SNAKE BITES/scorpion stings Snake bite is common life-threatening in many countries. Farmers, hunters, rice-pickers are at particular risk Prompt medical treatment is vital. 3-5 million victims /year, 50 000 deaths , 400 000 amputations. 40% of bites do not produce signs of envenoming. It is difficult to predict which bites will produce symptoms or the clinical outcome, all victims should be brought under medical care as quickly as possible. Poisonous species of snake fall into the families. Snake venoms are complex mixtures of proteins & small polypeptides with enzymatic activity. Snake venoms are neurotoxins, haematotoxins (haemorrhagic or coagulopathic) or cardiotoxins often occur in combination.
Clinical features & assessment Key questions to ask a victim are: The body part bitten? How long ago? What sort of snake? Friends / relatives will frequently bring the snake with the patient; it should be handled as little as possible since it may only be injured rather than dead. The amount of venom injected via a bite is highly variable, depending on the length of time since the snake last ate& its aggression. Snake venom detection kits are available in some countries.
Clinical features & assessment The venom is detected from a dry swab of the bite site using monoclonal antibody techniques. The 20-minute whole blood-clotting test is a useful bedside tool in remote areas; a 2-3 ml sample of venous blood from the victim is left undisturbed at ambient temperature for at least 20 minutes. The vessel containing the blood is then tipped once & may be compared with a normal control. If it has not clotted, there is haemostatic disturbance from systemic envenoming. All patients should have a full blood count, urea/electrolytes, liver function tests, creatine kinase, troponins, ECG.
Management: Reassuring the patient Immobilising the bitten area to minimise venom spread Identifying the snake. Application of a firm bandage to occlude lymphatic drainage is appropriate, but tourniquets are unhelpful since they do not prevent the spread of venom & frequently applied incorrectly. Incisions at the bite site &attempts to suck out the venom by mouth should not be made. A large-bore IV cannula inserted on an unaffected limb. BP, coagulation,renal, neurological, cardiorespiratory status must be monitored, as hypotension, anaphylactic shock, renal failure, respiratory distress may develop rapidly.
Management: All patients with suspected envenoming should be observed for 12-24 hours, as the initial manifestations may be delayed, especially with elapid bites. Pain/ vomiting should be managed symptomatically. Aspirin should not be used ,may aggravate bleeding. In severe coagulopathy with thrombocytopenia causing DIC, large quantities of fresh frozen plasma, cryoprecipitate , platelets are required if the response to antivenin is poor. The most appropriate therapy is timely administration of the species-appropriate antivenin when indications. Before starting antivenin, ask about history of allergy & intradermal sensitivity test performed by injecting 0.02 ml of saline-diluted antiserum at a site distant from the bite.
Management: The inj site is observed for at least 10 mins for the redness, hives, pruritus or other adverse effects. The shorter the interval between inj & reaction, the greater the degree of sensitivity. 0.5 ml 1:1000 adrenaline must be available when antiv given A negative skin test does not rule out a reaction following administration of the full antivenin dose. The rate antivenin should be based on the severity of the case& the patients tolerance to the antivenin. The entire initial dose should be given as soon as possible within 4 hours of the bite. In severe envenoming, antivenin given up to 24 hours after the bite has been shown to reverse coagulation deficits.
Management: INDICATIONS FOR ANTIVENIN ADMINISTRATION IN SNAKE BITES Cardiogenic shock Spontaneous systemic bleeding Incoagulable blood Neurotoxicity Haematuria Other evidence of haemolysis/rhabdomyolysis Rapidly progressive extensive local swelling Bites on digits by snakes with known necrotic venoms
SNAKE BITES There are three types of antivenin reaction: Early anaphylactoid Pyrogenic Late. If an immediate anaphylactoid reaction occurs, administration of antivenin should be immediately discontinued &the patient given an oral antihistamine or IM adrenaline ( 0.5 ml of 1:1000) as appropriate. Infusion of the antivenin can be restarted, but at a slower rate. Corticosteroids are commonly given to treat serum sickness, although their value remains to be established. Bites by large snakes may need relatively high antivenin doses, particularly in children or small adults.
SNAKE BITES Additional antivenin (e.g. the contents of 1-5 vials) should be administered if swelling progresses or if systemic features of envenoming increase in severity & new manifestations such as hypotension or reduced haematocrit appear. The use of ancillary drugs, such as anticholinesterases for neurotoxic envenoming, remains contentious. If pulses are lost in a bitten limb, compartment syndrome should be suspected & surgical assessment requested. Wound débridement& later skin grafting are occasionally required, especially in cobra & viper bites, but should never be carried out until the coagulation profile is normal. Awareness &avoidance of the habitat of snakes are the major means of preventing snakebite.
SCORPION STINGS The most important venomous animals after snakes. Most scorpion species produce a venom which causes only minor local reactions in humans, but in Mexico, Tunisia, Algeria, Morocco, Libya scorpion stings are a serious health hazard. Scorpions do not attack humans& escape when disturbed. Stings occur after a person accidentally steps on or involuntarily presses the scorpion (when it is trapped inside shoes or clothes) or when reaching under dead wood or stones. Clothes / shoes need to be inspected closely & shaken& sitting or sleeping places checked when camping in rural districts where scorpions are common
SCORPION STINGS Two types of scorpion venom exist: 1.Venom of genera Hadrurus, Vejovis, Uroctonus only effects, including sharp burning, swelling, discoloration,very rarely, anaphylaxis. In envenoming by more poisonous species, Leiurus, common in the M. East, systematic manifestations develop, transfer to ICU required. 2. Venom, of genera of the poisonous varieties of Centruroides / Mesobuthus, contains neurotoxins block sodium channels& leads to spontaneous depolarisation of parasympathetic &sympathetic nerves results in tachycardia, hypertension, sweating, piloerection, hyperglycaemia & pulm oedema (esp Mesobuthus species)& seizures.
SCORPION STINGS The sharp pain after a sting is quickly followed by paraesthesiae& numbness in the area due to peripheral nerve effects, muscle fasciculation& finally drowsiness. With Centruroides& Mesobuthus there is no swelling at the sting site.
SCORPION STINGS: Management Local pain & paraesthesiae are best treated with local compresses & oral analgesics. Patients with significant envenoming should be hospitalised for at least 12 hours& observed for cardiovascular / neurological sequelae. More severe symptoms may require airway support& 1-2 vials of IV antivenin. The effectiveness of antivenin is controversial, but it is beneficial in the very young, the elderly or those with severe hypertension. True anaphylaxis to antivenin occurs rarely. Serum sickness is common after antivenin but is usually self- limiting & easily controlled with corticosteroids/histamines.
SCORPION STINGS: Management Tachyarrhythmias can be treated with IV metoprolol or esmolol. Prazosin, an α-adrenoceptor antagonist, is indicated if hypertension or pulmonary oedema develops. Prazosin also stimulates the secretion of insulin (which often falls during envenoming) & prevents hyperglycaemia. Other treatments, as calcium or sympathomimetic drugs, are of little value.
Single-choice Qs:1. The most useful bed-side test to suggest snake bite envenemoation is:A. Prothrombin time.B.20 minute whole blood clotting test.C. INR.D.Plateletes count.E. PTT.
Single-choice Qs:2. Management of snake bite includes all except:A.Immobilize the bittenpart.B. Apply a firm bandage.C. Incision & sucking of the bittensite.D. IV cannula on unaffected limb.E.Reassure the ptient.
Single-choice Qs:3.The following features occur in scorpion sting rather than snake bites except:A. Piloerrection.B.hypoglycemia.C.Hyperglycemia.D. Hypertension.E.siezures.