Waveform of the week: Drive pressure too low

Driving pressure or set pressure during mechanical ventilation utilizing a pressure targeted mode (PC-CMV, PC-IMV, PC-CSV) may be inadequate for patients' inspiratory flow demands. 

A peak pressure of 15 to 20 cmH2O is generally needed to provide significant support if the goal is to off-load work of breathing and/or resting the patient.

By evaluating the flow waveform the operator can identify a appropriate pressure setting to meet patients inspiratory efforts. The flow waveform should have a constant linear deceleration for the inspiratory phase & a   constant acceleration to baseline during the expiratory phase. 

During the inspiratory phase once flow starts to decelerate it should not rise again. If the flow rises again this is a sign of an increased respiratory drive & that the pressure setting is too low. The below picture provides a example of both a normal flow waveform pattern & the dis-synchrony related to a high respiratory drive. 

Inadequate driving/set pressure during PC-CMV as evidence by 'camel backing' flow rising after  deceleration.

RELATED POST

What the heck is P0.1?

Obtaining P0.1 on various ventilators. 

A Quick & Easy Way to Set "T-Low" During Airway Pressure Release Ventilation

A quick & easy way to initially set "T-Low" during Airway Pressure Release Ventilation is to use the "Expiratory Time Constant (RCexp)". The RCexp indicates alveolar emptying time and it takes at least 4 time constants for adequate alveolar emptying (~99%).

References state set T-Low to obtain a "Peak Expiratory Flow Rate Termination Point (T-PEFR)" at 50 to 75% of the measured "Peak Expiratory Flow Rate"

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+

How to Save $200,000.00 in Anesthetic Agent

Due to the current health care reform legislation many hospitals are implementing recommendations from the "Institute for Health care Improvement" in  regards to reducing or eliminating wasted time, money, and energy in health care.
One area to eliminate waste and to increase savings is focusing on anesthetic agent use during general anesthesia procedures.

Apneic Oxygenation Diffusion to Determine Apnea: Is it Safe?

The apnea test is a component in the determination of brain death. One technique used to evaluate the absence of breathing drive is to perform the "Apneic Oxygenation Diffusion Technique" also know as a "CO2 Challenge". In 1995 the American Academy of Neurology published prerequisites and parameters to perform this clinical assessment[1].

In his recent journal article "A Critique of the Apneic Oxygenation Test for the Diagnosis of Brain Death"[2], Dr. James Tibballs provides a strong argument against the utility and questions the safety of the apnea test.

The author proposes four areas of concern to fortify his disagreement:

1. The reliability of apnea with a rise in PaCO2 as a neurological diagnostic of brain death.
2. The potential for injury due to the unpredictable rise in PaCO2.
3. The large amount of variability, in regards to performance of the technique.
4. There are other tests which can be performed, which are superior. 

TRENDS ASSOCIATED WITH FAILED WEANING INDICES

This Abstract was originally presented at the AARC 2007 Open Forum

Background:
The Successful wean & extubation of ventilated patients decreases hospital length of stay and reduces morbidity and mortality. One tool utilized to facilitate this process is “wean predictors” incorporated into RCP driven protocols to determine whether a patient may advance to a spontaneous breathing trial (SBT).
Hypothesis: Patients are less probable to be placed on a SBT due to weaning predictors that are not within the RCP’s scope of practice vs. predictors, which can be manipulated/controlled, by the RCP.
Design: Single center, nonrandomized, prospective, convenience cohort.
Setting- 18 bed general ICU. Patients- 91 adult patients requiring mechanical ventilation > 24 hours, admitted to the ICU between June 2006 and March 2007.

Adaptive Pressure Control Ventilation during Anesthesia: A False sense of Security

Adaptive pressure control (APC) is a ventilator modality which has been applied safely in intensive care units for greater than a decade. The mode delivers a pressure control breath that maintains a target tidal volume (Vt) at the lowest possible pressure, independently of changes in pulmonary mechanics.

Within the last few years in the United States ventilator manufactures have made this mode available on their newer generation anesthesia machines. Manufactures highly recommend APC during surgical procedures in which positioning or insufflation of the abdomen creates dramatic changes in pulmonary mechanics (e.g. laparoscopic, thoroscopic, prostatectomy).

Why is my Measured Peak & Plateau Pressures the Same?

Why are my measured peak & plateau pressures the same? Is this something to do with the ventilator, or the patient? Can this be right?

Application of Mid-Frequency Ventilation

Overview

My facility is a Long-term Acute Care Hospital licensed for 42 beds, which specializes in ventilator weaning and wound care management. In regards to ventilator weaning our patients primarily arrive from outlying intensive care units and been on mechanical ventilation for greater than seven days.
Our allotted hospital length of stay for patients „coded. for “Ventilator weaning” is twenty-five days. During this time period patients are either weaned from mechanical ventilation or placed for extended long-term care. December 2009 ventilator days were a mean of 6.5 days per patient (7 samples/patients), and when calculated for outliers to 3 standard deviations the mean decreased to 5.4 days (5 samples).
There are respiratory therapy driven ventilator guidelines which include ventilator management and ventilator weaning. The only ventilator we utilize is the Respironics Esprit which has been fine in our patient population, however, it has been cumbersome in patients which require additional respiratory mechanic measurements e.g. static compliance & resistance (in the Esprit you can only obtain these measurements in VC-CMV). “I guess I’m spoiled not having to calculate these parameters with other machines”. However, it is nice to polish my calculation skills ever so often.
Our standard modalities for ventilator management are PC-CMV and PC-CSV.

In the News -CMS Finalizes Inpatient Hospital Rules

The Centers for Medicare & Medicaid are proposing to change regulations which would allow Physician Assistants and Nurse Practitioners’ to write orders for Respiratory Care Services without a co-signature from a physician.

I believe this is an area of concern since respiratory care services specifically ventilator management is highly specialized. Additionally, there is no formal training regarding ventilator management in PA or NP programs, as a minimum pulmonary physicians have to train as fellow.
The below case study submitted from a colleague will articulate my point of view.

Flow Mismatch: Patient Ventilator Asynchrony Associated With Volume Ventilation

From post surgical patients to patients with ARDS volume ventilation (VC-CMV or VC-IMV) remains a very popular modality. Traditional volume ventilation is easy to use and comprehend, extensively available on numerous ventilators, and is able to provide adequate gas exchange by presetting minute ventilation. Additionally, VC-CMV is the most common mode used to ventilate patients with ARDS[i], due to fact that the operator may limit the delivered tidal volume thus insuring a low tidal volume strategy.