Anaesthesia for minimally invasive neurosurgery

Awake spine surgery: An eye-opening movement

Background:

Awake surgery is performed in multiple surgical specialties, but historically, awake surgery in the field of neurosurgery was limited to craniotomies. Over the past two decades, spinal surgeons have pushed for techniques that only require regional anesthesia as they may provide reduced financial burdens on patients, faster recovery times, and better outcomes. The list of awake spine surgeries that have been found in the literature include: laminectomies/discectomies, anterior cervical discectomy and fusions (ACDFs), lumbar fusions, and dorsal column (DC) stimulator placement.

Methods:

An extensive review of the published literature was conducted through PubMed database with articles containing the search term “awake spine surgery.” No date restrictions were used.

Results:

The search yielded 293 related articles. Cross-checking of articles was conducted to exclude of duplicate articles. The articles were screened for their full text and English language availability. We finalized those articles pertaining to the topic. Findings have shown that lumbar laminectomies performed with local anesthesia have shown shorter operating time, less postoperative nausea, lower incidence of urinary retention and spinal headache, and shorter hospital stays when compared to those performed under general anesthesia. Lumbar fusions with local anesthesia showed similar outcomes as patients reported better postoperative function and fewer side effects of general anesthesia. DC stimulator placement performed with local anesthesia is advantageous as it allows real time patient feedback for surgeons as they directly test affected nerves. However, spontaneous movement during the placement of DC stimulators is associated with higher failure rates when compared to general anesthesia (29.7% vs. 14.9%). Studies have shown that the use of local anesthesia during ACDFs has no significant differences when compared to general anesthesia, and patient’s report better tolerated pain with general anesthesia.

Conclusion:

The use of awake spine surgery is beneficial for those who cannot undergo general anesthesia. However, it is limited to patients who can tolerate prone positioning with no central airway (i.e., normal BMI with a healthy airway), have no pre-existing mental health conditions (e.g., anxiety), and require a minimally invasive procedure with a short operating time. Future studies should focus on long-term efficacies of these procedures that provide further insight on the indications and limitations of awake spine surgery.

Anesthesia for Endoscopic Third Ventriculostomy in Children

Neuroendoscopy has established itself as a routine neurosurgical procedure in pediatric population. To have an uneventful smooth perioperative course, it is important for anesthesiologist to know about the key steps, possible complications, and specific anesthetic requirements. Among neuroendoscopies, endoscopic third ventriculostomy is the commonly performed one.

Sedation for Percutaneous Endoscopic Lumbar Discectomy

Although anesthetic requirements for minimally invasive neurosurgical techniques have been described in detail and applied successfully since the early 2000s, most of the literature on this subject has dealt with cranial cases that were operated on in the supine or sitting positions. However, spinal surgery has also used minimally invasive techniques that were performed in prone position for more than 30 years to date. Although procedures in both these neurosurgical techniques require the patient to be awake for a certain period of time, the main surgical difference with minimally invasive spinal surgery is that the patients are in the prone position, which may result in increased requirement of airway management because of deep sedation. In addition, although minimally invasive spinal surgery progresses slowly and different techniques are used with no agreement on the terminology used to describe these techniques thus far, the anesthetist needs to understand the surgical and anesthetic requirements for each type of intervention in order to take necessary precautions. This paper reviews the literature on this topic and discusses the anesthetic necessities for percutaneous endoscopic laser surgery.

Pressure monitoring during neuroendoscopy: new insights

BACKGROUND

Significant increases in intracranial pressure (ICP) may occur during neuroendoscopic procedures. To detect and prevent serious and sustained increases, ICP should be monitored. At present, controversy exists on the optimal location of the monitoring sensor. Therefore, we conducted an in vitro study to estimate the pressure gradients between the ventricle, the 'gold standard' site, and the rinsing inlet and outlet.

METHODS

A head model and a standard endoscope were used. Rinsing was enforced by using a pressurized infusion bag. Using clinically relevant flow rates, pressure was measured at the rinsing inlet and outlet, in the ventricle, and at the distal end of the rinsing channel using a tip sensor or a capillary tube.

RESULTS

At a flow of 61 ml min(-1), the steady-state pressures measured at the rinsing inlet, in the ventricle, and at the rinsing outlet were 38, 26, and 12 mm Hg, respectively. At 135 ml min(-1), these increased to 136, 89, and 42 mm Hg. Transendoscopic pressure measurements were always within 1 mm Hg of the ventricular pressure.

CONCLUSIONS

During endoscopy, measurements at the rinsing inlet overestimated the ventricular pressure by ∼50 mm Hg during heavy rinsing, whereas measurements at the rinsing outlet underestimated the pressure by ∼50 mm Hg. An electronic tip sensor or a pressure capillary tube placed at the distal end of the lumen of the rinsing channel of the endoscope did not interfere with rinsing flow and produced measurements that were equal to ventricular pressures.

Pressure inside the neuroendoscope: correlation with epidural intracranial pressure during neuroendoscopic procedures

BACKGROUND

During neuroendoscopic procedures, pressure inside the neuroendoscope (PIN) monitored through the irrigation channel correlates with the occurrence of postoperative complications. Our aim was to analyze the reliability of PIN measurement as a surrogate for intracranial pressure (ICP) by comparing PIN with simultaneously epidural ICP measurement as the standard.

METHODS

Seventeen consecutive patients undergoing neuroendoscopy were studied prospectively. Type and length of procedure and PIN and epidural ICP values during neuroendoscopy were recorded. Lin's concordance coefficient and Bland-Altman analysis of agreement were used to assess correspondence between the 2 systems.

RESULTS

A consistent relation between PIN and epidural ICP waveforms was observed during neuroendoscopic navigation. A strong Pearson correlation between PIN and epidural ICP data were found in 15 patients. Epidural ICP values were systematically higher than PIN values in 15 patients. Lin concordance coefficients showed moderate global agreement between the 2 methods, at 0.58 (95% confidence interval, 0.577-0.592). In 6 cases (35.2%) concordance was good according to this analysis, in 7 cases (41.2%) agreement was moderate/fair, and in 4 cases (23.5%) agreement was poor. The Bland-Altman analysis of patient data showed good agreement between the PIN and epidural ICP measurements for most patients, although discrepancies were greater at higher ICP values for 11 patients. Bland-Altman analysis of the complete dataset, after the normalization of individual's measurements, showed good overall agreement.

CONCLUSIONS

PIN measurement seems useful for evaluating ICP changes related to neuroendoscopic procedures and seems to be more consistent than epidural ICP at high pressures.

Anaesthesia for endoscopic neurosurgical procedures

PURPOSE OF REVIEW

Endoscopic neurosurgical procedures are becoming more frequent and popular in the treatment of intracranial disease. When endoscopy involves the intraventricular structures, irrigating solutions are required and may contribute to sudden and sharp increases in intracranial pressure. More recently, nasal endoscopic approach has been used to perform skull base surgery for aneurysms and tumours. We have analysed published articles in order to detect anaesthesia management and perioperative complications.

RECENT FINDINGS

Sudden and dangerously low decreases in cerebral perfusion pressures do not provoke the 'traditional Cushing's response' usually associated with significantly high intracranial pressure. It is important to note that tachycardia (not bradycardia) and/or hypertension are the most frequent haemodynamic complications during neuroendoscopic procedures. With the transnasal approach severe intraoperative haemorrhage is the most important complication to consider followed by direct injury to surrounding neural structures.

SUMMARY

Invasive arterial blood pressure and intracranial pressure should be measured continuously during neuroendoscopies to detect early intraoperative cerebral ischaemia instead of waiting for the appearance of bradycardia which may be a late sign. General anaesthesia remains the technique of choice. Intracranial haemorrhage increases the likelihood of perioperative complications. Close postoperative monitoring is required to diagnose and treat complications such as convulsions, persistent hydrocephalus, haemorrhage or electrolytic imbalance.

Value of Cushing reflex as warning sign for brain ischaemia during neuroendoscopy † †This work was performed at the Department of Anaesthesia, Ghent University Hospital, Ghent, Belgium

BACKGROUND

During an endoscopic neurosurgical procedure a sudden increase in intracranial pressure may occur at any time. We present a prospective study of haemodynamic changes during such procedures.

METHODS

Physiological data were recorded during the whole operative procedure in 17 consecutive patients who underwent an endoscopic neurosurgical procedure under general anaesthesia. Monitoring included invasive blood pressure, intracranial pressure, electrocardiogram, end-expired carbon dioxide, pulse oximetry and heart rate. Pressure and ECG waveforms were recorded at 100 Hz and evaluated in a subsequent offline analysis.

RESULTS

In almost every case, the occurrence of hypertension and tachycardia was clearly the result of an increase in intracranial pressure. Also, a Cushing reflex developed in almost every case where the cerebral perfusion pressure dropped below 15 mm Hg. The occurrence of bradycardia was not systematically associated with a low cerebral perfusion pressure.

CONCLUSION

In this study, we describe the haemodynamic effects of increased intracranial pressure during endoscopic neurosurgical procedures and their respective sequence of events at high temporal resolution. Although most clinicians rely on the occurrence of bradycardia to diagnose intracranial hypertension during endoscopic neurosurgical procedures, we show that a simultaneous onset of hypertension and tachycardia is a better indicator of impaired brain perfusion. Waiting for a persistent bradycardia to alert the surgeon during endoscopic neurosurgical procedures could allow severe bradycardia or even asystole to develop.