Pneumocephalus in the sitting position is a well-known complication.
Although the sitting position may favour the development of tension pneumocephalus also other factors contribute to its pathogenesis. Finally, neither nitrous oxide nor temperature play any significant role in the development of this complication in the series of Di Lorenzo et al. 1).
Their incidence can be dramatically decreased with an accurate anesthesiological and neurosurgical management 2).
see Intraventricular pneumocephalus in the sitting position.
Its incidence and intensity were prospectively studied in 90 consecutive patients undergoing a posterior fossa procedure in this position.
Despite the hypothetical diverse effects of the three anesthetic techniques used in this series on cerebral hemodynamics, our results suggest that none of them has a substantial effect on the amount of intracranial air detected after posterior fossa procedures performed in seated individuals. To the best of our knowledge this is the first report that addresses in a prospective manner the effects of several habitual anesthetic techniques on the development of pneumocephalus in patients submitted to posterior fossa procedures performed in the sitting position 3).
The incidence of pneumocephalus and factors contributing to its occurrence were studied retrospectively in 100 consecutive patients who underwent posterior fossa or cervical cord surgery in the sitting, park-bench, and prone positions. Supine skull x-ray films taken immediately postoperatively were used to determine the presence of intracranial air. Surgery in the sitting position uniformly resulted in pneumocephalus (32/32 patients). Pneumocephalus also occurred frequently among patients in the park-bench (29/40) and prone positions (16/28). Intraventricular air occurred more frequently when patients were in the sitting position (25/32) than in the two other surgical positions (3/29 and 4/16, respectively, P less than 0.001). The high incidence of pneumocephalus and of intraventricular air that occurred when patients were in the sitting position is attributed to the large amount of cerebrospinal fluid drained due to gravitational effect. When surgical position is considered one of the contributing factors, only positions significantly affected the frequencies of pneumocephalus and intraventricular air accumulation. None of the 77 patients with pneumocephalus suffered neurologic change related to the presence of intracranial air. We conclude the following: pneumocephalus commonly occurs after posterior fossa or cervical cord surgeries, particularly when the surgery is performed in the sitting position; neurologic change caused by pneumocephalus is a rare complication after posterior fossa craniotomy; when a patient with coexisting hydrocephalus undergoes surgery, if the patient is in the sitting position, there is an increased risk of trapping a large amount of intracranial air 4).
Intracranial pressure was monitored through a ventriculostomy catheter after closure of the dura. In three patients nitrous oxide was added to the breathing mixture only after the baseline intracranial pressure had stabilised following closure of the dura. A marked rise in intracranial pressure was observed immediately. A rapid decrease in intracranial pressure occurred when nitrous oxide administration was stopped. Two patients were nitrous oxide from the beginning. No change in intracranial pressure was noted. Computerised tomogram on the first postoperative day revealed a significant amount of air in eight cases 5).
Two patients developed subdural tension pneumocephalus after undergoing posterior fossa surgery performed in the sitting position. The mechanism for entry of air into the intracranial compartment is analogous to the entry of air into an inverted soda-pop bottle. As the fluid pours out, air bubbles to the top of the container.
Lunsford et al. have thus referred to this as the “inverted pop-bottle syndrome.” Computerized tomography provided prompt diagnosis and confirmed brain displacement. Twist-drill aspiration of the air resulted in improvement in both patients, although one patient subsequently died from an intracerebellar hemorrhage. Tension pneumocephalus appears to be another potential complication of posterior fossa surgery in the sitting position. This condition is easily diagnosed and treated, and should be considered whenever a patient fails to recover as expected following posterior fossa surgery 6).
Kishan et al. encountered 2 patients with this complication amongst 60 patients operated during the past 2 years. All 60 patients had some amount of intracranial air at the end of surgery. The causative factors of tension pneumocephalus are briefly reviewed. Prompt recognition of this complication is very important. Diagnosis and management are discussed 7).