A standardized protocol for the prevention of clinically relevant venous air embolism during neurosurgical interventions in the semisitting position

Optimizing the selection of the endoscopically assisted supracerebellar transtentorial approach to the medial temporo-occipital region: Clinical application of one novel grid coordinate system

The endoscopically assisted supracerebellar transtentorial (eSCTT) approach is advocated for managing pathologies of the medial temporo-occipital region, but quantitative analysis is currently lacking. The aims of this study were to establish a grid coordinate system on the tentorium to model the anatomical relationship between medial temporo-occipital region pathology and the slope of the tentorium, and then to compare the paramedian eSCTT and extreme-lateral eSCTT approaches quantitatively. Bilateral paramedian and extreme-lateral eSCTT approaches were used to dissect three adult cadaveric heads anatomically. A grid coordinate system was established on the tentorium, and the angles of attack and depth of the surgical corridor of each coordinate point were obtained so that the two eSCTT approaches could be compared statistically. The measurements were then analyzed to determine the condition for selecting each eSCTT approach, and its clinical feasibility was assessed in three patients with large tumors in the medial temporo-occipital region. For coordinate points where the X-coordinate on the grid coordinate system was 1 cm outside the apex of the tentorium, the paramedian eSCTT approach had a significantly wider angle of attack and shorter depth of surgical corridor than the extreme-lateral eSCTT approach. In contrast, the extreme-lateral eSCTT approach was better for coordinate points where the Y-coordinate on the grid coordinate system was 1 cm in front of the apex of the tentorium. The long axis of each patient's tumor was projected on to the tentorium and its corresponding coordinate points were used to match the more appropriate eSCTT approach. Preliminary results for three patients treated with the eSCTT approach for large tumors in the medial temporo-occipital region were encouraging. When the eSCTT approach is applied to manage a large tumor of the medial temporo-occipital region, assessment of the long axis of the tumor and knowledge of the selective condition for each eSCTT approach can help in clinical decision-making.

Endoscopic-assisted paramedian supracerebellar infratentorial approach to the posterior portion of the third ventricle: anatomical study and surgical cases

BACKGROUND

To date, morphometrical data providing a systematic quantification of accessibility and operability parameters to the boundaries of the posterior portion of the third ventricle (PTV) when applying an endoscopic-assisted paramedian supracerebellar infratentorial approach (EPSIA) are lacking. We performed an anatomical study and complemented our findings with surgical cases.

METHODS

Eight EPSIAs towards the PTV were performed in cadaveric specimens. Optimal approach angles (OA), surgical freedom (SF) and operability indexes (Oi) to the PTV boundaries were assessed. Additionally, a 54-year-old man and 33-year-old woman were operated on PTV tumors applying the EPSIA.

RESULTS

Sagittal OA to ventricle's roof and floor was 36±1.4° and 25.5±3.5° respectively, axial OA to the ipsilateral and contralateral ventricle's wall were 9.5±1.3° and 28.5±1.6°. SF was maximal on the contralateral wall (121.2±19.3mm2), followed by the roof (112.7±18.8mm2), floor (106.6±19.2mm2) and ipsilateral wall (94.1±15.7mm2). SF was significantly lower along the ipsilateral compared the contralateral wall (P<0.01) and roof (P<0.05). Facilitated surgical maneuvers with multiangled exposure were possible up to 8.5±1.07mm anterior to ventricle's entrance, whereas surgical maneuvers were possible but difficult up to 15.25±3.7mm. Visualization of more anterior was possible up to a distance of 27±2.9mm, but surgical maneuvers were barely feasible. EPSIA enabled successful resection of both PTV tumors and postoperative course was uneventful.

CONCLUSIONS

EPSIA can be effective for approaching the PTV, enabling surgery along all boundaries, but especially on its roof and contralateral wall. In the not-enlarged ventricle, surgical maneuvers are feasible up to the level of the Monro foramen, becoming more limited anteriorly.

Advanced Surgical Techniques for Dural Venous Sinus Repair: A Comprehensive Literature Review

The dural venous sinus (DVS) is a thin-walled blood channel composed of dura mater that is susceptible to injury during common neurosurgical approaches. DVS injuries are highly underreported, which is reflected by a lack of literature on the topic. Neurosurgeons should be familiar with appropriate techniques to successfully repair an injured DVS and prevent associated complications. This study presents a literature review on the surgical techniques for DVS repair after DVS injury during common neurosurgical approaches. The databases PubMed and Scopus were queried using the terms "cranial sinuses," "superior sagittal sinus," "transverse sinuses," "injury," and "surgery." A total of 117 articles underwent full-text review and were analyzed for surgical approach, craniotomy, lesion location, lesion characteristics, and surgical repair techniques. A literature review was performed, and a comprehensive summary is presented. Data from publications describing DVS lacerations related to pathological conditions (eg, meningioma) were excluded. A total of 9 techniques aiding with bleeding control, hemostasis, and sinus repair and reconstruction were identified, including compression, hemostatic agents, bipolar cautery, dural tenting and tack-up suturing, dural flap, direct suturing, autologous patch, venous bypass, and ligation. The advantages and drawbacks of each technique are described. Multiple options to treat DVS injuries are available to the neurosurgeon. Treatment type is based on anatomic location, complexity of the laceration, cardiovascular status, the presence of air embolism, and the dexterity and experience of the surgeon.

Postoperative elevated bed header position versus supine in the management of chronic subdural hematoma: a systematic review and meta-analysis

BACKGROUND

Chronic subdural hematoma (CSDH) is a prevalent type of intracranial hemorrhage. Surgical interventions, such as Twist Drill Craniostomy and Burr Hole Craniostomy, are employed for its treatment. However, limited information exists regarding the impact of postoperative head position (supine vs. elevated) on clinical outcomes. We aim to assess whether patients' head position after surgery influences their prognosis.

METHOD

We conducted a PRISMA-compliant systematic review and meta-analysis. Our search encompassed PubMed, Cochrane CENTRAL, Scopus, Web of Science, and Embase databases to identify relevant published studies. Data were meticulously extracted, pooled using a fixed model, and reported as risk ratios (RR) with 95% confidence intervals (CI). Statistical analysis was performed using R and Stata MP v.17.

RESULTS

Five studies involving 284 patients were included in our meta-analysis. We focused on three primary clinical outcomes, comparing the supine and elevated header positions. Notably, there was no statistically significant difference between the supine and elevated positions in terms of recurrence rate (RR 0.77, 95% CI [0.44, 1.37]), second intervention for recurrence (RR 1.07, 95% CI [0.42, 2.78]) and postoperative complications (RR 1.16, 95% CI [0.70, 1.92]).

CONCLUSION

Current studies have proved no difference between supine and elevated bed header positions regarding recurrence rate, second intervention for recurrence, and postoperative complications. Future RCTs with long-term follow-ups are recommended.

Semisitting position for cerebello-pontine angle surgery: Analysis of complications and how to avoid it

OBJECTIVE

To analyze the primary complications related to semisitting position in patients undergoing cerebelo-pontine angle surgery.

METHODS

Retrospective data analysis from patients undergoing elective tumoral cerebelo-pontine angle surgery in a semisitting position. The incidence, severity, occurrence moment, treatment, duration, and outcomes of venous air embolism (VAE), pneumocephalus, postural hypotension, and other complications were recorded. Neurointensive care unit (NICU), length of stay (LOS), hospital LOS, and modified Rankin scale scores were calculated six months after surgery.

RESULTS

Fifty patients were operated on. Eleven (22%) presented VAE (mean duration 8±4.5min): five (10%) during tumor resection, and four (8%) during dural opening. Ten (20%) were resolved by covering the surgical bed, air bubbles aspiration, jugular compression, and one (2%) tilted to a steep Trendelenburg position. One (2%) had intraoperative hemodynamic instability. The only variable associated with VAE was meningioma at histopathology OR=4.58, p=0.001. NICU was higher in patients with VAE (5.5±1.06 vs. 1.9±0.20 days, p=0.01). There were no differences in the Rankin scale. All patients presented postoperative pneumocephalus with a good level of consciousness, except one (2%) who required evacuation. Seven patients (14%) showed postural hypotension, three (6%) after positioning, and one (2%) after developing a VAE; all were reversed with usual vasoactive drugs. No other position-related complications or mortality were registered in this series.

CONCLUSIONS

The semisitting position is a safe option with the knowledge, prevention, detection, and early solution of all the possible complications. The development of VAE rarely implies hemodynamic instability or greater disability after surgery. Postoperative pneumocephalus is very common and rarely requires evacuation. Excellent cooperation between anesthesia, nursing, neurophysiology, and neurosurgery teams is essential to manage complications.

Suspected systemic gas embolism associated with lung tissue perforation caused by a previously inserted chest drain in a dog

OBJECTIVE

To report a case of systemic gas embolism associated with removal of a chest drain perforating a lung lobe in a dog undergoing sternotomy under general anesthesia and intermittent positive pressure ventilation.

CASE SUMMARY

An 8-year-old Cocker Spaniel underwent an exploratory thoracotomy via median sternotomy for surgical management of pyothorax that was treated conservatively for 7 days prior to referral following bilateral chest drain placement. The surgical procedure consisted of a subphrenic mediastinectomy and pericardiectomy. During surgery, it became apparent that the right drain was perforating the right middle lung lobe. Sudden desaturation and rapid hemodynamic deterioration occurred after the drain was removed. A systemic gas embolism was suspected on the basis of clinical signs and results of an arterial blood gas analysis, and immediate supportive treatment was started with an adequate response. Once the surgical procedure was completed, a clear "mill wheel" sound was audible on cardiac auscultation and point-of-care cardiac ultrasound confirmed the presence of gas bubbles in the cardiac chambers. The dog recovered from anesthesia and was managed in the intensive care unit where arterial blood gas analyses were nearly normal and the dog made a full recovery.

NEW OR UNIQUE INFORMATION PROVIDED

In people, there are reports of fatal air embolism related to the use of chest drains. To our knowledge, this is the first case report in dogs of a systemic gas embolism during open-chest surgery caused by a chest drain perforating a lung lobe. Immediate recognition and aggressive treatment of this life-threatening condition should be provided in order to achieve a favorable outcome.

Dynamic Lateral Semisitting Position for Supracerebellar Approaches: Technical Note and Case Series

BACKGROUND

It has always been a matter of debate which position is ideal for the supracerebellar approach. The risk of venous air embolism (VAE) is the major deterrent for surgeons and anesthesiologists, despite the fact that sitting and semisitting positions are commonly used in these operations.

OBJECTIVE

To demonstrate a reduction on the risk of VAE and tension pneumocephalus throughout the operation period while taking advantages of the semisitting position.

METHODS

In this study, 11 patients with various diagnoses were operated in our department using the supracerebellar approach in the dynamic lateral semisitting position. We used end-tidal carbon dioxide and arterial blood pressure monitoring to detect venous air embolism.

RESULTS

None of the patients had clinically significant VAE in this study. No tension pneumocephalus or major complications were observed. All the patients were extubated safely after surgery.

CONCLUSION

The ideal position, with which to apply the supracerebellar approach, is still a challenge. In our study, we presented an alternative position that has advantages of the sitting and semisitting positions with a lower risk of venous air embolism.

The parietooccipital interhemispheric transtentorial approach for pineal tumors

Access to the pineal region has always been a challenge for neurosurgeons. The parietooccipital interhemispheric transtentorial approach is a slight variation of the traditional occipital transtentorial approach that provides adequate exposure to the lesions of the pineal region without introducing additional risks. In this study, the modified parietooccipital interhemispheric transtentorial approach is discussed including step-by-step anatomical cadaveric dissections and operative images. 27 adult patients (age > 18) who were operated over a 30-year period (1992-2022) by the senior author (M.N.P.) at two clinics, Marmara University, Department of Neurosurgery, Istanbul, Turkey and Acibadem Mehmet Ali Aydinlar University, Department of Neurosurgery, Istanbul, Turkey were analyzed. Only pineal region tumors were included in the analysis. Falcotentorial meningiomas and vascular lesions including cavernomas were excluded. 5 cadaveric specimens were dissected step by step following the surgical approach. Each step was documented using a Canon EOS 5D Mark II camera with Canon 100 mm Macro Lens. Step by step images of the dissections were presented including comparison with surgical images. Additional illustrations were used to describe the surgical corridor. The surgical corridor is maintained anterior to the parietooccipital sulcus along the medial of the precuneus. No retraction to the calcarine sulcus resulted in no postoperative hemianopsia. The neurovascular structures along the surgical corridor along with the nuances of the tentorium incision and splenium resection are discussed. The parietooccipital interhemispheric transtentorial approach provides a wide and safe corridor for surgical resection of pineal tumors.

Before the Knife: A Detailed Step-by-Step Description of an Optimized Semi-Sitting Position in Posterior Fossa Surgery

BACKGROUND

In an ample armamentarium in neurosurgery, the semi-sitting position has produced debate regarding its benefits and risks. Although the position is apparently intuitive, many have abandoned its use since its initial inception, because of reported complexity and potential complications, leading to impracticality. However, through standardization, it has been shown not only to be safe but to carry with it many advantages, including less risk of secondary neurovascular injuries and better visualization of the surgical field. As with any surgical technical nuance, the semi-sitting position has advantages and disadvantages that must be weighed before the decision is made to adopt it or not, not only in a case-by-case scenario but also from a departmental standpoint. As we attempt to show, the advantages from a standardized approach for the semi-sitting position in experienced institutions may be more than sufficient to significantly outweigh the disadvantages, making it the preferable option for most, although not all, posterior fossa surgical interventions.

METHODS

In the present study, we aim to elaborate a straightforward narrative of the steps before incision, in an attempt to simplify the complexity of the position, alleviating its disadvantages and exponentially concentrating on its benefits. In nearly 100 steps, we carefully describe the points that culminate with the skin incision, initiating the intraoperative part of the procedure. Each step, therefore, is detailed in full, not in an effort to create a strict manual of the semi-sitting position but rather to facilitate understanding and put the technique into effect in a real-life scenario, thus simplifying what some depict as complex and time consuming.

CONCLUSIONS

Although several of the steps described are also relevant and integral parts of other surgical positioning, we intend to create a protocol, in a stepwise fashion, to allow facilitated following, to be easily implemented in departments with different levels of experience. The steps comprise nursing care through to electrophysiologic and anesthesiologic approaches, along with neurosurgical cooperation, making it a team approach, not only to avoid position-related complications but also to optimize preoperative standardization, constructing a safe, efficient, and patient-centered scenario, to set the best possible stage for the next step: the intraoperative part of the intervention.

Analysis of Imaging Results for Semisitting Compared with Supine Positioning in the Retrosigmoid Approach for Resection of Cerebellopontine Angle Vestibular Schwannomas

OBJECTIVE

To compare the completeness of resection of vestibular schwannomas using three-dimensional segmented volumetric analysis of pre- and postoperative magnetic resonance imaging (MRI) of patients undergoing supine and semisitting positioning for the retrosigmoid approach.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary medical center.

PATIENTS

Patients with vestibular schwannomas undergoing surgical resection via the retrosigmoid approach.

INTERVENTIONS

Tumor resection via the retrosigmoid approach with different patient positioning: standard supine versus semisitting.

MAIN OUTCOME MEASURES

Preoperative versus postoperative three-dimensional segmented volumetric MRI analysis of vestibular schwannomas.

RESULTS

A total of 43 patients (15 supine and 28 semisitting) underwent retrosigmoid craniotomy for resection of vestibular schwannomas. For the conventional supine and semisitting positioning, mean preoperative tumor volumes were 12.65 and 8.73 cm 3 ( p = 0.15), respectively. Postoperative mean tumor volumes for the supine and semisitting positions were 2.09 and 0.48 cm 3 ( p = 0.13), respectively. There were 11 cases of postoperative sigmoid sinus thrombosis, 3 in the conventional supine group and 8 in the semisitting groups, and there were 6 cases of postoperative cerebrospinal fluid leaks, all in the semisitting group. The mean House-Brackmann scores for the supine and semisitting groups were 2.9 and 2.3, respectively. There was no statistically significant difference between groups in the rates of these or any other postoperative complications.

CONCLUSIONS

The semisitting position for the suboccipital retrosigmoid approach for vestibular schwannoma resection does not compromise the ability to adequately resect the tumor as seen by volumetric MRI results. Further studies are needed to establish the safety of this position compared with the traditional supine approach.

The semi-sitting position in patients with indwelling CSF shunts: perioperative management and avoidance of complications

OBJECTIVE

Posterior fossa or midline tumors are often associated with hydrocephalus and primary tumor removal with or without perioperative placement of an external ventricular drain (EVD) is commonly accepted as first-line treatment. Shunting prior to posterior fossa surgery (PFS) is mostly reserved for symptomatic cases or special circumstances. There are limited data regarding the anticipated risk for symptomatic pneumocephalus and the perioperative management using the semi-sitting position (SSP) in such a scenario. Here, we therefore assessed the safety of performing PFS in a consecutive series of patients over a period of 15 years to allow the elaboration of recommendations for perioperative management.

METHODS

According to specific inclusion and exclusion criteria a total of 13 patients who underwent 17 operations was identified. Supratentorial pneumocephalus was evaluated with semiautomatic-volumetric segmentation. The volume of pneumocephalus was evaluated according to age and ventricular size.

RESULTS

Ten of the 13 patients had a programmable valve (preoperative valve setting range 6-14 cmH20; mean 7.5 cmH20) while 3 patients had non programmable valves. A variable amount of supratentorial air collection was evident in all patients postoperatively (range 3.2-331 ml; mean 122.32 ml). Positive predictors for the volume of postoperative pneumocephalus were higher age and a preoperative Evans ratio > 0.3. In our series, we encountered no cases of tension pneumocephalus necessitating an air replacement procedure as well as no obstruction, disconnection, infection or hardware malfunction of the shunt system.

CONCLUSIONS

Our findings indicate that a CSF shunt in situ is not a contraindication for performing PFS in the semi-sitting position and it does not increase the pre-existing risk for postoperative tension pneumocephalus. In cases of primary shunting for hydrocephalus associated with posterior fossa tumors a programmable valve set at a medium opening pressure with a gravitational device is a valid option when PFS in the semi-sitting position is opted. In patients with an indwelling shunt diversion system special caution is indicated in order to prevent and detect overdrainage especially in not adjustable valves or shunts without antisiphon devices.

Resection of posterior fossa tumors in the semi-sitting position in children younger than 4 years of age

PURPOSE

The semi-sitting position for resection of posterior fossa tumors is a matter of ongoing debate. Here we report about our experience with this approach in children younger than 4 years of age.

METHODS

We retrospectively analyzed data of children younger than 4 years of age operated on in our institution in the semi-sitting position over a 15-year period. Patients were intraoperatively monitored for venous air embolism (VAE) by transthoracic Doppler (TTD) or transesophageal echocardiography (TEE). The severity of VAE was classified according to the Tübingen grading scale. Intraoperative incidents of VAE were recorded and the patients' course was followed postoperatively with a special focus on possible complications.

RESULTS

Twenty-four children (18 boys, 6 girls) were operated on in the semi-sitting position (26 operations). Mean age was 2.2 years (± 1.0), range between 0.4 and 3.9 years. External ventricular drains were inserted in 18 children with hydrocephalus preoperatively. VAE was detected in 6 instances during surgery (6/26 (23.1%)). In 3 patients with grade 1 VAE, no additional treatment was necessary. In one patient with grade 2 VAE, intracardiac air suction via the central venous catheter was performed, and in two patients with grade 4 VAE, additional cathecholamine-infusion was administered. No major intraoperative complications occurred. Postoperative CT images showed pneumocephalus in all children. In two children, small asymptomatic impression skull fractures at the site of the Mayfield pin occurred. Revision surgery was necessary in one child with a suboccipital CSF fistula.

CONCLUSION

The semi-sitting position for resection of tumors in the posterior fossa in children younger than 4 years of age can be safely performed in experienced centers taking special caution to detect and treat potential complications in an interdisciplinary setting.

Analysis of risk factors for venous air embolism in the semisitting position and its impact on outcome in a consecutive series of 740 patients

OBJECTIVE

Routine use of the semisitting position, which offers several advantages, remains a matter of debate. Venous air embolism (VAE) is a potentially serious complication associated with the semisitting position. In this study, the authors aimed to investigate the safety of the semisitting position by analyzing data over a 20-year period.

METHODS

The incidence of VAE and its perioperative management were analyzed retrospectively in a consecutive series of 740 patients who underwent surgery between 1996 and 2016. The occurrence of VAE was defined by detection of bubbles on transthoracic Doppler echocardiography (TTDE) or transesophageal echocardiography (TEE) studies, a decrease of end-tidal CO2 (ETCO2) by 4 mm Hg or more, and/or an unexplained drop in systolic arterial blood pressure (≥ 10 mm Hg). From 1996 until 2013 TTDE was used, and from 2013 on TEE was used. The possible risk factors for VAE and its impact on surgical performance were analyzed.

RESULTS

There were 404 women and 336 men with a mean age at surgery of 49 years (range 1-87 years). Surgery was performed for infratentorial lesions in 709 patients (95.8%), supratentorial lesions in 17 (2.3%), and cervical lesions in 14 (1.9%). The most frequent pathology was vestibular schwannoma. TEE had a higher sensitivity than TTDE. While TEE detected VAE in 40.5% of patients, TTDE had a detection rate of 11.8%. Overall, VAE was detected in 119 patients (16.1%) intraoperatively. In all of these patients, VAE was apparent on TTDE or TEE. Of those, 23 patients also had a decrease of ETCO2, 18 had a drop in blood pressure, and 23 had combined decreases in ETCO2 and blood pressure. VAE was detected in 24% of patients during craniotomy before opening the dura mater, in 67% during tumor resection, and in 9% during wound closure. No risk factors were identified for the occurrence of VAE. Two patients had serious complications due to VAE. Surgical performance in vestibular schwannoma surgery was not affected by the presence of VAE.

CONCLUSIONS

This study shows that the semisitting position is overall safe and that VAE can be managed effectively. Persistent morbidity is very rare. The authors suggest that the semisitting position should continue to have a place in the standard armamentarium of neurological surgery.

The effects of different surgical positions (semi-sitting and lateral position) on the surgical outcomes of large vestibular schwannoma: study protocol for a randomized controlled trial

Background

There is an ongoing discussion about the advantages and disadvantages of different surgical positions (semi-sitting and lateral position) for vestibular schwannoma surgery. Each position has its advantages, disadvantages, challenges, and risk profiles. The objectives of this study are to compare the effects of different surgical positions (semi-sitting and lateral position) on the outcomes of large vestibular schwannoma, primarily including effectiveness and safety.

Methods

In this single-centre, open, randomized controlled trial, we will recruit a total of 116 participants according to the inclusion and exclusion criteria who will be randomized to an experimental group or control group. Patients will undergo operations in semi-sitting and lateral positions. The primary endpoint will be the percentage of gross total resection. The secondary endpoints will include the facial nerve function, hearing preservation, surgical position placement time, time of operation (skin-to-skin surgical time), hospital stay, total hospitalization fee, and complications. The follow-up period will be at least 12 months, during which time patients will be evaluated both clinically and radiologically.

Discussion

This issue is still debated after 30 years since the first large comparative study was published in 1989, so the study will be useful. Therefore, more high-quality studies are required to compare clinical outcomes, complications, and other factors associated with these two positions.

Trial registration

Chinese Clinical Trial Registry ChiCTR1900027550. Registered on 17 November 2019

Occurrence and severity of venous air embolism during neurosurgical procedures in semi-sitting versus supine position

BACKGROUND

At our institution, patients undergoing neurosurgical procedures in the posterior cranial fossa are placed either in the semi-sitting or in the supine position. The major risk of the semi-sitting positioning is a venous air embolism (VAE), which may, however, also occur in the supine position.

METHODS

In a prospective single-center study with 137 patients, we evaluated the occurrence of VAEs in patients in the supine and in the semi-sitting position over the period from January 2014 until April 2015. All patients were monitored for VAE by the use of a transesophageal echocardiography (TEE).

RESULTS

50% of the patients experienced a VAE (with 56% of these patients underwent surgery in the semi-sitting and 11% in the supine position). 86% of the VAEs were just detected by the use of a TEE and did not lead to any changes in the end-expiratory (Et)CO₂. We only observed VAEs with a decrease in EtCO₂ in the semi-sitting position. However, none of the patients had any hemodynamic changes due to the VAE.

CONCLUSIONS

The semi-sitting position with TEE monitoring and a standardized protocol is a safe and advantageous technique, taking account of a significant rate of VAEs. VAEs also occur in the supine position, however, less frequently.

The semisitting position in pediatric neurosurgery: pearls and pitfalls of a 10-year experience

OBJECTIVE

The authors sought to investigate the pearls and pitfalls of using the semisitting position in pediatric neurosurgery, with special focus on related morbidity and surgical practicability.

METHODS

All pediatric cases at a single institution were evaluated retrospectively. Those patients who underwent procedures in the semisitting position between December 2010 and December 2020 were included in the final analysis. Results were compared with all children who underwent surgery in the prone position for posterior fossa lesions within the same time frame.

RESULTS

A total of 42 posterior fossa surgeries were performed in 38 children in the semisitting position between December 2010 and December 2020. The mean patient age at the time of surgery was 8.9 years (range 13 months-18 years). The data of 24 surgeries performed in the prone position in 22 children during the same time frame were analyzed in comparison. Three children (7.9%) were diagnosed with a persistent foramen ovale preoperatively. The surgery was completed in all cases. The incidence of venous air embolism (VAE) was 11.9%. There was no VAE-related hemodynamic instability, infarction, or death. Endoscopic techniques were applied safely in 14 cases (33.3%). Postoperative pneumocephalus occurred significantly more frequently in patients who had undergone procedures in the semisitting position (p < 0.05), but without the need for intervention. During 1 surgery (2.4%), the patient experienced a postoperative skull fracture and epidural bleeding due to the skull clamp application. Clinical status of the patients immediately after surgery was improved or stable in 33 of the 42 surgeries (78.6%) performed in the semisitting position.

CONCLUSIONS

With attentive performance and an experienced surgical team, the semisitting position is a safe option for posterior fossa surgery in the pediatric population. With a comparable complication profile, the semisitting position offers excellent anatomical exposure, which is ideal for the application of endoscopic visualization. Careful skull clamp application and appropriate monitoring are highly recommended.

Air-embolism in the semi-sitting position for craniotomy: A narrative review with emphasis on a single centers experience

Albeit the semi-sitting position in neurosurgery has been in use for several decades, its application remains controversial in the neurosurgical and neuro-anaesthesia communities. The imminent and most feared risk of the sitting position is air entry into the vascular system due to the negative intravascular pressure leading to potentially life-threatening air embolism with its consequences. Recent advents in neurosurgical (improvement of the operating microscope, employment of intra-operative neurophysiological monitoring) and neuro-anaesthesia care (new anaesthetics, advanced monitoring modalities) have significantly impacted the approach to these surgeries. Vigilant intra-operative observation by an experienced team and peri-operative patient management guided by institutional protocols improves the safety profile of these surgeries. This review outlines the workflow and protocols used in our institution for all cases of semi-sitting position for skull base neurosurgery.

History, Variations, and Extensions of the Retrosigmoid Approach: Anatomical and Literature Review

The retrosigmoid approach is the workhorse for posterior fossa surgery. It gives a versatile corridor to tackle different types of lesions in and around the cerebellopontine angle. The term “extended” has been used interchangeably in the literature, sometimes creating confusion. Our aim was to present a thorough analysis of the approach, its history, and its potential extensions. Releasing cerebrospinal fluid from the subarachnoid spaces and meticulous microsurgical techniques allowed for the emergence of the retrosigmoid approach as a unilateral variation of the traditional suboccipital approach. Anatomical landmarks are helpful in localizing the venous sinuses and planning the craniotomy, and Rhoton's rule of three is the key to unlock difficult neurovascular relationships. Extensions of the approach include, among others, the transmastoid, supracerebellar, far-lateral, jugular foramen, and perimeatal approaches. The retrosigmoid approach applies to a broad range of pathologies and, with its extensions, can provide adequate exposure, obviating the need for extensive and complicated approaches.

Awake surgery in sitting position for chronic subdural hematoma

BACKGROUND

Chronic subdural hematoma (CSDH) is a common pathology in neurosurgery, especially in the elderly patients, and its incidence is likely to double in the next decade. Considering various features of CSDH and the procedure itself, a sitting position may retain the best characteristics of classic positioning, while offering additional comfort for both the patient and the surgeon. The aim of this study was to describe the technical aspects of this procedure in the sitting position, to evaluate safety and discuss the benefits and shortcomings of this modification.

METHOD

This study included a series of 55 patients surgically treated for CSDH in a sitting position at our department between December 2017 and September 2019, representing all the patients operated on during the study period by a single surgeon. Bilateral hematomas were present in 19 patients. Outcomes, during the 6-month follow-up period, were defined as good (CSDH and symptoms resolved) or poor (lethal outcome or reoccurrence). All complications were noted, with emphasis on pneumocephalus, and complications related to the sitting position: tension pneumocephalus, venous air embolism, and compression nerve injury.

RESULTS

Complications previously associated with the sitting position were not noted. The Glasgow Coma Scale and Markwalder Grading Scale scores improved significantly after the surgery (p < 0.001 and p = 0.018). Complications were noted in 17 patients (30.9%), and included 5 cerebrospinal fluid drainages, 3 hematoma reoccurrences, 2 wound infections, and 9 more single-occurring complications. The in-hospital mortality was 5.4% (3 out of 55 patients), while the overall mortality was 16.4% within the 6-month follow-up period.

CONCLUSIONS

In our series, even the severely ill patients tolerated the position well. No complications associated with the sitting position were noted. Future studies should confirm the safety of this position and evaluate the potential advantages for both the patient and the surgeon.

Microvascular Decompression for Glossopharyngeal Neuralgia in the Semi-Sitting Position: A Report of Two Cases

The semi-sitting position is well known to neurosurgeons. However, there are few reports of microvascular decompression surgery for glossopharyngeal neuralgia performed using the semi-sitting position. The semi-sitting position is not widely adopted in Japan, but it is considered to be a very useful neurosurgical position. Microvascular decompression surgery for glossopharyngeal neuralgia is a relatively rare procedure, and the semi-sitting position is very effective, considering the possibility of intraoperative cardiac arrest and postoperative complications of lower cranial nerve palsy. This report describes two cases of glossopharyngeal neuralgia operated in the semi-sitting position. Microvascular decompression was performed on both patients, and postoperative pain controls were good and no complications were observed. We show that the use of the semi-sitting position to perform microvascular decompression for glossopharyngeal neuralgia provides an excellent surgical view of the brainstem.

[Intraoperative vascular air embolism : Evidence for risks, diagnostics and treatment]

The entry of gases into the vascular system is called vascular air embolism (VAE). The blocking of the pulmonary circulation by VAE can lead to fulminant right-sided heart failure and cardiocirculatory arrest. A VAE can occur at any time if there is an open connection between the environment and a venous vessel with subatmospheric pressure. This situation occurs during ear nose throat surgery, hip surgery, surgery of the lesser pelvis or breast surgery, if the surgical field is above the level of the heart; however, a VAE can also occur during routine tasks, such as insertion or removal of a central venous catheter or during endoscopic procedures with the insufflation of gas.Because during these procedures VAE is not the main focus of the anesthesia or surgery personnel, in such situations its sudden unexpected occurrence can have severe consequences. In contrast, in cardiac surgery or neurosurgery the risk of intraoperative VAE is much better known. In procedures with a higher risk of a clinically relevant VAE, a patent foramen ovale should be ruled out by preoperative transesophageal echocardiography (TEE). Intraoperatively TEE is the most sensitive procedure not only to detect a VAE but also to visualize the clinical expression, e.g. acute right heart overload.The avoidance of an initial and repeated air embolism is the primary measure to minimize the incidence and severity of VAE.Intraoperatively the following measures should be undertaken: excellent communication between anesthesia and surgery personnel with predetermined actions, maintenance of normal volume, patient positioning with minimal difference in height between heart and head, state of the art surgical technique with closure of potential air entry sites, sufficient detection of air by TEE, repeated jugular vein compression during neurosurgery, intraoperative Trendelenburg positioning of the patient during persisting or clinically evident VAE, differentiated adjustment of ventilatory settings and catecholamine treatment, aspiration of the blood-air mixture (air lock) at the junction of the superior vena cava and right atrium through a large bore central venous line and keeping check of the coagulation status.

Anatomic, qualitative, and quantitative evaluation of the variants of the infratentorial supracerebellar approach to the posteroinferior thalamus

The posteroinferior region of the thalamus is formed by the pulvinar, and it is surgically accessed through the infratentorial supracerebellar approach, between the midline and the retromastoid region. This study aimed to compare the paramedian, lateral, extreme lateral, and contralateral paramedian corridors with the posteroinferior thalamus through a suboccipital craniotomy and an infratentorial supracerebellar access. Ten cadavers were studied, and the microsurgical dissections were accompanied by the measurement of the variables using a neuronavigation system. Statistical analysis was performed using analysis of variance (ANOVA). The distance between the access midpoint at the cranial surface and pulvinar varied between 53.3 and 53.9 mm, the contralateral access being an exception (59.9 mm). The vertical angle ranged from 20.6° in the contralateral access to 23.5° in the lateral access. There was a gradual increase in the horizontal angle between the paramedian (17.4°), lateral (31.3°), and extreme lateral (43.7°) accesses. But, this angle in the contralateral access was 14.6°, similar to that of the paramedian access. The exposed area of the thalamus was 125.1 mm² in the paramedian access, 141.8 mm² in the lateral access, and 165.9 mm² in the extreme lateral access, which was similar to that of the contralateral access (164.9 mm²). The horizontal view angle increased with lateralization of the access, which facilitated microscopic visualization. With regard to the exposure of the microsurgical anatomy, the extreme lateral and contralateral accesses circumvent the neural and vascular obstacles at the midline, allowing a larger area of anatomical exposure.

Automatic detection of venous air embolism using transesophageal echocardiography in patients undergoing neurological surgery in the semi-sitting position: a pilot study

Neurological surgery in the semi-sitting position is linked with a pronounced incidence of venous air embolism (VAE) which can be fatal and therefore requires continuous monitoring. Transesophageal echocardiography (TEE) provides a high sensitivity for the intraoperative detection of VAE; however, continuous monitoring with TEE requires constant vigilance by the anaesthesiologist, which cannot be ensured during the entire surgical procedure. We implemented a fully automatic VAE detection system for TEE based on a statistical model of the TEE images. In the sequence of images, the cyclic heart activity is regarded as a quasi-periodic process, and air bubbles are detected as statistical outliers. The VAE detection system was evaluated by means of receiver operating characteristic (ROC) curves using a data set consisting of 155.14 h of intraoperatively recorded TEE video and a manual classification of periods with visible VAE. Our automatic detection system accomplished an area under the curve (AUC) of 0.945 if all frames with visible VAE were considered as detection target, and an AUC of 0.990 if frames with the least severe optical grade of VAE were excluded from the analysis. Offline-review of the recorded TEE videos showed that short embolic events (≤ 2 min) may be overseen when monitoring TEE video manually. Automatic detection of VAE is feasible and could provide significant support to anaesthesiologists in clinical practice. Our proposed algorithm might possibly even offer a higher sensitivity compared to manual detection. The specificity, however, requires improvement to be acceptable for practical application. Trial Registration: German Clinical Trials Register (DRKS00011607).

Estimation of the head elevation angle that causes clinically important venous air embolism in a semi-sitting position for neurosurgery: a retrospective observational study

Introduction:

The benefits of a sitting position for neurosurgery involving the posterior fossa remain controversial. The main concern is the risk of venous air embolism (VAE). A recent study showed that the rate of VAE was higher when the head was elevated to 45° than when it was elevated to 30°. However, the degree of head elevation that causes clinically important VAE is unclear. The purpose of this study was to estimate the head elevation angle at which the probability of VAE is 50% by using EtCO₂ monitoring to detect of VAE.

Methods:

The anesthesia records of 23 patients who underwent neurosurgery in a sitting position were reviewed retrospectively. Intraoperative ventilation was set to maintain EtCO₂ at approximately 38-42 mmHg. The head elevation angle in each case was determined from a photograph taken by the anesthesiologist or brain surgeon. Nineteen of the 23 cases had photographs available that contained a horizontal reference in the background. Seven cases were treated as VAE during the operation. Six of these cases met the criteria for VAE in this study. Data analysis was performed on a total of 18 patients. The angle between the line connecting the hip joint and the shoulder joint and the horizontal reference was obtained by ImageJ software. Logistic regression was performed using the Python programming language to determine the head elevation angle at which the probability of air embolism was 50%.

Results:

The decision boundary in the logistic regression was 35.7°. This head elevation angle was the boundary where the probability of VAE was 50%.

Conclusion:

The angle of head elevation that caused clinically important VAE was estimated to be 35.7°.

A critical comparison between the semisitting and the supine positioning in vestibular schwannoma surgery: subgroup analysis of a randomized, multicenter trial

OBJECTIVE

Patient positioning in vestibular schwannoma (VS) surgery is a matter of ongoing discussion. Factors to consider include preservation of cranial nerve functions, extent of tumor resection, and complications. The objective of this study was to determine the optimal patient positioning in VS surgery.

METHODS

A subgroup analysis of a randomized, multicenter trial that investigated the efficacy of prophylactic nimodipine in VS surgery was performed to investigate the impact of positioning (semisitting or supine) on extent of resection, functional outcomes, and complications. The data of 97 patients were collected prospectively. All procedures were performed via a retrosigmoid approach. The semisitting position was chosen in 56 patients, whereas 41 patients were treated while supine.

RESULTS

Complete resection was obtained at a higher percentage in the semisitting as compared to the supine position (93% vs 73%, p = 0.002). Logistic regression analysis revealed significantly better facial nerve function in the early postoperative course in the semisitting group (p = 0.004), particularly concerning severe facial nerve paresis (House-Brackmann grade IV or worse; p = 0.002). One year after surgery, facial nerve function recovered. However, there was still a tendency for better facial nerve function in the semisitting group (p = 0.091). There were no significant differences between groups regarding hearing preservation rates. Venous air embolism with the necessity to terminate surgery occurred in 2 patients in the semisitting position (3.6%). Supplementary analysis with a 2-tailed permutation randomization with 10,000 permutations of treatment choice and a propensity score matching showed either a tendency or significant results for better facial nerve outcomes in the early postoperative course and extent of resection in the semisitting group.

CONCLUSIONS

Although the results of the various statistical analyses are not uniform, the data indicate better results concerning both a higher rate of complete removal (according to the intraoperative impression of the surgeon) and facial nerve function after a semisitting as compared to the supine position. These advantages may justify the potential higher risk for severe complications of the semisitting position in VS surgery. The choice of positioning has to consider all individual patient parameters and risks carefully.

The impact of transesophageal echocardiography based protocol for management of adults in the sitting position on the incidence of clinically significant venous air embolism

The purpose of the study was to evaluate the impact of transesophageal echocardiography (TEE) – based protocol for management of adults in the sitting position during elective neurosurgical interventions on the incidence of clinically significant venous air embolism (VAE). Material and Methods ― The study involved 155 adult neurosurgery patients (70 in prospective group and 85 in retrospective group). Surgery in both groups was done in the sitting position. In the prospective group TEE-based protocol was used. Retrospective group served as control. The primary endpoint was considered to be a decrease in the frequency of clinically significant VAE in the prospective group in comparison with the retrospective one. In the prospective group, VAE with Tuebingen grade 3-5 was considered clinically significant. The PFO incidence and severity and the effect of the number of episodes of VAE per case on its maximum severity during surgery were also analyzed. Any complication in the postoperative period believed to be associated with the position of the patient on the table during the surgery was recorded. Results ― The incidence of the clinically significant VAE in the retrospective group was 23.5% (95% CI 15-34) and was 16.4% higher than the frequency in the prospective group (chi-square=7.6197, df=1, p=0.005). 50% (95% CI 38-62) of patients in prospective group developed VAE during surgery. In 16 cases, the number of episodes was more than one. The number of episodes of VAE in the observation was reliably associated with the maximum severity of VAE during the observation (Z=4.11; p<0.001). A moderate strength relationship was determined between them (SomersDelta=0.43; 95% CI 0.17-0.7). Not a single case of paradoxical air embolism was detected in a series of observations. None of the patients has got a neurological deficit or cardiopulmonary complications associated with the position on the surgical table in the postoperative period. Pneumocephalus was found in 100% of cases on head computed tomography, which, however, did not need surgical treatment. PFO in the prospective group was detected in 62% (95% CI 52-73) of patients. In 25% (95% CI 16-35), shunting was significant. A large PFO without Valsalva maneuver was detected in 12.5% (95% CI 6-21) of cases. Conclusion ― The use of the TEE-based protocol for the management of adult patients in a sitting position during elective neurosurgical interventions can reduce the incidence of clinically significant VAE.

The Effects of Patient Positioning on the Outcome During Posterior Cranial Fossa and Pineal Region Surgery

Background: Surgery on posterior cranial fossa (PCF) and pineal region (PR) carries the risks of intraoperative trauma to the brainstem structures, blood loss, venous air embolism (VAE), cardiovascular instability, and other complications. Success in surgery, among other factors, depends on selecting the optimal patient position. Our objective was to find associations between patient positioning, incidence of intraoperative complications, neurological recovery, and the extent of surgery.

Methods: This observational study was conducted in two medical centers: The Ohio State University Wexner Medical Center (USA) and The Burdenko Neurosurgical Institute (Russian Federation). Patients were distributed in two groups based on the surgical position: sitting position (SP) or horizontal position (HP). The inclusion criteria were adult patients with space-occupying or vascular lesions requiring an open PCF or PR surgery. Perioperative variables were recorded and summarized using descriptive statistics. The post-treatment survival, functional outcome, and patient satisfaction were assessed at 3 months.

Results: A total of 109 patients were included in the study: 53 in SP and 56 in HP. A higher proportion of patients in the HP patients had >300 mL intraoperative blood loss compared to the SP group (32 vs. 13%; p = 0.0250). Intraoperative VAE was diagnosed in 40% of SP patients vs. 0% in the HP group (p < 0.0001). However, trans-esophageal echocardiographic (TEE) monitoring was more common in the SP group. Intraoperative hypotension was documented in 28% of SP patients compared to 9% in HP group (p = 0.0126). A higher proportion of SP patients experienced a new neurological symptom compared to the HP group (49 vs. 29%; p = 0.0281). The extent of tumor resection, postoperative 3-months survival, functional outcome, and patient satisfaction were not different in the groups.

Conclusions: The SP was associated with, less intraoperative bleeding, increased intraoperative hypotension, VAE, and postoperative neurological deficit. More HP patients experienced macroglossia and increased blood loss. At 3 months, there was no difference of parameters between the two groups.

Clinical Trial Registration:ClinicalTrials.gov: registration number NCT03364283.

A modified park bench position: the "Dormeuse" position

BACKGROUND

Because of the restricted volume of the cisternal space, proper patient positioning on the operating table is of utmost importance during surgery by retrosigmoid approaches. Three positions are commonly used: supine, with the head rotated to the side contralateral to the lesion; the semi-sitting position; and the park bench position. Each position has advantages and disadvantages, and the surgeon should choose the one best suited to the individual patient and the pathology to be treated.

METHODS

We describe a modified park bench position that we call the Dormeuse position.

CONCLUSION

The Dormeuse position guarantees decrease in the posterior fossa pressure and allows optimal neural and vascular manipulation and control of any aspect of the cerebellopontine angle.

Venous air embolisms and sitting position in Helsinki pineal region surgery

Background

Nowadays, the sitting position has lost favor among neurosurgeons partly due to assumptions of increased complications, such as venous air embolisms (VAEs) and hemodynamic disturbances. The aim of our study is to describe the importance of some anesthetic considerations and the utility of antigravity trousers as well, together with a skillful neurosurgery and an imperative proper teamwork, in order to prevent the risk of severe VAE during pineal region surgery. We routinely use them for the variant of the sitting position we developed, the "praying position."

Methods

A retrospective review of 51 pineal lesions operated on in the "praying position" using antigravity trousers was carried out. In the "praying position" the legs of the patient are kept parallel to the floor. Hence, antigravity trousers are used to generate an adequate cardiac preload.

Results

VAE associated to persistent hemodinamic changes was nonexistent in our series. The rate of VAE was 35.3%. VAEs were diagnosed mainly by monitoring of the end-tidal CO₂ (83.33%). A venous system lesion was the cause in most of the cases. When VAE was suspected, an inmediate reaction based on a good teamwork was imperative. No cervical spine cord injury nor peripheral nerve damage were reported. The average microsurgical time was 48 ± 33 min.

Conclusions

The risks of severe VAE during pineal region surgery in the "praying-sitting position" may be effectively prevented by some essential anesthetic considerations and the use of antigravity trousers together with a skillful neurosurgery, and an imperative proper teamwork.

Noninvasive Hemodynamic Measurements During Neurosurgical Procedures in Sitting Position

BACKGROUND

Neurosurgical procedures in sitting position need advanced cardiovascular monitoring. Transesophageal echocardiography (TEE) to measure cardiac output (CO)/cardiac index (CI) and stroke volume (SV), and invasive arterial blood pressure measurements for systolic (ABPsys), diastolic (ABPdiast) and mean arterial pressure (MAP) are established monitoring technologies for these kind of procedures. A noninvasive device for continuous monitoring of blood pressure and CO based on a modified Penaz technique (volume-clamp method) was introduced recently. In the present study the noninvasive blood pressure measurements were compared with invasive arterial blood pressure monitoring, and the noninvasive CO monitoring to TEE measurements.

METHODS

Measurements of blood pressure and CO were performed in 35 patients before/after giving a fluid bolus and a change from supine to sitting position, start of surgery, and repositioning from sitting to supine at the end of surgery. Data pairs from the noninvasive device (Nexfin HD) versus arterial line measurements (ABPsys, ABPdiast, MAP) and versus TEE (CO, CI, SV) were compared using Bland-Altman analysis and percentage error.

RESULTS

All parameters compared (CO, CI, SV, ABPsys, ABPdiast, MAP) showed a large bias and wide limits of agreement. Percentage error was above 30% for all parameters except ABPsys.

CONCLUSION

The noninvasive device based on a modified Penaz technique cannot replace arterial blood pressure monitoring or TEE in anesthetized patients undergoing neurosurgery in sitting position.

Praying Sitting Position for Pineal Region Surgery: An Efficient Variant of a Classic Position in Neurosurgery

BACKGROUND

The sitting position has lost favor among neurosurgeons partly owing to assumptions of increased complications, such as venous air embolisms and hemodynamic disturbances. Moreover, the surgeon must assume a tiring posture. We describe our protocol for the "praying position" for pineal region surgery; this variant may reduce some of the risks of the sitting position, while providing a more ergonomic surgical position.

METHODS

A retrospective review of 56 pineal lesions operated on using the praying position between January 2008 and October 2015 was performed. The praying position is a steeper sitting position with the upper torso and the head bent forward and downward. The patient's head is tilted about 30° making the tentorium almost horizontal, thus providing a good viewing angle. G-suit trousers or elastic bandages around the lower extremities are always used.

RESULTS

Complete lesion removal was achieved in 52 cases; subtotal removal was achieved in 4. Venous air embolism associated with persistent hemodynamic changes was nonexistent in this series. When venous air embolism was suspected, an immediate reaction based on good teamwork was imperative. No cervical spine cord injury or peripheral nerve damage was reported. The microsurgical time was <45 minutes in most of the cases. Postoperative pneumocephalus was detected in all patients, but no case required surgical treatment.

CONCLUSIONS

A protocolized praying position that includes proper teamwork management may provide a simple, fast, and safe approach for proper placement of the patient for pineal region surgery.

The semisitting position: analysis of the risks and surgical outcomes in a contemporary series of 425 adult patients undergoing cranial surgery

OBJECTIVE

The objective of this study was to analyze the incidence of the primary complications related to positioning or surgery and their impact on neurological outcome in a consecutive series of patients undergoing elective surgery in the semisitting position.

METHODS

The authors prospectively collected and retrospectively analyzed data from adult patients undergoing elective surgery in the semisitting position for a cranial disease. Patients were managed perioperatively according to a standard institutional protocol, a standardized stepwise positioning, and surgical maneuvers to decrease the risk of venous air embolism (VAE) and other complications. Intraoperative and postoperative complications were recorded. Neurointensive care unit (NICU) length of stay (LOS) and hospital LOS were the intermediate endpoints. Neurological outcome was the primary endpoint as determined by the modified Rankin scale (mRS) score at 6 months after surgery.

RESULTS

Four hundred twenty-five patients were included in the analysis. VAE occurred in 90 cases (21%) and it made no significant statistical difference in NICU LOS, hospital LOS, and neurological outcome. No complication was directly related to the semisitting position, although 46 patients (11%) experienced at least 1 surgery-related complication and NICU LOS and hospital LOS were significantly prolonged in this group. Neurological outcome was significantly worse for patients with complications (p < 0.0001).

CONCLUSIONS

Even in the presence of intraoperative VAE, the semisitting position was not related to an increased risk of postoperative deficits and can represent a safe additional option for the benefit of specific surgical and patient needs.

Effect of the degree of head elevation on the incidence and severity of venous air embolism in cranial neurosurgical procedures with patients in the semisitting position

OBJECTIVE The semisitting position of a patient confers numerous advantages in various neurosurgical procedures, but venous air embolism is one of the associated complications of this position. To date, no prospective studies of the relationship between the degree of head elevation and the rate and severity of venous air embolism for patients undergoing a procedure in this position have been performed. In this study, the authors compared changes in the severity of venous air embolism according to the degree of head elevation (30° or 45°) in patients undergoing an elective cranial neurosurgical procedure in the semisitting position. METHODS One hundred patients undergoing an elective infratentorial craniotomy in the semisitting position were included, and each patient was assigned to 1 of 2 groups. In Group 1, each patient's head was elevated 30° during surgery, and in Group 2, each patient's head elevation was 45°. Patients were assigned to their group according to the location of their lesion. During surgery, the standard anesthetic protocol was used with total intravenous anesthesia, and transesophageal echocardiography was used to detect air in the blood circulation. Any air embolism seen on the echocardiography screen was classified as Grade 0 to 4. If multiple events occurred, the worst graded attack was used for statistical analysis. During hemodynamic changes caused by emboli, fluid and vasopressor requirements were recorded. Surgical and anesthetic complications were recorded also. All results were compared statistically, and a p value of < 0.05 was considered statistically significant. RESULTS There was a statistically significant difference between groups for the total rates of venous air emboli detected on transesophageal echocardiography (22.0% [n = 11] in Group 1 and 62.5% [n = 30] in Group 2; p < 0.0001). The rate and severity of air embolism were significantly lower in Group 1 than in Group 2 (p < 0.001). The rates of clinically important venous air embolism (Grade 2, 3, or 4, venous air embolism with decreased end-tidal carbon dioxide levels and/or hemodynamic changes) were 8.0% (n = 4) in Group 1 and 50.0% (n = 24) in Group 2 (p < 0.0001). There was no association between the rate and severity of venous air embolism with patient demographics (p > 0.05). An association was found, however, between the rate of venous air embolism and the type of surgical pathology (p < 0.001); venous embolism occurred more frequently in patients with a meningioma. There were no major surgical or anesthetic complications related to patient position during the postoperative period. CONCLUSIONS For patients in the semisitting position, an increase in the degree of head elevation is related directly to a higher rate of venous air embolism. With a 30° head elevation and our standardized technique of positioning, the semisitting position can be used safely in neurosurgical practice.

Suspected air embolism through the thoracic ventral internal vertebral venous plexus during hemilaminectomy in dogs

Venous air embolism entering via the ventral internal vertebral venous plexus was suspected during thoracic spinal surgery in two dogs. In both cases, air was seen bubbling from a pool of blood on the floor of the vertebral canal accompanied by sudden cardiopulmonary disturbances: low end-tidal carbon dioxide pressure, tachycardia and reduction in oxygen in the blood. One dog became dyspnoeic and one died.

Venous air embolism in the sitting position in cranial neurosurgery: incidence and severity according to the used monitoring

BACKGROUND

There is an ongoing debate about the sitting position (SP) in neurosurgical patients. The SP provides a number of advantages as well as severe complications such as commonly concerning venous air embolism (VAE). The best monitoring system for the detection of VAE is still controversial.

METHODS

In this retrospective analysis we compared 208 patients. Transesophageal echocardiography (TEE) or transthoracic Doppler (TTD) were used as monitoring devices to detect VAE; 101 cases were monitored with TEE and 107 with TTD.

RESULTS

The overall incidence of VAE was 23% (TTD: 10%; TEE: 37%), but the incidence of clinically relevant VAE (drop in end-tidal carbon dioxide above 3 mmHg) was higher in the TTD group (9 out of 17 VAE, 53%) compared to the TEE group (19 out of 62 VAE, 31%). None of the patients with recorded VAE had clinically significant sequelae.

CONCLUSIONS

In this small sample we found more VAE events in the TEE group, but the incidence of clinically relevant VAE was rare and comparable to other data. There is no consensus in the definition of clinically relevant VAE.

Venous air embolus during prone cervical spine fusion: case report

Venous air embolism (VAE) is a known neurosurgical complication classically and most frequently occurring in patients undergoing posterior cranial fossa or cervical spine surgery in a sitting or semi-sitting position. The authors present a case of VAE that occurred during posterior cervical spine surgery in a patient in the prone position, a rare intraoperative complication. The patient was a 65-year-old man who was undergoing a C1-2 fusion for a nonunion of a Type II dens fracture and developed a VAE. While VAE in the prone position is uncommon, it is a neurosurgical complication that may have significant clinical implications both intraoperatively and postoperatively. The aim of this review is 2-fold: 1) to improve the general knowledge of this complication among surgeons and anesthesiologists who may not otherwise suspect air embolism in patients positioned prone for posterior cervical spine operations, and 2) to formulate preventive measures as well as a plan for prompt diagnosis and treatment should this complication occur.

[Paradoxical air embolism resulted in acute myocardial infarction and massive ischemic brain injury in a patient operated on in a sitting position]

Paradoxical air embolism (PAE) is a rare life-threatening complication when air emboli enter arteries of the systemic circulation and cause their occlusion. Here, we describe a clinical case of PAE developed during neurosurgery in a patient in the sitting position. PAE led to injuries to the cerebral blood vessels, coronary arteries, and lungs, which caused death of the patient. An effective measure for preventing PAE is abandoning surgery in the sitting position in favor of surgery in the prone position.