Pediatric Index of Mortality-2 (PIM-2) and Pediatric Index of Mortality-3 (PIM-3) for Predicting Mortality in a Tertiary Care Pediatric Intensive Care Unit

Introduction:

Children have poor physiological reserves which deteriorate rapidly during life-threatening emergencies. Hence, mortality and morbidity of pediatric illnesses depends on the rapidity of response and target-oriented therapy.[1]Mortality reduction is the most fundamental aim of  a Pediatric Intensive Care Unit (PICU) and is achieved by intensively monitoring and treating critically ill patients considered at risk for dying.[2]Since predicting the final outcome (survival/ death) is difficult at the earlier stages of any illness, prognostic scores help in risk-stratification and determining the outcome (survival/death) as early as possible.[3]Mortality predictive models help to compare the performance of PICUs over time, to objectively assess the quality of care provided and thus frame possible improvement strategies. Two basicmodels have been implemented for prediction of mortality risk in the pediatric populationi.e., the Pediatric risk of mortality (PRISM) score and Pediatric Index of Mortality (PIM) score (in their different versions).

The PRISM score takes into consideration clinical and laboratory variables encompassing diverse organ functions. This prevents under-representation of any variable, which, in turn can avoid under-prediction. However, this score has methodological limitation of collection of large amount of information that is needed to calculate the PRISM score and is laborious. The PRISM score is well validated with a large sample size involving different PICUs.[2]

The PIM (Pediatric Index of Mortality) scores outperform the PRISM score in terms of simplicity in data collection and score-computation and the inherent capacity of not being affected by the treatment in PICU, as it is calculated within 1 hour of admission to the PICU.[1]The studies validating the latest mortality scores like the PIM-3 are limited in our country and it is important to check their applicability in different populations from time to time.[7] Hence the present study has been planned to validate the PIM-2 & PIM-3 scores for our tertiary care PICU.

Aims & Objectives:

The aims and objectives of the present study are:

Primary Objectives:

1.  To determine the performance of Pediatric Index of Mortality-2 (PIM-2) and Pediatric Index of Mortality-3(PIM-3) scores, by assessing their capability for discrimination and calibration in patients admitted to the pediatric intensive care unit (PICU).

2.  To compare performance of PIM-2 and PIM-3in patients admitted to the pediatric intensive care unit (PICU).

Materials & Methods:

Ethics: The study will be initiated after seeking approval from the “Institutional Ethics Committee (IEC)” of Seth G.S Medical College and K.E.M hospital. The study will be conducted in compliance with the “Ethical Guidelines for Biomedical Research on Human Participants” by the Indian Council of Medical Research.

**Consent & assent:**Case enrollment will be done after a written informed consent from the parent/guardian. Assent will be obtained from patients more than 7 years of age.Since patients in the PICU are critically ill, the assent will be procured from children aged 7 years and above once the clinical condition stabilizes and when they are in a position to give the assent.

Confidentiality: The participant’s details will not be disclosed at any point of time.

Type of Study: Prospective, non-interventional, observational, single center study.

Duration: The study will be conducted for a period of 18 months after the IEC approval or till the desired sample size is reached.Each patient will be in the study till his/her stay in the PICU.

Study site: The study will be conducted in patients admitted to the PICU of KEM hospital, Mumbai, which is a tertiary care, 14-bedded PICU with state-of-art facilities including mechanical ventilators, non-invasive monitors and other devices for delivering critical care. It is manned by at least 4 resident medical officers round the clock. One Additional Professor looks after the day-to-day clinical and administrative matters of the PICU and is assisted by one Associate Professor and one Assistant Professor. Fellows (MUHS) and senior registrars are also posted in the PICU (when available).

**InclusionCriteria:**All consecutive children aged 1 month to ≤12 years admitted to the PICU will be enrolled.

ExclusionCriteria**:**Following patientswill be excludedfromthestudy-

1.      Patients whose parent/ guardian refuse to give informed consent.

2.      Children dying within 1 hour of PICU admission (since the PIM scores are calculated at the end of 1 hour after admission to PICU).

 Sample Size calculation

The average monthly PICU admissions are around 30 per month (i.e. about 360/year). considering that about 2% patients dying within one hour of PICU admission, the anticipated sample size is 353.Considering a refusal rate of approximately 5%, the sample size would be 353+17=370.

Study Procedure:

Cases satisfying the inclusion criteria will form the study sample. Prospective data will be recorded from indoor case sheets/ papers when the patient is in the PICU.

Data Recording:Following data/information will be recorded in a pre-designed case record form- CRF (from the patient’s hospital case sheets/indoor medical papers)-

·         Demographic details: name (initials), age (in months), sex, date of admission to the hospital and date of admission to the PICU.

·         Clinical details: The following clinical details will be recorded-

1.      Indication for PICU admission,

2.      Chief clinical complaints at the time of admission,

3.      Important/Significant clinical examination findings at admission,

4.      Final complete diagnosis, and

5.      Primary system involved, significant/diagnostic investigations, complications &treatment

·         Outcome related data: Final outcome of the patient (survival/ death), morbidity/ sequelae at discharge, length of PICU stay and length of hospital stay will be noted.

·         Recording of PIM-2 & PIM-3:The clinical details and scores will be recordedat or about the time of first contact to 1 hour after arrival in the PICU. Thefirst value of each variable measuredwill be recorded in a pre-designed case record form.

·         The patient’s daily medical records will be scrutinized from admission until discharge/ death. All investigations done routinely in the PICU as a part of the treatment protocol will be recorded in the CRF. This study will not entail performing any new/ additional investigations or new/ additional treatment or any financial burden to the hospital or financial burden to the parent/ guardian.

Plan for Statistical Analysis:

The study shall be represented using descriptive analysis.

·         The etiology, need for ventilation, co-morbidities, complications & final outcome will be listed as percentage of total patients enrolled.

·         Outcome in terms of mortality, and morbidity/ sequelae will be listed as percentage.

·         Age (months), Weight (kg), length of PICU stay and length of hospital stay will be expressed as mean +/-SD, median and mode.

·        We record the observations at or about the time of first contact to 1 hour after arrival in your ICU. We use the first value of each variable measured which would be recorded in a pre-designed case record form. Mortality risk estimated from PIM2 and PIM3 score have been explained.

PIM-2 calculation

PIM 2 is calculated by multiplying the scores of each variable with the respective coefficient given in the above table. And then after addition of all those variables we get a PIM 2 score X.

Probability of Death = exp (X [1+exp (X)]

 PIM3 Calculation

PIM 3 is calculated by multiplying the scores of each variable with the respective coefficient given in the above table. And then after addition of all those variables we get a PIM 3 score X.

Probability of Death = exp(X)/(1+exp(X))

Calibration: will be assessed using Hosmer and Lemeshow’s goodness of fit chi- square testbasedon deciles of risk (analysis done using STATA 7.0 software) and by calculating the expected and observed number of survivors and deaths in various mortality risk groups[11]

·         Discrimination:will be assessed by the area under receiver operator characteristic (ROC) curve[11].

·         ROC curve will be plotted using (1-specificity) on the X axis and sensitivity on the Y axis. generated and comparisons made using STRATA 7.0 software[11]

References**:**

1.      Taori RN, Lahiri KR, Tullu MS. Performance of PRISM (Pediatric Risk of Mortality) score and PIM (Pediatric Index of Mortality) score in a tertiary care pediatric ICU. Indian J Pediatr. 2010;77:267-271.

2.      Shukla VV, Nimbalkar SM, Phatak AG, Ganjiwale JD. Critical analysis of PIM2 score applicability in a tertiary care PICU in western India. Int J PediatrSS.2014;2014:703942**.**

3.      Muthupandi V, Dianagrace R, Narayanan E, Sathya J. Comparison of PRISM III and PIM II Score in predicting mortalityinpaediatric intensive care unit: an observational study. J Clin Diagn Res. 2022;16:SC08-SC12.

4.      Slater A, Shann F, Pearson G; Paediatric Index of Mortality (PIM) Study Group. PIM2: a revised version of the paediatric index of mortality. Int Care Med. 2003;29:278-285.

5.      Straney L, Clements A, Parslow RC, Pearson G, Shann F, Alexander J, et al.Paediatric index of mortality 3: an updated model for predicting mortality in pediatric intensive care. Pediatr Crit Care Med. 2013;14:673-681.

6.      Quiñónez-López D, Patino-Hernandez D, Zuluaga CA, García ÁA, Muñoz-Velandia OM. Comparison of performance of the pediatric index of mortality PIM-2 and PIM-3 scores in the pediatric intensive care unit of a high complexity institution. Indian J Crit Care Med. 2020;24:1095-1102.

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10.  Imamura T, Nakagawa S, Goldman RD, Fujiwara T. Validation of pediatric index of mortality 2 (PIM2) in a single pediatric intensive care unit in Japan. Int Care Med.2012;38:649-654.

11.  Thukral A, Lodha R, Irshad M, Arora NK. Performance of Pediatric Risk of Mortality (PRISM), Pediatric Index of Mortality (PIM), and PIM2 in a pediatric intensive care unit in a developing country. Pediatr Crit Care Med. 2006;7:356-361.

12.  Sankar J, Gulla KM, Kumar UV, Lodha R, Kabra SK. Comparison of outcomes using Pediatric Index of Mortality (PIM-3) and PIM-2 Models in a pediatric intensive care unit. Indian Pediatr. 2018;55:972-974.

13.  Tyagi P, Tullu MS, Agrawal M. Comparison of Pediatric Risk of Mortality 3, Pediatric Index of Mortality 2, and Pediatric Index of Mortality 3 in predicting mortality in a pediatric intensive care unit. J Pediatr Int Care. 2018;7:201-206.

14.  Genu DH, Lima-Setta F, Colleti Jr J, de Souza DC, Gama SD, Massaud-Ribeiro L, et al. Multicenter validation of PIM3 and PIM2 in Brazilian pediatric intensive care units. Front Pediatr.2022;10:1036007.

15.  Niederwanger C, Varga T, Hell T, Stuerzel D, Prem J, Gassner M, Rickmann F, Schoner C, Hainz D, Cortina G, Hetzer B. Comparison of pediatric scoring systems for mortality in septic patients and the impact of missing information on their predictive power: a retrospective analysis. PeerJ. 2020;8:9993..

16.  Van Keulen JG, Polderman KH, Gemke RJ. Reliability of PRISM and PIM scores in paediatric intensive care. Arch Dis Child.2005;9:211-214.