Ultrasound-Guided Suprazygomatic Nerve Blocks to the Pterygopalatine Fossa: A Safe Procedure

Abstract

Objectives

Large-scale procedural safety data on pterygopalatine fossa nerve blocks (PPFBs) performed via a suprazygomatic, ultrasound-guided approach are lacking, leading to hesitancy surrounding this technique. The aim of this study was to characterize the safety of PPFB.

Methods

This retrospective chart review examined the records of adults who received an ultrasound-guided PPFB between January 1, 2016, and August 30, 2020, at the University of Florida. Indications included surgical procedures and nonsurgical pain. Clinical data describing PPFB were extracted from medical records. Descriptive statistics were calculated for all variables, and quantitative variables were analyzed with the paired t test to detect differences between before and after the procedure.

Results

A total of 833 distinct PPFBs were performed on 411 subjects (59% female, mean age 48.5 years). Minor oozing from the injection site was the only reported side effect, in a single subject. Although systolic blood pressure, heart rate, and oxygen saturation were significantly different before and after the procedure (132.3 vs 136.4 mm Hg, P < 0.0001; 78.2 vs 80.8, P = 0.0003; and 97.8% vs 96.3%, P < 0.0001; respectively), mean arterial pressure and diastolic blood pressure were not significantly different (96.2 vs 97.1 mm Hg, P = 0.1545, and 78.2 vs 77.4 mm Hg, P = 0.1314, respectively). Similar results were found within subgroups, including subgroups by sex, race, and indication for PPFB.

Discussion

We have not identified clinically significant adverse effects from PPFB performed with an ultrasound-guided suprazygomatic approach in a large cohort in the hospital setting. PPFBs are a safe and well-tolerated pain management strategy; however, prospective multicenter studies are needed.

Introduction

Peripheral nerve blocks are increasingly used either as a component of multimodal analgesia or even as a replacement for systemic pain medications [1]. Peripheral nerve blocks have been shown to be effective for the treatment of primary headache disorders [2] and secondary headaches [3, 4]. Despite increasing use of pterygopalatine fossa nerve blocks in the acute hospital setting [5], a systematic assessment of the safety of the procedure in large cohorts has not been published to date.

The pterygopalatine fossa (PPF) is a space at the skull base, situated between the maxilla, palatine bone, and sphenoid bone. It communicates with multiple other spaces in the skull and contains numerous important nervous system and vascular structures, including the maxillary division of the trigeminal nerve (V₂), the sphenopalatine pterygopalatine ganglion (SPG; also known as the pterygopalatine ganglion, Meckel’s ganglion, and the nasal ganglion), the greater petrosal nerve, and the vidian nerve. In addition to nervous system structures, there are important vascular structures that pass through or originate within the PPF, including the maxillary artery, the artery of the pterygoid canal, and the posterior superior alveolar, infraorbital, sphenopalatine, pharyngeal, and descending palatine arteries. Pterygopalatine fossa blocks (PPFBs) have been demonstrated to be of value for multiple conditions, including migraines, post–dural puncture headaches, headaches associated with intracranial bleeding, and perioperative analgesia for operations in the mid-face, nose, paranasal sinuses, palate, and proximal pharynx, as well as multiple idiopathic and complex facial pain syndromes [4, 6–20]. Interest in this technique is increasing as the understanding of the cholinergic mechanisms of headache develop and improve [21].

The PPFB targets the maxillary nerve and the sphenopalatine ganglion (SPG), a large extracalvarial autonomic ganglion that contains parasympathetic vasomotor fibers responsible for the vasodilatory trigemino-autonomic pain reflex. It is proposed that the post-ganglionic output from the block can lead to vasodilation of meningeal vessels, stimulation of mucous membranes surrounding the oropharynx, and activation of proinflammatory cascades involved in pain generation [22]. In experimental settings, SPG stimulation led to dilation of ipsilateral intracranial vasculature [23]. These features position PPFBs as a potential approach for treating refractory headache and vasospasm after subarachnoid hemorrhage (SAH). Additionally, they represent an opioid-sparing treatment strategy, positioning them as an attractive option for analgesia in the acute care setting. Despite these advantages, the lack of structured safety reports for this procedure and unfamiliarity with techniques for placement of PPFBs limit their broader adoption [24–29]. Several approaches to placing PPFBs have been described, including transnasal, intra-oral, infrazygomatic, and suprazygomatic approaches [11, 13], each associated with a different risk profile [13, 30–33]. The suprazygomatic approach makes use of the bony anatomy surrounding the PPF to allow easy passage of a needle through the pterygomaxillary fissure into the fossa while preventing inadvertent introduction of the needle through any of the other foramina from the PPF into other unintended locations [34]. To date, there have been no structured safety analyses in the literature pertaining to this approach, though no serious complications have been associated with the suprazygomatic approach in reports that used this approach.

In the present study, we report our experience with suprazygomatic PPFB in the hospital setting, with a specific focus on the safety of this procedure, to fill the gap in safety data for suprazygomatic PPFBs. We hypothesized that PPFB under the aforementioned conditions is a safe procedure.

Methods

Study Oversight

The present study was a retrospective chart review performed at the University of Florida. The study was approved by University of Florida local institutional review board (IRB202002307), including waiver of consent.

Study Population

We included patients admitted to University of Florida (UF) Health Shands Hospital between January 1, 2016, and August 30, 2020, who were at least 18 years old and received an ultrasound-guided suprazygomatic PPFB during their admission to the hospital. No other exclusion criteria were defined.

Data Collection

The Integrated Data Repository at the University of Florida, which compiles all clinical records across the UF Health system into a single database, furnished the list of patients eligible for the study on the basis of the aforementioned criteria. Quantitative and qualitative data were extracted for each patient from Epic© (Epic Systems Corporation) medical records system by two independent reviewers (AB and GC). A data collection manual was created to standardize the data extraction process between reviewers, and it used both flowsheet data and provider narratives via procedure notes. If a subject received a bilateral block during a single event, this was considered a single instance of PPFB for statistical analysis. Data elements were recorded into a REDCap© (REDCap electronic data capture tools hosted at UF) database, and variables were organized into four different categories: demographics, procedure characteristics, patient-level data, and laboratory results. Demographic data included age at the time of the procedure, race, ethnicity, and gender. Procedure characteristics included the indication for the block, laterality, the date and time the block was given, and premedications administered. Patient-level data included vital signs (systolic blood pressure [SBP], diastolic blood pressure [DBP], heart rate [HR], and oxygen saturation [SpO₂]), postprocedural pain scores (on a standard 0–10 scale), reported procedure-related side effects, and adverse events. For subjects admitted with SAH who received a PPFB for the treatment of refractory headache, blood flow velocities derived from daily, standard-of-care, transcranial Doppler ultrasound (TCD) were collected before PPFB and 24 hours after the procedure. Pain scores were also collected before and after the procedure in this subset of patients.

Nerve Block Procedure

Under ultrasound guidance, a 25-gauge, 50-mm Quinke-point spinal needle is inserted 1 to 1.5 cm superior to the zygomatic arch and posterior to the posterior orbital rim. The needle is inserted perpendicular to the skin and advanced to reach the greater wing of the sphenoid at an approximate 20-mm depth. The needle is then reoriented 30° to –45° caudad and 10° to –15° anterior and advanced an additional 25 to 30 mm, through the pterygomaxillary fissure and into the pterygopalatine fossa. The direction of the needle and the expected mean depth of the needle tip are usually independent of the age of the patient. For further details of the procedure itself, including a video demonstrating the procedure, please see the online supplemental content published by Cometa et al. [9].

Ultrasound images are obtained with a high-frequency linear array probe. The ultrasound transducer is placed in the infrazygomatic area, over the maxilla, angled approximately 45° cephalad. This probe position allows visualization of the PPF, limited anteriorly by the maxilla and posteriorly by the ultrasound shadow of the coranoid process of the mandible, which overlies the pterygoid process greater wing of the sphenoid. The needle is advanced with an out-of-plane approach, and the needle tip can usually be identified, although the out-of-plane imaging of a 25-guage needle is quite subtle. After the needle hub is left open to ambient pressure for 10 to 15 seconds to exclude inadvertent intravascular placement of the needle tip, the injectate can be delivered. For the cases analyzed in the present study, the injectate consisted of 4 mL of 0.5% ropivacaine combined with 1 mL of dexamethasone 4 mg/mL. The 5-mL injectate is delivered over 15 to 20 seconds, while the spread of the local anesthetic is observed under ultrasound. The same procedure is then repeated on the contralateral side. Figures 1 and 2 illustrate this process in a stepwise fashion.

Figure 1.

(A) An appropriate needle entry site is located approximately 1 cm posterior to the posterior orbital rim and approximately 1 cm superior to the superior edge of the zygomatic arch. (B) The ultrasound probe is applied inferior to the zygomatic arch, and the ultrasound beam is directed approximately 45 degrees cephalad to insonate PPF. (C) The needle is inserted, beginning at the predetermined insertion point. Initially the needle is inserted perpindicular to skin and advanced approximately 1 cm to pass the zygomatic arch, and the needle is directed approximately 30–45 degrees caudad. (D) The needle is advanced approximately 5 cm to pass through the pterygomaxillary fissure into the PPF. (E) Appropriate ultrasound imaging is confirmed, showing the maxilla anteriorly (1), the coranoid process of the mandible posteriorly and superficially (2), which overlies the pterygoid process posteriorly and deep (3). Deep, between the pterygoid process and maxilla, lies the pterygopalatine fossa (4), deep to the masseter (5) and pterygoid muscles (6). The needle tip is indicated by the asterisk (*). (F) The syringe is connected with a short piece of tubing, and the injection is delivered under live ultrasound visualization to confirm the spread of the injectate within the PPF. Of note, because the injectate volume exceeds the volume of the PPF, it is common to observe the injectate spread beyond the PPF superficially into parts of the infratemporal fossa.

Figure 2.

Needle trajectory during the suprazygomatic approach to the pterygopalatine fossa. The needle entry point is approximately 0.5–1 cm posterior to the posterior orbital rim and 0.5–1 cm superior to the superior edge of the zygomatic arch (1). The ultrasound probe is applied to the face approximately 2 cm inferior to the inferior edge of the zygomatic arch, and the beam is directed approximately 30–45 degrees cephalad to look through the muscles of mastication (2), over the mandible (3), through the infratemporal fossa, and into the pterygopalatine fossa (asterisk), which lies between the maxilla anteriorly (4) and the pterygoid process of the sphenoid bone posteriorly (5). The needle is directed approximately 30 degrees caudad and advanced approximately 5 cm through the muscles of mastication into the pterygopalatine fossa, between the maxilla anteriorly and the pterygoid process posteriorly.

For patients in whom the nerve block was placed for perioperative analgesia, the procedure was performed in the operating room after the induction of general anesthesia. For blocks placed outside of the perioperative environment, blocks were placed at the patient bedside (for intensive care unit patients) or in the block procedure rooms (for non–intensive care unit patients) without the use of any sedation. Block placement is, per institutional standard, confirmed by evaluation of numbness in the V2 trigeminal sensory distribution (either immediately after block placement in awake patients, or upon patients awakening from surgery in a follow-up visit in the post-anesthesia care unit). Of note, intact mental status with ability to reliably indicate tolerability and verbal pain scale scores was a prerequisite for all patients to whom the block was offered in the inpatient setting.

Statistical Analysis

Data were analyzed in SAS 9.4 (SAS Institute, Cary NC). Descriptive statistics, including mean, median, and standard deviation, were calculated for all quantitative variables and assessed for normal distribution. Percentages for categorical variables were calculated. An additional variable, mean arterial pressure (MAP), was calculated for both before and after the procedure on the basis of SBP and DBP. Paired t tests were used to determine significant differences between before and after the procedure on safety-related variables, as well as differences between pain scores in the SAH cohort. Subgroup analyses included the paired t test within groups based on indication (functional endoscopic sinus surgery and other), race (white and non-white), and sex (male and female). An alpha of 0.05 was used for all tests to determine significance.

Results

Cohort Characteristics

The record-screening process is detailed in Figure 3. A total of 411 subjects fulfilled the inclusion criteria for the study period. Demographics and clinical characteristics of all encounters are described in Table 1. We analyzed 429 instances of PPFB (404 bilateral blocks, 25 unilateral blocks) among those 411 subjects, for a total of 833 injections into the PPF. Fifty-nine percent of the cohort subjects were female (242/411), 77% were Caucasian (316/411), and 98% reported not being Hispanic or Latino (381/411). They had a mean age of 48.5 years. Twelve of the 411 subjects received a PPFB for the treatment of post-SAH headache refractory to conventional analgesia.

Figure 3.

Record-screening process.

Table 1.

Characteristics of unique encounters

Characteristic	N	%
Sex
Female	253	58.9
Male	176	41.1
Age
<30 years	78	18.2
30–60 years	227	52.9
>60 years	124	28.9
Ethnicity
Hispanic/Latino	21	4.9
Not Hispanic/Latino	398	92.8
Unknown / not reported	10	2.3
Race
American Indian / Alaska Native	2	0.3
Asian	11	2.6
Native Hawaiian or Other Pacific Islander	0	0
Black or African American	55	12.8
White	329	76.7
More than one race	0	0
Unknown / not reported	9	2.1
Other	23	5.4
Indication
Tonsillectomy	56	13.1
Endoscopic sinus surgery (FESS)	267	62.2
Headache	19	4.4
Cleft palate repair	0	0
Other	87	20.3
Laterality
Unilateral	25	5.9
Bilateral	403	94.2

FESS = functional endoscopic sinus surgery.

Physiological Monitoring

The detailed comparison of pre- and postprocedural vital signs is shown in Table 2. SBP, HR, and SpO₂ were statistically significantly different before and after the procedure on paired t tests (132.3 vs 136.4 mm Hg, P < 0.0001; 78.2 vs 80.8, P = 0.0003; and 97.8% vs 96.3%, P < 0.0001; respectively). MAP and DBP were not statistically significantly different (96.2 vs 97.1 mm Hg, P = 0.1545, and 78.2 vs 77.4 mm Hg, P = 0.1314, respectively). In subgroup analysis (see Table 3), SBP was statistically significantly different from before to after PPFB among Caucasians (131.5 vs 136.1 mm Hg, P < 0.0001), among those undergoing endoscopic sinus surgery (134.9 vs 140.2 mm Hg, P < 0.0001), and regardless of sex (136.1 vs 142.0, P < 0.0001, for males; 129.7 vs 132.6 mm Hg, P = 0.0073, for females). HR was not significantly different among females (79.5 vs 80.9, P = 0.0990) and among those undergoing PPFB for indications other than functional endoscopic sinus surgery (78.8 vs 80.8, P = 0.1057) but remained statistically significantly different regardless of race (78.3 vs 83.2, P = 0.0047, for non-white race; 78.1 vs 80.1, P = 0.0113, for white race). Differences in DBP and MAP between before and after PPFB were not statistically significant within all analyzed subgroups. SpO₂ remained significantly different among all subgroups (P < 0.0001 within all subgroups; 97.3% vs 95.9% among males, 98.0% vs 96.6% among females, 97.7% vs 96.2% among white subjects, 98.0% vs 96.6% among non-white subjects, 97.6% vs 95.9% among subjects undergoing endoscopic sinus surgery, and 97.9% vs 96.9% among subjects receiving PPFB for other indications). The results are described in Table 3.

Table 2.

Comparison between vital signs before and after the procedure

Variable	n	Before the Procedure Mean (SD)	After the Procedure Mean (SD)	P Value
HR	413	78.2 (14)	80.8 (13)	0.0003*
SBP	418	132.3 (17)	136.4 (19)	< 0.0001*
DBP	418	78.2 (11)	77.4 (12)	0.1314
MAP	418	96.2 (11)	97.1 (12)	0.1545
SpO2	416	97.8 (1.9)	96.3 (2.4)	< 0.0001*

^*Significant at level of <0.05.

Table 3.

Comparison of vital sign means before and after the procedure within relevant subgroups

Subgroup (n)	HR	SBP	DBP	MAP	SpO2
Sex
Male (n = 176)	76.2 vs 80.7 (P = 0.0004)*	136.2 vs 142.0 (P < 0.0001)*	81.0 vs 80.4 (P = 0.4080)	99.4 vs 100.9 (P = 0.0934)	97.3 vs 95.9 (P < 0.0001)*
Female (n = 253)	79.5 vs 80.9 (P = 0.0990)	129.6 vs 132.6 (P = 0.0073)*	76.2 vs 75.3 (P = 0.2065)	94.0 vs 94.4(P = 0.6294)	98.0 vs 96.6 (P < 0.0001)*
Race
White (n = 329)	78.2 vs 80.1 (P = 0.0113)*	131.6 vs 136.1 (P < 0.0001)*	77.8 vs 76.8 (P = 0.0550)	95.8 vs 96.5(P = 0.2671)	97.7 vs 96.2 (P < 0.0001)*
Not white (n = 100)	78.3 vs 83.2 (P = 0.0047)*	134.5 vs 137.5 (P = 0.1044)	79.1 vs 79.5 (P = 0.8714)	97.6 vs 98.8(P = 0.3570)	98.0 vs 96.6 (P < 0.0001)*
Indication
FESS (n = 267)	77.7 vs 80.8 (P = 0.0010)*	134.9 vs 140.2 (P < 0.0001)*	79.1 vs 78.2 (P = 0.2061)	97.7 vs 98.8(P = 0.0955)	97.6 vs 95.9 (P < 0.0001)*
Other (n = 162)	78.9 vs 80.8 (P = 0.1057)	127.9 vs 130.1 (P = 0.1033)	76.6 vs 76.1 (P = 0.4037)	93.7 vs 94.1P = 0.8362	97.9 vs 96.9 (P < 0.0001)*

FESS = functional endoscopic sinus surgery.

P values of paired t tests comparing means before and after the procedure within each subgroup are in parentheses.

^*Significant P values at a level of <0.05.

Tolerability

No subjects reported postprocedure adverse events, nor were any serious adverse events documented by medical staff. One subject experienced minor oozing from the insertion site that resolved within 1 minute of the application of pressure. No subjects declined to have the injection completed on the second side after completing the first injection.

Pain Scores

The mean postprocedure pain score among the entire cohort was 2.2 (standard deviation ±2) on the standard 0–10 numeric rating scale in 406 subjects. Postprocedure pain scores were not available for the remaining five subjects. Among subjects who received PPFBs for post-SAH headache, the difference between means (6 vs 2.5) was significantly different (P = 0.0014). One subject reported a slightly elevated pain score in the immediate postprocedural period (4 before the procedure vs 5 after the procedure) but subsequently reported a score of 0 an hour after the conclusion of the block.

TCD Blood Flow Velocities Among Subjects with SAH

We reviewed blood flow velocities and Lindegaard ratios in bilateral middle cerebral arteries on TCD before and 24 hours after the procedure for the 12 subjects with spontaneous post-SAH headache. Five subjects had angiographic vasospasm by TCD criteria before PPFB (defined as middle cerebral artery mean flow velocity >120 cm/s), but clinical evidence of vasospasm was not present [35]. Follow-up TCDs 24 hours after the procedure in select subjects demonstrated that four of five subjects had decreasing mean vascular flow velocities, and one subject had increasing mean vascular flow velocities (Table 4).

Table 4.

Blood flow velocities and Lindegaard ratios on TCD before and after PPFB in 12 subjects who presented with radiographic vasospasm after SAH

Subject	Variable	Before PPFB	After PPFB
1	L MCA	59	59
	R MCA	50	64
2	L MCA	185	135
	L LR	4.20	3.75
	R MCA	164	95
	R LR	3.34	2.31
3	R MCA	114	96
4	L MCA	226	212
	L LR	5.65	4.32
5	L MCA	57	48
	R MCA	58	59
6	L MCA	51	52
	R MCA	48	43
7	L MCA	87	Not performed
	R MCA	110
8	L MCA	188	247
	L LR	4.48	5.04
	R MCA	122	143
	R LR	2.90	3.48
9	L MCA	39	51
	R MCA	46	57
10	R MCA	136	121
	R LR	3.67	3.36
11	L MCA	80	95
12	L MCA	126	115
	R MCA	95	64

R = right; L = left; MCA = middle cerebral artery; LR = Lindegaard ratio.

Blood flow velocities are reported in cm/s.

Discussion

In this study of PPFB in the hospital setting in 411 patients with 833 PPFBs (i.e., 403 bilateral blocks) placed via the ultrasound-guided suprazygomatic approach, we found no serious complications, with an overall superb tolerance of the PPFB. One subject experienced minor oozing at the needle insertion site, which resolved within 1 minute with the application of pressure. No other patient-reported or staff-documented adverse events occurred. No differences were found in MAP and DBP periprocedurally. Although SBP, SpO₂, and HR were found to be statistically different before and after the procedure in this cohort, as well as within certain subgroups, these differences were not clinically meaningful (78 vs 80 for HR, 97.8% vs 96.3% for SpO₂, and 132 vs 136 mm Hg for SBP, before and after the procedure, respectively). Additionally, our study demonstrates in a small subset of subjects that PPFB may be an effective treatment strategy for post-SAH headache, expanding on our previously reported data.

Relevant Anatomy and Institutional Practice

The pterygopalatine fossa is a small space, yet it contains many important nervous and vascular structures. Given the multitude of structures within this space, and its relatively shielded position, it is not surprising that many physicians hesitate to attempt nerve blocks in this location on the basis of safety concerns, especially in the absence of larger cohort safety data and reliance on smaller case series.

The route chosen for the needle access to the PPF has a substantial impact on the safety profile of PPFBs. For example, the transnasal route provides unpredictable coverage of the contents of the PPF with the least durable results, and abnormal nasal anatomy can make the passage of an applicator difficult, and thus, can be associated with risk of bleeding [27, 28]. The intra-oral route is regarded as the most technically difficult, provides uncertain coverage of the PPF, and carries the highest risk of complications [9, 27]. Serious complications have been described with both the intra-oral approach (inserting the needle through the greater palatine foramen/palatine canal [widely regarded as the highest-risk approach to the PPF]) and infrazygomatic approach [29]. We first adopted the suprazygomatic approach for PPFB because of its suggested favorable safety profile in previously published experience for this technique in children [11, 36]. When safety events described with the use of other (infrazygomatic and intra-oral) approaches to the pterygopalatine fossa are examined, serious safety events, including needle entry into the orbit, needle entry into the nasal cavity, and serious bleeding events, have been described [29, 37]. In our work, reported on here, we have been able to systematically confirm the favorable safety profile of the suprazygomatic, ultrasound-guided PPFBs in a large cohort of patients [13, 38, 39]. The suprazygomatic approach makes use of the bony anatomy surrounding the PPF to both allow easy passage of a needle through the pterygomaxillary fissure into the fossa and prevent inadvertent introduction of the needle through any of the other foramina from the PPF. With the suprazygomatic approach, the trajectory of the needle is approximately 90 degrees to the opening of the infraorbital fissure, the foramen rotundum, and the pterygopalatine foramen. Inadvertent passage of the needle to either the orbit, middle fossa of the cranium, or the nasal cavity is virtually impossible without passing the needle through bone. Safety is further maximized by using the smallest, shortest needle that will achieve the desired needle tip placement; with usual anatomy, this is well accomplished by a 5-cm-long 25G spinal needle.

PPFB Among Patients with SAH

PPFB may be a potential alternative in pain management for a population with commonly severe headaches and limited efficacy of systemic pain regimens [5, 38]. However, because of the autonomic fibers in the PPF, there is a potential for a vasoreactivity effect when pterygopalatine fossa contents are modulated. This has been demonstrated in data stemming from parasympathetic stimulation of the SPG [23], but it is complex, with different findings and no equivocal measurable effect by others [39, 40]. Although no reports of vasospasm have been published in the setting of PPFB, even for repetitive SPG blockade in migraine patients [41], who are considered to have increased risk of ischemic stroke [42], we did not offer PPFB to patients in clinically apparent vasospasm. Our results indicate that there was no clinically significant increase in vascular flow velocities for all but one patient. This patient had received the PPFB in the setting of already elevated flow velocities but in the absence of clinically significant vasospasm. Overall, although in the remaining 11 patients there was a reduction of mean flow velocities for patients who presented with vasospasm before PPFB, the relationship between PPFB and vasoreactivity remains unclear. Although we obtained mean flow velocity data before and after the PPFB in all subjects with SAH, these were obtained from TCDs that were completed every morning as part of institutional practices for vasospasm monitoring, and their timing in relation to PPFB varied. Thus, we could not account for transient vascular effects shortly after the procedure. Although our results also indicate that there was a significant reduction of pain scores after the procedure, this was not the main focus of this study and will be explored further. Similarly, future prospective studies with standardized monitoring of mean flow velocities periprocedurally are warranted for further elucidation of short-term effects.

Limitations

The present study used data obtained from medical records to generate evidence that PPFB is a safe procedure when conducted under the outlined conditions and is subject to limitations inherent to its retrospective design. The lack of adverse events in our cohort, though clinically reassuring, prevents us from understanding the true incidence and severity of procedure-associated adverse events when they do occur—albeit seemingly very rarely. Furthermore, as the interval between the procedure and follow-up is variable, adverse events occurring days or weeks after the procedure would not be detected with this study design. Importantly, our data are generated from a single center with a robust teaching curriculum for this procedure and are likely not generalizable to other centers. However, the fact that the procedure was performed by a variety of providers indicates that this is a procedure that can be adopted if taught correctly. Moreover, our study was not designed to evaluate the efficacy of the nerve block; as such, we were unable to analyze detailed reports of successful block placement and were able to obtain postprocedural pain scores only for the assessment of its effect on pain control in the larger cohort. Additionally, the small sample size of the SAH cohort does not allow for robust assessment of the effect of PPFB on vascular flow velocities, especially in individuals who do not have altered cerebral vasoreactivity. Large-scale, multicenter, prospective studies with standardized collection of potential adverse events and periprocedural monitoring of intracranial mean flow velocities are needed to assess the prevalence of adverse events and more thoroughly describe the relationship between PPFB and vasoreactivity.

Conclusion

Only one mild adverse event was identified in a large cohort undergoing PPFB via the suprazygomatic approach, confirming its favorable safety profile in a center with rigorous training in craniofacial blocks. Although HR, SBP, and SpO₂ were significantly different before and after the procedure, these differences were not clinically meaningful. Prospective evaluation of safety data in a multicenter cohort, including a possible effect of PPFB on cerebral vasoreactivity, is needed for a broad characterization the safety of this procedure beyond a highly specialized tertiary care center.

 

Funding sources: Research reported in this publication was supported by the University of Florida Clinical and Translational Science Institute, which is supported in part by the NIH National Center for Advancing Translational Sciences under award number UL1TR001427. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Additionally, the authors would like to thank the Stephen O. Heard New Investigator fund for their support.

Disclosures and conflicts of interest: Dr. Maciel has received funding from Claude D. Pepper Older Americans Independence Center and the American Heart Association. All other authors have no disclosures or conflicts of interest.

Authors Carolina B. Maciel and Katharina M. Busl contributed equally to this study and article.