title: Determination of Normal Ranges of Shock Index and Other Haemodynamic Variables in the Immediate Postpartum Period: A Cohort Study.
abstract: OBJECTIVE
  To determine the normal ranges of vital signs, including blood pressure (BP), mean arterial pressure (MAP), heart rate (HR) and shock index (SI) (HR/systolic BP), in the immediate postpartum period to inform the development of robust obstetric early warning scores.
  
  
  METHODS
  We conducted a secondary analysis of a prospective observational cohort study evaluating vital signs collected within one hour following delivery in women with estimated blood loss (EBL) <500ml (316 women) delivering at a UK tertiary centre over a one-year period. Simple and multiple linear regression were used to explore associations of demographic and obstetric factors with SI.
  
  
  RESULTS
  Median (90% reference range) was 120 (100-145) for systolic BP, 75 (58-90) for diastolic BP, 90 (73-108) for MAP, 81 (61-102) for HR, and 0.66 (0.52-0.89) for SI. Third stage Syntometrine® administration was associated with a 0.03 decrease in SI (p = 0.035) and epidural use with a 0.05 increase (p = 0.003). No other demographic or obstetric factors were associated with a change in shock index in this cohort.
  
  
  CONCLUSIONS
  This is the first study to determine normal ranges of maternal BP, MAP, HR and SI within one hour of birth, a time of considerable haemodynamic adjustment, with minimal effect of demographic and obstetric factors demonstrated. The lower 90% reference point for systolic BP and upper 90% reference point for HR correspond to triggers used to recognise shock in obstetric practice, as do the upper 90% reference points for systolic and diastolic BP for obstetric hypertensive triggers. The SI upper limit of 0.89 in well postpartum women supports current literature suggesting a threshold of 0.9 as indicating increased risk of adverse outcomes.
authors.affiliation: Women's Health Academic Centre, King's College London, London, United Kingdom.
authors.forename: Hannah L
authors.initials: HL
authors.lastname: Nathan
authors.affiliation: Women's Health Academic Centre, King's College London, London, United Kingdom.
authors.forename: Kate
authors.initials: K
authors.lastname: Cottam
authors.affiliation: Women's Health Academic Centre, King's College London, London, United Kingdom.
authors.forename: Natasha L
authors.initials: NL
authors.lastname: Hezelgrave
authors.affiliation: Women's Health Academic Centre, King's College London, London, United Kingdom.
authors.forename: Paul T
authors.initials: PT
authors.lastname: Seed
authors.affiliation: Women's Health Academic Centre, King's College London, London, United Kingdom.
authors.forename: Annette
authors.initials: A
authors.lastname: Briley
authors.affiliation: Women's Health Academic Centre, King's College London, London, United Kingdom.
authors.forename: Susan
authors.initials: S
authors.lastname: Bewley
authors.affiliation: Women's Health Academic Centre, King's College London, London, United Kingdom.
authors.forename: Lucy C
authors.initials: LC
authors.lastname: Chappell
authors.affiliation: Women's Health Academic Centre, King's College London, London, United Kingdom.
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Shennan
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D001794:Blood Pressure / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D049590:Postpartum Period / Q000502:physiology; D011446:Prospective Studies; D006113:United Kingdom; D000094422:Secondary Data Analysis