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a Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, 8006 Australia
b Cardio-Pulmonary Exercise Testing Laboratory, Western Hospital, Footscray, Victoria, 3011 Australia
(Email: adrian_hall{at}bigpond.com).
Our work on assessment of operative risk [1–3], quoted by Forshaw and colleagues [4], demonstrated that oxygen consumption is increased after major surgery, and patients with decreased cardiopulmonary reserve have increased risk.
Esophageal surgery differs from other procedures with high surgery-specific risk such as colorectal or abdomino-vascular surgery. It not only increases oxygen consumption but also interferes with the cardiopulmonary "machinery." For this reason, our system of triage [3] mandated that all patients undergoing esophageal surgery were admitted to a high dependency environment. Our patients were not routinely ventilated; we believe the benefit of high dependency care derives from close monitoring and the continuous presence of trained medical staff, not ventilation per se.
Decreased functional reserve means decreased ability to transfer oxygen to metabolising tissue. It may be expressed in terms of a reduction in anaerobic threshold (AT), maximum oxygen consumption, or oxygen consumption–work rate relationship. Measures of peak or maximum oxygen consumption have no role in preoperative assessment. The AT relates to sustainable aerobic activity and has more relevance to the postoperative state. We prefer measurement of AT because it is non-volitional, reproducible, occurs at a lower work rate, and because many other physiological parameters are defined at the AT.
We congratulate Forshaw and colleagues [4] on the low mortality reported in their study. However, using the Common Terminology Criteria for Adverse Events (CTCAE) [5] as the measure of adverse events has confused the location and cause of the complications. Esophageal surgery is distinctive in that the operative fields and the local complications are proximate to the cardiopulmonary system. As Forshaw and colleagues [4] acknowledge, primary and secondary cardiopulmonary complications are significantly different. This is neglected in the analysis.
Atelectasis, or aspiration leading to pneumonia, or pleural effusion clearly involve the cardiopulmonary system, but are secondary to the location and nature of the surgery and are not predicable by cardiopulmonary exercise testing (CPX).
Assessment of functional reserve would be expected to, and does, predict the ability of the cardiopulmonary system to respond after complications have occurred. In Forshaw and colleagues' [4] study, the average AT in all but 1 of the patients suffering any complications was greater than 11 mL/min/kg, and only 1 death resulted; this patient had excellent cardiopulmonary reserve and survived 44 days. A late cardiovascular death [3] is often attributed to a dramatic terminal event. In our experience, such deaths are the end result of a prolonged inflammatory response necessitating inotropic, ventilatory, and nutritional support, and is accompanied by gradual, but inexorable, deterioration in cardiopulmonary function.
Selection bias is evident. The patient with an AT of 8.2 mL/min/kg suffered left ventricular dysfunction and survived; the CPX showed ventricular dysfunction preoperatively. Three patients considered medically unfit had similarly poor cardiopulmonary reserve with an AT of 8.1 to 9.1 mL/min/kg. Was 1 patient exposed to risk or were 3 potential survivors denied surgery?
In fact, the CPX tests in the Forshaw and colleagues [4] study gave very relevant information. This fully vindicates the use of CPX as a predictive tool for major surgery including esophageal resection.
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  M. J. Forshaw, D. C. Strauss, A. R. Davies, D. Wilson, B. Lams, A. Pearce, A. J. Botha, and R. C. Mason Reply Ann. Thorac. Surg., February 1, 2009; 87(2): 671 - 672. [Full Text] [PDF]
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