Anaesthesia for awake craniotomy with non-invasive positive pressure ventilation

F. Yamamoto, R. Kato*, J. Sato and T. Nishino

Department of Anesthesiology, Graduate School of Medicine, Chiba University 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan

Corresponding author. E-mail: rie.kato@anesth01.m.chiba-u.ac.jp
{dagger}LMA® is the property of Intavent Limited.

Accepted for publication: November 8, 2002


    Abstract
 Top
 Abstract
 Introduction
 Case reports
 Discussion
 References
 
Airway management during awake craniotomy is a crucial part of the anaesthetic technique, but it remains the subject of debate. We report two cases of anaesthesia for awake craniotomy using non-invasive positive pressure ventilation; biphasic positive airway pressure or proportional assist ventilation was employed. Both ventilatory techniques provided adequate lung ventilation, smooth transition between anaesthesia and arousal, and patient comfort.

Br J Anaesth 2003; 90: 382–5

Keywords: surgery, craniotomy; ventilation, pressure support


    Introduction
 Top
 Abstract
 Introduction
 Case reports
 Discussion
 References
 
Awake craniotomy allows cortical mapping with patient cooperation and helps prevent neurological dysfunction during brain tumour resection. Despite the widespread use of this surgical technique,1 2 its optimal anaesthetic management remains a challenge. It requires an adequate depth of anaesthesia for craniotomy, which should be followed immediately by clear consciousness for cortical mapping. During this dramatic change in conscious level, the patient must be kept immobile and comfortable, while lung ventilation is properly maintained.

Non-invasive positive pressure ventilation (NPPV) has been used widely to treat patients with a wide spectrum of respiratory diseases, avoiding the disadvantages of tracheal intubation or tracheostomy.3 Biphasic positive airway pressure (BIPAP)4 and proportional assist ventilation (PAV)5 are relatively comfortable modes of ventilatory support for patients. Thus, we anticipated: (1) that both BIPAP and PAV under NPPV would confer adequate minute ventilation during anaesthesia for craniotomy; and (2) that it would also facilitate a smooth transition from controlled ventilation to spontaneous breathing at emergence from anaesthesia, and so reduce the likelihood of cerebral oedema and/or herniation through the open dura. In this report, we present two cases of anaesthesia for awake craniotomy using NPPV with BIPAP or PAV.


    Case reports
 Top
 Abstract
 Introduction
 Case reports
 Discussion
 References
 
Two patients were to undergo resection of primary brain tumours. Because of the proximity of the tumour to functionally important regions of the cortex, awake cortical mapping was planned in both patients. No signs of increased intracranial pressure were found at preoperative examination. During the preoperative visit, the anaesthetic plan was thoroughly explained to the patients. Positive pressure ventilation via a nasal mask was tested on, and well tolerated by, each patient preoperatively.

Case 1
A 25-yr-old female (59 kg, 161 cm), complaining of visual disturbance, was to undergo tumour resection in the right frontal lobe. Awake craniotomy was planned to perform intraoperative cortical mapping for motor function. The patient was being treated with zonisamide, an anticonvulsant. Cinical history and examination were otherwise unremarkable.

The patient was premedicated with ranitidine and atropine. Standard anaesthetic monitoring (electrocardiogram, non-invasive arterial pressure, and pulse oximetry) was commenced on arrival in the operating theatre. A nasal mask was placed in position and adequate positive pressure ventilation was confirmed. After induction of anaesthesia, a catheter was inserted into the radial artery to allow continuous arterial pressure monitoring and intermittent blood gas analysis. Anaesthesia was induced with propofol (60 mg), and maintained with a continuous infusion of propofol (6–10 mg kg–1 h–1) and intermittent doses of fentanyl (total dose before cortical mapping 150 µg). BIPAP (BiPAPTM, Respironics Inc., Pennsylvania, PA, USA) via a nasal mask was started with a synchronized mode, and switched to a pressure control mode as spontaneous breathing diminished. Inspiratory and expiratory positive pressures (IPAP and EPAP) were carefully adjusted for satisfactory chest wall movement, pulse oximetric haemoglobin oxygen saturation (SpO2) and blood gas analysis. IPAP and EPAP ranged between 10–12 and 4–6 cm H2O, respectively. Local anaesthetic (a mixture of lidocaine 0.5% and bupivacaine 0.25%, with epinephrine 1:200 000) was infiltrated around the frame-pin sites and the skin flap incision. The patient was positioned supine and her head was fixed straight in a four-pin frame. The propofol infusion was terminated when the tumour was exposed. The patient regained spontaneous breathing gradually and smoothly. BIPAP as the control mode was switched to the synchronized mode at the emergence of spontaneous breathing. Nineteen minutes after the discontinuation of the propofol infusion, the patient became awake without ‘fighting’ against the mechanical ventilation. BIPAP was discontinued and the patient was left to breathe spontaneously with supplemental oxygen via nasal prongs. Following cortical mapping, flap closure was performed under anaesthesia with a propofol infusion (6–10 mg kg–1 h–1), a supplemental dose of fentanyl (50 µg) and local anaesthetic infiltration. With spontaneous breathing being diminished, BIPAP as the control mode was reintroduced to secure adequate minute ventilation. Anaesthesia was terminated on completion of surgery and the patient awoke uneventfully after 15 min. Arterial carbon dioxide pressure (PaCO2) remained below 44 mm Hg throughout anaesthesia.

Case 2
A 43-yr-old female (6l kg, 155 cm) was undergoing left temporal craniotomy and tumour resection. She had been complaining of headaches and difficulty with speech for 3 months. She was placed on anticonvulsant treatment of sodium valproate and phenytoin. Her medical history included hyperthyroidism and diabetes mellitus, which were treated with thiamazol and glibenclamide, respectively. She also had mild obstructive sleep apnoea. Intaoperative cortical speech mapping was planned.

The patient was premedicated with ranitidine and atropine. Standard anaesthetic monitoring was starting instrumented in the operating theatre. Supraoccular and occipital nerve blocks were performed with local anaesthetic (a mixture of lidocaine 0.5% and bupivacaine 0.25%, with epinephrine 1:200 000). Adequate positive pressure ventilation via a nasal mask was confirmed. Anaesthesia was induced with a bolus of propofol (30 mg) followed by infusion of the same drug (6–10 mg kg–1 h–1). Supplemental fentanyl (total dose before cortical mapping 250 µg) was administered to achieve an appropriate depth of anaesthesia. Additional local anaesthetic was infiltrated around the sites of the head frame pins and skin incision. A catheter was inserted into the radial artery after induction of anaesthesia for intermittent blood gas analysis and continuous arterial pressure monitoring. The patient was positioned supine with her head rotated to the right in a four-pin headholder. Her lungs were mechanically ventilated via a nasal mask with a pressure control mode using a ventilator equipped with PAV (BiPAP VisionTM, Respironics Inc.). After tumour exposure, the propofol infusion was discontinued. The patient was able to answer questions listed for speech assessment after 22 min. As she resumed spontaneous breathing, the pressure control mode was switched to PAV. The assist level of PAV was gradually reduced from 80 to 10% with increasing spontaneous breathing. PAV was then replaced with oxygen administered through nasal prongs. With cortical mapping completed, the propofol infusion (6 mg kg–1 h–1) was restarted. Supplemental doses of fentanyl (150 µg) and local anaesthetic infiltration were used for flap closure. PAV was reintroduced. The patient was awake within 15 min of com pletion of the surgery and there were no untoward events.

Throughout ventilatory support the FIO2 was 0.5 and PEEP was set at 3 cm H2O. With PAV, the flow and volume assist were started at the normal level (4 and 15 cm H2O litre–1, respectively). The assist level was adjusted variably at 10–80% to maintain the tidal volume at 300–500 ml. The peak inspiratory pressure was 7–14 cm H2O. The pressure control mode was combined with PAV while the spontaneous respiratory rate was below 10 min–1. The PaCO2 remained below 43 mm Hg throughout anaesthesia.

The intraoperative course was uneventful in both cases. There were no instances of oxygen desaturation or upper airway obstruction. Neither patient was observed to struggle against the ventilator. There were no features suggestive of stomach insufflation and neither patient vomited. The nasal mask remained in an appropriate position after patient positioning for surgery. Replacing the mask after cortical mapping was easy. There were no signs of brain swelling and haemodynamic variables remained stable during anaesthesia. Both patients were satisfied with their anaesthetic experience, when asked at postoperative interviews, including the placement of the mask and ventilatory support.


    Discussion
 Top
 Abstract
 Introduction
 Case reports
 Discussion
 References
 
Awake craniotomy requires: (1) sufficient depth of anaesthesia during opening and closing the bone flap; (2) full consciousness during cortical mapping; (3) smooth transition between anaesthesia and consciousness; (4) adequate ventilation; and (5) patient immobility and comfort throughout surgery. In an attempt to satisfy these requirements, some techniques have been established. These are summarized as sedation and local anaesthesia,1 2 810 and asleep– awake–asleep technique.6 7

Airway management is a major challenge during the sedation and transition (from asleep to awake) phases. However, no technique has proved ideal, hence the continued search for other options. Huncke and colleagues6 kept the trachea intubated during opening and closure of the skull and extubated during cortical mapping. They reportedly managed tracheal intubation, extubation, and reintubation with the patient’s head firmly positioned in a three-pin headholder. To avoid the gag and cough reflexes, lidocaine was continuously delivered to the upper airway via a catheter with multiple holes spiralled around the tracheal tube. Tracheal intubation ensures adequate ventilation and avoids aspiration. However, tracheal intubation in such compromised circumstances may not be always successful and safe to perform. Continuous topical anaesthesia to the upper airway might result in loss of airway reflexes, leading to aspiration postoperatively. In addition, awake intubation may be uncomfortable for the patient. Tongier and colleagues7 used a laryngeal mask airway (LMA{dagger}), which is easier to insert and less stressful to patients than tracheal intubation. However, similar advantages and disadvantages of intubation might be applied to LMA insertion.

Awake craniotomy has mostly been conducted without tracheal intubation or LMA insertion. In many cases, no treatment other than supplemental oxygen to spontaneous breathing was given.1 2 810 This in itself is comfortable for patients but the surgical procedure may distress the patient, because they are only lightly sedated to avoid upper airway obstruction and depressed ventilatory drive.1 2 810 Furthermore, transient desaturation (SpO2 <90%) and/or hypercapnia have been reflected.810 Hence a strategy is needed to maintain sufficient minute ventilation and to avoid upper airway obstruction without compromising patient comfort. Weiss11 placed a nasopharyngeal airway, which was then connected to a breathing circuit via a tracheal tube connector: thus enabled assisted ventilation.

NPPV can support ventilation and is usually well tolerated by patients.3 Several modes of ventilatory support can be used with NPPV.3 BIPAP can decrease upper airway obstruction and increase ventilation volume. Patients with obstructive sleep apnoea are treated with the application of BIPAP during sleep.12 BIPAP uses fixed inspiratory and expiratory pressures regardless of the degree of the patient’s ventilatory effort. Consequently, there is the possibility of stomach insufflation when the upper airway is obstructed: this can occur in sedated or anaesthetized patients. PAV provides pressure in proportion to the ventilation volume and flow generated by the patient’s own breathing effort5 and improves the comfort of NPPV.5 13 It was possible to reach 90% assist without arousal during non-REM sleep in normal subjects.14 PAV is less likely to cause insufflation of the stomach as no forced ventilation is given when there is no spontaneous flow as occurs during upper airway obstruction. The limitation of PAV is, however, that the minute ventilation can be less than adequate, if the patient’s respiratory effort is small.

From the cases we presented here, BIPAP and PAV via a nasal mask can be suggested as ventilatory management options for awake craniotomy. However, there are some limitations of this technique. First, it cannot be used in patients who have severe obstruction of the upper airway or who feel uncomfortable with the mask. Secondly, the strap that fixes a nasal mask can interfere with the surgical field in some cases. Thirdly, neither BIPAP nor PAV may be adequate for patients who need aggressive hyperventilation because of raised intracranical pressure. The upper airway should be secured in such cases.

Each airway management technique that has been used for awake craniotomy has its advantages and disadvantages. The most appropriate techniques should be chosen according to each patient’s requirements. We believe that the NPPV technique may be especially useful in patients with mild obstructive sleep apnoea and patients who need to avoid hypoventilation. However, a controlled study is needed to demonstrate the effect.

In conclusion, we report two cases of successful anaesthesia for awake craniotomy using NPPV either with BIPAP or PAV. This method can be used as one of the options for airway management in patients presented for awake craniotomy.


    References
 Top
 Abstract
 Introduction
 Case reports
 Discussion
 References
 
1 Taylor MD, Bernstein M. Awake craniotomy with brain mapping as the routine surgical approach to treating patients with supratentorial intraaxial tumors: a prospective trial of 200 cases. J Neurosurg 1999; 90: 35–41

2 Blanshard HJ, Chung F, Manninen PH, Taylor MD, Bernstein M. Awake craniotomy for removal of intracranial tumor: considerations for early discharge. Anesth Analg 2001; 92: 89–94[Abstract/Free Full Text]

3 Hess DR. Noninvasive positive pressure ventilation for acute respiratory failure. Int Anesth Clin 1999; 37: 85–102[ISI][Medline]

4 Hormann C, Baum M, Putensen C, Mutz NJ, Benzer H. Biphasic positive airway pressure (BIPAP)—a new mode of ventilatory support. Eur J Anaesthesiol 1994; 11: 37–42[ISI][Medline]

5 Younes M. Proportional assist ventilation. In: Tobin MJ, eds. Principles and Practice of Mechanical Ventilation. New York: McGraw-Hill Inc., 1995; 349–69

6 Huncke K, Van de Wiele B, Fried I, Rubinstein EH. The asleep– awake–asleep anesthetic technique for intraoperative language mapping. Neurosurgery 1998; 42: 1312–6[ISI][Medline]

7 Tongier WK, Joshi GP, Landers DF, Mickey B. Use of the laryngeal mask airway during awake craniotomy for tumor resection. J Clin Anesth 2000; 12: 592–4[CrossRef][ISI][Medline]

8 Gignac E, Manninen PH, Gelb AW. Comparison of fentanyl, sufentanil and alfentanil during awake craniotomy for epilepsy. Can J Anaesth 1993; 40: 421–4[ISI][Medline]

9 Herrick IA, Craen RA, Gelb AW, et al. Propofol sedation during awake craniotomy for seizures: patient-controlled administration versus neurolept analgesia. Anesth Analg 1997; 84: 1285–91[Abstract]

10 Hans P, Bonhomme V, Born JD, Maertens de Noordhoudt A, Brichant JF, Dewandre PY. Target-controlled infusion of propofol and remifentanil combined with bispectral index monitoring for awake craniotomy. Anaesthesia 2000; 55: 255–9[CrossRef][ISI][Medline]

11 Weiss FR, Schwartz R. Anaesthesia for awake craniotomy. Can J Anaesth 1993; 40: 1003

12 Sanders MH, Kern N. Obstructive sleep apnea treated by independently adjusted inspiratory and expiratory positive airway pressures via nasal mask. Physiologic and clinical implications. Chest 1990; 98: 317–24[Abstract]

13 Wrigge H, Golisch W, Zinserling J, Sydow M, Almeling G, Burchardi H. Proportional assist versus pressure support ventilation: effects on breathing pattern and respiratory work of patients with chronic obstructive pulmonary disease. Intensive Care Med 1999; 25: 790–8[CrossRef][ISI][Medline]

14 Meza S, Giannouli E, Younes M. Control of breathing during sleep assessed by proportional assist ventilation. J Appl Physiol 1998; 84: 3–12[Abstract/Free Full Text]