Unlike the TAP block, for which both a landmark and ultrasound guided technique have been described, the QL block is unusual in that it can only be performed under ultrasound guidance. A number of different ultrasound-guided approaches to the QL block have evolved over the last decade (Fig. 15.2). In the original description by Dr. Blanco, the patient is positioned in the lateral position and the ultrasound probe is placed above the iliac crest. A curved array probe is usually advised due to the depth required. The three abdominal muscle layers are identified. The probe is then moved posterolaterally until the transversus abdominis muscle becomes aponeurotic. This aponeurosis is followed until the quadratus lumborum muscle comes into view. This is approached from medial to lateral using an in-plane technique. After passing through the external and internal oblique muscles the local anaesthetic can be deposited on the anterolateral surface of QL in close proximity to the lateral aspect of the TAP [6]. This approach is dubbed QL1. Borglum modified this technique, passing the needle from lateral to medial to deposit local anaesthetic solution on the anterolateral aspect of the QL, dubbed transmuscular QL [12]. They further refined their approach by describing the Shamrock sign, to facilitate identification of the relevant structures. In this technique, the needle is passed in-plane, from posterior to anterior mimicking the landmark based approach to the psoas compartment block, through the body of QL to lie in the space between psoas and QL. As this required passing from the posterior to anterior and occasionally significantly deep views to be obtained to observe the erector spinae muscles, they modified the needle insertion point to be just medial to the probe position on the over the mid-axillary line [12]. This approach is referred to as the Shamrock QL. Blanco has subsequently revised his technique, dubbed QLB 2. He advises a more superficial approach, depositing local anaesthetic posterior or superficial to QL (Fig. 15.3). The needle passes only through subcutaneous tissue and the latissimus dorsi muscle. This approach provides a greater degree of paravertebral spread with improved safety margin [11].

Since the original description of the TAP block, there have been a plethora of studies detailing its efficacy. These have described its use in a wide variety of abdominal and pelvic procedures and have looked at outcomes such as reduction in pain scores, opioid consumption or opioid-related side effects. Essentially, when the block is used in the correct manner for an appropriate surgery, there will be analgesic benefit to the patient. When compared to placebo, the landmark TAP block shows significant analgesic benefit and opioid-sparing effect in patients, both adult and paediatric, undergoing abdominal and pelvic surgery [20–22]. This effect is not seen in lower segment caesarean sections when compared to intrathecal opioid [23]. Interestingly, recent reviews suggest that the posterior, landmark, TAP block provides more prolonged analgesia than the mid-axillary ultrasound guided approach [24, 25]. The reason for this is likely to be extension of the local anaesthetic into the paravertebral space. This paravertebral extension does not occur in the most commonly used ultrasound guided TAP blocks, with the probe positioned in the mid-axillary line or the subcostal areas. The realisation that posterior approaches improve efficacy has led to increased interest in the posterior ultrasound based TAP and the quadratus lumborum blocks. These blocks have demonstrated spread to the paravertebral space.

TAP blocks have also been compared to other regional analgesic techniques. When compared to epidural analgesia, patients with TAP blocks consumed significantly more opiate [26, 27]. TAP blocks have been compared with ilioinguinal and iliohypogastric nerve blocks for inguinal hernia repair surgery and have been shown to provide superior analgesia [28]. Continuous TAP infusions have been described using the ultrasound approach but they have not been compared to wound infiltration catheters, sited during surgery. As both techniques affect the abdominal wall it is probable that their effects will be similar. Abdominal wall blocks do not and should not be expected to confer similar analgesia to neuraxial blocks. However, they reduce opioid requirements when used as part of a multimodal approach.

There has been little research into the pharmacokinetics and pharmacodynamics of the local anaesthetics used in TAP and QL blocks. As these blocks have a centrally mediated effect, the appropriate volume seems to be important in ensuring spread to the paravertebral space. Doses of 0.3–0.6 ml/kg of local anaesthetic in low concentrations have been described but the exact volume needed to produce analgesia is unknown [29]. There have been some small studies looking at the addition of dexamethasone and dexmedetomidine to local anaesthetic for these blocks [30, 31]. Prolonged block duration was found in both cases but randomised trials are needed before the use of these adjuvants can be routinely advocated.

Clinically significant complications of transversus abdominis plan blocks are thankfully rare. However, with the introduction of more technically advanced blocks, such as the QL block, there is potential for an increase in complications, particularly with inexperienced sonographers. The TAP block uses high volumes of local anaesthetic and as a result there is a risk of toxic quantities of the agent being absorbed. Griffiths et al. measured the peak plasma concentration of ropivicaine after bilateral TAP blocks using ropivicaine 3 mg/kg [32]. They found a mean peak plasma ropivicaine level of 2.2 mcg/ml, which is above the minimum toxic plasma levels. There were no clinical sequelae associated with this potentially toxic level.

Interestingly, Griffiths proceeded to look at plasma ropivicaine levels in pregnant women undergoing bilateral TAP blocks for Caesarean sections [33]. Although peak plasma levels were in fact lower in this population, a number of women complained of symptoms of local anaesthetic toxicity. The mechanism for this toxicity was felt to be systemic absorption as opposed to intravascular injection, due to a 15-min delay between injection and onset of symptoms. Changes in cardiac output and blood flow during pregnancy may make these patients more susceptible to toxicity. This is further suggested by case reports of seizures following bilateral TAP blocks in this population. The patients received a similar dose of ropivicaine and their symptoms were rapidly reversed with lipid emulsion, supporting a diagnosis of local anaesthetic toxicity [34]. These reports should, however, alert one to the potential risks. The dose of local anaesthetic should be closely monitored and, in the case of these large field-like blocks, lower concentrations are advisable.

Patients with liver disease are similarly at increased risk of systemic absorption and toxicity. Landy et al. describe a case of local anaesthetic toxicity in a patient with chronic liver disease [35]. They hypothesized that the toxicity, which occurred after administering 3 ml/kg of ropivicaine, was due to a combination of reduced protein binding of local anaesthetic and increased abdominal wall vascularity from portal hypertension promoting systemic absorption.

Parturients and patients with chronic liver disease have a similar risk profile due to altered blood flow and protein binding. Caution is needed when performing local anaesthetic blocks in these populations. Similarly, as these blocks require a high volume of anaesthetic, paediatric and underweight patients are at particular risk of inadvertent overdose. Sakai et al. describe local anaesthetic toxicity following bilateral TAP blocks in a 40 kg patient who received 150 mg of ropivicaine (3.75 mg/kg). Although peak plasma levels of ropivicaine were not measured, it is reasonable to assume that they were significantly higher than the minimum toxic plasma level [36].

Damage to intraperitoneal organs has been described following both landmark and ultrasound guided TAP blocks. Farooq et al. described a liver laceration following landmark based TAP block, resulting in gross liver enlargement [37]. Similarly, Lancaster described a liver laceration after ultrasound TAP block for repair of an inguinal hernia. Poor needle visualization was felt to be the primary factor in this complication [38]. Although no reports of spleen or kidney injury have been reported, it is reasonable to assume that they are also at risk during TAP placement. Transient femoral nerve block is another complication, which can rarely be seen with TAP blocks [39]. Although transient, this may lead to delayed mobilisation and discharge, and should be considered before undertaking this block.