Pupillary Reflex for Evaluation of Thoracic Paravertebral Block: A Prospective Observational Feasibility Study

The pupillary dilation reflex to a nociceptive stimulus as a tool for analgesia management: A diagnostic study

BACKGROUND

More than 70% of patients demonstrate pain after endotracheal aspiration. Tools are needed to objectify the need for analgesia in non-communicative critically ill patients.

OBJECTIVE

The objective of this study was to identify the lowest intensity electrical stimulus for detecting pain before daily care interventions.

METHODS

Study of diagnostic tests to assess pupillometry to detect pain through the pupillary dilation response to noxious stimuli versus the Behavioural Pain Scale. Patients older than 18 years, under analgosedation, subjected to invasive ventilation, baseline Behavioural Pain Scale of 3, and Richmond Agitation-Sedation Scale between -1 and -4 were studied. We assessed the Behavioural Pain Scale and the pupillary dilation response to 10, 20, 30, and 40 mA stimuli. We studied the diagnostic performance based on sensitivity and specificity, negative predictive value, positive predictive value, and accuracy of the selected points after the different stimulations. AlgiScan® Pupillometer measured the pupillary dilation response. The presence of pain was considered as a Behavioural Pain Scale score of ≥4. Significance was defined as p <0.05.

RESULTS

Measurements were performed on 31 patients. In the 20 mA stimulus, we found an area under the curve of 0.85 (0.69-1.0). The cut-off point of pupillary dilation was 11.5%, with a sensitivity of 100% (34.2-100) and a specificity of 75.9% (57.9-87.8). This point had an accuracy of 77.4 (60.2-88.6) and a Youden's Index of 0.8.

CONCLUSIONS

Pupillary variation measurement during a 20 mA stimulus could help assess the need for analgesia before potentially painful interventions. Further studies are needed to confirm this.

REGISTRATION

Phase 1 of the project PUPIPAIN ClinicalTrials.gov Identifier: NCT04078113.

The value of pupillary diameter in evaluating pain perception after awakening in patients undergoing general anesthesia during orthopedic surgery

BACKGROUND

The pupillary response to tetanic electrical stimulation reflects the balance between nociceptive stimulation and analgesia. Although pupillary pain index (PPI) was utilized to predict postoperative pain, it depended on tetanic stimulation and was complex. We aim to describe the potential relationship between PD in the presence of surgical stimulation and pain levels after awakening.

METHODS

According to the Verbal Rating Scale (VRS) score after extubation, the patients were divided into painless group (VRS = 0) and pain group (VRS ≥ 1). Pupillary diameter (PD) and pupillary light reflex velocity (PLRV) were compared between two groups when patients entered the operating room (T1), before incision (T2), 10 s after incision (T3), 30 s after incision (T4), 1 h after incision (T5), at the end of surgery (T6), shortly after extubation (T7), and when patients expressed pain clearly (T8). The magnitude of PD change (ΔPD) compared to the baseline value after anesthesia induction (T2) was calculated. The correlations between pupillary parameters and pain after awakening were calculated.

RESULTS

Patients with VRS ≥ 1 had greater PD than painless patients at T3-7 (P = 0.04, 0.04, 0.003, <0.001, <0.001), and it was positively correlated with VRS score after awakening at T4-7 (r = 0.188, 0.217, 0.684, 0.721). The ability of T6ΔPD to predict VRS ≥ 1 was strong [threshold: 20.53%, area under the curve (AUC): 0.93, 95% confidence interval (CI): 0.89-0.97 ].

CONCLUSION

Our study indicates that PD is a useful index to direct the individualized analgesics used during operation, to better avoid the occurrence of pain during the postoperative emergence period.

TRIAL REGISTRATION

This study was registered with the Chinese Clinical Trial Registry (registration number: ChiCTR2000040908, registration date: 15/12/2020).

[New Approaches in Perioperative Algesimetry]

The measurement of anaesthetic depth and muscle relaxation have been routine procedures during general anaesthesia for years. Quantification of intraoperative nociception, on the other hand, is still largely impossible. Various methods have been tested and commercialised for more than 10 years. However, a real breakthrough has not yet been achieved and the routine application of all methods available so far is not without problems. This article explains methodological similarities, but also points to specific aspects of various commercial solutions for perioperative algesimetry.

Pupillary Pain Index Predicts Postoperative Pain but Not the Effect of Peripheral Regional Anaesthesia in Patients Undergoing Total Hip or Total Knee Arthroplasty: An Observational Study

Background and Objectives: The pupillary pain index (PPI) allows the evaluation of intraoperative nociception by measuring pupillary reaction after a localized electrical stimulus. It was the objective of this observational cohort study to investigate the pupillary pain index (PPI) as a method to evaluate the fascia iliaca block (FIB) or adductor canal block (ACB) sensory areas during general anaesthesia in orthopaedic patients with lower-extremity joint replacement surgery. Materials and Methods: Orthopaedic patients undergoing hip or knee arthroplasty were included. After anaesthesia induction, patients received an ultrasound-guided single-shot FIB or ACB with 30 mL and 20 mL of 0.375% ropivacaine, respectively. Anaesthesia was maintained with isoflurane or propofol/remifentanil. The first PPI measurements were performed after anaesthesia induction and before block insertion, the second at the end of surgery. Pupillometry scores were evaluated in the area of the femoral or saphenous nerve (target) and C3 dermatome (control). Primary outcomes were differences between PPIs before and after peripheral block insertion as well as the relationship between PPIs and postoperative pain scores; secondary outcomes were the relationship between PPIs and opioid requirements after surgery. Results: PPI decreased significantly from the first to the second measurement (4.17 ± 2.7 vs. 1.6 ± 1.2, p < 0.001 for target; 4.46 ± 2.7 vs. 2.17 ± 2.1, p < 0.001 for control). Control and target measurements did not show significant differences. A linear regression analysis showed that early postoperative pain scores could be predicted with intraoperative piritramide with improved prediction after adding PPI scores, PCA opioids and surgery type. Forty-eight-hour pain scores at rest and in movement were correlated with intraoperative piritramide and control PPI after the PNB in movement and with second-postoperative-day opioids and target PPI scores before block insertion, respectively. Conclusions: While the effect of an FIB and ACB could not be shown with PPI postoperative pain scores due to a large effect of opioids, perioperative PPI was shown to be associated with postoperative pain. These results suggest that preoperative PPI may be used to predict postoperative pain.

Different perspectives for monitoring nociception during general anesthesia

Safe anesthesia is achieved using objective methods that estimate the patient’s state during different phases of surgery. A patient’s state under anesthesia is characterized by three major aspects, which are linked to the main effects produced by each of the families of anesthetic agents administered: hypnosis, analgesia, and muscular relaxation.

While quantification techniques designed to assess muscular relaxation under neuromuscular blocking agents have a relatively long history with a high degree of standardization and understanding (e.g., the train-of-four), the knowledge and techniques used to the depth of hypnosis assessment suffer from a lesser degree in both standardization and interpretation due to brain complexity.

The problem of standardization and interpretation in the analgesia and nociception assessment increases since it involves more systems, the central nervous system, and the autonomic nervous system.

This helps to explain why there are multiple a priori valid approaches to develop nociception monitoring from different interpretations and physiological bases of noxious stimuli processing. Thus, in this review, the current monitoring technologies clinically available for estimating a patient’s nociception under general anesthesia are described.

Preoperative Paravertebral Block and Chronic Pain after Breast Cancer Surgery: A Double-blind Randomized Trial

BACKGROUND

The effectiveness of paravertebral block in preventing chronic pain after breast surgery remains controversial. The primary hypothesis of this study was that paravertebral block reduces the incidence of chronic pain 3 months after breast cancer surgery.

METHODS

In this prospective, multicenter, randomized, double-blind, parallel-group, placebo-controlled study, 380 women undergoing partial or complete mastectomy with or without lymph node dissection were randomized to receive preoperative paravertebral block with either 0.35 ml/kg 0.75% ropivacaine (paravertebral group) or saline (control group). Systemic multimodal analgesia was administered in both groups. The primary endpoint was the incidence of chronic pain with a visual analogue scale (VAS) score greater than or equal to 3 out of 10, 3 months after surgery. The secondary outcomes were acute pain, analgesic consumption, nausea and vomiting, chronic pain at 6 and 12 months, neuropathic pain, pain interference, anxiety, and depression.

RESULTS

Overall, 178 patients received ropivacaine, and 174 received saline. At 3 months, chronic pain was reported in 93 of 178 (52.2%) and 83 of 174 (47.7%) patients in the paravertebral and control groups, respectively (odds ratio, 1.20 [95% CI, 0.79 to 1.82], P = 0.394). At 6 and 12 months, chronic pain occurred in 104 of 178 (58.4%) versus 79 of 174 (45.4%) and 105 of 178 (59.0%) versus 93 of 174 (53.4%) patients in the paravertebral and control groups, respectively. Greater acute postoperative pain was observed in the control group 0 to 2 h (area under the receiver operating characteristics curve at rest, 4.3 ± 2.8 vs. 2.9 ± 2.8 VAS score units × hours, P < 0.001) and when maximal in this interval (3.8 ± 2.1 vs. 2.5 ± 2.5, P < 0.001) but not during any other interval. Postoperative morphine use was 73% less in the paravertebral group (odds ratio, 0.272 [95% CI, 0.171 to 0.429]; P < 0.001).

CONCLUSIONS

Paravertebral block did not reduce the incidence of chronic pain after breast surgery. Paravertebral block did result in less immediate postoperative pain, but there were no other significant differences in postoperative outcomes.

EDITOR’S PERSPECTIVE

Intraoperative Nociception Monitoring

Nociception refers to the process of encoding and processing noxious stimuli. Its monitoring can have potential benefits. Under anesthesia, nociceptive signals are continuously generated to cause involuntary effects on the autonomic nervous system, reflex movement, and stress response. Most available systems depend on the identification and measurement of these indirect effects to indicate nociception-antinociception balance. Despite advances in monitoring technology and availability, their limitations presently override their benefits. Hence, their utility and applicability in present-day anesthesia care is uncertain. Future technologies might allow automated closed-loop multimodal anesthesia systems, which includes the components of hypnosis and analgesic balance for a patient.

Infrared thermography for assessment of thoracic paravertebral block: a prospective observational study

Background

There was no “gold standard” to assess the success or failure of thoracic paravertebral block (TPVB). Measurement of skin temperature with infrared thermography (IT) would be a reliable method to evaluate the effectiveness of regional blocks. This study aimed to explore the feasibility of using skin temperature difference (Td) determined by IT between the blocked and unblocked side to predict the spread of TPVB.

Methods

Sixty-one patients undergoing elective unilateral breast or thoracoscopic surgery were enrolled in this prospective observational study. TPVB was performed at T4 and T5 under real-time ultrasound guidance with 10 mL of 0.4% ropivacaine for each patient, respectively. Td between the blocked and unblocked side were measured with IT from T2 to T10 at the anterior chest wall before TPVB and 5 min, 10 min, 15 min and 20 min after TPVB. Pinprick test was performed at 20 min after TPVB. Successful TPVB was defined as no sensation to pinprick in 3 or more adjacent dermatomes corresponding to the site of injection at 20 min after TPVB. Td was compared to pinprick test for evaluating its effectiveness in predicting the success of TPVB. The sensitivity, specificity, and cut-off value of Td for predicting successful TPVB were determined by receiver operator characteristic (ROC) curve analysis.

Results

Compared with the baseline value before block, Td from T2 to T10 were significantly increased at each time point in successful blocks. In failed blocks, Td was not increased in any dermatome. The increase of Td at T4-T7 was more than 1 °C 20 min after successful TPVB. Fifteen minutes after block, Td increase at T4 had the greatest potential to predict block success. The area under the ROC curve was 0.960 at a cut-off value of 0.63 °C with a sensitivity of 83.3% and a specificity of 100.0%.

Conclusions

This study suggested that the increase of Td at T4 dermatome determined by IT between the blocked and unblocked side is an early, quantitative, and reliable predictor of successful TPVB.

Trial registration

Clinical trial registration: NCT04078347.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-021-01389-4.

Pupillometry in perioperative medicine: a narrative review

PURPOSE

Pupillometry is a technique for objective quantification of nociception that takes into account the central processing of noxious stimuli and its sympathetic response. This narrative review provides an overview of the physiology of the pupil, the principles of pupillometry, and its potential application in the perioperative environment, especially in nociception monitoring and quantifying responses to opioids.

SOURCE

Relevant articles, including reports of original investigation, review articles, and meta-analyses were identified from searches of PubMed and Google Scholar databases. Articles that described pupillary physiology and pupillometry, along with original research reports of the application of pupillometry in perioperative and critical care environment were used to synthesize a narrative review.

PRINCIPAL FINDINGS

Pupillometry is emerging as an objective measure of nociception, especially in patients under general anesthesia, children, non-verbal patients, and critically ill patients who cannot effectively communicate ongoing pain. Portable automated pupillometers have made accurate quantification of pupillary reflexes, including light reflex and dilatation reflex, possible. This technique has been successfully studied in the perioperative setting for a number of applications, including quantification of nociception, response to analgesia, and assessing efficacy of regional blocks. Pupillary oscillations have shown promise in assessing central opioid effects. Pupillometers can also accurately quantify light reflexes during the neurologic evaluation of critically ill patients.

CONCLUSIONS

Pupillometry is an easy to use non-invasive bedside technique to quantify nociception and monitor opioid effects. It has the potential to personalize pain management in perioperative and intensive care unit environments. Additional studies are needed to further understand the utility of pupillometry in this context.

Objective monitoring of nociception: a review of current commercial solutions

Nociception, in contrast to pain, is not a subjective feeling, but the physiological encoding and processing of nociceptive stimuli. However, monitoring nociception remains a challenge in attempts to lower the incidence of acute postoperative pain and the move towards a more automated approach to analgesia and anaesthesia. To date, several commercialised devices promise a more accurate reflection of nociception than the traditionally used vital signs, blood pressure and heart rate. This narrative review presents an overview of existing technologies and commercially available devices, and offers a perspective for future research. Although firm conclusions about individual methods may be premature, none currently appears to offer a sufficiently broad applicability. Furthermore, there is currently no firm evidence for any clinically relevant influence of such devices on patient outcome. However, the available monitors have significantly aided the understanding of underlying mechanisms and identification of potential pitfalls.