Article Outline
CTSNet classification: 19, 31
To the Editor:
In a recent study Al-Rashidi and associates1 concluded that “bilateral … pulmonary collapse and successive filling of the lungs with … concomitant increase in mechanical ventilation during de-airing of the left side of the heart significantly reduces the number of systemic MES [microembolic signals]… and … air emboli.”
Inasmuch as the study's limitations were not mentioned, we would like to discuss a few:
1.Inasmuch as the patients were alternately allotted to control and study groups, the principle of randomization was ignored. Moreover, the principle of unbiased assessment was also compromised inasmuch as the single surgeon, who actively followed the degree of de-airing via transesophageal echocardiography (TEE) during the surgical de-airing maneuvers before the end of cardiopulmonary bypass (CPB), thus participated in the evaluation of the technique, which he himself had proposed.
2.The authors enumerate 9 exclusion criteria, including accidental opening of the pleural cavity and chronic obstructive lung disease, although all operations were performed by one highly experienced surgeon. Consequently, the generalizability of the results cannot but be very limited.
3.According to the Methods section, TEE and transcranial Doppler (TCD) measurements were only performed after CPB. However, in the Results section, the authors make comparisons with the number of MES before the end of CBP. Moreover, “The aortic root was de-aired” before release of the crossclamp only in the study group.
4.The possible risks of a left ventricular vent inserted through the apex of the heart (eg, bleeding and arrhythmias), a prerequisite of the technique, have not been mentioned.
5.In contrast to common practice as well as the study group, the control group patients had their lungs ventilated continuously during crossclamping and then fully already after release of the crossclamp. This may have negatively influenced the number of detected MES and TEE-detected air emboli in the control group.
6.The authors claim that “their results are similar, if not better, to those described with carbon dioxide insufflation” and refer to a study by us.2 We find this comparison inappropriate. Continuous carbon dioxide insufflaton of the open cardiothoracic cavity during open cardiac surgery with an effective device creates a local atmosphere of 100% carbon dioxide,3, 4 whereby only carbon dioxide and not air can enter the heart and the vessels directly. Thus, any gaseous microemboli detected with TEE or TCD during and after CPB must contain carbon dioxide and not air, unless air is introduced indirectly via cannulas. As expected, we found that the TEE-detected microemboli were fewer and disappeared much quicker in our treatment group receiving carbon dioxide.2 In contrast, the new surgical de-airing technique1 did not eliminate the risk of air embolism, inasmuch as air emboli were still present in the left side of the heart and MES containing air still occurred. Furthermore, our study2 randomized patients, all 6 surgeons were blinded to TEE findings, the apex of the heart was not cannulated, and we did not have exclusion criteria.
In conclusion, if proven able to reduce air embolization in a correctly performed randomized trial, the described technique1 may be a complement to de-airing with carbon dioxide only, if air has been introduced into the left heart and the great vessel directly, by use of an inappropriate carbon dioxide insufflation technique, or indirectly, through cannulas.
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References
- Al-Rashidi F, Blomquist S, Höglund P, Meurling C, Roijer A, Koul B. A new de-airing technique that reduces systemic microemboli during open surgery: a prospective controlled study. J Thorac Cardiovasc Surg. 2009;138:157–162
- Svenarud P, Persson M, van der Linden J. Effect of CO2 insufflation on the number and behavior of air microemboli in open-heart surgery: a randomized clinical trial. Circulation. 2004;109:1127–1132
- Svenarud P, Persson M, van der Linden J. Efficiency of a gas diffuser and influence of suction in carbon dioxide deairing of a cardiothoracic wound cavity model. J Thorac Cardiovasc Surg. 2003;125:1043–1049
- Persson M, Svenarud P, van der Linden J. What is the optimal device for carbon dioxide de-airing of the cardiothoracic wound and how should it be positioned?. J Cardiothorac Vasc Anesth. 2004;18:180–184
