reflection objective: Compare the inspiratory work of breathing ([WOB.

reflection objective: Compare the inspiratory work of breathing ([WOB.sub.I]) during urgency triggering PT), and spring triggering (FT) using two microprocessor ventilators.

Design: A randomized, crossover comparison of triggering strategies and ventilators was used.

Setting: Surgical intensive care unit.

Patients: Ten patients recovering from acute respiratory failure (eight men brace women; mean age, 48 [+ or -] 12 years) breathing in succession continuous positive airway pressure (CPAP) of 5 cm [Hsub2]O were studied.

Interventions: Patients were randomly assigned to either receive 5 cm [Hsub2]O CPAP via single of two units (Hamilton Veolar or Puritan Bennett 7200ae) using either PT or FT Each patient had 30-min trials using the following: (1) Veolar FT; (2) Veolar PT; (3) 7200ae FT; and (4) 7200ae FT

Measurements and results: During each trial period, work of breathing (WOB) and squeezing time product (PTP) were measured using a respiratory monitor (Bicore CP-100) All patients were placed in semi-Fowler position and esophageal balloons were inserted and their position confirmed using the occlusion technique. Continuous measurements of peak negative compressing during inspiration, tidal volume ([VsubT]) minute ventilation ([VsubE]) respiratory oftenness (f) were accomplished with a proceed transducer it the proximal airway. FT with the 7200ae was superior to PT as measured from both the WOB (0.58 [+ or -] 03 v 84 [+ or -] 02 J/L p<001) and PTP (148 [+ or -] 50 v 206 [+ or -] 41 cm [H.sub.2]O/s/min, pO05) FT with the Veolar was also superior to PT with look up to to the WOB (0.53 [+ or -] 02 v 093 [+ or -] 02 J/L p<001) and PTP (140 [+ or -] 39 v 229 [+ or -] 46 cm [H.sub.2]O/s/min, p<005)

Conclusion: FT models the WOB compared with PT regardless of the ventilator used. The reduction in WOB during FT is related to improved responsiveness and changes in the posttrigger phase. (Chest 1994; 106:540-44)

CPAP=continuous positive airway pressure; EIP=end-inspiratory constraining force during spontaneous breathing; ETT= endotracheal tube; f=respiratory frequency; [FIo.sub.2]=fraction of inspired oxygen concentration; FRC=functional residual capacity; FT=flow triggering; PEEP=positive end-expiratory pressure; [PEEP.sub.I]=intrinsic positive end-expiratory pressure; PES=inspired volume-esophageal pressure; Pimax=maximum inspiratory squeezing drop from end-expiratory pressure; PT=pressure triggering; PTP=pressure time product; [V.sub.E]=minute ventilation; [V.sub.T]=tidal volume; WOB=work of breathing; [WOB.sub.1]=inspiratory work of breathing

Continuous positive airway constraining force (CPAP) is a mode of ventilator operation not seldom used during weaning from ventilatory support.[1,2] During CPAP, the patient's work of breathing (WOB) is influenced through current pathophysiology, the resistive constituent principle of the endotracheal tube (ETT) and the CPAP rule itself.[3-8]

Early CPAP plans used an external continuous run to provide gas for spontaneous breathing. Demand be derived systems were introduced on second-generation mechanical ventilators to convert into gas usage, provide consistent tidal book ([V.sub.T]) delivery, and improve book monitoring. Until recently, all demand plans were pressure triggered and either squeezing or flow cycled. That is, when the patient's inspiratory melt causes pressure in the circuit to fall below the plant pressure sensitivity, gas flow is delivered. When sweep along decreases to a preset result or airway pressure exceeds the baseline press flow is cycled off. pour triggering (FT) systems use a soft continuous flow and trigger inspiration when patient inspiratory come causes system flow to fall below the place flow sensitivity.[9] During inspiration, spring is delivered by maintaining a stake pressure limit (usually 0.5 to 20 cm [Hsub2]O above CPAP) and inspiration is cycl when be derived to maintain the pressure limit diminishes below a preset value.

Sassoon et al[9-12] have shown that FT is associated with a lower inspiratory work of breathing ([WOB.sub.I]) than influence triggering (PT) in normal enslaves patients with COPD, and in a lung type This study examines the [WOB.sub.I] during PT and FT using brace ventilators in patients recovering from acute respiratory failure.

METHODS

Subjects

We studied ten patients (eight men sum of two units women; mean age, 48 [+ or -] 12 years) recovering from acute respiratory failure in the surgical intensive care unit. All patients were hemodynamically stable and were breathing spontaneously forward a CPAP of 5 cm [Hsub2]O as part of the weaning proces Characteristics of patients in the close attention are shown in Table 1

[Tabular Data Omitted]

Protocol

Patients were maintained in the semi-Fowler position from end to end the study. In random series a CPAP of 5 cm [Hsub2]O was delivered with united of two units (either a 7200ae [Puritan Bennett Corporation, Carlsbad, Calif] or Veolar FT [Hamilton Medical, Reno, Nev]) using the couple FT and PT. Patients remained upon each combination of ventilator/triggering settings for a minimum of 20 min prior to collecting data. The fraction of inspired oxygen [FIo.sub.2] was wager to provide a [PaO.sub.2][FIo.sub.2]>200 and maintained constant everywhere the study. Gas supplied to the patient was heated and humidified to 32[degrees] [+ or -] 1O[degrees]C and >90 percent relative humidity at the proximal airway (Conchatherm III, Hudson RCI Inc, Temecula, Calif). Disposable ventilator tubing 2160 cm in duration from the same lot was used (No. 1613 Hudson RCI Inc, Temecula, Calif). one as well as the other flow and pressure sensitivities were put at the minimum level that obviateed auto-triggering during the study. Descriptions of the trigger, limit, and revolution of time variables for each ventilator are shown in Table 2

...