UTILIZATION OF PROPORTIONAL ASSIST VENTILATION FOR PATIENTS WHO FAIL A SPONTANEOUS BREATHING TRIAL

Background
Unloading ventilatory muscles has been a primary issue with our ventilator population. After analyzing ninety samples, it was revealed that 81% of the failed spontaneous breathing trials (SBT) were related to rapid, shallow breathing. Our original process for resting patients who have failed a SBT was to ventilate the patient utilizing “Volume Control Ventilation plus” (VCV+). One disadvantage of using an assisted mode for resting patients is the inability to properly set the ventilator to provide adequate rest without over resting the ventilatory muscles. Another disadvantage is patient/ventilator asynchrony, which may occur at any phase of breath delivery. A study of “Proportional Assist Ventilation” (PAV) was initiated to explore potential advantages over VCV+.

The Problem with Adaptive Pressure Control Modes of Ventilation: a Case Study.

Introduction

Adaptive Pressure Control (APC) is a ventilator modality, which has been applied safely in ICU’s for greater than a decade.The mode delivers a pressure control breath that maintains a ‘target’ operator selected tidal volume (Vt) at the lowest possible pressure independently of changes in pulmonary mechanics (1).

APC is a very popular mode and readily available on various ventilators (fig. 1). What has made this mode so popular is that the practitioner can set a Vt & the flow is variable.

EFFECT OF THE RAPID RESPONSE TEAM ON RESPIRATORY AND CARDIOPULMONARY ARRESTS WITHIN NON-CRITICAL CARE UNITS

Background: Rapid Response Teams (RRT) are groups of healthcare practitioners who respond to acutely-deteriorated hospitalized patients. Various studies have shown that RRT’s may improve patient outcomes. Additionally, the Institute for Healthcare Improvement recommends the implementation of RRT’s as one of their initiatives to improve patient safety outcomes. 

Objective: We implemented an RRT (An Internal Medicine Physician, Registered Respiratory Therapist, Critical Care Registered Nurse and Nursing Supervisor) at Sentara Careplex Hospital in 2005 specifically to reduce the monthly rate of respiratory and cardiopulmonary arrests (codes) external to the intensive care units.

Design: Single center, non-randomized, prospective chart review.

Setting: 199 bed community hospital.

Interventions - The records of patients who required cardiopulmonary resuscitation external to the intensive care areas were reviewed before RRT implementation to determine activation criteria for the RRT. Codes were defined as respiratory or cardiopulmonary arrest. The incidence of these non-ICU codes before and after RRT implementation was recorded. The one-way analysis of variance (ANOVA) was used for statistical testing of differences between years 2004 (pre RRT implementation), 2005, 2006, and 2007. A p value < 0.05 was considered statistically significant.

Results: Previous to RRT implementation, the non-ICU code rate averaged 5.33 events per month. After implementation, the mean non-ICU code rate decreased by an average of 21%. Conversely, when testing for significant differences between pre & post RRT implementation, there were no statistical differences among the four years (p-value 0.15).

Conclusion: Although our facility met its goal by decreasing the non-ICU code rate by 10%, there was no significant statistical difference pre & post RRT implementation. The cost of intensive care unit length of stay and unplanned ICU admissions is of great relevance. Additionally, patient-centered outcomes such as health-related quality of life and hospital mortality rates must be addressed. 

THE AFFECT OF IN-LINE MEDICATION DELIVERY IN REGARDS TO PATIENT-VENTILATOR TRIGGER SYNCHRONY.

Background

Patients on mechanical ventilation may receive medications delivered via aerosol in-line with the patient-ventilator circuit. Some ventilators are not outfitted with a nebulizer port which propels the aerosolized medication and compensates for the additional added
flow. Consequently, an external flow source must be used to drive the nebulizer. Hypothesis- Utilizing an external flow source to deliver aerosolized medications will affect patient-ventilator trigger synchrony.

THE APPLICATION OF PROPORTIONAL ASSIST VENTILATION IN A PATIENT WITH DECOMPENSATED CONGESTIVE HEART FAILURE

Introduction

In patients who failed wean criteria, our standard of ventilator management utilized PC-CMV. However, it is well-known that positive pressure ventilation can profoundly alter cardiovascular function.

Admitted to our ICU was an 85 y/o male with an extensive cardiac history significant for Sick Sinus Syndrome, Paroxysmal Atrial Fibrillation, and Atherosclerotic Coronary Artery Disease, with an estimated Left Ventricular ejection fraction of 25%. The patient’s surgical history was significant for pacemaker placement and percutaneous coronary intervention. On ventilator day 3, the patient’s ventilator mode was changed from PC-CMV to Proportional Assist Ventilation (PAV) to allow for unhindered spontaneous breathing in an effort to increase cardiac output (C.O.)/index (C.I.).

Case Summary

The patient was intubated due to hypoxic ventilatory failure secondary to decompensated congestive heart failure. Immediately following the application of mechanical ventilation, the hypoxemia was reversed, yet the cardiac instability persisted and prevented the patient from progressing to spontaneous breathing trials. Initial ventilator settings were PC-CMV, Vt 450, RR 14, FiO2 30%, & PEEP of 5. Respiratory and hemodynamic measurements were obtained before switching the mode to PAV, 80% support, FiO2 30%, & PEEP of 5 and the patient was allowed one hour to stabilize after modality change before obtaining an additional set of parameters. Pharmacological agents included a Dobutamine infusion @ 4mcg/min and a Propofol infusion @ 5cc/hr. No pharmacological changes were completed during data collection or alternating between ventilator modes.

 Our patient’s initial C.O. on PC-CMV was 3.06 L/Min with a C.I. of 1.56 L/Min/M2. Upon conversion to PAV, the patient’s C.O. & C.I. increased by ~27% while the PaO2 increased by ~17% (Table 1). After observing hemodynamic improvement with PAV, the patient was maintained on PAV and the Propofol infusion was rapidly terminated. On ventilator day six, the Dobutamine infusion was discontinued and the patient was extubated without complication.

Discussion

 In our patient PAV produced a higher C.O. & C.I. over PC-CMV which is similar to the results Kondili documented when comparing PAV to pressure-support ventilation. Conversely, spontaneous variability of C.O. should be considered when evaluating two measurements taken at separate times. Sasse revealed that variability of C.O. may differ as much as 10%.  




1. Proportional Assist Ventilation: Guidelines for Using PAV+