436 Anll OphlhalmoI1993;25:436-439

Topical Anesthesia During Infant Eye Examinations: Does It Reduce Stress?

RICHARD A. SAUNDERS, MD, KAREN W. MILLER, RN, AND HURSHELL H. HUNT, PHD

We studied the effect of topical anesthesia on infant stress and corneal haze during the routine eye examination for retinopathy of prematurity. Using a double-blind protocol, 55 premature infants weighing less than 1501 g at birth were selected randomly to receive normal saline or proparacaine Hel 0.5% eye drops as a corneal wetting agent at their initial eye examination. Before, during, and after the procedure, infant stress was evaluated by heart rate, respiration rate, blood pressure, and transcutaneous oxygen saturation. Subjective assessment of the infant's cry intensity and corneal haze also were re­corded. Adequate data were collected on 42 patients. Using analysis of variance and chi­square tests, we found no difference in any of these parameters between the two patient groups. These data suggest that topical anesthetic agents offer no advantage over normal saline eye drops during the examination of premature infants.

R etinopathy of prematurity (RaP) is a potentially blinding disease of newborn

infants, primarily affecting babies with birth weights < 1500 g. Because transscleral cryopexy has been proved to be effective for the treat­ment of certain severe stages of Rap, nurs­ery examinations of at-risk infants currently is considered mandatory.l This usually con­sists of a dilated fundus examination of the posterior pole and retinal periphery using an indirect ophthalmoscope with scleral de-

pression. Although a protocol for the timing and

frequency of ocular examinations was es­tablished by the Cryotherapy for Retinopathy of Prematurity Cooperative Group,2 varia­tions in technique still occur between nurs­eries. These differences may be important because infant stress is a frequent and po­tentially harmful side effect of the examina­tion procedure. In an informal survey of five major neonatal intensive care units in the United States, we found no consensus of opinion on the value of topical anesthesia in reducing infant stress during the examina­tion. Some respondents routinely used topi­cal anesthetic drops, but others thought they made no difference in infant discomfort and often caused corneal clouding. These dif­ferences in nursery practice were found both between institutions and among examiners at the same institution. We therefore de­signed a prospective, randomized, double-

From the Departments of Ophthalmology and Biometry, Medical University of South Carolina, Charleston, South Carolina.

Presented at the 17th Annual Meeting of the American Association for Pediatric Ophthalmology and Strabismus, Montreal, Canada, May 15- 19, 1991.

Supported in part by an unrestricted grant to the Storm Eye Institute from Research to Prevent Blindness, Inc., New York.

Address for reprints: Richard A. Saunders, MD, Storm Eye Institute , 171 Ashley A ve., Charleston, SC 29425-2236.

blind study to assess the effect of topical anesthesia on infant stress and corneal clar­ity during routine examinations for ROP.

Materials and Methods

Fifty-five patients who had not undergone previous ophthalmologic examinations and met additional selection criteria were enrolled in the study. These criteria were birth weight < 1501 g, chronologic age of five to eight weeks, and absence of mechanical ventilation at the time of the examination. The study protocol was approved by the Institutional Review Board of the Medical University of South Carolina. Before the examination, in­formed consent was obtained from a parent or legal guardian.

The infants were assigned randomly to receive proparacaine HCI 0.5% or preserva­tive-free normal saline eye drops as a cor­neal wetting agent during routine eye ex­aminations for ROP. The solutions were received in identical sterile tuberculin sy­ringes from the hospital pharmacy. Neither the examining ophthalmologist nor the nurse assistant knew which agent was being used. The examinations were done either at the bedside for infants in the Neonatal Inten­sive Care Unit or after transfer to a radiant warmer in the Newborn Nursery. Comfort­ing measures, such as nonnutritive sucking, were withheld. Similar monitoring equip­ment was used in all cases. Baseline mea­surements of heart rate, respiratory rate, blood pressure, and oxygen saturation (Sa0

2)

by pulse oximetry were obtained with the infant at rest between one and five hours before the examination and again one minute before commencing the examination. One drop of the unknown solution then was in­stilled OU, and the examination began 30 to 60 seconds later. A Cook-style 3 (44 exami­nations) or wire (11 examinations) infant eyelid speculum was used to separate the eyelids. Scleral depression was obtained, as necessary, using a sterile Calgiswab (Inolex, Glenwood, IL). The cornea was rewetted with the unknown solution at intervals of not more than two minutes during the ex­amination of each eye. Physiologic data were recorded from the monitors one minute after

Volume 25 Number 12 Infants 437

insertion of the eyelid speculum and at two­minute intervals thereafter until the entire examination was complete. A final set of data then were collected with the infant at rest five minutes after the end of the exami­nation. All examinations except 11 were performed by one of the authors; the rest were done by a single retinal specialist know 1-edge able in ROP.

In addition to objective data, the examin­ing ophthalmologist subjectively assessed the clarity of the fundus view with the indi­rect ophthalmoscope. Clarity was recorded on a 0 to 3+ scale with 0 = no haze, 1+ = mild haze, 2+ = moderate haze, and 3+ = marked haze. A single value was assigned for view­ing clarity OU. A nurse-assistant experi­enced in the care of premature infants simi­larly assessed evidence of stress based on the movement of the baby's arms and legs and the cry intensity and duration during the examination. These were recorded on a 0 to 4+ scale with 0 = no crying, 1 + = mild agitation with intermittent crying, 2+ = cries frequently but calms down spontaneously, 3+ = cries frequently and does not calm down spontaneously, and 4+ = cries loudly and constantly with movement of the ex­tremities. The same person assisted with all examinations.

A total of 55 examinations for ROP were performed in which data collection was at­tempted. However, in 13 patients, uninten­tional protocol violations, equipment fail­ure, or inability to obtain one-minute pulse oximetry resulted in their exclusion from the study. The data were analyzed on the remaining 42 infants. Birth weights ranged from 600 to 1400 g (mean, 1093 g). Ad­justed gestational age ranged from 35 to 45 weeks (mean, 36 weeks). There were no complications during the procedure. How­ever, one infant had a cardiorespiratory ar­rest approximately 45 minutes after completion of the examination.

Results

Eighteen infants were examined using nor­mal saline eye drops and 24, using proparacaine HCl. An evaluation of the vital signs (heart rate, respiratory rate, blood pressure, and Sa0

2) appeared to result in unpredictable

438 Annals of Ophthalmology December 1993

Figure. 1 Formula for the heart rate stress index (HRI). The four data points are I minute before the examination, I and 2 minutes after the initiation of the examination, and 5 minutes after the completion of the examination. Similar indexes were used to evaluate changes in the respiratory rate, blood pressure, and arterial oxygen percent saturation.

increases or decreases in response to stress. Thus, averages of these positive and nega­tive changes would not yield meaningful information. It therefore seemed reasonable to take the differences of responses between successive periods and sum the squares of these differences. Then we took the square root of the average of these squared differ­ences to use as an index. This "stress index" formula was used to evaluate each response variable (Figure). Four data points were used, i.e., one minute before the examina­tion, one and two minutes after initiation of the examination, and fi ve minutes after comple­tion of the examination. Analysis of vari­ance using each of these indexes yielded no significant difference between either cor­neal wetting agent and any stress-related variable (Tables I-III), Although fundus clarity scores showed more haze in infants receiving topical anesthesia compared with normal saline eye drops, this difference was not statistically significant (Table IV). Us­ing the Hotelling J'2 test, both groups were found to be comparable with regard to birth weight, current weight, estimated gestational age, sex, and race,

Discussion

The desirability of reducing potentially painful stimuli in premature infants has recently been reviewed. 4 Based on studies of ana­tomic development, it appears that prema­ture infants are capable of experiencing pain after 24 weeks' gestation. 5 Behavioral changes associated with pain include movement of the extremities, facial grimacing, crying, and other more complex behavioral responses. In addition, painful stimuli cause physi­ologic derangements that potentially jeop-

Table I Stress Index Means for Heart Rate (HR) and Respiratory Rate (RR)

HR Index RR Index

Proparacaine Hel (n = 23) Saline (n = 18) Significance

20.8 23 .0

P = .45

14.8 16.2

P = .57

Table II Stress Index Means for Blood Pressure

Systolic Index Diastolic Index

Proparacaine Hel (n = 18) Saline (n = 13 ) Significance

13.6 11.7

P = .50

14.0 12.2

P = .58

Table III Stress Index Means for Arteri al Oxygen Percent Saturation (Sa0

2)

Proparacaine Hel (n = 20) Saline (n = 15) Significance

Table IV Subjective Assessments

Cry Factor

Sa02

Index

6.2 6.8

P = .74

Corneal Haze

Proparacaine Hel (n = 24) 2.63 0.96 Saline (n = 18) 2.44 1.22 Significance chi-square = 2.59, chi-square = 3.28,

(not significant) (not significant)

ardize an infant's health. An alteration in pulse rate (typically bradycardia), elevation in blood pressure, and reduction in Sa0

2 are

common. These physiologic indicators also were shown to correlate with the release of catecholamines and other adrenal stress hor­mones. Administration of local anesthesia before newborn circumcision, however, is effective in eliminating or reducing these responses. 6

Our data suggest that the use of topical anesthetic agents in lieu of normal saline eye drops is of little or no value in reducing infant stress during eye examinations for ROP. In so far as possible, we standardized our technique to limit the number of con­founding variables. The same nurse as

sistant was used in all cases, and a single ophthalmologist examiner conducted all but 11 tests. Nevertheless, we must ask whether our conclusions are warranted. A number of alternative explanations for the absence of differences between saline and anesthetic groups are possible.

First, our indicators of infant stress could be insufficiently sensitive or our cohort of patients might be too small to detect differ­ences between the study groups. Our mea­sures did not include serum stress hormone levels because this requires an invasive pro­cedure (blood drawing) and was shown pre­viously to correlate with changes in vital signs. 7 Also, analysis of our data was com­plex, and other statistical methods might yield different results.

Second, we eliminated 13 patients for unintentional protocol violations, equipment failure, or inability to obtain sufficient data during the examination. Because movement of the extremities interferes with obtaining pulse oximetry, 8 it is possible that elimina­tion of more active, stressed infants from the study biased our results. However, analysis of available data from excluded patients did not suggest higher stress levels. Birth weights, gestational ages, and subjective assessments also were similar in these infants.

Third, although we believe the use of anesthetic drops completely eliminated topical sensation during the examination procedure, we still noted evidence of stress in all in­fants. Physical restraint, insertion of an eyelid speculum, scleral depression, and indirect ophthalmoscopy are all sources of discom­fort that are not readily eliminated. These stimuli could have masked a small, benefi­cial effect from topical anesthetic drops.

This study was not directed primarily to­ward evaluating corneal clarity. We did not, however, find evidence to support the development of epithelial clouding after in­stillation of proparacaine Hei. Our haze score would have measured corneal clarity

Volume 25 Number 12 Infants 439

and the clarity of the ocular media, but the latter would not be expected to change dur­ing a brief examination. Nevertheless, any subjective assessment of corneal clarity is inherently imprecise and makes definitive conclusions difficult. It is also possible that the adverse effects of proparacaine Hel would be seen only during prolonged, difficult ex­aminations.

Although we expected to find a beneficial effect from using topical anesthetic eye drops during examinations for ROP, our data did not confirm this belief. In the absence of a documented benefit, saline eye drops are more readily available and less costly than are topical anesthetic drops. We did not demonstrate that proparacaine Hel has an adverse effect on corneal clarity, but we found no convincing evidence to justify its routine use. Perhaps corneal anesthesia should be reserved for those premature infants whose parents request it or who are found to be particularly unstable in whom even minimal reductions in examination-induced stress might be important.

References

1. Cryotherapy for Retinopathy of Prematurity Cooperative Group: Multicenter trial of cryotherapy for retinopathy of prematurity: One year outcome-structure and function. Arch Ophthalmol1990; 108: 1408-1416.

2. Cryotherapy for Retinopathy of Prematurity Cooperative Group: Multicenter trial of cryotherapy for retinopathy of prematurity preliminary results. Arch Ophthalmol 1988; 106:471-479.

3. Saunders RA: A speculum for small infants. J Pediatr Ophthalmol Strabismus 1981; 18:57-58.

4. Anand KJS, Phil D, Hickey PR: Pain and its effects in the human neonate and fetus. N EnglJ Med 1987;317:1321-329.

5. Franck LS: Physiology and management of pain in the neonate. Presented at the 6th Annual National Conference of Neonatal Nursing, San Diego, February 1988.

6. Williamson PS, Williamson ML: Physiologic stress reduction by a local anesthetic during newborn circumcision. Pediatrics 1983;71 :36-40.

7. Johnston CC, Stevens B: Pain assessment in newborns. J Perinat Neonatal Nurs 1990;4:41-52.

8. Levene S, Lear GH, McKenzie SA: Comparison of pulse oximeters in healthy sleeping infants. Respir Med 1983;83:233-235.