Reducing Opioid Dose Via Targeted Nociception Monitoring

Cardiac surgical procedures hold special status in perioperative anesthesia care: challenging factors include open-heart surgery, the use of the cardiopulmonary bypass machine, as well as differentiated hemodynamic monitoring.

The pain intensity expected in cardiac surgical procedures can be rated as moderate to high (1). The adequate treatment of acute postoperative pain is of crucial importance for treatment success and begins as early on as with the intraoperative administration of opioids. This is a prerequisite for fast postoperative rehabilitation and is able to reduce the risk of postoperative morbidity and mortality (2). Perioperative analgesia is also a crucial component of fast-track anesthesia concepts (3, 4). The aims of these concepts include fast and safe postoperative weaning from mechanical ventilation, as well as the avoidance of ventilation disorders and pulmonary infections, which can occur as a result of insufficient pain management. As such, perioperative analgesia is an integral component of modern fast-track protocols.

Pain intensity measurement is mandatory

Cardiac surgical patients represent a high-risk collective for the development of postoperative delirium due to the use of the cardiopulmonary bypass machine, among other factors. Inadequately treated postoperative pain is another significant trigger for delirium, which contributes in large measure to postoperative morbidity. Furthermore, the undertreatment of acute perioperative pain, particularly in the case of thoracotomy, can lead to late sequelae such as the chronification of postoperative pain. On the other hand, intraoperative overdose complicates the postoperative course: examples here include delayed extubation, ventilation disorders, nausea and vomiting, gastric atony, opioid-induced hyperalgesia, and the development of tolerance. Therefore, pain intensity measurement is mandatory and must form an integral part of perioperative patient care.

In the case of intubated patients compromised by a surplus of sedatives, as well as in cognitively impaired patients, the likelihood of analgesic undertreatment is high. Methods to objectively measure multimodal pain have been available for implementation for some years and have been successfully demonstrated in numerous studies on general anesthesia. Interest to date has focused mainly on postoperative pain management (5). The Analgesia Nociception Index, electrodermal activity measurements, as well as measurements by means of pupillometry have been investigated with promising results. Why should pain intensity assessment of this kind not also be used intraoperatively in cardiac surgical patients, thereby enabling indirect opioid management?

Assessment of pain intensity

Bartholmes et al. devoted their attention to this question as the basis for their study and investigated the use of pupillometry-guided sufentanil administration in cardiac surgical patients (6). Their prospective randomized controlled study was intended to provide information on the use of intraoperative opioids, catecholamine requirements, and postoperative outcome parameters, such as extubation and postoperative pain intensity. To ensure patient safety, it was possible to rule out awareness by using BIS monitoring and structured interviews (according to Brice). As reported in previous studies on general anesthesia (7), the present study also achieved a significant reduction in intraoperative opioid doses in cardiac surgical patients. In terms of modern fast-track anesthesia, postoperative outcome parameters are of crucial importance. Timely and safe extubation and transfer to the normal ward are key aspects of fast-track anesthesia.

Bartholmes et al. found no difference in ventilator weaning times; oxygenation disorders—as measured by arterial partial pressure of oxygen after 24 and 48 h—and frequencies of reintubation also did not differ between study and control groups (6). Other postoperative outcome parameters, such as the occurrence of delirium, nausea, and vomiting, were not related to opioid dosage.

Nevertheless, this study demonstrated an important ‘first’ in cardiac anesthesia: objective nociception monitoring reduced not only sufentanil consumption, but also intraoperative catecholamine doses, without increasing postoperative analgesic requirements. Conversely, a significant decrease in postoperative pain intensity was observed. Thus, Bartholmes et al. postulated that this would prevent opioid-induced hyperalgesia (6).

New Impulses

This promising study gives new impetus to modern cardiac anesthesiology with regard to patient-oriented, individualized opioid dosing, and could thus extend modern fast-track anesthesia concepts using nociception monitoring. Taking into consideration all the limitations of pupillometry, such as, e.g., Horner‘s syndrome, Adie‘s syndrome, senile miosis, and the use of intraocular lenses, this procedure is nevertheless a potential intraoperative bedside instrument for this particular patient population (8, 9). Although drug-induced impairment to the pupillary reflex is rare in cardiac anesthesia as a result of the limited use of dopamine 2 receptor antagonists, such as metoclopramide and anticholinergic drugs, the anesthesiologist needs to be aware of this eventuality when using pupillometry.

Thus, with their work, Bartholmes et al. lay the foundation for future studies in cardiac anesthesiology and provide an outlook on modern individualized opioid management (6).

The question of whether we can safely reduce opioids in cardiac surgical patients in the future with the aid of pupillometry could not be answered conclusively, but must form the subject of further prospective studies. Furthermore, the use of objective nociception monitoring in the postoperative phase needs to be investigated in particular in cognitively impaired, sedated, and mechanically ventilated patients in cardiac surgery in order to aid weaning from ventilation, prevent delirium, or indeed identify the latter, with the use of intraoperative pupillometry (10).