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PIM2: a revised version of the Paediatric Index of Mortality

  • Neonatal and Pediatric Intensive Care
  • Published:
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Abstract

Objective

To revise the Paediatric Index of Mortality (PIM) to adjust for improvement in the outcome of paediatric intensive care.

Design

International, multi-centre, prospective, observational study.

Setting

Twelve specialist paediatric intensive care units and two combined adult and paediatric units in Australia, New Zealand and the United Kingdom.

Patients

All children admitted during the study period. In the analysis, 20,787 patient admissions of children less than 16 years were included after 220 patients transferred to other ICUs and one patient still in ICU had been excluded.

Interventions

None.

Measurements and results

A revised model was developed by forward and backward logistic regression. Variable selection was based on the effect of including or dropping variables on discrimination and fit. The addition of three variables, all derived from the main reason for ICU admission, improved the fit across diagnostic groups. Data from seven units were used to derive a learning model that was tested using data from seven other units. The model fitted the test data well (deciles of risk goodness-of-fit χ2 8.14, p=0.42) and discriminated between death and survival well [area under the receiver operating characteristic (ROC) plot 0.90 (0.89–0.92)]. The final PIM2 model, derived from the entire sample of 19,638 survivors and 1,104 children who died, also fitted and discriminated well [χ2 11.56, p=0.17; area 0.90 (0.89–0.91)].

Conclusions

PIM2 has been re-calibrated to reflect the improvement that has occurred in intensive care outcome. PIM2 estimates mortality risk from data readily available at the time of ICU admission and is therefore suitable for continuous monitoring of the quality of paediatric intensive care.

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Acknowledgements

We thank the many nurses, doctors, research officers and secretaries who collected, entered and cleaned the data. We thank John Carlin for statistical advice and we gratefully acknowledge the support provided by the Australian and New Zealand Intensive Care Society.

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Authors and Affiliations

Authors

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Corresponding author

Correspondence to Anthony Slater.

Additional information

This paper was written on behalf of the PIM Study Group

Appendices

Appendix 1: General instructions

PIM2 is calculated from the information collected at the time a child is admitted to your ICU. Because PIM2 describes how ill the child was at the time you started intensive care, the observations to be recorded are those made at or about the time of first face-to-face (not telephone) contact between the patient and a doctor from your intensive care unit (or a doctor from a specialist paediatric transport team). Use the first value of each variable measured within the period from the time of first contact to 1 h after arrival in your ICU. The first contact may be in your ICU, your emergency department, a ward in your own hospital, or in another hospital (e.g. on a retrieval). If information is missing (e.g. base excess is not measured) record zero, except for systolic blood pressure, which should be recorded as 120. Include all children admitted to your ICU (consecutive admissions).

1. Systolic blood pressure, mmHg (unknown =120)1

2. Pupillary reactions to bright light (>3 mm and both fixed =1, other or unknown =0)2

3. PaO2, mmHg (unknown =0)

FIO2 at the time of PaO2 if oxygen via ETT or headbox (unknown =0)

4. Base excess in arterial or capillary blood, mmol/l (unknown =0)

5. Mechanical ventilation at any time during the first hour in ICU (no=0, yes=1)3

6. Elective admission to ICU (no=0, yes=1)4

7. Recovery from surgery or a procedure is the main reason for ICU admission (no =0, yes =1)5

8. Admitted following cardiac bypass (no =0, yes =1)6

9. High risk diagnosis. Record the number in brackets. If in doubt record 0.

  [0] None

  [5] Cardiomyopathy or myocarditis

  [1] Cardiac arrest preceding ICU admission7

  [6] Hypoplastic left heart syndrome9

  [2] Severe combined immune deficiency

  [7] HIV infection

  [3] Leukaemia or lymphoma after first induction

  [8] Liver failure is the main reason for ICU admission10

  [4] Spontaneous cerebral haemorrhage8

  [9] Neuro-degenerative disorder11

10. Low risk diagnosis. Record the number in brackets. If in doubt record 0.

  [0] None

  [1] Asthma is the main reason for ICU admission

  [2] Bronchiolitis is the main reason for ICU admission12

  [3] Croup is the main reason for ICU admission

  [4] Obstructive sleep apnoea is the main reason for ICU admission13

  [5] Diabetic keto-acidosis is the main reason for ICU admission

Coding rules. These rules must be followed carefully for PIM2 to perform reliably:

  1. 1.

    Record SBP as 0 if the patient is in cardiac arrest, record 30 if the patient is shocked and the blood pressure is so low that it cannot be measured.

  2. 2.

    Pupillary reactions to bright light are used as an index of brain function. Do not record an abnormal finding if this is due to drugs, toxins or local eye injury.

  3. 3.

    Mechanical ventilation includes mask or nasal CPAP or BiPAP or negative pressure ventilation.

  4. 4.

    Elective admission. Include admission after elective surgery or admission for an elective procedure (e.g. insertion of a central line), or elective monitoring, or review of home ventilation. An ICU admission or an operation is considered elective if it could be postponed for more than 6 h without adverse effect.

  5. 5.

    Recovery from surgery or procedure includes a radiology procedure or cardiac catheter. Do not include patients admitted from the operating theatre where recovery from surgery is not the main reason for ICU admission (e.g. a patient with a head injury who is admitted from theatre after insertion of an ICP monitor; in this patient the main reason for ICU admission is the head injury).

  6. 6.

    Cardiac bypass. These patients must also be coded as recovery from surgery.

  7. 7.

    Cardiac arrest preceding ICU admission includes both in-hospital and out-of-hospital arrests. Requires either documented absent pulse or the requirement for external cardiac compression. Do not include past history of cardiac arrest.

  8. 8.

    Cerebral haemorrhage must be spontaneous (e.g. from aneurysm or AV malformation). Do not include traumatic cerebral haemorrhage or intracranial haemorrhage that is not intracerebral (e.g. subdural haemorrhage).

  9. 9.

    Hypoplastic left heart syndrome. Any age, but include only cases where a Norwood procedure or equivalent is or was required in the neonatal period to sustain life.

  10. 10

    Liver failure acute or chronic must be the main reason for ICU admission. Include patients admitted for recovery following liver transplantation for acute or chronic liver failure.

  11. 11.

    Neuro-degenerative disorder. Requires a history of progressive loss of milestones or a diagnosis where this will inevitably occur.

  12. 12.

    Bronchiolitis. Include children who present either with respiratory distress or central apnoea where the clinical diagnosis is bronchiolitis.

  13. 13.

    Obstructive sleep apnoea. Include patients admitted following adenoidectomy and/or tonsillectomy in whom obstructive sleep apnoea is the main reason for ICU admission (and code as recovery from surgery).

Appendix 2: Example of PIM2 calculation

A patient with hypoplastic left heart syndromea is admitted to intensive care for recoveryb following an electivec Norwood procedured. At the time of admission he is ventilatede. The first recorded systolic blood pressure is 55 mmHgf, PaO2 is 110 mmHg, FiO2 0.5g, base excess −6.0h. The pupils are reactive to lighti. (The low risk diagnoses do not apply to this casej).

PIM2 = {0.01395* [absolute(55–120)]}f + (3.0791* 0)i + [0.2888* (100*0.5/110)]g + {0.104* [absolute(–6.0)]}h + (1.3352* 1)e – (0.9282* 1)c – (1.0244* 1)b + (0.7507 * 1)d + (1.6829* 1)a – (1.5770 * 0)j – 4.8841 = –1.4059

Probability of Death = exp (–1.4059) / [1+exp(–1.4059)] = 0.1969 or 19.7%

Appendix 3: Members of the PIM Study Group

The PIM Study Group included: A. O'Connell, A. Morrison, Children's Hospital, Westmead; B. Lister, P. Sargent, Mater Misericordiae Children's Hospital, Brisbane; R. Justo, E. Janes, J. Johnson, Prince Charles' Hospital, Brisbane; A. Duncan, Princess Margaret Hospital, Perth; J. McEniery, Royal Children's Hospital, Brisbane; F. Shann, A. Taylor, Royal Children's Hospital, Melbourne; B. Duffy, J. Young, Sydney Children's Hospital; A. Slater, L. Norton, Women's and Children's Hospital, Adelaide; E. Segedin, D. Buckley, Starship Hospital, Auckland; N. Barnes, Waikato Health Service, Hamilton; P. Baines, Alder Hey Children's Hospital, Liverpool; G. Pearson, J. Stickley, Birmingham Children's Hospital; A. Goldman, Great Ormond Street Hospital, London; I. Murdoch, Guy's Hospital, London.

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Slater, A., Shann, F., Pearson, G. et al. PIM2: a revised version of the Paediatric Index of Mortality. Intensive Care Med 29, 278–285 (2003). https://doi.org/10.1007/s00134-002-1601-2

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