Volume-Control to Pressure Control

Image 1: The Settings of VC-CMV. The settings highlighted in yellow are associated with patient-ventilator asynchrony. 

VC-CMV is likely the most utilized mode of mechanical ventilation. This is due to a few a reasons:

     1. VC-CMV is a standard mode on almost every intensive care ventilator (table 1).

     2. VC-CMV is one of the first modes of mechanical ventilation.

     3. VC-CMV is easy to understand in both theory and operation.

     4. VC-CMV is the standard of care when ventilating patients with Acute Respiratory Distress

          Syndrome (ARDS) and Acute Lung Injury (ALI).

Frustrated with Medical Therapy Options? Design Your Own.

Image 1: Modeled Aorta. 

Tal Goleworthy  frustrated with his options for conventional treatment of a dilated aorta decided to design his own therapy. 

Minimal Fresh Gas Flow: "A Reassuringly Safe Anesthetic Technique".

Image 1: Minimal FGF on the FLOW-i anesthesia delivery system

In this months Canadian Journal of Anesthesia authors of the article "Brief Review: Theory and Practice of Minimal Fresh Gas Flow Anesthesia", conclude that with newer anesthesia delivery systems that using minimal fresh gas flow and third generation of inhaled anesthetic agents is a safe technique with many benefits [1]. 

The authors review advantages, potential limitations, and safety considerations when utilizing minimal fresh gas flow technique (mFGF). 

Setting PEEP

There is many ways to set Positive End Expiratory Pressure (PEEP). Setting PEEP too low may result in under or tidal recruitment of the lung and PEEP that is too high results in over-distention, both contribute to Ventilator Induced Lung Injury (VILI).  This post provides a synopsis of the various techniques as well as potential pros & cons.

Vent Graphics Contest WINNERS

First, I would like to thank all my readers who entered the "Vent Graphics Contest" , I appreciate all of the efforts.

First Prize

John Priest

Equipment Used: Epiphan 

Image 1 & 2: Preventing auto-triggering.

NAVA vs. Pressure Support in Pediatric Patients

Pressure Support Ventilation can be  associated with 8 types of patient ventilator asynchronies. 

Overview

The researchers sought to determine if neurally adjusted ventilatory assist (NAVA) enhances asynchrony, ventilatory drive, breath-to-breath variability and COMFORT score when compared to pressure support (PS).  Twelve pediatric patients with asynchrony (auto-triggering, double triggering or non-triggered breaths) were enrolled in a non-randomized short-term cross-over trial.  Four sequential 10-min periods of data were recorded after 20 min of ventilatory stabilization (wash-out) at pre-determined settings.

Results

The median asynchrony index was notably lower during NAVA than during 2-PS(opt) and 4-PS(opt). In NAVA mode, the NAVA trigger accounted for approximately 66% of triggered breaths. The median trigger delay with respect to neural inspiratory time was considerably lower during NAVA than during 2-PS(opt) and 4-PS(opt). The median electrical activity of the diaphragm (EAdi) change during trigger delay normalized to maximum inspiratory. EAdi difference was notably lower during NAVA than during 2-PS(opt) and 4-PS(opt).  Additionally, NAVA produced a significantly higher coefficient of variation of tidal volume than 2-PS(opt) and 4-PS(opt). The median comfort score during NAVA was lower than that during 2-PS(opt) and 4-PS(opt).

Conclusion

This research shows that NAVA results in improved synchrony, reduced ventilatory drive, increased breath-to-breath mechanical variability and improved patient comfort compared to optimized PS.

Reference

De le Olivia, P., Schuffelmann, C., Gomez-Zamora, A., & Kacmarek, R. M., (2012). Asynchrony, neural drive, ventilatory variability and COMFORT: NAVA versus pressure support in pediatric patients. A non-randomized cross-over trial. Intensive Care Medicine, 38(5), 838-846.

Capture the Flag: Vent Graphics Contest

http://www.youtube.com/user/devinsupertramp

I have many people ask how I create and capture videos of ventilator waveforms. In this post I will describe  my techniques and introduce a ventilator screen capture contest for my new book Ventilator Graphics: Identifying Patient Ventilator Asynchrony & Optimizing Settings (2nd Ed).

Here are the contest prizes:

1. iTunes gift card ($50), free copy of the new book ($9.99), your screen shot will be used in the new book.
2. iTunes gift card ($25) free copy of the new book ($9.99), your screen shot will be used in the new book.
3. iTunes gift card ($10) free copy of the new book ($9.99), your screen shot will be used in the new book.

Why Aren't Your Patients Weaning? Don't Blame Nursing

http://respiratorytherapycave.blogspot.com/

The successful weaning and 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).

In a previous post [1] I mentioned that the level of sedation was the foremost reason why patients did not progress to a spontaneous breathing trial with a prevalence of 48%. 

This is concerning since it is a standard of care to provide ventilator patients with a daily "sedation vacation" or a interruption or decrease in sedation to assess neurological status and wean readiness.

This poses many questions:

ECLS for Patient Ventilator Synchrony?

Extracorporeal Cardiopulmonary Life Support. Image from MAQUET 

Introduction

Promoting patient  safety and comfort are two main goals when utilizing mechanical ventilation. In patients with severe lung failure maintaining both lung protective goals and patient comfort is a difficult task. One can provide safety by minimizing the set tidal volume to 4-6 ml/kg/IDBW however this leads to flow asynchronies in the patient who has a high inspiratory drive. One can utilize pressure control ventilation to prevent these flow asynchronies conversely this most likely results in tidal volumes greater than lung protective goals. In these patients it is very difficult to balance these two goals of mechanical ventilation and patient comfort is usually sacrificed, or is  accomplished with high levels of sedation and sometimes neuromuscluar blocking agents. 

Increasing sedation and administering neuromuscular blocking agents increases the risk for ventilator induced diaphragmatic dysfunction (VIDD), increased length of stay, and mortality. So it would be ideal to allow for both lung protection and patient comfort (ventilator synchrony) with minimal sedation use.

In the below summarized abstract [1] researchers couple Extracorporeal Cardiopulmonary Life Support (ECLS) with Neurally Adjusted Ventilatory (NAVA) Assist to balance lung protection and patient comfort with little sedation use. 

The Importance of Identifying Patient Ventilator Asynchrony

There are many factors that increase the risks for prolonged mechanical ventilation (PMV). So It is imperative that the practitioner is able to identify factors that they can proactively emend.

One factor associated with PMV is inappropriate ventilator settings. The below abstract reinforces how ventilator asynchrony increases the likelihood of  PMV. 

Electrolyte Imbalances During Mechanical Ventilation

Numerous factors contribute to ventilator dependence. However, one should focus on identifying factors that are potentially reversible. Electrolyte imbalances have a direct relationship to weaning from mechanical ventilation. 

Below is a summary of different electrolytes and how their imbalances may prolong mechanical ventilation. 

Inhaled Nitric Oxide Set-up for Cardiac Surgery

Another use for inhaled nitric oxide is for lowering pulmonary vascular resistance during cardiothoracic surgery. Administration is common during mitral valve replacements, heart transplants, and implantation of left ventricular assist devices.   

One concern is interfacing the INOVent with the anesthesia machine, primarily preventing "Nitric Dioxide" build up.

Here are the steps to interface the INOVent with the anesthesia machine:

The Worst Modes of Mechanical Ventilation

IMV one of the worst ventilator modes in regards to patient comfort. 

Many will argue the best mode of mechanical ventilation and prefer the mode that is most commonly used in their patient populations. Strict believers of the ARDS net protocol will favor VC-CMV to ensure lower tidal volume delivery. Pediatric centers will insist on Pressure targeted modes to limit high pressures, and trauma centers may favor biphasic modes of ventilation to obtain higher mean airway pressures.

However, some institutions use the worst modes of ventilation that directly impede on patient comfort. Promoting patient comfort is one of the main goals of mechanical ventilation [1] and not providing comfort may lead to over sedation, over ventilation, ventilator induced diaphragmatic dysfunction, and increased length of stay.

So what are the worst modes of ventilation specifically in regards to patient comfort?

Inhaled Nitric Oxide Set-up for Nitric Oxide Challenge

One off label use of inhaled nitric oxide is to use it to see if a patients pulmonary hypertension is responsive to vasodilator therapy. 

Due to inhaled nitric oxides quick onset and extremely short half life the "nitric oxide challenge" can be performed safely and efficiently in a cardiac cath lab.  

There are a few standard protocols which I will not go over, however I will go over device and patient interface setup for performing a nitric oxide challenge. 

Quantifying Patient Ventilator Asynchrony

SERVO-i Ventilator screen. Using NAVA monitoring & captured screen shots to quantify patient ventilator asynchrony.

Patient ventilator asynchrony is present in the majority of ventilated patients [1].

One of the most difficult components of patient ventilator assessment is actually recognizing asynchrony. Authors of the following study “Efficacy of ventilator waveforms observation in detecting patient–ventilator asynchrony” ‘[2] demonstrate how challenging identifying asynchrony is, even for the seasoned physician.

CPT Sham

Why do we keep on performing Chest Physical Therapy?


This recent Cochrane Database review reinforces that CPT does not improve outcomes [1]. 

Overview

This is a further update of the original Cochrane review published in 2005 and updated in 2007. Acute bronchiolitis is the leading cause of medical emergencies during winter in children younger than two years of age. The main objective of the study was to determine the efficacy of chest physiotherapy in infants aged less than 24 months old with acute bronchiolitis. A secondary objective was to determine the efficacy of different techniques of chest physiotherapy. The researchers searched various past studies including the Cochrane Central Register of Controlled Trials (CENTRAL) which contains the Cochrane Acute Respiratory Infections Group's Specialized Register.  Selection included randomized controlled trials (RCTs) in which chest physiotherapy were compared against no intervention or against another type of physiotherapy in bronchiolitis patients younger than 24 months of age. Finally, two review authors independently extracted data. The primary outcomes included respiratory parameters and improvement in severity of disease. The secondary outcomes included length of hospital stay, duration of oxygen supplementation and the use of bronchodilators and steroids. No pooling of data was possible.

The Minimal SSI Strategy

 

Stress Index (Si) Displayed on the SERVO-i Ventilator. 

In 2009 Brunner & Wysocki proposed that there is an optimal breathing pattern to minimize stress & strain during mechanical ventilation [1]. Stress and strain are primary causes of ventilator induced lung injury (VILI), so it would be imperative to provide a breathing pattern which decreases the chances of VILI. 

Proportional Assist Ventilation: Guidelines & standards for using PAV™*+

Now Available on Kindle

Universal Anesthesia Machine

"It's a Nail"



“Spoils of War” by Andy Ihnatko 2009.

 A colleague of mine described a presentation she attended today in which the speaker was describing the usefulness of the “Dynamic Lung” and how there was no use for those squiggly little lines (referring to ventilators waveforms).

Is this guy serious?

900 ML are you Serious?

Puffer Fish, by Karen Garrett de luna

Free Bronchoscopy Simulator

Free Bronchoscopy Simulator

http://www.thoracic-anesthesia.com/

APRV in the Operating Room is it Practical?

Airway Pressure Release Ventilation in the Operating Room is it Practical?
This is a good question, for one anesthesia delivery systems do not have APRV as a mode of ventilation available, so an ICU ventilator will need to be transported with the patient to the operating room.
Other considerations include:
-General anesthesia
-Hypo-ventilation
-Hypoxia

For more view the attached video

A Unique Way to Obtain the NIF



Using the trigger setting to quantify extubation readiness. Notice the measured PEEP value & set PEEP value, the patient is able to generate a NIF < -18 cmH2O.

There are multiple ways to obtain the Negative Inspiratory Force (NIF) NIP (negative inspiratory pressure), or MIP (maximal inspiratory pressure) measurement. The NIF “corresponds to the negative pressure generated by the inspiratory muscles during a maximal inspiratory effort, performed during temporary occlusion of the airway opening” [1]. This parameter is used to quantify that the respiratory drive is sufficient (paralytics, narcotics, sedation is worn off after general anesthesia) or that there is no respiratory muscle fatigue or exhaustion.

Waveform of the Week: “Golden Moment”

Image 1: Screen of the FLOWi anesthesia delivery system, showing the "Golden Moment" highlighted with blue circle.

It has been over a year since writing a waveform of the week post; however I have incorporated ventilator waveform pictures in recent posts. The waveform for this week is termed the “Golden Moment”

Decreasing Dyspnea during Mechanical Ventilation

Flow Mismatch Associated with VC-CMV

Utilizing Volume Control-Continuous Mandatory Ventilation (VC-CMV) may lead to patient ventilator asynchrony [1] and dyspnea. The main reason for these issues is the fixed (constant) flow rate associated with VC-CMV.

Automatic Setting of T-Low during Airway Pressure Release Ventilation: Is it Beneficial?

http://www.draeger.com/UK/en/products/medical_ventilation/adult_icu_ventilation/rsp_evita_infinity_v500_sw2.jsp

Setting T-Low during APRV (a.k.a. Bi-Level, Bi-Vent) can be confusing and time consuming, to make it even more complicated there are three published techniques on how to set T-Low [1].

One method is setting T-Low based on the measured peak expiratory flow rate [2, 3]. The new Draeger Evita Infinity V500 ventilator allows the operator to set an “Auto-release” based on zero (0)-to- 80% of the Peak expiratory flow. This feature is nice since the operator does not have to continually assess the waveform &titrate the T-Low setting.

Conversely, this may be the least effective way to set T-Low in regards to lung protective goals, due to the inconsistent exhaled tidal volumes & auto-PEEP created with this technique [4].

Reference

[1]. Siddiqul,M. et.al.(2010). Comparison of Three Methods to Set T-Low on Airway Pressure Release Ventilation: A Model Study. Respiratory Care. 2010

[2]. Richey, S. (2009). Optimal T-Low Settings.

http://kscottrichey.blogspot.com/2009/03/optimal-t-low-settings.html

[3]. Richey, S. (2010). A Quick & Easy Way to Set T-Low During Airway Pressure Ventilation. http://kscottrichey.blogspot.com/2010/12/quick-precise-way-to-set-t-low-during.html

[4]. Richey, S. (2011). Setting T-Low During Airway Pressure Release Ventilation to Achieve Lung Protective Goals. http://kscottrichey.blogspot.com/2011/08/setting-t-low-during-airway-pressure.html

Change Your Ventilator Management



In last months article “Effects of Implementing Adaptive Support Ventilation in a Medical Intensive Care Unit” in the Respiratory Care Journal [1], Chew & colleagues discovered that ASV provided a quicker time to extubation readiness then their standard ventilation protocol.

These results are not surprising, especially after reviewing their standard way of managing ventilator patients. This study was a poor comparison of practitioner guided ventilator management versus an automated ventilator mode.

Let’s compare & contrast the differences in the ASV study group versus the traditional ventilator management there are three (3) main areas to investigate.

Setting T-Low during Airway Pressure Release Ventilation to Achieve Lung Protection Goals

Setting a T-Low based on a 50-75% PEFR may contribute to excessive exhaled tidal volumes

There are three published techniques to set T-Low when utilizing Airway Pressure Release Ventilation (APRV) or mimicking (BiVent, BiLevel) the application.

They include:

Adaptive Support Ventilation: Set it & forget it?

http://blog.poplabs.com/2008/07/set-it-and-forget-it-why-roncos-showtime-rotisserie-cant-run-your-marketing-campaign/

I once mentioned in a previous posting (Adaptive Support Ventilation: the Pareto Principle of Mechanical Ventilation) that “ASV requires little operator input and provides substantial benefits”. However this does not mean “set it & forget”, a phrase I  over-heard from an ASV in-service.

 This is not a Ronco Rotisserie Oven ® this is a mechanical ventilator and the operator needs to be engaged and assess patient-ventilator interaction.

Here are some areas of focus:

Switching from Pressure Control to Volume Control Ventilation

During patient ventilator transports one may have to switch from pressure control (PC-CMV) to volume control (VC-CMV) ventilation, because the available transport ventilator does not have PC-CMV. Another reason is the operator is unfamiliar with PC-CMV.

Here are the steps and additional considerations to safely switch the patient over.

Obtaining Pulmonary mechanics with the PB840 Ventilator

In my opinion I believe the PB840 ventilator is an outdated platform. One thing that frustrates me is that additional functions/features cost the purchaser extra, where on most ventilators these functions are standard.

Examples:

-Trending

-P0.1

-No low flow lung mechanics tool.

The only thing I believe is useful is Proportional Assist Plus, however this is still a software upgrade charge.

Another frustration when using the PB840 is obtaining pulmonary mechanics measurements correctly.

When properly obtaining these measurements one has to place the patient in VC-CMV (volume controlled ventilation) and perform an additional three steps.

Here are the steps:

1. Place the patient in VC mode (if the patient is in another mode)

2. Change the flow waveform setting to a Square (constant) flow waveform pattern.

3. Change the flow setting value to obtain a I-time which matches the previous set I-time.

4. Perform an inspiratory pause, by pressing the inspiratory pause button (insp pause)

Capnography the Importance of Perfusion

Capnography/ETCO2 monitoring (ETCO2) has been used for many years in the operating room to confirm endo-tracheal tube placement and to evaluate the patient’s ventilatory status. Since the technology has become more portable and affordable, it has migrated to intensive care units, emergency rooms, ambulances, and even step down units. Due to this prevalence Capnography/End-tidal carbon dioxide monitoring is becoming the “fifth” vital sign [1].

Sun Glasses at Night?

http://en.wikipedia.org/wiki/Sunglasses_at_Night


In his 1984 single “Sunglasses at Night” singer Corey Hart sings about wearing his sun glasses to watch his lover, as she lies and cheats on him or this is what I think the lyrics mean? I’m not one to decipher song lyrics; I just thought it was a pretty catchy tune when it was first released. Wearing sun glasses at night seems pretty idiotic, but what about night shift workers wearing sun glasses?


 

4 Reasons Not to Use APRV

Over Inflated

Airway Pressure Release Ventilation is a modality of ventilation that has been in use for greater than 20 years. Some practitioners' believe APRV is the panacea of mechanical ventilation and utilize the mode on every ventilated patient. Before initiating APRV one should consider 4 arguments against its use.

Performing a T-Piece Trial with the Ventilator

Utilizing the Pressure/Volume Loop to determine the appropriate pressure support level during  a simulated T-piece trial.

Many institutions perform spontaneous breathing trials with the ventilator using a small amount of PEEP (~ 5 cmH2O) and automatic tube compensation or a small amount of pressure support (~ 5 to 10 cmH2O). However, occasionally a traditional T-Piece trial may prove to be more beneficial [1].

Utilizing pressure support during a spontaneous breathing trial to off-set the work of breathing related to the artificial airway may lead to false positives, due to over compensation.

Why is this?

Ventilator Graphics: Identifying Patient Ventilator Asynchrony and Optimizing Settings

NOW AVAILABLE on Kindle

SmartCare PS: Concerns with Delayed Cycling

SmartCare/PS® or SmartCare Pressure support (™ Draeger Medical, Telford, PA) is the only automated weaning ventilator mode in the United States that relies entirely on a rule-based expert system[1]. Automated modes may be useful however; the operator needs to realize the limitations before utilizing the mode in all patient populations.

Smartcare is a spontaneous mode of ventilation (CSV), which uses pressure support to augment the inspiratory efforts. The operator is allowed to change the pressurization rate (rise time), however has no control of the “Expiratory Cycling Threshold” which is one of the determinates of how a pressure support breath ends.

A Review of Pressure Support Termination

The Utilization of Mid-Frequency Ventilation with a Sophisticated Transport Ventilator: a Case Study

Background




Mid-Frequency Ventilation was first described in the medical literature by Mireles-Cabodevila & Chatburn in 2008 [1]. The authors describe Mid-Frequency Ventilation (MFV) as setting ventilator frequencies greater than 35 cycles per minute, during Pressure Control-Continuous Mandatory Ventilation (PC-CMV) to provide increased minute ventilation support in patients with severe Acute Respiratory Distress Syndrome (ARDS). In this initial article the authors tested their theory on both a computer simulation model and bench study using newer generation conventional intensive care unit ventilators. Both test simulations where successful.


In 2010 Mireles-Cabodevila & al. applied the theory in a live neonatal & pediatric animal model; the results reinforced the previous hypothesis showing the potential benefits of MFV [2].


As of to date there have been no cases reported in the medical literature of MFV being applied in humans. I previously presented a case where MFV was applied for a patient with serve hypercapnia; however this was never submitted for publication [3].


The following case involves using MFV on a sophisticated transport ventilator, thus reinforcing the versatility of MFV. The operator does not need a special ventilator (e.g. oscillator) or mode (e.g. APRV). Even though one does not need a specific ventilator the device still needs to safely and effectively ventilate injured lungs. The transport ventilator used during this case is considered a “sophisticated” transport ventilator, one that can effectively ventilate injured lungs [4].

Chest Physical Therapy Catastrophes

http://respiratorytherapycave.blogspot.com/

Background

Chest Physical Therapy (CPT) is ordered at many institutions for numerous conditions, from patients with chronic respiratory conditions-to-Acute Respiratory Distress Syndrome. The main goal of these therapies is to augment secretion mobilization & airway clearance[1]. Even though CPT is ordered liberally it does have associated risks and there is no supporting evidence that CPT is more valuable than a direct cough (Schans, 2007). At one institution I work at there have been 4 adverse events related to CPT in a short six month time span. I previously described two of the incidences on the same patient in the posting “Shook to Death: a Case Study of High-Frequency Chest Wall Compression”. The other two cases will be presented.

Case 1

An 83 year old patient whose initial compliant was for abdominal pain and nausea and vomiting. The patient was ordered CPT via Vest every four hours for unknown reasons (probably because the physician observed COPD in then dictated medical history). The patient’s pre-existing medical history included COPD, atrial fibulation, and left lung resection.  CPT was initiated and the patient immediately went into atrial fib, the therapy was stopped to make sure the vibrations did not cause an inappropriate reading of the ECG. The A-fib remained present after stopping the CPT and the patient had to be medically treated for her symptoms. Thus increasing her ICU observation period.

Case 2

A 60 year old female patient admitted for respiratory distress was ordered CPT via percussion secondary to a left lower lobe infiltrate. The patients pre-existing medical history included cardiomyopathy, diabetes, hypertension, chronic renal insufficiency.

During the CPT procedure the patient experienced cardiopulmonary arrest, secondary to mucus plugging. The patient was resuscitated, placed on mechanical ventilation, and bronchoscopy was performed the following day. The patient had a lengthy intensive care unit stay and was eventually discharged.

Summary

CPT is a commonly prescribed therapy, with little evidence of success. Practitioners’ should be aware of the risk factors associated CPT and screen patients appropriately for their ability to clear the mobilized secretions. Always, consider if there is a rational for CPT and which therapy is likely to provide the greatest benefit with the least amount of harm.

---

[1] Schans, C. (2007). Conventional Chest Physical Therapy for Obstructive Lung Disease. Respiratory Care. 52 (9): 1198.