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|Year : 2018 | Volume
| Issue : 1 | Page : 223-225
The sitting position for Neurosurgery: A bane or a boon
Department of Neuroanesthesiology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
|Date of Web Publication||11-Jan-2018|
Dr. Shashi Srivastava
Department of Neuroanesthesiology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Srivastava S. The sitting position for Neurosurgery: A bane or a boon. Neurol India 2018;66:223-5
In neurosurgical practice, sitting position for posterior fossa lesions has always been a topic of controversy. It was first utilized in 1931 and remained popular until the 1970s. In the latter years, its use declined due to a few inherent complications associated with it and the physiological challenges it poses to the anesthesiologists. The sitting position is still being practiced at some centers in India and Europe. However, there is no strong scientific data which can justify the relinquishment of its use in patient positioning; in fact, recent literature proves its safety with appropriate monitoring. The conduction of anaesthesia in this position, however, mandates the presence of an experienced anesthesiologist throughout the surgical procedure.
Gupta et al., in their study focusing on complications related to the sitting position in children, reviewed the data of 97 patients to assess the perioperative complications that occurred in the sitting position. In their preoperative workup, they did not clinically find a septal defect or a patent foramen ovale in any of their patients. The incidence of patent foramen ovale (PFO) is high in the general population (10-30%), hence if a sitting position is planned, it is important to rule out the presence of PFO utilizing a precordial or a transoesophageal echocardiography. Prior to the performance of cranial surgery, the PFO closure is advisable, to prevent paradoxical pulmonary embolism. However, Feigl et al., have demonstrated that with a careful intraoperative management of patients with PFO, a semisitting position is associated with a very low risk of venous air embolism. An interdisciplinary dialogue between neurosurgeons and neuroanesthesiologists is an essential requirement prior to the adoption of sitting position for surgery. Assessment of the relative risk-benefit ratio of sitting position for surgery has to be individualized based on the physical status of the patient and the specific intracranial pathology that the surgery is supposed to address. An appropriate patient selection, anticipation of the potential complications and a careful perioperative monitoring facilitates the safe use of the sitting position.
Sitting position, however, presents with certain physiological challenges to the neuroanesthesiologist. When changing the patient's position from the supine to the sitting one, there may be significant haemodynamic instability. Systemic hypotension may lead to a decrease in the cerebral perfusion pressure (CPP) and may lead to the occurrence of cerebral hypoxia. This can be further intensified by jugular venous obstruction caused by an uncomplimentary head and neck position. To avoid this position-related haemodynamic instability, the patient's positioning should be done incrementally. Dehydration should be avoided; therefore, adequate pre-positioning controlled preloading of the vascular system with an infusion of intravenous fluids should be done. An intermittent sequential compression device applied to the lower extremities is a simple and effective method to reduce the chances of position-related, intraoperative hypotension.
Positioning of the head should ideally be done under neurophysiological monitoring (utilizing somatosensory evoked potentials) to detect the occurrence of spinal cord ischemia due to hypotension or cord compression from excessive neck flexion. The anesthesiologist should have a good access to the patient at all times without disturbing the surgical area. Since its introduction, the sitting position has been revised to a modified semi-sitting or a lounge chair position to reduce the risk of venous air embolism. The latter positions help in achieving a positive venous pressure by a combination of adjustments.
The authors used an O2:N2O mixture along with sevofurane or isoflurane, and intermittent boluses of fentanyl for the maintenance of anaesthesia. The usage of nitrous oxide is controversial while administering anaesthesia in the sitting position. Although the use of nitrous oxide is associated with a stable hemodynamic status and good surgical conditions, due to its unfavorable effects on intracranial dynamics, its role in the expansion of gas-filled spaces, and its role in the precipitation of postoperative nausea and vomiting, its usage has been avoided during neurosurgical procedures. Instead, total intravenous anesthesia, using a continuous infusion of propofol (6-8mg/kg/hr) with supplemental boluses of the opioids, fentanyl or remifentanil, has been the commonly advocated maintenance technique.
For the monitoring of venous air embolism, transesophageal echocardiography (TEE) is considered the gold standard modality. It has the highest sensitivity and gives adequate information about the size of the embolus and whether or not it is ongoing. TEE is expensive and requires expertise; therefore, it not in routine practice in all the centers in which Neurosurgery is undertaken. In this study also, TEE was used only in 8 patients. Capnography, which measures the end-tidal carbon-dioxide, is a basic anesthesia monitoring equipment in neuroanesthesiological practice. The venous air embolism detectable by capnography is always clinically significant. Capnography is less sensitive in its ability to detect a minor episode of venous air embolism and it is not reliable in the presence of associated hypotension. For the detection of venous air embolism during the sitting position, a multimodality monitoring is more useful as no single monitor is completely reliable.
In this study, none of the patients developed a paradoxical air embolism (PAE), which may occur when venous air embolism leads to systemic circulation embolism through the PFO. An intrapulmonary transmission of air can also lead to PAE in the absence of PFO. As stated previously, the incidence of PFO is relatively high in the general population (10-30%); hence, a preoperative screening to rule out a right-to-left shunt should be done in all those cases who are to be operated in a sitting position. The flow across the PFO is functional, and under normal circumstances, the left atrial pressure is usually slightly higher than the right atrial pressure. A right- to-left shunting occurs when the pressure in the right atrium exceeds the left atrial pressure which may lead to a paradoxical air embolism. The left atrial pressure may become low during hypovolemia, after placement of the patient in a sitting position, during the episode of venous air embolism, as well as during the application and the release of positive end expiratory pressure. All these conditions, therefore, have been associated with a right-to-left shunt.
Other complications worth mentioning are the precipitation of a massive venous air embolism or the presence of a large embolus obstructing the right ventricular outlet, resulting in a sudden onset right heart failure and cardiac arrest. The pulmonary signs of venous air embolism include the presence of wheeze and crepitations. The occurrence of coagulation abnormalities, including the precipitation of severe thrombocytopenia, is an under-recognized complication of venous air embolism. Thromboelastography allows an immediate and sophisticated analysis of the platelet function and the whole-blood coagulation profile. Pulmonary edema is another atypical manifestation of VAE.
Tension peumocephalus was seen postoperatively in this study in 6% of the included patients. The treatment for this serious complication was only partly mentioned by the authors. Following the occurrence of tension pneumocephalus, postoperatively, the patients may present with delayed recovery with or without seizures, as well as arterial hypertension and reflex bradycardia (Cushing's reflex) due to the mass effect. The radiological sign that is generally reported as being specific for tension pneumocephalus is the 'Mount Fuji' sign, which is detected when the presence of the subdural free air causes the compression and separation of the frontal lobes. Apart from the subdural space, air may also get trapped within the subarachnoid and ventricular spaces. Various strategies have been recommended to reduce the potential for pneumocephalus after surgical procedures in the sitting position, like the discontinuation of nitrous oxide before dural closure; however, these strategies may often not be very effective. Avoidance of nitrous oxide in cases of re-exploration performed within 15 days, flushing of the subdural space with saline, and avoidance of hyperventilation prior to the dural closure will facilitate brain expansion and prevent the occurrence of pneumocephalus. An immediate aspiration of air through the burr holes on either side of the vertex, using a needle attached to a syringe filled with water (the release of bubbles through the water-seal, marking the release of air into the syringe) is indicated if tension pneumocephalus is diagnosed. For less severe cases, a high flow oxygen is recommended. Tension pneumoventricle is another rare complication of the sitting position. The breach of the third ventricle in the presence of other contributing factors may result in a massive loss of cerebrospinal fluid, which possibly leads to accumulation of air within the ventricles. The treatment of this condition is also twist drill/burr hole aspiration of air under a water seal drainage.
Another important point to consider in the sitting position is the proper establishment of hemostasis of the tumor bed by the surgeon after the intracranial surgery has been completed. As the venous channels are either under low or negative pressure in the siting position, the surgeon must utilize every means possible, including the ascertainment of the blood pressure, a gentle irrigation of the tumor bed with saline for an adequate period of time, and the utilization of the Valsalva maneuver to ensure that an adequate hemostatsis has been achieved. This will prevent the subsequent occurrence of a hematoma when the venous pressure normalizes on bringing the patient back to the supine position.
In summary, the complications encountered during the sitting position for performance of neurosurgical procedures in children that are described in this study are not different from those encountered in adults. The sitting position is a safe surgical positioning technique if a transoesophageal monitoring is simultaneously used. In our modern operation rooms, the sitting position can be adopted with a very low incidence of clinically relevant complications; however, cooperation and team-work between the surgeons and anesthesiologists is mandatory for the successful conduction of surgery utilizing this position.
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