Introduction
Strabismus, an ocular misalignment, affects approximately 3%–5% of children worldwide, and surgical correction remains one of the most effective therapies [1]. The frequency of strabismus correction surgery in the pediatric population increased by 38% from 2000 to 2013, which was attributed to improved awareness of the functional and psychological benefits of correcting strabismus [2].
Strabismus correction surgery has become the most common ophthalmic surgery in children, and pediatric general anesthesia is generally performed because of patient non-cooperation. Ophthalmic surgery is a well-known risk factor for emergence agitation (EA) following pediatric general anesthesia [3,4]. In addition to negative postoperative behaviors, the development of EA in pediatric patients often requires extra medical staff and results in prolonged post-anesthesia care unit (PACU) stays [5]. Thus, identifying optimal methods to prevent EA without increasing adverse events during recovery in the PACU is essential.
One previous study demonstrated that after ophthalmic surgeries involving covering the operated eyes with patches or applying ointments, visual disturbances play an important role in EA [6]. Our previous study also demonstrated that visual preconditioning by covering the eyes to be operated on the day before surgery can reduce EA incidence [5]. Additionally, early binocular vision has been reported to aid in the recovery of binocular visual function after surgery [7].
Following ophthalmic surgeries that involve small incisions with a low incidence of bleeding and surgical site infections, eye shields are typically applied as dressings after incision closure to prevent patients from touching their operated eyes [8,9]. However, the use of sterilized medical gauze dressings disturbs vision and may confuse and disorient children, increasing the risk of EA and exacerbating the risks of suture dehiscence and accidental removal of intravenous catheters [10,11]. Therefore, a light-transmitting eye shield for wound dressings may offer significant benefits in the postoperative care of pediatric ophthalmic patients. In the present study, we aimed to investigate the impact of light-transmitting eye shields versus traditional medical gauze eye shields in preventing EA in pediatric patients undergoing bilateral strabismus surgery.
Materials and Methods
Study design
This prospective, single-center, randomized controlled trial was conducted from November 2018 to October 2019 and included a blinded outcome analysis. The study was approved by the Institutional Review Board of Zhongshan Ophthalmic Center, Sun Yat-sen University (2018KYPJ105) and preregistered at the Chinese Clinical Trial Registry (Identifier No. ChiCTR1800018848; October 14, 2018). The Consolidated Standards of Reporting Trials (CONSORT) statement was also adhered to for this study, and the CONSORT flow chart is presented in Fig. 1. This study was conducted in accordance with the ethical principles of the Helsinki Declaration 2013. Written informed consent was obtained from all participants during the screening visit. The full trial protocol is presented in Supplementary Material 1.
Participants
Children aged 3–7 years with American Society of Anesthesiologists physical status classifications I or II undergoing bilateral strabismus surgeries were enrolled in this study. The exclusion criteria were (1) allergy to medical gauze or plastic materials, (2) receiving any sedative drugs within 72 h before surgery, (3) any neuropsychiatric disorders, (4) developmental delay, (5) acute upper respiratory tract infection, (6) history of ophthalmic surgery, or (7) the parent refused to participate.
Randomization and allocation concealment
All eligible patients were randomly assigned at a ratio of 1:1 to either the intervention (light-transmitting eye shield group, LT group) or control group (medical gauze eye shield group, MG group) using block randomization (block size, 4). An independent research staff member not involved in the study prepared a computer-generated random number table using SAS® version 9.4 (SAS Institute Inc.). The randomized numbers were sealed in sequentially numbered opaque envelopes. On the morning of the surgery, an independent research nurse who was not involved in patient care or data collection opened the envelope to reveal the group allocation before the administration of anesthesia.
Because of the nature of the intervention, only the data processing staff (those responsible for data collection and analysis) were blinded to the group allocation. The participants, their guardians, and the nurses who were responsible for managing the dressings at wound closure completion could not be blinded.
Preoperative evaluation
On the morning of surgery, parents were given a short questionnaire to provide demographic information (including age, height, weight, sex, and family history) and the medical history (including history of ophthalmic surgery) of their child in the preoperative holding area. Preoperative anxiety was evaluated using the modified Yale Preoperative Anxiety Scale (m-YPAS) [12]. These evaluations were conducted by a trained research nurse who was not otherwise involved in the study.
Anesthesia management
All patients fasted for 6 h for solids and 4 h for clear liquids and received no premedication before anesthesia. Upon arrival at the operating room, participants were routinely monitored for the following: electrocardiography, heart rate (HR), non-invasive blood pressure, pulse oxygen saturation (SpO2), and capnography. Anesthesia was induced with sevoflurane inhalation via a face mask by gradually increasing the concentration of up to 8% vol along with 100% oxygen. The Pediatric Anesthesia Behavior (PAB) score was used to assess the degree of mask acceptance by an independent anesthesiologist who was blinded to the group assignment [13]. A PAB score of 3 was considered unsatisfactory, and propofol (1 mg/kg) was intravenously injected as a rescue method for rapid induction. After loss of consciousness, fentanyl (1 μg/kg), cisatracurium (0.1 mg/kg), and penehyclidine (0.01 mg/kg) were subsequently administered for induction. A laryngeal mask airway (LMA; The Laryngeal Mask Company Limited) was inserted after achieving a sufficient depth of anesthesia. Ventilation was applied in volume-controlled mode with a tidal volume of 8–10 ml/kg. The respiratory rate was adjusted to maintain end-tidal carbon dioxide (EtCO2) between 35 and 45 mmHg (1 mmHg: 0.133 kPa). A combination of dolasetron (0.35 mg/kg, maximum dose of 12.5 mg) and dexamethasone (0.1 mg/kg, maximum dose of 5 mg) was administered for antiemetic prophylaxis. Anesthesia was maintained with sevoflurane to reach an end-tidal concentration of 1–1.5 minimal alveolar concentration. All patients received topical anesthesia with 0.5% proparacaine hydrochloride at the beginning of the surgery, supplemented with nonsteroidal anti-inflammatory drugs (NSAIDs; intravenous [IV] flurbiprofen axetil, 1 mg/kg) at the completion of the surgery to prevent postoperative pain. At the end of surgery, sevoflurane was discontinued, and patients with an LMA were transferred to the PACU for synchronized intermittent mandatory ventilation. The LMA was then removed by a skilled pediatric anesthesiologist in the PACU, ensuring that the patient was awake and responsive to verbal commands after using a combination of neostigmine (0.02 mg/kg) and atropine (0.01 mg/kg) to reverse residual muscle relaxation.
Postoperative wound care protocol
The light-transmitting eye shields (Tanbu Xinyi Plastic Co.), which are made of perforated polyethylene with multiple evenly distributed light-transmitting holes on the surface, were preserved in vacuum packaging after sterilization with pressure steam before use (Fig. 2). Upon completion of the surgery, an antibiotic ointment and either sterilized light-transmitting or medical gauze eye shields were applied to the eyes for additional protection. All patients in both groups were asked to return for a postoperative visit the next day, during which the ophthalmologist in charge thoroughly assessed the operated eyes to verify wound healing progress and an absence of any infection indicators. Depending on recovery outcomes, the ophthalmologist either opted to retain or remove the eye shields.
After the eye shields were removed, the ophthalmologist provided comprehensive postoperative care instructions encompassing the correct use of eye drops, ointments, and other medications as well as advice on safeguarding the eyes in daily life to prevent external injuries.
Postoperative care
The patients were continuously monitored for HR and SpO2 in the PACU and cared for by PACU nurses. An oxygen flow rate of 2 min/L was administered through a mask until the patient recovered consciousness. Behavior on emergence was measured every 5 min in the PACU until discharge. We evaluated the incidence of EA using Aono’s four-point scale and further assessed the severity of EA using the Pediatric Anesthesia Emergence Delirium (PAED) scale [14,15]. EA was defined as a score ≥ 3 on Aono’s four-point scale. In cases where EA occurred, the severity was further quantified using the PAED scale. A PAED score ≥ 16 indicated severe agitation, for which patients were administered an additional dose of propofol (10–20 mg IV) or a repeat dose of propofol within 3 min as necessary. The procedure for evaluating and managing EA is detailed in Supplementary Fig. 1. Postoperative pain intensity was assessed using the Face, Legs, Activity, Cry, and Consolability (FLACC, five items with a maximum score of 10) scale every 10 min in the PACU [16]. Another dose of flurbiprofen axetil (1 mg/kg) was intravenously administered for a FLACC score ≥ 4, and fentanyl (0.5 µg/kg) was administered as rescue if the FLACC score remained ≥ 4. Severe and persistent postoperative nausea and vomiting (PONV) was treated with droperidol (10 μg/kg IV) as necessary.
All patients were assessed every 15 min starting on arrival in the PACU and were transferred from the PACU to the day surgery ward when a score of 12 points was reached on the physiological criteria-based discharge scoring system [17]. In the day surgery ward, patients were considered safe for home discharge once they achieved a score of 9 or 10 on the post-anesthetic discharge scoring system (PADSS) [18].
Outcome measures
The primary outcome was the incidence of EA, defined as a score ≥ 3 on Aono’s four-point scale (Supplementary Table 3). The secondary outcomes included the peak PAED score, and the frequency of propofol rescue administration for severe agitation (PAED score ≥ 16, Supplementary Table 4). We also collected data on the time to LMA removal (from discontinuation of sevoflurane to LMA removal), time to emergence (from discontinuation of sevoflurane to eye opening or purposeful movement in the PACU), PACU recovery time (from arrival in the PACU to time of a score of at least 12 points in the physiological criteria-based discharge scoring system), postoperative pain (FLACC score), and occurrence of any adverse events. Outcome measurements were conducted in the PACU and assessed by an independent nurse who was not involved in the study.
Stereopsis and best-corrected visual acuity (BCVA) were examined on postoperative day 1. The BCVA measured on the Landolt chart was converted into the logarithm of the minimum angle of resolution [19]. Stereopsis was evaluated using the Titmus stereo test (TST), which was performed at a standard viewing distance of 40 cm under correction. The results for the TST was expressed in “seconds of arc,” and converted to logarithms for statistical evaluation [20]. Patients were followed up for indications of surgical site infections, including conjunctivitis and endophthalmitis, within 1 month of surgery.
Statistical analysis
The sample size was calculated based on the incidence of EA using PASS (version 15.0; NCSS). A previous study reported that the incidence of EA was 80% in children undergoing ophthalmic surgery under sevoflurane anesthesia [21]. We considered a 50% reduction in the incidence of EA between the two study groups to be clinically relevant. Therefore, a sample size of 27 patients per group would have a power of 90% to reject the null hypothesis of equal proportion using a two-sample, two-sided equality test at the 0.05 significance level. Considering a dropout rate of 20%, at least 70 patients were required.
The outcomes were analyzed according to the intention-to-treat principle in the full analysis set. Data analyses were performed using SPSS Statistics® version 26.0 (IBM Corp.) Descriptive analysis was used to assess the baseline characteristics of the patients in each group. Data were inspected and assessed for distribution according to the Kolmogorov–Smirnov normality analysis. Continuous variables are presented as the mean ± standard deviation (SD) or median (Q1, Q3) and were analyzed using an independent t test or the Mann–Whitney U test, respectively. The median difference was calculated using the Hodges–Lehmann estimate. Categorical variables are expressed as numbers (percentages, %) and were compared using Pearson’s χ2 test or Fisher’s exact test, as appropriate. Logistic regression analysis was employed for univariable and multivariable analyses to explore the relationships between patient characteristics and the presence of EA. The potential variables included in the multivariable model presented a two-tailed P value ≤ 0.05 in the univariable analyses. The results are presented as the odds ratio (OR) and 95% CI. Statistical significance was set at two-sided P < 0.05. We present the Benjamini–Hochberg (BH) critical value for multiple testing corrections of primary and secondary outcomes. The false discovery rate was set to 0.05. Variables with P values < P*, where P* was the largest P value that was smaller than the BH critical value, were considered statistically significant.
Results
Of 80 participants assessed for eligibility, 10 were excluded for the following reasons: 2 underwent unanticipated monocular surgery, 4 experienced unexpected upper respiratory tract infections, and 4 received additional sedative medications because they were unable to cooperate with the establishment of IV access in the preoperative holding area. Finally, 70 patients (median [Q1, Q3] age, 6.0 [4.0, 6.0] years; 38 boys [54.3%] and 32 girls [45.7%]) were randomized to the intervention and control groups. All 35 patients in each group completed the study and were included in the final intention-to-treat analysis (Fig. 1). The baseline demographic and clinical characteristics of the 70 participants according to group are provided in Table 1.
A significant reduction in the median (Q1, Q3) peak score of the Aono’s four-point scale was found in the LT group compared to the MG group (2.0 [1.0, 2.0] vs. 2.0 [1.0, 3.0]; median difference: −1.00, 95% CI [−1.00 to 0], P = 0.024; BH critical value = 0.050) (Table 2). Even after adjusting for age and sex, those in the LT group were less likely to develop EA than those in the MG group (5 of 35 children [14.3%] vs. 15 of 35 children [42.9%]; adjusted OR, 95% CI: 0.28, 0.08–0.94; P = 0.040) (Table 3).
As described in Table 2, the number of agitated patients with a peak PAED score ≥ 16 was higher in the MG group than in the LT group (OR: 5.71, 95% CI [1.14–28.75], P = 0.022, BH critical value = 0.038). Among children who were severely agitated during anesthesia emergence (PAED score ≥ 16), 3 (8.6%) and 11 (31.4%) in the LT and MG groups, respectively, received propofol rescue (OR: 4.89, 95% CI [1.23–19.47], P = 0.017, BH critical value = 0.025) (Table 2).
None of the patients experienced moderate-to-severe postoperative pain as no significant difference was found in the peak FLACC score in the PACU between the two groups. Other in-hospital complications, including PONV, pharyngalgia, and dizziness, were comparable between the groups. Notably, none of the patients developed surgical site infections, including either conjunctivitis or endophthalmitis, within one month of surgery (Supplementary Table 1).
The emergence time was slightly but significantly prolonged in the MG group compared to the LT group (P = 0.029), whereas the LMA removal time and PACU recovery time were not statistically different between the two groups (Supplementary Table 1). In terms of changes in vision, neither the BCVA nor stereopsis in the TST were different between the two groups before or after strabismus surgery (Supplementary Table 2).
Discussion
In this study, we found that the application of light-transmitting eye shields for wound dressing could reduce EA incidence in preschool children undergoing bilateral strabismus surgery under sevoflurane anesthesia without influencing the recovery of vision or incidence of surgical site infections. Our findings confirm the feasibility of using light-transmitting eye shields for dressing the operated eyes after pediatric bilateral strabismus surgery.
Although the underlying mechanism of EA remains unclear, pediatric ophthalmic surgery is widely associated with a high incidence of EA [22]. A previous study revealed that the EA incidence in children undergoing cataract surgery under sevoflurane anesthesia can be as high as 80% [21]. EA involves crying, agitation, and confusion during emergence [23]. Because the eyes are covered with patches after ophthalmic procedures, postoperative visual disturbances contribute to alterations in the children’s awareness of the surrounding environment and possibly induce EA [24]. To address this factor, our previous study corroborated the potential role of visual preconditioning, a simple non-pharmacological intervention, in reducing EA incidence in preschool children undergoing ophthalmic surgery [5]. By preemptively familiarizing children with visual input before surgery, visual preconditioning aims to mitigate sensory shock caused by postoperative visual disturbances, potentially reducing the incidence of EA.
Strabismus surgery, which is common in preschool children, typically involves small conjunctival incisions with minimal bleeding [1]. Using a gentle technique to avoid excessive pressure on the eye, postoperative patching usually lasts from a few hours to a full day [25]. Postoperative patching has also been reported to protect against complications such as endophthalmitis [26]. However, light-transmitting eye shields made from perforated polyethylene are increasingly being used to protect the eyes after minimally invasive ophthalmic surgeries, such as laser-assisted in situ keratomileusis. These eye shields are designed to allow a certain degree of visual input through small holes to potentially reduce psychological distress and mitigate certain aspects of visual disturbance. The “instant vision” generated by the use of a visual dressing on the operated eye not only provided better orientation and improved vision immediately after surgery but also significantly reduced patient hospitalization anxiety [27]. In terms of optimizing light transmission, light-transmitting eye shields may help reduce visual disturbances and, consequently, improve both patient comfort and outcomes. In future studies, we plan to further explore the potential benefits of light-transmitting eye shields for reducing EA occurrence in pediatric ophthalmic surgeries.
The psychological issues surrounding strabismus surgery have gained increased attention in recent years. Many patients may experience negative social effects because of ocular deviation, including negative reactions from others, difficulties with socialization, and impaired employment prospects. Preoperative anxiety is a significant risk factor for EA [28], with 24% of patients with strabismus reportedly experienced clinical levels of anxiety before surgery [29]. In the present study, to alleviate preoperative anxiety, the children were permitted to be accompanied by their parents in the preoperative holding room until anesthesia induction. This approach helped minimize preoperative anxiety, as reflected in the comparable m-YPAS anxiety scores between the groups.
Considering that strabismus surgery is a minimally invasive procedure with minimal associated postoperative pain, we used a combination of sufficient topical anesthesia and an additional dose of flurbiprofen axetil (1 mg/kg) for pain management [30]. This approach resulted in satisfactory pain control, as reflected by mild postoperative pain scores on the FLACC scale and an absence of additional doses of fentanyl as a rescue analgesic in our study. Based on these findings, we can reasonably exclude postoperative pain as a major contributor to EA in our study. Considering that PONV has long been identified as one of the major causes of delayed discharge in patients undergoing strabismus surgery, the lower rate of PONV in our results is also noteworthy [31]. One potential explanation is the use of a well-managed multimodal strategy with a 5-hydroxytryptamine receptor antagonist and dexamethasone during anesthesia induction to prevent PONV at our center [32]. In addition, no complaints were reported by the patients regarding the use of medical gauze or light-transmitting eye shields, indicating good patient acceptability of both interventions.
Although no statistically significant differences were observed, our data suggest that patients with a history of ophthalmic surgery or higher PAB scores (which reflect reduced mask acceptance) may have an elevated risk of developing EA. Notably, both factors were more prevalent in the medical gauze eye shield group, which may have contributed to the observed between-group differences. These findings highlight the need for further investigation to confirm the role of these factors in predicting EA.
Our study has some limitations. First, we used a single-center design focusing on pediatric patients undergoing ophthalmic surgery, which is a recognized risk factor for EA. Therefore, the external validity of our findings may be limited. Second, although preoperative parental accompaniment can help alleviate preoperative anxiety in children, the anxiety level of the parents themselves may influence the occurrence of EA [33]. Further research is needed to explore this relationship. Third, the PAED scale, which includes an item on eye contact, may have limited accuracy due to the bilateral eye shields worn by the patients. This may have influenced the accuracy of the EA level measurements. Nevertheless, the PAED scale remains a widely accepted tool for assessing EA in pediatric patients after ophthalmic surgeries [34,35]. Additionally, the sample size calculation was based on our previous study, which reported an incidence of 80% for EA in children undergoing ophthalmic surgery with sevoflurane anesthesia. However, the observed incidence of EA in this study was lower, at 14.3% in the light-transmitting and 42.9% in the medical gauze eye shield groups. This deviation may be due to the more rigorous composite scoring method used for EA in the present study. Despite the small sample size, the statistical power of our primary outcome was > 0.9, and a significant difference was observed between the two groups.
In conclusion, this randomized clinical trial showed that the use of light-transmitting eye shields as a simple, safe, and non-pharmacological intervention may effectively reduce the occurrence of EA in preschool children undergoing bilateral strabismus surgery under general anesthesia without disturbing vision recovery or increasing the incidence of surgical site infections. These findings support further research exploring the role of visualization in other nursing care and health service settings to optimize EA prevention.
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