PROGNOSIS

Cohort studies

Distressed 3100g male newborn

At delivery Limp, cyanotic, no spontaneous respiratory

effort, heart rate 50 beats/min. Suction - no grimace, cough or sneeze Vigorous resuscitation

At 1 minute: Apgar score = 1 At 5 minutes: Apgar score = 2, 110

beats/min. At 10 minutes: Apgar score = 3

APGAR SCORE FOR EVALUATION OF NEONATAL ASPHYXIAAdapted from Apgar V, James LS. Am J Dis Child 1962; 104:419

Score The values for each of the five categories are added to yield a result from 0 to 10

Sign

0

1

2

Heart rate (beats/min)

Absent

<100

≥100

Respiration

Absent

Slow, irregular

Regular, crying

Muscle tone

Limp

Slow flexion

Active motor

Colour

Blue, pale

Body pink, extremities

blue

Completely pink

Reflex response to catheter in nostril

None

Grimace

Cough, sneeze

Distressed 3100g male newborn

At delivery Limp, cyanotic, no spontaneous respiratory

effort, heart rate 50 beats/min. Suction - no grimace, cough or sneeze Vigorous resuscitation

At 1 minute: Apgar score = 1 At 5 minutes: Apgar score = 2, 110

beats/min. At 10 minutes: Apgar score = 3

PROGNOSIS??

Objectives

Cohort study describe structure and analysis interpret and calculate relative and absolute

measures of effect identify potential for bias

RCT / Cohort

EXPOSED GROUP (eg treatment) NO DISEASE DISEASE NON EXPOSED GROUP (eg no treatment)

NO DISEASE

DISEASE

START

Apgar scores as predictors of chronic neurologic disabilities

Nelson KB, Ellenberg JH, Pediatrics, 1981; 68:36 49000 infants followed for 7 years.

Apgar scores recorded at 1 and 5 minutes (and for infants with AS<8 at 10, 15 & 20 minutes)

Histories recorded at 4, 12, 18 months and then yearly to age 7

Relationship between 10-minute Apgar scores and risk of death in the 1st year of life among children with birth weight of at least 2500g

Risk in ‘exposed’ = ? Risk in ‘less’ exposed = ?Relative risk = ?Risk difference = ?Attributable risk % = RD/ R(exp) = ?

Dead Notdead

Total

'Exposed'(Apgar score 0 - 3)

42 80 122

'Not exposed'(Apgar score 4 - 6)

43 302 345

Total 85 382 467

Relationship between 10-minute Apgar scores and risk of death in the 1st year of life among children with birth weight of at least 2500gRisk in exposed = 42 / 122 = 0.344 = 34.4%

Risk in less exposed = 43 / 345 = 0.125 = 12.5%

Relative risk = 0.344 / 0.125 = 2.8

Risk difference = 34.4 - 12.5 = 21.9%

Attributable risk % = RD / R(exp) = 0.219 / 0.344 = 64%

Dead Notdead

Total

'Exposed'(Apgar score 0 - 3)

42 80 122

'Not exposed'(Apgar score 4 - 6)

43 302 345

Total 85 382 467

Bad outcome eg death, h'capped infant

If exposure good/protective If exposure harmful (folate supplements, high AS (foetal distress, smoking)

<1 1 >1Relative risk

If exposure If exposure good

harmful

Good outcome eg cure,

'normal' infant

55% of cerebral palsy (CP children had 1 minute scores >= 7

99 survivors with scores 0 - 3 (at 10, 15 or 20 minutes, all birth weights) 80% free of major handicap 12 had CP

11 mentally retarded, 1 normal10 had had seizures on day of birth

1 in 8 asphyxiated neonates have CP and developmental delays << 1in 8 of those without seizures

What is key difference between RCT and cohort study?

RCT Random allocation of intervention/exposure by

investigator

CohortSelf selection of exposure/risk factor