Assessment of Dyspnea in Critically Ill Patients: A Comparative Analysis of Evaluation Scales

Purpose This study aimed to evaluate the Respiratory Distress Observation Scale (RDOS), Intensive Care RDOS (IC-RDOS), and Mechanical Ventilation RDOS (MV-RDOS) as potential markers of dyspnea in ICU patients by describing their relationship with the Dyspnea Visual Analog Scale (D-VAS). Materials and methods A researcher and a trained nurse independently assessed ICU patients simultaneously. One researcher assessed the RDOS (IC/MV-RDOS) and the depth of sedation. An objective evaluation using the observational D-VAS was simultaneously performed by a trained nurse. Results The correlation coefficients for each scale were 0.338 for the D-VAS and RDOS, 0.239 for the IC-RDOS, and 0.237 for the MV-RDOS, indicating a low correlation. The prediction of self-reported dyspnea showed that each scale's area under the curve (AUC) as a predictor of D-VAS ≥4 was 0.79 (95% Confidence Interval [CI] 0.71-0.87) for RDOS, 0.77 (95% CI 0.68-0.84) for IC-RDOS, and 0.73 (95% CI 0.64-0.81) for MV-RDOS. Conclusions The objective rating scales RDOS, IC-RDOS, and MV-RDOS can predict subjective dyspnea to a certain extent; however, they have limitations in accurately discriminating dyspnea intensity.


Introduction
Dyspnea is one of the most distressing and serious symptoms in the intensive care unit (ICU) and may be indicative of impending patient death [1].Approximately 50% of ventilated patients experience dyspnea, which is associated with adverse patient outcomes such as anxiety, prolonged mechanical ventilation, noninvasive ventilation failure, and mortality [2][3][4].Therefore, it is important to assess and quantify dyspnea in critically ill patients.
Several tools are available for assessing dyspnea.The Dyspnea Visual Analog Scale (D-VAS), a subjective assessment, is a valid tool for patients who can self-report, but it is not applicable for those who cannot selfreport [5].The Respiratory Distress Observation Scale (RDOS) was developed to objectively assess physical and behavioral signs of dyspnea [6].Subsequently, tools such as the Intensive Care RDOS (IC-RDOS) for patients admitted to the ICU and the Mechanical Ventilation RDOS (MV-RDOS) for ventilated patients have been developed [7,8].However, the most suitable tools for assessing dyspnea in ICU patients remain unclear.This novel study compared the validity of the D-VAS, a subjective dyspnea assessment, with objective assessment tools such as RDOS, IC-RDOS, and MV-RDOS.

Patients and setting
This prospective observational study was conducted in a 12-bed general ICU at an 800-bed university hospital from February 2020 to February 2021.This study aimed to evaluate RDOS, IC-RDOS, and MV-RDOS as putative markers of dyspnea in ICU patients by describing their relationship with the D-VAS.
In this study, adult ICU patients who had been receiving ventilation for >24 hours were included.Exclusion criteria included patients aged <20 years, patients predicted to die within 48 hours, those who received mechanical ventilation for ≥24 hours before ICU admission, those who received neuromuscular blocking agents, those who had paralysis/neuromuscular disorders, and those with a history of psychiatric illness and could not understand Japanese.

Ethics review and informed consent
The study was approved by the review committees of the Institutional Review Board of the Study Coordinator Center of Ibaraki Christian University (approval #2019-013) and the Clinical Research Ethics Review Committee of the University of Tsukuba Hospital (approval #R01-184).Informed consent was obtained in writing after explaining the details of the study to the patients or their relatives in accordance with Institution Review Board recommendations.

Data collection
Recorded baseline characteristics included age, sex, BMI, reason for ICU admission, and severity of illness.The severity of illness was calculated using the Acute Physiology and Chronic Health Evaluation II at ICU admission.Depth of sedation was assessed using the Richmond Agitation-Sedation Scale at the time of dyspnea measurement.The use of sedative analgesics and ventilation status were investigated at the time of dyspnea measurement.
The RDOS is an eight-item ordinal scale (heart rate, respiratory rate, restlessness, abdominal paradox, neck muscle use during inspiration, grunting, nasal flaring, facial expression of fear) designed to measure the presence and intensity of respiratory distress in adults [6].The IC-RDOS evaluates five items, including heart rate, neck muscle use during inspiration, abdominal paradox, facial expression of fear, and supplemental oxygen, which were modified from the RDOS for patients admitted to the ICU [8].The MV-RDOS is a tool that modifies the IC-RDOS supplemental oxygen item to respiratory rate in patients requiring ventilation [7].The intensity of dyspnea was assessed by D-VAS (10 cm VAS, from "no respiratory discomfort" to "unbearable respiratory discomfort"); a D-VAS of 4 or greater was indicative of dyspnea [7].
A researcher and a trained nurse were responsible for the evaluation.This pair assessed ICU patients simultaneously and independently.One researcher assessed RDOS (IC/MV-RDOS) and depth of sedation.One trained nurse simultaneously performed objective assessments using the observational D-VAS.

Sample size
Owing to the lack of dyspnea data in the ICU population, formal sample size estimation was not conducted; however, based on a previous study [7], we set the observation point at around 120.

Data analysis
Data were presented as numbers and percentages for qualitative data.For quantitative data, data were presented as means and standard deviations for parametric distribution data and medians and interquartile ranges for nonparametric distribution data.
The association between RDOS, IC-RDOS, MV-RDOS, and D-VAS was examined using Spearman's rankorder correlations.A correlation coefficient of <0.20 was considered as a "slight, almost negligible correlation," 0.20-0.40 as "low correlation," 0.40-0.70 as "moderate correlation," 0.70-0.90as "high correlation," and >0.90 as "very high correlation." The area under the receiver operating characteristic curve (AUC) was employed to evaluate the predictive ability of RDOS in detecting patients with self-reported dyspnea.The sensitivity and specificity of the various RDOS cutoff points were calculated, and the optimal RDOS cutoff score for our sample was determined using the Youden index.Analysis was performed using STATA version 17.0 statistical software.

Sample characteristics
In total, 719 patients were admitted to the ICU, and 656 were excluded (Figure 1).Data for the remaining 63 patients were collected, and their characteristics are shown in Table 1.Each participant was evaluated once or twice, and 112 observations were recorded.Self-reported dyspnea was present in 8.0% (9/112) of patients, and the mean D-VAS was 0.98 (1.20).

Research question results
Regarding the correlation coefficients for each scale, both D-VAS and RDOS were 0.338, the IC-RDOS was 0.239, and the MV-RDOS was 0.237, indicating a low correlation.Furthermore, both the RDOS and IC-RDOS were 0.641, the MV-RDOS was 0.715, and the IC-RDOS and MV-RDOS were 0.901, indicating a high correlation (Table 2).Prediction of self-reported dyspnea showed that each scale's AUC as a predictor of D-VAS ≥4 was 0.79 (95% confidence interval [CI] 0.71-0.87)for RDOS, 0.77 (95% CI 0.68-0.84)for IC-RDOS, and 0.73 (95% CI 0.64-0.81)for MV-RDOS (Figure 2).The optimal cutoff points and sensitivity and specificity of each scale revealed that RDOS had the highest sensitivity and specificity of 88.9 and 56.3, respectively, when the cutoff was ≥1.IC-RDOS had the highest sensitivity and specificity of 66.7 and 81.6, respectively, when the cutoff was ≥2.5, whereas MV-RDOS had the highest sensitivity and specificity of 77.8 and 68.0, respectively, when the cutoff was ≥2 (Table 3).
RDOS, Respiratory Distress Observation Scale; IC-RDOS, Intensive Care Respiratory Distress Observation Scale; MV-RDOS, Mechanical Ventilation Respiratory Distress Observation Scale; AUC, area under the receiver operating characteristic curve; CI, confidence interval.

Discussion
These results suggest that an objective rating scale may predict dyspnea to a certain degree.However, using an objective rating scale to accurately discriminate dyspnea, which is a subjective symptom, may be difficult.
Regarding the correlation between D-VAS and RDOS, the results of previous studies were similar to those of the present study [7].The correlation between D-VAS and IC/MV-RDOS was low, although it was moderate in previous studies [7,8].This discrepancy may be attributed to fewer patients (8%) reporting dyspnea in the present study and the resulting differences in analysis methods.Moreover, these findings suggest that higher RDOS, IC-RDOS, and MV-RDOS scores do not necessarily have a linear relationship with the intensity of symptoms accompanying subjective dyspnea.
Moreover, the concurrent validity of the D-VAS and objective rating scale was evaluated.Based on the AUCs of each scale in the present study, the predictive ability of self-reported dyspnea severity was high for the RDOS, IC-RDOS, and MV-RDOS.The AUCs for each measure in this study were first-rate; however, compared to previous studies, the AUCs for RDOS, IC-RDOS, and MV-RDOS were 0.75, 0.86, and 0.77, respectively [7,8], indicating that the predictive ability of IC-RDOS was slightly inferior.This difference may also be attributed to the small sample size of patients who reported dyspnea.No large differences were observed in the AUC for RDOS compared to previous studies.Furthermore, although it was low (0.338), the correlation coefficient was the highest of the three.Therefore, in the ICU setting, the RDOS is the most appropriate because these are the only three tools available to assess dyspnea in patients who cannot selfreport.
IC-RDOS and MV-RDOS were highly correlated, the only differences being the oxygen supply and respiratory rates.Therefore, when objectively assessing dyspnea in the ICU, either IC-RDOS or MV-RDOS may be employed regardless of whether or not the patient is on a ventilator.However, the MV-RDOS is composed of respiratory rates, which allow for fine differences in scores and may be versatile for ICU patients.
This study had several limitations.First, this observational study was conducted at a single-center university hospital, and its generalizability was low.Second, to evaluate the correlation with the D-VAS score, patients were assessed after they had recovered sufficiently to be able to self-report.Therefore, the proportion of patients who reported dyspnea was small, which may have influenced our present results.Dyspnea should be assessed under more severe conditions.Third, we set a goal of approximately 120 observations based on the sample size of previous studies, with multiple observations per patient.This could affect the incidence of dyspnea.In the future, a multicenter study will be required to improve sampling efficiency and assure external validity.

Conclusions
In this study, the objective rating scales RDOS, IC-RDOS, and MV-RDOS were evaluated as putative markers of dyspnea in patients admitted to the ICU by describing their relationship with D-VAS.RDOS, IC-RDOS, and MV-RDOS were found to predict subjective dyspnea to a certain extent; however, it is difficult to discriminate dyspnea accurately.RDOS has the highest correlation with D-VAS of the three tools.Therefore, RDOS may be appropriate when objectively assessing dyspnea in the ICU.

FIGURE 1 :
FIGURE 1: The flowchart depicts the patient recruitment ICMJE uniform disclosure form, all authors declare the following: Payment/services info: This work was supported by the Japan Society for the Promotion of Science Kakenhi (Grants-in-Aid for Scientific Research) (Grant Number 19K10859).The funders played no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work.Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.

TABLE 3 : Optimal cutoff points, sensitivity, and specificity of each scale
RDOS, Respiratory Distress Observation Scale; IC-RDOS, Intensive Care Respiratory Distress Observation Scale; MV-RDOS, Mechanical Ventilation Respiratory Distress Observation Scale.