BÀI SOẠN VỀ SIÊU ÂM CHẨN ĐOÁN

Siêu âm ngực phát hiện sớm viêm phổi do đại dịch cúm H1N1 năm 2009, Americo Testa, Gino Soldati, Roberto Copetti, Rosangela Giannuzzi, Grazia Portale, Nicolo Gentiloni-Silveri, Critical Care 2012, 16:R30

Dẫn nhập: Hình ảnh lâm sàng của đại dịch cúm A (H1N1) thay đổi từ một nhiễm trùng tự giới hạn đến viêm phổi tiến triển nhanh. Cần chẩn đoán ngay và điều trị đúng lúc.

Chụp x-quang ngực (CRx) thường không phát hiện giai đoạn mô kẽ sớm. Mục đích của nghiên cứu này là để đánh giá các vai trò của siêu âm ngực cạnh giường bệnh trong việc xử trí sớm nhiễm virus cúm A (H1N1) 2009.

Phương pháp: 98 bệnh nhân gửi đến khoa cấp cứu vì triệu chứng giống như bệnh cúm đã được ghi danh trong nghiên cứu.

Bệnh nhân không có biểu hiện các hội chứng suy hô hấp cấp tính đã được xuất viện mà không cần khảo sát thêm. Trong số các bệnh nhân bị nghi ngờ lâm sàng của viêm phổi mắc phải, các trường hợp có chẩn đoán khác hoặc có bệnh khác kèm theo đều được loại trừ khỏi nghiên cứu.

Bệnh sử, xét nghiệm, Xquang ngực, CT scan nếu có chỉ định, góp phần xác định chẩn đoán viêm phổi ở các bệnh nhân còn lại. Siêu âm ngực được thực hiện bởi một bác sĩ cấp cứu, tìm hội chứng mô kẽ, đông đặc phế nang, đường màng phổi bất thường và tràn dịch màng phổi, trong 34 bệnh nhân có chẩn đoán sau cùng của viêm phổi, 16 ca có Xquang phổi bình thường ban đầu, và 33 ca không có viêm phổi, là nhóm chứng.

Kết quả: Siêu âm ngực ở tất cả đối tượng, được thực hiện mà không gây bất tiện, chỉ trong một thời gian tương đối ngắn (9 phút, khoảng 7-13 phút).

Kiểu siêu âm bất thường được phát hiện ở 32/34 bệnh nhân viêm phổi (94,1%). Kiểu SA của hội chứng mô kẽ được phát hiện ở 15/16 bệnh nhân có Xquang phổi bình thường đầu tiên, trong số đó 10 ca (62,5%) có chẩn đoán cuối cùng của viêm phổi virus (H1N1).

Bệnh nhân viêm phổi và Xquang phổi bất thường ban đầu, trong số đó chỉ có 4 ca có chẩn đoán cuối cùng của viêm phổi virus (H1N1) (22,2%, P< 0,05), chủ yếu là hiển thị kiểu siêu âm đông đặc phế nang. Cuối cùng, kiểu SA hội chứng mô kẽ dương tính được tìm thấy trong 5/33 ca nhóm chứng (15,1%).

Âm tính giả gồm 2/34 trường hợp (5,9%) và dương tính giả là 5/33 ca (15,1%), với độ nhạy 94,1%, độ đặc hiệu 84.8%, giá trị tiên đoán dương tính là 865% và giá trị tiên đoán âm tính là 93,3%.

Kết luận: SA ngực tại giường là công cụ hiệu quả để chẩn đoán viêm phổi ở khoa cấp cứu. Ngoài ra, SA ngực có thể phát hiện chính xác giai đoạn sớm bệnh nhân viêm phổi virus (H1N1) mà ban đầu có hình Xquang phổi bình thường.

Đề xuất tích hợp SA ngực vào xử trí lâm sàng theo lệ (routine).

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Kiểu SA của hội chứng mô kẽ (Interstitial syndrome): Có ít nhất 3 ultrasound lung comets trên mặt cắt dọc giữa 2 xương sườn từ mặt phân cách phổi-thành ngực trải ra theo hình nan quạt (xem hình dưới bên phải).

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Đọc thêm về ultrasound lung comet và sonographic interstitial syndrome:

Sonographic Interstitial Syndrome: The Sound of Lung Water

Gino Soldati, Roberto Copetti, Sara Sher, JUM February 1, 2009.

Objective. Ultrasound lung comets (ULCs) now have an acknowledged correlation with extravascular lung water, but they present in different orders and numbers in different pathologic pulmonary entities. How these artifacts are created is not yet known, and the literature gives discordant hypotheses.

Understanding their formation is the first step in understanding lung disease. The purpose of this study was to show the morphologic and genetic variability of interstitial lung disease studied with echography and thus to propose a unitary mechanism for the formation of ULCs.

Methods. This study included 3 parts: (1) a retrospective analysis of echographic lung images of patients with interstitial syndrome; (2) an analysis of the literature for definitions of the size of the pulmonary lobule; and (3) an experimental model of different air-water interfaces scanned with varying ultrasonic frequencies.

Results. The retrospective analysis of echographic lung images included 176 patients with diffuse ULCs: 118 patients had acute pulmonary edema; 18 had acute lung injury/acute respiratory distress syndrome; and 40 were premature neonates with respiratory distress syndrome. Experimental models permitted us to discover that ring-down artifacts are produced only by single and double layers of bubbles in specific structural settings.

Conclusions. Reverberation between bubbles with a critical radius seems to be at the origin of ring-down artifacts. Echographic manifestations of interstitial lung disease, whose genesis lies in the partial air loss of lobes and segments, are acoustic phenomena originating from variations in the tissue-fluid relationship of the lung. A correlation between anatomopathologic characteristics and structures of sonographic artifacts could allow more rapid and noninvasive diagnoses.

Key words: resonance, reverberation, ultrasound lung comets.

In recent years, lung sonography has undergone rapid development and gained increasing diagnostic potential. The evidence of echographic interstitial syndrome, in particular, has shown a significant correlation with extravascular lung water¹^,² in both adults and neonates³ in cases of pulmonary edema and noncardiogenic pulmonary edema (acute lung injury [ALI]/acute respiratory distress syndrome [ARDS]).⁴^,⁵ This has enabled sufficiently accurate diagnoses in the fields of cardiology, pediatrics, intensive care, and emergency medicine, helping differentiate bronchial disease from that of the interstitial space and alveoli.⁶^,⁷ Although clinical and experimental studies have confirmed the existing correlation between the artifacts that constitute interstitial syndrome (known as B-lines or ultrasound lung comets [ULCs]) and interstitial lung disease, the essence of the artifacts themselves, their biophysics, and their genesis are scarcely known.⁸^,⁹

Analysis of recent literature appears limited to the contributions on “ring-down artifacts” given by Avruch and Cooperberg¹⁰ and Lichtenstein et al,⁸ who actually recognize different anatomic substrates and different causal mechanisms as the origin of the echographic images. Lichtenstein et al⁸ attribute the origin of ULCs to the thickening of subpleural interlobular septa, which would cause “fragmentation” of the pleural specular reflector at the points of greatest impedance. Although they indicate that computed tomographic (CT) ground glass areas also produce closely related artifacts, a biophysical explanation able to clarify their origin (reverberation, resonance, or other) is not given. According to these authors, the pleural projection of interlobular septa and thus their correspondence with B-lines would be at a mean distance of 7 mm. Other authors of cardiologic extraction reproduced a similar hypothesis, which could be defined as “septal.”¹¹

Completely different is the hypothesis proposed by Avruch and Cooperberg¹⁰ in the gastroenterologic field¹² and later reviewed by Kremkau and Taylor,¹³ which, however, does not take into consideration the behavior of the lung, which was proposed by Kohzaki et al.¹⁴ In these cases, what the authors propose is a mechanism of resonance among groups of air bubbles in which the vibrating structure is the liquid film interposed between gaseous collections.
Because clinical evidence brings us to think that a different concentration and distribution of artifacts in each single intercostal thoracic scan is able to indicate different pathologic situations both for etiology and severity (eg, cardiogenic versus noncardiogenic pulmonary edema), we designed this study to better understand and delineate the biophysical basis of sonographic artifact formation in interstitial lung disease.
We hypothesized that the mechanism underlying artifact formation in interstitial lung disease is reverberation coherent with topologic and pathologic variations of the lung interstice, and we designed this study to validate this hypothesis.

Definitions

Practice in this field has produced terminology that has been described in both a review and a monograph. The following is a summary of the terms used in the article:

Comet tail artifact—

Sonographic artifact with an appearance similar to that of the ring-down artifact but more attenuated, shorter, and tapering in depth as in the tail of a comet. The mechanism underlying comet tail artifact formation is reverberation.

Interstitial-alveolar syndrome—

Interstitial syndrome with ULCs separated by a distance inferior to that present in septal syndrome and up to their confluency (Figure 1c).

Interstitial syndrome—

The presence of multiple ULCs (at least 3 in a longitudinal scan between 2 ribs) fanning out from the lung-wall interface.

Ring-down artifact—

Ultrasound artifact that appears as a series of bands or solid narrow-based spreading streaks radiating from a gas collection to the edge of the screen. Analysis of this artifact shows an acoustic signal with electronic processing converting this sound wave into a series of bands (Figure 1). In the literature, the mechanism producing ring-down artifacts is debated.

Septal syndrome—

The presence of interstitial syndrome with ULCs separated by a distance equivalent to that of the superficial pleural projections of interlobular septa (Figure 1, a and b).

Ultrasound lung comets—

Also known in the literature as B-lines, hyperechoic narrow-based artifacts (ring-down artifacts) spreading like laser rays from the pleural line to the edge of the screen. We considered the terms lung comets and ULCs equivalent when used to indicate a pulmonary interstitial syndrome. We did not consider comet tail artifacts, as described by Shapiro and Winsburg, equivalent to ULCs.

White lung—

Completely white echographic lung field with coalescent ULCs and no horizontal reverberation (Figure 1d).