At the time PDR were measured, the mean (standard deviation) remifentanil effect-site concentration was 0.06 ng/mL−1 (0.09), the expired fraction of sevoflurane was 1.4 (0.7), or the expired fraction of desflurane was 2.5 (1.6).
The median (IQR) PDR were 9% (4%–13%) and 41% (27%–66%) on the TPVB side and on the control side, respectively (Figure 2). There was a significant difference in the PDR between TPVB side and control side with a median difference of 37% points (95% confidence interval [CI], 25–52, P < .001). The initial pupil diameter was 2.3 mm (0.6) without a difference between the initial pupil diameter for the 2 stimulations.
Postoperative pain scores (median [IQR]) in the PACU were 1 (0–3) at rest and 1 (0–3) during mobilization, respectively. No patient required morphine titration, 7 patients (22%) received tramadol (100 mg), and 3 patients (9%) received nefopam (20 mg) during the PACU stay.
Figure 3 shows maximal postoperative pain score depending on the PDR recorded on the TPVB side. There was a linear correlation between pain scores and the PDR with a Pearson’s correlation coefficient r = 0.40 (95% CI, 0.06–0.66, P = .02). The difference between the PDR on TPVB side and the PDR on the control side was not correlated to postoperative pain score (P = .89). No correlation was found between the number of blocked dermatomes and the maximal postoperative pain scores (r = −0.35, 95% CI, −0.63 to 0.02, P = .06) or between the number of blocked dermatomes and the PDR recorded on the TPVB side (r = −0.27, 95% CI, −0.58 to 0.10, P = .15).
No local complications occurred owing to pupillometry. Nausea, vomiting, and the use of antiemetic therapy during PACU were rare.
This prospective single-center, observational study showed that the PDR was diminished by TPVB performed before general anesthesia in patients scheduled for breast surgery.
Monitoring TPVB by the PDR could improve the quality of care. If the PDR can predict ineffective TPVB before the patient has recovered, the clinician can prevent acute postoperative pain by administering analgesic medications or infiltrating the surgical wounds with local anesthetics.17 On the 1 hand, we believe that the PDR is more interesting than other preoperative predictors such as the loss of cold sensation to predict TPVB failure. Indeed, the PDR can be recorded immediately before the patient recovers consciousness, when TPVB should be the most effective. On the other hand, the clinical loss of cold sensation or the pinprick test can only be assessed before surgery when the onset time and the quality of blockade can result in false-negative results or after recovery when the assessment of blocked dermatomes has no value to adjust the analgesic approach. In this study, loss of the cold sensation was evaluated after a mean of 15 minutes, which is premature because the onset time of ropivacaine is more than 20 minutes.18 Delaying surgery to assess the loss of the pinprick and cold sensations after 40 minutes might have improved the correlation between the sensory test and the pain scores in the PACU as well as between the sensory test and the PDR. Nevertheless, the PDR provides objective results, unlike sensory tests, which depend on patient sensitivity and understanding.
Moreover, if a clinician could reliably control the effectiveness of TPVB, he or she could more easily decrease perioperative opioid infusion. This is highly important because decreasing perioperative opioid use could influence long-term outcomes such as cancer recurrence19 or chronic postoperative pain.20
Initial pupil size by general anesthesia was similar to previous findings.7,21 Numerous drugs modify pupil diameter under general anesthesia. All measurements were made before the use of a reversal agent for neuromuscular blocking. Droperidol was only used as a rescue treatment in the PACU for nausea or vomiting because neuroleptic drugs have a pupilloconstrictive effect.22 Finally, there was no difference between basal pupil size between the 2 measurements, meaning that pupil diameter promptly returned to its baseline after the PDR measurements on both sides. The PDR expressed as percentages of initial pupil diameters can thus be compared in this study.
Our study was powered to detect a 10% point difference based on preliminary data. These data were obtained with a similar protocol but posterior chest wall stimulation. The difference found in the present study with anterior chest wall stimulation was more robust. Thus, although the present study was overpowered, the results are clinically relevant with a median difference of 37% points.
The correlation between pain scores and the PDR on the TPVB side was weaker than expected. More than half of the patients had ALND in addition to their breast surgery and felt pain in the axilla and inner arm. These areas can be under brachial plexus innervation, which is not anesthetized by TPVB, or a T1 intercostal nerve, which could be missed by insufficient cephalic spread of TPVB. Our assessment of overall pain without discriminating between locations probably led to a confusion factor explaining the weak relationship between pain scores and the PDR. Moreover, deep planes of the chest are under medial pectoral and lateral pectoral nerves (innervation of pectoralis major and pectoralis minor muscles), which also derive from brachial plexus.
Our study has certain limitations. The site of noxious stimulation in the patient’s anterior chest wall creates 3 issues: first, the manufacturer of Algiscan recommends stimulation of the ulnar nerve at the wrist; thus, it has not been validated in other areas. However, pupillometry has been successfully performed in the ankle to evaluate popliteal sciatic nerve block8 and with C5 and L4 dermatome stimulation during epidural anesthesia.23 Larson et al6 observed that the PDR accurately predicted the level of sensory block within 2 dermatomes during combined epidural–general anesthesia. A neutral stimulation site (such as the ulnar nerve) should have been used for validation of our data. Second, pupil constriction by opiate drugs is well known and has been described with remifentanil.21 Opioid-induced pupillary constriction could bias the PDR. Remifentanil, a short-acting opioid, was stopped at least 5 minutes before the PDR was recorded, resulting in a low and probably nonconfounding effect-site concentration of remifentanil.21 Third, the common practice of long-acting opioid administration probably limits the generalizability of this strategy. Nonetheless, PDR shows good results for monitoring the analgesia level with long-acting opioid like alfentanil9 during anesthesia and sufentanil10 in the immediate postoperative period or fentanyl13 in intensive care. The validation of our strategy with long-acting opioids still needs further studies.
TPVB is known to have a low side effect rate,24 and there were no side effects from TPVB in this small cohort.
In conclusion, this feasibility study assessed and confirmed the value of PDR in detecting the success of unilateral TPVB during general anesthesia. A marked difference was found between the PDR on the blocked side and the unblocked side. This approach supports previous studies using the PDR to evaluate sensory blockade during general anesthesia, but further studies comparing the PDR with sensory tests are needed to show improvement in the quality of care with this approach.
Thanks to Mehdi Benichou (London, England) and Ugo Coltel (Cork, Ireland) who critically reviewed the proposal and Dale Roche-Lebrec (Paris, France) for language editing.
Name: Baptiste Duceau, MD.
Contribution: This author helped in study design, patient recruitment, data collection and analysis, and writing up of the first draft of the paper.
Name: Mélanie Baubillier, MD.
Contribution: This author helped in study design and patient recruitment, data collection, and analysis.
Name: Gaëlle Bouroche, MD.
Contribution: This author helped in study design and critical revising of the draft.
Name: Aline Albi-Feldzer, MD.
Contribution: This author helped in study design, patient recruitment, and critical revising of the draft.
Name: Christian Jayr, MD, PhD.
Contribution: This author helped in study design, patient recruitment, critical revising, and final approval of the draft.
This manuscript was handled by: Richard Brull, MD, FRCPC.
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