximized. METHODS: Flow-triggering (FT) was evaluated in the Siemens SV300 and Puritan-Bennett 7200ae (7200FT), and pressure-triggering (PT) was evaluated in the Newport E200, Bird VIP, and Puritan-Bennett 7200ae (7200PT). PS was used to eliminate target pressure variables that would favor some ventilators and have a negative impact on others. Patient efforts were simulated by using a ventilator to drive one compartment of a simulator, adjusted to produce inspiratory efforts of 2 L/min, 5 L/min, or 25 L/min in the dependent compartment. T_r began when pressure rose in the drive compartment and ended when pressure in the patient compartment returned to baseline. RESULTS: The E200 was quicker to respond than other ventilators for all endotracheal tube (ETT) sizes. VIP exhibited marked difficulty in triggering at 2 L/min inspiratory flow. VIP's response time was 40-75 ms slower than the E200. SV300 was 10-48 ms slower than E200. 7200PT was faster than 7200FT. BF had a significant impact on some ETT-PS combinations. PS at 3 cm H2O and 2.5 mm ETT resulted in a 30 ms increase in T_r. CONCLUSIONS: Results indicate BF levels should be tailored to individual patient requirements, particularly in neonatal and pediatric applications. We conclude that when a combination of BF, continuously adjustable sensitivity control, and proximal pressure monitoring are used FT provides no measurable advantage over PT. The site and method of measurement as well as the interaction of demand system components determines the total response to inspiratory efforts.

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References

Marini

, Capps

, Culver

. The inspiratory work of breathing during assisted mechanical ventilation. Chest 1985;87(5):612–618.

Martin

, Rafferty

, Wetzel

, Gioia

. Inspiratory work and response times of a modified pediatric volume ventilator during synchronized intermittent mandatory ventilation and pressure support ventilation. Anesthesiology 1989;71(6):977–981.

Gurevitch

, Gelmont

Importance of trigger sensitivity to ventilator response delay in advanced chronic obstructive pulmonary disease with respiratory failure. Crit Care Med 1989;17(4):354–359.

Messinger

, Banner

, Blanch

, Layon

. Using tracheal pressure to trigger the ventilator and control airway pressure during continuous positive airway pressure decreases work of breathing. Chest 1995;108(2):509–514.

Bernstein

, Cleary

, Heldt

, Rosas

, Schellenberg

, Mannino

. Response time and reliability of three neonatal patient-triggered ventilators. Am Rev Respir Dis 1993;148(2):358–364.

Sassoon

, Lodia

, Rheeman

, Kuei

, Light

, Mahutte

. Inspiratory muscle work of breathing during flow-by, demand-flow, and continuous-flow systems in patients with chronic obstructive pulmonary disease. Am Rev Respir Dis 1992;145(5):1219–1222.

Saito

, Tokioka

, Kosaka

Efficacy of flow-by during continuous positive airway pressure ventilation. Crit Care Med 1990;18(6):654–656.

Jager

, Tweeddale

, Holland

Flow-triggering does not decrease the pressure-time product in COPD patients. Respir Care 1994;39(9):892–896.

Sassoon

CSH

, Mahutte

. What you need to know about the ventilator in weaning. Respir Care 1995;40(3):249–256.

10.

Carmack

, Torres

, Anders

, Wilson

, Holt

, Heulitt

. Comparison of inspiratory work of breathing in young lambs during flow-triggered and pressure-triggered ventilation. Respir Care 1995;40(1):28–34.

11.

Konyukov

, Takahashi

, Kuwayama

, Hotta

, Takezawa

, Shimada

Estimation of triggering work of breathing. The dependence on lung mechanics and bias flow during pressure support ventilation. Chest 1994;105(6):1836–1841.

12.

Branson

. Flow-triggering systems. Respir Care 1994;39(2):138–144.

13.

Newport E200 ventilator manual. Newport Beach CA: Newport Medical Instruments; 1991:51–52.

14.

Epstein

. The sensitivities and response times of ventilatory assistors. Anesthesiology 1971;34(4):321–326.

15.

Campbell

, Branson

. Ventilatory support for the 90's: pressure support ventilation. Respir Care 1993;38(5):526–537.

16.

Sassoon

CSH

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

17.

Branson

, Davis

Jr . Work of breathing imposed by five ventilators used for long-term support: The effects of PEEP and simulated patient demand. Respir Care 1995;40(12):1270–1278.

18.

McPherson

. Respiratory therapy equipment. St Louis: CV Mosby; 1981:22.

19.

Banner

, Kirby

, Blanch

. Site of pressure measurement during spontaneous breathing with continuous positive airway pressure: Effect on calculating imposed work of breathing. Crit Care Med 1992;20(4):528–533.

20.

Banner

, Blanch

, Kirby

. Imposed work of breathing and methods of triggering a demand-flow, continuous positive airway pressure system. Crit Care Med 1993;21(2):183–190.

21.

Sassoon

, Giron

, Ely

, Light

. Inspiratory work of breathing in flow-by and demand-flow continuous positive airway pressure. Crit Care Med 1989;17(11):1108–1114.

22.

Patel

, Petrini

, Norman

. Work of breathing and pressure-time product on pressure support ventilation, continuous positive airway pressure, and T-piece. Respir Care 1996;41(11):1013–1019.