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Therapeutic Plasma Exchange for Venom-Induced Thrombotic Microangiopathy Following Hump-Nosed Pit Viper (Genus: Hypnale) Bites: A Prospective Observational Study
Department of Pharmacology, Faculty of Medicine, Sabaragamuwa University of Sri Lanka, Hidellana, Ratnapura, Sri LankaDepartment of Veterinary Pathobiology, Faculty of Veterinary Medicine and Animal Science, University of Peradeniya, Peredeniya, Sri LankaIntensive Care Unit, Teaching Hospital Ratnapura, Sri Lanka
—Thrombotic microangiopathy (TMA), which is the triad of acute kidney injury (AKI), microangiopathic hemolytic anemia (MAHA), and thrombocytopenia, is a rare complication of snakebites, and in Sri Lanka, it is commonly seen with hump-nosed pit viper (HNPV) bites.
Methods
—We conducted a prospective observational study of patients with AKI caused by HNPV bites in Teaching Hospital, Ratnapura, Sri Lanka for 6 y, commencing in June 2015. Some patients with TMA underwent therapeutic plasma exchange (TPE) and some did not. These 2 groups were compared. Statistical analysis was carried out using Minitab 18.1. Data were presented as median (IQR).
Results
—There were 52 (8%) patients with TMA, of whom 21 (45%) were in the TPE group and 26 (55%) were in the non-TPE group. TPE improved time to platelet correction (4 d [IQR, 4–5 d] vs 7 d [IQR, 5–9 d]; P=0.009), time to MAHA correction (5 d [IQR, 3–4 d] vs 7 d [IQR, 6–9 d]; P=0.004), time to prothrombin time (PT)/international normalized ratio (INR) correction (1 d [IQR, 1–2 d] vs 3 d [IQR, 3–4 d]; P=0.003), and time to 20 min whole blood clotting test (WBCT20) correction (2 d [IQR, 1–2 d] vs 3 d [1QR 2–3 d]; P=0.020). Renal recovery was predicted by TPE (P=0.048) and highest creatinine level (P=0.001). There was no association between TPE and dialysis dependency at discharge (P=0.597), length of hospital stay (P=0.220), and the number of dialysis cycles prior to discharge (P=0.540). TPE did not improve the number of blood transfusions (5 packs [IQR, 3–8.5 packs] vs 4 packs [IQR, 0–9 packs]; P=0.290).
Conclusions
—TPE is effective for TMA in the early correction of platelet counts, MAHA, PT/INR, and WBCT20 in HNPV bites.
There are 7 highest medically important land snakes in Sri Lanka: Russell’s viper (Daboia russelii), saw-scaled viper (Echis carinatus), cobra (Naja naja), Ceylon krait (Bungarus ceylonicus), common krait (Bungarus caeruleus), hump-nosed pit viper (HNPV) (Genus: Hypnale), and Sri Lankan Green pit viper (Craspedocephalus trigonocephalus). Out of these, HNPV causes the commonest venomous snakebites in Sri Lanka
and is widely distributed all over the country except in Jaffna peninsula in northern Sri Lanka. The genus comprises 3 species, namely, H hypnale, H zara, and H nepa. Thrombotic microangiopathy (TMA) is a clinicopathological condition that includes the triad of microangiopathic hemolytic anemia (MAHA), thrombocytopenia, and microvascular thrombi that cause end-organ damage like in acute kidney injury (AKI), pituitary infarction, and digital gangrene. The recognized syndromes associated with TMA are hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP), which have almost similar clinical and laboratory features and are, therefore, known as TTP/HUS clinical syndrome. Thrombotic microangiopathy has been previously reported following bites by H hypnale
Thrombotic microangiopathy, haemolytic uremic syndrome and thrombotic thrombocytopenic purpura following hump-nosed pit viper (Genus: Hypnale) envenoming in Sri Lanka.
As no antivenom is currently available for HNPV envenoming in Sri Lanka or India, these patients endlessly suffer from severe morbidities, particularly AKI, which progresses to chronic kidney disease (CKD) that needs regular renal replacement therapy. On the other hand, acute deaths may occur due to complications of venom-induced consumption coagulopathy (VICC) such as pulmonary hemorrhage,
Venom-induced consumption coagulopathy following hump-nosed pit viper (Genus: Hypnale) envenoming in Sri Lanka: uncertain efficacy of fresh frozen plasma.
Therefore, alternative treatment modalities instead of antivenom have to be followed for HNPV bites.
According to the American Society for Apheresis guidelines, the indication of TPE in snakebites is classified under category III Grade 2C recommendation.
Guidelines on the use of therapeutic apheresis in clinical practice-evidence-based approach from the Apheresis Applications Committee of the American Society for Apheresis.
Thrombotic microangiopathy, haemolytic uremic syndrome and thrombotic thrombocytopenic purpura following hump-nosed pit viper (Genus: Hypnale) envenoming in Sri Lanka.
Snakebite associated thrombotic microangiopathy: a systematic review of clinical features, outcomes, and evidence for interventions including plasmapheresis.
The HNPVs are medically important because of 2 reasons: no antivenom is currently available for their bites in Sri Lanka or India and the occurrence of unpredictable complications after their bites such as VICC and AKI, which progress to CKD.
Venom-induced consumption coagulopathy following hump-nosed pit viper (Genus: Hypnale) envenoming in Sri Lanka: uncertain efficacy of fresh frozen plasma.
Because of the severity of complications, the World Health Organization categorized H hypnale under the category I snake (highly venomous), which requires the development of antivenom.
Bon C, Burnouf T, Gutiérrez JM, Padilla A, Ratanabanangkoon A, Warrell DA. WHO Guidelines for the Production, Control and Regulation of Snake Antivenom Immunoglobulins; WHO Technical Report Series; WHO: Geneva, Switzerland, 2010.
Considering the unique nature of epidemiology and clinical manifestations of HNPV bites with the unavailability of antivenom, the objectives of this study were to describe the outcomes of patients with TMA treated with TPE and to compare them with those in the non-TMA group of HNPV bites.
Methods
This prospective observational clinical study was conducted from June 2015 to May 2021 in the Teaching Hospital, Ratnapura, the only tertiary care center in Sabaragamuwa Province in Sri Lanka, approximately 100 km away from the capital Colombo. The hospital receives transfers from other local hospitals situated all over the Ratnapura District with a population of 3 million and approximately 138,000 patients present at the hospital per year, of which 280 to 350 are admitted because of snakebites. Ethical approval for the study was obtained from the Faculty of Medicine, University of Peradeniya (2015/EC/20).
All adult patients with AKI following HNPV bites were included in the study. On admission, they were assessed by the corresponding author and reassessed daily until hospital discharge (primary data). Epidemiological information, clinical manifestations, laboratory findings, treatment, and outcomes were recorded in a formatted data sheet. In order to assess the renal function, urine output, blood urea, serum creatinine, and serum potassium levels were measured. Coagulopathy was assessed by looking for bleeding manifestations, 20-min whole blood clotting test (WBCT20), and clotting profile (prothrombin time [PT]/international normalized ratio [INR], activated partial thromboplastin time [aPTT]). The reference ranges of INR and hemoglobin (Hb) were 1 to 1.4 and 11 to 16 g·dL−1, respectively. AKI and CKD were defined according to the Kidney Disease: Improving Global Outcomes criteria.
Microangiopathic hemolytic anemia was defined as anemia with the presence of fragmented red blood cells in the peripheral blood film. A platelet count of less than 150 × 103 μL−1 was considered to be thrombocytopenia. The diagnosis of TMA was made when a patient had the triad of AKI, thrombocytopenia, and microangiopathic hemolysis. In TMA, if renal impairment was predominant without neurological involvement, it was considered HUS, whereas the presence of neurological manifestations with renal impairment was diagnosed as TTP.
According to the treating physician’s clinical judgment regarding the severity of the patient, some patients with TMA underwent TPE, whereas others did not. Mainly, this decision was based on platelet counts, creatinine levels, PT/INR, urine output (oliguria/anuria), and the duration (d) after the snakebite. However, clear cut-off values were not used for these parameters. Thus, we had 2 groups of patients with TMA—a group with TPE and a group without TPE (non-TPE group). These 2 groups were compared in order to assess the effectiveness of TPE for TMA using the following outcomes: 1) days taken to normalize the platelet counts (>150 × 103 μL−1); 2) number of blood transfusions needed to correct anemia; 3) days needed to reduce the percentage of fragmented red blood cells in a high power field of peripheral blood film (days of starting the correction of microangiopathic hemolysis); 4) days needed for the clotting profile (PT/INR and WBCT20) to normalize; 5) number of in-patient hemodialysis cycles; 6) length of hospital stay; 7) dialysis dependency at discharge; and 8) renal recovery at discharge or after following up 2 to 6 mo of discharge with serum creatinine levels and renal ultrasound scan.
Hemodialysis and TPE were performed via a femoral venous catheter. Fresh frozen plasma (FFP) was used as the replacement fluid in TPE. All live or dead specimens of the offending snakes were identified by the corresponding author using a standard key.
The ground color of HNPVs vastly differs according to the geographical area that they inhabit (Figure 1). The morphological characteristics of all snakes, such as sex, head length, tail length, snout-to-vent length, total length, and scale counts, were recorded, and dead specimens were preserved in 10% formalin and labeled with the patient’s serial number and the date of admission. They were deposited at the Teaching Hospital, Ratnapura, for proof, and the live snakes were released into their natural habitat. All statistical analyses were carried out using Minitab 18.1. Normally distributed data are presented as mean±SD (range). Nonnormally distributed data are presented as median and interquartile range (IQR). Differences between the medians were compared using the Mann-Whitney U test. Differences between categorical variables were analyzed using the Pearson χ2 and Fisher exact tests. Kaplan-Meier method was used in calculating the survival estimates and creating the survival plot. Log-rank test was used to compare survival data. A 2-tailed P value of <0.05 was considered statistically significant.
Figure 1Ground color variations of adult Hypnale hypnale in different locations of Ratnapura District (06°40’ N, 80°24’ elevation 130 m [430 ft]) in Sri Lanka: A, Gilimale. B, Ratnapura. C, Ehaliyagoda. D, Kuruvita. E, Hangamuwa. F, Balangoda.
Out of 77 patients in the cohort of AKI, 32 (42%) brought the specimens of HNPV, of which 29 (90%) were killed specimens and 3 (9%) were live snakes. Photographs of live snakes were available for 3 (4%) patients. Out of 35 specimens, 33 (94%) were H hypnale, and 2 (6%) were H zara. Female snakes were 23 (72%), and male snakes were 9 (28%). The total length was 407±74 mm, snout-to-vent length was 349±68 mm, head length was 23±5 mm, and tail length was 57±10 mm. The number of scale counts were 147 (143–152), 41 (38–45), and 15 (15–17) for ventral, subcaudal, and mid-dorsal scales, respectively. Forty-two (54%) patients did not bring the offending snake to the hospital.
There were 683 HNPV bites during the study period, and 77 (11%) patients who were bitten had AKI. TMA was found in 52 (8%) patients. Epidemiological features are shown in Table 1. In the cohort of AKI, the male patients (n=61; 79%) outnumbered the female patients (n=16; 21%), and the age was 58±14 (25–93) y. Most patients (n=49; 64%) were bitten at day time (0600–1759) on the lower limbs (n=50; 65%) in their home gardens (n=28; 36%). The length of hospital stay ranged from 2 to 47 d (median, 12 d; IQR, 6–18 d). In the non-TMA group, it was 2 to 39 d (median, 5 d; IQR, 3–9 d), whereas in the TMA group, it was 5 to 47 d (median, 15 d; IQR, 10–22 d). The duration from the day of bite to the first cycle of TPE was 4 d (IQR, 4–6 d).
Table 1Epidemiological features of the cohort of acute kidney injury following hump-nosed pit viper bites
Local pain was observed as mild (n=21; 27%), moderate (n=22; 29%), and severe (n=28; 36%). Local swelling was also graded as mild (n=17; 22%), moderate (n=37; 48%), and severe (n=17; 22%). Other local manifestations were necrosis at the site of bite (n=25; 33%), hemorrhagic blistering (n=20; 26%), bruising (n=16; 21%), lymphadenopathy (n=15; 20%), and local bleeding (n=8; 10%). Myalgia (n=27; 35%), thrombocytopenia (n=56; 73%), and microangiopathic hemolysis (n=57; 74%) were also found. In the whole group of AKI, VICC developed in 19 (25%) patients, and in the TMA group (n=52), VICC was observed in 18 (35%) patients. CKD was diagnosed in 19 (25%) patients in this AKI cohort from which, 16 (21%) were in TMA group [4 (5%) in TPE group and 12 (16%) in non-TPE group] and 3 (4%) were in non-TMA group.
Out of 77 patients, 52 (68%) fulfilled the criteria for the inclusion of TMA (TMA group). Of the patients who did not fulfill the criteria for TMA (non-TMA group), 4 had only thrombocytopenia and 5 had only MAHA. Four patients from the TMA group and 2 from the non-TMA group were lost to follow-up. Thus, 48 patients from the TMA group and 23 patients from the non-TMA group were available for the comparison of the outcome analysis. Two patients from the TMA group died on Days 4 and 35. The patient who died on Day 4 was excluded from the final outcome analysis because of inadequate data. Thus, 21 (45%) patients who underwent TPE and 26 (55%) who did not undergo TPE were available for the final analysis (Figure 2). The clinico-epidemiological features of the TPE and non-TPE groups are shown in Tables 2 and 3, respectively.
Figure 2Flow chart of the study (52 patients with TMA vs 25 patients without TMA leading to acute kidney injury following hump-nosed pit viper bites). LAMA, left against medical advice; TMA, thrombotic microangiopathy; TPE, therapeutic plasma exchange.
Comparison between the TMA and non-TMA groups (all patients with AKI) is shown in Table 4 and Figure 3. Patients who underwent TPE had significantly higher blood transfusions than patients who did not undergo TPE. There were no significant associations between TPE and dialysis dependency at discharge, length of hospital stay, and number of dialysis cycles prior to discharge. Renal recovery depends on TPE (P=0.048) and the highest creatinine level (P=0.001). Multiple linear regression models were fitted to determine the exposure variables for number of blood transfusions and the number of dialysis cycles prior to discharge. A significant regression equation was found for the number of blood transfusions (P<0.000; R2=0.56). The lowest Hb (P<0.001 ) and highest creatinine (P=0.026) levels significantly predicted the number of blood transfusions of the patients. However, TPE did not improve the number of blood transfusions of the patient (P=0.290) (Figure 4). The best model that predicted number of dialysis cycles prior to discharge was significant (P<0.000; R2=0.56). Highest creatinine level, urine output, and hypertension significantly predicted the number of dialysis cycles prior to discharge. However, TPE was not associated with number of dialysis cycles prior to discharge.
Table 4Comparison of the TMA group (n=48) and the non-TMA group (n=23)
Epidemiological, clinical, and laboratory parameters
Figure 3Comparison of TMA and non-TMA groups: A, Renal recovery; B, Myalgia; C, Dialysis-dependent at discharge; D, VICC; E, Number of dialysis cycles prior to discharge. TMA, thrombotic microangiopathy; VICC, venom-induced consumption coagulopathy.
Figure 4Effects of the highest creatinine and lowest Hb levels on the number of blood transfusions in the TPE and non-TPE groups. Hb, hemoglobin; TPE, therapeutic plasma exchange.
Linear logistic models were fitted to determine the exposure variables for renal recovery and selected exposure variables. The best model predicting the renal recovery is summarized in Table 5. The goodness-of-fit test deviance (P=0.423), Pearson χ2 test (P=0.444), and Hosmer-Lemeshow test (P=0.607) indicated that the model was adequate. According to the model, renal recovery could be significantly predicted by TPE (P=0.048) and the highest creatinine level (P=0.001) (Figures 5A and B). The best linear logistic model that predicted dialysis dependency at discharge is summarized in Table 6. The goodness-of-fit test deviance (P=0.774), Pearson χ2 test (P=0.676), and Hosmer-Lemeshow test (P=0.384) indicated that the model was adequate. The highest creatinine level significantly predicted the dialysis dependency at discharge (P=0.012) (Figures 5C and D), and there was no sufficient evidence to show an association between TPE and dialysis dependency at discharge (P=0.597). Further, TPE significantly improved the time to platelet correction, time to the initiation of microangiopathic hemolysis correction, time to PT/INR correction, and time to WBCT20 correction (Table 7 and Figure 6). We did not observe any adverse reaction related to TPE, including FFP transfusion in any patient of this cohort.
Figure 5Effects of age and highest creatinine level on renal recovery and the probability of dialysis dependency at discharge in the TPE and non-TPE groups. TPE, therapeutic plasma exchange.
Figure 6Survival plots for the TPE and non-TPE groups: A, time to platelet correction; B, time to initiation of microangiopathic hemolysis correction; C, time to PT/INR correction; D, time to WBCT20 correction. INR, international normalized ratio; PT, prothrombin time; TPE, therapeutic plasma exchange; WBCT20, 20 min whole blood clotting test.
In the current study, the prevalence of AKI and TMA were 11% and 8% of all HNPV bites, respectively. These manifestations are caused by both H hypnale and H zara in different frequencies. TMA following snakebites is a rare complication; in Sri Lanka and India, it is caused by Viperidae snakes, including HNPV
Thrombotic microangiopathy, haemolytic uremic syndrome and thrombotic thrombocytopenic purpura following hump-nosed pit viper (Genus: Hypnale) envenoming in Sri Lanka.
Envenoming by some non–Sri Lankan species may also cause TMA; these include Australian elapids such as several species of Australian brown snakes (Pseudonaja spp),
It is also an occupational hazard, mostly affecting the agricultural regions. The ideal therapy for snakebite envenoming is antivenom specific to the species that inflicted the bite. However, these antivenoms are not available in every country for even some of the most medically important species. Another important consideration is the high risk of adverse side effects, including anaphylaxis, that are associated with some antivenoms.
Therefore, alternatives to antivenom, when unavailable, can comprise an essential approach to managing seriously envenomed patients. One such option is TPE; however, because of the mixed evidence concerning this intervention, TPE should be considered on a case-by-case basis for life-threatening envenoming when antivenom is not available.
In the current study, the length of hospital stay, number of blood transfusions, number of dialysis sessions prior to discharge, VICC, and laboratory findings such as highest creatinine, lowest Hb, lowest platelet count, highest total bilirubin and highest serum glutamic-oxaloacetic transaminase/serum glutamic-pyruvic transaminase levels were higher in patients in the TMA group than in those in the non-TMA group. Patients in the TMA group needed more blood transfusions, more dialysis cycles, and lengthier hospital stay. Also, more patients in the TMA group had VICC, myalgia, anuria, and oliguria. Patients in the non-TMA group had less severe laboratory findings related to platelet counts, Hb, creatinine, total bilirubin, and liver enzymes. These findings are compatible with Indian studies regarding snakebite-associated TMA.
Renal recovery and dialysis dependency at discharge were not different in both the TMA and non-TMA groups (Table 4). This is because, in the current study, all patients in the non-TMA group had AKI, and some of these patients (4%) progressed to CKD. These findings are compatible with those of a study conducted in Sri Lanka.
Days to platelet correction, days to starting the correction of microangiopathic hemolysis, and days to PT/INR and WBCT20 correction were significantly lower in the TPE group than in the non-TPE group (Table 7), which conveys the effectiveness of TPE in the early correction of TMA. However, a previous systematic review concluded that TPE is not effective for TMA.
Snakebite associated thrombotic microangiopathy: a systematic review of clinical features, outcomes, and evidence for interventions including plasmapheresis.
The time lapse from snakebite to the first cycle of TPE is a very crucial factor when assessing the effectiveness of TPE. This should be as short as possible because when the time goes on, kidney damage is possible because the envenoming-induced kidney damage is progressive and the resulting damage cannot be reversed by any procedure. In the current study, this median time lapse was 4 d, and our outcomes such as dialysis dependency at discharge, length of hospital stay, and the number of dialysis cycles prior to discharge might be improved if the first TPE cycle could have been performed within 2 to 3 d of snakebite. Therefore, from our perspective, in order to optimize the efficacy of TPE, it should be performed within the shortest possible time following the snakebite. Unfortunately, some patients are initially directed to native treatment and get late admission to the hospital. Out of the 2 groups in the current study, the non-TPE group included more individuals with chronic potentially vasculopathic diseases (hypertension and diabetes) and older age, which could have skewed the results in favor of the TPE group. Even though theoretically there is a potential risk of using TPE because of its adverse effects such as hypotension and allergic reactions, we did not observe any of them in this study. The disadvantages of TPE are that it is costly and needs experienced hands to perform. In the current study, the improvement of PT/INR and a rising trend of platelet counts were the treatment endpoint of TPE.
Limitations
There were some limitations of the current study; the sample size (n=47) was small, the study recruitment was nonrandomized, and TPE was offered to patients with more severe disease who were nonresponsive to the standard treatments. This adds a bias to the study. Also, it is important to reinforce that when the use of TPE is considered, risk vs benefit must be carefully assessed on a patient-by-patient basis. Further, randomized controlled trials may be needed in the field to generate more evidence.
Conclusions
Among our small sampling of patients, TPE was effective in the early correction of platelet counts, microangiopathic hemolysis, PT/INR, and WBCT20 for HNPV envenoming complicated with TMA. Renal recovery was associated with both TPE and creatinine level. However, dialysis dependency at discharge, length of inpatient management, and the number of dialysis cycles prior to discharge are not improved by TPE. Further, dialysis dependency at discharge depends on the highest creatinine level. While among this series of patients TPE was deemed beneficial, further evidence is required in order to support the use of this intervention in patients with similar clinical presentations.
Acknowledgments: The authors thank Prof R.P.V.J. Rajapakse (Department of Veterinary Pathobiology, Faculty of Veterinary Medicine & Animal Science) and Prof W.D.S.J. Wickramasinghe (Department of Parasitology, Faculty of Medicine) of the University of Peradeniya for their assistance in the project.
Author Contributions: patients’ management and literature search (RMMKNR, PEANR); snake handling and obtaining their morphological features (RMMKNR); statistical analysis (KS, RMMKNR); drafted the first manuscript (RMMKN, SAMK, PEANR); reading of final manuscript (RMMKN, SAMK, PEANR, KS); approval of final manuscript (RMMKN, SAMK, PEANR, KS).
Financial/Material Support: None.
Disclosures: None.
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et al.
The global burden of snakebite: a literature analysis and modelling based on regional estimates of envenoming and deaths.
Thrombotic microangiopathy, haemolytic uremic syndrome and thrombotic thrombocytopenic purpura following hump-nosed pit viper (Genus: Hypnale) envenoming in Sri Lanka.
Venom-induced consumption coagulopathy following hump-nosed pit viper (Genus: Hypnale) envenoming in Sri Lanka: uncertain efficacy of fresh frozen plasma.
Guidelines on the use of therapeutic apheresis in clinical practice-evidence-based approach from the Apheresis Applications Committee of the American Society for Apheresis.
Snakebite associated thrombotic microangiopathy: a systematic review of clinical features, outcomes, and evidence for interventions including plasmapheresis.
Bon C, Burnouf T, Gutiérrez JM, Padilla A, Ratanabanangkoon A, Warrell DA. WHO Guidelines for the Production, Control and Regulation of Snake Antivenom Immunoglobulins; WHO Technical Report Series; WHO: Geneva, Switzerland, 2010.
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