Infants born prematurely must grow and develop in an environment that is highly stressful compared with the womb. Multiple, repeated stressors in the NICU, both painful and nonpainful, cannot fail to have an effect on vulnerable and immature central nervous systems of preterm infants. The experience of stress in the perinatal period is believed to influence structural and functional brain development, yet the assessment and prevention of stress do not receive the same attention as the assessment and management of pain in the neonate.

Newnham and colleagues1 developed and tested a tool called the Neonatal Infant Stressor Scale (NISS). The NISS comprises 44 acute, potentially stressful events organized into categories such as general nursing care, peripheral venous or arterial access, central vascular access, ventilation, feeding, medical/surgical procedures, radiological procedures, and miscellaneous items. Furthermore, the tool includes 24 chronic living conditions experienced by preterm infants, such as receiving intranasal oxygen, being jaundiced, and having a systemic infection. One hundred thirty neonatal staff members (88% nurses and 12% physicians) were asked to rate the severity of infant stress that they believed was associated with each procedure or condition, using a Likert-type scale that ranged from 1 (not stressful) to 5 (extremely stressful). Staff rated stress levels of 3 groups of preterm infants on the basis of postconceptional age (<28, 28-32, or 32-27 weeks).

Participating respondents perceived that almost every aspect of preterm infant handling, except feeding-related items, were to some degree stressful. Severity of perceived stress correlated to infants' postconceptional ages. The most highly stressful events were intubation, chest tube insertion, insertion of vascular catheters (any type), oral/nasal suctioning, lumbar puncture, eye examinations, and heelsticks. When multiple attempts were required to accomplish a single procedure, it was judged to be extremely stressful for all infants. Procedures such as diaper changes, repositioning, taking infant out of the incubator, removing intravenous catheters, providing nasal continuous positive airway pressure, inserting nasogastric tubes, and performing echocardiograms were judged as moderately stressful. Most other nursing items were considered to be mildly or not stressful. However, a wide range of individual stress ratings was observed for various procedures, and, clearly, there is a great deal of overlap between stress and pain.

Chronic living conditions considered most stressful for infants were having a systemic infection and receiving mechanical ventilation without sedation. Being nursed on a radiant warmer was judged more stressful than in an incubator because of increased handling and noise associated with radiant warmer use.

The goal of the NISS is to measure, track, and manage presumed accumulated stress in preterm infants. The authors' vision for the NISS is to provide a tool for staff members to choose a maximum (preferred) stress score for each infant for a specific period of time, such as 2 hours. Then, infants would be assigned actual stress score points for each chronic condition or procedure. Ideally, the infant's cumulative score would remain below the maximum desired NISS, but if not, caregivers must take steps to reduce stress or delay the performance of additional stressful procedures so the preferred NISS is not exceeded. The NISS has not been validated with physiologic measures of stress, and the high variability among individuals assigning stress scores must be addressed. Additional research is also needed to correlate NISS scores with infant outcomes. However, the development of the NISS represents an important step in the recognition of the toll that stress takes on the recovery, growth, and development of preterm infants in the NICU.

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