Is it an Emergency?

Inquire

• time of the bite,
• local pain,
• nausea, vomiting, abdominal pain,
• paraesthesias of the extremities and around the mouth,
• muscle pain.

Assess

• state of consciousness.

Measure

• blood pressure/pulse,
• respiratory rate,
• oxygen saturation (pulse oximeter),
• 20WBCT (bedside test), in settings where resources are immediatelly accessible, go directly to 'Laboratory and physical investigations' below,

Observe/investigate

• bite marks,
• extent and intensity of local swelling and beyond,
• enlargement and painfulness of regional lymph nodes,
• swelling in the facial region, including the larynx/pharynx (angio-oedema),
• clinical signs of shock,
• bleeding from bite marks and other injuries,
• subcutaneous bleeding in the region of the swelling,
• gingival bleeding,
• blood-stained sputum, vomit ("coffee ground vomitus"), stools (melaena) or urine,
• acute abdomen (intra-abdominal bleeding!),
• focal neurological deficits, meningismus (intracranial bleeding!),
• cranial nerve deficits, such as ptosis, ophthalmoplegia, dysphagia, dysarthria,
• paralysis of the skeletal musculature including the respiratory musculature (→ respiratory failure),
• flank pain and renal bed sensitive to percussion.

Varibility of symptoms and degree of envenoming

The symptoms and degree of envenoming depend not only on the amount of venom injected and numerous other variables, but also on the time that has elapsed since the bite. This variable factor must be taken into account when making the following decisions:

• exclusion of envenoming 
• the time interval between clinical examinations
• emergency care (see below)

Bite marks and dry bites

The fact that a patient has been bitten by a known venomous snake and the presence of bite marks do not automatically allow the conclusion that a clinically relevant injection of venom has taken place. It is estimated that in 75% of North American crotalid bites no clinically relevant envenoming occurs (Minton 1987a); in contrast, in only 40–75% of Micrurus fulvius bites does envenoming not take place (Russell 1983, Kitchens and van Mierop 1987).

Local signs & symptoms

Crotalids 

Following North American crotalid bites, strong local pain, swelling, discolouration of the skin and occasionally hyposensitivity in the region of the bite are early signs of a relevant injection of venom. If these do not occur within 15–30 min after the bite, it is highly likely that no venom was injected. Important exceptions to this rule are some populations of Crotalus scutulatus ("type A"), C. mitchelli, C. lepidus and C. tigris, which can cause systemic envenoming without significant local effects (Minton 1987a). Local symptoms may also be relatively insignificant following bites by C. adamanteus, even if systemic effects, including incoagulability of the blood, are present (Kitchens and Van Mierop 1987). The same applies to all bites in which direct intravenous injection of venom occurs (Minton 1987a). Within an hour after an effective crotalid bite the regional lymph nodes are generally swollen and painful. Haemorrhagic blisters usually develop within less than 2 h after a rattlesnake bite, but can also occur after a long delay (Minton 1987a).

Severe local tissue damage including impairment of function and loss of limbs are undoubtedly possible complications of North American crotalid bites but are much less frequent if rational first aid and therapeutic measures are applied (Dart et al. 1992, Hardy 1992b).

The incidence of sequelae of crotalid bites, including those that most treating doctors would not classify as severe, but which are troublesome for the patient, has been underestimated to date (Dart et al. 1992). In the past it was estimated that 10% of patients suffered permanent damage following a bite (Russell 1969, 1983). A prospective study of the consequences of crotalid bites, in which patients themselves evaluated permanent damage, resulted in estimates of >20 % (Dart et al. 1992).

Tourniquets can cause local swelling and mimic local venom effects. If this type of first aid measure is applied following North American crotalid bites, the risk of ischaemia distal to the tourniquet is high. Furthermore, as the venom of these crotalids is rich in components with a local cytotoxic effect, this favours the process of necrotisation in the region where venom was injected (Willson 1908, Hardy 1992b).

Coral snakes
North American elapid bites (Micrurus fulvius) cause only minor local signs of envenoming. Bite marks may be so small as to be invisible. These bites are not particularly painful, there is no discolouration of the skin, and swelling, if it occurs at all, is insignificant.

Compartment syndrome

Even extensive swelling of the extremities is not necessarily an indication of compartment syndrome. The decision to perform a fasciotomy must have a rational basis (evidence of increased intra-compartmental pressure; reduced or absent arterial blood flow).

In a retrospective study of patients who were primarily bitten by Crotalus atrox and C. s. scutulatus, 64 had swelling that extended as far as the axilla or inguinal region. None of these patients required surgical intervention. None of them developed symptoms that could have been attributed to compartment syndrome. All patients regained full functionality of the affected limb (Hardy 1991).

In a prospective study in which the majority of patients had been bitten by C. atrox and a smaller number by C. s. scutulatus, C. m. molossus and C. cerastes (snakes identified according to geographical criteria), patients were investigated using non-invasive angiological methods (pulse volume amplitude, blood pressure, skin temperature). In only one case was a reduced pulse volume amplitude recorded. This patient also had a decrease in blood pressure and the skin temperature of the bitten extremity. On angiography, thrombosis of the popliteal artery and the deep femoral artery was seen. The patient had applied a tourniquet following the bite, which may have caused the thrombosis. The thrombus was successfully removed using a Fogarty catheter (Curry et al. 1985).

Following C. adamanteus bites, there is almost never the need to perform fasciotomy. Local necrosis is rare, even with bites that cause massive swelling (Kitchens 1992, pers. comm.).

In 700 patients who had suffered a rattlesnake bite, the need for surgical decompression was extremely rare, using objective criteria for the determination of increased intra-compartmental pressure (pressure >30–40 mmHg, measured with a Wick catheter). In this study surgical decompression was evidently only necessary in one patient. None of the patients experienced a neurological or functional deficit of the affected extremity that could have been attributed to increased intra-compartmental pressure (Garfin 1982).

These clinical findings indicate that following crotalid bites, intra-compartmental pressure does not increase to such an extent that ischaemia occurs. Massive swelling with restricted movement of the fingers and severe pain can, however, mimic compartment syndrome.

The decision to perform surgical decompression should only be made when the risk of ischaemia has been established objectively. There needs to be evidence of increased intra-compartmental pressure and reduced arterial blood flow, as well as exclusion of the possibility of arterial thrombosis (Curry et al. 1985, Hardy 1991). 

Arterial hypotension and shock

Progressive arterial hypotension, leading to loss of consciousness and cardiovascular failure, is one of the most significant complications of North American rattlesnake bites and is a certain sign of severe envenoming (Minton 1987a).

The causes are anaphylactoid reactions (nausea, vomitting and diarrhoe are also attributable to theses reactions), direct effects of the venom on blood vessels during the early phase of envenoming and anaphylaxis (rare; requires sensitisation). Arterial hypotension occurring later in the course of envenoming is caused by a reduction in the intravascular fluid volume, in the majority of cases most probably due to increased vascular permeability (Dart et al. 1992). This leads to systemic sequestration of large volumes of fluid, in addition to fluid sequestration within the bitten extremity. Pulmonary and cerebral oedema can also be explained by changes in vascular permeability. Bleeding into the extremity in which venom was injected contributes to the development of hypovolaemia. Untreated, there is a risk of hypovolaemic shock. Of 9 fatalities that were attributable to snakebites according to the registry of deaths in Arizona between 1969 and 1984, 5 were evidently caused by multiple organ failure as a consequence of persistent arterial hypotension. 2 of the victims kept snakes as pets (C. s. scutulatus), and the other 7 bites were attributed to C. atrox or C. s. scutulatus according to epidemiological criteria (Hardy 1986). Adequate intravenous fluid replacement and antivenom administration would very probably have prevented most of these fatalities, if not all of them. It is important to reverse the development of hypovolaemia as early as possible, which may require large volumes of intravenously administered fluids (Hardy 1991).

Bleeding and non-clottable blood

Apart from ecchymoses in the region of the swelling, bleeding, in particular life-threatening bleeding, is very uncommon with North American crotalid bites. This is so despite the fact that marked defibrinogenation and thrombocytopaenia can occur and although the venoms contain haemorrhagins. However, the haemorrhagins appear to be primarily locally active. In particular following bites by crotalids, whose venoms possess only direct fibrinogen-coagulating activity ("thrombin-like" activity), the haemostatic defect usually only manifests itself in the form of abnormal clotting test results and not clinically (Kitchens 1991, pers. comm.). However, fatal bleeding complications have been reported (Lavonas et al 2011). For this reason coagulation should always be monitored if a crotalid bite has taken place or is suspected.

Even coagulation disorders that are severe according to laboratory tests may only be clinically apparent to a slight degree or not at all (see Crotalus admanteus). Although defibrinogenation, caused by the direct fibrinogen-coagulating activity of the venom, generally has a benign course, there is nonetheless a risk of spontaneous haemorrhage with extensive loss of blood or focal bleeding (e.g. intracranial; Kitchens and Eskin 2008) as long as the haemostatic defect is not corrected (untreated, i.e. without antivenom treatment, days to weeks). The risk is even greater if a patient does not receive appropriate treatment at a hospital and is then exposed to trauma, even very minor trauma (Boyer et al 2001). Loss of large volumes of blood can occur due to blood oozing from the bite wound or from injuries or due to medical or paramedical intervention.

Recurrent and persistent coagulopathy following pit viper envenoming (various Crotalus sp.): “Significant hypofibrinogenemia and thrombocytopenia, lasting up to 2 weeks, may be common after envenomation by North American" (Boyer et al 1999).

Agkistrodon sp. bites carry an extremely low risk of bleeding.

Paraesthesias and muscle fasciculation 

Paraesthesias of the extremities and perioral paraesthesias as well as myocomia⁺ are reported surprisingly frequently following rattlesnake bites (paraesthesias in 63%, myocomia⁺ in 41% of cases; Russell 1983). Limb and perioral paraesthesias could be due to hyperventilation. However, an argument that is raised to counter this explanation is that this type of symptom is seen much less frequently following bites by other species of snakes.

Electrophysiological investigations in patients who had suffered a Crotalus horridus bite showed that the clinical observations can be explained by a reversible effect of the venom on the excitability of peripheral nerves.

⁺Myocomia

Myocomia occurs in envenoming by some species of North American rattlesnakes (eg, Crotalus adamanteus, Crotalus horridus, Crotalus scutellatus, Crotalus lutosus, and Crotalus helleri) and the common lancehead pit viper (Bothrops atrox) in Trinidad" (Warrell and Willimas 2023, cit Lewis and Gutmann 2004, video: Ramcharan et al. 2016). 

Descending paralysis / Respiratory failure

Rattlesnakes

With one exception, neurological manifestations following North American crotalid bites are limited to the signs and symptoms discussed above. In addition to local swelling and haemostatic defects, C. s. scutulatus ("type A") bites can also cause neurological symptoms of envenoming, including paralysis. However, there are very few reports of obvious neurotoxic symptoms of envenoming following bites from this geographical variant of a single subspecies (Minton 1990a).

Coral snakes

Micrurus fulvius venom causes paralysis that can progress to paralysis of the respiratory musculature and to respiratory failure, which may only appear several hours after the bite (Minton 1987a).
The venom of Micruroides euryxanthus also contains neurotoxic components. However, to date only insignificant symptoms of envenoming have been reported following bites by this species, or none at all.

Muscles pain (active and passive); secondary effects of rhabdomyolysis

Significant systemic rhabdomyolysis is very rarely reported following North American crotalid bites. In contrast, local myonecrosis is common if the venom was injected intramuscularly. Local myonecrosis develops as the result of a complex process in which local thromboses and other causes of ischaemic tissue damage are also involved. However, in most bites the venom only reaches the subcutaneous tissue.

Observed very raely in coral snake envenoming (Micrurus fulvius) (Kitchens and Van Mierop, 1987).

Acute kidney injury (AKI) and chronoc kidney disease

Envenoming by many snake species occasionally results in acute kidney injury. Direct venom nephrotoxicity, renal ischaemia secondary to shock, disseminated intravascular coagulation with thrombotic microangiopathy (TMA), haemoglobinuria, myoglobinuria, and hyperkalaemia contribute to acute tubular necrosis (Sitprija 2006; Warrell 2004, 2023; Warrell and Williams 2023).

Monitoring for signs and symptoms that would indicate systemic envenoming for at least 24 h.

At least hourly

• state of consciousness,
• ptosis,
• heart rate and rhythm,
• blood pressure,
• respiratory rate,
• bleeding,
• local swelling,
• other newly appearing signs and symptoms.

6-hourly (or more frequently if there is cause for suspicion)

• 20WBCT (bedside test); in settings where resources are immediatelly accessible, go directly to 'Laboratory and physical investigations' above,
• CK, GOT (AST),
• urine output.

The absence of signs of envenoming in the first hours after the bite does not exclude the possibility that a relevant injection of venom has taken place. There may be a long delay before systemic signs of envenoming develop.

Following crotalid bites, whose venom is known to cause defibrinogenation, there may be a delay of several hours before this condition is detectable on laboratory tests. Also, the absence of local signs of envenoming does not exclude the later development of a haemostatic defect (Van Mierop and Kitchens 1980, Kitchens and Van Mierop 1983). The same is true for other systemic signs of envenoming, including arterial hypotension. Several patients developed cardiovascular failure following progressive arterial hypotension that first occurred hours after the bite (Hurlburt et al. 1988).

In a group of 45 patients, initially none or only one had minimal swelling and no other local or systemic signs of envenoming such as nausea, vomiting, perioral paraesthesia, alteration of consciousness, ecchymosis, blistering or marked pain. 24 (53%) later developed significant signs of envenoming such as moderate to marked swelling, thrombocytopaenia or cardiovascular failure. Of these 24 patients, 11 (46%) deteriorated within 4 h, 5 (21%) within 4–8 h and 6 (25%) within >8 h (no data for 2 patients) (Hurlburt et al. 1988).

Following Micrurus sp. bites the problem of assessing the risk of a clinically relevant envenoming is even greater. Minimal or no local signs of envenoming are the rule, and systemic signs of envenoming only develop after a long delay.