|Year : 2021 | Volume
| Issue : 3 | Page : 160-164
Shock index and modified shock index among survivors and nonsurvivors of neonatal shock
Ramitha R Bhat, Prerna Batra, Deepika Harit
Department of Pediatrics, University College of Medical Sciences and Guru Tegh Bahadur Hospital, Delhi, India
|Date of Submission||04-Jan-2021|
|Date of Decision||04-Jun-2021|
|Date of Acceptance||11-Jun-2021|
|Date of Web Publication||28-Jul-2021|
Department of Pediatrics, University College of Medical Sciences and Guru Tegh Bahadur Hospital, Delhi - 110 095
Source of Support: None, Conflict of Interest: None
Background: Neonatal shock is associated with high mortality and morbidity. Shock index (SI), a ratio of heart rate (HR) to systolic blood pressure (BP), has been evaluated as a simple tool for early predictor of mortality in adult as well as pediatric patients. Objective: The objective of this study was to compare SI and modified SI (MSI) among survivors and nonsurvivors of neonatal shock and healthy controls. Materials and Methods: HR and BP were measured in neonates presenting with clinical shock at 0, 2, and 6 h after admission and in healthy controls. SI and MSI were calculated and compared between three groups. Results: The mean (standard deviation) SI was significantly higher at 2 and 6 h of admission (2.57 [0.54] vs. 2.93 [0.78], P = 0.029; 2.42 [0.41] vs. 3.04 [0.91], P = 0.0005) among nonsurvivors of neonatal shock as compared to survivors. MSI was also significantly raised at both 2 and 6 h of admission in nonsurvivors (3.32 [0.64] vs. 3.78 [1.05], P = 0.03; 3.16 [0.63] vs. 4.10 [1.85], P = 0.005). Conclusions: SI and MSI are significantly higher in nonsurvivors of neonatal shock than survivors and healthy controls. These metrics can be used as bedside tools for early identification of at-risk neonates with shock.
Keywords: Modified shock index, neonates, shock index, shock
|How to cite this article:|
Bhat RR, Batra P, Harit D. Shock index and modified shock index among survivors and nonsurvivors of neonatal shock. J Clin Neonatol 2021;10:160-4
|How to cite this URL:|
Bhat RR, Batra P, Harit D. Shock index and modified shock index among survivors and nonsurvivors of neonatal shock. J Clin Neonatol [serial online] 2021 [cited 2021 Sep 17];10:160-4. Available from: https://www.jcnonweb.com/text.asp?2021/10/3/160/322533
| Introduction|| |
Shock index (SI), defined as the ratio of heart rate (HR) and systolic blood pressure (SBP), may be a good and noninvasive measure of the degree of hemodynamic stability. In the 1960s, Allgower and Buri first introduced SI as a marker that can be used to predict the severity of hypovolemic shock. They observed that the normal value of SI ranges from 0.5 to 0.7 in healthy adults. Studies on adult patients showed an association of initial SI and persistent elevation of SI >0.9 with cardiac dysfunction, tissue hypoxia, and higher mortality requiring need for immediate resuscitation, hospitalization, and intensive care management.,, In most studies, elevated SI was considered a valuable tool even when HR and blood pressure (BP) were normal.
SI has been evaluated as a tool in conditions such as septic shock and head trauma in children., SI could identify severe sepsis earlier than HR and SBP alone and could be used as a clinical predictor of mortality. As HR and BP values vary widely in different age groups in children, it becomes difficult to provide a clear cutoff to identify high-risk babies. Yasaka et al. assessed the change in SI over the first 6 h of intensive care unit (ICU) admission and compared with outcome in children with sepsis/septic shock. Their observation showed that children with elevated SI benefitted from a higher level of care and aggressive resuscitation. They tried to determine the cutoff values of SI to identify risk for mortality across various age groups but could not determine any clear cutoff SI value in any age group.
SI has not been studied widely in neonatal conditions. Owing to the high mortality associated with neonatal shock, early identification and its quick management becomes crucial. Modified SI (MSI), defined as a ratio of HR to mean BP (MBP), is another parameter shown to predict mortality in patients presenting to the emergency department (ED) when SI could not. SI and MSI may be used as noninvasive vital parameters for early identification of neonates at risk of mortality due to shock. Thus, we planned this study with the primary objective of comparing SI among survivors and nonsurvivors of neonatal shock and healthy controls. The secondary objective was to compare MSI in above groups. Identification of patients at risk of mortality using SI and MSI values may help in more aggressive and focused management approach in emergencies of resource-limited countries.
| Materials and Methods|| |
This observational study was conducted in the department of pediatrics of a tertiary care teaching hospital over a duration of 1 year. An approval from the “Institute Ethical Committee-Human Research” was obtained. Written deferred consent was taken from the parents or guardian of cases for participation and written informed consent was taken for control group.
Neonates aged 0–7 days with clinical symptoms and signs of shock as per updated American College of Critical Care Medicine-Pediatric Advanced Life Support (PALS) Guidelines for Management of Pediatric and Neonatal Septic Shock were included in the study. This included neonates with tachycardia, respiratory distress, poor feeding, poor tone, poor color, tachypnea, diarrhea, or reduced perfusion with capillary refill time >2 s. Neonates with known/suspected congenital heart disease and hypovolemic shock were excluded from the study. Gestational age- and gender-matched healthy controls were also enrolled on the same day of case enrollment.
HR and noninvasive BP (systolic, diastolic, and mean) were measured at 0, 2, and 6 h using EDAN UDA iM70 patient monitor, and the values were used for calculation of SI and MSI. Babies were managed as per unit protocol based on treating clinician's decision and were independent of the study. The enrolled neonates were followed up till discharge or death to identify the outcome. Shock management was done by fluid resuscitation with isotonic boluses (20 mL/kg over 15 min each) to a maximum volume of 60 mL/kg, correction of hypoglycemia and hypocalcemia, vasoactive agents with dopamine as the first-line agent, and hydrocortisone therapy if necessary. Survivor group was defined as babies who were discharged. Nonsurvivors were the babies who died during hospital stay.
HR, BP, SI, and MSI were also measured once in gestational age- and gender-matched controls, which were selected on the day of enrollment of case.
The primary outcome of our study was SI in survivors and nonsurvivors of enrolled neonates at 0, 2, and 6 h and healthy controls. The secondary outcome was to MSI in above group.
We could not find a study on determining SI values in neonatal shock. In the study by Yasaka et al. conducted on 544 patients below 18 years admitted to pediatric ICU with diagnosis of sepsis and/or septic shock, the mean (standard deviation [SD]) of SI for survivor group was found to be 1.5 (0.45) and for nonsurvivor group 1.7 (0.60) at 0 h. With the variance of 0.3, as a clinically important difference between survivors and nonsurvivors, 80% power, and 5% level of significance, sample size was calculated to be 50 in each group. Hence, we enrolled 50 survivors, 50 nonsurvivors, and 50 controls.
All the data were entered in MS EXCEL sheet, and statistical analysis was done using Software SSPS version 20.0 (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp.). Mean gestational age, birth weight, HR, BP, SI, and MSI between survivor and nonsurvivor groups were compared by unpaired t-test. Mean gestational age, birth weight, SI, and MSI among survivor, nonsurvivor, and control groups were compared by ANOVA test. Blood culture and sepsis screen positivity between survivors and nonsurvivors were compared using two-sample t-test for proportions. P < 0.05 was considered statistically significant.
| Results|| |
A total of 180 neonates with clinical symptoms and signs of shock were eligible for inclusion in the study at admission. During hospital stay, fifty of these expired and were included as nonsurvivors. Out of 130 neonates with shock who survived during study period, fifty consecutive babies were included as survivors for the purpose of the study. Fifty healthy controls were taken on the day of enrollment of case [Figure 1]. [Table 1] shows the baseline demographic profile, blood culture, and sepsis screen positivity in enrolled patients. Cause of death was sepsis in 25 (50%) of nonsurvivors, followed by severe birth asphyxia and severe meconium aspiration syndrome in six each. Three babies died due to respiratory distress syndrome and ten had other causes.
[Table 2] shows the mean HR, SBP, and diastolic BP (DBP) of neonates in survivor, nonsurvivor, and control groups. The mean SBP and DBP were comparable at 0 and 2 h and were significantly different only at 6 h of admission (P = 0.004 and P = 0.005, respectively). The mean HR was significantly higher than controls in neonates with shock but was comparable between survivors and nonsurvivors.
|Table 2: Mean and standard deviation of heart rate, systolic blood pressure, and diastolic blood pressure of enrolled neonates|
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[Table 3] shows the mean (SD) of SI and MSI in all three groups. There was a statistically significant difference in SI between survivor and nonsurvivor groups at 2 and 6 h of admission (P = 0.029 and 0.00, respectively). When compared among all three groups, there was a statistically significant difference in mean SI. The difference in MSI was statistically significant between survivor and nonsurvivor groups at 2 and 6 h of admission (P = 0.03 and 0.005, respectively). MSI calculated at the time of admission shows a significant difference among the three groups.
|Table 3: Mean and standard deviation of shock index and modified shock index of enrolled neonates|
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| Discussion|| |
Our study showed that the neonates who succumbed to shock had higher SI values at 2 and 6 h of admission than those who survived. MSI was also found to be significantly higher at 2 and 6 h in nonsurvivors. The values for SI and MSI were significantly higher than controls at 0 h also.
Initial resuscitation of shock is commonly guided by the normalization of hemodynamic and laboratory variables such as HR, BP, central venous pressure, and lactic acid. SI may be a good and noninvasive measure of the degree of hemodynamic stability and may be used as an indicator of tissue perfusion. It has been shown to correlate with other indices of end-organ perfusion such as central vena cava oxygen saturation and lactate concentration. SI is a sensitive indicator of left ventricular dysfunction in acute circulatory failure, and a marker for significant injury in patients with trauma with hypovolemic shock. In adults, it has been shown to predict mortality in several conditions such as sepsis, trauma, pulmonary embolism, and community-acquired pneumonia. SI is used as a tool in patients with blunt trauma at risk of massive transfusion and to predict ongoing hemorrhage during gastrointestinal bleeding, rupture of ectopic pregnancy, and fluid responsiveness in patients with septic shock. A study by Rady et al. found that a SI ≥0.9 at admisssion was associated with immediate treatment necessity at the triage, higher hospital admission rates, also intensive therapy on admission than conventional vital signs like pulse or BP alone, thus suggesting that SI may be a valuable tool for the early recognition and evaluation of critical illnesses in the ED and also to track the progress of resuscitation.
Difficulty arises in determining a normal range of SI in pediatric population as normal ranges of vital signs vary with age. Yasaka et al. studied an association between SI and mortality in children with sepsis/septic shock and tried to determine a cutoff value of SI. Five hundred forty-four children included and were stratified by age (<1, 1–3, 4–11, and >12 years). As per the range of normal vital sign values, normal SI varied between 0.8 and 2.3 in infant age group. Children with elevated SI benefitted from a higher level of care and aggressive resuscitation. The utility of age-adjusted SI to predict negative outcomes in pediatric trauma was studied by Strutt et al. where elevated SI could accurately predict morbidity and mortality in pediatric trauma patients. SI as an early index of prognosis for septic shock in children was studied by Rousseaux et al. SI was calculated at 0, 1, 2, 4, and 6 h after admission in 146 children with septic shock, and values at 0, 4, and 6 h were found to be predictive of death. In a retrospective analysis of 48 children with severe head trauma, initial SI at the accident site was significantly associated with a poor outcome. In a cohort of 1510 children with shock, early implementation of Pediatric Advanced Life Support (PALS)/Advanced Pediatric Life Support (APLS) recommended therapies was associated with an improved SI (from 2.274 to 1.774 with PALS/APLS vs. from 2.415 to 2.457 without PALS/APLS treatment; P < 0.05).
A retrospective analysis by Liu et al. in a cohort of patients admitted to ED and received intravenous fluids, MSI, a ratio of HR to MBP, was a clinically significant predictor of mortality, whereas SI was not significantly correlated with mortality rate. DBP of the patients falls earlier than SBP. As MBP can best represent tissue perfusion status, MSI can be a better predictor than HR and BP alone. Singh et al. suggested that MSI should be used in the triage of serious patients including trauma patients in ED. MSI ≥0.93 identified patients with signs of heart failure and could predict 6 months' mortality.
Although we tried to exclude neonates with known cardiogenic and neurological causes of shock, still the population we included might have neonates with heterogeneous etiologies. We could determine all-cause mortality and did not look into specific cause of mortality. Further studies are needed to define gestational age and chronological age-specific cutoffs in neonates for having SI and MSI values as reference.
| Conclusions|| |
SI and MSI can serve as noninvasive markers for identifying neonates at risk of mortality than HR and BP alone in neonates. These may be used as an additional bedside assessment tool – a “red flag” for severe disease. It can be integrated in monitors and computerized apps that give electronic alerts allowing for early recognition of neonatal shock and management.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]