Validating respiratory rate measurements in patients receiving high flow nasal cannula: a comparative study of Nellcor PM1000N and visual inspection

Abstract

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-flow 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.
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 coefficients, intraclass correlation coefficients (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.
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 to 0.2987) and p < .001 (95% CI 16.4609–17.9532), respectively.
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.

Full text

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Discover Medicine
Research
Validating respiratory rate measurements inpatients receiving
high flow nasal cannula: acomparative study ofNellcor PM1000N
andvisual inspection
TakumaIwaya1· JunpeiHaruna1,2· AkiSasaki1· SayakaNakano1· HiroomiTatsumi2· YoshikiMasuda2
Received: 8 March 2024 / Accepted: 4 November 2024
© The Author(s) 2024 OPEN
Abstract
Purpose Recently, the Nellcor PM1000N was developed for the concurrent assessment of respiratory rate and percuta-
neous 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 coecients, intraclass correlation coecients (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 dierences were p = 0.947 (95% CI −3.186 to 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 eective application in patients receiving HFNC.
1 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 measure-
ment 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
* Junpei Haruna, jp.haruna@hotmail.co.jp | 1Department ofNursing, Sapporo Medical University Hospital, Sapporo, Japan. 2Department
ofIntensive Care Medicine, Sapporo Medical University School ofMedicine, South-1, West-16, Chuo-Ku, Sapporo, Hokkaido060-8543,
Japan.

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optical-based respiration rate monitoring [12]. However, in general ward settings, the enumeration of respiratory rate typi-
cally 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, 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 eects on work breathing com-
pared 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 (Nellcor™ 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 ecacy 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 dierence
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.
2 Methods
2.1 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).
2.2 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 respira-
tory rate was not recorded in the EHR were excluded from this study.
2.3 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 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 from an ECG impedance (BSM-1763 Life-
scope PT, Nihon Kohden Co. Ltd., Tokyo, Japan: ECG impedance) 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.
2.4 HFNC initiation criteria
In our ICU, the HFNC initiation criteria include sharing of the patient’s condition and a discussion regarding the appropri-
ateness of introducing HFNC according to the HFNC guidelines by the intensivist, attending physician, and ICU medical
sta [22].

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2.5 Respiratory rate measurement procedure
2.5.1 PM1000N
An adhesive SpO2 measurement sensor (Nellcor™ OxySensor III), utilized in conjunction with the PM1000N, was axed
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. In our ICU,
the PM1000N sensor is attached to a sensor on the digit opposite the arm where blood pressure is measured.
2.5.2 ECG impedance
The electrodes were axed to the patient’s skin at the anterior and lateral chest walls using bipolar leads for all induc-
tions. 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 modication of the respiratory measurement current.
The subsequent amplication and computation of this signal yielded a visually represented respiratory curve.
2.5.3 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.
2.6 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. The secondary endpoint was to validate the dierence in correlation
coecients between respiratory rate measured with PM1000N and ECG impedance and visual inspection.
2.7 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 coecients and intraclass correlation coecients (ICC) were calculated for each
measurement method based on visual inspection to validate the accuracy of the PM1000N and ECG impedance. 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 dierence. 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 signicance was set at p < 0.05. In addition,
a correlation coecient dierence test was performed to compare the high usefulness of PM1000N and ECG impedance.
Statistical analyses were performed using the SPSS software version 27 (IBM Corp., Armonk, NY, USA).
3 Results
3.1 Patient characteristics
Of the 354 individuals admitted to our ICU during the study period, 334 were ineligible based on the prespecied exclu-
sion criteria. Excluded patients comprised 330 patients who did not use HFNC and 4 patients whose respiratory rate
was not recorded.
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 aecting 11 (55%) patients, representing approximately 50% of all cases.

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During the observation period, the respiratory rate was recorded 119 times. Visual inspection and ECG impedance
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, ECG impedance,
and PM1000N were 17.7 ± 3.9, 18.3 ± 3.7, and 17.2 ± 3.9, respectively.
The intra-class correlation coecients between the ECG impedance and PM1000N, based on visual inspection, are
listed in Table2. The correlation of respiratory rate by each measurement method based on visual inspection and the
Bland–Altman plot and linear correlation plot are shown in Figure1. The correlation coecients between the ECG imped-
ance and PM1000N based on visual inspection were 0.85, p < 0.001 and 0.84, p < 0.001, respectively. Furthermore, a cor-
relation coecient dierence test revealed that PM1000N was more useful than ECG impedance in measuring respiratory
rate (p = 0.01).
The respiratory rate could not be measured at 20 points using PM1000N. A comparison of the measurable and non-
measurable points for the respiratory rate using PM1000N is shown in Table3.
Arrhythmias were signicantly more common at non-measurable points than at measurable points (54 (27.3%) vs.
36 (90), P < 0.01).
4 Discussion
This study aimed to validate the automated respiratory rate measurement of PM1000N in patients using HFNC. Respira-
tory rate measurements with the PM1000N showed a better correlation with visual inspection than with the impedance
method by ECG impedances, 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 varia-
tions: 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 [23]. 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 cu, the measured value will be unstable [24]. However, in this study, we believe that this eect was
avoided by attaching the sensor to the nger opposite the arm where the blood pressure was measured.
Table 1 Patient characteristics
IQR interquartile range
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)
Table 2 Intra-class correlation
coecient for each
measurement method
IQR interquartile range: PM1000N, Nellcor™ PM1000N: ICC intraclass correlation coecients
Variables ICC (95% condence
interval) F test with true value 0
Value df1 df2 p-value
Bedside monitor 0.85 (0.79–0.89) 12.012 118 118 < 0.001
PM1000N 0.92 (0.88–0.94) 23.346 98 98 < 0.001

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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 Lynn etal. [25] 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 scor-
ing component [26, 27]. 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 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
Fig. 1 Bland–Altman and linear correlation plots of respiratory rate for various combinations of visual inspection, bedside monitoring, and
PM1000N
Table 3 Comparison
of the measurable and
non-measurable points
for respiratory rate using
PM1000N
IQR interquartile range
The measurable
points (n = 99) The non-measurable
points (n = 20) 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

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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 percentage of
patients at the non-measurable points had arrhythmia than those at the measured points. Moreover, the safety and ecacy
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 respira-
tory 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.
Lynn etal. [25] 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 intu-
bation in patients on HFNC includes the respiratory rate as a scoring component [26, 27]. Moreover, continuous, rather than
cross-sectional, physiological monitoring based on these scores and indicators is useful for the early detection of patient dete-
rioration. 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 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 percentage of
patients at the non-measurable points had arrhythmia than those at the measured points. Moreover, the safety and
ecacy 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.
4.1 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 obser-
vational study. Additionally, the patients’ diseases and other backgrounds varied, which may have resulted in dierent
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.
4.2 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.
5 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 accuracy as visual inspection.
Thus, the PM1000N may be used to accurately measure the respiratory rates of patients in general wards.

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Acknowledgements We would like to thank the patients who participated in this study.
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 manu-
script. 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.
Funding The authors have not received any funding.
Data availability The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable
request.
Code availability None.
Declarations
Ethics approval and consent to participate This study was conducted in accordance with the principles of the Helsinki Declaration of 1975.
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. Due to the observational nature of this study, the information was released
on an opt-out basis. Note that this study is not an experiment on human subjects and/or a study using human tissue samples. 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
by the IRB of Sapporo Medical University.
Consent for publication Owing to the retrospective observational nature of this study, consent for publish was released on an opt-out basis.
Competing interests The authors declare no competing interests.
Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which
permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to
the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modied the licensed material. You
do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party
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