Obtaining the MIP without a Manometer.

I always hate trying to find equipment, especially if your in the ICU & have to go to the basement where respiratory supplies are located. This quick trick is a very convenient way to obtain the Maximal Inspiratory Pressure at Low Volume, without a analogue pressure manometer.

Using Volumetric Carbon Dioxide Measurements to Optimize “P-High” During Airway Pressure Release Ventilation

There are many concerns when utilizing Airway Pressure Release Ventilation (aka. APRV, BiLevel, BiVent) in regards to lung injury.

 Inappropriate P-High settings may lead to large release-volumes resulting in over-distention, and volume induced lung injury [1].

Determinants and limits of the Draeger Narkomed Anesthesia machine in regards to ventilating the morbidly obese patient.

*Correspondence from 2007

Purpose

Determinants and limits of the Draeger Narkomed Anesthesia machine in regards to ventilating the morbidly obese patient.

A Problem with Plateau Pressures

When utilizing mechanical ventilation the plateau pressure is commonly evaluated to identify the potential for lung injury.  Many protocols (sepsis, ARDS) indicate targeting plateau pressures ≤ 30 cmH2O as a lung protective tactic.  

Unfortunately, in some patients the Plateau pressure may be falsely elevated and be relatively different then the transpulmonary/pleural pressure.

The MIP: a review of obtaining Maximal Inspiratory Pressure

“Breathe in as hard as you can”, a Respiratory Therapist yells to her ventilated patient. She is trying to coach the patient during a Maximal Inspiratory Pressure (MIP) maneuver, also known as the Negative Inspiratory Force (NIF).

This coaching is very common but is it necessary?

Can one obtain an adequate reading without coaching the patient or in a patient that is unresponsive?

First, think of the last time someone has had to yell at you, for you to initiate a breath?

It has probably never happen (not in less you overdosed on medication or illicit drugs)?

If the patient’s brainstem is intact and they have an adequate respiratory drive then a MIP can be obtained even if they are unresponsive.

So why do practitioners still yell at patients, & say the MIP is unobtainable?

Well it is most likely the result of poor technique.

So here are a few steps to guarantee that the technique is performed correctly, with measurable & reproducible results.

1. Patient criteria: the patient’s brainstem should be intact (no ischemic injuries).I don’t know why anyone would want to perform a MIP on a brain dead patient, when you should be performing an “Apneic Oxygenation Diffusion” test.

-One should caution performing the procedure in patients that are young, strong,

athletic, and have been mechanically ventilated for a short amount of time.  In these

stronger patients there have been incidences of rapid pulmonary edema secondary to

negative pressures created during inspiration against an occluded airway [1].

2. Respiratory Drive
   : the patient must have a strong inspiratory drive; the clinician must evaluate the common causes of a low respiratory drive (e.g. sedation, narcotics, hypocapnia, high levels of assist) and reverse/decrease these if they are present before the procedure.

3. Actively breathing: the patient must be actively breathing ideally in a spontaneous mode, or a partially assisted mode if needed. Make sure the ventilator is not auto-triggering.

4. Muscle Loading: the respiratory muscles should be loaded, by dropping support before the maneuver.

5. No muscle Fatigue: the patient should not be fatigue before the procedure, obtaining the MIP after a spontaneous trial will provide poor results.

Procedure

There are two main techniques used to perform the MIP. One is the Measurement at end-expiratory lung volume and the second is measurement at low lung volume.

Measurement at end-expiratory lung volume

This measurement is based on a total occlusion of the airway opening & easy to perform with the automated function of various newer mechanical ventilators.

The maneuver should be performed for at least 20 seconds or ten occluded efforts, and no longer than 25 seconds, making sure that the patients’ vital signs remain stable. 

Fig 1: MIP procedure performed on the Respironics Esprit Ventilator. 

Fig 1. Shows the maneuver for the MIP measurement obtained with the end-expiratory occlusion function of an Esprit ventilator. The maneuver starts at zero time and goes for 24 seconds. The first few efforts show negative deflations only in the range of -10 cmH2O. If one would end the procedure at this point one might assume that the patient is too weak. However, notice as the procedure is continued air hunger forces the patient to progressively increase his inspiratory efforts, which leads to a final measurement of -29.3.

The procedure should be repeated no more than twice.

Measurement at low lung volume

The second method is obtained below the function residual capacity (FRC); results are typically higher in this test since the respiratory muscles perform better under low lung volumes.

This test is performed with a simple t-piece device, & manometer. 

Example of a device used to obtain MIP at low lung volume

The test is performed by hooking up the patient per instructions, and occluding the ambient port at any time during the respiratory cycle.

Perform the test for the same amount of time, while assessing the patient for deleterious side effects.

Document the most negative number generated. 

RELATED POST

Obtaining the MIP without a Manometer

A Unique way to Obtain the NIF

Reference 

Lotti, G. & Braschi, A. (2009). Measurement of Respiratory Mechanics During Mechanical Ventilation. Rhazuns, Switzerland.

Negative Pressure Pulmonary Edema Reference

1. Postobstructive pulmonary edema following anesthesia - Elsevier

   by IA Herrick - 1990 - Cited by 25 - Related articles

   Keywords: Anesthesia, general; complications, airway obstruction, pulmonary edema; airway, obstruction, laryngospasm; lung, pulmonary edema ...
   ►
2. 
   

   Jornal Brasileiro de Pneumologia - Negative-pressure pulmonary ...

   
   

   by RK Mussi - 2008 - Cited by 1 - Related articles

   
   

   ... after procedures involving upper airway instrumentation. Keywords: Hemorrhage;Pulmonary edema; Airway obstruction; Abscess; Prostheses and implants. ...

3. Acute Pulmonary Edema Caused by Choking in An Adult Patient

   
   

   File Format: PDF/Adobe Acrobat - Quick View

   Noncardiogenic pulmonary edema, Airway obstruction, Choking. 1Department of Emergency Medicine, Hualien Armed Forces General Hospital,. Hualien, Taiwan ...

   
   

   www.tsim.org.tw/journal/jour18-2/07.PDF - Similar
4. 
   

APRV: Setting P-High based on the Static Pressure Volume Curve

Some newer mechanical ventilators provide the operator with automated tools to obtain a static Pressure Volume (P/V) Curve in the ventilated patient. These tools provide the clinician a simple, safe, and reproducible method to assess the P/V curve for various pulmonary conditions. 

Photo 1: Hamilton G5 ventilator screen, showing the "P/V tool" software to obtain a static P/V curve.

The Constant Low Flow Method: Utilizing the PB840 part two (video)

Additional Reading:

The Acute Effectiveness & Safety of the Constant-Flow, P/V Curve to Improve Hypoxemia in ALI.

Identifying Optimal PEEP with the PB 840 Ventilator: the "Constant Low Flow Method"

Evaluating the Pressure/Volume curve for the lower inflection point, provides the operator a idea of where to appropriately set the level of PEEP. The curve identifies where lung recruitment begins and at what pressure/volume creates over distention and/or injury.

In newer generation ventilators (Draeger's Evita XL or Hamilton's Galileo or G5 platforms) obtaining the static pressure/volume curve at a low flow state is simple via the machines automated tools.

Conversely, in other ventilators obtaining a static low flow P/V curve can be complicated if not impossible to perform.

The PB 840 does not have a automated tool for performing a "Low Flow" maneuver, however the practitioner can do the maneuver manually using the following steps (1):

The "ASV Target Point": Adjusting the %MinVol setting During Adaptive Support Ventilation

After a few years of implementing Adaptive Support Ventilation (ASV), I still receive questions from staff members and physicians regarding the ideal %MinVol target setting when initially setting-up ASV. I usually respond by asking, “do you want to wean or rest the patient”?

Shook to Death: a Case Study of High-Frequency Chest Wall Compression

Background

There are a variety of techniques used as "Chest Physical Therapy" (CPT), for patients with airway diseases. The main goal of these therapies is to augment secretion mobilization & airway clearance[1].

One of these techniques utilizes high-frequency chest wall compression a.k.a "The Vest" (® Hill-Rom). The manufacturers of the Vest list numerous conditions that the device may be used for, from patients with chronic respiratory conditions-to-Acute Respiratory Distress Syndrome[2].

Conversely, there are no contra-indications, considerations when not to use the device, or patients that may be at risk listed in the product information.

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. 

Waveform of the week: Inspiratory time too short

Inappropriate termination during breath delivery may be the result of an inspiratory time which is too short for the patients inspiratory time constant, when utilizing PC-CMV or PC-IMV.

The above image demonstrates a I-time set too short as evidence of the inspiratory flow waveform not fully decelerating to baseline (shown by red the arrow).

Ideally the operator should titrate I-time to allow for full deceleration of the inspiratory flow waveform. When flow is allowed to fully decelerated, alveolar recruitment, alveolar ventilation, & mean airway pressure is maximized.

The below video clip shows the titration of I-time to allow for a fully decelerating flow waveform, observe the increase in Vt even when the pressure, compliance, & resistance remains constant.

Waveform of the week: Rise time too fast

Setting the rise time too fast, especially in combination with a small E.T. tube or high airway resistance may result in noticeable pressure over-shooting during the early stage of inspiration. This pressure over-shooting may lead to the inappropriate termination of inspiration by setting off the pressure limitation threshold.

Waveform of the week: Rise time too slow

Rise time setting too slow as evidence by the sloping pressure waveform.

A slow rise time may cause increased work of breathing for patients with a high inspiratory drive, decreases mean airway pressure & alveolar time which may decrease the delivered tidal volume.

The following video clip demonstrates the increase in tidal volume with the speeding up of rise time to achieve the optimal rectangular pressure waveform.

Waveform of the week: Flow Mismatch

W

Flow Mismatch as evidence by the scooping in the pressure waveform, a indication of inappropriate inspiratory flow to meet patient demands.


Flow Mismatch

Flow mismatch happens during volume ventilation (VC-CMV or VC-IMV) as a patients respiratory drive increases the fixed/set flow rate does not provide enough assist for the patients demands.
Flow mismatch is easy to identify by recognizing pressure scooping in the pressure waveform. Additionally, the practitioner can evaluate P0.1 to quantify excessive effort.
To correct or prevent flow mismatch the operator can simply adjust the flow rate to match patient demands. However, spontaneous decreases in ventilatory demand will result in unnecessarily higher than average ventilator assist which may result in respiratory muscle disuse, a lower PaCO2 set-point, and delay weaning.
Other actions include; switching from a constant flow pattern to a decelerating flow pattern
, this provides a high initial peak flow, which provides lower peak airway pressures, improved gas exchange, and less patient work.
The operator may also switch to an "Adaptive Pressure Control" mode, pressure control (PC-CMV, PC-IMV) , knowledge based control, or to "Proportional Assist Ventilation".
Lastly, consider increasing sedation if patient demand & or tidal volume exceed clinical goals.

RELATED POST

Flow Mismatch: Patient ventilator asynchrony associated with volume ventilation

What the heck is P0.1?

Obtaining P0.1 on various ventilators

Waveform of the week: Auto-PEEP

Auto-PEEP indicated by the expiratory flow (red arrow) waveform not returning to baseline (pink arrow).

Auto-PEEP/Intrinsic PEEP (PEEP i)

PEEP-i is actually expiratory asynchrony however, it has a effect on patient triggering. 

The pressure associated with the trapped volume acts as a inspiratory load to be over come by the patient during spontaneous breathing. 

Increased Risks of PEEP-i

• Minute ventilation greater than 15 lpm.
• Airway resistance greater than 15 cmH2O.
• Evidence of expiratory flow obstruction (e.g. expiratory time constant > 1.2 seconds).

Strategies to Reduce PEEP i

• Increase expiratory time.
• decrease respiratory rate.
• Decrease expiratory resistance. 

RELATED POST

The importance of identifying patient ventilator asynchrony.

The intrinsic diaphragmatic frequency.

Waveform of the week: Ineffective efforts.

Weaning: APRV optimization of settings.

When utilizing certain ventilators there is no need to switch to a different mode of ventilation to wean the patient from APRV. Weaning is accomplished simply by decreasing the CPAP level (p-High) while simultaneously increasing the CPAP time (t-High). 

Decreasing the p-High in increments of 1-2 cmH2O, while increasing the t-High by 0.5 seconds per cmH2O reduction in p-High.

When p-High is at an acceptable CPAP level, the patient may be considered for extubation. Additionally, spontaneous breaths may be supported with automatic tube compensated to elevate work of breathing associated with the artificial airway.

Decreasing PaCO2: APRV optimization of settings.

• First, assess the patients level of sedation, if sedation is used it should be titrated so the patient is easily awakened with light stimuli, and spontaneous breathing is promoted. 

• Second, reassess expiratory flow make sure that T-PEFR is within 50-75% . If T-PEFR is greater than or equal to 75% and oxygenation is acceptable, consider increasing t-Low by 0.05-0.1 increments to achieve a 50% T-PEFR.

• Third, if not contraindicated increase minute ventilation by increasing p-High or p-High and t-High.

• Lastly, if oxygenation is acceptable and paCO2 is a concern the practitioner may increase minute ventilation by decreasing t-High and increasing p-High simultaneously. 

note- decreasing t-High will increase frequency however, mean airway pressure is sacrificed and less end expiratory lung volume is generated. The t-Low should be reassessed & titrated to allow for appropriate release time. 

Additionally, t-Low should not be extended solely to allow for paCO2 removal, increasing the t-Low may lead to alveolar derecruitment.

Improving Oxygenation: APRV optimization of settings.

Improving Oxygenation: titrating t-Low

To improve oxygenation one of the first goals when utilizing APRV is to maximize end-expiratory lung volume.

To do this assess the T-PEFR; if the T-PEFR is less than 50% decrease the release time until a T-PEFR of 75% is obtained. 

*the above image shows a measured PEFR of 50%, even if the calculated value is 50% or greater the operator can still adjust the t-Low setting to obtain a T-PEFR of up to 75% to maximize lung recruitment. 

Improving Oxygenation: increasing p-High or p-High & t-High

Another way to improve oxygenation during APRV is to increase mean airway pressure. 

One way is to increase p-High to recruit aveoli by achieving threshold opening pressure, p-High should be adjusted at only 2-5 cmH2O increments while monitoring the patients hemodynamic status. 

Furthermore, t-High can be lengthened, this increases gas mixing & recruits alveoli with longer time constants.

note- always assess hemodynamics if increasing p-High or t-High. 

If increasing settings is limited due to decreased cardiac output or hypotension, consider therapeutics which increase cardiac output & blood pressure.

Optimal t-Low settings

Optimal t-Low settings are displayed in the images to the left.

 T-PEFR at 50, 60, & 75 percent of the peak expiratory flow rate. 

Notice these precise adjustments of t-Low.