Key learning points

Introduction

The last 20 years has seen a paradigm shift from traditional external approaches to the skull base to a completely endoscopic endonasal approach, made possible with the advent of improved technological developments, surgical instrumentation, and an improved understanding of the endoscopic endonasal anatomy. The advantages of endoscopic techniques over traditional external approaches include improved visualization, reduce hospital admission times, avoiding minimal sacrifice of intervening structures, and avoiding external skin incisions.

Transsphenoidal pituitary surgery is common and has an incidence of ICA rupture rate of approximately 1.1%. Ciric and colleagues used a postal questionnaire survey, involving more than 900 neurosurgeons, inquiring about their complication profile. Surgeons who had performed in excess of 500 transsphenoidal pituitary approaches had a 50% chance of being in the situation where they had to manage the carotid artery catastrophe. This finding implies that the increased subspecialization of endonasal skull base surgery is associated with a greater chance of experiencing a carotid artery injury (ie, subspecialty surgeons need to be geared up to manage an ICA injury). More advanced surgical resections center on the management of the ICA and, hence, have a greater chance of ICA injury. Endoscopic resections of craniopharyngiomas, clival chordomas, and chondrosarcomas have an ICA rupture rate of between 5% and 9%. The increasing use of endoscopic approaches to the skull base increases the risk of encountering potential vascular injuries; it is essential that the specialist endoscopic skull base surgeon has appropriate training, not only in endonasal skull base anatomy and the avoidance of complications but also in managing a carotid artery catastrophe.

Introduction

The last 20 years has seen a paradigm shift from traditional external approaches to the skull base to a completely endoscopic endonasal approach, made possible with the advent of improved technological developments, surgical instrumentation, and an improved understanding of the endoscopic endonasal anatomy. The advantages of endoscopic techniques over traditional external approaches include improved visualization, reduce hospital admission times, avoiding minimal sacrifice of intervening structures, and avoiding external skin incisions.

Transsphenoidal pituitary surgery is common and has an incidence of ICA rupture rate of approximately 1.1%. Ciric and colleagues used a postal questionnaire survey, involving more than 900 neurosurgeons, inquiring about their complication profile. Surgeons who had performed in excess of 500 transsphenoidal pituitary approaches had a 50% chance of being in the situation where they had to manage the carotid artery catastrophe. This finding implies that the increased subspecialization of endonasal skull base surgery is associated with a greater chance of experiencing a carotid artery injury (ie, subspecialty surgeons need to be geared up to manage an ICA injury). More advanced surgical resections center on the management of the ICA and, hence, have a greater chance of ICA injury. Endoscopic resections of craniopharyngiomas, clival chordomas, and chondrosarcomas have an ICA rupture rate of between 5% and 9%. The increasing use of endoscopic approaches to the skull base increases the risk of encountering potential vascular injuries; it is essential that the specialist endoscopic skull base surgeon has appropriate training, not only in endonasal skull base anatomy and the avoidance of complications but also in managing a carotid artery catastrophe.

Simulation training

A simulator is defined as a device or model that is used to train people by imitating the situations that they will need to deal with. It allows users to gain experience and to observe and interact with the simulation via realistic visual, auditory, or tactile cues. The main goals of surgical simulation is for research and development, to develop and teach surgical skill acquisition and excellence, and to transfer the learned techniques to the body of patients in the operating room.

There are a range of different types of surgical simulators, each with their own advantages and disadvantages. Bench models are easily portable and cheap and require no specific supervision but are the least realistic and inanimate. Cadavers are the most anatomically accurate and have high fidelity but are expensive with limited availability of material and are not suitable for vascular injury. Virtual reality surgical simulators are reusable and anatomically accurate, with immediate objective feedback; but the sense of realism varies greater and may also appear inanimate. Animal models have played an important role in surgical education and training and have been used in the medical field since 384 bc . Live animals have a high level of fidelity and offer the most realistic experience with regard to major vascular injuries and tissue hemostasis. The main disadvantages include anatomic differences, high costs, and special facilities are required. There are also ethical dilemmas and animal welfare laws, which need to be addressed sensitively and appropriately.

Simulation of vascular injury for endoscopic sinus and skull base surgery

If simulated training in vascular injuries is to be effective, then the surgical environment needs to be recreated. Surgeons need to be immediately familiar with the surgical environment and instruments that they will be using to control the vascular event. The utilization of standard instrumentation is ideal. The acquisition of surgical skills is impeded if using new unfamiliar instrumentation is required and, hence, unrealistic during the pressures of a major vascular event.

Vascular injuries take on a range of configurations. Each scenario may have a challenging unique set of circumstances. The ideal animal model needs to recreate these challenges and circumstances. The endoscopic vascular injury occurs down a narrow nasal corridor where even a small amount of blood may immediately disorientate the surgeon and disrupt the surgical field. Surgical exposure to the site of vascular injury may range from limited (ie, during sphenoidotomy, during endoscopic sinus surgery) to wide surgical access, such as during an expanded endonasal resection. Simulation needs to be able to recreate both these different circumstances.

The type of vascular injury may also vary in configuration depending on the surgical instrument that has caused the injury. Padhye and colleagues investigated various hemostatic techniques in a range of injury configurations. Injury types investigated included a 3-mm punch injury, a 4-mm linear injury, and a 4-mm stellate injury. This study identified that the linear injury type was associated with the greatest volume of blood loss and the longest time to achieving hemostasis.

Challenging surgical scenarios may occur within high-flow/low-pressure vessels, such as during cavernous sinus bleeding, or within high-flow/high-pressure vessels, such as the carotid artery. High-flow/low-pressure scenarios are considered easier to control during the endoscopic approaches as the surgical field is less threatened. It makes it easier for the surgical team to visualize the defect and act accordingly. However, high-flow/high-pressure injuries are much more challenging because of the pulsatile nature of the blood stream, making visualization of the injury site much more difficult. Rapid exsanguination from an ICA rupture may occur, which will change the vascular event rapidly from a high-flow/high-pressure scenario to the high-flow/low-pressure scenario. Thus, rapid active resuscitation is important during ICA vascular injury simulation to maintain high-flow/high-pressure characteristics.

Short-term and long-term complications following vascular injury are well known and include secondary bleed, pseudoaneurysm formation, and vascular occlusion. Minimizing morbidity following a carotid artery injury relies firstly on achieving hemostasis but secondarily on maintaining vascular patency. Simulating vascular injuries for the purpose of ongoing research and development requires ongoing assessment of the injury site over time to allow analysis of the occurrence of these complications and minimizing these to determine the best management algorithm.

Simulating the clinical scenario has shown to improve skill acquisition, particularly when the environment is simulated. The use of anesthetic machines, monitoring equipment and pressure bag resuscitation and the ability to monitor blood pressure and pulse parameters immediately recreates the familiarity of a working operating room. Perhaps most importantly, live animal surgery creates an environment of life or death placing the trainee under immediate pressure. Large animals are ideal in vascular catastrophe simulation as they have a similar blood volume to humans, have similar blood pressure and pulse characteristics, and are robust.