Anesth Analg 2003;96:1537
© 2003 International Anesthesia Research Society
LETTERS TO THE EDITOR
Continuous Peripheral Neural Blockade for Postoperative Analgesia: Practical Advantages
Bruce Ben-David, MD, and
Jacques E. Chelly, MD PhD, MBA
Department of Anesthesiology, University of Pittsburgh Medical Centers, Pittsburgh, PA
To the Editor:
Continuous femoral nerve blockade (CFNB) has been advocated as an alternative to epidural analgesia (EA) or intravenous opiate administered by PCA for acute pain management following major orthopedic surgery (1,2). Both EA and CFNB provide effective postoperative pain control, reduce opiate requirements and associated side effects, and improve functional recovery. CFNB reduces hospital length of stay and the frequency of serious complications (2) while conveniently avoiding the risk of epidural hematoma associated with the use of anticoagulants (3). Although a local anesthetic (LA) infusion could conceivably produce systemic toxic effects including confusion, hypotension, hypoxia, seizure, arrhythmia, and even coma, there have been few such cases reported (4). Presumably this is due to the low concentrations of LA used for these infusions and perhaps also to the premonitory appearance at lower blood levels of symptoms such as dizziness, lightheadedness, tinnitus, visual disturbance, and perioral tingling or numbness. On the other hand, hypotension with or without associated neurologic and/or cardiorespiratory effects are not uncommon with EA. This may represent an important advantage of CFNB over EA, as illustrated by this case.
An 83-year-old 65-kg woman with noninsulin-dependent diabetes mellitus, chronic obstructive pulmonary disease, hypertension, and osteoarthritis underwent bilateral total knee arthroplasties at UPMC Shadyside Hospital in Pittsburgh. Preoperatively, bilateral perineural femoral nerve catheters were placed and 15 mL ropivacaine 0.35% was injected at each site. In addition, bilateral single infragluteal sciatic blocks (5) were also performed with 10 mL ropivacaine 0.35% at each site. The operation was conducted uneventfully under light general anesthesia. In the recovery room, infusions of both perineural femoral catheters were begun using ropivacaine 0.2% at a rate of 5 mL/h each. On the evening of surgery the patient was alert and comfortable as she was likewise the afternoon of the following day. Later that evening, however, she became confused, hypotensive, and her oxygen saturation decreased to less than 90% despite administration of oxygen via nasal cannula. An EKG was little changed from the preoperative cardiogram, revealing neither ischemia nor arrhythmia. The patient was promptly taken for a ventilation-perfusion scan that demonstrated a high probability of pulmonary embolus. She was transferred to the intensive care unit, and a heparin infusion was begun. The continuous femoral infusions of 0.2% ropivacaine were continued, and she remained comfortable and in need of minimal supplemental analgesics. She recovered fully over the next several days.
This case illustrates two further advantages of CFNB. First, the use of CFNB did not delay or distract from the correct diagnosis and management of the patient’s pulmonary embolus. While LA toxicity may have accounted for the altered mental status, in the absence of more profound neurologic change, the hypotension and hypoxia were unlikely to be a result of LA toxicity. This is particularly so in view of the small doses of LA being infused. In contrast, had this patient had EA, her hypotension, hypoxia, and confusion would likely have been ascribed to "the epidural until proven otherwise." In this respect, CFNB simplifies the differential diagnosis and represents a real advantage. Second, CFNB did not have to be discontinued because of the administration of therapeutic doses of heparin. This was fortunate because the nursing staff would have likely been reluctant to give the patient morphine in her state of confusion and hypoxemia. Thus she would have been condemned to even further suffering and stress.
With regard to peripheral nerve blocks, it is important to recognize that lumbar plexus blocks, while also indicated for total knee arthroplasty, have been reported to produce hypotension with associated confusion and hypoxia (6). This difference in the safety profile of femoral nerve block versus lumbar plexus block is one advantage of using the former technique for postoperative pain management following total knee replacement.
In summary, this case exemplifies certain practical advantages of CFNB over EA. The unlikely occurrence of associated hypotension and/or hypoxia with CFNB, while an advantage in its own right, simplifies the differential diagnosis when they do occur and facilitates prompt assessment and treatment. Moreover, neither the symptoms nor their treatment are likely to require the cessation of pain management with CFNB.
References
- Singelyn FJ, Deyaert M, Joris D, et al. Effects of intravenous patient-controlled analgesia with morphine, continuous epidural analgesia, and continuous three-in-one block on postoperative pain and knee rehabilitation after unilateral total knee arthroplasty. Anesth Analg 1998; 87: 88–92.[Abstract/Free Full Text]
- Chelly JE, Greger J, Gebhard R, et al. Continuous femoral blocks improve recovery and outcome of patients undergoing total knee arthroplasty. J Arthroplasty 16; 2001: 436–45.[Web of Science][Medline]
- Horlocker TT, Wedel DJ. Anticoagulation and neuraxial block: historical perspective, anesthetic implications, and risk management. Reg Anesth Pain Med 1998; 23: 129–34.[Web of Science][Medline]
- Chelly JE. Complications. In: Chelly JE, Casati A, Fanelli G, eds. Continuous peripheral nerve block techniques. Philadelphia: Mosby, 2001: 21–5.
- Di Benedetto P, Bertini L, Casati A, et al. A new posterior approach to the sciatic nerve block: a prospective, randomized comparison with the classical posterior approach. Anesth Analg 2001; 93: 1040–4.[Abstract/Free Full Text]
- Auroy Y, Benhamou D, Bargues L, et al. Major complications of regional anesthesia in France: the SOS Regional Anesthesia Hotline Service. Anesthesiology 2002; 97: 1274–80.[Web of Science][Medline]
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