This study was done to identify pain perception (P-PER) by nurses and pain expression (P-EXP) by patients in critical care units (ICUs) and degree of agreement between nurses' P-PER and patients' P-EXP.

Nurses' P-PER was measured with a self-administered questionnaire completed by 99 nurses working in ICUs during May, 2013. Patients' P-EXP was measured with the Critical Care Non-Verbal Pain Scale through observations of 31 ICU patients during nine nursing procedures (NPs) performed between May and July, 2013.

Nurses' P-PER was from 4.49 points for nasogastric tube (NGT) insertion to 0.83 for blood pressure (BP) measurement based on a 9-point scale, Patients' P-EXP was 4.48 points for NGT to 0.18 for BP measurement based on a 10-point scale. Eight NPs except oral care showed higher scores for nurses' P-PER than for patients' P-EXP. Position change (p=.019), subcutaneous injection (p<.001), blood sugar test (p<.001), and BP measurement (p<.001) showed significant differences between nurses' P-PER and patients' P-EXP.

Nasogastric tube (NGT) insertion was scored highest by both nurses and patients. Eight NPs except 'oral care' showed nurses' P-PER was higher or similar to patients' P-EXP, which indicates that nurses may overestimate procedural pain experienced by patients.