1 Introduction

Interfascial plane block (IFPB) is a new method of regional anesthesia [1]. IFPBs are usually performed under ultrasound guidance by injecting the local anesthetic into the interfascial space [2]. We analyzed the research data of IFPBs from 2002 to 2023. We found that studies on IFPBs have increased rapidly since 2016 (Fig. 1). IFPBs have been used to relieve chronic neuropathic pain and visceral pain and manage perioperative pain during trunk and limb surgeries [3, 4].

Fig. 1
figure 1

Publications change over the years

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2 Methods

2.1 Anatomy of the interfascial plane

According to its structure and function, the fascia is divided into the superficial fascia and deep fascia. The interfascial plane is generally considered the space between two deep fascia layers. The interfascial space, comprising fat, elastin, and reticular fibers, covers the surface of vital structures, such as the nerves, blood vessels, bones, organs, and muscles, and plays a role in fixing, cushioning, and lubrication [2]. The thickness of the deep fascia differs in various parts of the human body. The deep fascia is always thinner in the trunk area and thicker in the limbs. The fascia are layered and connected, such as the abdominal fascia and thoracolumbar fascia [1]. The extensibility and plasticity of the potential space between two deep fascia layers make IFPB administration feasible. The fascia has proprioceptive fibers and innervations by multimodal free nerve endings of unmyelinated (C) and thinly myelinated (A-delta) neurons that respond to mechanical, thermal, and chemical stimuli [5]. Injection of local anesthetics in the interfascial space can block the nerve endings within it and the nerve branches innervating the two fascia layers, thus achieving the purpose of regional anesthesia [6]. Due to the anatomical specificity of the fascial attachment points at different sites, the injection site significantly affects the diffusion mode of local anesthetics; thus, the effectiveness of IFPBs is uncertain. Since the three pathways of the cervical plexus block are the superficial cervical fascia and investing fascia (superficial layer of the deep cervical fascia), the investing fascia and prevertebral fascia (deep layer of the deep cervical fascia), and the prevertebral fascia and scalenus fascia, it is also considered an IFPB [7]. Moreover, due to the uneven distribution of low-pressure areas within the fascia and susceptibility to multiple factors, such as muscle tension, position, and respiratory movements, diffusion of local anesthetics in IFPBs requires the operator’s experience to determine whether multi-site injections are necessary [8]. In areas with fascial fusion bands or physical barriers of fascia, a multi-site block may result in widespread diffusion.

2.2 Importance of ultrasonic guidance

There is uncertainty in locating the interfascial space based on manual perception only. Ultrasound can help locate the deep fascia precisely; hence, various IFPBs of the trunk and limbs have received renewed attention. Moreover, real-time ultrasound guidance can avoid puncturing the vital nerves, blood vessels, and organs and reduce complications related to puncture [9]. Elsharkawy et al. suggested that the biomechanical properties of the fascia could play an important role in the diffusion of local anesthetics [8]. Ultrasound can detect changes in the interfascial space following movement and monitor the local anesthetic diffusion. Thus, the development of IFPBs has benefited from the advances in ultrasound technology.

2.3 Analgesia principle and classification of IFPBs

IFPBs mainly fulfill three functions. First, IFPBs interrupt the transmission of pain and mechanical, thermal, and chemical signals of the fascia itself. Second, they occlude the communication between the nerve branches passing through the fascia and nervus centralis. Third, the absorption of the local anesthetic contributes to systemic analgesic effects [10]. Therefore, IFPBs can be used in operations involving the fascia itself or surgical areas innervated by the nerve branches in the interfascial space.

In general, IFPBs are divided into the following three categories:

  • (1) Cervical fascial block, applied in sternocleidomastotomy, carotid endarterectomy, thyroidectomy, and clavicular, shoulder, or upper arm surgeries with a cervical plexus or high-level brachial plexus block.

  • (2) Thoracic wall block, including the clavipectoral fascia plane block, pectoral nerve block I or II, serratus anterior plane block, retrolaminar block, and erector spinae plane block (ESPB), applied for the clavicle, sternoclavicular or acromioclavicular joint, thoracic vertebra, chest wall, and anterolateral abdominal wall surgery with the supraclavicular, subclavian nerve, medial and lateral thoracic nerve, intercostal nerve, and dorsal rami of the spinal nerve blocks.

    Low-level serratus intercostal plane block may have a larger block range than the subcostal transverse abdominis plane (TAP) block by the lateral cutaneous branch instead of the anterior cutaneous of the intercostal branch block [11].

  • (3) Abdominal wall block, including the ESPB, quadratus lumborum block, TAP, and iliofascial block, applied for the lumbar vertebra, abdominal wall, and hip joint surgery with the dorsal rami of the spinal nerve and intercostal nerve branches blocks.

The IFPB between the iliopsoas and iliac periosteum was recently found to overcome preoperative pain by the nerve branch block of the hip joint.

3 Discussion

IFPBs affect the nerve innervation of the skin, subcutaneous tissue, muscle, bone, and organs. Therefore, some types of anesthesia involving above structures can be achieved by administering IFPBs with conservative intravenous analgesia. However, since IFPB does not resolve visceral pain effectively, it is often used as an auxiliary analgesic method combined with general anesthesia in cardiopulmonary, hepatobiliary, and gastrointestinal operations involving visceral nerves.

After years of development, IFPBs have been used by an increasing number of anesthesiologists. Compared with intraspinal or plexus block, the IFPBs have the following advantages: (1) simple procedure and requires minimal hemostasis; (2) easy identification of the fascia on ultrasound; (3) low risk of nerve damage or vascular invasion; (4) freely available puncture paths; (5) sliding structure of the interfascial space facilitates diffusion of the local anesthetic; and (6) additional analgesic effects are produced by the local anesthetic spreading outside the fascial space due to the fascial foramens for the passage of nerves or blood vessels.

It is difficult to mark the blocking range of the IFPBs, and the hypoalgesic area shows irregular distribution on continuous observation. Many clinical studies on IFPBs have reported statistically significant reductions in pain scores and opioid consumption in the absence of documented skin sensory loss. A pooled review of ESPBs indicated that only 34.7% of the cases recorded an assessment of sensory or motor blocks [12]. Thus, the analgesic effect of IFPBs is not strongly related to the sensation and movement of the target area, and the analgesic effect depends on the chief complaint and perioperative opioid demand of the patients.

The IFPBs mainly diffuse along the natural interfascial space, and abnormalities of the interfascial space hinder the liquid flow. Moreover, the potential space between the fascia layers is often difficult to distinguish on ultrasonic images. The diameter of the anesthetic needle tip always exceeds the interfascial space, and the local anesthetic is inevitably injected outside the interfascial space. Pre-injection of the nerve or vascular sheath may significantly increase the accuracy of locating the fascia layer. For instance, we can proceed with pre-injection of the femoral nerve sheath to separate the iliac fascia above the inguinal ligament or with a pre-injection of the periclavicular fascia to divide the clavipectoral fascia. Using a needle with a thin caliber in the water-separation technique may ensure precise injection [2]. Artificial intelligence equipment may improve the ability to recognize ultrasonic images, thus improving the accuracy of the injection sites [13].

Despite the obvious advantages of IFPBs, they do have some limitations. First, the blocking effect of the IFPBs depends on the diffusion of the local anesthetics; therefore, for the interfascial spaces with sparse nerve distribution, a larger volume of local anesthetic should be used to ensure an adequate range of analgesia. De Cassai et al. found that the ESPBs are at a higher risk of local anesthetic systemic toxicity than the other IFPBs due to a larger anatomical space and higher local anesthetic absorption rate [14]. Because of the limited management of visceral pain with IFPBs, there is a risk of an incomplete block. However, patient satisfaction remains high, owing to the reduction in perioperative analgesics.

4 Conclusion

IFPBs should be considered as the new anesthetic technique rather than a block technique. The effects of IFPBs need to be investigated further to update their clinical applications. The selection of an IFPB or a combination of IFPBs mainly depends on the interfascial plane anatomy, surgical site, and operator experience. Owing to the development of ultrasonic visualization, IFPBs could play an important role in easy diagnosis and treatment as a routine anesthetic technique or in combination with other anesthetic methods.