Does This Patient Have a Severe Snake Envenomation?

Abstract

IMPORTANCE Venomous snakebite severity ranges from an asymptomatic dry bite to severe envenomation and death. The clinical evaluation aids in prognosis and is essential to determine the risks and potential benefits of antivenom treatment.OBJECTIVES To identify historical features, clinical examination findings, basic laboratory testing, and clinical grading scales that will risk-stratify patients with pit viper snake envenomation for severe systemic envenomation, severe tissue injury, and/or severe hematologic venom effects.DATA SOURCES We conducted a structured search of PubMed (1966-October 3, 2017 and Embase database (1980( -October 3, 2017 to identify English-language studies that evaluated clinical features predictive of severe envenomation. STUDY SELECTIONWe included studies that evaluated the test performance of at least 1 clinical finding with an acceptable reference standard of severe envenomation for venomous snakes of the Western Hemisphere. Only studies involving the most common subfamily, Crotalinae (pit vipers), were evaluated. Seventeen studies with data were available for abstraction. DATA EXTRACTION AND SYNTHESISThe clinical features assessed and severity outcome measures were extracted from each original study. We assessed severity in 3 categories: systemic toxicity, tissue injury, and hematologic effects. Differences were resolved by author consensus. RESULTSThe pooled prevalence of severe systemic envenomation was 14% (95% CI, 9%-21%). The pooled prevalence of severe tissue injury and severe hematologic venom effects were 14% (95% CI, 12%-16%) and 18% (95% CI, 8%-27%), respectively. Factors increasing the likelihood of severe systemic envenomation included the time from bite to care of 6 or more hours (likelihood ratio [LR], 3.4 [95% CI, 1.1-6.4]), a patient younger than 12 years (LRs, 3.2 [95% CI, 1.5-7.1] and 2.9 [95% CI, 1.3-6.2]), large snake size (LR, 3.1 [95% CI, 1.5-5.7]), and ptosis (LRs, 1.4 [95% CI, 1.0-2.1] and 3.8 [95% CI, 1.8-8.3]). Envenomation by the genus Agkistrodon (copperhead and cottonmouth), as opposed to rattlesnakes, decreased the likelihood of severe systemic envenomation (LR, 0.28 [95% CI, 0.10-0.78]). Initial hypofibrinogenemia (LR, 5.1 [95% CI, 1.7-15.0]) and thrombocytopenia (LR, 3.7 [95% CI, 1.9-7.3]) increased the likelihood of severe hematologic venom effects. Other clinical features from history, physical examination, or normal laboratory values were not discriminative.CONCLUSIONS Clinical features can identify patients at increased risk of severe systemic envenomation and severe hematologic venom effects, but there are few features that are associated with severe tissue injury or can confidently exclude severe envenomation. Physicians should monitor patients closely and be wary of progression from nonsevere to a severe envenomation and have a low threshold to escalate therapy as needed.

Validity and reliability of telephone administration of the patient-specific functional scale for the assessment of recovery from snakebite envenomation

“…Additionally, our study is specific to copperhead envenomation, which on average has less severe envenomation than other snakebites such as rattlesnakes or tropical venomous snakes. [36, 37] In generalizing our results to other snake species, there is risk that the early floor effects would be greater. However, these floor effects disappear over time during recovery.…”

Association of a Network of Immunologic Response and Clinical Features With the Functional Recovery From Crotalinae Snakebite Envenoming

“…In doing so, we are able to overcome some of the limitations of the initial forays into prognostication in SBE. For example, a multitude of basic clinical features have been assessed in predicting severe SBE (33,34,36,37,40,43,56,67,68). A number of these established clinical features, such as young age and time to care, are now known to increase the likelihood of a severe envenoming.…”

“…A number of these established clinical features, such as young age and time to care, are now known to increase the likelihood of a severe envenoming. However, none can adequately exclude severe SBE (40). Consequently, they have not been assessed as a tool to determine the need to treat or not to treat with antivenom.…”

“…The clinical courses of SBE patients are highly variable, even within a single envenoming species, which further contributes to uncertainty regarding both the value of administering antivenom and how much is necessary for an individual patient (39). Unfortunately, there is no validated and reliable method of predicting severity or recovery in SBE (40). Historically clinicians have had to rely primarily on their own clinical experience.…”

“…Clinical features alone have not shown adequate prognostic performance in SBE, despite having some predictive value (37,38,40,55,56). Combining clinical features with immunologic markers has been used to prognosticate outcomes in other disease states (57)(58)(59)(60).…”