Pressure Support Ventilation Mode Research Articles

Respiratory response to CO2 during pressure-support ventilation in conscious normal humans.

The respiratory response to CO2 during pressure-support ventilation (PSV) was studied in 16 conscious normal humans. The subjects breathed through a mouthpiece connected to a ventilator in PSV mode, with pressure set to the highest comfortable level for each subject (10.1 +/- 0.6 cm H2O, mean +/- SE). Compared with breathing spontaneously through the ventilator (CPAP mode with zero positive end-expiratory pressure), with PSV, tidal volume (VT) increased significantly (1.16 +/- 0.1 versus 0.85 +/- 0.04 L), whereas breathing frequency (f) remained stable (16.0 +/- 0.9 versus 15.6 +/- 1.1 breaths/min). As a result, the subjects hyperventilated, decreasing significantly end-tidal PCO2 (PETCO2, 23.5 +/- 1.2 versus 35.5 +/- 1.1 mm Hg). Fraction of inspired CO2 (FICO2) was then increased in steps, and changes in respiratory motor output were quantitated from changes in f, VT, ventilation (VI), peak inspiratory flow (Vpeak), and muscle pressure (Pmus). Pmus was calculated by the equation of motion, based on respiratory system mechanics, which were measured previously by airway occlusion at end-inspiration, VT, VI, and Pmus increased significantly with increasing PETCO2, and the response was detectable even below eupneic levels; f remained relatively stable over a wide range of PETCO2 (23 to 45 mm Hg) and increase significantly only when PETCO2 approached 50 mm Hg. These results indicate that in conscious normal humans during PSV, CO2 responsiveness extends well into hypocapnia and is expressed principally as an increase in intensity of respiratory motor output with little change in respiratory rate.

Comparative Physiologic Effects of Noninvasive Assist-Control and Pressure Support Ventilation in Acute Hypercapnic Respiratory Failure

To compare the effects of noninvasive assist-control ventilation (ACV) and pressure support ventilation (PSV) by nasal mask on respiratory physiologic parameters and comfort in acute hypercapnic respiratory failure (AHRF). A prospective randomized study. A medical ICU. Fifteen patients with COPD and AHRF were consecutively and randomly assigned to two noninvasive ventilation (NIV) sequences with ACV and PSV mode, spontaneous breathing (SB) via nasal mask being used as control. ACV and PSV settings were always subsequently adjusted according to patient's tolerance and air leaks. Fraction of inspired oxygen did not change between the sequences. ACV and PSV mode strongly decreased the inspiratory effort in comparison with SB. The total inspiratory work of breathing (WOBinsp) expressed as WOBinsp/tidal volume (VT) and WOBinsp/respiratory rate (RR), the pressure time product (PTP), and esophageal pressure variations (deltaPes) were the most discriminant parameters (p<0.001). ACV most reduced WOBinsp/VT (p<0.05), deltaPes (p<0.05), and PTP (0.01) compared with PSV mode. The surface diaphragmatic electromyogram activity was also decreased >32% as compared with control values (p<0.01), with no difference between the two modes. Simultaneously, NIV significantly improved breathing pattern (p<0.01) with no difference between ACV and PSV for VT, RR, minute ventilation, and total cycle duration. As compared to SB, respiratory acidosis was similarly improved by both modes. The respiratory comfort assessed by visual analog scale was less with ACV (57.23+/-30.12 mm) than with SB (75.15+/-18.25 mm) (p<0.05) and PSV mode (81.62+/-25.2 mm) (p<0.01) in our patients. During NIV for AHRF using settings adapted to patient's clinical tolerance and mask air leaks, both ACV and PSV mode provide respiratory muscle rest and similarly improve breathing pattern and gas exchange. However, these physiologic effects are achieved with a lower inspiratory workload but at the expense of a higher respiratory discomfort with ACV than with PSV mode.

Pressure vs Flow Triggering During Pressure Support Ventilation

Adult mechanical ventilators have traditionally been pressure- or time-triggered. More recently, flow triggering has become available and some adult ventilators allow the choice between pressure or flow triggering. Prior studies have supported the superiority of flow triggering during continuous positive airway pressure, but few have compared pressure and flow triggering during pressure support ventilation (PSV). The purpose of this study was to compare pressure and flow triggering during PSV in adult mechanically ventilated patients. The study population consisted of 10 adult patients ventilated with a mechanical ventilator (Nellcor-Puritan-Bennett 7200ae) in the PSV mode. In random order, we compared pressure triggering of -0.5 H2O, pressure triggering -1 cm H2O, flow triggering of 5/2 L/min, and flow triggering 10/3 L/min. Pressure was measured for 5 min at the proximal endotracheal tube using a data acquisition rate of 100 Hz. From the airway pressure signal, trigger pressure (deltaP) was defined as the difference between positive end-expiratory pressure (PEEP) and the maximum negative deflection prior to onset of the triggered breath. Pressure-time product (PTP) was defined as the area produced by the pressure waveform below PEEP during onset of the triggered breath. Trigger time (deltaT) was defined as the time interval below PEEP during onset of the triggered breath. A pressure trigger of -0.5 cm H2O was significantly more sensitive than the other trigger methods for deltaP, PTP, and deltaT (p<0.001). There was also a significant difference between patients for deltaP, deltaT, and PTP for each trigger method (p<0.001). For this group of patients, flow triggering was not superior to pressure triggering at -0.5 cm H2O during PSV.

Comparison of Pressure Support Ventilation and Assist-Control Ventilation in the Treatment of Respiratory Failure

To assess whether pressure support ventilation (PSV) could be used as an alternative ventilatory mode to assist-control (A/C) ventilation in the treatment of respiratory failure. A short-term (4-h) prospective study in which the beneficial effect of PSV on respiratory mechanics, gas exchange, arterial oxygenation, cardiovascular hemodynamics, and oxygen consumption was compared with A/C ventilation. ICU of a community hospital. Forty-five patients (mean age, 62.8 [11.8] years) with respiratory failure secondary to COPD, restrictive disorders, or neuromuscular disease requiring mechanical ventilatory support in the ICU were selected for study. The mean duration of mechanical ventilation before the study was 7.16 (8.64) days. Patients were switched to the PSV mode of the mechanical ventilator for a period of 4 h after which conventional A/C ventilation was resumed. Patients supported with PSV compared with A/C ventilation showed significantly higher tidal volume, minute ventilation, and inspiratory time in association with significantly lower pressure in the airway and I:E ratio. With regard to gas exchange data, an increase in dead space/tidal volume ratio (VD/VT), decrease in PaO2, and statistically but not clinically significant alteration of arterial oxygenation indexes were noted. However, when patients with COPD, restrictive disorders, and neuromuscular disease were compared, significant changes in arterial oxygenation parameters were found only in patients with restrictive disorders. There were significant decreases in heart rate, systolic pulmonary artery pressure, and pulmonary capillary wedge pressure when PSV was applied. Oxygen transport and oxygen consumption were unchanged. PSV could be a possible alternative to A/C ventilation in patients with respiratory failure. PSV caused an increase in VD/VT in association with a significantly lower pressure in the airway and I:E ratio. Randomized studies are needed to define the long-term benefits of both respiratory modes and the conditions in which PSV may be a valuable alternative to A/C ventilation.

Estimation of Triggering Work of Breathing: The Dependence on Lung Mechanics and Bias Flow During Pressure Support Ventilation

Work of breathing necessary to trigger a ventilator (WOBtr) was calculated during pressure support ventilation (PSV), and the effect of bias flow on WOBtr was evaluated. A spring-loaded bellows type lung model with two bellows placed in series was used to simulate spontaneous breathing. A Venturi mechanism of jet flow generated subatmospheric pressure inside the diaphragm bellows simulated inspiratory effort. The lung compliance (CL) was set at 0.3 L/cm H2O or 0.05 L/cm H2O. The airway resistance (Raw) was set at 5, 20, or 50 cm H2O/L/s. Pressure support levels were increased from 0 to 45 cm H2O. Sensitivity was set at 2 cm H2O. No bias flow was used at first. The WOBtr was calculated using a pressure-volume (P-V) loop derived from the diaphragm bellows movement during the triggering period. We determined WOBtr and its dependence on the various pressure support (PS) levels, CL and Raw. To evaluate the effects of bias flow on WOBtr and triggering delay, a ventilator was put in the PSV mode, with various bias flow rates (from 0 to 20 L/min) at a sensitivity of 2 cm H2O. We found that when no bias flow was used, WOBtr increased with an increase in both Raw and end-expiratory lung bellows pressure which was considered as auto-PEEP. With bias flow, both triggering delay and WOBtr increased. An increase in bias flow at a given PS level resulted in both decreased pressure support time and tidal volume (VT). It is concluded that the bias flow system is not desirable for use during PSV.

Effect of body position on spontaneous respiratory rate and tidal volume in patients with obesity, abdominal distension and ascites

Nursing textbooks and tradition suggest that the high-Fowler's position is best to optimize diaphragmatic excursion and effective breathing pattern. The optimal position for intubated patients with obesity, ascites or abdominal distention has yet to be determined but is important because weaning trial outcomes may reflect the effect of position rather than weaning trial tolerance. To determine the body position that optimizes breathing pattern (tidal volume and respiratory rate) in spontaneously breathing, intubated patients with a large abdomen. Nineteen intubated patients with abdominal distention, ascites or obesity who were on continuous positive airway pressure or the pressure support ventilation mode were studied in the 0 degrees, 45 degrees, 90 degrees and reverse Trendelenburg's at 45 degrees positions for 5 minutes prior to data collection. The RT at 45 degrees position resulted in a significantly larger tidal volume and lower respiratory rate than the 90 degrees position in intubated, spontaneously breathing patients with a large abdomen. The 45 degrees position resulted in a significantly lower respiratory rate than at 90 degrees; however, no difference in tidal volume was demonstrated. A high respiratory rate and low tidal volume potentiates atelectasis and ultimately failure to wean. It is important that the effect of positioning on breathing pattern in intubated patients be determined so that care planning results in optimal outcomes. The results of this study have implications for the selection of chair and bed positioning during weaning trials.

Trigger sensitivity of Servo 300 (Siemens Elema) for pressure support ventilation in an infant

SummaryThe trigger sensitivity for pressure support ventilation (PSV) with a Servo 300 ventilator was evaluated in a 6‐month‐old male infant ventilated with synchronized intermittent mandatory ventilation (SIMV) of 14 c.min−1 and PSV of 4 cmH2O. The delay time between onset of inspiration and the trigger signal was 42 and 139 msec for trigger sensitivity of –2 and –4 cmH2O, respectively. On the former sensitivity, the inspiration was sensed by a decrease of expiratory bias flow before the airway pressure decreased to the set level. The time between the trigger signal and the flow delivery was 7 msec. The supplied volume exceeded the spontaneous breath on both trigger sensitivities. Using Servo 300, the constant expiratory bias flow, the use of a flow trigger and the mechanical improvement of the inspiratory valve contribute to reduced delay time in the trigger function, making the ventilator well suited, set in the PSV mode, even at high spontaneous respiratory rates for infants.

The Addition of Sighs During Pressure Support Ventilation: Is There a Benefit?

The purpose of this study was to determine if sigh breaths delivered during pressure support ventilation (PSV) were beneficial in maintaining arterial oxygenation (PaO2) and pulmonary mechanics. Ten patients being weaned from mechanical ventilation in the PSV mode were studied. All patients were ventilated for 4 h without sighs, 4 h with sighs, and again for 4 h without sighs. During each 4-h period, continuous measurements of ventilatory volumes and airway pressures were accomplished. At the end of each 4-h period, an arterial blood gas determination was obtained. There were no statistically significant differences in any of the measured variables during the different periods of ventilation. We conclude that the sigh breath is of no benefit during PSV. The purpose of this study was to determine if sigh breaths delivered during pressure support ventilation (PSV) were beneficial in maintaining arterial oxygenation (PaO2) and pulmonary mechanics. Ten patients being weaned from mechanical ventilation in the PSV mode were studied. All patients were ventilated for 4 h without sighs, 4 h with sighs, and again for 4 h without sighs. During each 4-h period, continuous measurements of ventilatory volumes and airway pressures were accomplished. At the end of each 4-h period, an arterial blood gas determination was obtained. There were no statistically significant differences in any of the measured variables during the different periods of ventilation. We conclude that the sigh breath is of no benefit during PSV.

A knowledge-based system for assisted ventilation of patients in intensive care units.

The procedure for weaning a patient with respiratory insufficiency from mechanical ventilation may be complex and requires expertise obtained by long clinical practice. We designed a knowledge-based system for the management of patients receiving respiratory support and implemented a weaning procedure. The system is intended for patients whose spontaneous respiratory activity is assisted by a Hamilton Veolar ventilator delivering a positive pressure plateau during inspiration (Pressure Support Ventilation mode). Our closed-loop real-time system running on a Personal Computer continuously adapts the assistance provided by the ventilator to the patient's evolution, and indicates when the patient can be withdrawn from the ventilator. Three parameters are used to appreciate the 'respiratory comfort' of the patient: breathing frequency, which we consider the most informative index, tidal volume and end-tidal CO2 pressure. A preliminary study of 19 patients was performed to evaluate the ability of our system to adapt the assistance to the patient's needs, with the main objective of facilitating weaning by gradually lowering the level of assistance. In 10 of these patients, considered as good candidates for weaning on the strength of objective criteria, the system maintained the breathing pattern in a zone of comfort for 95% of the period of assisted ventilation and stated that they were 'weanable'. This was consistent with the clinical evolution of all 10 patients. These results show that such a system can provide effective management for mechanically ventilated patients.

Comparison of Inspiratory Work of Breathing in T-Piece Breathing, PSV, and Pleural Pressure Support Ventilation (PPSV)

We have compared the inspiratory work of breathing during T-piece breathing, pressure support ventilation (PSV), and pleural pressure support ventilation (PPSV) by using a lung model with variable compliance and resistance, under simulated spontaneous breathing. Our lung model consists of two spring-loaded bellows, representing the lung and diaphragm, placed in an airtight container. Inspiration begins with the withdrawal of air from the diaphragm bellows by a time-cycled jet-flow-creating Venturi mechanism. Expiration occurs by opening the diaphragm bellows to the atmosphere. Work of breathing (WOB) is calculated by plotting the pressure-volume curve, with pressure corresponding to intrabox pressure and volume corresponding to the tidal volume; PPSV is a new mode of mechanical ventilatory support accomplished by setting the ventilator (Servo 900C) into the PSV mode with a level of 0 cm H2O, using the pleural pressure as the input and target signal. The PPSV maximally reduces WOB under any circumstances. The PSV sufficiently reduced WOB only in the normal lung and the lung with low compliance; however, a pressure supporting time is diminished in the lung with low compliance. The serious limitations of PSV remain in its application to the lung with high resistance. It is concluded that PPSV is closer to the actual patient's signal and has a potential advantage in reducing WOB in the lung with low compliance or high resistance (or both). The lung with flow limitation is still a challenging issue for mechanical ventilatory assistance.