Clipping of aneurysm
1 General management of a major craniotomy
2 Anaesthesia for clipping of aneurysm
3 The concept of neuroprotection.
2A03, 2F01
As mentioned in Case 7.3, there will still continue to be a need for clipping of aneurysms. A 44-year-old female right-handed lecturer was admitted following a spontaneous grade I SAH. She had been standing in her classroom and developed sudden onset of severe headache and collapsed to the ground. After a brief loss of consciousness, she awoke surrounded by colleagues. She did not have any focal weakness but noticed her speech slurred.
Imaging confirmed a diffuse SAH. Urgent cerebral angiography showed two aneurysms. A middle cerebral artery (MCA) aneurysm was successfully coiled the day after admission, but a complex aneurysm of the anterior communicating artery (ACOM) was found to be uncoilable. It was thought that the MCA aneurysm was an incidental finding, and the ACOM aneurysm had bled. Following coiling, she was transferred to the neurosurgical HDU, pending surgical clipping of the ACOM aneurysm. The patient was taken to theatre for this procedure the next day.
The patient arrived in the anaesthetic room (GCS 15), with a left radial arterial line, a large-bore cannula in the left cephalic vein, and a urinary catheter in situ. She was induced with remifentanil TCI 4 ng/mL (weight 68 kg, height 1.67 m, BP before induction 124/78, pulse 68), propofol 150 mg, and vecuronium 10 mg. Anaesthesia was maintained with remifentanil TCI and desflurane in an oxygen/air mix, FiO2 0.4. She was ventilated to maintain an ETCO2 of 4%. She was positioned semi-recumbent, a gel pad behind the left shoulder and the head tilted to the right and held in Mayfield tongs. Surgery proceeded via a pterional craniotomy.
Prior to the definitive clipping of the ACOM aneurysm, the surgeon applied a temporary clip to the feeding artery to improve access to the neck of the aneurysm. In order to protect the brain from a period of anoxia, due to an interrupted blood flow, thiopentone 375 mg was delivered IV. The temporary clip was applied for 3 min; a permanent 10 mm clip was applied to the neck of the ACOM aneurysm, and the temporary clip removed. The time taken for surgery was 2 hours and 15 min. Five 0.5 mg increments of metaraminol were delivered IV during surgery to maintain a CPP of 60 mmHg. The patient received ondansetron 4 mg and cyclizine 50 mg plus morphine 6 mg prior to emergence.
After dressings were applied to the wound, and the Mayfield tongs removed, the patient was allowed to waken. She was extubated on return of airway reflexes and adequate respiratory effort. Over a period of 1 hour in the recovery suite, the highest recorded GCS was 9. She maintained adequate respiratory parameters and blood oxygenation throughout, and blood gases revealed PaO2 20.5 kPa (oxygen 4L/min via Hudson mask), PaCO2 5.5 kPa, H+ 45 nmol/L, HCO3– 23 mmol/L, and BE –0.9 mmol/L. Post-operative CT brain showed a small pneumocranium, consistent with surgery, no increase in subarachnoid blood load, and no subdural collection of blood or fluid.
Due to a persisting low GCS, the patient was intubated prior to transfer to intensive care, with an ICP monitor sited and a plan to treat a raised ICP, if and when it occurred, and to sedate overnight and re-evaluate the next day. The ICP fluctuated but did not rise sufficiently to require treatment. She was extubated the morning after admission to the ICU. Thereafter, she was E3–4 M6 V1–4 (i.e. GCS quite variable although always obeying commands). She developed a high-volume, low-osmolarity urine flow, which was treated with desmopressin for 24 hours.
It became apparent that she had a left 6th nerve palsy, with an accompanying left-sided proptosis, as well as a conjunctival infection. Despite, on paper, GCS being 15, she did have marked neuropsychological issues which required inpatient rehabilitation. The rehabilitation issues were as follows:
1 Mood and cognition: she had cognitive impairments across a broad spectrum of domains, with frontal lobe functions, in particular, being affected, with mild executive impairments, impaired judgement and insight, and also with reduced spatial awareness. Forgetfulness and impairments of short-term memory were also problematic. In addition, she was quite tearful
2 Communication: she scored well on formal tests, including the Galveston Orientation and Amnesia Test (GOAT) 100/100 and Frenchay Aphasia Screening Test (FAST) 27/30. She was easily distracted. She was able to touch-type, but not as efficiently as previously
3 Cranial nerves: lateral rectus palsy is gradually improving and is expected to recover fully
4 Upper and lower limb function: peripheral neural examination was broadly normal, although she did have reduced sensation, with sensory inattention on the left. This is gradually improving
5 Long-term prognosis: she is continuing to improve; now that her aneurysms have been successfully treated, hopefully there should be no recurrence.
When access to the aneurysm may be difficult, the surgeon may wish to apply a temporary clip. This stops the blood flow in a small portion of the cerebral circulation. Obviously, this may cause ischaemia. If the CMRO2 can be reduced, then the period of ischaemia can be prolonged.
Many methods have been tried. None has been an undisputed success.
Hypothermia has been intermittently in and out of fashion. The Intraoperative Hypothermia for Aneurysm Surgery Trial (IHAST) of 1001 patients found mild hypothermia (33°C vs 36.5°C) did not improve the neurological outcome after clipping, as judged by comparing GCS at 90 days post-operatively. This study also noted the following:
◆ Post-operative bacteraemia was commoner in the hypothermic group (5% vs 3%)
◆ 25% of the hypothermic group were still intubated 2 hours post-operatively. That said, so were 13% of the normothermic group.
Summary
As mentioned in Case 7.3, although the majority of SAHs caused by berry aneurysms can now be treated with an endovascular procedure, there will still be a need to treat some aneurysms with the older clipping technique for the foreseeable future. This may require the placement of a temporary clip to allow better access to the aneurysm. This will be applied for as short a time as possible, but this period can be prolonged if the CMRO2 is reduced, necessitating neuroprotection. Methods of affecting this are controversial.
The rehabilitation of a patient after an SAH is an important component of management.