The relationship between movement-evoked versus spontaneous pain and peak expiratory flow after abdominal...

The pathogenesis of postoperative lung dysfunction implies a role for movement-evoked pain (e.g., splinting/hypoventilation because of pain avoidance). However, interactions between evoked pain and respiratory physiology are poorly understood. Thus, we examined the relationship between evoked versus spontaneous pain and one index of pulmonary function. In 25 patients having undergone a hysterectomy, visual analog scale ratings (100 mm) for spontaneous pain (REST) and pain during sitting (SIT), forced expiration (BLOW), and coughing (COUGH) were measured together with peak expiratory flow (PEF) at eight time points during postoperative Days 1 and 2. Secondary outcome measures included oxygen saturation and oxygen requirements. Pain was significantly correlated with PEF for COUGH, SIT, BLOW, and REST at eight, seven, four, and two of the eight studied time points, respectively. Mean visual analog scale scores [SE] for COUGH (26.1 mm [1.7]) and SIT (21.5 mm [1.5]) were greater (P < 0.05) than REST (10.5 mm [0.8]), and COUGH was greater (P < 0.05) than BLOW (16.8 mm [1.3]). All pain measures diminished (P < 0.05), and PEF reductions improved (P < 0.05) across the study period. We hypothesize that the consistent negative correlation of COUGH-evoked pain with PEF is, in part, caused by avoidance of coughing, which ultimately limits deep inspiration, lung reexpansion, and clearance of secretions.

Movement-evoked pain may be an important contributor to postoperative complications, but its mechanisms are poorly understood. This study provides the first evidence that postoperative evoked pain correlates with lung function and highlights the need for future research on mechanisms and implications of this phenomenon.