Clinical Toxicology (2014), 52, 948–951 Copyright © 2014 Informa Healthcare USA, Inc. ISSN: 1556-3650 print / 1556-9519 online DOI: 10.3109/15563650.2014.958613
CRITICAL CARE
Sonographic signs of snakebite R. VOHRA,1 C. RANGAN,2 and R. BENGIAMIN3 1UCSF
Fresno Medical Center, California Poison Control System, Fresno, CA, USA Angeles Department of Public Health, Children’s Hospital Los Angeles, CA, USA 3UCSF Fresno Medical Center, Fresno, CA, USA
Clinical Toxicology Downloaded from informahealthcare.com by Nyu Medical Center on 06/08/15 For personal use only.
2Los
Background. Crotaline snakebites are routinely assessed with serial external examinations. We sought to correlate external findings with changes observed on ultrasound imaging. Methods. This was a prospective, observational study of consecutive rattlesnake envenomation in patients treated at a single hospital in central California. Information recorded for each case included clinical data, gross external examination, and ultrasound images of tissue edema, localized fluid collections, and video footage of muscle fasciculations. Results. Thirteen patients were enrolled. Ultrasound imaging of the bitten extremity was consistent with external examination of the bitten limb. The most common sonographic finding was subcutaneous tissue edema. Edema and necrosis in 3 patients with rapidly progressive leg swelling spared the deeper muscle layers and fascial planes. In 2 patients with bites on the fingers, edema and tendon involvement were readily visualized using a water-bath technique (placement of the hand in a pool of water, allowing more detailed examination of the tissue planes). Conclusion. Ultrasound imaging may allow for a more complete understanding of the local effects of snakebite. We were also able to document normal deeper muscle integrity in cases with diffuse leg edema. More studies are needed to fully elaborate the strengths and limitations of bedside ultrasound as a diagnostic adjunct in envenomation assessment. Keywords
Snakes/snakebite; Toxinology; Diagnostic ultrasound; Soft tissue complications of poisoning
center in a largely rural area of central California from 2010 to 2013. Patients with “dry bites” or those refusing to consent for the study were excluded. After informed consent was obtained in patient’s native language, diagnostic ultrasound imaging of the area of the snake bite was performed by one of the authors. For each case, after clinical data and gross external examination findings were noted, ultrasound images of the bitten and contralateral extremities were collected using an 8-mHz linear array probe. Imaging was focused to identify the depth and location of tissue edema, the presence of blisters or fluid collections, evidence of muscle fasciculation, and lesions of the fascia and tendons. Ultrasound imaging was performed in transverse and longitudinal planes in 3–5 sites around the area of the snakebite. In all cases, the area of the bite, the area of maximal swelling, and the leading edge of induration were always included for imaging; other sites were also chosen to better visualize soft tissue structures such as tendons and deep muscles. For each location, the corresponding contralateral location was also imaged, to serve as a “negative control” for each case. Imaging of fingers and hands was facilitated by placing the hand and the probe in a pan of water, which provides an acoustic enhancing medium even when the probe is not in contact with the skin.
Introduction Crotaline snakebites are routinely assessed using serial measurements of limb edema, functional impairment, and pain around the bitten area to gauge the extent of tissue damage.1 These parameters are limited by interobserver variability and the inability to assess the depth of injury. A more complete, reproducible, anatomically detailed diagnostic adjunct may thus help address the current limitations in snakebite assessment. The use of ultrasound technology in acute care has become increasingly more common. Emergency clinicians use it to confirm or exclude a range of soft tissue diagnoses, such as infections, foreign bodies, internal bleeding, and vascular conditions.2,3 This study is a pilot investigation using ultrasound imaging for the assessment of rattlesnake bite injuries. The objective of this pilot investigation was to determine whether sonography was capable of assessing the location and associated signs of local tissue injury.
Methods This was a prospective, observational (Institutional Review Board) IRB-approved study in consecutive patients treated for rattlesnake bite at a single, tertiary-care medical
Received 22 June 2014; accepted 21 August 2014.
Results
Address correspondence to Dr. Rais Vohra, MD, UCSF Fresno Medical Center, Department of Emergency Medicine, Fresno, CA USA. Email: [email protected]
There were 14 patients with crotaline bites, who were treated at our hospital from 2010 to 2013. One patient with 948
Sonographic signs of snakebite Table 1. Bite sites and ultrasound imaging findings in 12 rattlesnake bite victims, 2010–2013. Patient (age, gender)
Bite site
Sonographic findings
A (48 years, M)
Medial L heel
B (16 years, M)
Lateral L shin
C (29 years, M)
I (51 years, F)
L second finger PIP joint R third finger pulp Dorsal L thumb Distal L third finger Dorsal L third DIP joint Dorsal L third PIP joint Medial L heel
SCE in the thigh; F; normal DM SCE in the knee; F; normal DM FPD in the entire finger; SCE in the shoulder
J (50 years, F) K (5 years, M)
Medial R heel Dorsal R foot
L (39 years, F) M (63 years, M)
Medial R heel L third digit
D (55 years, M) E (50 years, M)
Clinical Toxicology Downloaded from informahealthcare.com by Nyu Medical Center on 06/08/15 For personal use only.
F (76 years, M) G (49 years, M) H (22 years, M)
FPD limited to finger SCE, B, and TSF in the bitten thumb SCE in the wrist Extensive SCE in the forearm SCE in the wrist; no TSF noted SCE in the hip; F; normal DM SCE in the knee; normal DM SCE/F in the foot; normal SC/DM in leg SCE in the thigh; normal DM SCE in the forearm
L, left; R, right; PIP, proximal interphalangeal joint; DIP, distal interphalangeal joint; SCE, subcutaneous edema; F, fasciculations; B, blister formation; FPD, finger pulp disruption; TSF, tendon sheath fluid—a marker of tenosynovitis; DM, deeper musculature Ultrasound imaging of the bite site was performed; the area of maximal swelling and the edge of induration were determined by external examination. The Findings listed represent observations made at any point in the course of hospitalization.
a “dry bite” was not enrolled. Demographic details and bite locations of the 13 patients who were enrolled are listed in Table 1. There were 3 female patients, and 6 of the bites occurred in lower extremity, with the remainder in the upper extremity. All 13 patients developed local swelling, pain, and transient limitation in mobility due to discomfort and/or swelling. Thrombocytopenia was seen in 4 (31%) of patients, and international normalized ratio (INR) was normal in all cases, except one patient whose highest INR was 1.5. All patients received Crotalidae Polyvalent Immune Fab (ovine) antivenom (mean total dose, 12.8; range, 2–32) vials. Twelve
949
patients were discharged from the emergency department or hospital with a mean length of stay: 3 (range, 1–9) days, one patient was transferred to a different hospital, and two patients required readmission. One patient (patient C) was readmitted 7 days after the bite due to bacterial superinfection of his bite wound, and required intravenous antibiotics and delayed fingertip amputation due to septic gangrene 10 days after the bite. Another patient (patient J) was readmitted due to menorrhagia coincident with low platelet count, and was treated with additional antivenom and blood product transfusions. Bedside ultrasound imaging confirmed injury to the cutaneous and subcutaneous tissue planes in all patients. The most common sonographic finding was subcutaneous tissue disruption consistent with edema. A variety of other sonographic findings were noted in 1 or more patients. In patient A, fasciculations were readily apparent (see Supplementary Video File to be found online at http://www. informahealthcare.com/doi/abs/10.3109/15563650.2014. 958613) on ultrasound imaging even in areas where they were not externally visible. Diffuse, rapidly progressive edema in the bitten legs of 5 patients (A, B, I, J, and L) was clearly subcutaneous, sparing the deeper muscle layers and fascial planes (Fig. 1). Patient I was a 51-year-old woman who was transferred from another hospital 2 days after her bite due to suspected compartment syndrome, based on progressive swelling from the heel to the buttocks, despite antivenom treatment. Ultrasound examination of the bitten and contralateral extremities confirmed that the edema was confined to subcutaneous and dermal layers, and the intact architecture of the fascial planes and deeper muscles in all compartments of the leg. In 6 patients (C–H) with bites in the hands, the soft tissues were readily visualized using a water-bath technique (placement of the hand in a pan of water, allowing more detailed examination of the tissue planes). Tracking was observed along the tendon sheath consistent with tenosynovitis in 1 patient (patient E) who sustained a dorsal thumb bite at the proximal nail fold, with localized oozing of serosanguinous fluid and edema up to the wrist (Fig. 2). This patient also demonstrated a fluid-filled collection evident on ultrasound imaging, beneath an area near the dorsal interphalangeal joint. The collection was not drained, and it was found from telephonic follow-up that the patient had made a full recovery within 3 weeks.
Fig. 1. A 16-year-old male was bitten in the anterior left shin (Panel B). Ultrasound of the bitten extremity (Panel C) shows thickening and edema of the subcutaneous tissues. However, the architectures of the fascia and the anterior tibial muscle compartment are normal and appear to be similar to the nonbitten extremity (Panel A). White rectangles indicate thickness of the skin in each leg (colour version of this figure can be found in the online version at www.informahealthcare.com/ctx). Copyright © Informa Healthcare USA, Inc. 2014
950
R. Vohra et al.
Fig. 2. A 50-year-old man was bitten on the left dorsal thumb, resulting in edema and oozing of serosanguinous fluid (Panel B). Ultrasound imaging of the dorsal interphalangeal joint of the bitten thumb (Panel A) demonstrated that the area of edema surrounded a well-demarcated fluid collection, and fluid was also lining the extensor tendon, indicating tenosynovitis. The normal thumb base was imaged (Panel C), which demonstrated no subcutaneous edema, fluid collection, or fluid tracking along the extensor tendon. White rectangles indicate the depth of subcutaneous tissues (colour version of this figure can be found in the online version at www.informahealthcare.com/ctx).
Clinical Toxicology Downloaded from informahealthcare.com by Nyu Medical Center on 06/08/15 For personal use only.
Discussion Our study demonstrates that ultrasound imaging can be used for evaluating severity of snakebite. Compared with the contralateral (e.g., nonbitten) limb, lesions in a bitten extremity are clearly identifiable on ultrasound imaging. In our study population, the depth of the lesions was limited to the superficial layers of the skin and soft tissues, sparing the deeper muscle compartments of the arms and legs. These findings suggest that ultrasound can aid in the external assessment of bite-related injuries by providing useful information on internal changes. For example, the involvement of tendons and the presence of well-formed fluid collections (Fig. 2), which are not externally evident, can be documented using ultrasound imaging. Pre-intervention determination of healthy (if edematous) tissue versus necrotic debris could be a valuable finding in cases where localized debridement or fluid collection drainage is being considered. Our study suggests that ultrasound imaging may also be useful in assessing deep muscle compartments after snakebite. Normal deeper muscle integrity was documented in 5 cases with rapidly evolving, circumferential leg edema, including 1 patient (I) who was transferred from another facility to our hospital due to suspected compartment syndrome based on progressive edema. None of the patients in our study required compartment pressure monitoring. The use of ultrasound in the assessment of soft tissue lesions affecting deeper muscle compartments has been reported in a variety of clinical contexts. Ultrasound has been used to document rhabdomyolysis from trauma or immobilization,4–6 and to assess perfusion of muscles at risk of ischemia due to peripheral vascular disease.7 Sonographic assessment is also increasingly used to exclude infectious myonecrosis and fasciitis,8 and one case report describes the use of ultrasound in diagnosing posterior compartment syndrome of the leg in a 12-year-old patient with combined tibia–fibula fracture.6 The bulk of the scientific literature does not support the use of fasciotomy for crotaline snakebite in North America, but this invasive surgical procedure is still done in some cases, where myonecrosis due to compartment syndrome is suspected.9 Although it is not a substitute for compartment pressure measurement, sonographic imaging may be valuable in assessing muscle integrity and vascular supply in high-risk cases, particularly when edema limits move-
ment, obscures pulses, and inhibits capillary refill. Our study population and sample size did not permit us to address this issue directly, but we believe that additional studies could help clarify the use of ultrasound in the workup of suspected compartment syndrome and other acute surgical complications of envenomation. The limitations of our study include the small number of patients and the lack of blinding. Repeat (serial) scans were not always performed, so the evolution of the injury could not be fully assessed using ultrasound imaging. The timing of the scan in relation to the time of bite was not standardized, which probably added an element of variability in our study. Independent confirmation of the findings with formal studies by the radiology department was not performed, so it is possible that subtle sonographic findings were either missed or misinterpreted. Finally, we recognize the preliminary nature of this investigation. More high-quality evidence to determine what, if any, role sonography has in assessing rattlesnake bites could come from enrolling a greater number of patients with more diverse presentations, using vascular techniques to document perfusion patterns in affected extremities and a multicenter approach.
Conclusions Bedside ultrasound is a simple technique which can quickly detect the depth and spread of envenomation injuries. Although more research is needed, our work demonstrates how ultrasound imaging might allow for a more complete understanding of the local effects of snakebite with regard to venom-induced tissue injury.
Declaration of interest The authors report no declarations of interest. The authors alone are responsible for the content and writing of the paper.
References 1. Anz AW, Schweppe M, Halvorson J, Bushnell B, Sternberg M, Andrew Koman L. Management of venomous snakebite injury to the extremities. J Am Acad Orthop Surg 2010; 18:749–759. 2. Moore CL, Copel JA. Point-of-care ultrasonography. N Engl J Med 2011; 364:749–757. 3. Arienti V, Camaggi V. Clinical applications of bedside ultrasonography in internal and emergency medicine. Intern Emerg Med 2011; 6: 195–201. Clinical Toxicology vol. 52 no. 9 2014
Sonographic signs of snakebite 4. Kaplan GN. Ultrasonic appearance of rhabdomyolysis. Am J Roentgenol 1980; 134:375–377. 5. Su BH, Qiu L, Fu P, Luo Y, Tao Y, Peng YL. Ultrasonic appearance of rhabdomyolysis in patients with crush injury in the Wenchuan earthquake. Chin Med J (Engl) 2009; 122:1872–1876. 6. Auerbach DN, Bowen AD. Sonography of leg in posterior compartment syndrome. Am J Roentgenol 1981; 136:407–408.
Supplementary material available online
Clinical Toxicology Downloaded from informahealthcare.com by Nyu Medical Center on 06/08/15 For personal use only.
Supplementary Video File
Copyright © Informa Healthcare USA, Inc. 2014
951
7. Owen AR, Roditi GH. Peripheral arterial disease: the evolving role of non-invasive imaging. Postgrad Med J 2011; 87:189–198. 8. Chau CL, Griffith JF. Musculoskeletal infections: ultrasound appearances. Clin Radiol 2005; 60:149–159. 9. Shaw BA, Hosalkar HS. Rattlesnake bites in children: antivenin treatment and surgical indications. J Bone Joint Surg Am 2002; 84-A:1624–1629.
CRITICAL CARE
Sonographic signs of snakebite R. VOHRA,1 C. RANGAN,2 and R. BENGIAMIN3 1UCSF
Fresno Medical Center, California Poison Control System, Fresno, CA, USA Angeles Department of Public Health, Children’s Hospital Los Angeles, CA, USA 3UCSF Fresno Medical Center, Fresno, CA, USA
Clinical Toxicology Downloaded from informahealthcare.com by Nyu Medical Center on 06/08/15 For personal use only.
2Los
Background. Crotaline snakebites are routinely assessed with serial external examinations. We sought to correlate external findings with changes observed on ultrasound imaging. Methods. This was a prospective, observational study of consecutive rattlesnake envenomation in patients treated at a single hospital in central California. Information recorded for each case included clinical data, gross external examination, and ultrasound images of tissue edema, localized fluid collections, and video footage of muscle fasciculations. Results. Thirteen patients were enrolled. Ultrasound imaging of the bitten extremity was consistent with external examination of the bitten limb. The most common sonographic finding was subcutaneous tissue edema. Edema and necrosis in 3 patients with rapidly progressive leg swelling spared the deeper muscle layers and fascial planes. In 2 patients with bites on the fingers, edema and tendon involvement were readily visualized using a water-bath technique (placement of the hand in a pool of water, allowing more detailed examination of the tissue planes). Conclusion. Ultrasound imaging may allow for a more complete understanding of the local effects of snakebite. We were also able to document normal deeper muscle integrity in cases with diffuse leg edema. More studies are needed to fully elaborate the strengths and limitations of bedside ultrasound as a diagnostic adjunct in envenomation assessment. Keywords
Snakes/snakebite; Toxinology; Diagnostic ultrasound; Soft tissue complications of poisoning
center in a largely rural area of central California from 2010 to 2013. Patients with “dry bites” or those refusing to consent for the study were excluded. After informed consent was obtained in patient’s native language, diagnostic ultrasound imaging of the area of the snake bite was performed by one of the authors. For each case, after clinical data and gross external examination findings were noted, ultrasound images of the bitten and contralateral extremities were collected using an 8-mHz linear array probe. Imaging was focused to identify the depth and location of tissue edema, the presence of blisters or fluid collections, evidence of muscle fasciculation, and lesions of the fascia and tendons. Ultrasound imaging was performed in transverse and longitudinal planes in 3–5 sites around the area of the snakebite. In all cases, the area of the bite, the area of maximal swelling, and the leading edge of induration were always included for imaging; other sites were also chosen to better visualize soft tissue structures such as tendons and deep muscles. For each location, the corresponding contralateral location was also imaged, to serve as a “negative control” for each case. Imaging of fingers and hands was facilitated by placing the hand and the probe in a pan of water, which provides an acoustic enhancing medium even when the probe is not in contact with the skin.
Introduction Crotaline snakebites are routinely assessed using serial measurements of limb edema, functional impairment, and pain around the bitten area to gauge the extent of tissue damage.1 These parameters are limited by interobserver variability and the inability to assess the depth of injury. A more complete, reproducible, anatomically detailed diagnostic adjunct may thus help address the current limitations in snakebite assessment. The use of ultrasound technology in acute care has become increasingly more common. Emergency clinicians use it to confirm or exclude a range of soft tissue diagnoses, such as infections, foreign bodies, internal bleeding, and vascular conditions.2,3 This study is a pilot investigation using ultrasound imaging for the assessment of rattlesnake bite injuries. The objective of this pilot investigation was to determine whether sonography was capable of assessing the location and associated signs of local tissue injury.
Methods This was a prospective, observational (Institutional Review Board) IRB-approved study in consecutive patients treated for rattlesnake bite at a single, tertiary-care medical
Received 22 June 2014; accepted 21 August 2014.
Results
Address correspondence to Dr. Rais Vohra, MD, UCSF Fresno Medical Center, Department of Emergency Medicine, Fresno, CA USA. Email: [email protected]
There were 14 patients with crotaline bites, who were treated at our hospital from 2010 to 2013. One patient with 948
Sonographic signs of snakebite Table 1. Bite sites and ultrasound imaging findings in 12 rattlesnake bite victims, 2010–2013. Patient (age, gender)
Bite site
Sonographic findings
A (48 years, M)
Medial L heel
B (16 years, M)
Lateral L shin
C (29 years, M)
I (51 years, F)
L second finger PIP joint R third finger pulp Dorsal L thumb Distal L third finger Dorsal L third DIP joint Dorsal L third PIP joint Medial L heel
SCE in the thigh; F; normal DM SCE in the knee; F; normal DM FPD in the entire finger; SCE in the shoulder
J (50 years, F) K (5 years, M)
Medial R heel Dorsal R foot
L (39 years, F) M (63 years, M)
Medial R heel L third digit
D (55 years, M) E (50 years, M)
Clinical Toxicology Downloaded from informahealthcare.com by Nyu Medical Center on 06/08/15 For personal use only.
F (76 years, M) G (49 years, M) H (22 years, M)
FPD limited to finger SCE, B, and TSF in the bitten thumb SCE in the wrist Extensive SCE in the forearm SCE in the wrist; no TSF noted SCE in the hip; F; normal DM SCE in the knee; normal DM SCE/F in the foot; normal SC/DM in leg SCE in the thigh; normal DM SCE in the forearm
L, left; R, right; PIP, proximal interphalangeal joint; DIP, distal interphalangeal joint; SCE, subcutaneous edema; F, fasciculations; B, blister formation; FPD, finger pulp disruption; TSF, tendon sheath fluid—a marker of tenosynovitis; DM, deeper musculature Ultrasound imaging of the bite site was performed; the area of maximal swelling and the edge of induration were determined by external examination. The Findings listed represent observations made at any point in the course of hospitalization.
a “dry bite” was not enrolled. Demographic details and bite locations of the 13 patients who were enrolled are listed in Table 1. There were 3 female patients, and 6 of the bites occurred in lower extremity, with the remainder in the upper extremity. All 13 patients developed local swelling, pain, and transient limitation in mobility due to discomfort and/or swelling. Thrombocytopenia was seen in 4 (31%) of patients, and international normalized ratio (INR) was normal in all cases, except one patient whose highest INR was 1.5. All patients received Crotalidae Polyvalent Immune Fab (ovine) antivenom (mean total dose, 12.8; range, 2–32) vials. Twelve
949
patients were discharged from the emergency department or hospital with a mean length of stay: 3 (range, 1–9) days, one patient was transferred to a different hospital, and two patients required readmission. One patient (patient C) was readmitted 7 days after the bite due to bacterial superinfection of his bite wound, and required intravenous antibiotics and delayed fingertip amputation due to septic gangrene 10 days after the bite. Another patient (patient J) was readmitted due to menorrhagia coincident with low platelet count, and was treated with additional antivenom and blood product transfusions. Bedside ultrasound imaging confirmed injury to the cutaneous and subcutaneous tissue planes in all patients. The most common sonographic finding was subcutaneous tissue disruption consistent with edema. A variety of other sonographic findings were noted in 1 or more patients. In patient A, fasciculations were readily apparent (see Supplementary Video File to be found online at http://www. informahealthcare.com/doi/abs/10.3109/15563650.2014. 958613) on ultrasound imaging even in areas where they were not externally visible. Diffuse, rapidly progressive edema in the bitten legs of 5 patients (A, B, I, J, and L) was clearly subcutaneous, sparing the deeper muscle layers and fascial planes (Fig. 1). Patient I was a 51-year-old woman who was transferred from another hospital 2 days after her bite due to suspected compartment syndrome, based on progressive swelling from the heel to the buttocks, despite antivenom treatment. Ultrasound examination of the bitten and contralateral extremities confirmed that the edema was confined to subcutaneous and dermal layers, and the intact architecture of the fascial planes and deeper muscles in all compartments of the leg. In 6 patients (C–H) with bites in the hands, the soft tissues were readily visualized using a water-bath technique (placement of the hand in a pan of water, allowing more detailed examination of the tissue planes). Tracking was observed along the tendon sheath consistent with tenosynovitis in 1 patient (patient E) who sustained a dorsal thumb bite at the proximal nail fold, with localized oozing of serosanguinous fluid and edema up to the wrist (Fig. 2). This patient also demonstrated a fluid-filled collection evident on ultrasound imaging, beneath an area near the dorsal interphalangeal joint. The collection was not drained, and it was found from telephonic follow-up that the patient had made a full recovery within 3 weeks.
Fig. 1. A 16-year-old male was bitten in the anterior left shin (Panel B). Ultrasound of the bitten extremity (Panel C) shows thickening and edema of the subcutaneous tissues. However, the architectures of the fascia and the anterior tibial muscle compartment are normal and appear to be similar to the nonbitten extremity (Panel A). White rectangles indicate thickness of the skin in each leg (colour version of this figure can be found in the online version at www.informahealthcare.com/ctx). Copyright © Informa Healthcare USA, Inc. 2014
950
R. Vohra et al.
Fig. 2. A 50-year-old man was bitten on the left dorsal thumb, resulting in edema and oozing of serosanguinous fluid (Panel B). Ultrasound imaging of the dorsal interphalangeal joint of the bitten thumb (Panel A) demonstrated that the area of edema surrounded a well-demarcated fluid collection, and fluid was also lining the extensor tendon, indicating tenosynovitis. The normal thumb base was imaged (Panel C), which demonstrated no subcutaneous edema, fluid collection, or fluid tracking along the extensor tendon. White rectangles indicate the depth of subcutaneous tissues (colour version of this figure can be found in the online version at www.informahealthcare.com/ctx).
Clinical Toxicology Downloaded from informahealthcare.com by Nyu Medical Center on 06/08/15 For personal use only.
Discussion Our study demonstrates that ultrasound imaging can be used for evaluating severity of snakebite. Compared with the contralateral (e.g., nonbitten) limb, lesions in a bitten extremity are clearly identifiable on ultrasound imaging. In our study population, the depth of the lesions was limited to the superficial layers of the skin and soft tissues, sparing the deeper muscle compartments of the arms and legs. These findings suggest that ultrasound can aid in the external assessment of bite-related injuries by providing useful information on internal changes. For example, the involvement of tendons and the presence of well-formed fluid collections (Fig. 2), which are not externally evident, can be documented using ultrasound imaging. Pre-intervention determination of healthy (if edematous) tissue versus necrotic debris could be a valuable finding in cases where localized debridement or fluid collection drainage is being considered. Our study suggests that ultrasound imaging may also be useful in assessing deep muscle compartments after snakebite. Normal deeper muscle integrity was documented in 5 cases with rapidly evolving, circumferential leg edema, including 1 patient (I) who was transferred from another facility to our hospital due to suspected compartment syndrome based on progressive edema. None of the patients in our study required compartment pressure monitoring. The use of ultrasound in the assessment of soft tissue lesions affecting deeper muscle compartments has been reported in a variety of clinical contexts. Ultrasound has been used to document rhabdomyolysis from trauma or immobilization,4–6 and to assess perfusion of muscles at risk of ischemia due to peripheral vascular disease.7 Sonographic assessment is also increasingly used to exclude infectious myonecrosis and fasciitis,8 and one case report describes the use of ultrasound in diagnosing posterior compartment syndrome of the leg in a 12-year-old patient with combined tibia–fibula fracture.6 The bulk of the scientific literature does not support the use of fasciotomy for crotaline snakebite in North America, but this invasive surgical procedure is still done in some cases, where myonecrosis due to compartment syndrome is suspected.9 Although it is not a substitute for compartment pressure measurement, sonographic imaging may be valuable in assessing muscle integrity and vascular supply in high-risk cases, particularly when edema limits move-
ment, obscures pulses, and inhibits capillary refill. Our study population and sample size did not permit us to address this issue directly, but we believe that additional studies could help clarify the use of ultrasound in the workup of suspected compartment syndrome and other acute surgical complications of envenomation. The limitations of our study include the small number of patients and the lack of blinding. Repeat (serial) scans were not always performed, so the evolution of the injury could not be fully assessed using ultrasound imaging. The timing of the scan in relation to the time of bite was not standardized, which probably added an element of variability in our study. Independent confirmation of the findings with formal studies by the radiology department was not performed, so it is possible that subtle sonographic findings were either missed or misinterpreted. Finally, we recognize the preliminary nature of this investigation. More high-quality evidence to determine what, if any, role sonography has in assessing rattlesnake bites could come from enrolling a greater number of patients with more diverse presentations, using vascular techniques to document perfusion patterns in affected extremities and a multicenter approach.
Conclusions Bedside ultrasound is a simple technique which can quickly detect the depth and spread of envenomation injuries. Although more research is needed, our work demonstrates how ultrasound imaging might allow for a more complete understanding of the local effects of snakebite with regard to venom-induced tissue injury.
Declaration of interest The authors report no declarations of interest. The authors alone are responsible for the content and writing of the paper.
References 1. Anz AW, Schweppe M, Halvorson J, Bushnell B, Sternberg M, Andrew Koman L. Management of venomous snakebite injury to the extremities. J Am Acad Orthop Surg 2010; 18:749–759. 2. Moore CL, Copel JA. Point-of-care ultrasonography. N Engl J Med 2011; 364:749–757. 3. Arienti V, Camaggi V. Clinical applications of bedside ultrasonography in internal and emergency medicine. Intern Emerg Med 2011; 6: 195–201. Clinical Toxicology vol. 52 no. 9 2014
Sonographic signs of snakebite 4. Kaplan GN. Ultrasonic appearance of rhabdomyolysis. Am J Roentgenol 1980; 134:375–377. 5. Su BH, Qiu L, Fu P, Luo Y, Tao Y, Peng YL. Ultrasonic appearance of rhabdomyolysis in patients with crush injury in the Wenchuan earthquake. Chin Med J (Engl) 2009; 122:1872–1876. 6. Auerbach DN, Bowen AD. Sonography of leg in posterior compartment syndrome. Am J Roentgenol 1981; 136:407–408.
Supplementary material available online
Clinical Toxicology Downloaded from informahealthcare.com by Nyu Medical Center on 06/08/15 For personal use only.
Supplementary Video File
Copyright © Informa Healthcare USA, Inc. 2014
951
7. Owen AR, Roditi GH. Peripheral arterial disease: the evolving role of non-invasive imaging. Postgrad Med J 2011; 87:189–198. 8. Chau CL, Griffith JF. Musculoskeletal infections: ultrasound appearances. Clin Radiol 2005; 60:149–159. 9. Shaw BA, Hosalkar HS. Rattlesnake bites in children: antivenin treatment and surgical indications. J Bone Joint Surg Am 2002; 84-A:1624–1629.
