The extradural space can be approached by either the midline or the paramedian route (1). The advantages of the paramedian approach (1–4) include a reduced likelihood of piercing the dura mater, a straighter course for the epidural catheter, a decreased frequency of intravascular catheterization, and a decreased incidence of paresthesia (2). In this approach, the vertebral lamina provides a bony landmark just proximal to the ligamentum flavum (1). The paramedian approach is superior to the midline approach in cases in which the lumbar spinous processes are difficult to identify (3). The factors responsible for these differences are thought to be the different angle of the epidural needle and the restricted mobility of the dura mater caused by the dorsomedian connective tissue band (4).
Positioning for extradural analgesia in patients with lower limb skeletal injuries is difficult because of pain at the fracture site and other injury sites and the presence of traction devices or splints. In the classic lateral position for epidural catheterization, the patient’s back is at the edge of the operating table and parallel to it. The knees are flexed and drawn up to the abdomen as much as possible, and the head is brought down towards the knees. Special care is required to avoid rotation of the hips and shoulders (1).
It may be difficult for patients with lower extremity injuries to turn laterally, and the flexion of the back may be prevented by pain or the presence of a splint. This study was designed to compare the difficulties in identifying the epidural space and the occurrence of technical problems and complications of needle and catheter insertion in lower extremity trauma patients without the aid of spinal flexion.
After we obtained approval from the institutional human investigation committee, this randomized, prospective study was conducted in 50 patients with injury of the lower extremity. Patients were scheduled for operative reduction and fixation of the bone after adequate fluid resuscitation and stabilization of the fracture with traction or splint. All patients had received preoperative nonsteroidal antiinflammatory drugs for pain relief. Patients with a history of head injury or other intracranial pathology, unstable hemodynamic status, or herniation of an intervertebral disk and those not willing to receive regional anesthesia were excluded from the study. Written, informed consent was obtained from each patient. The patients were randomly allocated to one of two groups, which received epidural block through either the midline or the paramedian approach.
One of the authors examined the patients before surgery, performed the epidural block, and assessed the technical difficulties. Another author conducted a postoperative interview 24 h after surgery.
All patients were premedicated with 1 mg of midazolam IV on the operating table. No further sedation or analgesic was given. Patients were preloaded with isotonic saline 20 mL/kg over 20 min before epidural drug injection.
The patient was transferred to the operating table in supine position, with traction and splints as needed. After transfer, the immobilizers were removed in the presence of the operating surgeon. The table was tilted to a 15°–20° head-up position, and then the patient was supported in the sitting position without moving the legs. The head of the table was then flexed, making it horizontal, with the foot of the table containing the injured limb and having a downward slope. The anesthesiologist performing the block approached the patient from the left side of table and performed the epidural block with an 18-gauge Tuohy needle in the L3-4 interspace.
Five milliliters of lidocaine (10 mg/mL) was infiltrated in the subcutaneous tissue, muscle, ligaments, and periosteum, depending on the approach. Patients were supported in the modified sitting position without active spinal flexion, such that their position could be maintained without any discomfort or pain. Active spinal flexion of the patient was planned if two attempts at epidural needle insertion failed. The midline approach was used with the needle inclined 90°–110° cephalad to the skin. The paramedian approach was performed as described by Bonica (1). The skin puncture point was 1.5 cm lateral to the caudal end of the spinous process of the L4 vertebra. The needle was directed medially and cephalad so that its axis made an angle of approximately 15° with the midsagittal plane and 135° with the long axis of the spine. The needle was advanced through the paraspinal muscles until contact was made with the ipsilateral lamina of the vertebra or engaged in the ligamentum flavum. If the needle made contact with the lamina, it was maneuvered to walk off the lamina and was engaged in the ligamentum flavum. The need to withdraw and change the direction of the needle because of encountering resistance by hitting bone other than the lamina or after maneuvering the superior surface of the lamina was counted as one attempt (3). The need to withdraw and change the direction of the needle because of hitting the bone was counted to be one attempt for the midline approach.
The epidural space was identified by loss of resistance to saline. Any leakage of blood or cerebrospinal fluid (CSF) was noted. An 18-gauge epidural catheter was advanced to a depth of 5 cm in the epidural space. All catheters were from Portex, UK, made of nylon, with a bullet tip and three lateral openings. Any resistance to catheter advancement or paresthesia reported by the patient was also noted. Paresthesia was defined as an unpleasant tingling sensation in the back, with or without radiation into the leg. The catheter was observed for the appearance of blood or CSF either spontaneously or on aspiration. In the presence of blood, the catheter was withdrawn in 1-cm increments until blood flow disappeared. After a successful test dose of 60 mg of lidocaine and 15 μg of epinephrine in 3 mL, the total dose of local anesthetic was injected. Any resistance while injecting the drug was noted. Thereafter, the table was returned to the horizontal position, and the patient was placed in the supine position.
Twenty-four hours after surgery, the epidural catheter was removed and inspected for abnormalities or blood. Patients were asked to rate discomfort during the procedure of epidural anesthesia, including that due to positioning as a whole, by using a four-point scale with no, mild, moderate, or severe discomfort. The incidence of backache was also noted.
Differences between groups in age, number of attempts without spinal flexion, and total number of attempts (including after spinal flexion) required for successful catheter placement were assessed with the two-tailed Student’s t-test. Discomfort during the procedure was assessed with the Mann-Whitney U-test. Blood or CSF in the needle, blood or CSF in the catheter, resistance to catheter introduction or to injection, and paresthesia were analyzed with two-tailed Fisher’s exact tests. A P value <0.05 was considered significant.
Patients in both groups were comparable in age (35 ± 8 yr versus 34 ± 9 yr), sex (male/female, 22:3 versus 22:3), and ASA physical status (I/II, 22:3 versus 21:4). The total number of attempts (including repositioning with spinal flexion) for successful catheter placement was 2.56 ± 1; the maximum number of attempts needed was 4 for the midline group. The total number of attempts was 1.44 ± 0.6; the maximum number of attempt was 3 for the paramedian approach. The difference was significant (P < 0.01). Seventeen patients in the midline group required more than two attempts for epidural insertion, with active flexion of the back required for needle insertion. Only one patient in the paramedian group required more than two attempts (Table 1). There were more catheter-related problems in the midline group, including resistance to catheter advancement (P = 0.023), blood in the catheter (P = 0.022), and paresthesia (P = 0.010). In addition, the midline approach was associated with more discomfort than the paramedian approach (Table 2).
Inadequate positioning of the patient during extradural blockade will negate an otherwise meticulous technique and should be avoided (1,2). However, adequate positioning may be difficult in patients with traumatic injuries, severe preoperative pain, or obesity (5). The sitting position with the patient’s feet resting on a stool or chair may be preferable for extradural blockade in patients with lower extremity fractures. The patient is often encouraged to flex the spine, but this may be painful (6).
In this study, we have compared the technical difficulties and complications of needle/catheter insertion associated with the paramedian and midline approach without active spinal flexion. To decrease the pain caused by the sitting position, and also to minimize dislodgement of fractured bone, we used a modified sitting position which prevents any movement of the lower extremities except the flexion at the hip joint. The downward slope of the lower end of the table also provides some traction to the limbs because of gravity.
Blomberg et al. (7) and Griffin and Scott (8), in two separate studies, compared the midline and the paramedian approaches prospectively. Blomberg et al. (7) demonstrated a less frequent incidence of difficulty in localization of the epidural space and less resistance to catheter introduction and anesthetic solution injection with the paramedian approach. They also found a less frequent incidence of paresthesia with this approach. Likewise, Jaucot (9) demonstrated fewer intravascular catheter placements with the paramedian approach. However, Griffin and Scott (8) could not establish any significant differences between the approaches.
This study found a frequent incidence of intravascular catheter placement with the midline (24%) compared with the paramedian (0%) approach. The unrecognized, unintentional intravascular injection of local anesthetics has been stated to be the most important hazard of epidural blockade and is more likely with epidural anesthesia than with other regional anesthetic techniques because of the rich plexus of veins filling the epidural space (10). The reported incidence of intravascular injection in general during epidural anesthesia varies from 0.2% to 11%, with a typical frequency of 2% (11). The study by Stone et al. (12), in parturients, found evidence of blood vessel puncture in 18% of patients in the sitting position and 12% in the lateral position; this difference was not statistically significant. The authors theorized that in the sitting patient, the increased epidural venous pressure would increase the incidence of vessel puncture. The experience of the anesthesiologist with a particular position may also result in an increased risk of vascular puncture when performing epidural block with alternate positions.
In our study, the effect of positioning and trauma may have resulted in an increased epidural venous plexus pressure. The presence of a dorsomedian connective tissue band, which results in relative immobility of the dura mater, may have caused unpredictable changes in the direction of the extradural catheter when it was inserted midline (13,14). The anesthesiologist’s unfamiliarity with performing the midline block in an unflexed spine may also have caused the increased incidence of intravascular catheter placement. In contrast, with the paramedian approach, the catheter easily advances cephalad without coming into contact with lateral areas of the epidural space, which contains large vessels and nerve roots (14).
Paresthesias during epidural catheter introduction in the lumbar region are probably due to contact with a nerve root or lateral deviation of the catheter (7). Lateral or caudal deviation of epidural catheter has occurred during epiduroscopy in autopsy subjects (13,14). The reduced incidence of paresthesia observed in our study with the paramedian approach is presumably because of the straighter and more midline course taken by the catheter (14).
In this study, patients in the paramedian group experienced less pain during the procedure. This can be attributed to patient positioning, 5 mL of lidocaine (10 mg/mL) infiltration, avoidance of puncture of tough ligaments, and/or avoiding active spinal flexion by the patient.
We could not devise a way to perform the study in a blinded fashion. This introduces the possibility of bias in assessment of the results. In addition, the study population comprised mainly young and otherwise healthy men. Hence, it may not be possible to generalize these results to other population groups.
We conclude that it is possible to avoid spinal flexion with the paramedian approach to epidural anesthesia with the patient in the sitting position. This decreases pain to the injured site in trauma patients undergoing lower limb orthopedic surgery when compared with the midline approach.
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© 2004 International Anesthesia Research Society
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