Snake-bite Envenomation: A Comprehensive Evaluation of Severity, Treatment and Outcome in a tertiary Care South Indian Hospital
K Sam, M Khan, S Peerally, P Kumar, P Rao
antivenom, cobra, king cobra, krait, snakebite, snakebite severity score, viper
K Sam, M Khan, S Peerally, P Kumar, P Rao. Snake-bite Envenomation: A Comprehensive Evaluation of Severity, Treatment and Outcome in a tertiary Care South Indian Hospital. The Internet Journal of Emergency Medicine. 2008 Volume 5 Number 1.
Snake bite is a known cause for increased morbidity and mortality in India. A six year retrospective review of medical records was carried out to study the trends, epidemiology, snakebite severity, treatment, and outcome among 252 patients of snakebite in a tertiary care South Indian hospital. Severity assessment showed an average grade of 3.3 with moderate injury. Hemotoxicity and Cellulitis was the most common complications among unidentified snake bites and cobra bites. An average of 11.9 ± 9.3 vials (N=2994) were administered and 96 (48%) anaphylactic reactions were observed. The mortality rate was 10.7% (n=27) while 78.9%of patients improved with 8.2±8.3 day hospitalization period. Severity scores, complications and outcomes were significantly associated with type of snakes, age distribution and linearly correlated to the time elapsed between snake bite instance and hospitalization. Mortality and morbidity can be minimised by the early interventions following identification of snakes, associated sign, symptoms and severity.
In India, it is estimated that up to 20,000 people die annually from snake bites. Morbidity is also significant and there seems to have been little improvement in reducing the fatalities over the years in spite of now having good supplies of polyvalent anti-snake venom (ASV) available in all population centers. The major reason for high mortality rate (about 5% to 10% of all those reporting bites) is the delay in getting the victim to a well-equipped casualty treatment facility fast enough. Snake bite, an important cause of death in rural patients in developing countries, is a neglected public health problem. Worldwide, of the estimated 5 million people bitten by snakes each year, about 1,25,000 die. 1 More than 2,00,000 cases of snake bite are reported in India each year and 35,000–50,000 of them have turned out to be fatal. Reports from Maharashtra, State in India, disclose that an estimated 10,000 annual venomous snake bites account for 2000 deaths. 2 Romulus Whitaker, pointed out that, the Indian cobra (
The type of snake bite varies from region to region. Wherever one species prevails, the chances of humans coming into their contact is higher, then the bite of that species will be more common. 3 Snake bite is continuing to be a major medical concern in India. World Health Organization survey reports that 1.2–2.4 deaths occur per 100,000 victims with a mortality level of 25,000 per annum. There are many causal factors that contribute to this mortality rate, and many questions remain unanswered. To make more meaningful use of resources such as antivenom, ventilator therapy and renal support systems in patients with snake bite, it is important that the healthcare providers aptly identify those at high risk of potentially fatal complications. Simple demographic and clinical characteristics could be used to help doctors distinguish between high-risk and low-risk patients. To be useful, the predictors like snake bite severity score should be simple, accurate and clinically credible.
There has, however, been very little qualitative herpetological work in India, since the 1940s. Limited statistics on mortality and morbidity due to envenomation are available. Such data have recognizable limitations. 4 There are very limited Indian studies which have assessed severity and its role in predicting outcome of snake envenomation. The factors, like time-lags from exposure till hospitalisation, influencing the severity and outcome, are not captured during epidemiological studies. The present study was carried to out to estimate the snake bite related epidemiology, clinical characteristics, severity and outcome. An attempt was made to evaluate the predictors of severity, relationship between type of snake, clinical severity, complications, outcome and usage pattern of polyvalent anti snake venom (ASV).
Materials and Methods
A retrospective review of medical records was carried out to determine the pattern of snake bite envenomation cases admitted to Kasturba hospital. Medical records of patients admitted for six years during the period January 2002 to December 2007 were reviewed. All patients of snake bite that were presented to our institution over a period of 6 years were included in the present study. The study aimed to assess the time lag between snake bite and hospitalisation, severity of patient at hospitalisation and subsequent development of complications, treatment provided and the outcome of 252 patients who became eligible for the study.
Study was conducted by carrying out a review of envenomed patients presenting to the emergency centre. The cases were identified from medical records which were arranged according to ICD-10 classification of diseases. A computer generated list, of patients with hospital numbers was collected. The medical records of patients, discharged with diagnosis of envenomation due to venomous snakes were obtained from the medical record office. Records with diagnosis of envenomation from arthropods, or other animals were excluded. Epidemiological data collected from the medical records were categorized into type of snake identified; time lapsed from the time of bite till the time of hospital admission, clinical characteristics of snake bite, severity, quantity of polyvalent antisnake venom used, outcome in terms of duration of hospitalisation, and clinical status at discharge.
The severity of envenomation was assessed using to the modified snakebite severity score (SSS) according to Dart et al.,1996 and Nualnong et al., 2005. 5,6 Occurrence of a particular symptom was checked against the chart (Table 1) and graded. The severity grading assigned to a case was determined by the most severe symptom(s) or signs(s) observed. The severity was graded from 0 to 4 ranging from no envenomation to severe life threatening symptoms and death taking into consideration clinical signs/symptoms and/or laboratory data. The four levels represent as follows; grade 0 for no symptoms or signs, grade 1 for mild, transient and spontaneously resolving symptoms or signs, grade 2 for moderate, pronounced or prolonged symptoms or signs, grade 3 for severe or life threatening symptoms or signs, while grade 4 represents extremely severe envenomation leading to mortality. The factors that affect SSS like pre-hospitalization period, demographical variables, type of snakebite and the outcome were evaluated.
Outcomes like hospitalization period and clinical condition at the time of discharge were determined. The clinical outcomes were sorted out using three variables, namely improved, morbid state or fatal outcome. The variable ‘improved status' was defined as state of complete recovery with no associated permanent physical or physiological abnormality. ‘Morbidity state' was defined as a state of either clinically unstable vital functions or disturbed physical, functional and physiological state. ‘Fatality' was defined as clinical state of brain death as certified by the physician. Factors affecting clinical outcome, like demographical factors, prehospitalization period and SSS were assessed.
Assessment of Treatment
The treatment provided was assessed in terms of the quantity of polyvalent anti snake venom vials (ASV) administered during the hospitalisation and compared with the severity and outcome. The time lapsed was compared to assess its role in predicting severity and outcome. The patient's records were evaluated from day of admission to discharge in order to note any subsequent development of complications. The incidence of complications like renal failure, neurotoxicity including ptosis, breathing difficulty, and hematological toxicity including, bleeding time, clotting time, prothrombin time, active prothrombin time, and cellulitis were evaluated and compared with the type of snake implicated in the envenomation .
Results were expressed as frequency percentages. The categorical data collected was summarized using proportions by chi-square test. Pearson's correlation test was used to study the linear correlation between various scores. A probability of P?0.05 was considered statistically significant. SPSS version 13, 2004 statistical software was used for evaluation. Chi-square analysis was carried out to assess the association of severity, clinical complications and outcome with parameters like type of snake involved, the demographical parameters, site of bite, time lapsed after bite, number of ASV vials.
Patient Characteristics and Demographic analysis of snake bite patients:
Two hundred and fifty two patients of snake bites became eligible for the study, over a period of 6 years. Majority were aged between 11- 50 years, the youngest patient was one year old, age was 82 years. Gender distribution revealed that 154(61.1%) patients were males while 98 (38.9%) were females.
The relationship between the various determinants affecting severity and outcome are summarized in Table2 and Table 3. The mean time elapsed between snake bite and time of hospital admission was 28.97 ±77.7 hours with a median time of 6 hours. Majority of patients N=169 (67.1%) had a severity grade between 2 and 3 and 95 (37.7%) of them had a grade 3 severity which denotes occurrence of severe life threatening symptoms. Assessment of the determinants of severity grading score showed that there was a statistically significant (P<0.000) association with the type of snake and the severity scores.
The retrospective analysis of outcome among cases of snake bite envenomation in 6 years from 2002 to 2007 showed that among the total of 252 snake bite cases, 27 patients (10.7%) died. Twenty six patients did not improve while the remaining 199 cases improved at the time of discharge. The average hospitalisation period of all cases was 8.19± 8.3 days. Among the 27 (10.7%) fatal cases due to snake envenomation there were 13 (8.4%) males and 14 (14.3%) females. The average age of patients who died due to snake bite was 42.11±22.02 years (median 35.0). Majority of fatality N=6(13%) occurred in the age group of 41- 50 years. A total of 2994 vials of ASV were employed in the management, while 66 (26.3%) patients had anaphylactic reaction following ASV injections and hence were administered corticosteroids and antihistamines injections. An average of 11.9 ± 9.3 vials (median=10) were administered to 216 patients, while 36 patients did not receive ASV because they had no symptoms. The mean hospitalisation period was 8.19 ± 8.3 days with a median value of 6 days.
Determinants of severity grading index (Table 2, Table 3)
On comparing the age distribution with the severity grading score using a cross tabulation there was a statistically (P?0.010) significant linear relationship between the age groups and the severity grading scores. There was a linear correlation between age distribution and the severity grade scores (p=0.010) with R=0.162. However no significant (P=0.841) variation of severity grading scores occurred between the genders.
There was a statistically (P=0.010) significant linear association between the time lapsed to the severity grading score (R=0.163). There was no influence of the site of bite on the severity grading score. There was a significant (P<0.0001) linear correlation of the number of ASV vials required and the severity grading scores (R=0.309). There was a significant (P=0.004) difference in the observed median hospitalization period for the various severity grading scores. There was also a statistically significant (P=0.001) difference of median hospitalisation days, time lapsed before admission and number of ASV vials with respect to the severity grade scores (Table 3).
Assessment of clinical outcome and the factors affecting outcome and mortality (Table 5)
Evaluation of the factors that influence the clinical outcome showed that there was no association between the type of snake; time lapsed before admission with the outcome of the patients. Gender and age distribution revealed no significant association with the outcome of the patients. A total of 13 males (8.4%) and 14 females (14.3%) died. However there was a statistical significant P= 0.013 linear relationship between the hospitalisation period and the outcome analysis. A total of 184 patients were bitten at the lower limb and 23 (13.0%) among them died, while 68 of them were bitten in the upper limb and four (6%) victims among them died. There was a significant (P=0.028) association between the site of bite and the outcome of patients. There was a statistically significant (0.000) association between the severity grading score and the outcome in terms of mortality, squeal and improvement. Among 60 patients who had renal failure, a significantly high number 12 (20%) of them died.
Association of clinical complications and the type of snakes (Table 6)
A comparison of clinical features of various types of snakes is shown in table 3. There was a significant association (P=0.030) between the type of snake and the occurrence of renal failure. Maximum cases of renal failure were observed among the viper bites N=19 (31%) followed by N=31 (29.52%) patients with unknown snake envenomation. There was a statistically significant association (P=0.005) between the type of snake and the occurrence of ptosis. Maximum cases of ptosis were observed among cobra envenomation N=28 (43.75%) followed by N=22 (20.95%) patients with unknown snake envenomation.
Dyspnea was observed among unknown snake envenomation N=32 (30.47%) followed by N=25 (39.06%) patients with cobra snake envenomation. There was a statistically significant association (P=0.006) between the type of snake and the occurrence of cellulitis. Cellulitis was observed among cobra envenomation N=44 (68.75%) followed by N=57 (54.2%) patients with unknown snake envenomation.
Association of laboratory parameters with type of snakes
On assessment of the extent of haemotoxicity it was observed that, 59 patients had prolonged clotting time and the average clotting time was 7.5±2.8 minutes (Normal 8-10 minutes), 45 patients had prolonged bleeding time with an average of 4.3±2.9 (2-6 minutes), 223 patients had abnormal PT with an average of 25.7± 28.8 seconds (Normal=13.0 seconds with a control value of 12 seconds), 154 patients had abnormal APTT with an average of 36.8±21.9 seconds. (Normal= 29 seconds at a control value of 27 seconds). The total number of patients with renal failure was 60 (23.8%), 77 (30.55%) had breathing difficulty, 69 (27.4%) cases had ptosis; while maximum number of patients had cellulitis 142 (56.34%).
There was a statistically significant association (P<0.05) between the type of snake and the occurrence of abnormal bleeding time and clotting time. Abnormal bleeding time was observed among viper envenomation N=19 (31.66%) followed by N=18 (17.14%) patients with unknown snake envenomation. Prolonged clotting time was observed among viper envenomation N=15 (25%) followed by N=8 (7.6%) patients with unknown snake envenomation. Two cases of decreased clotting time were observed among viper envenomation. Abnormal prothrombin time was observed among Cobra envenomation N=60 (93.75%) followed by N=51 (85%) patients with viper snake envenomation and 94 (89%) cases with unknown snake envenomation. Maximum number of cases with abnormal prothrombin time were observed among viper envenomation N=46 (76.66%), while abnormal APTT was observed among N=60 (57.14%) patients exposed to unidentified snake envenomation. There were N=36 (56%) cases of abnormal APTT among cobra envenomation cases.
Worldwide, the published statistics on the incidence, morbidity and mortality of snakebites are largely based on the hospital data and are grossly inadequate except for few countries where snake bite is rare or correctly reported. In Asia alone, it has been estimated that four million snake bites occur each year of which 50% are envenomed resulting in 100,000 annual deaths. 7 Hospitals are a rich source of epidemiological data with respect to snake bite. 8 The severity of clinical manifestations and mortality is related to the biting species, and effective management relies on accessibility and availability of antivenom and facilities for ventilation and dialysis. 9
As observed in this study, majority of the envenomation was due to unidentified snakes 105 (42%) It is suggested by many studies that a significant number of dead species should be brought to the hospital by the victims, and it is essential that these specimens be preserved in formalin and properly identified by a qualified herpetologist. This will provide sound epidemiological data and positively identify which species are causing morbidity and mortality in a given area. This is a high priority as it directly impacts patient care. If there are species that are currently regarded as harmless, yet are causing morbidity and mortality, it is essential that this be established and that effective antivenoms are developed in order to reduce morbidity and save lives. The clinical scoring system is highly suitable for use in community-based surveys to identify and differentiate between bites of highly venomous snakes. The use of clinical scores may overcome some of the difficulties of identification of snakes in such settings, where the biting species is unidentified and where individuals frequently misidentify venomous and non-venomous species. 9
Delay in admission can play a major role in deciding the severity and outcome. Those patients who were admitted late had higher severity scores, poor outcome and higher number of complications like renal failure (52%), breathing difficulty (42%), cellulitis (40%), abnormal PT and APTT in 42% and 39% of cases respectively. There was a significant association between the time lapsed and severity index. Mortality rate was the highest (16%) and higher morbidity and squeal were observed among patients (18%) who were admitted after 24 hours of envenomation. Majority (64%) of those admitted after 13-18 hours seemed to have grade 3 severity with life threatening symptoms, while those patients (82%), who were admitted within six hours, had improved. The delay in the availability of prompt treatments had significantly increased the severity and outcome. This observation showed that there was a direct proportion of severity and outcome to the duration of venom in the blood prior to neutralization by ASV due to late arrival of patient at the hospital. Early administration of antivenom is beneficial in preventing complications and morbidity associated with systemic envenomation. 10 Monospecific antivenoms are more effective and less likely to cause allergic reactions than polyspecific antivenoms. 9 Antivenom producers, especially those in less-developed countries that have excess production capability, should be encouraged to manufacture geographically relevant antivenoms. 11
Snake bite severity scores were significantly associated with factors like type of snakes, age distribution and were directly proportional to the time elapsed between snake bite instance and hospitalisation time. Outcome measures like clinical status at discharge depended on the factors like site of bite, occurrence of renal failure, quantity of ASV administered, and severity grading scores. Maximum incidence of haemotoxicity was observed among unidentified snake bites, and those with viper and cobra bites. Cellulitis was the most common complication seen among patients with unidentified snakes and cobra bites. Delay in hospitalisation increased the incidence of the complications, severity index and outcome. The early administration of ASV is beneficial in preventing complications, however severe the systemic envenomation. Clinical severity scoring will give us a more accurate estimation of the burden of snakebite even if the envenoming species are not available and help decision makers to take appropriate decisions.
The authors wish to thank the staff of medical records department, Kasturba Hospital, Manipal for extending their cooperation in accessing the medical records, and the Medicine Department of KMC, for rendering assistance in completing the study.
Kishore Gnana Sam Senior Lecturer, Department of Pharmacy Practice, Manipal College of Pharmaceutical Sciences, Manipal University, Manipal Karnataka India -576104 Email: firstname.lastname@example.org Fax: 91820 2571998