Anesthetic Management of Posterior Fossa Surgery in the Sitting Position

Abstract

From the surgical aspect, the sitting position gives good surgical access to the operative site, improves venous drainage, gives a better view of facial area for monitoring evoked responses from cranial nerve stimulation and allows for better ventilation. Conversely, the sitting position can present complications such as air emboli, postural hypotension and serious cardiac arrhythmias due to surgical stimulation of cranial nerves and brainstem.This paper presents our clinical experience in 180 neurosurgical procedures on the posterior fossa in the sitting position. The standardized anesthetic technique consisted of narcotic, muscle relaxant, nitrous oxide and controlled ventilation. All patients were monitored with EGG, direct arterial and venous pressure, discontinuous blood gases, and expiratory CO, and urinary output. Air embolism was detected via Doppler ultrasonic detector and evacuated through a right atrial catheter.Air was detected, visualized and aspirated in 45 cases for an incidence of 25%, with most episodes occurring early in the procedure. In 11 cases (6%) air was detected on closure. There were no deaths in this series.Fifty-eight patients (32%) had a 10-20 mmHg drop in blood pressure on reaching the sitting position, 19 became temporarily hypertensive (10.5%), and the remainder were normotensive. In 46 patients (25%), bradycardia developed during retraction-manipulation-stimulation of structures on or adjacent to brainstem as well as to cranial nerves. Surgical stress also accounted for the 13 patients (7%) having frequent premature ventricular extrasystoles. One case of profound hypotension and another case of virtual cardiac standstill were noted during the use of the bipolar electrocautery at or near the fifth nerve exit from brainstem. Additional hemodynamic data, the physiopathology, diagnosis and treatment of air embolism is discussed.

A prospective study observing outcome following posterior fossa craniotomy in patients with sitting position

“…Although these local mechanisms and reflexes work in concert, anaesthesia can blunt the response of each element of the system, thereby altering the final response in either direction. Different studies show that change in the patient position was associated with various cardiovascular changes [1,5,6]. In our study pulse rate increased statistically significantly during positioning and till 30 min.…”

“…As much as 1500 ml may be sequestered in venous system of lower limbs because of the effect of the gravity [8]. Different authors have described hypotension in different ranges in their studies [1,[9][10][11] but in our study hypotension was considered if there was decrease of 20% or more in systolic blood pressure from ward pressure. Systolic and diastolic blood pressure decreased statistically significantly during positioning and till 30 min.…”

“…The junction of superior vena cava and right atrium is optimum catheter position for maximum efficacy for aspirating air [14] Precordial Doppler is one of the sensitive monitors to diagnose VAE. In a study of Albin et al [1] done in 180 patients, they used precordial Doppler for diagnosis of VAE and the incidence of VAE they found was 25%. By monitoring ETCO 2 some authors have described the incidence of VAE from 7% to 40% [15][16][17].…”

“…The use of the sitting or upright position for patients undergoing posterior fossa surgery facilitates surgical access but presents unique physiological challenges for the anesthetists with the potential for serious complications such as undesirable hemodynamic instability, venous air embolism, pneumocephalous, complications related to positioning like lingual/laryngeal oedema, brachial plexus injury, sciatic nerve injury, quadriparesis etc [1][2][3]. However the specific advantages which made this position popular include improved surgical exposure, provides good surgical assess, anatomical orientation, facilitates cerebral decompression, gravity aided blood and CSF drainage, decreased bleeding, less impairment of diaphragmatic movement leading improved ventilation with lower airway pressure, improved access to endotracheal tube, thorax, extremities, ability to observe face for signs of surgical stimulation of cranial nerves [1][2][3].…”

“…Although there is much debate on advantages and disadvantages of sitting position for neurosurgery, it is routinely used in many institutes including our for posterior fossa surgeries [1,3]. Assessment of relative risk and benefit of sitting position surgery for the individual patient, based on physical status and specific intracranial pathology is, IJBAR (2016) 07 (09) www.ssjournals.com therefore, of paramount importance.…”