Types of PatternsEarly deceleration (headcompression):Late deceleration uteroplacentalinsufficiencyVariable deceleration (cordcompression)Combined or mixed patternsDecreased beat-to-beat variability
Types of Patterns ◼ Early deceleration (head compression): ◼ Late deceleration ( uteroplacental insufficiency ◼ Variable deceleration (cord compression) ◼ Combined or mixed patterns ◼ Decreased beat-to-beat variability
Earlydeceleration(headcompression)Definition:The onset,购勿形态maximum fall, and recovery正常基底线心率160thatiscoincidentwiththe120小幅度（<s0bpm）onset,peak, and of the uterine开始早惊医后时间contraction.15短复原时（<15移）Significance: This pattern isdiseen when engagement of thefetalheadhasoccurred.Early胎心率早期减速图型图37-3-Bdecelerations are not thoughtto be associated withfetaldistrss.MMechanism:The pressureonthe fetal head leads toincreasedintracranialpressurethat elicits a vagal responsesimilar to the valsalvamaneuver in the adultFigure 10-3.Early deceleration.Note that the deceleration starts and ends with the uterinecontraction,Goodbeat-to-beatvariabilityis demonstrated
Early deceleration (head compression) ◼ Definition: The onset, maximum fall, and recovery that is coincident with the onset, peak, and of the uterine contraction. ◼ Significance: This pattern is seen when engagement of the fetal head has occurred. Early decelerations are not thought to be associated with fetal distrss. ◼ Mechanism: The pressure on the fetal head leads to increased intracranial pressure that elicits a vagal response similar to the valsalva maneuver in the adult
Late deceleration(uteroplacentalinsufficiency)Definition:The onset,maximaldecrease, and recovery that is shifted这光意to the right in relation to the开饨AE(<03pm)送contraction.长系时间Significance:The severity of late(0~0decelerations is graded by themagnitude of the decrease in FHRan%1图然心晚期成高图型the nadir of he deceleration.Fetalhypoxia and acidosis areusuallymore pronounced with severedecelerationsMechanism:Late decelerations aregenerally associated with low scalpblood PH values and high basedeficits,indicating metabolic acidosisfrom anaerobic netabolism
Late deceleration (uteroplacental insufficiency) ◼ Definition: The onset, maximal decrease, and recovery that is shifted to the right in relation to the contraction. ◼ Significance: The severity of late decelerations is graded by the magnitude of the decrease in FHR an the nadir of he deceleration. Fetal hypoxia and acidosis are usually more pronounced with severe decelerations. ◼ Mechanism:Late decelerations are generally associated with low scalp blood PH values and high base deficits, indicating metabolic acidosis from anaerobic netabolism
MechanismofLatedecelerations The degree of fetal acidosis can be measured bysampling blood from the presenting part.ThePHof fetal scalp blood normally variesbetween7.25 and 7.30.Values below 7.20 are considered to beabnormal but not necessarily indicative of fetalcompromiseLatedecelerationsaregenerally associated withlowscalp blood PH values and high base deficits, indicatingmetabolicacidosisfromanaerobicnetabolismThepatial pressureof carbon dioxide (Pco)inthefetal blood is usually in the normal range, and the fetalblood oxygen partial pressure (Po2) is only slightlybelow normal because of the Bohr effect-the shift tothe left of the oxygen dissociation curve caused by theacidosis
Mechanism of Late decelerations • The degree of fetal acidosis can be measured by sampling blood from the presenting part. • The PH of fetal scalp blood normally varies between 7.25 and 7.30.Values below 7.20 are considered to be abnormal but not necessarily indicative of fetal compromise • Late decelerations are generally associated with low scalp blood PH values and high base deficits, indicating metabolic acidosis from anaerobic netabolism • The patial pressure of carbon dioxide (Pco2) in the fetal blood is usually in the normal range, and the fetal blood oxygen partial pressure (Po2) is only slightly below normal because of the Bohr effect-the shift to the left of the oxygen dissociation curve caused by the acidosis
Variabledeceletation(cord compressionDefinition:This pattern has a变化形态正常基底线心车160variable time of onset and ayvariable form and may be大幅度(>70bpm)nonrepetitive迅速复原实益下降开始早晚不定Significance:Variabledecelerations are caused byumbilical cordcompression.Thedniseverity of variable decelerationsis graded by their duration.图37-3-D胎心率变异减速图型whentheFHRfallsbelow80beats/minute during the nadirforthe deceleration,there is usuallya loss of P-wave in the fetalelectrocardiogram,indicating anodal rhythm or a second-degreeheart block伟举水过步过期性服光民的产安排
Variable deceletation (cord compression) ◼ Definition: This pattern has a variable time of onset and a variable form and may be nonrepetitive ◼ Significance: Variable decelerations are caused by umbilical cord compression. The severity of variable decelerations is graded by their duration. ◼ when the FHR falls below 80 beats/minute during the nadir for the deceleration, there is usually a loss of P-wave in the fetal electrocardiogram, indicating a nodal rhythm or a second-degree heart block