Penehyclidine mitigates intraoperative oculocardiac reex and postoperative nausea and vomiting in the patients with strabismus surgery: a prospective, randomized, double-blinded comparison

PONV is one of the most frequent complications following anesthesia and strabismus surgery. Penehyclidine, an anticholinergic, is widely and preoperatively used for reducing glandular secretion in patients. This study investigated the effect of penehyclidine on PONV in strabismus surgery. In this prospective, randomized, and double-blinded study, patients of strabismus surgery under general anesthesia were randomly assigned to either penehyclidine (n = 114) or normal saline (NS, n = 104) groups. Penehyclidine was administrated immediately after anesthesia induction, and patients treated with NS served as controls. PONV was investigated within 48 h after surgery. Intraoperative OCR was also recorded. effective protector against intraoperative oculocardiac reex and postoperative nausea and vomiting in the patients with strabismus surgery. PONV incidence in strabismus surgery, we found 54.8% of overall PONV incidence in normal saline group in this investigation. We also found that the patients showed a signicant higher PONV incidence within 6 h after strabismus surgery. Notably, we demonstrated that administration of penehyclidine after anesthesia induction pronouncedly attenuated PONV incidence in patients with strabismus surgery. The severity of PONV was mitigated and the PONV incidence was signicantly reduced in the underaged and adult male patients as well as in the adult female patients following penehyclidine administration.

Penehyclidine mitigates intraoperative oculocardiac re ex and postoperative nausea and vomiting in the patients with strabismus surgery: a prospective, randomized, double-blinded comparison Background Strabismus surgery is a common ophthalmic surgical procedure, especially in pediatric patients.
Intraoperative oculocardiac re ex (OCR) and postoperative nausea and vomiting (PONV) are the most frequent complications following anesthesia and strabismus surgery (1,2). OCR, also known as the Aschner re ex, is de ned as a decrease in heart rate (HR) by greater than 20% following eyeball pressure or traction of the extraocular muscles (3). The incidence of OCR ranges from 14 ~ 90% during strabismus surgery (4). The re ex commonly results in bradycardia and associates with reduced arterial pressure, arrhythmia, asystole, and even cardiac arrest (5). As for PONV, the incidence has been shown as high as 38 ~ 68.2% in pediatric and 45.2% in adult patients with strabismus surgery (6)(7)(8)(9). Besides increasing unpleasant experience and delaying discharge, PONV can lead to postoperative complications that include uid and electrolyte imbalances, suture tension, esophageal tear, increased intracranial pressure, and pulmonary aspiration (1,10). Therefore, both OCR and PONV remain main concerns in strabismus surgery (11).
Penehyclidine is an anticholinergic agent with an elimination half-life over 10 h. As described a selective blocker of type 1 and type 3 muscarinic acetylcholine receptors, penehyclidine is widely used in preoperative medication mainly for reducing glandular secretion (12,13). Moreover, penehyclidine is used to reverse organic phosphorus pesticide poisoning (12). Interestingly, Type 3 and type 5 muscarinic acetylcholine receptors have been shown playing roles in the development of motion sickness, a risk factor of PONV (14). Moreover, type 1 muscarinic acetylcholine receptors present at high levels in vestibular system, and anticholinergics block cholinergic transmission from the vestibular nuclei to higher CNS centers as well as from the medullary reticular formation to the vomiting center (15). When taken into account that the muscarinic acetylcholine receptors are involved in the development of PONV through multiple mechanisms, it is possible, therefore, that penehyclidine may play a role in preventing patients from PONV in strabismus surgery. As penehyclidine weakly blocks type 2 muscarinic acetylcholine receptors, its possible effect on OCR during strabismus surgery is also worth exploring.
This prospective, randomized, and double-blinded study was designed to identify whether penehyclidine functions as an effective protector against intraoperative oculocardiac re ex and postoperative nausea and vomiting in the patients with strabismus surgery. guidelines. The patients with obvious vital organ diseases, motion sickness, previous PONV history, smoking, medication with steroids or proton pump inhibitors, or did not cooperate with the investigation were excluded. All cases were prospectively and randomly divided into penehyclidine group and normal saline group. The primary outcome for our study was the effect of penehyclidine on the incidence of nausea and vomiting during the rst 48 hours postoperatively. The secondary outcome was the possible effect of penehyclidine on the occurrence of OCR during surgery. Anesthesia recovery. Propofol and remifentanil infusion were discontinued as surgery completed and all patients were spontaneously recovered without use of neostigmine and atropine to reverse residual muscle relaxant. During the recovery period, patients who complained of severe pain were treated with parecoxib at a dose of 1.0 mg·kg − 1 with an upper limit to 40 mg and patient who complained of severe PONV was rescued by granisetron at a dose of 50 µg·kg − 1 with an upper limit to 3.0 mg.

Patients
Penehyclidine treatment. Simple randomization was employed by lottery method and the patients were randomly allocated into penehyclidine or normal saline groups with equal chance. Penehyclidine was administrated immediately after anesthesia induction, and the equal volume of normal saline served as controls. Penehyclidine was administrated with the dosage of 10 µg·kg − 1 and with an upper limit to 0.5 mg. The lots were prepared by a resident and penehyclidine or normal saline was given by an attending doctor according to the lot drawn from the envelope. Patients were unaware of the treatment groups.

Postoperative nausea and vomiting (PONV)
Nausea and vomiting were investigated within 48 h after strabismus surgery by a resident who was blinded to the treatment of penehyclidine or normal saline. The occurrence of PONV was recorded by interviewing with the patients or the legal guardians of children patients at 2, 6 and 24 h after surgery in the hospital and by a telephone call after discharge (48 h). The severity of PONV was scored using a numeric rank scoring system according to previous method (16). The scoring system was composed of four levels of PONV: 0, no nausea or vomiting; 1, nausea but no vomiting; 2, vomiting once or twice; 3, vomiting on more than two occasions. PONV was expressed as incidence (percentage) of patients.
The patients with severe (scored at 3) and intolerable PONV were treated with antiemetics granisetron at a dose of 50 µg·kg − 1 with an upper limit to 3.0 mg.
Oculocardiac re ex (OCR) OCR was de ned as a decrease in heart rate (HR) by greater than 20% following eyeball pressure or traction of extraocular muscles(3). Once OCR was observed, the operation was paused to relieve OCR, and the operation restarted when heart rate returned to baseline value. If HR did not recover in 30 s or severe bradycardia (HR < 60 bpm for aged 3 ~ 7 years, and < 50 bpm for over 7 years old) sustained for over 10 s, intravenous atropine 10µg·kg − 1 with an upper limit to 0.5 mg was administered.

Sample size estimation and statistical analysis
Pre-study power analysis indicated that 94 cases in each group were required based on 50% incidence of PONV following strabismus surgery without antiemetics and 30% with penehyclidine (α = 0.05 and 1-β = 0.8). With an anticipation of 10% dropout, at least 105 cases in each group were required for randomization.
Data analysis was performed using IBM SPSS software, version 24.0 (IBM Corp., Armonk, NY, USA). Continuous variables conforming to normal distribution were expressed as mean ± standard deviation and Student's two-tailed unpaired t-test was used for comparison between two groups. Non-normal continuous variables were expressed as median (interquartile range, IQR) and Mann-Whitney U test was used for comparison between two groups. Categorical variables were expressed as number and percentage, and analyzed by Fisher's exact test. For ranked data, Mann-Whitney U test was used for comparison between two groups. Subgroup analysis was performed to explore whether the anti-emetic effect of penehyclidine is in uenced by gender and age. Univariable logistic regression was used to identify the potential risk factors that might affect PONV incidence, and the factors with P < 0.10 were included in the multivariable logistic regression. A P value < 0.05 was considered as signi cant.

Patients in the investigation
From July 20, 2019 to November 1, 2019, 228 patients were randomly allocated to penehyclidine or normal saline groups. Among them, 10 patients dropped out due to lost contact or due to using inhalation anesthesia induction in pediatric patients who did not cooperate with intravenous induction. Therefore, 218 patients were nally analyzed. The consort ow diagram was shown in Fig. 1.
Between penehyclidine and normal saline control groups, the patients showed comparable general characteristics, including age, gender, body weight, body height, duration of surgery, duration of anesthesia, unilateral or bilateral operation of eye, and numbers of operated muscles (Table 1).

Administration of penehyclidine reduces overall incidence of PONV in strabismus surgery
To investigate the effect of penehyclidine on PONV in patients with strabismus surgery, we recorded the occurrences of PONV within 48 h after surgery. As shown in Fig. 2A, PONV incidence was 30.7% (35/114) in patients treated with penehyclidine and 54.8% (57/104) in patients treated with normal saline. Therefore, penehyclidine signi cantly reduced PONV incidence by 44.0% (P < 0.001).

Administration of penehyclidine mitigates the severity of PONV in strabismus surgery
The effect of penehyclidine on the severity of PONV after strabismus surgery was analyzed. The severity of PONV was scored using a numeric rank scoring system which ranging from 0 to 3, wherein 0 represented no nausea and no vomiting and 3 represented vomiting on more than two occasions (16).
Notably, penehyclidine administration signi cantly mitigated the severity of PONV within 48 h after surgery as compared to normal saline controls (P < 0.001) (Fig. 2B).
4. The anti-PONV effect of penehyclidine over time

Penehyclidine shows pronounced protection from PONV within 6 h after strabismus surgery
The effect of penehyclidine on PONV incidence over time postoperatively were similarly observed It was found that following penehyclidine administration, the incidences of PONV were 25.4%, 18.4%, 5.3% and 0% in the periods of 0 ~ 2, 2 ~ 6, 6 ~ 24 and 24 ~ 48 h after strabismus surgery. Notably, penehyclidine administration signi cant reduced PONV incidence by 37.0% and 48.2% in the periods of 0 ~ 2 and 2 ~ 6 h after surgery, respectively, when compared to the time-matched normal saline-treated controls (P < 0.05 or 0.01) (Fig. 3). No signi cance of PONV incidence was observed after 6 h post-surgery between penehyclidine and its normal saline control group. The data suggest a pronounced protection of penehyclidine from PONV within 6 h after strabismus surgery.

The anti-emetic effect of penehyclidine is affected by gender and age of patients
To explore whether the anti-emetic effect of penehyclidine is in uenced by gender and age, patients were divided into 4 subgroups according their genders (male and female) and ages (underage of 3 ~ 17 and adult of 18 ~ 65 years old). As shown in Fig. 4, penehyclidine signi cantly reduced the incidence of PONV in male patients aged 3 ~ 17 and 18 ~ 65 years old, respectively, when compared to the age-and gendermatched normal saline controls (P < 0.01 or 0.05). Female patients aged 18 ~ 65 years old also showed signi cantly reduced PONV incidence following penehyclidine administration compared to their gender and age-matched normal saline controls (P < 0.05). No difference was found in female patients aged 3 ~ 17 years old. The data indicate that gender and age impacts the penehyclidine-induced protection from PONV after strabismus surgery.

Penehyclidine independently reduces PONV risk in patients with strabismus surgery
To exclude the confounding factors those potentially interfere the anti-PONV effect of penehyclidine, logistic regression analysis was conducted. Multivariable logistic regression showed that operation with 4 ~ 6 muscles independently increased PONV risk in strabismus surgery (Odds Ratio, 3.553; 95% con dence interval, 1.909 ~ 6.615; P < 0.001). Gender, age, occurrence of OCR, duration of surgery, and duration of anesthesia were not associated with PONV in this study. Most importantly, the logistic regression showed that penehyclidine was an independent protective factor (Odds Ratio, 0.330; 95% con dence interval, 0.178 ~ 0.609; P < 0.001) that reduced PONV risk in patients with strabismus surgery ( Table 2). Univariable logistic regression was performed rst and the factors with P < 0.10 were included in the multivariable logistic regression. As a result, age, extraocular muscles operated, occurrence of oculocardiac re ex and use of penehyclidine were selected for multivariable logistic regression. CI, con dence interval; EOM, extraocular muscles.
7. Administration with penehyclidine reduces incidence and severity of oculocardiac re ex (OCR) during strabismus surgery OCR, de ned as a decrease in heart rate by greater than 20% following eyeball pressure or traction of extraocular muscles, is a frequent and serious complication during strabismus surgery. Interestingly, it was found that a 25.7% lower OCR incidence in the patients received penehyclidine administration (66/114) than that in the normal saline control patients (81/104) during strabismus surgery (P < 0.01) (Fig. 5A).
Severe OCR, as indicated by sustained decrease of heart rate greater than 20% of basal value or severe bradycardia, may cause hypotension and even cardiac arrest. Atropine is usually used to rescue severe OCR. Notably, signi cant reduction of OCR patients needing atropine rescue was observed in penehyclidine group (51/66) compared to that of OCR patients in normal saline group (73/81) (P < 0.05) (Fig. 5B). The data indicate that penehyclidine administration signi cantly mitigated the severity of OCR during strabismus surgery.
In line with the ndings in OCR severity, we also found that penehyclidine administration signi cantly attenuated the strabismus surgery-induced decrease of heart rate by 19.0% in the patient with OCR (P < 0.05) (Fig. 5C).

Penehyclidine shows no obvious negative effect on anesthesia recovery
To investigate whether penehyclidine administration after anesthesia induction will impact anesthesia recovery, we analyzed the time to extubation, time stay in post-anesthesia care unit, use of antiemetics and analgesics, occurrence of severe dry mouth, facial ush, and drowsiness. As shown in Table 3, no signi cant difference was detected between penehyclidine and normal saline groups in all the indexes mentioned above. The ndings suggest that penehyclidine did not delay anesthesia recovery or increase possible adverse effects. Occurrence of post-operative antiemetic or analgesic requirement, severe dry mouth, facial ushing and drowsiness are expressed as numbers and percentages (%) of patients, and compared by Fisher's exact test between normal saline group and penehyclidine group. Time to extubation and PACU stay time are expressed as medium (IQR) and compared by Mann-Whitney U test between normal saline group and penehyclidine group. PACU, post-anesthesia care unit.

Discussion
The signi cant nding in this study is that administration with penehyclidine after anesthesia induction signi cantly attenuated incidence and severity of both postoperative oculocardiac re ex and postoperative nausea and vomiting in the patients with strabismus surgery. Penehyclidine should be considered as an effective intervention for the prevention of intraoperative oculocardiac re ex and postoperative nausea and vomiting in strabismus surgery.
PONV is a common complication after general anesthesia for surgery patients including those who undergoing strabismus surgery. The risk factors for the development of PONV include patient-related factors, anesthetic techniques, and type of surgery (17,18). It is well known that female, non-smokers, PONV or motion sickness history, and the use of opioids are the most common risk factors (18). The inhalational anesthetics, ketamine, and etomidate increase the incidence of PONV, while the use of propofol, midazolam and free uid infusion technique are believed to reduce its incidence (1,19). Also, PONV risk is affected by different kinds of surgeries including strabismus surgery. For underaged patients, duration of surgery ≥ 30 min, age ≥ 3 years and receiving strabismus surgery are all independent risk factors of PONV (20,21). Many drugs have been used for the prevention or treatment of PONV. The most widely used antiemetic drugs are 5-hydroxytryptamine (5-HT 3 ) receptor antagonists. The NK-1 receptor antagonists, corticosteroids, butyrophenone and antihistamines are also recommended. However, Each kind of antiemetic drugs raises different concerns just like the risk of QT prolongation in 5-HT 3 receptor antagonists and the effect on postoperative infection as well as blood glucose levels in corticosteroids (21,22). Here in this study, we demonstrated that penehyclidine, an anticholinergic agent, signi cantly reduced PONV in strabismus surgery patients.
Consistent with previous reports that showing 38 ~ 68.2% PONV incidence in strabismus surgery, we found 54.8% of overall PONV incidence in normal saline group in this investigation. We also found that the patients showed a signi cant higher PONV incidence within 6 h after strabismus surgery. Notably, we demonstrated that administration of penehyclidine after anesthesia induction pronouncedly attenuated PONV incidence in patients with strabismus surgery. The severity of PONV was mitigated and the PONV incidence was signi cantly reduced in the underaged and adult male patients as well as in the adult female patients following penehyclidine administration.
Unexpectedly, we also found a signi cant effect of penehyclidine on the attenuation of oculocardiac re ex during strabismus surgery though that penehyclidine was previously considered as having no obvious effect on heart rate (12). Oculocardiac re ex is observed frequently in strabismus surgery with an incidence of 14 ~ 90% (4). Once stimulated by manipulation, the ophthalmic branch of the trigeminal nerve transports the sensory message to central nervous system, thereby causing impulses to exit the brainstem and transmit to the sinoatrial node and activate the vagal motor response, and ultimately leading to sinus bradycardia, atrioventricular block, ventricular ectopy, ventricular brillation, hypotension, or even asystole (5). Thus, prevention and management of OCR is important. Several approaches have been applied to decrease the incidence of OCR. Immediately pausing surgery can suspend the re ex through removal of pressure to the eyeball or extraocular muscles; however, repeated pauses may disturb the process of surgery (5). Pretreatment with atropine or glycopyrrolate can attenuate the negative effect of vagus nerve on heart rate during OCR through blocking peripheral type 2 muscarinic receptors of the heart; however, atropine or glycopyrrolate may result in undesirable dysrhythmia such as sinus tachycardia which may diminish cardiac output (5,23). In this study, an overall OCR incidence of 77.9% was found in strabismus surgery patients while administration with penehyclidine signi cantly attenuated OCR. Penehyclidine reduced overall OCR incidence, and reduced the OCR severity as indicated by requirement for atropine to rescue. However, it is not clear whether the effect of penehyclidine on OCR is caused by its intrinsic type 2 muscarinic receptor block effect.
The main side effects of penehyclidine include dry mouth and central anticholinergic syndrome, similar to other anticholinergics (15). Moreover, its central sedative effect sometimes delays anesthesia recovery. In our investigation, 10 µg·kg − 1 with an upper limit to 0.5 mg penehyclidine was used. The anesthesia recovery, as indicated by the time to extubation and the time staying post-anesthesia care unit, was not delayed in penehyclidine group compared to normal saline group. No patient complained of severe dry mouth and no patient developed central anticholinergic syndrome postoperatively. These may possibly be explained by limited maximal dose difference, and our patients undergoing minor surgery could drink free after surgery (24).
The anesthesia scheme design enhanced the strengths of this study. Agents including midazolam, etomidate, inhalational anesthetics or neostigmine were not used because potential effects on PONV. Besides, the randomization and double-blinded technique were strictly carried out during the investigation. As randomization was achieved by lottery method, patients allocated into the two groups were not equal. In subgroup analysis, the sample size of the subgroups also appeared imbalanced. In order to get more reliable outcomes, a strati ed random sampling method is more suitable for predesigned subgroup analysis.

Conclusions
In conclusion, this study identi ed penehyclidine, a widely preoperatively used anticholinergic drug in clinic, as an effective protector against intraoperative oculocardiac re ex and postoperative nausea and vomiting in the patients with strabismus surgery.

Declarations
Ethics approval and consent to participate