We read with interest the meta-analysis of Cheng et al.  1recently published in Anesthesiology and agree in considering it the best evidence on which to base future treatment decisions and research directions.2 

With the aim of adding a piece of evidence, we reviewed all of the 37 randomized controlled trials included in the meta-analysis, focusing on the reported incidence of conversion from off-pump (OP) to standard cardiopulmonary bypass (CPB) technique. This is a common event during OP surgery and is caused by either deep intramural vessels (elective) or hemodynamic instability (urgent).

We were surprised to note that only 13 of 37 studies (35.1%) of the meta-analysis stated that they adopted the intention-to-treat analysis, whereas 18 of 37 studies avoided citing this important point, 4 studies affirmed that the patients who crossed over from OP to CPB were excluded from the analysis, and 2 studies considered the converted patients in the CPB group. Only 1 study reported the outcome of the converted patients.

Conversion from OP to standard CPB technique is a common but underreported event, with poor outcome and increased perioperative mortality. An extensive Medline search evidenced only five studies focusing on conversion from OP to CPB, with a cumulative incidence of conversion of 4.85% (202 of 4,163 patients) and a range from 3.7 to 13.3%. Mortality in these patients is 25 in 202 (12.3%). These data are consistent with our experience (Landoni et al. , unpublished data, Vita-Salute University of Milan, IRCCS San Raffaele Hospital, Milan, Italy, June 2001–July 2003) of a conversion rate of 37 in 450 (8.2%), with 2 in 37 deaths (5.4%).

We suggest that conversion from OP to standard CPB is underreported in literature and recommend that outcome of converted patients should be reported in future randomized controlled studies.

*Vita-Salute University of Milan, IRCCS San Raffaele Hospital, Milan, Italy. landoni.giovanni@hsr.it

Cheng DC, Bainbridge D, Martin JE, Novick RJ: Evidence-based Perioperative Clinical Outcomes Research Group. Does off-pump coronary artery bypass reduce mortality, morbidity, and resource utilization when compared with conventional coronary artery bypass? A meta-analysis of randomized trials. Anesthesiology 2005; 102:188–203
Floyd T, Fleisher LA: Off-pump coronary artery bypass and the hypothesis from which it grew: Is it yet to be tested? What are the downsides of the lingering questions? Anesthesiology 2005; 102:3–5