We prospectively collected information on a cohort of adult patients who were beneficiaries of the public health insurance scheme and who were admitted to the HMV program with well-defined inclusion and exclusion criteria. The most frequent diagnoses observed in the cohort were COPD with 35%, OHS with 23.9% and NMD with 16.3%, these results are explained for the last three national health surveys in Chile (20), where the prevalence of smoking (daily or occasional) in 2003, 2010 and 2017 was 43.5%, 39.8% and 33.3%, respectively. In turn, the 2004 PLATINO survey established a prevalence of COPD in Chile of 16.9% in individuals over 40 years of age (21). In the same Chilean health surveys, the prevalence of obesity in 2003, 2010 and 2017 was 23.2%, 28.4% and 34.4%, respectively, and the expected number of mega-obese individuals (BMI >40) increased from 148,000 people in 2003 to 415,000 in 2017 (20). We analyzed eight similar works published in the last 18 years, (table 4) From Janssens et al, in 2003 (22) to Cantero in 2020 (9), it is observed that OHS represents between 15.7% to 34% in those cohorts, except Windisch's work in 2003, In Australia and New Zealand, the most common indication for HMV was OHS in 31% cases of cases and NMD in 30% of cases (23). The prevalence of overweight and obesity reported in Australia was 63.4%, and in Tasmania, that of obesity was 32.3% (24). In Sweden, an analysis of 1526 patients with HMV between 1995 and 2006 showed that the most frequent diagnoses were OHS with 28%, COPD with 16%, non-ALS NMD with 15% and ALS with 11% (25).
The frequency of COPD varies between 6.3 % up to 34.5% y 39% (7,18,9), similar to that of our cohort which was 35%. The median age in Chilean program people was 59 years, similar to the published reports, however Melloni (7) and Cantero (9) reported a median age that exceeds 70 years (table 4).
Schwartz et al (26) and Laub and Midgren (25) describe baseline PaCO2, 52.5 and 53.6 mmHg respectively, prior to the onset of HMV, in our cohort was 58.2 mmHg, possibly representing the admission of patients with more severe disease or suboptimal therapeutic control. In addition, in our program 72.6% of patients started HMV in a stable chronic condition, similar to what is reported by Povitz et al (8) and Laub and Midgren (25); while the Cantero cohort only 55% patients started HMV in this condition (table 4).
A explanation for more ALS patients entering HMV programs over the past two decades relates to the increased availability of flow-cycled and pressure-limited equipment with alarm systems that are cheaper and easier to implement at patients' homes, there is also an increasing group of physicians and physiotherapists who are experts in this type of support which has allowed a growing number of patients to use this therapy at home.
In the series analyzed (table 4) the percentage of patients invasively ventilated through tracheostomy (TIV) varies between 3.1% and 12.4% (25,23,8,26) whereas in our cohort it was only 5.24%, this difference may be a consequence of the fact that in the Canadian program the most frequent diagnosis was NMD (30.4%) while the English cohort reported that it had 21.6% of patients with a diagnosis of ALS (26).
The HMV Chilean program includes socioeconomically vulnerable patients with a low monthly income and low educational level (27) but receive this home benefit at no cost, financed by the national public health insurance scheme. The baseline overall SRI score was 47 (35-62.1) points and expresses the severe limitation and alteration of the perception of quality of life of patients. Valko et al. reported an overall SRI score of 57.7 (± 14) (28), which is higher than ours. In our cohort, the APGAR family dysfunction score, which evaluates the functionality of the family group, was 10, and indicates important family support to the patient for the management of their disease (15,16).
The admission of patients with CRF to our program could be considered late compared to other countries as suggested by the PaCO2 levels, but we respect the indications of the 1999 consensus. Another reason that explains this is that among the criteria for admission to the Chilean national program, it is established that "the patient must have had been hospitalized for decompensation with CRF in the last 12 months". This condition was necessary at the time of the creation of the program to reduce the number and duration of hospitalizations of the most severe patients, but now we must review the admission criteria and modify them so that patients are admitted to the program early.
In 2020, Schwarz et al. analyzed the time elapsed from admission to death of 1,210 patients on HMV in England and described that patients with ALS had the lowest mean survival, of 7 (3-14) months, whereas patients with OHS on HMV had the longest survival, 33 (13-75) months, and the mean survival of the overall cohort was 19.5 (6-55) months; in addition, 150 patients (12.4%) were ventilated through tracheostomy (26). The Swedish group describes that of its 1526 patients, only 6% were ventilated through tracheostomy and that the worst survival was observed in patients with ALS, with 20% survival at 2 years and 5% at 5 years (25). In the Chilean program, the mean time in HMV of patients with OHS was 42.3 (± 32.4) months, while in patients with ALS, it was 14.8 (± 10.4) months.
Program weaknesses and strengths
Baseline functional data at program admission, such as maximum inspiratory pressure (MIP), lung volumes and capacities, carbon monoxide diffusing capacity (DLCO) and polygraphs, were not available for all patients because some hospitals where the patients were evaluated did not have the equipment acquire these data. The measurement of DLCO and lung volumes and capacities has been described as having prognostic value, especially in COPD patients (29).
The SRI questionnaire was completed by all patients who had the ability to provide reliable information. At the beginning of the program, we did not have the validated Chilean version of the SRI questionnaire. The present cohort only represents the adult beneficiaries of the Chilean public health system, and it does not consider adults with private health insurance in need of HMV, whose number we do not know.
The strengths of this study include the fact that the HMV program was started gradually, first in the metropolitan region, which includes the capital of Chile, Santiago de Chile (6,1 million inhabitants); 3 years later, it was expanded to different regions of the country, and 6 years later, patients who needed invasive ventilation were included. Additionally, there has been low turnover in the technical team responsible, which includes medical doctors, physiotherapists and nurses as well as professionals in the hospitals located in different regions of the country. This differs from other countries in which care is often provided by private health care companies or community providers (30).