In the present study we compared postsurgical pain monitoring strategies, based on subjective and objective indicators of pain levels, in a group of patients exposed to classical music and in a group of patients who received only the pharmacological treatment. Specifically, we evaluated the efficacy of the skin conductance algesimeter index - number of skin conductance fluctuations (NSCF) per second -, as compared to the Numerical Rating Scale (NRS), in perioperative pain monitoring of thyroidectomy patients. In line with previous research, our results, showed that both NRS and NSCF per second allow the detection of changes in the level of pain during the postoperative period. Moreover, in the same patients we investigated the effect of classical music listening on postoperative pain as compared to the classical pharmacological treatment alone, and we demonstrated that this approach can help to reduce the amount of administered opioid, with similar levels of perceived pain, as measured by both the NSCF and the NRS.
Previous investigations showed that NSCF is correlated with perioperative stress [11
] and with NRS [3
], which is considered one of the most accurate methods for evaluating postoperative pain [12
]. Indeed, our results confirmed that both NSCF and NRS can reliably detect changes in pain level throughout the postoperative period. In addition, we identified a significant correlation between the two methods when obtained measures were averaged across the whole Recovery Room stay. On the other hand, we did not observe a significant correlation between the NSCF and the NRS approaches at each evaluated time-point (T0, T1, T2), in line with previous work [13
Importantly, the NSCF per second has been already used successfully to monitor acute pain during anesthesia, intensive care, and for neonates [11
]. When the level of analgesia increases in patients who reported moderate and severe pain, the NSCF per second and the reported pain are reduced [3
]. As a matter of fact, changes in NSCF reflect alterations in the emotional portion of the sympathetic nervous system, which is distinct from the part influencing the micro circulation, and are therefore not associated with relevant temperature modifications [17
]. Indeed, the NSCF per second correlates with changes in skin sympathetic nerve activity [17
]. Skin sympathetic nerve activation results in the filling of the palmar and plantar sweat glands, which is followed by a transient increase in skin conductance, before the sweat is reabsorbed and the skin conductance decreases: in this condition a skin conductance fluctuation is observed. Therefore, an increase in the NSCF per second can be interpreted as the sign of activity bursts in the skin sympathetic system, and directly depends on the interaction of the neurotransmitter acetylcholine with muscarinic receptors [17
]. This parameter is not influenced by hypovolemia, adrenergic receptor active agents, small room temperature changes or muscle relaxing agents [17
]. Moreover, the NSCF per second reacts very rapidly, within 1-2 sec, to nociceptive or painful stimuli [17
]. The combined use of functional magnetic resonance (fMRI) and the visual analogue scale (VAS) for pain estimation during acute pain in awake volunteers demonstrated that the NSCF per second increases in parallel with pain-evoked brain responses, consistent with a correlation of the NSCF per second with pain-related autonomic processes [22
]. Moreover, the NSCF per second has been shown to represent a reliable measure of patients’ clinical stress during tetanic stimulation and is inversely related to the dose of administered opioids [24
Despite this body of evidence - including present results - clearly substantiate the use of the NSCF to evaluate pain levels in the postoperative period, further studies will be required to better define the reason of the discrepancies between this objective parameter and the subjective pain perception. In fact, our results indicate that while the NSCF could represent an easy to learn, and low-cost parameter for measuring postoperative pain, it may not fully reflect the actual pain perceived by the patient. Given these premises the use of the NSCF approach should be mainly limited to cases in which the patient’s capability to communicate with the external world is reduced. In other conditions, the NRS should represent the preferential approach.
A second aim of the present study was to evaluate the effects of music listening on postoperative pain perception. We demonstrated that environmental isolation during the Recovery Room stay, obtained with classical music, allows reaching the same pain control as standard treatment with a significantly inferior use of morphine and other analgesic drugs. Indeed, previous studies showed that music can efficiently contribute to pain control, especially after non-cardiac surgery [8
One review including 42 randomized controlled trials of the effects of music interventions in perioperative settings showed that music intervention had positive effects on reducing patients’ anxiety and pain in approximately half of the papers reviewed [25
]. Our results further confirmed what is well known for example for spinal anesthesia [26
], although some authors do not agree regarding general anesthesia [29
]. A possible reason for these contrasting results could lie in the different kind of surgery, which influences immediate postoperative levels: generally lower in thyroid surgery as compared to other types of surgical interventions (as we also observed from our results on pain trend during Recovery Room and hospital stay). Indeed, previous studies indicate that music intervention can have multiple, desirable clinical effects, primarily including reduction of pain, anxiety, and stress (reviewed in [25
]). Music intervention is easy to implement, and patients usually enjoy the music and can use it as a self-management technique for distraction or relaxation [25
]. In previous studies, most of the music interventions were performed postoperatively and the listening period lasted from 15 to 30 minutes. As in our own investigation, most of the studies used headphones to provide music to the patients [25
]. The type of music was soothing (i.e. 60 to 80 beats per min), and in most of the studies self-selected music was used [25
]. The self-selected music included the patients’ own favorite music chosen from a selected list of musical genres. In other studies, one specific genre of music was provided by the researchers. This included new age music, classical music, slow instrumental music, piano, and pan flute [25
]. Interestingly, the genre and duration of the soothing music do not seem to influence the effectiveness of the music intervention [31
]. It has been reported that the tempo of the music is the most important factor, with slow and flowing music with 60 to 80 beats per min having positive outcomes on relaxation and pain relief [25
]. Based on previous observations, it has been suggested that the music used therapeutically should be non-lyrical, with low tones, minimal bass and percussion, and volume level at maximum of 60dB [25
]. The possibility to reduce postoperative levels of pain with lower doses of analgesics may allow the reduction of the incidence of relevant side effects, such as nausea, vomiting, and respiratory depression. If these side effects are reduced, also a shorter hospital stay could be expected. More research is needed to find out if classical music should be included as a standard procedure to reduce acute pain.
In conclusion, the present study showed that the Skin Conductance Algesimeter, the NSCF per second can rapresent a valid approach when monitoring pain postoperatively in thyroidectomy patients, especially for those individuals that are not able to communicate with the external world, and that classical music listening may have a positive effect on pain control by reducing the need for analgesics.