Background
High-altitude pulmonary edema (HAPE) refers to the onset of breathlessness, cough, and fever at rest after arriving at high altitudes [
1]. It is a common high-altitude illness that occurs when individuals rapidly ascend to altitudes typically above 2,500 m [
2]. It is characterized by the accumulation of fluid in the lungs, leading to severe respiratory distress [
3]. With the increasing popularity of high-altitude tourism and mountaineering in high-altitude regions, the overall number of HAPE cases has also been on the rise [
4]. HAPE poses a significant health risk to individuals who venture into high-altitude regions.
Currently, the main treatment options for HAPE include descending to lower altitudes, supplemental oxygen, and the use of medications such as nifedipine [
5]. However, these interventions may not always be readily available or effective in all cases.
Furosemide, a diuretic medication, acts by inhibiting the reabsorption of sodium and chloride in the renal tubules, resulting in increased urine output and subsequent reduction in fluid overload [
6]. Its use in the treatment of HAPE is controversial, and there is limited research on this topic [
6]. However, in China, furosemide is included as a routine treatment measure for HAPE [
7,
8].
Therefore, it is crucial to study the efficacy of furosemide in the treatment of HAPE, as it has the potential to significantly impact the management and prognosis of HAPE patients. The aim of this study is to determine the overall effectiveness of furosemide as a therapeutic agent for HAPE.
Methods
Study subjects
We conducted a retrospective analysis of patients with HAPE admitted to the People’s Hospital of Shigatse City from January 2018 to September 2023. Inclusion criteria were age greater than or equal to 18 years and onset of symptoms within one week of arrival in high-altitude areas. Exclusion criteria were pregnancy or lactation, average arterial pressure < 65mmHg on admission, hospitalized for less than 3 days, and incomplete data (patients who did not undergo lung Computed Tomography (CT) assessments before and after treatment). The follow-up period extended from the time of admission to discharge. This study was approved by the Ethics Committee of the People’s Hospital of Shigatse City, and written informed consent was obtained from each patient or their family members (2023RKZRMYY12M008).
Patient management
During the emergency department visit, all patients underwent lung CT scans to confirm the presence of pulmonary edema. Upon admission, all patients received supplemental oxygen and bed rest. Symptomatic supportive treatment, including appropriate anti-infection and antihypertensive therapy, was administered based on the presence of complications such as respiratory tract infections and hypertension. The use of diuretics was determined by the attending physician’s experience. All patients completed lung CT examination three days after treatment. Patients were divided into a furosemide group and a control group based on whether furosemide was used on the day of admission. Subgroup analysis was further conducted based on the dosage and duration of furosemide use.
Clinical variables
Clinical variables were obtained by retrieving relevant data from the electronic medical record system and manually reviewing them, including demographic information, comorbidities, clinical assessments (vital sign), inflammatory markers (white blood cell count, C-reactive protein, procalcitonin), biochemical analysis (aspartate aminotransferase, total bilirubin, blood urea nitrogen, serum creatinine, potassium, glucose), D-dimer and arterial blood gas. The HAPE prognostic indicators recorded in this study included hospitalization duration and in-hospital mortality.
Radiographic assessment of pulmonary edema severity was performed by two experienced radiologists using the CT Severity Score. This method assigns a percentage score to pulmonary edema in each of the five lung lobes [
9]. The total CT score is the sum of scores from all lobes, ranging from 0 (no involvement) to 25 (maximum involvement). The specific scoring for each lung lobe is as follows:
1 point, < 5% involvement;
2 points, 5-25% involvement;
3 points, 26-49% involvement;
4 points, 50-75% involvement;
5 points, > 75% involvement.
Statistical analysis
Clinical data were analyzed using SPSS 26.0 statistical software. For missing values within 10% of the data, the mean substitution method is used, and for missing values exceeding 10%, the data are excluded. Independent sample t-tests or Mann-Whitney U tests were used for comparison of means, while chi-square tests or Fisher’s test were used for comparison of categorical variables. P-value < 0.05 was considered statistically significant.
Discussion
The findings of this study indicate that although the use of furosemide can accelerate the absorption of lung infiltrates in patients with HAPE. However, the clinical implications of these improvements in imaging findings on prognosis are still unclear, possibly due to the limited number of cases. It does not have a significant impact on reducing the length of hospital stay and in-hospital mortality.
HAPE is a non-cardiogenic pulmonary edema and differs from cardiogenic pulmonary edema, such as congestive heart failure [
10]. Cardiogenic pulmonary edema occurs when heart disease leads to a weakened pumping function of the heart or an excessive cardiac load, resulting in pulmonary congestion and increased pulmonary capillary pressure, ultimately causing fluid leakage into the lungs [
11]. Diuretics are commonly used medications for treating congestive heart failure, as they promote urine excretion to reduce fluid retention in the body and alleviate pulmonary edema symptoms [
12]. However, HAPE is caused by factors such as thin air at high altitudes and pulmonary vasoconstriction [
13]. Pulmonary vasoconstriction is associated with increased pulmonary vascular resistance and pulmonary artery pressure in patients [
14]. These changes result in an increase in pulmonary capillary hydrostatic pressure, followed by fluid leakage from the vascular space into the interstitium and alveolar spaces [
15]. Diuretics have limited effectiveness in treating HAPE, possibly due to the different pathogenesis of HAPE compared to congestive heart failure, and their limited ability to improve pulmonary vasoconstriction. Furosemide, as a loop diuretic, was found in our study to accelerate the absorption of lung infiltrates.
Through the study of lung imaging, it was found that although there was no difference in the severity scores of lung CT between HAPE patients before and after treatment, there was a difference in the change in scores. Patients who received furosemide showed a more significant reduction in lung infiltrates. Subgroup analysis further revealed that the longer the duration of furosemide use, the more pronounced the improvement in lung CT scores. Previous study [
16] primarily focused on the impact of diuretics on blood pressure and did not compare changes in pulmonary imaging. However, nifedipine, as one of the therapeutic drugs, may also have an effect on blood pressure [
17]. Therefore, this should not be a reason to hinder the use of diuretics in HAPE.
However, we also observed that although there may be improvements in imaging, these improvements may not necessarily translate into substantial improvements in prognosis, possibly due to the limited number of cases included. In the two cases of mortality, one was complicated by high-altitude cerebral edema, while the other had a high suspicion of pulmonary embolism. It is important to note that the length of hospital stay can be influenced by various factors, including subjective symptoms reported by patients, psychological factors, and transportation issues.
It is noteworthy that the mortality rate is high in HAPE patients who do not receive effective treatment [
18‐
20]. One of the most crucial measures for managing HAPE is to promptly descend to a lower altitude [
15]. However, it is interesting to observe that all the patients included in this study chose to remain at an altitude of 3820 m in the People’s Hospital of Shigatse City for treatment, and they achieved favorable treatment outcomes. This suggests that in cases where HAPE occurs, if a standardized treatment center can be promptly accessed, the descent to a lower altitude may be delayed without compromising the effectiveness of treatment. Marieke et al [
21]. reported that the majority of HAPE patients transported to the hospital fully recovered, which is consistent with our study.
The average age of the patients enrolled in this study was 34.15 years, and there was a minimal presence of patients with pre-existing chronic conditions. This could be attributed to the fact that individuals visiting high-altitude areas are aware of the potential impact on their physical health, which seems to be different from what was previously described in the literature [
22] as a lack of understanding among novices regarding the hazards of high-altitude exposure. Consequently, the study population consisted of individuals who were generally in good health prior to the onset of HAPE, with even patients who had comorbidities such as diabetes and hypertension being scarce.
The average time of onset for HAPE in this study was approximately 4 days after arriving at high-altitude areas, which is consistent with the 2–5 days reported in the previous literature [
23]. The latest onset of symptoms in our study occurred on the tenth day after entering the high-altitude area, which is later than what has been reported in the literature [
24]. This difference may be related to variations in factors such as oxygen supply facilities, level of exertion, and individual susceptibility.
Further research with larger sample sizes and longer follow-up periods is needed to elucidate the impact of imaging improvements on clinical outcomes and to better understand the various factors influencing hospital stay duration in HAPE patients.
Limitation
As our study is retrospective, it is prone to bias. The mortality rate of patients with HAPE after formal treatment is lower, and a larger sample size is needed to determine the effect of furosemide on in-hospital mortality in patients with HAPE.
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