Table 2.

Suggested starting point for defining the pain terms used for neonatal pain

Pain term	Onset	Duration	Charactera	Primary hyperalgesia
Acute episodic	Immediate	0–120b minutes	Sharp, well‐localised	Present, mild, short‐lasting
Acute recurrent	Immediate	variable	Sharp, well‐localised	Present, moderate or severe
Prolongedc	Rapid, may be gradual	One hour to 24b hours	Sharp, diffusely localised	Present, moderate or severe
Persistentc	Rapid or gradual, cumulative	one to seven days	Dull/sharp, diffusely localised	Present, moderate or severe
Chronic	Usually gradual	Eight days or longer	Dull, diffusely localised	May be present or absent, mild if present

Pain term	Secondary hyperalgesia	Allodynia	Behavioural phenotype	Physiological phenotype
Acute episodic	Probably absent	Probably absent	Strongly reactive and reflexive	High peak, sympathetic activation
Acute recurrent	Present, mild or moderate	Probably absent	Weakly reactive or reflexive	Prolonged peak, sympathetic activation
Prolongedc	Mild or absent	Probably absent	Strongly reactive on stimulation	High plateau, sympathetic activation
Persistentc	Present, mild or moderate	May be present, mild/moderate	Hyperreactive initially, later hyporeactive	Normal or low sympathetic activation
Chronic	Present, moderate or severe	May be present, moderate/severe	Hyporeactive more often, could also be hyperreactive	Normal or suppressed sympathetic drive

^aBased on descriptions in adult patients, but may be discerned by a careful physical examination.

^bSome infants with increased sensitivity to pain may have a slower decay of the acute pain following an invasive procedure, thus justifying some overlap in the durations of acute episodic pain and prolonged pain.

^cContinuous pain may be characterised as either ‘prolonged’ or ‘persistent’.