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Snake Bites

Snake bite

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Snake Bites

  1. 1. SNAKE BITES Dr. Wong July '15
  2. 2. Case (1) • 17 year old boy was brought to ED with alleged snake bite over his left index finger • Occurred at 1pm and arrived to ED at 2pm • Patient was digging for worms for fish bait and he was suddenly bitten by a small viper like snake • No bleeding or LOC • Left hand becomes painful and tender
  3. 3. • Noted 2 superficial bite marks over index finger with generalized swelling over his left hand • Pulses were palpable, able to move his fingers, sensation intact Case (2)
  4. 4. • Admission to ward, noted 6 hours after bite , Lt hand was swollen • Swelling was decreasing on next day • Noted INR 2.08 → 1.85 • Repeated next day, INR 9.75 Case (3)
  5. 5. • At 1pm, he was administered 2 vials of monovalen antivenom • Subsequently started on IV Piriton 10mg stat • On the following day, noted that swelling was subsiding and PT/INR was down-going in trend, INR 1.45 • BP remains stable • At D3 of bite, swelling has reduced and patient was able to move his hands and discharge well Case (4)
  6. 6. Introduction (1) • Snakebite is a serious medical problem in Malaysia • From 1978 to 2000, there were 55000 cases of snakebites recorded in the hospitals in Malaysia • The mortality rate of snakebite in Malaysia is only 0.3 per 100000 population but the local necrotic effects of some venoms can cause prolonged morbidity or even crippling deformity
  7. 7. Types of snakes • In Malaysia and the coastal waters of the region, there are at least 18 different species of venomous front fanged land snakes and more than 22 different species of sea snakes • These venomous snakes belong to the following 5 subfamilies: 1. Crotalinae: represented by the two genera Calloselasma and Trimeresurus. 2. Elapinae: represented by the five genera Naja, Bungarus, Ophiophagus, Maticora and Calliophis; 3. Laticaudinae, represented by the genus Laticauda 4. Hydrophiini, represented by the six genera Enhydrina, Kerilia, Hydrophis, Thalassophis, Pelamis and Kolpophis 5. Ephalophiini, represented by the only genus Aipysurus.
  8. 8. • not all snakes are venomous • In Malaysia there are approximately 40 species of venomous snakes (18 land snakes, all 22 of sea snakes) belonging to two families: • - Elapidae – have short, fixed front fangs. The family includes cobras, kraits, coral snakes and sea snakes. - Viperidae – have a triangular shaped head and long, retractable fangs. The most important species in Malaysia are Calloselasma rhodostoma (Malayan pit viper) and Trimeresurus genus (green viper)
  9. 9. Introduction (2) Malayan pit viper are common esp. in northern peninsular, but not found in Sabah & Sarawak Cobra & Malayan pit vipers cause most of snake bites in Malaysia Bites by sea snakes, coral snakes and kraits are uncommon
  10. 10. Introduction (3) Snake venom is made up of > 20 components: Procoagulant enzymes (activate coagulation cascade) Phospholipase A2 (myotoxic, neurotoxic, cardiotoxic – cause haemolysis ( ↑ vascular permeability) Proteases (tissue necrosis) Polypeptide toxins (disrupt neuromuscular transmission
  11. 11. Biochemical composition of Snake Venoms (1) • Dried snake venom contains mainly proteins (70- 90%) and small amounts of metals, amino acids, peptides, nucleotides, carbohydrates, lipids and biogenic amines • The protein components include enzymes and non-enzymatic proteins/polypeptides • The main toxins in the venoms of elapid snakes (cobras, kraits and sea snakes) include: polypeptide postsynaptic neurotoxins, cardiotoxins and phospholipases A that may exhibit presynaptic neurotoxicity or myotoxicity
  12. 12. • The main toxins of crotalid (pit viper) snake venoms, on the other hand, are thrombin-like enzymes, hemorrhagic proteases and platelet- aggregation inducers Biochemical composition of Snake Venoms (2)
  13. 13. Elapid Venom Poisoning (1) • Elapid venoms (cobras, kraits and sea snakes) generally exhibit neurotoxicity and cardiotoxicity • The earliest symptom of systemic elapid poisoning is a feeling of drowsiness or intoxication, which starts from 15 min to 5 hr after cobra bites
  14. 14. • Difficulty in opening the eyes (bilateral ptosis: eyelids may remain completely closed though the patient usually remains conscious until respiratory failure is advanced), speaking, opening the mouth, moving the lips and in swallowing follows within 1 to 4 hrs • Breathing becomes increasingly difficult. In severe poisoning, respiratory failure sets in rapidly Elapid Venom Poisoning (2)
  15. 15. Neurotoxicity (1) Neurotoxins block transmission at the NM junction Flaccid/Respiratory paralysis Non - physiologic drowsiness
  16. 16. • The neurotoxic effects are mainly at the postsynaptic level of the neuromuscular junction where the neurotoxins block acetylcholine receptors, thereby producing muscular paralysis and respiratory failure • The major neurotoxins are usually basic polypeptides Neurotoxicity (2)
  17. 17. Cardiotoxicity (1) • Cardiotoxicity is caused by polypeptide cardiotoxin that affects both excitable and non-excitable cells, causing irreversible depolarization of the cell membrane and consequently impairing the structure and function of various cells, thus contributing to muscle paralysis and leading to circulatory and respiratory failure and systolic arrest
  18. 18. • Cobra venom also causes extensive local necrosis, which requires treatment • The local necrosis is presumably caused by the combine action of cardiotoxin and phospholipase A2 • Sea snake venoms contain both polypeptide neurotoxins (homologous to elapid neurotoxins) and myotoxins, which are basic phospholipase A2. • The venom causes respiratory failure (neurotoxic effect), myonecrosis, myoglobinemia and acute renal failure
  19. 19. Renal failure/rhabdomyolysis ATN: hypotension/hypovolemia, DIC, direct toxic effect on tubules, hemoglobinuria, myoglobinuria Generalized rhabdo: Release of myoglobin, muscle enzymes, uric acid, K (presynaptic neurotoxins)
  20. 20. Local necrosis Increased vascular permeability Swelling and brusing Myotoxins Ischemia/thrombosi s Venom ophthalmia
  21. 21. Pit Viper Venom Poisoning (Viperidae) • The venom of pit vipers causes local swelling, necrosis and systemic bleeding. Hemorrhage is the outstanding symptom of systemic pit viper poisoning • Clotting defect usually accompanies hemorrhage. The commonest and earliest hemorrhagic manifestation is hemoptysis, which may be seen as early as 20 minutes after the bite • Bleeding from the gum is less common and follows later after the bite
  22. 22. • Discoid ecchymoses appear in the skin an hour or so later • Bleeding into the brain or other vital organ may be fatal. • In severe cases, loss of blood may lead to hypovolemic shock • In Malayan pit viper bite, the clotting defect is primarily due to thrombocytopenia aggravated by defibrination syndrome Pit Viper Venom Poisoning (Viperidae)
  23. 23. Recovery times • In the absence of necrosis, pain after viper bites rarely exceeds 2 weeks. • When necrosis develops (in about 10% of cases) pain may remain severe for a month. • Swelling usually resolves completely in 2-3 weeks. • Healing time of local necrotic lesions varies greatly according to the extent of the lesion and the treatment given, but may requires 1-6 months or longer.
  24. 24.  Hemorrhagic effects in viper bites are also short-lived and rarely exceed a week but the coagulation defect may persist for 3-4 weeks  Neurotoxic symptoms usually resolve in 2-3 days
  25. 25. Management: (a) First aid (1) Aims are to retard absorption of venom, provide basic life support & prevent further complications Reassure victim (anxiety ↑ venom absorption) Immobilise bitten limb with splint/sling (retard venom absorption)
  26. 26. Management: (a) First aid (2) Apply firm bandage for some elapid bites (delay absorption neurotoxic venom) but not for viper whose venom cause local necrosis Leave the wound alone – DO NOT incise, apply ice/other remedies Tight (arterial) tourniquet are not recommended
  27. 27. Management: (a) First aid (3) Do not attempt to kill the snake However, if it is killed, bring snake to hospital for identification Do not handle snake with bare hands as even a severed head can bite! Transfer victim quickly to nearest health facility
  28. 28. Management: (b) Treatment in hospital (1) Do rapid clinical assessment & resuscitation, including Airway, Breathing, Circulation & level of consciousness Monitor vital signs (BP, RR, PR) Establish IV access, give O2 & other resuscitation as indicated History: inquire part of body bitten, timing, type of snake & h/o atopy
  29. 29. Management: (b) Treatment in hospital (2) Examine: Bitten part for fang marks, swelling, tenderness, necrosis Distal pulses ( ↓ / or in compartment syndrome) For bleeding (tooth sockets, conjunctiva, puncture sites) For neurotoxicity (ptosis, ophthalmoplegia, bulbar & respiratory paralysis)
  30. 30. Management: (b) Treatment in hospital (3) For muscle tenderness, rigidity (sea snakes) Urine for myoglobinuria Send blood investigations (FBC, RFT, PT/PTT, GXM) Perform a 20-min whole blood clotting test (if unclotted after 20 min → suggests hypofibrinogenaemia due to pit viper bite & rule out elapid)
  31. 31. Management: (b) Treatment in hospital (4)  Review immunisation history: give booster ATT if indicated  Venom detection kits to identify species of snake are not available in Malaysia  Admit to ward for at least 24 hours (unless snake is definitely non-venomous)  All cases should be supervised by a physician or clinical toxinologist who are familiar and experienced with snakebite and envenomation management in Malaysia
  32. 32. Management: (c) Antivenom treatment Antivenom is only specific treatment for envenomation Give early for best result However, it can be given as long as signs of systemic envenomation are still present For local effect, antivenom is not effective if given > few hours after envenomation
  33. 33. Antivenom in Hosp. Sg Bakap
  34. 34. Management: (d) Indications for antivenom (1) Haemostatic abnormalities e.g. spontaneous systemic bleeding, incoagulable blood/thrombocytopenia (<100 x 109 /L) Neurotoxicity CV dysfunction eg hypotension/shock Generalised rhabdomyolysis (muscle ache & pain)
  35. 35. Management: (d) Indications for antivenom (2) Significant local effect, e.g. local swelling > ½ bitten limb, extensive blistering/bruising, bites on digit/rapid progression of swelling Helpful laboratory investigations suggesting envenomation include anaemia, thrombocytopenia, leucocytosis, raised serum enzymes (CK, AST, ALT), hyperkalaemia, myolobinuria
  36. 36. Management: (e) Choice of antivenom (1) If biting species is known, give monospecific/monovalent antivenom (more effective, less adverse reactions) If unknown, clinical manifestations may suggest offending species: • Local swelling + neurological signs = cobra bites • Extensive local swelling + bleeding tendency = Malayan pit viper
  37. 37. Management: (e) Choice of antivenom (2) If still uncertain, give polyvalent antivenom No antivenom is available for Malaysian kraits, coral snakes & some species of green vipers Fortunately, bites by these species are rare & usually cause only trivial envenoming
  38. 38. Management: (f) Dosage & route administration (1) Amount given is usually empirical Recommendations from manufacturers are usually conservative as they are mainly based on animal studies
  39. 39. Management: (f) Dosage & route administration (2) Repeat antivenom administration until signs of envenomation resolved Give through IV route only Dilute antivenom in any isotonic solution (5- 10ml/kg) Bigger children dilute in 500ml / IV solution) & infuse whole amount in 1h
  40. 40. Management: (f) Dosage & route administration (3) Infusion may be discontinued when satisfactory improvement occurs, even if recommended dose has not been completed Do not perform sensitivity test as it poorly predicts anaphylactic reactions Do not inject locally at bite site
  41. 41. Management: (f) Dosage & route administration (4) Prepare adrenaline, hydrocortisone, antihistamine & resuscitative equipment & be ready if allergic reactions occur Pretreatment with adrenaline SC remains controversial Small controlled studies in adults showed it effective in reducing risk of reactions
  42. 42. Management: (f) Dosage & route administration (5) However, its effectiveness & appropriate dosing in children have not been evaluated There is no strong evidence to support use of hydrocortisone/antihistamine as premedications Consider their use in patients with atopy
  43. 43. Management: (g) Antivenom reactions (1) 3 types: (a) Early anaphylactic reactions Occur 10-180mins after starting antivenom Symptoms range from itching, urticaria, nausea, vomiting, palpitation to severe systemic anaphylaxis – hypotension, bronchospasm & laryngeal oedema
  44. 44. Management: (g) Antivenom reactions (2)(contd) Stop antivenom infusion: give adrenaline IM (0.01ml/kg of 1 in 1000) Antihistamines eg. Chlorpheniramine 0.2mg/kg, hydrocortisone 4mg/kg dose & IV fluid (if hypotensive) If mild reactions restart infusion at a slower rate
  45. 45. Management: (g) Antivenom reactions (3) (b) Pyrogenic reactions Develops 1-2h after treatment & are due to endotoxins in antivenom Symptoms include fever, rigors, vomiting, tachycardia & hypotension Give treatment as above Treat fever with paracetamol & tepid sponging
  46. 46. Management: (g) Antivenom reactions (4) (c) Late reactions Occur about 1 wk later It is a serum sickness-like illness (fever, arthralgia, lymphadenopathy, etc) Treat with chlorpheniramine 0.2mg/kg/day in divided doses x 5d If severe, give oral prednisolone (0.7- 1mg/kg/day) x 5-7d
  47. 47. Management: (h) Anticholinesterases (1) They should always be tried in severe neurotoxic envenoming, especially when no specific antivenom is available eg. bites by Malaysian krait & coral snakes These drugs have a variable but potentially useful effect
  48. 48. Management: (h) Anticholinesterases (2) Give test dose of edrophonium chloride (Tensilon) IV (0.25mg/kg, adult 10mg) with atropine sulphate IV (50-100ug/kg; adult 0.6mg) If patients respond convincingly, maintain with neostigmine methylsulphate IV (50- 100ug/kg) & atropine, 4hrly by continuous infusion
  49. 49. Management: (i) Supportive / Ancillary treatment (1) Clean wound with antiseptics Give analgesia to relief pain (avoid aspirin) In severe pain, use morphine (watch for respiratory depression) Give antibiotics if wound look contaminated / necrosed e.g. IV C Pen + gentamicin, amoxy-clav, erythromycin / 3rd generation cephalosporin
  50. 50. Management: (i) Supportive / Ancillary treatment (2) Respiratory support – respiratory failure may require assisted ventilation Watch for intracompartment syndrome – pain, swelling, cold distal limbs & muscle paresis Get early orthopaedic / surgical opinion
  51. 51. Management: (i) Supportive / Ancillary treatment (3) Patient may require urgent fasciotomy Correct coagulation abnormalities with fresh frozen plasma & platelets before any surgery Desloughing of necrotic tissues should be carried out as required
  52. 52. Management: (i) Supportive / Ancillary treatment (4) For oliguria & renal failure, e.g. due to sea snake envenomation, measure daily urine output, Sr creatinine, urea & electrolytes If urine output fails to increase after rehydration & diuretics (e.g. frusemide), start renal dose of dopamine (2.5ug/kg/min IV infusion) & place on strict fluid balance Dialysis is rarely required
  53. 53. Pitfalls in management (1) (a) Giving antivenom “prophylactically” to all snake bite victims Not all snake bite by venomous snakes will result in envenoming On average, 30% bites by cobra, 50% by Malayan pit vipers & 75% by sea snakes DO NOT result in envenoming
  54. 54. Pitfalls in management (2)(contd) Antivenom is expensive & carries risk of causing severe anaphylactic reactions (as derived from horse / sheep serum) Hence it should be used only in patients in whom the benefits of antivenom are considered to exceed risks
  55. 55. Pitfalls in management (3) (b) Delaying in giving antivenom in district hospitals until victims are transferred to referral hospitals Antivenom should be given as soon as it is indicated to prevent morbidity & mortality District hospitals should stock important antivenoms & provide care & safe monitoring for antivenom infusion
  56. 56. Pitfalls in management (4) (c) Giving polyvalent antivenom for envenoming by all types of snakes Polyvalent antivenom does not cover ALL types of snakes E.g. Sii polyvalent (India) is effective in cobra & some kraits envenomation but is not effective against Malayan pit viper Refer to manufacturer drug insert for details
  57. 57. Pitfalls in management (5) (d) Giving smaller doses of antivenom for children Dose should be same as for adults Amount given depends on the amount of venom injection rather than size of victim
  58. 58. Pitfalls in management (6) (e) Giving pretreatment with hydrocortisone / antihistamine for snake bite victim Snakebites do not cause allergic / anaphylactic reactions These drugs may be considered in those who are given ANTIVENOM
  59. 59. Resources: http://mstoxinology.blogspot.com/p/recs.html Snakebite Management Guide for Healthcare Providers in Malaysia (2014) Image Gallery of Land Snakes of Medical Importance in Malaysia (2013) Snake Antivenom Guide for UKMMC (2014) Snake Antivenom Guide for Sabah (2014) http://www.junglecraft.com.my/index.php/snake-bite/