While LPs can be performed in the sitting position, the lateral decubitus position is used when the patient is to be sedated. Furthermore, this position allows better distribution of injected chemotherapy through the CSF. The patient’s legs are flexed toward the chest, and the shoulders and pelvis are square and perpendicular to the bed, as shown in Fig. 15.1 [31]. In this position, an imaginary vertical line drawn between the posterior superior iliac crest would approximately cross the L4 spinous process. LPs can be done in the L3-L4, L4-L5, or L5-S1 interspace. LPs should be avoided at higher interspaces, as this risk injuring the conus medullaris. Conversely, LPs performed at lower interspaces increase the difficulty of palpating the spinous processes.

Wearing sterile gloves and a mask, the operator should cleanse the puncture site with an antiseptic solution. Sterile drapes should be applied, leaving the intended puncture site exposed.

The stylet should be in place within the needle. The needle should only be advanced with the stylet in place, or else the needle bore can become obstructed with a core of tissue and increase the risk of developing an epidermoid cyst.

The tip of the spinous process superior to the chosen interspace should be palpated. The needle should be inserted inferior to this tip, midway between two spinous processes.

If a traditional Quincke or bevel-tip needle is used, the bevel face should be oriented parallel to the long axis of the spine, so as to separate the longitudinal fibers of the dura rather than transect them. Thus, in a child lying in a left lateral decubitus position, the bevel should face up toward the ceiling. Several studies have shown that this bevel orientation helps reduce the rate of PDPH [32, 33].

The needle should be advanced slowly at a slight cephalic angle so as to move parallel to the angle of the spinous processes and avoid bony contact [34]. In most patients, this angle can be approximately achieved by advancing the needle as though aiming for the umbilicus. If bony contact occurs or resistance is felt, the needle should be withdrawn to the subcutaneous position and reinserted at a slightly different angle.

Usually, a pop is felt when the needle penetrates the ligamentum flavum. However, in young children or in patients who have had repeated LPs, the pop may not be a reliable sign. Therefore, once the needle has reached close to the estimated depth of insertion, the stylet should be removed to check for CSF flow. If there is no fluid, reinsert the stylet and advance the needle slightly, withdrawing the stylet and checking for fluid after each movement.

If a bloody tap occurs, it is advisable to remove the needle, obtain a new needle, and reattempt the LP at a different interspace. If the LP fails a second time, a different person should attempt it, especially if a more experienced operator is available. After a bloody tap, however, the presence of a small hematoma may make a successful procedure more difficult in spite of the operator’s proficiency. In such cases, the LP should be attempted again after a few days, allowing time for the hematoma to resolve.

ICP can be measured by connecting a manometer to the needle or via a stopcock, and allowing CSF to flow into the manometer until the fluid level ceases to rise. This procedure is not often used in practice, but may be performed in cases of suspected ICP. There will be normal variation in the fluid level with respiration. After the measurement is obtained, the CSF in the manometer should be released into a collection tube using the stopcock rather than be wasted.

ICP should be measured with the patient in the lateral decubitus position. It can be falsely elevated if the patient is in the sitting position [35] or if the head is elevated above the level of the needle. The range of normal opening pressure is 11.5–28 cm of water [36].

CSF should be allowed to drip into the collecting tubes. It should never be aspirated into a syringe as this could result in significant negative pressure. For most LPs performed for delivery of intrathecal chemotherapy, a tube is collected for cytospin and another for biochemistry (protein and glucose). With LPs done for patients with brain tumors or solid tumors, a tube for cytology should also be obtained. In the case of suspected meningitis, additional tubes for bacterial studies (gram stain, culture, and sensitivity) and/or viral studies should be obtained.

For a diagnostic LP, only the minimal required CSF volume should be collected. Excess CSF removal will increase the risk of a PDPH. Conversely, where intrathecal chemotherapy is to be administered, it is advisable to remove a CSF volume equal to the volume of drug that will be administered. Theoretically, a large net positive infusion volume may increase the risk of intracranial hypertension. Recognizing the limitations of time in the procedure room, some leukemia protocols recommend that clinicians should aim to remove at least 50 % of the volume of drug to be injected.

Once CSF collection is completed, the needle hub should be connected to the chemotherapy syringe and a tight seal obtained. The needle should be stabilized with the non-dominant hand to ensure that its position is not altered during this maneuver, as seen in Fig. 15.2. Slowly inject the chemotherapy. Resistance usually increases as the injection proceeds. However, if excessive resistance is felt, cease administration and remove the syringe to ensure that CSF is still free flowing.

One study [37] found that reinserting the stylet after a diagnostic LP was associated with reduced rates of PDPH. The authors hypothesized that strands of dura may enter the needle bore during CSF sampling and be threaded back during removal of the needle, producing a larger dural defect and allowing longer leakage of CSF. Replacing the stylet may allow the strands to be pushed out, reducing the risk of prolonged leakage.

If this postulated mechanism is correct, then it is reasonable to assume that injecting medication through the needle may achieve the same desired effect. Therefore, if IT chemotherapy was injected, the needle and syringe can be removed as a unit without reinserting the stylet. However, if the LP was done for diagnostic sampling only, the stylet should always be reinserted prior to removing the needle [38].

After withdrawing the needle, manual pressure using gauze should be applied for a few minutes, with longer times preferred in those with lower platelet counts or traumatic procedures.

In patients who have received intrathecal chemotherapy, lying supine for 1–2 h is advisable as it facilitates distribution of chemotherapy throughout the CSF. However, in patients who have received a diagnostic LP only no specific bed rest is required and patients may ambulate once they have recovered from the effects of sedation [39].

As for all procedures, proper documentation of consent, orders, and the procedure details should be carefully documented. The operator should properly document any problems encountered, the number of attempts, and chemotherapy administration. Standardized procedure forms or templates can be useful to allow efficiency in this regard.

Figures 15.3, 15.4, 15.5, and 15.6 show samples of standardized documentation used at our institution for LPs and bone marrow aspirates/biopsies. Figure 15.3 is a standardized consent form; Fig. 15.4 is a preprinted orderset for intrathecal chemotherapy; Fig. 15.5 is a procedure documentation form; and Fig. 15.6 is a wall poster used for “time-out” safety checking. The use of such template documentation instruments can help facilitate the efficiency and quality of care in the procedure room.

The most common complication of an LP is PDPH. It can be defined as any headache after an LP that worsens within 15 min of sitting or standing and is relieved within 15 min of lying down. Most PDPHs occur within 3 days of the procedure. They are believed to be caused by a puncture in the dura that allows CSF leakage. The reported rate of PDPH varies across studies from 2 to 60 %, depending on the setting [2]. As mentioned, the rates of PDPH have been shown to decrease with atraumatic needles, smaller gauge needles, maintaining the needle bevel direction parallel to the dural fibers, and reinserting the stylet in diagnostic LPs. Bed rest and fluid supplementation do not prevent PDPH [40]. For the management of PDPH, the reader is referred to recent Cochrane systematic reviews [41, 42].

The most significant complications include cerebral herniation, spinal hematomas, and inadvertent administration of incorrect IT chemotherapy. Other complications include backache, subdural fluid collections, epidermoid cysts, and infectious complications such as cellulitis, skin abscess, discitis [43], and epidural abscess [44].

Bone marrow aspirations (BMA) are used for the diagnostic investigation or monitoring of patients with abnormal blood counts, hematologic disorders, suspected malignancies, or metabolic, infiltrative, or infectious diseases that can involve the bone marrow. Additionally, bone marrow trephine biopsies (BMB) are performed when an assessment of bone marrow cellularity, architecture, or focal lesions is required, when there is inadequate marrow aspiration, and for the staging of lymphomas and small round blue cell tumors of childhood [45]. The bone marrow aspirate and trephine biopsy are complementary procedures and are usually performed together (BMAT).

When performed by a trained operator, BMATs are generally safe procedures and adverse events are uncommon [46]. The most frequent complications are bleeding and pain. Rare cases of severe bleeding with large hematomas [47], anemia, and death [48] have been reported. Hemorrhagic disorders, severe thrombocytopenia, and anticoagulation may be considered relative contraindications and their correction should be considered before the procedure whenever feasible [49]. Local skin or bone infections should exclude the use of that particular site for the procedure.