The Clinical Manifestations of Taiwan Cobra Bite and Risk Factors of Severity---2 Medical Centers’Experience

• Main Authors: Yan-Chiao Mao, 毛彥喬
• Other Authors: Chen-Chang Yang
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/04639553778098941128

碩士 === 國立陽明大學 === 環境與職業衛生研究所 === 101 === Abstract There are 6 major venomous snakes in Taiwan including Viridovipera stejnegeri, Protobothrops mucrosquamatus, Deinagkistrodon acutus, Daboia russelli siamensis, Naja atra, and Bungarus multicinctus. N. atra envenoming is relatively uncommon and frequently results in serious morbidity or even mortality. The epidemiological data are still scarce and fragmented. In our study, there was a high incidence of wound infection, cellulitis, local tissue necrosis, necrotizing fasciitis, and various degrees of limb swelling after Taiwan cobra envenoming. In contrast, neurological manifestations were uncommon, only transient and slight, if any. Most patients did not receive first aid such as incision and suction, arterial tourniquet, cold packing, or herbs coverage because of the rapid transportation and easy access to medical care in Taiwan. The management of Taiwan cobra bites involves prompt administration of antivenom, adequate antibiotic coverage, or surgical intervention; thus, a multidisciplinary approach is usually required. Four types of antivenom are produced by the Vaccine Center, including “hemorrhagic” bivalent for P. mucrosquamatus and V. stejnegeri, “neurotoxic” bivalent for N. atra and B. multicinctus, and 2 monovalent antivenoms for D. acutus and D. r. siamensis. The “neurotoxic” antivenom contains 2000 units per vial [1 unit neutralized 1 median lethal dose (LD50) of venom intraperitoneally injected in a mouse weighting 13 g; or at least 1000 Tanaka units). Based on animal studies and clinical observation, 6–10 vials are recommended for the treatment of N. atra bites. According to the instruction leaflet, an antivenom skin sensitivity test should be performed prior to administration. Only a few cases had positive skin reactions. In these cases, the clinicians still used antivenom therapy, and even fewer cases developed a skin rash, which was amenable to antihistamine/or steroid treatment. There is plentiful evidence that the antivenom skin test did not predict early adverse antivenom reaction; however, it is still a common practice in Taiwan, possibly due to medico-legal issues. In cases of Taiwan cobra bites, more than half of the patients underwent surgery. The most commonly performed procedure was debridement. Notably, several cases underwent fasciotomy or fasciectomy for necrotizing fasciitis or compartment syndrome. Compartment pressure was measured with an infusion technique using traditional criteria (＞30–45 mmHg) as the indication for surgery. However, it is unknown whether the treatments used for patients with suspected compartment syndrome after traumatic injury are applicable to snakebites. Considering that antivenom could lower intracompartment pressure in animal studies and human cases after viper envenomation, a trial of sufficient doses of antivenom in Taiwan cobra envenoming as well as serial measurement of the intracompartment pressure in suspicious cases prior to fasciotomy or fasciectomy is encouraged. To identify the potential risk factors associated with surgery after a bite, we compared demographic data between patients who underwent surgery and those who did not. We found that the following clinical manifestations varied significantly (Chi-square test) between the 2 patient groups shortly after bites: cellulitis, wound ecchymosis/necrosis, fever, necrotizing fasciitis, blisters/bullae formation, compartment syndrome, higher grade of swelling, and presence of gastrointestinal (GI) effects. Furthermore, multiple regression analysis adjusted for the first dosage of antivenom, presence of cellulitis, blister/bullae, and grade 4 swelling found fever, local necrosis, and presence of GI effects to be positively associated with risk of surgery. We also preliminarily compared demographic data between patients with severe swelling (grade 4) and those with nonsevere swelling (grade 1–3). However, these results lacked clinical interest. Although a severity score may be helpful in the management of snakebite and in comparative studies of different populations, the current score involves only a single parameter (swelling) and is insufficient for these purposes. A more comprehensive scoring system should be established for cobra envenoming in Taiwan. Lastly, the bacteriology of bite wounds was analyzed. A total of 23 organisms were isolated from 50 patients. The most common pathogens were Gram-negative rods, e.g., the Enterobacteriaceae family, followed by Gram-positive cocci. Morganella morganii, Enterococcus spp., Proteus spp., and Aeromonas hydrophilia were common pathogens (listed in the descending order). Meanwhile, Bacteroides spp. was the only anaerobe implicated in Taiwan cobra bites. Most of these Gram-negative rods were susceptible to trimethoprim-sulfamethoxazole, piperacillin-tazobactam, third-generation cephalosporin, aminoglycosides, ciprofloxacin and imipenem. Bacteroides spp. was susceptible to chloramphinicol, clindamycin, or metronidazole. In conclusion, Taiwan cobra bite is a medical emergency necessitating a multidisciplinary approach. More than half of the patients developed wound infections requiring surgical intervention. This study could be helpful for the clinicians or first-line medical staff in treating bites of N. atra, a relatively uncommon venomous snake in Taiwan.