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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.
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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
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
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 2500gRisk in ‘exposed’ = ?Risk in ‘less’ exposed = ?Relative risk = ?Risk difference = ?Attributable risk % = RD/ R(exp) = ?
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 = 2.8Risk difference = 34.4 - 12.5 = 21.9%Attributable risk % = RD / R(exp) = 0.219 / 0.344 = 64%
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 normal • 10 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 • Cohort • Self selection of exposure/risk factor