Shock is an acute condition when the circulatory system fails to provide sufficient oxygen and nutrients to satisfy the metabolic requirements of essential organs. Extensive cellular demise leads to multi-organ failure.¹ Shock is classified into hypovolemic, distributive, cardiogenic, obstructive and dissociation. Sepsis is a predominant cause of morbidity and mortality in infants and children globally, especially in resource-constrained environments such as India. Septic shock significantly contributes to about 60% of global mortality in children under five.². Most pediatric hospital fatalities often occur within the initial 24 hours of admission.³ Timely identification and intervention for shock and hemodynamic instability are crucial in reducing both short-term and long-term sequelae.⁷

Instruments for assessing the risk of mortality and morbidity in patients including the Pediatric Risk of Mortality Score and the Pediatric Index of Mortality.⁴ In resource-limited environments, basic metrics such as Shock Index, Modified Shock Index and Shock Index Pediatric age-Adjusted might serve as instruments for the triage and management of children admitted to the PICU.⁵

The SI is calculated by dividing the HR by the SBP⁶. The usual cutoff value for adults is generally 0.9⁷; however, the vital signs of pediatric patients vary according to age⁸. The SI has been utilized to forecast mortality in individuals with medical diseases including sepsis, pulmonary embolism and community-acquired pneumonia.⁹ Modified SI [HR/mean arterial pressure (MAP)] and age SI (age × SI) have been suggested to enhance predictive value. While SI (heart rate divided by SBP) is a useful early marker of hemodynamic instability.

SIPA is determined by dividing the highest heart rate by the minimum systolic blood pressure, adjusted for age¹⁰. SIPA was developed, demonstrating greater accuracy in predicting outcomes such as the necessity for urgent surgery, endotracheal intubation, early blood transfusion, ICU admission, prolonged hospital stays, and fatality rates¹¹. It also assist in triaging patients in primary and secondary healthcare settings, enabling the identification of severely ill patients and their rapid referral to advanced facilities¹².

This study aims to evaluate the predictive utility of the SI, MSI and SIPA in determining hospital length of stay and clinical outcomes. This study also seeks to enhance early identification of critically ill patients requiring intensive monitoring and timely intervention upon PICU admission.

This prospective, observational, community-based study was conducted in the Paediatric Intensive Care Unit of the Department of Paediatrics, JLN Medical College, Ajmer, Rajasthan, following institutional ethical committee approval. The study period was from September 2023 to August 2024, with an additional 6 months allocated for data analysis.   A Sample of 82 children was calculated at 95% confidence and 10% absolute error to verify the expected proportion of 30.5% of survival among children admitted with shock in PICU (Meiring Gaigonglung et al¹³). Considering 20% non-response rate sample size was further enhanced to 100 children admitted with shock in PICU. 

This study included children of both sexes admitted to the PICU with shock, aged between 1 month and 18 years, whose parents provided written informed consent. Exclusions comprised patients in the PICU for less than 2 hours, those outside the 1 month to 18 year age range, individuals with multiple congenital anomalies, patients admitted with continuous CPR who did not achieve stable vital signs for over 2 hours, and referred shock patients arriving at the hospital more than 4 hours after diagnosis, as well as children whose parents did not give consent. Ethical Information was collected from them using a pre-structured Proforma. 

Upon admission, each child’s heart rate (or pulse rate), systolic and diastolic blood pressure, and mean arterial pressure (MAP) were recorded.

 SIPA thresholds were based on age-adjusted norms: <1.5 for children aged 0-12 months, <1.4 for children aged 1-3 years, <1.22 for children aged 4–6 years, <1.00 for children aged 7–12 years, <0.90 for children aged 13–16 years.

Patients were categorized according to their provisional diagnosis at admission. SI, MSI, and SIPA values were used to stratify patients into respective risk groups. Specifically, patients were grouped based on: SI > 0.7 and SI ≤ 0.7, MSI > 1.3 and MSI ≤ 1.3

SIPA thresholds based on the age group as noted above

For each group, the length of PICU stay and clinical outcome (survival or mortality) were recorded at discharge.

 Statistical Analysis

The collected data was entered into a Microsoft Excel sheet. Continuous or quantitative data were summarized using mean and standard deviation. The difference between two means was assessed using Student’s t-test. Discrete or qualitative data were presented as proportions, and the significance of differences in proportions was evaluated using the chi-square test. A 95% confidence level was maintained for all statistical analyses

Table 1 Comparison Between Patients Requiring and Not Requiring Mechanical Ventilation at Different Time Intervals (i) Shock Index (ii) Modified Shock Index

Table 2–Comparison Between Patients Requiring and Not Requiring Ionotropic support at Different Time Intervals (i) Shock Index (ii) Modified Shock Index

Table 3– Association Between SIPA Values and Mortality at Different Time Intervals

Table 4- Association Between SIPA Values and length of hospital stay at Different Time Intervals

Table 5- Predictors of outcome among study participants

Given the pressing need for rapid, cost-effective, and accessible triage tools, this study was planned to evaluate the predictive utility of SI, MSI, and SIPA in determining the hospital length of stay and mortality among children admitted to the PICU at JLN Medical College and Hospital. The study also aims to support the use of these indices in early identification of critically ill pediatric patients to guide timely and appropriate clinical intervention.

 Comparison of SI & MSI Between Patients Requiring and Not Requiring Mechanical Ventilation at Different Time Intervals

In our study, significantly higher Shock Index (SI) and Modified Shock Index (MSI) in children who required mechanical ventilation, compared to those who did not, across all time intervals.  Elevated SI reflects a compensatory tachycardia in response to falling systolic blood pressure, often seen in distributive or hypovolemic shock. Similarly, a high MSI, which considers mean arterial pressure, points to low stroke volume and systemic vascular resistance, hallmarks of a hypodynamic state requiring intensive support. The probable explanation for this persistent elevation is that patients requiring mechanical ventilation are often in advanced stages of systemic compromise conditions that reduce tissue perfusion and oxygenation. Therefore, higher SI and MSI serve as predictive markers for both the need for ventilation and worse outcomes.

Comparison of SI & MSI Between Patients Requiring and Not Requiring Ionotropic support at Different Time Intervals

The present study revealed a strong and statistically significant association between the need for inotropic support and elevated values of both the Shock Index and Modified Shock Index at all observed time intervals. Patients requiring inotropes consistently demonstrated higher SI and MSI, indicating greater hemodynamic instability throughout the first 24 hours of PICU admission. Patients requiring inotropes are often in decompensated stages of shock, where compensatory mechanisms fail, and pharmacologic support becomes essential to maintain perfusion to vital organs. These findings align with previous studies. Rousseaux et al² demonstrated that SI measured at admission was a strong predictor of the need for intensive interventions, including inotropic support and mechanical ventilation. Likewise, in a cohort of 295 patients with severe sepsis, it was reported that 38.6% of patients with a sustained elevation in SI >0.8 across 80% of emergency department readings required vasopressors within 72 hours, compared to only 11.6% in those without sustained elevation¹⁴.

This supports our observation that persistent elevation in SI and MSI correlates with worse clinical status and the subsequent need for vasopressor therapy.

 Association Between SIPA Values and Mortality at Different Time Intervals

In the current study, a clear and statistically significant association was observed between abnormal Shock Index Pediatric Age-Adjusted (SIPA) values and mortality in children admitted to the PICU (p<0.05). At all time intervals—baseline, 2 hours, 4 hours, 6 hours, and 24 hours—mortality occurred exclusively in patients with abnormal SIPA, whereas no deaths were recorded among those with normal SIPA values. Moreover, there was a progressive increase in the number of survivors with normal SIPA scores—from 10 at baseline to 48 at 24 hours—indicating favorable clinical progression in this group. These findings are consistent with and supported by existing literature. Vandewalle et al¹⁵ demonstrated that pediatric patients who initially had normal SIPA but developed abnormal values within the first 12 hours of admission had significantly worse outcomes, including increased mortality, longer ICU and hospital stays, and greater need for mechanical ventilation. This underscores the role of dynamic monitoring of SIPA, rather than relying on a single-time value, in recognizing patients whose condition is deteriorating despite initial stability. Moreover, studies have shown that SIPA is a more specific indicator of critical illness than traditional vital signs or SI alone. In one such study, a higher percentage of patients with elevated SIPA were found to have Injury Severity Scores (ISS) >24, increased in-hospital mortality, and a greater need for blood transfusions within 24 hours, suggesting its superior predictive capacity¹².

Furthermore, in a study of 559 children aged 5–16, SIPA was found to more accurately predict the need for surgery, endotracheal intubation, and blood transfusion than systolic blood pressure-based hypotension criteria¹⁶. SIPA has emerged as a non-invasive, reliable marker of mortality risk.  A retrospective analysis of 146 children with septic shock showed that persistently elevated SIPA values beyond 6 hours were significantly associated with increased mortality². A separate prospective study of 120 children under 14 years supported this, suggesting that SIPA cutoffs can help identify children at high risk of early death in severe sepsis or septic shock¹⁶.

Additionally, Tanveer A et al¹⁷ reported that children with abnormal SIPA values had higher rates of mechanical ventilation (56.1% vs. 32.9%) and inotropic support (59.8% vs. 35.6%), confirming that elevated SIPA is strongly linked with the need for advanced critical care interventions. Huang KC et al¹⁸ reinforced the importance of SIPA trends at 24 hours, showing that abnormal SIPA at this point correlated with higher mortality, mechanical ventilation, inotropic support, and prolonged hospital stay. Importantly, while both elevated SI and SIPA were associated with poor outcomes, SIPA offered enhanced age-specific sensitivity, making it a more appropriate tool for pediatric assessments.

Similarly, Acker SN et al¹¹ observed that 30% of patients needing operative intervention and 40% of ventilated children showed increasing SIPA values, further supporting SIPA as a dynamic and predictive tool for escalating care needs. A 2018 study also found that children presenting with normal SIPA that later worsened within 48 hours had significantly higher adverse outcomes in cases of pediatric blunt trauma¹⁵. This reinforces the current findings and highlights the importance of early and continued SIPA monitoring.

At baseline, children with abnormal SIPA demonstrated a higher proportion of prolonged hospital stays, with 35.6% requiring hospitalization for 8–15 days and 15.6% for more than 15 days. This trend indicates that initial hemodynamic instability, may be linked to more severe illness requiring extended hospital care. At the 2-hour, the distribution of hospital stay durations appeared similar between the normal and abnormal SIPA groups. Approximately 38.5% and 39.1% of patients in the respective groups stayed 3–7 days, and around one-third required hospitalization for 8–15 days. A comparable pattern persisted at the 4-hour interval, with 43.5% of the normal SIPA group and 37.7% of the abnormal group staying 3–7 days, while about one-third in each group remained hospitalized for 8–15 days. By 6 hours, the normal SIPA group showed 34.5% of children each in the 3–7 day and 8–15 day hospital stay categories, with 20.7% staying more than 15 days. This was slightly higher than the abnormal SIPA group, where only 15.5% of children stayed beyond 15 days. However, it was at the 24-hour interval that a more noticeable difference emerged. Among children with normal SIPA values at 24 hours, only 14.6% required hospital stays exceeding 15 days, compared to 19.2% in the abnormal SIPA group. This suggests that normalization of SIPA within 24 hours may be associated with better clinical stabilization and earlier discharge. Overall, these findings highlight that while SIPA values in the early hours post-admission may not strongly predict length of hospital stay, persistently abnormal SIPA at 24 hours may serve as a subtle indicator of prolonged hospitalization. Continuous monitoring of SIPA could therefore be a useful non-invasive tool for anticipating the clinical course and resource needs in critically ill pediatric patients.

The predictive strength of SIPA lies in its integration of age-adjusted heart rate and systolic blood pressure, offering a nuanced assessment of cardiovascular status. An elevated SIPA indicates compromised perfusion and impaired compensatory capacity, common in sepsis, trauma, and severe systemic illness. Persistently elevated SIPA reflects ongoing circulatory distress, which if not rapidly addressed, may lead to multi-organ dysfunction and death. Conversely, improvement in SIPA values over time suggests restoration of hemodynamic stability, explaining the higher survival in patients with normalized SIPA.

This prospective observational study was conducted to evaluate the predictive utility of the Shock Index (SI), Modified Shock Index (MSI), and Shock Index Pediatric Age-Adjusted (SIPA) in assessing the severity of illness, predicting clinical outcomes, and determining the hospital length of stay in pediatric patients admitted to the Pediatric Intensive Care Unit (PICU).

The study provides strong evidence to support the incorporation of SI, MSI, and SIPA into routine clinical assessment in pediatric intensive care. These indices, if used systematically, can improve the early detection of hemodynamic instability, aid in timely escalation of care, and potentially reduce morbidity and mortality in critically ill children. Their integration into pediatric shock management protocols could enhance early diagnosis, guide therapeutic interventions, and improve overall quality of care. Future multicentric studies with larger populations are recommended to validate these findings and develop standardized age-specific cut-off values for broader clinical application.

This study concluded that elevated Shock Index (SI), Modified Shock Index (MSI), and abnormal SIPA values at admission and during early monitoring were significantly associated with increased mortality, greater need for inotropic or ventilatory support, and longer hospital stays, establishing their prognostic relevance in pediatric shock.