related complications: prospective study of 1119 consecutivepatients. Am Heart J 2000;139:282–7.

ReplyTo the Editor:

We appreciate the comments by Drs Christenson and Cohen.However, we believe we might have been misunderstood. Weagree entirely with the correspondents that intraaortic balloonpump (IABP) and inotropic drugs are often needed to supportthe heart after surgery and do not intend to imply that IABPinduces an increase in lactate production. Indeed, we stronglyadvocate the use of IABP under circumstances of low cardiacoutput. The aim of our article was not to link IABP and lactateproduction but to find a simple, early, clinically available way ofdetecting patients who are so sick that, despite inotropic supportand IABP, they will go on to die [1]. If patients whose expectedmortality, despite IABP support, is still close to 100% can beindentified early, then more advanced extracorporeal life sup-port (ECMO or VADs) can be applied rather than persisting witha strategy which is insufficient to meet the patient’s physiolog-ical needs [2].

The presence of a high lactate (greater than 10 mmol/L) in thefirst few hours of postoperative support in patients already onIABP is a useful marker of patients who need more advancedsupport. Thus, we strongly support the use of IABP in selectedpatients but also stand by our conclusion that in a postoperativepatient who is already on inotropic support and IABP, thedevelopment of a lactate greater than 10 mmol/L should triggerstrong consideration of more advanced mechanical cardiovas-cular support.

Andrew Davies, FRACPRinaldo Bellomo, MDJai Raman, FRACSGeoffrey Gutteridge, FANZCABrian Buxton, MD

Intensive Care Unit (Austin Campus)Austin and Repatriation Medical CentreStudley RdHeidelberg, Victoria 3084, Australiae-mail: rb@austin.unimelb.edu.au.

References

1. Davies AR, Bellomo R, Raman JS, Gutteridge GA, Buxton BF.High lactate predicts the failure of intraaortic balloon pump-ing after cardiac surgery. Ann Thorac Surg 2001;71:1415–20.

2. Smith C, Bellomo R, Raman J, et al. An extracorporealmembrane oxygenation-based approach to cardiogenic shockin an older population. Ann Thorac Surg 2001;71:1421–7.

Problems in the Evaluation of Thymectomy forMyasthenia GravisTo the Editor:

In a recent issue of The Annals, Budde and colleagues reported a25-year retrospective review of 113 consecutive thymectomiesperformed at their institution for myasthenia gravis (MG) [1].They concluded that sex, age, and thymic pathology werepotential predictors of outcome and that severity of illness andtype of resection were not. These conclusions were based onstatistical comparisons between “benefit” (a combination of

remission plus clinical improvement) and “worse.” In addition,they compared their results with reports of others.

The problems with the present report are:

1. The “benefit” designation is not a reliable measurementsince it includes “improvement” which is not quantita-tively determined. Objective criteria, such as an objectivequantitative scoring system, are required to determineimprovement in MG. Accordingly, conclusions concerningpredictors of outcome cannot be determined from thisanalysis because comparisons are not based on objectivecriteria.

2. The use of an Osserman-type classification to compareresults is not a reliable measure because it is also notobjective. The Osserman classification was developed todescribe typical clinical patterns in MG and is not suited todescribe changes in disease severity.

3. The meta-analysis reported (Table 1) compares uncor-rected crude remission and improvement rates of eightstudies. Although this format has been frequently used tocompare the result of thymectomy from different institu-tions, the comparisons are not valid and this type ofanalysis should be abandoned. Uncorrected crude datacannot be used to compare results of thymectomy: (a) Itdoes not correct for length of follow-up which must beincluded since the longer these patients are followed afterthymectomy the better the results. This becomes veryapparent when uncorrected crude data are correctedfor length of follow-up [2]. (b) The crude data denominatorin these comparisons is not constant, further invalidatingthe comparisons. Some use “patients followed” and othersuse “patients operated upon.” (c) The determination ofimprovement is neither standard nor objective; and(d) thymomas and multiple surgical techniques are in-cluded in some of the studies listed and not in others.There is considerable evidence that these may distort theresults.

Unfortunately, the overall evaluation of thymectomy has beenhampered by the lack of well-defined and widely acceptedobjective definitions of disease severity and response to therapy.Prospective studies are required to resolve the many issuesraised in this report, especially since MG is such an extremelyvariable and unpredictable illness. A Task Force of the Myas-thenia Gravis Foundation of America has recently publishedrecommendations for clinical research standards in MG, whichinclude definitions of clinical classification, disease severity,postintervention status, and an overview of the appropriatemethods of analysis [3–5]. It is urged that future studies ofthymectomy in the treatment in MG incorporate the conceptsdelineated in the Task Force report.

Alfred Jaretzki III, MDHenry J. Kaminski, MDL. H. Phillips II, MDDonald B. Sanders, MD

Evaluation Standards Review CommitteeMedical Scientific Advisory BoardMyasthenia Gravis Foundation of America, Inc5841 Cedar Lake Rd (Suite 204)Minneapolis, MN 55416

1027Ann Thorac Surg CORRESPONDENCE2002;73:1020–8

© 2002 by The Society of Thoracic Surgeons 0003-9475/02/$22.00Published by Elsevier Science Inc