Influence of Pre- and Intraoperative Local Anaesthetic in Strabismus Surgery under General Anaesthesia in Adults.

BACKGROUND: As studies have shown a reduction in the occurrence of the oculocardiac reflex with the addition of local anaesthesia, we changed our care regime accordingly a few years ago. To promote and establish better patient care, we retrospectively analysed the files of our patients who underwent strabismus surgery from 2013 to 2021 in order to compare strabismus surgery under general anaesthesia with and without local anaesthetics in a routine clinical setting. PATIENTS AND METHODS: Data from 238 adult patients who had undergone strabismus surgery could be extracted from the files: G1: n = 102, only general anaesthesia; G2: n = 136, preoperative application of tetracaine eye drops and intraoperative subtenon lidocaine/levobupivacaine in addition to general anaesthesia. We compared the two groups in regard to the frequency of oculocardiac reflex, the amount of atropine needed to treat, as well as the amount of antiemetic and analgesic medication given, and time spent in the recovery room. RESULTS: Mean age of G1 was 50 years and 52 years in G2. There was no significant difference between the kind of surgeries (recessions/resections), the number of patients who had undergone a reoperation, or the duration of the operations. Adding local anaesthetics resulted in significantly less occurrence of oculocardiac reflex (p = 0.009), a reduction in the need for atropine, analgesic, or antiemetic medication, as well as reduced time in the recovery room. CONCLUSION: As this increases patient safety and comfort and is cost-effective (less time in the recovery room), we recommend adding perioperative local anaesthesia to strabismus surgery performed under general anaesthesia.

Perioperative dexmedetomidine reduces emergence agitation without increasing the oculocardiac reflex in children: A systematic review and meta-analysis.

BACKGROUND: Intravenous dexmedetomidine (DEX) has been used to prevent emergence agitation (EA) in children. The aim of this meta-analysis was to evaluate whether DEX decreases EA incidence without augmenting oculocardiac reflex (OCR) in pediatric patients undergoing strabismus surgery. METHODS: We searched PubMed, EMBASE, Chinese National Knowledge Infrastructure (CNKI), Wan Fang, and the Cochrane Library to collect the randomized controlled trials (RCTs) investigating the effects of intraoperative DEX in children undergoing strabismus surgery from inception to October 2019. Postoperative Pediatric Agitation and Emergence Delirium (PAED) score, postoperative EA, extubation or laryngeal mask airway (LMA) removal time, postanesthetic care unit (PACU) stay time, OCR, and postoperative vomiting (POV) were evaluated. RESULTS: 11 RCTs including 801 patients were included in this study. Compared with control group, intravenous DEX significantly reduced postoperative PAED score (WMD, 3.05; 95% CI: -3.82 to -2.27, P = .017) and incidences of postoperative EA 69% (RR, 0.31; 95% CI: 0.17 to 0.55, P < .00) and POV (RR, 0.28; 95% CI: 0.13 to 0.61, P = .001). Furthermore, the use of DEX significantly delayed extubation or LMA removal time (WMD, 2.11; 95% CI: 0.25 to 3.97, P < .001). No significant difference was found in the incidence of ORC and PACU stay time. CONCLUSION: Intravenous DEX reduced the incidences of EA without increasing OCR in pediatric patients undergoing strabismus surgery. Meanwhile, DEX infusion decreased the incidence of POV in children.

Penehyclidine mitigates postoperative nausea and vomiting and intraoperative oculocardiac reflex in patients undergoing strabismus surgery: a prospective, randomized, double-blind comparison.

BACKGROUND: Postoperative nausea and vomiting (PONV) is one of the most frequent complications following strabismus surgery. Penehyclidine, an anticholinergic agent, is widely used as premedication. This study investigated the effect of preoperative penehyclidine on PONV in patients undergoing strabismus surgery. METHODS: In this prospective, randomized, double-blind study, patients scheduled for strabismus surgery under general anesthesia were randomly assigned to either penehyclidine (n = 114) or normal saline (n = 104) group. Penehyclidine was administrated immediately after anesthesia induction, and normal saline was substituted as control. PONV was investigated from 0 to 48 h after surgery. Intraoperative oculocardiac reflex (OCR) was also recorded. RESULTS: Compared with normal saline, penehyclidine significantly reduced PONV incidence (30.7% vs. 54.8%, P < 0.01) and mitigated PONV severity as indicated by severity scoring (P < 0.01). Compared with normal saline, penehyclidine also significantly reduced OCR incidence (57.9% vs. 77.9%, P < 0.01) and mitigated OCR severity, as indicated by the requirement for atropine rescue (77.3% vs. 90.1%, P < 0.05) and the maximum decrease of heart rate during OCR (23.1 ± 9.4 bpm vs. 27.3 ± 12.4 bpm, P < 0.05). The recovery course did not differ between groups. CONCLUSIONS: Penehyclidine administrated after anesthesia induction significantly reduced the incidence of PONV and alleviated intraoperative OCR in patients undergoing strabismus surgery. TRIAL REGISTRATION: ClinicalTrials.gov ( NCT04054479 ). Retrospectively registered August 13, 2019.

Dexmedetomidine use in pediatric strabismus surgery: A systematic review and meta-analysis.

BACKGROUND: Common complications of pediatric strabismus surgery, including emergence agitation (EA), postoperative nausea and vomiting (PONV), and postoperative pain, may be prevented using dexmedetomidine, which is an anxiolytic and analgesic. This systematic review and meta-analysis assessed the effects of dexmedetomidine in patients who had undergone pediatric strabismus surgery. METHOD: Five databases were searched for randomized controlled trials published from database inception to April 2020 that compared dexmedetomidine use with placebo or active comparator use and evaluated EA, PONV, or postoperative pain incidence (main outcomes) in patients who had undergone pediatric strabismus surgery. Oculocardiac reflex (OCR) incidence and postanesthesia care unit (PACU) stay duration were considered as safety outcomes. All meta-analyses were performed using a random-effects model. RESULTS: In the nine studies meeting our inclusion criteria, compared with placebo use, dexmedetomidine use reduced EA incidence [risk ratio (RR): 0.39; 95% confidence interval (CI): 0.25-0.62, I2 = 66%], severe EA incidence (RR: 0.27, 95% CI: 0.17-0.43, I2 = 0%), PONV incidence (RR: 0.33, 95% CI: 0.21-0.54, I2 = 0%), analgesia requirement (RR: 0.38, 95% CI: 0.25-0.57, I2 = 0%), and pain scores (standardized mean difference: -1.02, 95% CI: -1.44 to -0.61, I2 = 75%). Dexmedetomidine also led to lower EA incidence in the sevoflurane group than in the desflurane group (RR: 0.26 for sevoflurane vs. 0.45 for desflurane). Continuous dexmedetomidine infusion (RR: 0.19) led to better EA incidence reduction than did bolus dexmedetomidine infusion at the end of surgery (RR: 0.26) or during the peri-induction period (RR: 0.36). Compared with placebo use, dexmedetomidine use reduced OCR incidence (RR: 0.63; I2 = 40%). No significant between-group differences were noted for PACU stay duration. CONCLUSION: In patients who have undergone pediatric strabismus surgery, dexmedetomidine use may alleviate EA, PONV, and postoperative pain and reduce OCR incidence. Moreover, dexmedetomidine use does not affect the PACU stay duration.

Effect of dexmedetomidine on prevention of postoperative nausea and vomiting in pediatric strabismus surgery: a randomized controlled study.

BACKGROUND: Postoperative nausea and vomiting (PONV) are common side-effects following strabismus surgery. The present study aimed to compare the effects of different doses of dexmedetomidine (DEX) on PONV incidence in pediatric patients undergoing strabismus surgery. METHODS: In this prospective randomized double-blinded study, 126 pediatric patients undergoing strabismus surgery were randomized into one of three groups: Placebo group, normal saline; DEX1 group, 0.3 µg/kg dexmedetomidine, and DEX2 group, 0.5 µg/kg dexmedetomidine. Oculocardiac reflex (OCR) events were recorded during surgery. PONV or postoperative vomiting (POV) was recorded for 24 h in the ward. Pediatric anesthesia emergence delirium (PAED) scale and emergence agitation (EA) scale were recorded in the recovery room. RESULTS: Intraoperative OCR was significantly reduced in DEX2 group (42%) as compared to that of Placebo group (68%) (p = 0.0146). During the first 24 h post-op, the overall incidence of PONV was significantly lower in DEX2 group (10%) than that of Placebo group (32%) (p = 0.0142). There was no significant difference in POV among the three groups. PAED or EA scores among the three groups were similar during recovery time. CONCLUSION: Dexmedetomidine (0.5 µg/kg) reduced OCR and PONV without lengthening extubation time or recovery time in pediatric patients undergoing strabismus surgery. TRIAL REGISTRATION: The trial was prospectively registered before patient enrollment at Chinese Clinical Trial Registry (Clinical Trial Number: ChiCTR1800020176, Date: 12/19/2018).

Prevalence of and covariates associated with the oculocardiac reflex occurring in dogs during enucleation.

OBJECTIVE: To determine the prevalence of and covariates associated with the oculocardiac reflex (OCR) occurring in dogs during enucleations. SAMPLE: 145 dogs that underwent enucleation at 2 veterinary teaching hospitals between January 2010 and June 2015. PROCEDURES: Information was collected from the medical records of included dogs regarding age and body weight at hospital admission, breed (for classification of brachycephalic status), and whether they had received anticholinergic drugs or a retrobulbar nerve block (RNB) prior to enucleation. An OCR was considered to have occurred if there was a sudden decrease of ≥ 30% in heart rate from the baseline value (mean heart rate prior to the sudden decrease) during surgery in the absence of intraoperative administration of opioids or α2-adrenoceptor agonists. Associations were explored between the collected data and the prevalence of OCR by means of binomial logistic regression. RESULTS: 4.8% (7/145) of dogs had an OCR noted during enucleation. Dogs that received a preoperative RNB (n = 82) had significantly lower odds of an OCR being observed than dogs that received no preoperative RNB (OR, 0.12). No association with OCR was identified for age or brachycephalic conformation or for preoperative administration of anticholinergic drugs. CONCLUSIONS AND CLINICAL RELEVANCE: These findings suggested that preoperative administration of an RNB, but not preoperative administration of anticholinergic drugs, was associated with a lower prevalence of OCR in dogs during enucleations.

Reduction of oculocardiac reflex with Tetracaine eye drop in strabismus surgery.

INTRODUCTION: Recently, to reduce the incidence of oculocardiac reflex (OCR) in strabismus surgery, retrobulbar block and anticholinergic drugs or local anesthesia are also used. The present study evaluated the effects of Tetracaine eye drop as a topical nerve blocker on OCR during strabismus surgery. METHODS AND MATERIALS: In this randomized trial, 70 strabismus surgery candidates were randomly divided into placebo or synthetic teardrop (E) and Tetracaine eye drop (T) groups, so 3 drops of each solution were dropped in four directions of patients' eye immediately after applying anesthesia and before surgery. The incidence and severity of OCR during the stages of muscle release and incision (cutting), hemodynamic changes, the required time for OCR recovery and atropine dose were assessed. RESULTS: OCR was more seen in release phase compared to cutting phase. There were no significant differences between two group regarding the incidence and severity of OCR in the release phase (p > 0.05), but the incidence and severity of OCR in the cutting phase was more in group E than group T (p = 0.02, for both). The duration of OCR improvement (p-value = 0.74) and Atropine consumption (p-value = 0.92) did not differ between the groups. CONCLUSION: Tetracaine eye drop only reduces the incidence and severity of OCR during the incision stage of strabismus surgery.

The oculocardiac reflex and depth of anesthesia measured by brain wave.

BACKGROUND: The oculocardiac reflex (OCR), bradycardia that occurs during strabismus surgery is a type of trigemino-cardiac reflex (TCR) is blocked by anticholinergics and enhanced by opioids and dexmedetomidine. Two recent studies suggest that deeper inhalational anesthesia monitored by BIS protects against OCR; we wondered if our data correlated similarly. METHODS: In an ongoing, prospective study of OCR/TCR elicited by 10-s, 200 g square-wave traction on extraocular muscles (EOM) from 2009 to 2013, anesthetic depth was estimated in cohorts using either BIS or Narcotrend monitors. The depth of anesthesia was deliberately varied between first and second EOM tested. RESULTS: From 1992 through 2013, 2833 cases of OCR during strabismus surgery were monitored. Excluding re-operations and cases with anticholinergic, OCR from first EOM traction averaged - 20.2 ± 21.8% (S.D.) with a range from - 95 to + 25% in patients aged 0.2 to 90 (median 6.5) years. We did not find correlation between %OCR and brain wave for 97 patients with BIS monitoring and 91 with Narcotrend. With intra-patient controls between first and second muscle, the difference in brain wave did not correlate with difference in %OCR for BIS (r = 0.0002, 95% C. I -0.0002, 0.002, p = 0.30) or for Narcotrend (r = - 0.001, 95% C. I -0.004, 0.001, p = 0.32). Secondary multi-variable analysis demonstrated significant association on %OCR particularly with BIS monitor, opioid, propofol and nitrous oxide concentration in the second EOM tensioned. Sevoflurane concentration correlated better with BIS monitor in second and third EOM tension. %OCR correlated with younger age (p < 0.01). OCR with rapid onset was more profound than those with gradual onset (difference in means 18, 95% C. I 10, 26%). CONCLUSIONS: We were unable to confirm a direct correlation between brain wave monitor and OCR when using multifactorial anesthetic agents. The discrepency with other studies probably reflects direct impact of inhalational agent concentration and less deliberate quantification of EOM tension. We found no level of BIS or Entropy EEG monitoring that uniformly prevents OCR. TRIAL REGISTRY: NCT03663413. DATA: http://www.abcd-vision.org/OCR/OCR%20Brainwave%20de-identified.pdf .

Intravenous dexmedetomidine augments the oculocardiac reflex.

BACKGROUND: We reported that premedication with nasal dexmedetomidine was associated with a more intense oculocardiac reflex (OCR). In this study we performed an intrasubject, intravenous comparison to test our hypothesis that this alpha-adrenergic agonist potentiates the trigemino-vagal reflex. METHODS: OCR (greatest change heart rate/baseline heart rate) was prospectively monitored with 10-second, square-wave 200 g tension on the inferior rectus or other muscles during strabismus surgery. Between the first and second muscle, intravenous dexmedetomidine 0.5 µg/kg was delivered. RESULTS: All patients had no anticholinergic agents. A total 842 historic control patients (median age, 5.5 years) with no dexmedetomidine between muscles experienced the first OCR of 75% ± 24% (SD) and the second OCR of 77% ± 22%. The 33 study patients (median age, 5.6 years) experienced the first OCR 84% ± 16% and dexmedetomidine second OCR of 66% ± 25% for a bradycardia augmentation of 18% ± 19% (P < 0.01 [Mann-Whitney]). CONCLUSIONS: Similar to the effect of fentanyl, intravenous fast-push dexmedetomidine augmented the bradycardia associated with extraocular muscle traction.

Exaggerated Oculocardiac Reflex Elicited by Local Anesthetic Injection of an Empty Orbit: A Case Report.

We report the first description of oculocardiac reflex elicited with injection of local anesthetic in an empty orbit, and highlight clinical indicators for patients that may be at risk for an exaggerated oculocardiac reflex. We describe a patient with prior head and eye trauma treated for anophthalmic socket reconstruction at an outpatient eye surgery center. Injection of local anesthetic into the empty orbit induced an extended sinus arrest. This exaggerated response was avoided in a subsequent surgery by pretreatment with high-dose anticholinergics.

Dexmedetomidine Injection during Strabismus Surgery Reduces Emergence Agitation without Increasing the Oculocardiac Reflex in Children: A Randomized Controlled Trial.

OBJECTIVE: Dexmedetomidine is known to reduce the incidence of emergence agitation, which is a common complication after inhalational anesthesia like sevoflurane or desflurane in children. However, the dose of dexmedetomidine used for this purpose is reported variously and the most effective dose is not known. In this study, we tried to find the most effective dose of dexmedetomidine to reduce the incidence of emergence agitation in children undergoing strabismus surgery without the complications like oculocardiac reflex (OCR) or postoperative vomiting. METHODS: We randomized 103 pediatric patients aged 2-6 years and undergoing elective strabismus surgery into four groups. Anesthesia was induced with sevoflurane and maintained with desflurane. At the start of induction, dexmedetomidine, delivered at 0.25, 0.5, or 1 µg/kg, or saline was infused intravenously in the D0.25, D0.5, D1 groups, respectively. The primary outcome measure was the incidence of emergence agitation and the secondary outcome measure was the incidence of intraoperative OCR, postoperative vomiting, and desaturation events. RESULTS: The incidence of emergence agitation was 60, 48, 44, and 21% (P = 0.005) and the incidence of intraoperative OCR was 36, 36, 36, and 37% (P = 0.988) in the control, D0.25, D0.5, and D1 groups, respectively. And, postoperative vomiting rate and desaturation events were low in the all groups. CONCLUSION: Dexmedetomidine decreased the incidence of emergence agitation without increasing intraoperative oculocardiac reflex. Dexmedetomidine delivered at 1 µg/kg was more effective at reducing emergence agitation than lower doses in children undergoing strabismus surgery under desflurane anesthesia. TRIAL REGISTRATION: Clinical Research Information Service KCT0000141.

Subtenon block combined with general anesthesia for vitreoretinal surgery improves postoperative analgesia in adult: a randomized controlled trial.

STUDY OBJECTIVE: To evaluate the effects of subtenon block (SB) as an adjunct to general anesthesia on intraoperative oculocardiac reflex (OCR), postoperative pain, and postoperative nausea and vomiting (PONV) for vitreoretinal surgery. DESIGN: Prospective, randomized, double-blinded clinical trial. SETTING: Operating room, postanesthesia care unit, and ward at a university-affiliated hospital. PATIENTS: Eighty patients aged 40 to 65 years of American Society of Anesthesiologists I to II requesting general anesthesia for vitreoretinal surgery. Intervention and Measurements Patients were randomly assigned to 1 of 2 groups receiving either SB with mixture of 4 mL of 2% lidocaine and 0.5% bupivacaine (50:50) in group SB or subtenon injection of saline in group C after induction of anesthesia and before surgery in a double-blind manner. The time to first postoperative analgesic dose, incidence of intraoperative OCR, postoperative pain scores, perioperative analgesic requirements, number of patients requiring rescue analgesics during the 24-hour study period, incidence of PONV, and possible complications were recorded. RESULTS: Time to first postoperative analgesia was significantly longer in group SB (P= .002). Pain scores at the first 6 hours postoperatively were significantly lower in group SB (P= .002). Intraoperative and postoperative analgesic requirements were significantly reduced in group SB (P= .015). The incidence of OCR and PONV also significantly decreased in this group (P= .001 and P= .011, respectively). CONCLUSION: Use of SB combined with general anesthesia in patients undergoing vitreoretinal surgery reduces postoperative analgesic requirements and complications such as intraoperative OCR and PONV.

An asystolic event after eyelid skin bupivicaine injection during chalazion surgery.

We report an asystolic event in an 8-year-old girl under general anesthesia that occurred after bupivicaine was injected into the eyelid during routine chalazion incision and drainage surgery. Because the bupivacaine was injected directly into the subcuticular space and not intravascularly, we concluded that the patient's asystolic event was induced by an oculocardiac reflex.

Ketamine or atropine: which one better prevents oculocardiac reflex during eye surgery? A prospective randomized clinical trial.

Profound bradycardia during eye surgery is a potentially serious event. In clinical practice oculo-cardiac reflex (OCR) is most often encountered during squint surgery. The objective of this study was to assess the occurrence of OCR and prove the effect of ketamine as an induction drug and anticholinergic premedication (atropine) to prevent OCR. This study comprised 90 patients (aged 4-10 years) operated for squint surgery under general anesthesia. Patients were divided into three groups. Using block randomization, each patient enrolled in one of the three groups based on organized random table prepared by statistician. Group K received ketamine as an induction drug, Group A was premedicated with intravenous injection of atropine and Group C did not receive any premedication. Patients were monitored during operation for any bradycardia or dysrhythmias. The observed data showed occurrence of 63% OCR in Group C as compared to 43% in group A and only 20% in Group K. Current study showed that induction with ketamine in the patients of squint surgery under general anesthesia definitely obtunds OCR and prevents any untoward effects of dysrhythmias during eye surgery.

A randomised comparison of lidocaine 2% gel and proparacaine 0.5% eye drops in paediatric squint surgery.

We conducted a randomised trial comparing lidocaine 2% gel with proparacaine 0.5% eye drops in children having elective squint surgery. One hundred and forty children aged between 3 and 14 years were recruited. The requirement for intra-operative fentanyl and postoperative ibuprofen was significantly less in the lidocaine group compared with the proparacaine group (1 (1.7%) vs 12 (18.5%), p=0.002 and 16 (27.6%) 38 (58.5%), p=0.001, respectively). The incidence of postoperative nausea and vomiting was significantly less in the lidocaine group compared with the proparacaine group (6 (10.3%) vs 16 (24.6%), p=0.04). There were no differences between the groups in terms of incidence and severity of the oculocardiac reflex. We conclude that, compared with proparacaine 0.5% eye drops, a single application of lidocaine 2% gel improves peri-operative analgesia and reduces the incidence of postoperative nausea and vomiting in elective paediatric squint surgery.

Efficacy of subtenon block in infants - a comparison with intravenous fentanyl for perioperative analgesia in infantile cataract surgery.

BACKGROUND: General anesthesia with opioids provides good perioperative analgesia in infantile ocular surgeries but is associated with the risk of respiratory depression and postoperative emesis. This study aimed to assess the effectiveness of subtenon block for providing perioperative analgesia in infants undergoing cataract surgeries. METHODS: In this prospective, randomized, controlled, double-blinded trial, 63 infants of ASA grade I and II (1-12 months) were recruited to receive either subtenon block (Group SB) or 1 µg·kg(-1) i.v. fentanyl (Group F) after induction of anesthesia. Primary outcome was the number of infants requiring rescue analgesia during 4-h study period before discharge of the infants. Secondary outcomes assessed were CRIES pain score, incidence of oculocardiac reflex, surgical difficulty, and incidence of postoperative emesis. RESULTS: The number of infants requiring rescue analgesia during 4-h study period was significantly less in Group SB (n = 6/32, 18.8%) compared to Group F (n = 14/31, 45.2%, P = 0.032). CRIES scores were significantly lower at and after 40 min compared to immediate postoperative period in Group F while these were comparable at all time intervals in Group SB. CRIES scores were significantly lower in Group SB compared to Group F at all time intervals except at 1 h. The incidence of oculocardiac reflex and the postoperative emesis were comparable in both the groups. CONCLUSION: Subtenon block is an effective superior technique for postoperative analgesia compared to intravenous fentanyl in infants undergoing cataract surgery.

The oculocardiac reflex may mimic signs of intracranial hypertension in patients with combined cerebral and ocular trauma.

BACKGROUND: In the setting of head trauma, progressive bradycardia may raise suspicion for intracranial hypertension, especially when accompanied by pupillary abnormalities or systemic hypertension. METHODS: We describe the case of a patient with concomitant cerebral and ocular trauma who presented with a fixed and dilated pupil and progressive bradycardia due to an oculocardiac reflex. RESULTS: The oculocardiac reflex is an unusual cause of bradycardia due to stimulation of the ophthalmic division of the trigeminal nerve and has been described in a variety of clinical settings. CONCLUSIONS: Clinicians should be aware that the oculocardiac reflex might mimic signs of intracranial hypertension in patients with combined facial and cerebral trauma.

[Pitfalls of anesthesiologic management in paediatric strabismus surgery]. / Tipps und Tricks---Anästhesie bei Strabismusoperationen im Kindesalter.

Strabismus surgery is one of the most common paediatric operation procedures. As associated with congenital syndrome, congenital heart disease and neuromuscular disorder, the anesthesiologic management has to be planned carefully. Considering high incidences of oculocardiac reflex (OCR) and postoperative nausea and vomiting (PONV) anesthesia can be performed to decrease both. Induction of anesthesia with ketamine or midzolam reduces risk of oculocardiac reflex, whereas propofol or remifentanil lead to higher incidences of OCR. A combination anti-emetic therapy from different drug classes is recommend to patients at high risk for nausea and vomiting like patients undergoing strabismus surgery. A combination therapy of ondansetron and dexamethasone lead to a risk reduction of PONV to at least 10 %. Further, the incidence of OCR and PONV is significantly reduced in children receiving peribulbar block on top of general anaesthesia.

Orbital trauma, bradycardia, and vomiting: trapdoor fracture and the oculocardiac reflex: a case report.

The presentation of vomiting and bradycardia after closed head trauma should invariably prompt concern for significant intracranial injury, yet other less common causes for the clinical picture do exist. This case reports one such scenario in which fracture to the patient's inferior orbital wall resulted in the rare though potentially life-threatening oculocardiac reflex, a vagally mediated phenomenon with possible respiratory, cardiovascular, and gastric motility effects.