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Validating Respiratory Rate Measurements in
Patients Receiving High Flow Nasal Cannula: A
Comparative Study of Nellcor PM1000N and visual
inspection
Takuma Iwaya
Sapporo Medical University Hospital
Junpei Haruna
Sapporo Medical University
Aki Sasaki
Sapporo Medical University Hospital
Sayaka Nakano
Sapporo Medical University Hospital
Hiroomi Tatsumi
Sapporo Medical University
Yoshiki Masuda
Sapporo Medical University
Research Article
Keywords:
Posted Date: April 29th, 2024
DOI: https://doi.org/10.21203/rs.3.rs-4043306/v1
License: This work is licensed under a Creative Commons Attribution 4.0 International License.
Read Full License
Additional Declarations: No competing interests reported.
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Abstract
Purpose:
Recently, the Nellcor PM1000N was developed for the concurrent assessment of respiratory rate
and percutaneous oxygen saturation. However, the validation of respiratory rate measurements in
patients receiving a high-ow nasal cannula (HFNC) using the PM1000N remains unestablished.
Therefore, this study aimed to assess the validity of respiratory rate measurements obtained using
PM1000N in patients receiving HFNC.
Methods:
A retrospective assessment was conducted on the respiratory rate measurements obtained
using the PM1000N and electrocardiogram (ECG) impedance methods in comparison to those visually
assessed by nurses. This evaluation included patients admitted to the Intensive Care Unit (ICU) of
Sapporo Medical University Hospital who received HFNC between June 2022 and December 2022.
Correlation coecients, intraclass correlation coecients (ICCs), Bland-Altman plots, and t-tests were
employed to assess the concordance between the visually observed respiratory rates by nurses and those
recorded by the PM1000N and ECG impedance.
Results:
Twenty patients were enrolled in this study. Among them, 119 instances of respiratory rate were
recorded. The ICCs for the PM1000N and impedance methods were 0.918 and 0.846, respectively,
compared with the rates visually assessed by nurses. The mean differences were p=0.947 (95% CI: -3.186
– 0.2987) and p < .001 (95% CI: 16.4609–17.9532), respectively.
Conclusion:
The PM1000N demonstrated superiority over ECG impedance in measuring respiratory rate in
patients with HFNC. Furthermore, PM1000N shows promise for effective application in patients receiving
HFNC.
Introduction
Among the pivotal vital signs measured in daily patient care, respiratory rate is reportedly correlated with
in-hospital mortality and serious adverse events(1,2). Therefore, respiratory rate has emerged as a more
discerning prognostic indicator, such as mortality, than traditional metrics, such as blood pressure or
pulse rate(3,4).
However, many acute care hospitals report that blood pressure, pulse rate, temperature, and SpO2 are
recorded, instead of the respiratory rate(5,6). The rationale for not measuring respiratory rate may be the
lack of awareness among nurses and junior healthcare professionals(7)and the complexity of the
method of measurement(8); because several measurement methods are available. Capnography is the
standard method for accurately measuring respiratory rate(9). Other methods include electrocardiogram
(ECG) - derived respiration rate(10), radar-based respiration rate monitoring(11), and optical-based
respiration rate monitoring(12). However, in general ward settings, the enumeration of respiratory rate
typically relies on ECG impedance, a method susceptible to inaccuracies(13). Visual observation of
respiratory rate by healthcare professionals is also widely used in several patient care settings; however,
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this approach is labor-intensive and often results in low adherence to respiratory rate
measurements(14).
Recently, high-ow nasal cannulas (HFNC) have been widely used in patients with acute respiratory
failure(15). HFNC slightly increases positive airway and intrathoracic pressures(16), manifesting distinct
effects on work breathing compared with conventional low-ow oxygen delivery systems. Although HFNC
is often used in patients with respiratory failure in ICUs and general wards, capnography cannot
concurrently correctly measure respiratory rate because there is no position to attach the capnograph. In
addition, the accuracy of ECG impedance is reduced by patient movement, physiological movements of
the chest wall, such as coughing, and placement of ECG electrodes(17,18).
However, a new device (NellcorTM PM1000N, Medtronic Japan, Co. Ltd., Tokyo, Japan) that facilitates the
concurrent measurement of the respiratory rate and percutaneous oxygen saturation is now available.
The veracity of this device has been substantiated in cohorts undergoing low-ow oxygen therapy and in
healthy individuals(3,19–21). However, the ecacy of Nellcor PM1000N (PM1000N) in gauging the
respiratory rate in HFNC-utilizing patients remains unclear. PM1000N, which is intended for error-free
application, holds promise for accurately ascertaining the respiratory rate of patients receiving HFNC
therapy in general ward settings. Therefore, we hypothesized that there would be no difference between
the number of breaths per minute measured visually by nurses (hereafter referred to as "visual
inspection") and the number of breaths per minute measured by the PM1000N in patients receiving HFNC
therapy and aimed to investigate this hypothesis.
Methods
Design and Setting
This single-center, retrospective, observational study was conducted at a university hospital. The study
design and protocol were approved by the Institutional Review Board (IRB) of Sapporo Medical University
(IRB-authorized number: 342-242, December 12th, 2022).
Participants
Patients who received HFNC therapy in the intensive care unit (ICU) of Sapporo Medical University
Hospital between June 2022 and December 2022 were selected based on their electronic health records
(EHR).Patients who were under 18 years of age, frequently removed their own cannula, unable to wear the
SpO2 probe on their nger, or whose respiratory rate was not recorded in the EHR were excluded from this
study.
Data collection
Patient data including age, sex, and primary pathology were extracted from the hospital’s EHR.
Additionally, parameters including respiratory rate, heart rate, arrhythmia presence, systolic and diastolic
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blood pressure, and SpO2 during HFNC use were recorded. The respiratory rate was visually inspected at
3:00, 7:00, 11:00, 15:00, 19:00, and 23:00 and manually recorded in the EHR. Furthermore, the measured
respiratory rates obtained by the impedance method from a bedside monitor (BSM-1763 Lifescope PT,
Nihon Kohden Co. Ltd., Tokyo, Japan: bedside monitor) and PM1000N were automatically recorded in the
EHR. Respiratory rate recordings from the three modalities were retrospectively compiled from the EHR.
Three investigators procured data from records between August 2023 and December 2023.
Respiratory rate measurement procedure
PM1000N
An adhesive SpO2 measurement sensor (NellcorTM OxySensor III), utilized in conjunction with the
PM1000N, was axed to the patient’s digit. A Nellcor OxySensor III was applied according to the
instructions, positioning the sensor window adjacent to the terminal joint on the nail side and orienting
the sensor cable to the dorsal aspect of the hand.
Bedside monitor
The electrodes were axed to the patient’s skin at the anterior and lateral chest walls using bipolar leads
for all inductions. The impedance method was used for these measurements. The operational concept
involves the application of a respiratory measurement current via an electrode designed for ECG
assessment. The resultant impedance alteration in the thoracic region induced by respiratory activity
manifests as a modication of the respiratory measurement current. The subsequent amplication and
computation of this signal yielded a visually represented respiratory curve.
Visual observation by the nurse (visual inspection)
During each designated observation interval, nursing practitioners positioned themselves proximal to the
patient at the bedside, undertaking direct scrutiny of the vertical excursion of the thoracic region. Each
observation spanned one minute, and the documented respiratory was derived from the observed
ndings inscribed in the patient's EHR.
Outcomes
The primary outcome was to validate the concordance rate of the respiratory rate measured using the
PM1000N, with the visual inspection respiratory rate as the reference.
Statistical Analysis
Data were assessed for Gaussian distribution using the Shapiro–Wilk normality test. Normally distributed
data were presented as the mean ± standard deviation (SD), and non-normally distributed data were
presented as the median and interquartile range (IQR). Correlation coecients and intraclass correlation
coecients (ICC) were calculated for each measurement method based on visual inspection to validate
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the accuracy of the PM1000N and bedside monitors. We also calculated the standard deviation of the
respiratory rate measured by the three methods, created a Bland–Altman plot, and performed a
t
-test on
the mean difference. To evaluate the background of the inability to measure respiratory rate with the
PM1000N, the patients were divided into two groups: a measurement group and a non-measurement
group, and the ow of HFNC and the presence of arrhythmia were compared. Statistical signicance was
set at p < 0.05. Statistical analyses were performed using the SPSS software version 27 (IBM Corp.,
Armonk, NY, USA).
Results
Patient Characteristics
Of the 354 individuals admitted to our ICU during the study period, 334 were ineligible based on the
prespecied exclusion criteria. Patient characteristics are shown in Table 1. The resulting cohort
consisted of 20 participants (5.6%), characterized by seven (35%) males and a median age of 75.6 years
(interquartile range: 69.8–80.4). Cardiovascular disease was the predominant disease affecting 11 (55%)
patients, representing approximately 50% of all cases.
The respiratory rate recorded by each measurement method is shown in Table 2. During the observation
period, the respiratory rate was recorded 119 times. Visual inspection and bedside monitoring were used
to record respiratory rate at all time points. However, PM1000N did not measure the respiratory rate at 20
time points. The time periods for which the respiratory rate could not be measured with PM1000N were
treated as missing values and excluded from the primary analysis. The mean respiratory rate observed by
visual inspection, bedside monitor, and PM1000N were 17.7 ± 3.9, 18.3 ± 3.7, and 17.2 ± 3.9, respectively.
The intra-class correlation coecients between the bedside monitor and PM1000N, based on visual
inspection, are listed in Table 3.
The correlation of respiratory rate by each measurement method based on visual inspection and the
Bland–Altman plot and linear intubation plot are shown in Figure 1. The correlation coecients between
the bedside monitor and PM1000N based on visual inspection were 0.85, p < .001 and 0.84, p < .001,
respectively.
The respiratory rate could not be measured at 40 points using PM1000N. A comparison of the
measurable and non-measurable points for the respiratory rate using PM1000N is shown in Table 4.
Arrhythmias were signicantly more common at non-measurable points than at measurable points (54
(27.3%) vs. 36 (90), P < 0.01).
Discussion
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This study aimed to validate the automated respiratory rate measurement of PM1000N in patients using
HFNC. Respiratory rate measurements with the PM1000N showed a better correlation with visual
inspection than with the impedance method by bedside monitors, indicating that the PM1000N can
provide favorable outcomes in determining respiratory rate comparable to visual respiratory rate
measurements in patients with HFNC.
However, there are some concerns about accurately measuring the respiratory rate using the PM1000N in
patients with HFNC. First, the PM1000N measures the respiratory rate by analyzing three types of
respiratory pulse wave variations: respiratory sinus arrhythmia, pulse wave baseline variations, and pulse
wave amplitude variations, sensed by a sensor attached to the nger. Among these, respiratory sinus
arrhythmia captures changes in the heart rate associated with the respiratory cycle(22). Therefore, as a
precaution when using the PM1000N, it is indicated that if the pulse wave becomes small owing to
peripheral circulatory failure or pressure on the arm on the side where the sensor is worn by the blood
pressure cuff, the measured value will be unstable(23).However, in this study, we believe that this effect
was avoided by attaching the sensor to the nger opposite the arm where the blood pressure was
measured.
The second concern was the baseline and pulse wave amplitude variations. To measure the respiratory
rate with the PM1000N, it is necessary to capture the variation in the venous annulus caused by changes
in the intrathoracic pressure during the respiratory cycle. Airway pressure in patients using HFNC is higher
in the closed state than in the open state, and increases with an increase in ow(24). Flow settings of 30
and 50 L/min with the mouth closed reportedly produce average airway pressures of approximately 3
cmH2O and 5 cmH2O, respectively(16). In contrast, a study investigating the effects of ventilator-assisted
PEEP on circulatory dynamics reported no signicant changes in circulatory dynamics with the addition
of 0 cmH2O and 5 cmH2O PEEP levels(25). Because ventilator-induced PEEP occurs continuously in a
closed respiratory circuit, and does not affect circulatory dynamics, the intermittent changes in airway
pressure produced by HFNC should have little effect on circulatory dynamics. The HFNC ow in this study
was treated over a wide range of 30 L–60 L. The comparison of the ow of HFNC between the
measurable and non-measurable groups also showed no signicant difference, suggesting that changes
in intrathoracic pressure due to HFNC are unlikely to affect respiratory rate measurements with the
PM1000N. Therefore, we believe that even if HFNC caused changes in intrathoracic pressure, the baseline
and pulse wave amplitude uctuations would be less affected, and an accurate respiratory rate could be
measured even with the PM1000N using HFNC.
Lynn et al.(26)found that an increased respiratory rate was a more important predictor of sudden
deterioration than decreased SpO2. Moreover, the respiratory rate and oxygenation (ROX) index used to
predict the progression to tracheal intubation in patients on HFNC includes the respiratory rate as a
scoring component(27,28). Moreover, continuous, rather than cross-sectional, physiological monitoring
based on these scores and indicators is useful for the early detection of patient deterioration. Therefore,
continuous monitoring of the respiratory rate is important, regardless of the section. Further, although
several conventional methods for measuring the respiratory rate exist, visual measurement by nurses is
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time-consuming and labor-intensive. Moreover, the impedance method allows continuous measurement
with equipment, however, it is prone to errors due to the position of the electrode and patient's body
movements. Conversely. in this study, the PM1000N was found to measure the respiratory rate with high
accuracy, even in patients using HFNC. Thus, the PM1000N solves the problems of conventional
measurement methods because it is easy to install and minimizes the burden on patients. In addition, the
previously uncertain validity and reliability of HFNC use were also assessed in this study, indicating that
respiratory rate measurement with the PM1000N is also useful for monitoring the respiratory rate in
patients using HFNC.
In contrast, 16.8% of the patients in the PM1000N group were not measurable. Additionally, a higher
percentageof patients at the non-measurable points had arrhythmia than those at the measured points.
Moreover, the safety and ecacy of measuring respiratory rate with the PM1000N in patients with
arrhythmia, such as three or more irregular events within 30 s, have not been established because they
may result in inaccurate respiratory rate values and loss of displayed respiratory rate information.
Consequently, respiratory rate monitoring in combination with visual or other reliable measurement
methods is necessary for patients with detectable arrhythmias or an unstable cardiovascular status.
Strengths and Limitations
To our knowledge, this is the rst study to validate respiratory rate measurement with PM1000N in
patients using HFNC; however, there are some limitations. First, the number of patients was limited
because this was a retrospective observational study. Additionally, the patients' diseases and other
backgrounds varied, which may have resulted in different patient conditions. Therefore, further studies
with larger sample sizes are warranted. Second, the data used in this study analyzed respiratory rates
recorded every four hours, which suggests accuracy in intermittent measurements but did not verify
whether respiratory rates were measured with high accuracy on a continuous basis. Consequently, Further
validation is required to clarify whether a continuously accurate respiratory rate can be measured. Third,
this study was conducted in an ICU setting. The same study should be conducted in patients treated in
general wards.
Implications for Clinical Practice
This study found that the PM1000N can easily and continuously measure the respiratory rate with the
same accuracy as visual inspection, even in patients with changes in intrathoracic pressure caused by
HFNC. Therefore, the PM1000N can be used in general hospital beds for patients with HFNC to accurately
measure their respiratory rate and detect changes in their condition.
Conclusion
In this study, we evaluated the validity of measurements using the PM1000N in patients receiving HFNC
therapy. The PM1000N was able to measure the respiratory rate in patients with HFNC with the same
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accuracy as visual inspection. Thus, the PM1000N may be used to accurately measure the respiratory
rates of patients in general wards.
Declarations
Funding:
The authors have not received any funding.
Conicts of interest/Competing Interest:
The authors declare that they have no competing interests.
Data availability statement:
The datasets used and/or analyzed during the current study are available
from the corresponding author on reasonable request.
Code availability(software application or custom code):
None.
Author Contributions:
TI, JH, AS, SN, and HT designed the work, collected and analyzed the data. JH and
TI wrote the initial draft of the manuscript. TI, JH, AS and MY contributed to the analysis and
interpretation of the data and assisted in the preparation of the manuscript. All authors critically revised
the manuscript and approved the nal version for publication.
Acknowledgements
We would like to thank the patients who participated in this study.
Ethics Approval:
This single-center, retrospective, observational study was conducted at a university hospital. The study
design and protocol were approved by the Institutional Review Board (IRB) of Sapporo Medical University
(IRB-authorized number: 342-242, December 12th, 2022). This study does not constitute research using
human samples or tissues.
Consent to participate:
Owing to the retrospective observational nature of this study, the information was released on an opt-out
basis.The need for informed consent was waived bythe IRB of Sapporo Medical University
Consent to publish:
Owing to the retrospective observational nature of this study,consent for publish wasreleasedon an opt-
out basis.
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Tables
Table 1. Patient characteristics
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Variables (n = 20)
Age (years), Median [IQR] 75.6 [69.8 – 80.4]
Males, n (%) 7 (35.0)
Reasons for ICU admission
Cardiovascular surgery, n (%) 11 (55.0)
Sepsis, n (%) 2 (10.0)
Respiratory failure, n (%) 3 (15.0)
Cerebrovascular disease, n (%) 2 (10.0)
Other 2 (10.0)
Abbreviations: IQR, interquartile range
Table 2. Respiration rate for each measurement method
Variables Respiratory rate
(n = 99)
Visual inspection, mean ± SD 17.4 ± 3.9
Bedside monitor, mean ± SD 18.3 ± 3.7
PM1000N, mean ± SD 17.2 ± 3.9
Abbreviations: SD,standard deviation: PM1000N, NellcorTM PM1000N: ICC, intraclass correlation
coecients
Table 3. Intra-class correlation coecient for each measurement method
Variables ICC (95% condence interval) F test with true value 0
Value
df1 df2
p-value
Bedside monitor 0.85 (0.79 – 0.89) 12.012 118 118 < .001
PM1000N 0.92 (0.88 – 0.94) 23.346 98 98 < .001
Abbreviations: IQR, interquartile range: PM1000N, NellcorTM PM1000N: ICC, intraclass correlation
coecients
Table 4. Comparison of the measurable and non-measurable points for respiratory rate using PM1000N
Page 12/13
the measurable
points
(n= 198)
the non-measurable
points
(n = 40)
p -
value
Vital signs
Body temperature (°C), [Median, IQR] 37.3 [36.7–37.6] 37.4 [37.2–37.6] 0.77
Pulse rate (/min), [Median, IQR] 85 [75–98.8] 84 [79.5–92] 0.49
Systolic arterial pressure (mmHg),
[Median, IQR] 122 [113–133.8] 133.5 [115.5–151.8] 0.02
SpO2 (%), [Median, IQR] 96 [95–97] 96.5 [95–98] 0.12
Arrhythmia, n (%) 54 (27.3) 36 (90) < 0.01
HFNC setting
FIO2 0.5 [0.4–0.5] 0.5 [0.4–0.6] 0.03
Flow 40 [40–50] 40 [40–50] 0.93
Abbreviations: IQR, interquartile range
Figures
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Figure 1
See image above for gure legend
