Regional anesthesia to scalp for craniotomy surgery

Pathomporn Pin-on＊

Department of Anesthesiology, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand

INTRODUCTION

Insufficient treatment of postoperative pain after craniotomies can lead to major complications such as increased intracranial pressure, intracerebral hemorrhage, surgical bed hematoma, seizures, cerebral infarction, etc. It also decreased patients and their families’ satisfaction. Postcraniotomy pain has been described as a somatic pain,originated from pericranial muscles and soft tissue. There were reported 55-60% of patients suffered moderate to severe headache within the first 12 hours after craniotomy(De Benedittis et al., 1996; Mordhorst et al., 2010). The incidence of pain depends on the surgical site (Thibault et al., 2007). The extended damage of temporal muscle and posterior temporal muscles provides that subtemporal and suboccipital approaches gain more pain severity compared to frontal craniotomies (Thibault et al., 2007; Flexman et al., 2010). For each neurological procedure, the level of noxious stimuli and nociception vary according to the stage of surgery. It has been illustrated by the graph of chloroform requirements during each step of craniotomy surgery(Bruder and Ravussin, 2010). Once the dura is opened, there is no pain receptor located on the brain parenchymal tissue.The anesthetic requirement is dramatically reduced (Horsley, 1906; Mordhorst et al., 2010). To this pathophysiologic knowledge, blockade of the afferent nerves innervated scalp might reduce the severity of acute postoperative pain and headache after craniotomy. Even opioid is potent analgesic,systemic opioid administration should be used cautiously in neurosurgical patients because the systemic effect obscure signs of intracranial emergencies.

SCALP INNERVATION AND SCALP BLOCKADE

The scalp is innervated by the branches of trigeminal and spinal nerves. The trigeminal nerve supplies anterolaterally and the spinal nerve supplies posteriorly. The ophthalmic division (V1) gives the supraorbital and supratrochlear nerves. The maxillary division (V2) gives the infraorbital,zygomaticofacial, and zygomaticotemporal nerves. The mandibular division (V3) gives the auriculotemporal cutaneous nerve. The greater and the lesser occipital nerves emerge from the second and third cervical spinal nerve root(C2, C3) (Liu, 2005; Kemp et al., 2011). A scalp blockade refers to the administration of local anesthetic (LA) of the nerves that supply sensation to the scalp. The technique is to infiltrate 2-3 mL of LA solution over the regions that these nerves emerge with a 25-27 G needle. To block the supratrochlear and supraorbital nerves, the LA is infiltrated above the eyebrow. The auriculotemporal is blocked with LA injected anterior to the ear, approximately at the level of the tragus. The zygomaticofacial, and zygomaticotemporal nerves are blocked by infiltrated LA subcutaneously between the lateral of the eye to the tragus. The greater and lesser occipital nerves are blocked with the injection of LA along the superior nuchal line between each side of mastoid process (Pinosky et al., 1996; Geze et al., 2009). The scalp blockade can be performed prior to the skull pin insertion in order to blunt the hemodynamic response and also decrease the systemic opioid requirement during the surgery(Pinosky et al., 1996; Song et al., 2015). Some authors performed blockade after the craniotomy procedure for the transitional analgesia, decreasing post-craniotomy pain and analgesic requirement (Nguyen et al., 2001; Ayoub et al.,2006; Hernández Palazón et al., 2007; Song et al., 2015).Recently, Song et al. (2015) supported that preemptive LA for scalp was significantly more efficacious in terms of pain severity and cumulative morphine consumption, compared to LA application before skin closure.

Epinephrine is usually added to the LA such as lidocaine or long-acting local anesthetics (i.e., bupivacaine,ropivacaine, levobupivacaine). The concentration ranges from 1:80,000 to 1:200,000 (10-25 µg/mL, respectively)(Nakamura et al., 2001). Many previous studies agreed that epinephrine added to local anesthetics for either local infiltration or nerve blockade showed a small but not clinically important increase in cardiovascular parameters after injection (BP, PR and HR), particularly in healthy patients (Silvestre et al., 2001; Meral et al., 2005; Faraco et al., 2007; Ketabi et al., 2012). The advantages are to decrease systemic absorption of LA, enhance the onset of LA, decrease systemic toxicity, and prolong duration of LA.However, these benefits are weakened when epinephrine is added to high-potency and long-acting LA. Accidental intravascular injection is possible in scalp blockade because of rich vascular supply. This complication is preventable by aspiration in each site of LA injection. Thus this complication quite rarely occurs in experienced hands. Nevertheless,if epinephrine is added and in the worst case, intravascular injection is unidentified, it may lead to toxic levels, presenting with tachycardia, hypertension, seizures and cardiac toxicity (Chakrabarti et al., 2014).

CONTROVERSIAL ISSUES

There are several studies of regional scalp block and its efficacy. However, the conclusion cannot be drawn because of relatively small sample size, difference in LA solution and its combination, the technique of scalp block, and the presence of concomitant procedures (i.e., LA infiltration on the skull pin site, opioid intermittent bolus, or opioid continuous infusion, etc.) (Guilfoyle et al., 2013). Biswas and Bithal showed that a scalp infiltration with 0.25%bupivacaine did not have any significant effect on postcraniotomy pain and analgesic requirement, but delay the requirement of the first analgesic dose (Biswas and Bithal,2003). Our previous study showed that the patients who received 0.5% bupivacaine for scalp blockade required intraoperative fentanyl less than the patients in the control group, 5.8 ± 3.0 μg/kg vs. 6.4 ± 3.2 μg/kg, P = 0.33. The increase of mean arterial pressure during the skull pin application was greater in the control group, especially in patients with underlying hypertensive disease (14 ± 7 mmHg vs. 11 ± 9 mmHg, P = 0.38) (Pin-on et al., 2014).However, these two studies cannot be compared because the pre-emptive analgesic techniques are different, scalp infiltration vs. scalp blockade, and also the difference in LA concentration. Our study agree with Pinosky et al.(1996), who demonstrated that 0.5% bupivacaine for scalp block could maintain hemodynamic profiles (SBP, DBP,MAP, HR) within the normal range as prior to the skull pin insertion compared to the control group. However,Bloomfield et al. (1998) showed that a significant reduction in postoperative pain in patients who received a bupivacaine scalp block did not correlate to heart rate or mean arterial pressure reduction. Hwang et al. (2015) demonstrated that scalp block with 0.75% levobupivacaine improved recovery profiles in terms of postoperative pain scores, PCA consumption, rescue analgesics, hemodynamic profile, and PONV compared to normal group. Among these studies,levobupivacaine showed promising outcome because of greater anesthetic potency than bupivacaine. In my routine practice, I have found that a combination of scalp blockade and scalp infiltration with potent LA such as ropivacaine,bupivacaine, or levobupivacaine as well as the addition of lidocaine with or without epinephrine provide the most effective pre-emptive analgesia for craniotomy procedures.Chaki et al. (2016) demonstrated that the blood concentration of the LA mixture of lidocaine and ropivacaine for scalp blocks and local infiltration did not increase above half of the known toxic level.

CONCLUSION

The efficacy of scalp blockade is needed for further studies in various perspectives, for example, the blood concentration of other potent LA (i.e., levobupivacaine, bupivacaine,with or without lidocaine, with or without epinephrine addition, etc).

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