The Sarnat exam is a specialized neurological assessment for newborns, particularly those suspected of having neonatal encephalopathy (NE). This condition can arise from various factors, with hypoxic-ischemic encephalopathy (HIE) being a common cause, resulting from a lack of sufficient oxygen around the time of birth. The exam evaluates brain function to diagnose and assess severity, guiding immediate care decisions.
First described in 1976, the exam has been adapted into the “modified Sarnat exam.” This assessment tool is widely accepted for providing a clear picture of neurological status. Performed within six hours of birth, early diagnosis influences treatment effectiveness.
Key Areas of Assessment
The Sarnat exam evaluates six categories of neurological function in newborns:
Level of consciousness
Spontaneous activity
Posture
Muscle tone
Specific reflexes
Autonomic responses
Level of Consciousness
Observing the newborn’s alertness and responsiveness assesses consciousness. A healthy newborn appears calm and awake, reacting to stimulation like crying, touch, and visual attention. An infant with moderate encephalopathy might appear lethargic and less responsive, while severe encephalopathy can manifest as a comatose or unresponsive state.
Spontaneous Activity
Spontaneous activity refers to unprompted movements. A healthy baby exhibits movements in all extremities and the trunk. Reduced movements suggest moderate encephalopathy, while a complete absence indicates severe encephalopathy.
Posture
Posture is evaluated by observing the resting position. A normal infant keeps their arms and legs drawn towards the torso, with elbows and knees flexed. Infants with moderate encephalopathy might show distal flexion, while a completely flaccid posture with extended limbs can be seen in severe cases.
Muscle Tone
Muscle tone is assessed by evaluating resistance to movement in the extremities, trunk, and neck. Lifting an infant’s leg or arm, for instance, helps observe resistance and flexion. A healthy baby maintains some flexion when a leg is lifted. Reduced resistance and diminished effort to maintain head position can indicate moderate encephalopathy, while a complete lack of resistance suggests severe encephalopathy.
Specific Reflexes
Two primitive reflexes, the suck and Moro, are examined. The suck reflex is observed by offering a finger or pacifier, noting if the infant sucks reflexively. A weak or incomplete suck suggests moderate encephalopathy, with an absent suck indicating a more severe condition. The Moro reflex, a startle response, is assessed by observing the infant’s reaction to sudden movements or sounds. A normal Moro reflex is symmetric and complete, while an incomplete or absent Moro reflex can indicate moderate or severe encephalopathy.
Autonomic Responses
Autonomic responses are evaluated by checking heart rate and pupillary response. A normal heart rate is expected in a healthy infant. Bradycardia, a lowered heart rate, may be observed in moderate encephalopathy, and a variable heart rate can be a sign of severe encephalopathy. Pupils should be reactive to light. In moderate encephalopathy, pupils might be sluggish or constricted, while fixed, non-reactive, or asymmetric pupils can be present in severe cases.
Interpreting Severity Levels
Sarnat exam observations classify neonatal encephalopathy severity. Abnormal encephalopathy requires at least three abnormal findings across categories. Overall severity (mild, moderate, or severe) is determined by the majority of findings.
Mild Encephalopathy
Mild encephalopathy displays hyperalertness or irritability. Spontaneous activity is normal or slightly increased, and muscle tone is normal or mildly increased in the trunk and extremities. Primitive reflexes like the suck and Moro reflexes are normal or only mildly affected, such as a weak suck or an exaggerated Moro. Autonomic responses, including pupillary reaction and heart rate, are normal or show minor variations like tachycardia or dilated pupils.
Moderate Encephalopathy
Moderate encephalopathy appears lethargic or obtunded, showing reduced responsiveness. Spontaneous activity is decreased, and muscle tone presents as hypotonia, affecting the trunk, extremities, or both. The posture might involve strong distal flexion. Primitive reflexes, such as the suck and Moro, are weak or incomplete. Autonomic signs can include constricted pupils or bradycardia, and periodic breathing may be observed.
Severe Encephalopathy
Severe encephalopathy is characterized by stupor or coma, with minimal or no response to painful stimuli. There is an absence of spontaneous activity, and muscle tone is flaccid, meaning there is no resistance to movement. The posture may involve complete extension. Primitive reflexes, including the suck and Moro, are absent. Autonomic responses can include pupils that are fixed, dilated, or non-reactive to light, a variable heart rate, or episodes of apnea.
Guiding Care and Predicting Outcomes
The Sarnat exam guides immediate medical care and predicts long-term neurological outcomes for newborns with neonatal encephalopathy, with its severity classification directly informing treatment decisions. For moderate to severe encephalopathy, therapeutic hypothermia (cooling therapy) is a common, effective intervention when initiated early.
During the 72-hour cooling period, the Sarnat score is documented every 12 hours to monitor neurological response. After therapeutic hypothermia, the exam is performed daily until discharge for ongoing assessment. The evolution of Sarnat findings, particularly after rewarming, predicts long-term prognosis. A normal outcome is observed in a higher percentage of infants with a normal Sarnat score after rewarming compared to those with moderate or severe scores.
Persistent or worsened severity on the Sarnat exam after rewarming is associated with higher odds of adverse outcomes, including death or neurodevelopmental impairment. Conversely, improvement in Sarnat scores after rewarming suggests a better prognosis. Exam findings, alongside other diagnostic tools like brain MRI and electroencephalogram (EEG), contribute to understanding the infant’s neurological status and future challenges. This information helps plan follow-up care and provides informed counseling to families regarding the expected neurodevelopmental trajectory.