European Journal of Cardiovascular Medicine

Respiratory failure occurs when the lungs are no longer able to adequately provide oxygen to the bloodstream or effectively remove carbon dioxide, compromising one or both critical aspects of gas exchange. Severe hypoxemia with PaO2 less than 60 mmHg without presence of hypercapnia is termed as acute hypoxemic respiratory failure (AHRF) otherwise known as type 1 respiratory failure. Multiple pathophysiological mechanisms are said to be associated with AHRF - decreased inspired Po2, impaired diffusion, hypoventilation, ventilation-perfusion mismatch, and right-to-left shunt.1

Managing respiratory failure involves addressing the root cause of the condition while simultaneously ensuring adequate oxygen delivery and ventilatory support. Initial management of acute respiratory failure include systematic assessment of the airway, breathing, and circulation (ABC). Further supportive interventions depend upon presence of patent airway to facilitate adequate gas exchange and normalize arterial blood gas parameters.1

Non-invasive oxygen delivery methods, including high-flow nasal cannula (HFNC) and continuous positive airway pressure (CPAP), are used as first-line interventions for managing respiratory failure.2,3

When less invasive interventions fail to achieve adequate respiratory support, endotracheal intubation and initiation of mechanical ventilation become necessary.2

One of the most important advantages of NIV is that, it can be managed by the nurses in the wards without the need for presence of physician, anesthesiologist/intensive care specialist. However, this process is associated with higher failure rate which is reported to range between 25% to 49%.4

Since the success rate is less, a prediction score was developed by Duan et al based on various clinical parameters which include Heart rate, acidosis, level of consciousness, oxygenation and respiratory rate – specified as HACOR score.5

Availability of such score helps in early prediction/identification of cases in whom NIV might fail and need further invasive ventilation.

Since the HACOR score is based on clinical parameters that can be assessed at bedside, this can easily be administered to predict the need for invasive ventilation. This would be helpful in initiating intubation at the earliest and reduce the mortality. Despite notable progress in therapeutic approaches, acute hypoxemic respiratory failure (AHRF) continues to be associated with high mortality rates—approximately 40% among patients admitted to intensive care, regardless of the underlying etiology.6 Thus, research studies are needed to identify its usefulness.

Objectives

1. To predict NIV failure in patients with hypoxemic respiratory failure.
2. To identify the outcomes in high-risk NIV failure patients who underwent intubation at different time points.

This study was performed in the intensive care unit (ICU) of a Khaja Banda Nawaz Teaching and Genera hospital Kalaburagi. The study group comprised of 42 patients admitted in ICU, based on inclusion and exclusion criteria mentioned below.

Inclusion Criteria: All patients who were admitted to the ICU for NIV due to hypoxemic respiratory failure were enrolled in the study.

Exclusion Criteria:

·         Presence of do-not-intubate orders.

·         Requirement for emergency intubation

·         NIV intolerance.

Informed consent was obtained from patients or their family members. The decision to initiate NIV was made by the attending physicians/ Intensivists based on the following criteria.

Clinical presentation of respiratory distress at rest (such as active contraction of the accessory inspiratory muscles or paradoxical abdominal motion),

Partial pressure of arterial oxygen (PaO2) of <60mmhg or a PaO2/fraction of inspired oxygen (Fio2) ratio of <300 with supplemental oxygen.

At the beginning of treatment, continuous use of NIV was encouraged. Once the patient recovered from respiratory failure, NIV was used intermittently until the patient could be completely weaned from it.

NIV failure was defined as requirement of intubation after NIV intervention based on the following criteria: respiratory or cardiac arrest, failure to maintain a PaO2/ FiO2 of >100, development of conditions necessitating intubation to protect the airway (coma or seizure disorders) or to manage copious tracheal secretions, inability to correct dyspnoea, lack of improvement of signs of respiratory muscle fatigue, and hemodynamic instability without response to fluids and vasoactive agents.

Sample size: According to the reference article the mean HACOR SCORE in NIV failure patients was found to be 7.3 and standard deviation of 3.5.5 Considering 1% level of significance and also with 20% relative precision around the estimated mean, the total sample size for the present study was determined as 42.

Sampling Method: Consecutive sampling method (A Non-random sampling method).

Statistical Analysis Plan (SAP): Summary measures like mean and standard deviation were used to estimate the HACOR score. Frequency and proportion were used to describe the patients demographic and clinical factors.

Receiver Operating Characteristic (ROC) curve was used to predict the classification ability of HACOR score to predict the failure of NIV among acute hypoxaemia respiratory failure.

Binary logistic regression analysis was used to estimate the risk of failure of NIV compared with success. Significance was considered at 5% significance level (p<0.05).

The study included a total of 42 patients with acute hypoxemic respiratory failure.

The characteristics of the patients are depicted in the table 1. The mean age was similar among patients in whom NIV was success and failure. Majority of the patients in both the groups were males. The mean age of the patients admitted was 57.2 years and majority were male. The comorbidities such as diabetes mellitus, systemic hypertension and chronic kidney disease were present among 26.2%, 31% and 11.9% respectively. The duration of hospital stay was more among patients in whom NIV has failed and there was a need to intubate compared to cases in whom NIV was successful (9.39 days vs 6.67 days). Among the 42 patients with AHRF, NIV was successful in 57.1% and failed in 42.9% resulting in intubation. (Figure1)

The mean HACOR score was significantly high among patients in whom NIV has failed (7.67) compared to score of 5.13 days among cases in whom NIV was successful. (Table 2) The sensitivity and specificity of HACOR in predicting the failure of NIV among the patients was 94.4% and 95.8% respectively. (Table 3) The area under the curve (AUC) was 0.96. The risk of failure of NIV is more when the HACOR score is 4 and less. (Figure 2)

Table 4 describes the outcome of the patients based on the success or failure of NIV. Among the patients in whom NIV was successful, 1 died (4.2%) and among the patients in whom NIV has failed, 2 have died resulting in proportion of 11.1%. The death rate was high among patients in whom NIV has failed, yet this was not significant with p value of 0.38.

Table 1: Characteristic of the patients with acute hypoxemic respiratory failure

Table 2: The mean HACOR score between the patients with NIV success and failure

Table 3: Sensitivity and specificity of HACOR in predicting NIV failure

Table 4: Outcomes in high-risk NIV failure patients who underwent intubation

The present study was conducted among patients with acute hypoxemic respiratory failure. In the present study NIV has failed in 42.9%. As per a review by Nair et al, NIV has high failure rate among patients with AHRF which ranges from 25% to 49%.4 The failure rate in the present study is within this range. The intubation rate specified in a study by Frat et al among patients with acute hypoxemic respiratory failure managed with NIV was 50%.3 The rate of requirement for intubation with NIV management was high in this study compared to the present study (50% vs 42.9%). The failure rate of NIV in a study by Magdy et al was 33.3% which is less than the current study. The higher rate of NIV failure in our study could be due to higher proportion of patients being admitted with severe illness which resulted in the need for invasive ventilation.7

The failure rate of NIV as per the reports of Duan et al was 47.8% in the initial cohort in whom the scoring pattern was first studied. This proportion is higher than the present study.5

The NIV failure rate reported in a study by Carrillo et al was 35% which is less than the present study.8

In the present study, the ROC curve showed that patients with HACOR score of more than 4 has high risk of NIV failure.  A study by Duan et al reported that the HACOR score of more than 5 has high chance of NIV failure.5

In their study among non-COPD patients with AHRF, Ding et al reported that patients in whom the HACOR was high, the chance of NIV failure was also high. The proportion of patients those who required tracheal intubation was 13% which is an indication of NIV failure.9 In the current research work, we have also found that the chance of failure is high in patients with high HACOR score.

The present study, the sensitivity and specificity of HACOR in predicting the failure of NIV was 94.4% and 95.8% respectively at cutpoint of 4. In their study, Ding et al reported sensitivity and specificity of HACOR score of 5 as 90% and 85% respectively. This study also assessed HACOR and its prediction on NIV at various time periods – 12, 24 and 48 hours with which it was found that score of <6 has failure of less than 85%.

A study by Magdy et al reported sensitivity and specificity of 81.2% and 91% at HACOR score of >6. The present study had better sensitivity and specificity compared to this study at cut point of >4.7  

Similar to the present study, another study done by Guia et al also reported that HACOR had good performance in predicting the CPAP failure among COVID-19 patients and also its related complications.10

A study by Carrillo et al reported optimal cutoff point of 8 at first hour of initiation of NIV as having best predictive ability and had concluded that HACOR accurately predicts NIV failure.8 

Another study by Teh et al done among patients with acute decompensated heart failure also reported that HACOR score is useful in predicting the failure of NIV.11

The study finding shows that HACOR can be used as an effective tool among patients with AHRF in predicting NIV failure. The patients with high score has higher chance of failure. The results of the study indicates that patients with HACOR score of more than 4 may end up in need of intubation from initial management with NIV.

1.       Mirabile VS, Shebl E, Sankari A, et al. Respiratory Failure in Adults. [Updated 2023 Jun 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526127/

2.       Acute Respiratory Failure. BMJ Best Practice. https://bestpractice.bmj.com/topics/en-gb/853

3.       Frat JP, Thille AW, Mercat A, Girault C, Ragot S, Perbet S et al. High-Flow Oxygen through Nasal Cannula in Acute Hypoxemic Respiratory Failure. N Engl J Med 2015;372:2185-96.

4.       Nair A, Esquinas A. HACOR score to predict failure of non invasive ventilation in patients with acute hypoxemic respiratory failure: When simplicity is best. Saudi J Anaesth 2022;16:267 8.

5.       Duan J, Han X, Bai L, Zhou L, Huang S. Assessment of heart rate, acidosis, consciousness, oxygenation, and respiratory rate to predict noninvasive ventilation failure in hypoxemic patients. Intensive Care Med 2017;43:192 9.

6.       McNicholas B, Rezoagli E, Laffey JG. Acute hypoxaemic respiratory failure and acute respiratory distress syndrome. InMechanical ventilation from pathophysiology to clinical evidence 2022 Mar 17 (pp. 149-163). Cham: Springer International Publishing.

7.       Magdy DM, Metwally A. The utility of HACOR score in predicting failure of high flow nasal oxygen in acute hypoxemic respiratory failure. Adv Respir Med 2021;89:23 9.

8.       Carrillo A, Lopez A, Carrillo L, Caldeira V, Guia M, Alonso N et al. Validity of a clinical scale in predicting the failure of non-invasive ventilation in hypoxemic patients. Journal of Critical Care. 2020;60:152-158.

9.       Ding M, Han X, Bai L, Huang S, Duan J. Impact of HACOR Score on Noninvasive Ventilation Failure in Non-COPD Patients with Acute-on-Chronic Respiratory Failure. Canadian Respiratory Journal. 2021; ID 9960667.

10.    Guia MF, Boleo-Tome JP, Imitazione P, Polistina GE, Alves C, Ishikawa O et al. Usefulness of the HACOR score in predicting success of CPAP in COVID-19-related hypoxemia. Respiratory Medicine. 2021;187:106550.

11.    Teh YH, Nazri MZAM, Azhar AMN, Alip RM. HACOR Score in Predicting Non-invasive Ventilation Failure in Acute Decompensated Heart Failure and AECOAD Patients. Eurasian J Emerg Med. 2022;21(3): 165-75.