eugene y sohn, m.d., m.p.h.1,2 3 article...simv- synchronized intermittent mandatory ventilation...

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le Eugene Sohn ORCID iD: 0000-0001-9730-3320

Comparison of SIMV+PS and AC modes in chronically ventilated children and effects on speech.

Eugene Y Sohn, M.D., M.P.H.1,2, Katy Peck, M.A., CCC-SLP, CBIS, CLC, BCS-S3,

Rory Kamerman-Kretzmer, M.D.4, Roberta Kato, M.D.1, Thomas G. Keens, M.D.1, Sally

L. Davidson Ward, M.D.1

1Division of Pediatric Pulmonology and Sleep Medicine, Children’s Hospital Los

Angeles, USC Keck School of Medicine, Los Angeles, CA.

2Department of Pediatrics, Southern California Permanente Medical Group, Los Angeles,

CA.

3Division of Speech Therapy, Children’s Hospital Los Angeles, USC Keck School of

Medicine, Los Angeles, CA.

4Division of Pediatric Pulmonology, University of California Davis, Sacramento, CA.

Address correspondence to:

Eugene Y Sohn, M.D., M.P.H.

Division of Pediatric Pulmonology and Sleep Medicine

http://crossmark.crossref.org/dialog/?doi=10.1002%2Fppul.25102&domain=pdf&date_stamp=2020-10-02


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Children’s Hospital Los Angeles

4650 Sunset Boulevard, MS# 83

Los Angeles, California 90027-6062

Tel: 323 - 361 – 2101

Fax: 323 – 361 – 1355

E-mail: [email protected]

Financial Disclosures: No author of this manuscript has any financial disclosure that

needs to be considered.

Conflict of Interest: No author of this manuscript has any conflict of interest that needs

to be considered.

Keywords: home mechanical ventilation, ventilator modes, assist control, SIMV,

pressure support, pediatrics, speech

Abbreviated Title: SIMV+PS and AC modes in ventilated children and effects on

speech

Abstract:

Background:

Two modes of ventilation commonly used in children requiring chronic home mechanical

ventilation (HMV) via tracheostomy are Assist Control (AC) and Synchronized

Intermittent Mandatory Ventilation with Pressure Support (SIMV+PS). There has been

no study comparing these two modes of ventilation in children requiring chronic HMV.


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Methods:

We studied children requiring HMV capable of completing speech testing. Study

participants were blinded to changes and studied on both modes, evaluating their oxygen

saturation, end tidal carbon dioxide (PETCO2), heart rate, respiratory rate, and respiratory

pattern. Subjects completed speech testing and answered subjective questions about their

level of comfort, ease of breathing, and ease of speech.

Results:

Fifteen children aged 12.3±4.8 years were tested. There was no difference in mean

oxygen saturation, minimum oxygen saturation, mean PETCO2, maximum PETCO2, mean

heart rate, and mean respiratory rate. The maximum heart rate on AC was significantly

lower than SIMV+PS, p=0.047. Subjects breathed significantly above the set rate on

SIMV+PS (p=0.029), though not on AC. Subjects found it significantly easier to speak

on AC, though there was no statistically significant difference in speech testing. Four

subjects had multiple prolonged PS breaths on SIMV+PS. Many subjects exhibited an

abnormal cadence to speech, with some speaking during both inhalation and exhalation

phases of breathing.

Conclusions:

There were few differences between AC and SIMV+PS, with a few parameters favoring

AC that may not be clinically significant. This includes subjective perception of ease of

speech. We also found unnatural patterns of speech in children requiring HMV.


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Abbreviations:

AC- Assist Control

CPAP- Continuous Positive Airway Pressure

HMV- Home Mechanical Ventilation

MPT- Maximum Phonation Time

PEEP- Positive End Expiratory Pressure

PETCO2- Partial pressure of end tidal CO2

PIP- Peak Inspiratory Pressure

PMV- Passy Muir Speaking Valve

PS- Pressure Support

Spo2 – Arterial oxygen saturation of hemoglobin

SIMV- Synchronized Intermittent Mandatory Ventilation

SIMV+PS- Synchronized Intermittent Mandatory Ventilation with Pressure Support

INTRODUCTION.

Since its beginning during the polio epidemics of the 1940’s and 1950’s1, the

indications for home mechanical ventilation (HMV) have expanded to include chronic

alveolar hypoventilation from ventilatory muscle dysfunction, abnormalities of central

respiratory control, restrictive lung disease, obstructive lung disease, large airway

compromise, and intrinsic lung disease2,3,4,5,6. These patients depend on a secure method

to provide chronic positive pressure ventilation. HMV is a safe and, relative to inpatient

hospital care, inexpensive therapy that enhances psychosocial development and reduces

the healthcare cost and morbidity associated with these conditions7,8.6.9.


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Chronic HMV is often provided via cuffless tracheostomy tubes with a portable

positive pressure ventilator 3. Cuffless tracheostomy tubes facilitate ease of speech,

minimize the risk of tracheomalacia or tracheal mucosal damage, and may be safer in the

event of tracheostomy tube plugging3. Gilgoff found that cuffless tracheostomy tubes

were associated with hypoventilation in patients ventilated by setting tidal volume but

that this resolved when the control variable was changed to pressure10. Therefore, it has

become our practice to use pressure as our control variable for ventilation in our patients

requiring HMV.

There is no definitive text comparing the benefits and disadvantages of two

common modes of HMV: Assist Control (AC) and Synchronized Intermittent Mandatory

Ventilation (SIMV) with Pressure Support (PS). These two modes have been compared

in adult and neonatal acute respiratory failure. However, the ventilation strategy used in

HMV often differs from the strategy used in acute respiratory failure, since the former

focuses on complete and chronic assistance of ventilation.

In theory, the full support for each breath on AC would result in decreased work

of breathing compared to SIMV+PS, which provides partially supported PS breaths when

patients breathe above the set rate. Previous research in this area has not consistently

found one mode outperformed the other. Some studies have supported the possibility that

AC produces more ventilation for the same amount of work compared with SIMV1,11,12,13.

However, Shelledy compared AC, SIMV, and SIMV+PS modes in spontaneously

breathing adult subjects who were ventilated via mouthpiece using volume determined

ventilation and found that SIMV+PS resulted in greater ventilation for the same amount

of oxygen consumed compared with AC and SIMV14. In 2015, Luo found that SIMV+PS


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was associated with earlier improvements in oxygenation as well as lower PEEP and

FiO2 requirements in adults with ARDS when compared with AC15. Ortiz found no

difference in mortality in adult patients treated with SIMV+PS compared with AC for a

variety of causes of respiratory failure, though they did find a trend toward a lower

sedation in those using SIMV+PS16.

A child’s ability to communicate verbally greatly affects their quality of life.

Laasko documented that patients requiring HMV had difficulties with communication

and did not feel their providers were knowledgeable about their concerns17. Recently

published research focused on the optimization of speech for patients requiring HMV has

not examined the role of mode of ventilation. Instead, publications in the past two

decades have primarily focused on adults and examined speech using various types of

tracheostomy tubes18,19,20,21. Two studies have examined the role of PEEP or patient-

controlled PEEP in speech22,23. We identified only one study comparing the effects on

speech of two ventilatory modes in patients requiring HMV via tracheostomy, but this

was in adult patients comparing AC and PEEP+PS24. Prigent found no significant

differences in ventilatory characteristics at rest between both modes except for a slightly

higher oxygen saturation on PEEP+PS.

A recent Cochrane review looked at studies of various modes of synchronized

ventilation in neonates and compared SIMV and AC mode but did not make a

comparison of SIMV+PS and AC25. No studies have evaluated these two modes of

ventilation in the pediatric population requiring HMV. Moreover, there has been no study

in pediatric populations evaluating the effect of the mode of ventilation on speech. The


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aim of this study was to compare the effects of two modes of ventilation on physiologic

parameters, speech, and subjective perception of comfort in the pediatric population.

Materials and Methods:

Subjects:

We studied 15 subjects 6 to 21 years of age with chronic respiratory failure

requiring HMV via tracheostomy. Subjects were recruited from the Pediatric

Pulmonology Clinic at Children’s Hospital Los Angeles (CHLA) and studied between

December 2008 and May 2009. Inclusion criteria included the need for HMV via

tracheostomy for at least 3 hours during the daytime, ensuring they needed to speak while

using the ventilator, and the ability to speak in English or Spanish. Subjects with known

laryngeal dysfunction or who were non-verbal were excluded. The protocol was approved

by the institutional review board at CHLA, and written informed consent was obtained

from the parents with written assent by the subjects who were ≥7 years old.

Study Design:

We studied the effect of ventilator mode on perception of comfort, ability to

speak, and physiologic parameters. A computerized multi-channel data acquisition

system (VIASYS Somnostar Pro, Cardinal Health, Dublin, OH), monitored chest and

abdominal bands to record movement, a pulse oximeter, ECG leads, and PETCO2

monitors.

Subjects used their personal home ventilators except for those using home

mechanical ventilators incapable of providing PS. These patients were switched to a


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Newport HT-50 (Newport Medical Instruments, Costa Mesa, CA) ventilator for the study

using their usual settings except for the addition of PEEP 4 cm H2O, as these subjects had

no PEEP on their personal ventilators. For those subjects who did not already use

SIMV+PS, PS of 10 cm H2O was provided during the SIMV+PS phase. PS of 10 cm H2O

was chosen as it resulted in a total peak pressure during a PS breath that was less than the

PIP set on the ventilator as this is our usual practice when using SIMV+PS.

The study was divided into two phases and subjects were randomly assigned to

either mode for each phase. Real or mock changes were made to the ventilator mode in

order to facilitate blinding of subjects. Ventilation was controlled by the pressure variable

in all subjects, both at baseline at home and throughout the entire study period.

Subjects were given 15-20 minutes to equilibrate after each change. After

equilibration, physiologic data were recorded for five minutes before a speech language

pathologist (SLP) conducted speech testing for 5-15 minutes on each mode. Subjects,

their caregivers, and the SLP were blinded to the changes (mock or real) made to the

ventilator mode.

Subjective Measurements:

At the end of each phase, subjects were asked to answer three questions: "How

comfortable are you?", "How easy is it to breathe?", and "How easy is it to speak?"

utilizing a visual analogue scale (VAS) and the Wong-Baker FACES pain scale drawings

adapted for these questions. Answers ranged from "Very comfortable" to “Very hard,”

"Very easy" to “Very hard,” and "Very easy" to “Very hard” in response to the 3

questions, respectively. Subjects were blinded to their previous answers during the

second phase. After subjects completed their study visits, VAS scores were translated


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into numerical scores from 0-10 (0=left most side, 10=right most side) and FACES

drawings were assigned a numerical value (0-10). At the end of the visit, the subject and

the caretaker were asked which mode (first or second) the subject liked the most or

produced the best speech.

Speech Testing:

Speech testing was conducted by the same SLP and was recorded digitally for

later review for consistency and detailed evaluation. Objective and subjective measures

of speech are found in Table 1. Subjects were instructed to complete each speech task

within a predetermined number of trials to avoid fatigue. Behavioral interventions were

not used to enhance participation; however, subjects were given a gift card upon

completion of the study.

Statistical Analysis:

Results are presented as mean and standard deviation. Percent differences are

reported for each parameter expressed as the difference between the SIMV+PS value and

the AC value divided by the AC value: (SIMV+PS-AC)/AC. Paired t-tests were

performed to determine the presence of a significant difference in parameters on each

mode of ventilation, with a p-value <0.05 as the threshold for statistical significance.

Results:

The mean age of our study group was 12.3±4.8 years. Nine males and six females

were tested. The most common indication for ventilator dependence was ventilatory

muscle weakness (13 of the 15 subjects). Of these thirteen, 11 had genetic disorders

leading to ventilatory muscle weakness, one subject had C2-level quadriplegia, and one

subject had Chronic Inflammatory Demyelinating Polyneuropathy. One subject had


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congenital central hypoventilation syndrome, and another subject had restrictive lung

disease from spina bifida and severe scoliosis. All subjects were full time ventilator

dependent except for two subjects who spent <4 hours a day off the ventilator.

Most subjects were using ventilators with PEEP that were capable of PS

ventilation. Nine were using Newport HT-50 ventilators, and two were using Pulmonetic

LTV-950 (Cardinal Health, Minneapolis, MN) ventilators. Four of the subjects were

switched from a Puritan Bennett LP-10 ventilator (Mallinckrodt, Boulder, CO) to a

Newport HT-50 per protocol. Ten subjects were on AC at baseline, while 5 were on

SIMV+PS at baseline.

There were no adverse events, and most subjects did not feel uncomfortable at

any point. Two subjects on AC at baseline were uncomfortable when switched to

SIMV+PS. Both had ventilator auto-triggering with the mode change leading to breath

stacking, but both completed the study. Three of the four subjects switched from LP-10 to

HT-50 ventilators had auto-triggering, so the pressure trigger setting had to be increased

until this stopped, though this made them unable to trigger the ventilator above the set

rate.

Physiologic Measurements:

Overall, there was no difference in mean and lowest oxygen saturation, mean and

highest PETco2, mean HR, and mean RR. These values and the mean percent differences

are expressed in Table 2. The maximum HR on AC (111.7±18.8bpm) was significantly

lower than SIMV+PS (116.1±18.0bpm), p=0.047. The lowest oxygen saturation was not

significantly different (p=0.055). There was a significant difference between the

respiratory rate on SIMV+PS (mean 21.3±3.7bpm) and the ventilator set rate throughout


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the study (mean 19.6±2.7bpm), p=0.029. However, there was no significant difference

between the respiratory rate on AC (mean 20.9±3.5bpm) and the ventilator set rate.

All 15 subjects had the same or a more regular breathing pattern using AC when

compared with their breathing pattern using SIMV+PS. Chest and abdomen movements

had consistent amplitude and frequency during AC for 14 subjects. Three subjects had

variable amplitude in their chest and abdominal movements, variable frequency of

breaths, and dysynchronous breathing during the SIMV+PS phase. One subject on AC

had this respiratory pattern, likely due to concomitant talking or laughing and this

continued in the SIMV+PS phase. During both phases of the study, most subjects were

breathing at or close to the set rate of the ventilator for most of the data collection period.

Speech Testing:

Speech test results are presented in Table 3. There were no significant differences

in objective speech parameters between the two modes of ventilation. The only test

parameter with an accepted normal value is the S/Z ratio which should be 1 in all ages.

The mean S/Z ratio for both modes of ventilation was abnormal (>1 for all subjects) but

not significantly different between the two modes (5.4 for AC, 5.5 for SIMV+PS). The

S/Z ratio is a maximum phonation measure obtained by prolonging the “S” and “Z”

phonemes and taking the ratio of the respective durations. The “S” phoneme requires

airflow and tongue movements without any vibration of the vocal folds. The “Z”

phoneme is the counterpart to “S” phoneme and requires vibration of the vocal folds.

Subjective Measurements:

The average values for scores on the VAS and FACES questionnaires regarding

comfort level, ability to breathe, and ease of speech are shown in Table 4. Mean scores


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on SIMV+PS were equal or higher (less comfortable, less easy to speak, or less easy to

breathe) for all test scores compared with AC, but only one difference was significant.

Subjects found it easier to speak on AC (score 2.8±2.7) compared with SIMV+PS (score

3.4±2.5), p=0.025, though responses for the same question using the FACES scale were

not significantly different.

Nine subjects preferred AC, 5 preferred SIMV+PS, and one stated they were the

same. Notably, 7 of the 9 who preferred AC used AC at home, while 3 of the 5 who

preferred SIMV+PS used SIMV+PS at home. Eleven of the subjects felt they had better

speech on AC, 2 felt their speech was best on SIMV+PS, and 2 felt they were the same.

All 5 subjects using SIMV+PS at baseline felt that AC produced better speech. Six

caregivers felt their child was more comfortable on AC (5 of these 6 caregivers cared for

children that used AC at baseline), 2 chose SIMV+PS (none used SIMV+PS at baseline),

and 7 felt they appeared the same on both modes. Six of the caregivers felt that their child

had the best speech on AC (5 of these 6 caregivers cared for children that used AC at

baseline), while 2 caregivers felt their child’s best speech was while on SIMV+PS (1

used SIMV+PS at baseline).

Discussion:

This study in pediatric subjects on chronic HMV did not find a significant

difference between AC and SIMV+PS with respect to oxygen saturation, PETCO2, heart

rate, and respiratory rate. Subjects breathed faster than the ventilator set rate on

SIMV+PS but not on AC both at rest and while speaking. In addition, maximum HR was

also significantly lower on AC compared with SIMV+PS. However, these differences

were small and likely not clinically significant. Mean speech test scores were not


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different between the two modes, though intelligibility improved substantially in two

subjects and intensity improved in one of these subjects on AC compared with

SIMV+PS. We found statistically insignificant trends of improved subject-perceived

level of comfort, ability to breathe, and ability to speak on AC compared with SIMV+PS.

There was a significant improvement in subject-identified ease of speech on AC

compared with SIMV+PS, but this was by only a small margin. Overall, these findings do

not make a compelling case for favoring one mode of ventilation over another.

Notably, however, four of the subjects had abnormally long PS breaths with

inspiration times of 3 seconds, corresponding with the maximum cut-off time for PS

breaths built into the HT-50 ventilator. These subjects appeared less comfortable with

these breaths. On the VAS, these subjects scored SIMV+PS as marginally less

comfortable, less easy to breathe, and less easy to speak on compared to AC, but they

gave both modes the same scores using the FACES questionnaire. This implies that

patients who experience these prolonged PS breaths may not perceive or report

discomfort despite appearing uncomfortable.

Continuous flow home ventilators terminate delivery of a pressure support breath

when (1) flow to the patient drops below a specific threshold, (2) the target airway

pressure is exceeded by a specific amount, or (3) after a manufacturer (or user)-

determined time period. Large air leaks around cuffless tracheostomy tubes commonly

used in children requiring HMV may allow the inspiratory flow to remain above (and the

airway pressure to remain below) the preset triggers as flow is diverted around the

tracheostomy tube. In this instance a PS breath will not cycle off until the manufacturer

set inspiratory time limit. This can be dangerous, uncomfortable, and lead to insufficient


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ventilation. First described in 1988, Black and Grover reported two cases of adults who

had adverse events associated with the initiation of PS leading to high levels of prolonged

CPAP due to air leak26. They had tachypnea, tachycardia, and a fall in blood pressure

attributed to continuous high levels of CPAP causing decreased venous return and a

cardiac tamponade-like effect. Indeed, this potential problem is well understood in

literature discussing non-invasive ventilation27,28,29,30,31. Two papers have cited this

warning specifically in the pediatric population, though neither of these in the setting of

ventilation via tracheostomy32,33.

Younger children require higher respiratory rates, in which case an increased

inspiratory time could interfere with ventilation and cause discomfort. Even in adult

patients, an inspiratory time of 3 seconds would be uncomfortable and could potentially

impair ventilation. Most of our subjects were older and did not require higher respiratory

rates. Only one of our subjects expressed displeasure with SIMV+PS because of the

frequent episodes of prolonged PS breaths, while the others did not comment on it when

it occurred.

Our study showed no significant differences in speech testing results between

modes. Without normal values for pediatric patients for most speech tests, it is difficult to

draw objective conclusions about speech in our population. The S/Z ratio is the only test

completed with an established normal value and this was abnormally elevated in both

modes of ventilation. While this usually indicates a problem with vocal fold function

producing short “Z” phoneme duration, we speculate that it is due to the cuffless

tracheostomy tube and PEEP in our subjects. Constant air flow from PEEP and a cuffless

tracheostomy tube seemed to allow many subjects to sustain long “S” phoneme duration


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exceeding the ranges produced by normal children and adults which resulted in the high

S/Z ratios. Subjects did not have to pause to breathe during speech because they were

provided breaths by the ventilator without needing to initiate an inhalation. Subjects were

found to exhibit an abnormal rhythm and cadence to speech, speaking on both inhalation

and exhalation, along with altered frequency of initiated replenishing breaths during

connected speech. This is a negative maladaptive behavior which could result in

laryngeal damage due to vocal fold overuse. Physicians should screen their patients for

discoordination of respiration and phonation to optimize respiratory support during

speech production, reduce laryngeal tension, and avoid potential vocal fold abuse.

There were limitations to this study that may have affected our ability to identify

significant differences between the two ventilator modes. All subjects continued their

home baseline ventilator settings (e.g. pressures, rate, i-time) except for the mode

throughout the study. HMV patients followed at CHLA are hyperventilated (mean

PETCO2 for our study group was <30 torr) for comfort and safety3. Without significant

respiratory drive, subjects mostly breathed at the set ventilator rate. Since AC and

SIMV+PS deliver the same fully supported breath when the subject is spontaneously

breathing at or below the set rate when intentionally hyperventilating chronically

ventilated children, there does not seem to be a significant difference between AC and

SIMV+PS. However, we speculate that at lower ventilator set breath rates, there may be a

larger difference between the modes. Any differences would be further diluted by the fact

that the pressure trigger for 3 of our study subjects had to be increased past where they

could effectively trigger the ventilator, which diluted any differences between the two

modes of ventilation in our small sample size. With twice as many subjects using AC at


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baseline, there may also be a selection bias. While we excluded patients with known

laryngeal dysfunction, we did not record or require swallowing assessments in our

subjects which could have implications for their ability to speak adequately.

We would also like to address the age of the data presented. While the original

research was conducted 11 years ago, there is still no comparison of these two commonly

used modes of ventilation in pediatric HMV patients. Ventilator technology has advanced

since the data was collected and we anticipate newer ventilators may have better leak

compensation to mitigate our finding of prolonged PS breaths on SIMV+PS mode in

some patients with large air leaks. However, we still treat some patients who are using

these older ventilators and pulmonologists across other world regions may still be using

older models, so we believe this warning is broadly useful. Future research may be

considered in patients requiring HMV with newer ventilator models to determine if newer

technology elucidates a difference between these common modes of ventilation or if our

findings are replicated.

The philosophy of the home ventilator program at Children’s Hospital Los

Angeles has always been to use the available technology to support gas exchange and

patient comfort as effectively as possible. The beauty of natural ventilation is that it

functions in the background, seamlessly directing the ventilatory muscles and integrating

with voluntary activities without compromising critical functions. We believe that despite

the limitations of artificial mechanical ventilation, children on ventilators should be

supported in this same way, and need not focus on breathing, but rather on normal

childhood activities to their level of capability. This study was designed to uncover if

different modes of ventilation offered physiologic advantages and to describe how


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mechanical ventilation interacts with speech. The finding that neither mode studied

offered clinically significant advantages to gas exchange allows us to have confidence

that we can select the mode of ventilation that best suits each patient without fear of some

innate compromise. Moreover, the finding that continuous flow ventilation can allow for

an unusual cadence of speech, one without natural pauses, can be used to guide parents

and therapists so that children are not unnecessarily stigmatized by this difference and

they limit this practice to prevent laryngeal injury.

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Table 1: Speech testing probes

Probe: Definition: Purpose:

1 Maximum Phonation Time (MPT)

Maximum amount of time a child can sustain “ah.”

Evaluate sustained phonation time as a measure of airflow. Male average MPT is usually longer than female MPT. MPT varies significantly with age in children.

2 How Rate Affects Voice- Rate Analysis

The number of words, syllables, and breaths during a 60 second period of reading or speaking.

Measure how breaths are used during speaking or reading. Patients with pulmonary insufficiency may use very short phrases because of limited vital capacity. Reading rate may appear rapid as a result of inefficient use of tidal breathing, poor coordination of airflow and voicing, or excessive laryngeal tension in attempts to conserve reduced air capacity.

3 Intelligibility during oral passage reading

Number of words understood divided by the number of words expressed during 60 seconds of speech.

To evaluate intelligibility during oral reading.

4 Count aloud 1-20

Number of breaths delivered by the ventilator and time to complete a count from 1 to 20.

S/Z Ratio Patient is timed while sustaining production of “s” and “z” for as long as possible.

A duration measure. “S” and “z” are produced in the same way, but “z” is a voiced sound and “s” is not.

Ideal ratio= 1

Ratio >1 implies difficulties in vocal


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fold closure (glottal valving).

Diadochokinetic Rate or Maximum Repetition Rate (MRR)

Subject repeats the phonemes “puh,” “tuh,” and “kuh” each 20 times and “puhtuhkuh” 10 times. The time in seconds to complete each repetition is recorded.

Used to measure how quickly a subject can correctly articulate a series of rapid, alternating sounds. Performance during this task is highly reliant upon neuromuscular functioning and respiration.

Table 2: Respiratory function data: AC vs SIMV+PS. Data expressed as mean ± standard

deviation. * p<0.05

AC SIMV+PS % difference (SIMV-AC)/AC

O2 sat mean (%) 97.0±1.5 96.6±1.6 -0.3±1.0

O2 sat min (%) 95.3±1.3 94.7±1.5 -0.7±1.3

PETCO2 mean (torr) 23.7±7.1 23.8±4.8 3.8±15.4

PETCO2 max (torr) 28.3±7.8 28.5±6.3 2.7±14.9

HR mean (bpm) 105.3±17.9 105.4±15.2 0.7±6.1

HR max (bpm) 111.7±18.8* 116.1±18.0* 4.4±7.2


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Table 3: Speech test data: AC vs SIMV+PS. Data expressed as mean ± standard deviation.

AC SIMV+PS % difference

(SIMV-AC)/AC n

MPT (sec) 14.2±21.7 12.7±16.8 11.0±93.3 15

Longest "s" (sec) 15.2±21.3 10.3±13.8 -7.1±52.4 14

Longest "z" (sec) 3.5±4.0 3.3±3.7 -0.7±42.1 14

s/z ratio 5.4±7.4 5.5±11.2 -1.6±49.1 14

Vowel repetition (seconds) 6.4±3.5 7.2±3.8 11.1±60.2 12

Count 1-20: time (sec) 15.5±13.0 16.2±12.4 6.1±41.7 13

Count 1-20: breaths (breaths) 6.1±5.1 5.6±4.9 0.8±32.9 14

Syllable rate "Puh" (syllables/sec) 6.2±1.8 6.7±2.8 10.3±42.7 13

Syllable rate "Tuh" (syllables/sec) 9.6±8.7 8.8±4.6 -0.5±42.1 14

Syllable rate "Kuh" (syllables/sec) 8.0±4.3 7.8±4.2 -7.2±34.2 12


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Table 4: Subjective questionnaire data: AC vs SIMV+PS. Data expressed as mean ±

standard deviation. *p<0.05

AC SIMV+P

S % difference (SIMV-AC)/AC

Comfort VAS 3.1±2.3 4.1±2.5 77.2±184.2

Comfort FACES 1.7±0.8 2.0±1.1

26.7±60.7

Breathe VAS 3.3±2.5 3.9±2.5 39.1±68.3

Breathe FACES 1.9±1.1 1.9±1.0 10.0±44.9

Speak VAS 2.8±2.7* 3.4±2.5* 45.7±63.7

Speak FACES 1.8±1.1 2.1±1.2 27.8±71.7

Syllable rate "PuhTuhKuh" (syllables/sec) 7.8±3.8 7.7±3.4 3.0±21.2 13

1min speech: breaths (breaths/min) 20.5±3.6 21.2±3.9 4.3±17.2 13

1min speech: syllables (syllables/min) 99.9±65.0 97.7±56.1 2.6±17.5 14

1min speech: words (words/min) 74.9±48.7 67.9±36.0 -2.3±21.5 14

eugene y sohn, m.d., m.p.h.1,2 3 article...simv- synchronized intermittent mandatory ventilation...

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