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

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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.

Ten Reasons to Trade in the Babylog 8000

Image 1 : Front view of the Babylog 8000 neonatal ventilator.

The Babylog 8000™ (Draeger Medical, Telford, PA) is a neonatal specific ventilator that has been in use for over twenty years. At inception the Babylog was a unique platform providing high-tech applications in regards to breath delivery. This advance technology surpassed the available devices and provided a foundation for present day neonatal ventilators. Even with the success of this ventilator platform there are reasons one may consider trading in their machines.

The rationale for replacing the Babylog is related to technological advances, the lack of upgrade availability, and safety concerns.

Airway Obstruction Secondary to Growing Granulomatous Tissue in the Tracheostomy Tube

 Introduction: Airway patency is arguably the most important factor of the cardiopulmonary system. It is imperative that the bedside Respiratory Care Practitioner (RCP) can rapidly detect and treat airway emergencies. One tool for assisting the RCP in detecting airway displacements and obstructions is the use of capnography. At our institution capnography is routinely used for confirmation of tracheostomy placement following tube placement or tube changes. This case study presents the effectiveness of capnography for detecting a partial airway obstruction with the correct placement of the tracheostomy tube.

The Intrinsic Diaphragmatic Frequency

Image 1: Missed trigger attempts, notice the flow distortions (purple flow waveform) without associated breaths. Ventilator measured rate 12 bpm, however true intrinsic rate 30 bpm. 

Many patients receiving mechanical have high intrinsic diaphragmatic rates (≥30 breaths per minute) even when very well assisted [1]. This is usually unnoticed because the ventilator only measures machine or patient triggered breaths; however the patient’s true respiratory rate may be higher. This can be problematic when performing a spontaneous breathing trial (SBT) for a couple of reasons.

Adaptive Pressure Control Ventilation and Severe Sepsis a Grueling Combination

Mentioned in previous postings Adaptive Pressure Control (APC) should be used cautiously in patients with high inspiratory drives. In patients with sepsis APC can become problematic by weaning the driving pressure prematurely due to a vigorous respiratory drive associated with lactic acidosis. The lower driving pressures will not efficiently off load the respiratory muscles leading to increased work of breathing, ventilatory muscle fatigue, and may initiate lung injury. 

Provided are two examples of APC utilized in sepsis patients:

The Least Work of Breathing: Applying principles of Adaptive Support Ventilation

Adaptive Support Ventilation (ASV) is an advanced closed-loop mode of ventilation only available on Hamilton Medical ventilators (G5, Galileo, C2) in the United States.


ASV is considered an “Optimal” mode of ventilation, in which the ventilator automatically adjusts multiple set-points (pressure, tidal volume, frequency, & I: E ratio). Furthermore, the ventilator applies a mathematical model (Otis equation) to find the least work of breathing.


Providing minimal work of breathing is a primary goal for the mechanically ventilated patient. A load that is too high will eventually lead to ventilatory muscle fatigue and may lead to lung injury and/or liberation failure. Every practitioner should attempt to minimize the work of breathing (WOB) by continuously assessing the patient ventilator interaction and adjusting settings appropriately.


If available the practitioner could employ ASV, however what if you don’t have a Hamilton ventilator or unfamiliar with ASV?

The RT Hoarder

http://cache.gawker.com/assets/images/gawker/2009/10/cats.jpg

I admit I have turned into a hoarder, not the typical hoarder seen on television living amongst their bodily waste or sharing their house with 50 cats. My story is not as disturbing and goes unnoticed.

Dead of Night shift

http://en.wikipedia.org/wiki/File:DeadOfNight1.jpg

After six years of being a day walker I have returned to my origin as a night shift healthcare provider. I enjoy the pace and the autonomy of night shift however, it is sometimes torturous. 

I feel like “Walter Craig” in the 1945 British film “Dead of Night”, in which the character experiences a recurring nightmare with the same cast of house guests. Instead of “Pilgrims Farm” I’m stuck in a hospital interacting with it's own recurring cast of personalities; the non-compliant patient, the substance abuse patient, the medical resident who thinks he’s M.D. “House”, the nurses who are fueled on cigarettes & Red Bull.  Yes, I’m dead of night shift; indifferent, cold, and apathetic. Additionally, night shift is slowly killing me.

Night shift work has been associated with a number of maladies including:

Metabolic syndrome [1& 2]

Increased vascular stress [3 & 4]

Induced Apnea [5]

In regards to me it is vitamin D deficiency. Yearly, I have a few blood tests performed to check for abnormal values. Before returning to night shift my previous vitamin D levels were normal, I lived in the Midwest, and had no additional vitamin D supplementation. After starting night shift I began supplementing my vitamin D intake with 1000 micro units/day & I also moved to the east coast (more sun), conversely my results were below normal. I always have these test performed in February, so the amount of sunlight/day/month is not a factor.

[1] Biggi, N. et. Al. (2008). Metabolic Syndrome in Permanent Night Shift Workers. Chronobiol Int.

[2] Pietroiusti, A. et. Al. (2010). Incidence of Metabolic Syndrome Among Night-Shift Healthcare Workers. Occup Environ Med.

[3] Lo, SH. et.al. (2010). Working Night Shift Causes Increased Vascular Stress and Delayed Recovery in Young Women. Chronobiol Int.

[4] McCubbin, JA. et. Al. (2010). Blood Pressure Increases During a Simulated Night Shift in Persons at Risk for Hypertension. Int J Behav Med.

[5] Laudencka, A. et. Al. (2007). Does Night-Shift Work Induce Apnea Events in Obstructive Sleep Apnea Patients? J Physiol Pharmacol.

Setting Ventilator Alarms Diagnostically

Many practitioners set alarm thresholds thoughtlessly due to the fact that many ventilators do a poor job of filtering alarm nuisances versus 'high-risk' alarms. Many times I see the high respiratory rate alarm set at threshold in which the patient would have severe air trapping and dynamic hyperinflation before the alarm threshold is met.

When using controlled modes of ventilation (VC-CMV & PC-CMV) it is extremely important to set the high respiratory rate alarm threshold appropriately.

During both machine and patient initiated breaths the inspiratory time is fixed, so any additional breaths takes away from the expiratory time which can quickly lead to a inverse inspiratory-to-expiratory (I: E) ratios.

How to set the High Respiratory Rate Alarm Diagnostically

In patients with obstructive airway disease I prefer to set my high
respiratory rate based on a 1:1, I: E ratio. 
That is when the patient sets off the high respiratory rate alarm I know that they are breathing at a 1:1 ratio and that any additional breaths will be an inverse I: E ratio, putting the patient at a increased risk for dynamic hyperinflation.

This is easy to calculate based on the patient's set inspiratory time.

Formula: x = 60/(I-time * 2)
X (high respiratory rate alarm)
60 (total cycle time)
I-time (machine set I-time)

A common I-time is 1.0 second this would equal a high respiratory rate alarm of 30 breaths/minute. This stays the same if the set rate is 8 or 25; the 1:1 threshold is at 30 breaths/min.

The 0.25 Second difference

If air trapping is a concern just decrease the I-time.
A 0.25 second change is significant. 


Decreasing the I-time from 1.0 second to 0.75 second increases the
alarm threshold to 40 bpm.

Low Peak Inspiratory Pressures During Adaptive Pressure Control Ventilation: an Indication for Weaning

Low Peak Inspiratory Pressures (PIP) during Adaptive Pressure Control (APC) may be a sign of distress in patients with increased inspiratory efforts (e.g. high metabolic rate, sepsis, and hypercapnea) [1], or may be a sign that the patient is ready for spontaneous breathing trials.




In the patient that is not in distress and the PIP is low (≤ 15 cmH20) consider evaluation for liberation. If the PIP is low one can presume that the patients’ pulmonary mechanics have improved or within the normal range and that the workload imposed by low compliances or high resistances have decreased.


Example Case


80 female patient with the following ventilator settings:


Mode- APC, Rate- 12, Vt- 500, Fio2- 35%, PEEP- +5 cmH2O


Discovered from the ventilator patient assessment that the patient’s PIP was only 13 cmH2O and the patient was resting comfortably. At this institution spontaneous breathing trials are performed with CSV-PS, Pressure Support of 7 cmH2O & a PEEP +5 (PIP total 12 cmH2O).


The measured PIP over the previous 48 hours was a ~ mean of 13 cmH2O.


This was significant, the patient was basically on the same control pressure as what this facility does SBT’s on, indicating that the patient should have been weaned or liberated 48 hours earlier.


After this finding the patient was immediately placed on a Trach collar trial. The trial was successful with no complications and the patient was transferred to a general medical floor within 48 hours.


Conclusion


Low PIP during APC ventilation should always be evaluated further for the potential for liberation from mechanical ventilation or the need for adjusting ventilator settings to decrease the work of breathing.

[1] The Problem With Adaptive Pressure Control Modes of Ventilation: a Case Study.

Delayed Cycling

One form of delayed cycling  is when the operator inappropriately sets the inspiratory time too
long.

However, delayed cycling is also very common during CSV-PS.

A pressure spike at the end of inspiration may indicate delayed cycling however this is not always associated with expiratory muscle activity . The spike may also be due to the relaxation of the inspiratory muscles, the spike is caused by the returning of pressure creating a temporary increase in pressure (usually associated with higher levels of pressure support > 10 cmH2O). 

Always evaluate the patient for distress to determine if it is delayed cycling vs. muscle relaxation. If the patient looks relaxed and the P0.1 is within limits then the spike is most likely due to muscle relaxation.

A 25% expiratory cycling threshold is a common default setting in most mechanical ventilators. This setting is appropriate in a large percent of the patient population. As previously mentioned a default setting of 25% may be too short in patients recovering from ALI, conversely , in patients with histories of airway obstruction this setting may be too long.


Prolonged expiratory cycling in the COPD patient may increase work of breathing, intrinsic PEEP, and trigger asynchronies (ineffective efforts).Waveform book  at