Local Anesthesia for Vitrectomy

Abstract

We read with interest Lai et al’s article1Lai M.M. Lai J.C. Lee W.H. et al.Comparison of retrobulbar and sub–Tenon’s capsule injection of local anesthetic in vitreoretinal surgery.Ophthalmology. 2005; 112: 574-579Abstract Full Text Full Text PDF PubMed Scopus (42) Google Scholar comparing retrobulbar and sub–Tenon’s capsule injection of local anesthetic in vitreoretinal surgery. The validity of the study relies on an accurate and reproducible documentation of the primary outcome—namely, intraoperative eye pain. We are concerned that some very important confounding factors pertaining to the methodology might have been overlooked.First of all, the authors adopted the 11-point numerical visual analog scale and stated that the numerical scale was sufficiently sensitive and reliable for pain assessment. We note that DeLoach et al have produced counterevidence showing that patients with a cognitive impairment were vulnerable to inconsistent visual analog scale scoring.2DeLoach L.J. Higgins M.S. Caplan A.B. Stiff J.L. The visual analog scale in the immediate postoperative period: intrasubject variability and correlation with a numeric scale.Anesth Analg. 1998; 86: 102-106Crossref PubMed Google Scholar Dr Lai et al had excluded subjects with known histories of dementia or psychiatric illness. However, even for those mentally competent individuals enrolled, concomitant IV sedation could affect the cognition and understanding of the visual analog scale scoring system significantly. In Lai et al’s study, more than 70% of patients in both arms (85.3% retrobulbar vs. 70% sub–Tenon’s capsule) were given supplemental IV sedation. The authors have tried to offset this drug influence by repeating the scoring on the day after the surgery. Nevertheless, the postsedation hanging-over side effect commonly seen in elderly has not been taken into account. The severity and extent of this confounding influence should not be underestimated.Second, the pain scoring system has its weaknesses and inconsistencies. The numerical visual analog scale is a derivative of the standard visual analog scale.3Price D.D. McGrath P.A. Rafii A. Buckingham B. The validation of visual analogue scales as ratio scale measures for chronic and experimental pain.Pain. 1983; 17: 45-56Abstract Full Text PDF PubMed Scopus (2603) Google Scholar, 4Price D.D. Bush F.M. Long S. Harkins S.W. A comparison of pain measurement characteristics of mechanical visual analogue and simple numerical rating scales.Pain. 1994; 56: 217-226Abstract Full Text PDF PubMed Scopus (900) Google Scholar It is linear, but the data are not necessarily always normally distributed. This characteristic may influence the statistical test employed. For example, most of the time patients may not use all of the scale, and repeated scoring with a visual analog scale can carry a variance as high as 20%.5Rosier E.M. Iadarola M.J. Coghill R.C. Reproducibility of pain measurement and pain perception.Pain. 2002; 98: 205-216Abstract Full Text Full Text PDF PubMed Scopus (144) Google Scholar Theoretically, this could severely bias the pain scores, amounting to approximately a 30% to 33% reduction of the rating.6Farrar J.T. Portenoy R.K. Berlin J.A. et al.Defining the clinically important difference in pain outcome measures.Pain. 2000; 88: 287-294Abstract Full Text Full Text PDF PubMed Scopus (797) Google Scholar, 7Farrar J.T. Young Jr, J.P. LaMoreaux L. et al.Clinical importance of changes in chronic pain intensity measured on an 11-point numerical pain rating scale.Pain. 2001; 94: 149-158Abstract Full Text Full Text PDF PubMed Scopus (3633) Google ScholarOn the other hand, it is rather unusual for surgeons to provide their assessments of intraoperative eye pain. Pain is entirely subjective, and its links with pathology are indirect. Hence, the most suitable way to assess pain is to believe patients’ comments on their perceived pain severity.8Williamson A. Hoggart B. Pain: a review of three commonly used pain rating scales.J Clin Nurs. 2005; 14: 798-804Crossref PubMed Scopus (1619) Google Scholar What the surgeons noted during the operation may not correlate well with a patient’s actual pain perception in light of the differences in tolerance and pain threshold among patients. For instance, the actual perceived pain may be masked during the operation in patients having higher pain tolerance.Finally, we also were interested to know whether the enrolled patients may have long-term use of ordinary oral analgesics such as over-the-counter pain killers for other purposes, which may affect the pain score assessment. We read with interest Lai et al’s article1Lai M.M. Lai J.C. Lee W.H. et al.Comparison of retrobulbar and sub–Tenon’s capsule injection of local anesthetic in vitreoretinal surgery.Ophthalmology. 2005; 112: 574-579Abstract Full Text Full Text PDF PubMed Scopus (42) Google Scholar comparing retrobulbar and sub–Tenon’s capsule injection of local anesthetic in vitreoretinal surgery. The validity of the study relies on an accurate and reproducible documentation of the primary outcome—namely, intraoperative eye pain. We are concerned that some very important confounding factors pertaining to the methodology might have been overlooked. First of all, the authors adopted the 11-point numerical visual analog scale and stated that the numerical scale was sufficiently sensitive and reliable for pain assessment. We note that DeLoach et al have produced counterevidence showing that patients with a cognitive impairment were vulnerable to inconsistent visual analog scale scoring.2DeLoach L.J. Higgins M.S. Caplan A.B. Stiff J.L. The visual analog scale in the immediate postoperative period: intrasubject variability and correlation with a numeric scale.Anesth Analg. 1998; 86: 102-106Crossref PubMed Google Scholar Dr Lai et al had excluded subjects with known histories of dementia or psychiatric illness. However, even for those mentally competent individuals enrolled, concomitant IV sedation could affect the cognition and understanding of the visual analog scale scoring system significantly. In Lai et al’s study, more than 70% of patients in both arms (85.3% retrobulbar vs. 70% sub–Tenon’s capsule) were given supplemental IV sedation. The authors have tried to offset this drug influence by repeating the scoring on the day after the surgery. Nevertheless, the postsedation hanging-over side effect commonly seen in elderly has not been taken into account. The severity and extent of this confounding influence should not be underestimated. Second, the pain scoring system has its weaknesses and inconsistencies. The numerical visual analog scale is a derivative of the standard visual analog scale.3Price D.D. McGrath P.A. Rafii A. Buckingham B. The validation of visual analogue scales as ratio scale measures for chronic and experimental pain.Pain. 1983; 17: 45-56Abstract Full Text PDF PubMed Scopus (2603) Google Scholar, 4Price D.D. Bush F.M. Long S. Harkins S.W. A comparison of pain measurement characteristics of mechanical visual analogue and simple numerical rating scales.Pain. 1994; 56: 217-226Abstract Full Text PDF PubMed Scopus (900) Google Scholar It is linear, but the data are not necessarily always normally distributed. This characteristic may influence the statistical test employed. For example, most of the time patients may not use all of the scale, and repeated scoring with a visual analog scale can carry a variance as high as 20%.5Rosier E.M. Iadarola M.J. Coghill R.C. Reproducibility of pain measurement and pain perception.Pain. 2002; 98: 205-216Abstract Full Text Full Text PDF PubMed Scopus (144) Google Scholar Theoretically, this could severely bias the pain scores, amounting to approximately a 30% to 33% reduction of the rating.6Farrar J.T. Portenoy R.K. Berlin J.A. et al.Defining the clinically important difference in pain outcome measures.Pain. 2000; 88: 287-294Abstract Full Text Full Text PDF PubMed Scopus (797) Google Scholar, 7Farrar J.T. Young Jr, J.P. LaMoreaux L. et al.Clinical importance of changes in chronic pain intensity measured on an 11-point numerical pain rating scale.Pain. 2001; 94: 149-158Abstract Full Text Full Text PDF PubMed Scopus (3633) Google Scholar On the other hand, it is rather unusual for surgeons to provide their assessments of intraoperative eye pain. Pain is entirely subjective, and its links with pathology are indirect. Hence, the most suitable way to assess pain is to believe patients’ comments on their perceived pain severity.8Williamson A. Hoggart B. Pain: a review of three commonly used pain rating scales.J Clin Nurs. 2005; 14: 798-804Crossref PubMed Scopus (1619) Google Scholar What the surgeons noted during the operation may not correlate well with a patient’s actual pain perception in light of the differences in tolerance and pain threshold among patients. For instance, the actual perceived pain may be masked during the operation in patients having higher pain tolerance. Finally, we also were interested to know whether the enrolled patients may have long-term use of ordinary oral analgesics such as over-the-counter pain killers for other purposes, which may affect the pain score assessment.