Transcutaneous electrical nerve stimulation – an important tool in person-centered multimodal analgesia

1 New treatment modalities are needed to treat postoperative pain

Despite receiving conventional anesthesia, patients still wake up to severe pain in the post-anesthesia care unit (PACU) after common surgical procedures, and more than 10% of patients report moderate-to-severe pain 12 months after surgery [1,2]. Opioids have long been the cornerstone for treating postoperative pain. However, they have a range of acute side effects, including sedation, nausea and vomiting, respiratory depression, impaired bladder and bowel function, as well as opioid-induced hyperalgesia.

The concept of multimodal analgesia has been introduced to reduce opioid doses and minimize their side effects [3]. Nevertheless, the “opioid crisis” in North America has raised awareness of the harmful effects of both short- and long-term opioid treatment. About 6–8% of patients face the risk of developing problematic opioid use after minor and major surgery [4,5]. Hence, conventional multimodal analgesia is falling short in providing adequate and safe postoperative pain relief. From both the medical and the patient perspective, there is a need to broaden the multimodal analgesia concept and introduce new, person-centered treatment modalities that can address the drawbacks of current options for postoperative pain relief. It is also high time to involve patients in the process.

2 Despite evidence, transcutaneous electrical nerve stimulation (TENS) is not used for postoperative pain relief

TENS has been used to treat acute and chronic pain conditions for decades. Yet, it is sparingly used in clinical practice for post-anesthesia care, as profiled by Diwan et al. [6]. Historically, the modality has been considered to be safe with few adverse effects [7], although its efficacy was a matter of debate, as the evidence was largely based on small and heterogeneous studies. In 2022, a systematic review and meta-analysis by Johnson et al. – including 381 randomized controlled trials (RCTs) with a total of 24,532 participants – demonstrated the effectiveness of TENS for acute and chronic pain relief [8]: during or immediately after TENS, pain intensity was lower compared with placebo, e.g., sham TENS device with no electrical current or pulses current that fade to 0 mA within 1 min (moderate-certainty evidence), without any serious adverse events, and that the pain relieving effect was of clinical importance. Several recent RCTs have since affirmed that TENS reduces the need for opioids and analgesics in the PACU [9,10,11]. When using a high-frequency, high-intensity stimulation regime, the pain-relieving effect of TENS can be assessed within 5 min, which allows switching patients over to conventional opioids without delay if TENS does not provide adequate pain relief [9]. Furthermore, TENS has high patient-reported satisfaction and acceptability [9,12], and its most frequent side effect is skin irritation, though it is uncommon when used for short durations to treat postoperative pain.

3 Why bother with alternatives when opioids work?

Although TENS is effective and safe for treating postoperative pain, the modality is underused in clinical practice [6]. Many physicians and healthcare professionals question the need for TENS when “opioids work.” Opioids are considered a “simple” and practical treatment for postoperative pain, taught in both nursing and medical undergraduate education. However, this view neglects the potential serious side effects of opioids in the PACU that require monitoring as well as preventive and ad-hoc pharmacological treatment. In contrast, TENS does not require ongoing monitoring or pharmacological treatment of side effects in the postoperative setting. In addition, assistant nurses can be involved in pain care using TENS, enabling “workshifting” and freeing up resources for registered nurses and advanced practice registered nurses. Finally, the patient can be educated to self-administer TENS after instruction and testing for continuous pain relief throughout the hospital stay.

Ultimately, the main reason for introducing TENS as a part of multimodal analgesia is that patients require alternatives to pharmacological treatment of postoperative pain that are safe to use and also patient-controlled [13]. In this qualitative interview study by Angelini et al., patients described TENS as a safe and fast-acting alternative to opioids that made it possible to manage their own pain. While using TENS, patients highlighted being in control and not having to wait out side effects or the medication wearing off. The majority would have liked to borrow a TENS device for managing their postoperative pain at home after discharge [9]. One drawback of TENS is that it is not as effective in severe pain [9,13,14]. In an RCT, severe postoperative pain (i.e., pain intensity 6–10 on the numeric rating scale [NRS, 0–10]) was identified as a negative predictor of response to TENS. Despite this, TENS was preferred over opioids, supporting the importance of patient autonomy.

Pain relief with opioids is usually considered when patients report a pain intensity of >3–4 on the visual analogue scale or the NRS in the PACU. This is an “unwritten rule” in post-anesthesia care, most likely due to pragmatic reasons, secondary to the potential side effects of opioids and the need to monitor the patient due to the risk of respiratory depression. Even though the negative effects of postoperative pain on recovery are well established, we still do not treat pain that we – physicians and healthcare professionals – consider “mild.” But, pain is subjective and defined as “an unpleasant sensory and emotional experience…” [15]. Should we not let the patient decide if he/she needs pain relief? TENS is a safe option, one that lets the patient decide when pain relief is needed. This is also an important aspect in the development of hospital@home^[1], making it possible for relatives to support the patient in the treatment of pain at home.

4 Guidelines and education are the way forward

We have evidence in support of TENS, and the patients prefer it, yet it is rarely used in the postoperative setting. To understand this disparity, Diwan et al. [6] conducted a web-based survey of staff in anesthesiology departments in Sweden, including anesthesiologists, nurse anesthetists, critical care nurses, and registered nurses with basic education working in perioperative settings. The majority of the respondents shared the information that TENS was not used in their practice. They reported lacking adequate knowledge about administering TENS and that clinical guidelines were absent or unknown to them. However, 60% of the respondents expressed an interest in developing theoretical knowledge and practical skills for administering TENS.

The substantial knowledge gaps and the lack of clear clinical guidelines limit the use of TENS for treating acute postoperative pain, despite the existing body of evidence. To address this, there is a need to implement TENS education in nursing and medical undergraduate education, as well as in higher education for anesthesiologists, nurse anesthetists, and critical care nurses. Furthermore, there is a need to develop and implement evidence-based clinical guidelines for treating postoperative pain with TENS and tailor clinical education for anesthesiology department staff. It is crucial that clinical researchers/experts work together with hospital leadership and professional bodies to support this process.

5 TENS – A natural part of modern multimodal analgesia

We argue that TENS should be an integral part of modern multimodal analgesia, given its effectiveness and safety profile. This approach enables a partnership between patients and healthcare professionals, where both parties are actively involved in planning and managing perioperative care. In this way, person-centered postoperative pain management becomes a shared responsibility and an ongoing dialogue, rather than being seen solely from the patient’s perspective. While it can be as effective as opioids, we should regard TENS as an add-on treatment to conventional multimodal analgesia that can reduce the need for opioids. If there are no contraindications, patients should be offered TENS in the same way that we use paracetamol for postoperative pain. TENS should be routinely considered for patients at an increased risk of opioid side effects, where the respiratory system may be affected (e.g., patients with morbid obesity or neuromuscular disease), as well as those with a high risk of developing or history of substance abuse or addiction.

To enhance the use of TENS in the perioperative setting, we need to better understand the factors that facilitate its adoption among healthcare professionals and identify which educational initiatives are the most effective. There is also a need for studies evaluating the impact of TENS use in surgical wards following discharge from the PACU, particularly regarding bowel and bladder function as well as postoperative mobilization. Additionally, the effectiveness of TENS for postoperative pain relief after discharge should be investigated, alongside comprehensive health economic evaluations. Finally, more evidence is needed regarding the use of TENS in the context of hospital@home and other innovative care models outside traditional healthcare facilities.

Further research and education are certainly warranted. But there is an urgent need for person-centered interventions in the perioperative setting, namely, tailoring the treatment to the patient’s preferences and for improved pain relief. We have to ask ourselves, why do we consider pain below a predetermined intensity “acceptable”? Should we not strive for the patients to be as pain-free as possible in order to improve mobilization and minimize the risk of complications? And should it not be the patient who decides if the postoperative pain requires pain relief or not? TENS as a part of multimodal analgesia allows the patient to choose pain relief for herself/himself.