Regional blockade and pre-existing medical conditions
THE PATIENT WITH CARDIAC DISEASE
D. A. Scott
St. Vincent's Hospital Melbourne, Fitzroy, Vic
An increasing proportion of the population is presenting for surgical procedures having pre-existing cardiac disease. The widely recognised benefits of regional anaesthesia, including the potential use of catheter infusions for postoperative analgesia, mean that consideration must be given to the risks and benefits of regional techniques in patients with cardiac disease. Regional anaesthesia has the potential to reduce nociceptive input into the central nervous system and attenuate the stress response, however this requires blockade of all noxious afferents which is seldom achievable.
The presence of Ischaemic Heart Disease presents challenges for all modes of anaesthesia. With respect to epidural anaesthesia, a meta-analysis of 17 trials showed a reduction in post operative myocardial infarction (POMI) with thoracic, but not lumbar, epidural anaesthesia (extending for 24h into the postoperative period) (Beattie et al. 2001). A reduction in POMI was also found in a large randomised controlled trial (RCT) of abdominal surgical patients (n=1021) who had epidural anaesthesia combined with general anaesthesia compared with general anaesthesia alone (Park et al. 2001). This may reflect the benefits of cardiac sympathetic modulation by thoracic block, as also occurs with systemic beta-adrenergic blockade (Mangano et al. 1996). However, not all investigators have confirmed this benefit (Rigg et al. 2002), and the use of epidural analgesia as a component of anaesthesia and post-operative care in cardiac surgery remains controversial (Liu et al. 2004; Chaney 2006). Failure to fully block afferent stimulation may explain why regional anaesthesia in patients having awake carotid endarterectomy has not consistently been shown to reduce the incidence of POMI in randomised trials, although a reduction was shown in larger numbers of patients in non-randomised investigations (Rerkasem et al. 2005). Studies of perineural infusions have been insufficiently powered to establish an effect on adverse myocardial outcomes (Richman et al. 2006). Spinal anaesthesia would be expected to provide more complete deafferentiation, especially for urological and orthopaedic procedures. In a meta-analysis by Rogers et al (Rodgers et al. 2000), spinal anaesthesia was associated with a lower mortality than general anaesthesia but the association with POMI was not specifically investigated.
An increasing problem with regional anaesthesia in patients with IHD is that of the use of potent antiplatelet drugs, in particular the ADP-antagonist thienopyridines (e.g. clopidogrel). Although these drugs may be prescribed as an alternative to aspirin in some patients, if the indication is to prevent thrombosis in a recently placed intracoronary stent then it may be unwise to discontinue the drug in order to make regional anaesthesia safer. An unendothelialised stent should be considered equivalent to an unstable coronary syndrome and so the antiplatelet therapy should be continued for at least 6 weeks with bare-metal stents and for 6 to 12 months with drug-eluting stents. Although the risk of perioperative bleeding is greater, should POMI occur it carries a high mortality (Wilson et al. 2003). The bleeding risk associated with peripheral nerve blockade and antiplatelet drugs has not been established, although it seems appropriate to avoid deep and/or transmuscular blocks.
Cardiac failure presents a high risk for anaesthesia whatever the modality (Eagle et al. 2002). Neuraxial analgesia presents the main challenges in this patient group as opposed to perineural block because of the potential fluid shifts and changes in afterload. The most important factor in managing these patients is an awareness of the potential effects of changes in preload and in particular how these may change once the block wears off. During establishment of the block, careful fluid loading needs to be balanced with judicious vasopressor use. Following surgery, as the block regresses, the patients posture and fluid balance may need to be adjusted and the possible need for diuretics considered.
In valvular heart disease, the most significant concern is with moderate to severe grades of aortic stenosis and neuraxial anaesthesia. A number of case reports have been published and reviewed (McDonald 2004), and these generally attest to the safety of spinal or epidural anaesthesia provided that afterload is carefully maintained. This is often achieved by titration of the epidural or spinal block in a gradual fashion until it is adequate for surgery. An alternative is to use a combined-spinal epidural technique with a small intrathecal dose. The asymptomatic patient with aortic stenosis should thus be managed in a similar way to the hypertensive patient with left ventricular hypertrophy i.e. afterload support, maintenance of sinus rhythm, careful volume management and avoidance of tachycardia. Clearly, if significant symptoms are present (angina, syncope or failure) then a full review of both anaesthetic and surgical indications is warranted. Mitral stenosis is less common nowadays, however it still presents occasionally in obstetrics. The principles of careful monitoring, dose titration and preload maintenance have been described in the literature (Pan et al. 2004).
Patients with mechanical valve prostheses or atrial fibrillation may be anticoagulated with warfarin. Most operative procedures require normalisation of coagulation and guidelines to achieve this are readily available. Even with a borderline or high residual INR, perineural blockade may still be considered a relatively safe option, provided it is not in a confined or incompressible site. Ultrasound guidance of needle placement may help to avoid vessel injury (especially arterial).
Finally, the direct myocardial depressant effects of systemic levels of local anaesthetics needs to be considered. In blocks where large doses of local anaesthetic are given, the enantiomerically pure local anaesthetics ropivacaine and levobupivacaine are less cardiac depressant and should be used in reference to bupivacaine. Likewise systemic absorption of adrenaline pre-mixed with local anaesthetics may result in tachycardia and therefore the dose of adrenaline should be kept to the minimum necessary.
In summary, regional anaesthesia including neuraxial blockade, can be safely provided to patients with cardiac disease provided that simple precautions are taken, thus enabling these patients to receive the benefits of these techniques.
Time of Presentation
Saturday 13 May 2006 - 1330-1500
References
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2. Chaney, M. A. (2006). Anesth Analg 102(1): 45-64.
3. Eagle, K. A., et al. (2002). Anesthesia & Analgesia 94(5): 1052-64.
4. Liu, S. S., et al. (2004). Anesthesiology 101(1): 153-61.
5. Mangano, D. T., et al. (1996). N Engl J Med 335(23): 1713-20.
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Pan, P. H., et al. (2004). Reg Anesth Pain Med 29(6): 610-5.
7. Park, W. Y., et al. (2001). Ann Surg 234(4): 560-9; discussion 569-71.Rerkasem, K., et al. (2005). Cochrane Database of Systematic Reviews(2). Richman, J. M., et al. (2006). Anesth Analg 102(1): 248-57. Rigg, J. R., et al. (2002). Lancet 359(9314): 1276-82.Rodgers, A., et al. (2000). Bmj 321(7275): 1493. Wilson, S. H., et al. (2003). Journal of the American College of Cardiology 42(2): 234-40.
