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Clinical Reliability and Validity of the N-PASS Neonatal Pain

Clinical Reliability and Validity of the N-PASS Neonatal Pain - Clinical Hub, UW Health Clinical Tool Search, UW Health Clinical Tool Search, Questionnaires, Related

Clinical reliability and validity of the N-PASS: neonatal pain,
agitation and sedation scale with prolonged pain
P Hummel
, M Puchalski
, SD Creech
and MG Weiss
Loyola University Medical Center, Maywood, IL, USA;
Elmhurst Memorial Hospital, Elmhurst, IL, USA and
Statistically Significant
Consulting, LLC, Addison, IL, USA
Objective: To establish beginning evidence of clinical validity and
reliability of the Neonatal Pain, Agitation and Sedation Scale (N-PASS) in
neonates with prolonged pain postoperatively and during mechanical
Study Design: Prospective psychometric evaluation. Two nurses
administered the N-PASS simultaneously and independently before and
after pharmacologic interventions for pain or sedation. One nurse also
administered the premature infant pain profile (PIPP) concurrently with
the N-PASS. The setting consisted of 50-bed level III neonatal intensive
care unit. Convenience sample of 72 observations of 46 ventilated and/or
postoperative infants, 0 to 100 days of age, gestational age 23 to 40 weeks
was used. Outcome measures comprised convergent and construct
validity, interrater reliability and internal consistency.
Result: Interrater reliability measured by intraclass coefficients of 0.85 to
0.95 was high (P<0.001 to 0.0001). Convergent validity was
demonstrated by correlation with the PIPP scores (Spearman’s rank
correlation coefficient of 0.83 at high pain scores, 0.61 at low pain
scores). Internal consistency, measured by Cronbach’s a, was evident with
pain scores (0.82), and with sedation scores (0.87). Construct validity was
established via the Wilcoxon signed-rank test, comparing the distribution
of N-PASS scores before and after pharmacologic intervention showing
pain scores of 4.86 (3.38) and 1.81 (1.53) (mean (s.d.), P<0.0001) and
sedation scores of 0.85 (1.66) and �2.78 (2.81) (P<0.0001) for pre- and
postintervention assessments, respectively.
Conclusions: This research provides beginning evidence that the
N-PASS is a valid and reliable tool for assessing pain/agitation and
sedation in ventilated and/or postoperative infants 0 to 100 days of age,
and 23 weeks gestation and above.
Journal of Perinatology (2008) 28, 55–60; doi:10.1038/sj.jp.7211861;
published online 25 October 2007
Keywords: neonatal pain; neonatal pain assessment; neonatal sedation;
neonatal sedation assessment; infant pain; N-PASS: neonatal pain,
agitation and sedation scale
Pain and sedation assessment in the neonatal intensive care unit
(NICU) is an essential and often difficult process. Infants,
incapable of verbal self-report, provide behavioral and physiological
cues to indicate the presence of pain and sedation. Infants in the
NICU experience multiple acute/procedural pain events as well as
prolonged pain and distress postoperatively and due to mechanical
ventilation. Analgesics and sedatives are commonly administered to
infants in the NICU with wide variance in practice among units.
Assessment of the infant’s level of pain and sedation assists in
clinical management and evaluation of therapies. Clinical goals
include analgesics to relieve pain, and may include analgesics and/
or sedatives to attain sedation. Optimal levels of sedation are not
known for preterm or full-term infants in various situations in the
The American Academy of Pediatrics and Canadian
Paediatric Society policy statement on the prevention and
management of pain in the neonate recommends routine pain
assessment in neonates, and summarizes nine commonly used
pain assessment scales, including the Neonatal Pain, Agitation and
Sedation Scale (N-PASS).
Sedation is a concept less studied in the
neonatal population; no sedation assessment tool was available for
infants. Cochrane’s review of sedative use in neonates recognizes
the need for a validated neonatal sedation tool.
Pain in the NICU can be categorized into three types: (1) acute-
procedural pain, where pain results from a specific nociceptive
event that is self-limited, (2) acute-prolonged pain, where there is
a clear stimulus, with a clearly definable beginning and an
expected end point and (3) chronic pain, a pathological pain state
without apparent biological value that has persisted beyond the
normal tissue healing time, usually 3 months.
These three types of
pain are not well delineated, and may occur simultaneously.
Several infant pain assessment tools have been developed for acute-
procedural pain; few are designed for prolonged or chronic pain.
Received 2 May 2007; revised 31 August 2007; accepted 5 October 2007; published online
25 October 2007
Correspondence: P Hummel, Neonatology, Loyola University Medical Center, Perinatal
Center, 2160 South First Avenue, Maywood, IL 60153, USA.
E-mail: phummel@lumc.edu
Journal of Perinatology (2008) 28,55–60
r 2008 Nature Publishing Group All rights reserved. 0743-8346/08 $30

Although neonates are routinely sedated in the NICU, a sedation
assessment tool had not been developed for clinical or research use.
Sedation is defined as a calm tranquil state that allays anxiety and
The American Society of Anesthesiologists delineates a
continuum of sedation from minimal (anxiolysis) to general
In this continuum, levels of sedation are evaluated by
assessing responsiveness, airway, spontaneous ventilation and
cardiovascular function, items particularly important in the
perioperative or procedural/diagnostic situations. Optimal sedation
levels are not known for neonates, with wide variations in practice.
Postoperative infants require analgesia; some are sedated as a side
effect of analgesia or the goal may be sedation in addition to
analgesia. Goals for ventilated infants include analgesia and
possibly sedation. The N-PASS was developed as a clinically
relevant tool to assess primarily acute-prolonged pain and also
sedation in infants, with further research planned to evaluate the
N-PASS with acute-procedural and chronic pain states. This study
was designed to investigate the validity and reliability of the N-PASS
tool with acute-prolonged pain and sedation; specifically,
mechanical ventilation and/or postoperative states.
Tool development
The literature was searched for clinically usable pain and sedation
assessment tools, suited to all NICU infants, and applicable in all
pain states. Many tools, such as the Premature Infant Pain Profile
or Neonatal Infant Pain Scale
are excellent tools for acute
pain but are more difficult to apply to prolonged pain. The Crying,
Requires oxygen for saturation, Increased vital signs, Expression,
Sleepless (CRIES) tool, developed for postoperative pain, does not
appear to be valid for the premature infant.
The Echelle Douleur
Inconfort Nouveau-Ne (EDIN) tool, more recently developed to
assess prolonged pain in the ventilated premature infant, does not
assess sedation levels.
Detailed reviews of pain assessment tools
are available elsewhere.
The N-PASS was designed as a clinically useful tool for all
infants in the NICU. Indicators were chosen from literature review
and expert opinion based on clinical applicability, ease of
assessment and established validity. Consistent with the hospital
standard, a 0 to 10 scale was selected. Five criteria are graded 0, 1
or 2 for pain/agitation and 0, �1or�2 for sedation. A high pain/
agitation score indicates more frequent or intense behaviors, and a
low sedation score indicates a decreased response to stimulation, or
a deeper level of sedation. Electronic cardiac and pulse oximetry
monitoring are helpful, but not required, as auscultated heart rate
and/or respiratory rate facilitate use with well infants in the NICU
or the newborn nursery.
The pain assessment portion of the N-PASS is labeled ‘pain/
agitation’ due to clinical difficulties in differentiating these two
entities clinically, particularly in prolonged or chronic pain
situations. Although researchers have attempted to categorize
behaviors into typical of ‘pain’ and typical of ‘agitation,’ many
commonalities exist. An infant who appears to be in pain or
agitated should be evaluated within the context of the situation in
an attempt to determine causality for the behavior, guiding
Because premature infants have a limited ability to display and
maintain behavioral or physiological manifestations of pain, points
are added to the preterm infant’s pain score to approximate the
normal response of a full-term infant.
Gestational age categories
and points assigned are based on the PIPP tool categories.
Corrected gestational age determines the number of points added to
the score. The sedation score does not require this adjustment as
gestational age is not known to affect the premature infant’s ability
to exhibit signs of sedation.
Five indicators are included in the N-PASS, chosen for their
established validity, clinical applicability and ease of assessment:
crying/irritability, behavior/state, facial expression, extremities/tone
and vital signs (heart rate, respiratory rate, blood pressure and/or
oxygen saturation). Within each category, examples of criteria are
provided to assist in the assignment of a numerical value. The
N-PASS can be viewed at www.n-pass.com.
Behavioral and physiological manifestations of pain in the
neonates have been well researched. The five indicators utilized in
the N-PASS are included in various neonatal pain assessment
Sedation indicators are less well researched. Sedated
infants were observed to establish behaviors indicating sedation
utilizing the same five indicators. The sedation indicators are
consistent with the State Behavioral Scale, the COMFORT scale and
the Modified Glasgow Coma Scale.
The Modified Glasgow
Coma Scale evaluates level of consciousness, scoring the best eye,
verbal and motor responses, and is not widely used clinically for
sedation assessment. The State Behavioral Scale was tested in
mechanically ventilated infants and children from 6 weeks to 6
years old, providing systematic description of the sedation–
agitation continuum in young pediatric patients supported on
mechanical ventilation. Indicators of sedation and agitation
included in this scale are respiratory drive, response to ventilation,
coughing, best response to stimulation, attentiveness to care
provider, tolerance to care, consolability and movement after being
The COMFORT tool was developed to assess distress in
the Pediatric Intensive Care Unit and has been researched in the 0-
to 3-year-old postoperative population.
The COMFORT indicators
include alertness, calmness, respiratory response, movement, mean
arterial blood pressure, heart rate, muscle tone and facial
expression. Low scores indicate coma or sedation, moderate scores
indicate lack of distress and high scores indicate distress.
Crying is a distress signal, a response to both acute and
prolonged pain.
A ‘pain cry’ is described as more persistent and
higher pitched in acute pain situations, and longer in duration
with prolonged pain. A decreased or absent cry is observed in a
Clinical validity of N-PASS
P Hummel et al
Journal of Perinatology

sedated state, as the baby is less responsive.
Consolability is
utilized in pain and sedation assessment, as an indicator of pain,
pain relief and agitation.
Consolability is also included in the
EDIN tool and the State Behavioral Scale.
Behavior/state is assessed by observing body movements, such as
arching and kicking, and the ability to rest and sleep, indicative of
the general comfort level.
Lack of body movement and
decreased arousal to stimuli are observed in a sedated state. The
State Behavioral Scale and the COMFORT Scale include parameters
of arousal and body movement.
Facial expression has been extensively researched as a valid and
reliable pain behavior.
Facial changes indicative of pain include
lowered brows drawn together, bulge between brows, eye squeeze,
nasolabial furrow, nose broadened and bulging, cheeks raised and
mouth open and squarish.
Due to the decreased predictability
of facial expression over time, facial expressions should be
combined for assessment of prolonged pain.
A sedated infant
exhibits a decrease in facial expression with stimuli. The
COMFORT tool includes a lack of facial expression as an
Observing the position of the extremities, fisting/clenching,
finger splay and general tone of the body assist in evaluating
comfort and relaxation, and is helpful in assessing both acute and
prolonged pain.
Flexion of the arms and legs and leg extension
movements are associated with pain.
The sedated infant exhibits
a suppression of the grasp reflex and muscle tone is decreased. The
COMFORT tool includes a loss of muscle tone as an indicator.
Vital sign changes are related to the autonomic stress response
associated with pain.
Heart rate, blood pressure and respiratory
rate increase above baseline in painful situations. Vital signs
changes may be less useful with chronic pain, as these may return
to baseline with variances among infants. Vital sign changes are
the sole indicator of pain and sedation available for use during
neuromuscular blockade.
Oxygen desaturation per pulse oximetry
is observed in both acute and established pain situations.
For ease
of assessment vital sign changes were categorized into modest
increases (10 to 20% from baseline) or larger increases (>20%
from baseline). A loss of variability in vital signs with stimulation
and depressed ventilatory effort are physiological signs of sedation.
Respiratory drive and response are sedation indicators in the State
Behavioral Scale and in the COMFORT tool.
N-PASS users are
instructed to choose vital sign criteria appropriate to the clinical
Formatting the N-PASS utilizing the same criteria to assess both
pain/agitation and sedation allows evaluation of the infant on a
theoretical continuum. An infant’s behavior can range from deeply
sedated, to lightly sedated, to normal, to mild pain/agitation, to
severe pain/agitation. Despite this theoretical continuum, pain and
sedation must be evaluated and scored as separate entities since
both can occur simultaneously, although it is recognized that
increasing levels of sedation may mask the infant’s response to
Clinically, infants that become sedated due to analgesics are
not likely to be in pain, but pain may be masked by sedative
administration. Sedation behaviors and neurological depression
behaviors are similar, and neurological irritability and pain behaviors
are similar, highlighting the difficulties with pain and sedation
assessment in an infant with an abnormal neurological status.
Study design
The N-PASS tool was introduced into a 50-bed level III NICU
following education of the nursing staff. No formal method of pain
or sedation assessment was in place prior to N-PASS
implementation and clinical management was based upon the
subjective assessment of the team.
Following Institutional Review Board (IRB) approval, a select
group of 10 nurses were further trained for data collection. Parents
were informed of the study via an admission letter; the IRB
determined that formal consent was not required due to the
noninvasive nature of this observational study. The N-PASS and the
PIPP instruments were reviewed with each data collector. The PIPP
was chosen for convergent validity due to established validity and
applicability with premature as well as term infants, and because
there was no well researched tool for prolonged pain available for
use in preterm infants at the time of this research. Although
primarily an acute-procedural assessment tool, the PIPP was widely
used clinically with prolonged pain at the time of data collection.
The nurse scored the behavioral state category of the PIPP prior to
the assessment period.
Ventilated and/or postoperative infants with prolonged pain were
evaluated before and after pharmacologic intervention.
Pharmacologic intervention was not controlled. Infants received an
opioid and/or a sedative, based upon standard unit practices.
Morphine was administered by bolus in the majority of infants to
achieve analgesia and/or sedation. Lorazepam was administered
when the clinical goal was sedation. The N-PASS tool was
independently and concurrently administered when two data
collection nurses were present, for 5 to 10 min before and 1 hour
after analgesic and/or sedative administration on an infant with a
pain score over 3. One nurse also administered the PIPP tool
concurrently with the N-PASS.
Statistical analysis
The primary analysis focused on the reliability and validity of the
sum score derived from the N-PASS instrument. Two measures of
instrument reliability were used: (1) intraclass correlation
coefficient (ICC), as a measure of interrater reliability and; (2)
Cronbach’s a, as a measure of internal consistency. The ICC
corresponds to a one-way random effects model, with each neonate
representing a level of the random person factor. The ICC (1, 2)
model produces two different ICC estimates: one for the reliability
of a single rating, and one for the reliability of the mean of two
Clinical validity of N-PASS
P Hummel et al
Journal of Perinatology

Two measures of instrument validity were applied:
(1) Spearman’s rank correlation between the N-PASS and the
PIPP as a measure of convergent validity and (2) Wilcoxon signed-
rank test to compare the distribution of N-PASS scores before and
after pharmacologic intervention as a measure of construct
Counts and percentages were reported for categorical variables
and range; median, mean and standard deviation for continuous/
ordinal data. A Spearman’s rank correlation coefficient was utilized
to evaluate associations between continuous/ordinal variables and
N-PASS score. The Kruskal–Wallis or Wilcoxon rank-sum test was
applied as appropriate to compare N-PASS scores between
categorically defined groups.
Sample size
The power calculations were done in PASS2000. Data from several
earlier studies of pain assessment tools indicate high interrater
reliability as measured by the ICC (0.6 to 0.95).
A total of 32
neonates were evaluated for pain and sedation prior to and after
intervention by two raters each. A sample size of 32 neonates (and
2 raters) achieved 80% power to detect a difference of 0.22 between
the null hypothesis ICC of 0.6 and the alternative hypothesis ICC of
0.82 using an F-test with a significance level of 0.05.
A total of 46 neonates were evaluated for pain and sedation at
least once by multiple raters for a total of 72 evaluations. Since
different raters performed the evaluations of a given neonate, the
72 observations were treated as independent. The standard
deviation of the pain scale prior to intervention was 3.4. A sample
size of 72 achieved 80% power to detect a difference of 1.2 between
the null hypothesis mean of 0.0 (average difference between pre-
and postintervention N-PASS pain score) and the alternative
hypothesis mean of 1.2 with an estimated standard deviation of 3.4
and with a significance level (a) of 0.05 using a two-sided
Wilcoxon signed-rank test.
A convenience sample of intubated and/or postoperative neonates
admitted to the NICU, who were receiving pharmacologic
interventions, opioids, sedatives or both, were included in the study
when two data collectors were present. Data collection continued
until 72 data sets (before and after intervention assessments) were
obtained on 46 infants. Data were collected up to three times per
infant, on different days. A total of 21 infants (46%) were male and
25 (54%) were female. Twelve infants were assessed postoperatively;
surgeries included bowel resection, exploratory laparatomy for
necrotizing enterocolitis (NEC), esophageal atresia with
tracheoesophageal fistula repair and patent ductus arteriosus
ligation. Ten infants were assessed within 5 days postoperatively,
two infants with prolonged pain postoperatively due to NEC were
assessed at 7 to 10 days postoperatively, when their pain scores were
over 3. Infants ranged from 23 to 40 weeks gestation at birth and
were 0 to 100 days of age at assessment. (See Table 1 for
gestational age distribution).
Interrater reliability analysis
Pain scale. For the first observation of a neonate (prior to any
intervention for pain or sedation), the ICC estimates (95%
confidence interval, CI) of the pain scale were 0.95 (0.90, 0.97)
and 0.97 (0.95, 0.99) for a single rating and average of two
independent ratings, respectively. Similarly, for the second
observation of a neonate (after an intervention for pain or
sedation), the ICC estimates (95% CI) of the pain scale were 0.92
(0.85, 0.96) and 0.96 (0.92, 0.98) for a single rating and average
of two independent ratings, respectively. F-tests, carried out to test
the null hypothesis that the ICC (single rating) was 0.6 or less
(versus >0.6) were highly significant (preintervention F¼ 9.65,
P<0.0001 and postintervention F¼ 6.36, P<0.0001).
Sedation scale. The ICC estimates (95% CI) of the first
observation of a neonate prior to any intervention for pain or
sedation were 0.85 (0.72, 0.92) and 0.92 (0.83, 0.96) for a single
rating and average of two independent ratings (F¼ 3.06,
P¼ 0.001). The ICC estimates (95% CI) of the second observation
of a neonate after an intervention for pain or sedation were 0.90
(0.80, 0.95) and 0.95 (0.89, 0.97) for a single rating and average
of two independent ratings (F¼ 4.63, P<0.0001).
Internal consistency analysis
The mean (s.d.) pain scores were 4.9 (3.4) and 5.5 (3.1) for raters
1 and 2, respectively, and the medians (range) were 5 (0, 12) and
5 (0, 12). Cronbach’s a for the five-item pain scale was 0.82 and
0.72 for raters 1 and 2, respectively. The mean (s.d.) sedation
scores were –2.78 (2.81) and –1.68 (2.23) for raters 1 and 2,
respectively and the medians (range) were �2(�8, 0) and �1
(�8, 0). Cronbach’s a for the five-item sedation scale was 0.89
and 0.89 for raters 1 and 2, respectively.
Convergent validity analysis
The correlations between the preintervention N-PASS pain scale
and the PIPP were 0.83 and 0.81 for raters 1 and 2, respectively.
Table 1 Gestational age distribution
Gestational age (weeks) Percent
>35 30.6
32–35 22.2
28–31 27.8
<28 19.4
Total 100
Clinical validity of N-PASS
P Hummel et al
Journal of Perinatology

Postintervention, the correlations between the N-PASS pain scale
and the PIPP were 0.61 and 0.61 for raters 1 and 2, respectively.
Construct validity analysis
The mean (s.d.) preintervention pain score was 4.86 (3.38), which
fell to 1.81 (1.53) after analgesic intervention (P<0.0001).
Similarly, there was a decrease in mean sedation scores from
–0.85 (1.66) to –2.78 (2.81) after pharmacologic intervention
Prematurity points
Table 2 shows the mean preintervention pain scores for each group
of premature infants. Scores given include points added for
prematurity. The sample size was not sufficient to analyze each
group separately.
The correlation between the PIPP and the N-PASS was strong,
particularly at high pain scores. The correlation was lower for low
pain scores, but acceptable, possibly because the PIPP tool assigns
a higher score for a quiet infant, while the N-PASS gives a lower
score for a quiet infant, resulting in a lower behavior score
The addition of points to the premature infant’s pain score is
based upon the research-supported premise that premature infants
are less able to exhibit signs of pain than the term infant.
scores for each gestational age group are similar without
prematurity points added, and therefore may not support the
current method of adding points for prematurity. (Table 2) This
will be reevaluated following validity and reliability research
utilizing the N-PASS with acute-procedural pain. More research is
needed on the appropriateness of adding points to the premature
infant’s score.
Difficulties in behavioral pain assessment and research
Establishing the validity of a behavioral pain and sedation
assessment tool is difficult in the absence of a gold standard.
Clinically, it is often difficult to interpret the infant’s behavior, or
determine the etiology of the behavior. A biological marker
specifically for pain has not been identified, leaving the clinician
with behavioral assessment parameters and clinical judgment to
guide management.
Interpretation of the pain and sedation behavior scores within
the context of the situation is necessary when utilizing a behavioral
pain assessment scoring system.
Pain behaviors, exposure to
events likely to instigate pain, infant characteristics and health
status, presence of other conditions likely to cause distress, such as
fatigue, hunger, withdrawal, response to medications and
consolability are integrated into pain assessment.
Some infants
may appear sedated without medication administration, such as
septic/lethargic infant or an infant with an abnormal neurological
status. Premature infants may also exhibit a ‘shut down’ reaction
to unrelenting or overwhelming pain, and appear sedated.
Preterm infants show a heightened motor response to tactile
procedures following a painful event.
A high degree of suspicion
and utilizing preemptive analgesia in known pain situations are
important aspects of pain management in any nonverbal
The N-PASS was studied in the clinical setting rather than by
videotaped or laboratory methods due to the goal of developing a
clinically usable tool, and the difficulty of videotaping prolonged
pain. Bias is unable to be controlled in such a setting. The findings
should be interpreted cautiously due to the moderate sample size.
The generalizability is limited to one NICU in the Midwest. Further
testing is required in other populations and settings and with larger
samples to validate our findings.
Further research
The N-PASS tool requires validity and reliability testing with
procedural pain and with various nonverbal populations and
management styles. Pain assessment of pharmacologically
paralyzed and neurologically compromised infants is clinically
challenging, requiring further research.
This research provides beginning evidence that the N-PASS is a
clinically usable, reliable and valid tool to assess ongoing pain/
agitation and sedation in ventilated and/or postoperative infants in
the NICU.
We thank the NICU staff nurses, nurse practitioners and physicians in
the Ronald McDonald Children’s Hospital at Loyola University Medical
Center for their cooperation in this research, especially those nurses who
collected data. We also thank KJS Anand, MBBS, D.Phil for manuscript review.
This research was supported via internal research funds, Loyola University
Medical Center.
Table 2 N-PASS scores by gestational age group
Gestational age
Mean (prematurity
points added)
Median s.d.
>35 12 4.75 5 2.45412
32–35 13 4.7692 4 2.65059
28–31 18 7.1161 6.5 2.68438
<28 13 7.0769 6 2.56455
N is larger than sample N as some infants were assessed more than once, at varying
gestational ages.
Clinical validity of N-PASS
P Hummel et al
Journal of Perinatology

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