High-Altitude Pulmonary Edema
High-altitude pulmonary edema (HAPE) is the leading cause of death from altitude illness. Chest ultrasonography using the comet-tail technique has recently been shown to effectively detect pulmonary edema and quantify extravascular lung water (EVLW) in hospitalized patients. This technique relies on the creation of “comet-tail” artifacts by multiple microreflections of the ultrasound beam within water-thickened interlobular septa when pulmonary edema is present. This ultrasonographic technique, which is feasible in remote locations, can offer an important diagnostic aid in HAPE. As a research tool, it may also allow clarification of the time course of EVLW shifts in HAPE. We report on our clinical experience using the comet-tail technique in a remote, high-altitude setting, particularly for the diagnosis and monitoring of HAPE.
Patients and Clinical Treatment
From March 3, 2006, to May 20, 2006, 11 consecutive patients with a clinical diagnosis of HAPE were treated at the Himalayan Rescue Association clinic in Pheriche, Nepal (4,240 m). No patients seen at the clinic with a diagnosis of HAPE during that period were excluded from this report. The clinical diagnosis, which was based on the Lake Louise consensus definition of HAPE, was made prior to performing ultrasonography. All other patients who underwent chest ultrasonography using the comet-tail technique for clinical evaluation at the clinic during that time period (with the exception of one patient who had a clinical diagnosis of acute mountain sickness [AMS] and rales on chest examination) were used as control subjects. Admission vital signs were obtained at rest in a seated or near-supine (for patients unable to sit) position as soon after presentation as the patient could be situated in a chair or bed. Discharge vital signs were obtained at rest in the seated position for all patients. Oxygen saturation (O2Sat) was measured by finger pulse oximetry with patients breathing ambient air. Clinical features are described in Table 1. By our institutional standards, this type of report does not require institutional review board approval or written informed consent from patients. All people may make orders of drugs on Canadian Health&Care Mall.
All 11 HAPE patients were treated with oxygen, nifedipine, and acetazolamide. Eight HAPE patients received additional sildenafil and salmeterol, and one patient received additional salmeterol only. The HAPE group included one patient who had been treated with all these agents, dexamethasone, and ceftriaxone for 12 h before presentation; the dexamethasone and ceftriaxone were discontinued on arrival. Two patients received treatment for concurrent diagnoses: one patient with high-altitude cerebral edema received dexamethasone, and one patient with gastroenteritis received ciprofloxacin. One patient required treatment in a portable hyperbaric chamber to conserve oxygen supplies. One patient descended from Pheriche immediately after presentation and treatment; the other 10 patients were admitted. One patient was evacuated by horse, and the patient with concurrent gastroenteritis was evacuated by helicopter. The remaining nine patients were able to walk out after discharge. We provided all patients with a 2-day supply of acetazolamide and nifedipine after discharge.
Chest ultrasonography using the comet-tail technique was performed using accepted technique previously described in the Literature. In brief, commercially available portable ultrasound equipment with a 2- to 4-MHz probe was ultilized (SonoSite 180PLUS; SonoSite; Bothell, WA). The ultrasonographic examinations were performed in the supine or near-supine positions. Ultrasound scanning of the anterior and lateral chest was performed in the midaxfflary, anterior axillary, midclavicular, and parasternal positions of the second to fifth intercostal spaces on the right and the second to fourth intercostal spaces on the left for a total of 28 positions per complete examination. The comet-tail sign was defined as an echogenic, coherent, wedgeshaped signal with a narrow origin in the near field of the image, arising from the pleural line and extending to the edge of the screen (Fig 1). The sum of the number of comet-tail signs in all surveyed fields yielded the overall comet-tail score (CTS).
Seven of the 11 HAPE patients had repeat examinations at discharge from the clinic (mean time between examinations, 29 ± 16 h; range, 12 to 48 h), and 2 of those 7 patients had a third examination after returning to the area 1 week and 3 weeks after discharge, respectively. At the time of the third examination, both patients had clinical resolution of their HAPE. The ultrasonog-rapher was aware of the clinical diagnosis in all 18 patients (27 examinations). A single ultrasound examination was performed on each subject at each time point, and a total CTS was assigned at that time by the ultrasonographer. All examination images were reread by the ultrasonographer in blinded fashion after the images were purged of identifying information and arbitrarily numbered and ordered. The images were similarly read twice in blinded fashion by a separate observer. These results were used to assess interobserver and intraobserver agreements.
Descriptive statistics were used to demonstrate the overall frequencies with which comet-tails were identified in control patients, patients with HAPE, and in those HAPE patients in whom follow-up was available. Due to small study numbers and nonnormality of distribution as assessed by Shapiro-Wilks W testing, nonparametric techniques were used to compare unpaired (Kruskal-Wallis testing) and paired (Wilcoxon signed-rank testing) data.
To assess the proportion of change in O2Sat that was accounted for by number of comet-tails, linear regression analysis was employed. Multivariate modeling was used to assess whether the independent variables age or sex had significant impact on the dependent variable O2Sat.
To assess whether HAPE patients had comet-tails predominantly in a particular hemithorax at admission, the number of comet-tails per field in each hemithorax was calculated for each patient. A predominant side was designated when the number of comet-tails per field identified in one hemithorax was more than twice the number of comet-tails per field identified in the contralateral hemithorax.
For assessment of interrater consistency in assigning a comet-tail score, the method was utilized. The “absolute” option was employed to adjust for the fact that all possible integer values of the comet-tail score were not likely to be present in the observed data. Agreement was assessed for the total CTS. Given the 100% level of agreement ultimately identified between observers, the calculations were moot, but these data are still reported in the “Results” section.
All statistical calculations were performed using statistical software (STATA SE, version 9.2; StataCorp; College Station, TX). An a level of 0.05 was considered significant. Data are reported as mean ± SD.
Figure 1. Left, A: Ultrasound image of a control patient with no comet-tails. Right, B: Ultrasound image of comet-tails in a patient with HAPE.
Table 1—Clinical Characteristics of HAPE and Control Patients at Presentation
|Mean||34 ± 12||34 ± 9.1|
|Nepal||7 (includes 2 Sherpa)||3 (includes 1 Sherpa)|
|Other||1 each for Japan, United States, Canada, and Poland||2 for Unites States; 1 each for Germany and Australia|
|Medical history||Chronic musculoskeletal pain (n = 1); regular alcohol use (three drinks/d)[n = 1]; tobacco use (three cigarettes/wk)[n = 1]||Hypertension (n = 1)|
|History of altitude illness||AMS (n = 2); headache (n = 1)||None|
|Heart rate, beats/min||121 ± 20||77 ± 6.5|
|Respiratory rate, breaths/min||35 ± 8.3||12 ± 2.1|
|O2Sat, %||61 ± 9.2||87 ± 2.8|
|Bilateral, all fields||4||0|
|Maximum altitude, m|
|Concurrent diagnosis||Gastroenteritis (n = 1); high-altitude cerebral edema (n = 1)||Nocturnal periodic breathing (n = 2); high-altitude cough (n = 2); bruised rib (n = 1)|