Methylene Blue Diffusion After Multilevel Thoracic Paravertebral Blocks

One-Lung Anesthesia Alters the Magnitude of Aortic Regurgitation Because of a Reduction in Intrathoracic Pressure

3. Pinsky MR: Hemodynamic effects of ventilation and ventilator maneuvers, in Scharf SM, Pinsky MR, Magder S (eds): RespiratoryCirculatory Interactions in Health and Disease. New York, NY, Marcel Dekker, 2001, pp 183-218 doi:10.1053/j.jvca.2010.09.014

To the Editor: al1

I read with great interest the case report by Sinha et regarding the effects of one-lung ventilation (OLV) on the dynamics of aortic regurgitation (AR). The reduction in the magnitude of AR has been ascribed to a rise in intrathoracic pressure (ITP), which in turn reduces the left ventricular (LV) preload and afterload. However, during OLV, the withdrawal of ventilation results in a reduction of ITP to atmospheric pressure, in the nondependent hemithorax and the pericardium. The amount of externally applied peak airway pressure actually transmitted to the intrathoracic structures is of importance to interpret filling pressures of the heart in order to define its loading conditions.2 With cardiac dilatation, as seen in AR, the elasticity of the pericardium becomes greater and has greater effects on LV surface pressure as the cardiac surface pressure is the arithmetic sum of ITP and pericardial elastic pressure.3 The pericardial pressure, which determines the cardiac preload change in mechanical ventilation, is not affected by changes in ITP after the cessation of ventilation, in OLV, and upon opening of the nondependent hemithorax. The reduction of pressure over the pericardium and the outflow vessels offsets the restrictive effects of ITP on the LV end-diastolic volume and also results in lower LV afterload. The reduction of pressure over the outflow vessels, upon initiation of OLV, offsets the restrictive effects of ITP on the LV end-diastolic volume and also results in lower LV afterload. The change in the magnitude of AR possibly can be explained by this reduction in afterload because the pericardial pressure is not affected by changes in ITP of the ventilated hemithorax. Sinha et al1 continued to ventilate the dependent lung at the same tidal volume and at a low respiratory rate of 10 beats/min, possibly causing hypercapnia, which aggravated the OLVinduced hypoxic pulmonary vasoconstriction. The rise in hypoxic pulmonary vasoconstriction also could have contributed to a reduction of the preload of the left heart. The reappearance of the AR on aortic clamping was, of course, caused by a rise in the afterload. The persistence of the AR on resumption of ventilation was caused by the loss of the aforesaid benefit of OLV.

Methylene Blue Diffusion After Multilevel Thoracic Paravertebral Blocks To the Editor: Thoracic paravertebral nerve blockade (TPVB) has been reported to be used in different scenarios like cardiac, thoracic, and breast surgery; chronic pain management; and unilateral surgical procedures of the abdomen.1,2 Few studies investigated local anesthetic spread into the paravertebral space.3-5 Naja et al6 observed 4 different spreading patterns of TPVB: pure longitudinal, longitudinal ⫹ intercostal, intercostal, and cloud-like. The purpose of our study was to evaluate the spreading patterns from the paravertebral space using a solution of methylene blue and local anesthetic. Ten patients scheduled for video-assisted thoracoscopy received 2 TPVB at T3 and T7 levels using a 20-mL solution of local anesthetic and methylene blue (ropivacaine, 100 mg-10 mL; methylene blue, 50 mg-5 mL; and saline, 5 mL). Paravertebral injection was performed after the induction of general anesthesia, with patients in the lateral position with one-lung ventilation according to the percutaneous approach technique described by Conacher and Slinger.7 The presence and spreading patterns of the solution into the paravertebral space were checked after the introduction of the thoracoscopy camera into the chest; the classification used was the same proposed by Naja et al.6 In one patient we saw an intercostal spread from the vertebral bodies of T2 and T8 (Fig 1), in 4 patients a longitudinal diffusion from T2 to T8 and intercostal spreads at T2-T3 and T7-T8 were noted (Fig 2), in 2 patients we observed a cloud-like pattern at T2-T3 and T7-T8 (Fig 3), and in 3 patients we did not see any diffusion of the solution into the chest. No complications related to the block (pleural puncture, and vascular puncture) or methylene blue (neurotoxicity) were observed. A small amount of local anesthetic and methylene blue solution was found out of the thoracic paravertebral space and endotho-

Mukul C. Kapoor, MD, DNB, MNAMS Department of Anaesthesiology Command Hospital Lucknow, UP, India REFERENCES 1. Sinha PK, Misra S, Koshy TK: One-lung ventilation can alter the severity of aortic regurgitation. J Cardiothorac Vasc Anesth 24:736738, 2010 2. Luecke T, Pelosi P: Clinical review: Positive end-expiratory pressure and cardiac output. Crit Care 9:607-621, 2005

Fig 1. Intercostal methylene blue diffusion. (Color version of figure is available online.)

Journal of Cardiothoracic and Vascular Anesthesia, Vol 25, No 2 (April), 2011: pp e5-e9

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LETTERS TO THE EDITOR

Fig 2. Longitudinal and intercostal methylene blue diffusion. (Color version of figure is available online.)

2. Davies RG, Myles PS, Graham JM: A comparison of the analgesic efficacy and side-effects of paraverteral vs epidural blockade for thoracotomy—A systematic review and meta-analysis of randomized trials. Br J Anaesth 96:418-426, 2006 3. Naja ZM, El-Rajab M, Al-Tannir MA, et al: Thoracic paravertebral block: Influence of the number of injections. Reg Anesth Pain Med 31:196-201, 2006 4. Karmakar MK, Kwok WH, Kew J: Thoracic paravertebral block: Radiological evidence of controlateral spread anterior to the vertebral bodies. Br J Anaesth 84:263-265, 2000 5. Conacher ID: Resin injection of thoracic paravertebral spaces. Br J Anaesth 61:657-661, 1988 6. Naja MZ, Ziade MF, El Rajab M, et al: Varying anatomical injection points within the thoracic paravertebral space: Effect on spread of solution and nerve blockade. Anaesthesia 59:459-463, 2004 7. Conacher ID, Slinger P: Pain Management, in Joel A Kaplan, Peter D Slinger (ed): Thoracic Anesthesia (ed 3). Oxford, UK, Churchill Livingstone 2003, pp 436-462 doi:10.1053/j.jvca.2010.07.023

Initial Anesthetic Experience During Combined Epicardial-Endocardial Treatment of Atrial Fibrillation To the Editor:

Fig 3. Cloud-like methylene blue diffusion. (Color version of figure is available online.)

racic fascia into the chest of all 7 patients. There was evidence of subparietal pleura hematoma at the T3 and T7 levels where the injections were performed in 1 of the 4 patients with longitudinal and intercostal spreads; this did not require any surgical actions. According to the pattern, the best block could be the one that allows longitudinal and intercostal diffusion. Vanni Agnoletti, MD Emanuele Piraccini, MD Ruggero Corso, MD Felice Avino, MD Carmen Rotondo, MD Stefano Maitan, MD Giorgio Gambale, MD Emergency Department Anaesthesia and Intensive Care Unit GB Morgagni-Pierantoni Hospital Forlì, Italy REFERENCES 1. Karmakar MK: Thoracic paravertebral block. Anesthesiology 95: 771-780, 2001

Initial treatment for symptomatic atrial fibrillation (A-fib) is primarily medical. If antiarrhythmic drug therapy does not yield satisfactory results, catheter-based endocardial ablation or surgical intervention can be effective.1 However, a combined catheter-based endocardial and thoracoscopic epicardial or hybrid procedure may increase the percentage of patients maintaining sinus rhythm while minimizing the risk of thromboembolic events, and may offer distinct advantages over either a catheter-or surgical-based approach alone for chronic A-fib. The thoracoscopic surgery consists of exclusion of the left atrial appendage and epicardial radiofrequency ablation (RFA) of the pulmonary veins, vagal ganglionic plexi, and vena cavae. The performance of pulmonary vein isolation under direct vision may minimize the risk of damage to mediastinal structures, whereas catheter-based A-fib ablations can be associated with a risk of esophageal complications ranging from asymptomatic ulcerations that resolve spontaneously to devastating atrial-esophageal fistula formation.2-5 The percutaneous catheter component of the procedure includes RFA of the cavotricuspid isthmus and mitral isthmus, entrance and exit block testing of all ablation lines, and mapping/ablation of complex fractionated atrial electrograms that are believed to sustain A-fib.6 Any “gaps” found in the ablation lines are filled in with additional endocardial RFA. Figure 1 summarizes the hybrid procedure. Permission was obtained from the Institutional Review Board to conduct a retrospective chart review of patients undergoing the combined ablation procedure. All patients referred for hybrid A-fib ablation procedure had experienced unsatisfactory results with antiarrhythmic therapy. Our hybrid operating room was used for patients undergoing this procedure. Cutaneous sensors for the CARTO (Biosense