Effect of Different Levels of Pressure Support and Proportional Assist Ventilation on Breathing Pattern, Work of Breathing and Gas Exchange in Mechanically Ventilated Hypercapnic COPD Patients with Acute Respiratory Failure

Abstract

Background: Proportional assist ventilation (PAV) has been shown to maintain better patient-ventilator synchrony than pressure support ventilation (PSV); however, its clinical advantage regarding invasive ventilation of COPD patients has not been clarified. Objectives: To compare the effect of PAV and PSV on respiratory parameters of hypercapnic COPD patients with acute respiratory failure (ARF). Methods: Nine intubated hypercapnic COPD patients were placed on the PAV or PSV mode in random sequence. For each mode, four levels (L₁–L₄) of support were applied. At each level, blood gases, flow, tidal volume (V_T), airway pressure (Paw), esophageal pressure (Pes) (n = 7), patient respiratory rate (fp), ventilator rate (fv), missing efforts (ME = fp – fv) were measured. Results: We found increases in ME with increasing levels of PSV but not with PAV. PO₂and V_T increased whereas PCO₂decreased significantly with increasing levels of PSV (p < 0.05). With PAV, PCO₂decreased and V_Tincreased significantly only at L₄ whereas PO₂increased from L₁ to L₄. Runaways were observed at L₃and L₄of PAV. The pressure-time product (PTP) was determined for effective and missing breaths. The mean total PTP per minute (of effective plus missing breaths) was 160 ± 57 cm H₂O/s·min in PSV and 194 ± 60 cm H₂O/s·min in PAV. Conclusion: We conclude that in COPD patients with hypercapnic ARF, with increasing support, PSV causes the appearance of ME whereas PAV develops runaway phenomena, due to the different patient-ventilator interaction; however, these do not limit the improvement of blood gases with the application of both methods.

Cheyne-Stokes Respiration in Congestive Heart Failure: Continuous Positive Airway Pressure of 5–8 cm H₂O for 1 Year in Five Cases

“…Such optional modes of assisted ventilation other than CPAP are adaptive pressure support servoventilation [2], bilevel positive airway pressure [7], and proportional assist ventilation [8]. Further studies are mandatory on which of these modes would be most favorable in an overall treatment strategy for CHF patients with CSR/CSA.…”

Tracheal pressure regulated volume assist ventilation in acute respiratory failure

“…4,5,12,21,[27][28][29][30] Navalesi and coworkers specifically characterized the consequences of increasing levels of VAV on total work of breathing over a wide range of support. 3 The reduction in elastic work achieved with VAV was offset in part by an increase in resistive work so that the decrease in total work of breathing was less than expected.…”

Proportional Assist Ventilation: Back to the Future?

“…In this issue of Respiration, Passam et al [5] analyzed in a physiologic study the response of sedated patients with chronic obstructive pulmonary disease to increasing levels of PSV and PAV. The most interesting characteristic of this paper is that low and high limits of PAV and PSV support were investigated.…”

“…As a matter of fact, increasing levels of PSV were associated with an increasing number of inspiratory efforts not able to trigger the ventilator (missing efforts, ME), whereas increasing levels of PAV were associated with the occurrence of runaway breaths [1]. Passam et al [5] concluded that this different response cannot support the advantage of one method over the other since, despite the associated phenomena of each method, there is no limitation in blood gas improvement. However, lessons from mechanically ventilated patients with acute respiratory distress syndrome should remind us that not always arterial blood gas improvement has to be regarded as the main goal of ventilatory assistance in order to provide the patients with the most effective treatment [6,7].…”

“…However, lessons from mechanically ventilated patients with acute respiratory distress syndrome should remind us that not always arterial blood gas improvement has to be regarded as the main goal of ventilatory assistance in order to provide the patients with the most effective treatment [6,7]. The study of Passam et al [5] is important since it focuses on ME and runaway breaths as mechanical ventilation markers of overassistance, potentially useful to set upper limits of pressure delivered by the ventilator during PSV and PAV, respectively. In this connection, ME during PSV may be viewed as a protective mechanism against excessive overinflation.…”