The effect of decerebrate rigidity on the intracranial pressure: an experimental study

The mechanical effect of acute decerebrate rigidity upon the ICP and the mechanisms underlying the relationship between them have been investigated with experiments performed on 26 cats. It has been shown that: a) Extreme rigidity of the peripheral musculature with or without partial activation of the trunkal muscles produces no change in ICP, b) the simultaneous elevation of the intra-thoracic and intra-abdominal pressures is the factor primarily operative in raising and maintaining the elevated ICP, c) when cerebrovascular homeostasis is already defective a subsidiary but not unimportant role is played by the elevation of the systemic arterial pressure, d) under conditions of normal brain elastance mild and short-lasting spasms produce no effect on the ICP. In an animal, however, in which the brain elastance had been increased by inflating a small air-filled balloon, similar spasms produced a marked increase in ICP.

Anesthetic management of posterior fossa surgery in the sitting position

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 ECG, direct arterial and venous pressure, discontinuous blood gases, and expiratory CO2 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.

Paediatric neurosurgical and neuroradiological anaesthesia

Summary Anaesthesia for paediatric neurosurgery and neuroradiology involves all the problems pertinent to

(i) management of infants and small children during procedures which may be relatively protracted;

(ii) avoidance or correction of disturbances of intracranial pressure and cerebral perfusion;

(iii) assessment of patients with depression of consciousness or of other neurological functions;

(iv) adoption of unusual positions for the conduct of procedures with special risks and limited access for the anaesthetist;

(v) providing optimum conditions for radiologists and avoiding radiation risks.

The effect of passive hyperventilation on intraventricular pressure in the dog

✓ The effectiveness of passive hyperventilation in reducing intracranial pressure was studied in mongrel dogs by varying the levels of end-tidal pCO2 and airway pressure, and comparing the positive-negative and positive-atmospheric pressure. It has been shown that there is a point beyond which reduction of pCO2 does not affect cerebral blood flow. The present study demonstrates that another limiting factor is the degree of positive or negative airway pressure. Positive airway pressure impedes venous drainage, thereby increasing intracranial pressure. This increase could only partly be offset by applying negative expiratory airway pressure, since it was found that excessive negative airway pressure (greater than static recoil pressure of the lung) may trap air in alveoli. An optimal range of positive and negative airway pressures is defined.