Limits of Intermittent Jugular Bulb Oxygen Saturation Monitoring in the Management of Severe Head Trauma Patients (2001)

In reply: We thank Drs. Stocchetti and Rossi for giving us the opportunity to clarify some aspects of our article (8). With regard to low SjO2 monitoring being less than 50% or less than 55%, the answer is simple: it is not difficult to find investigators who, like us, used the 50% threshold, and they were cited in our article. The real problem is methodological in nature. How can clinicians objectively decide what is the best or the worst value? If the desaturation episodes should serve to detect or to prevent cerebral ischemia, a comparative study in which the new method (SjO2 monitoring) is compared with a putative “gold standard” for diagnosing ischemia (which might be computed tomography, MRI, positron emission tomography, or neurological examinations) is needed. Such comparative studies increasingly are conducted for procedures in other fields of medicine. Consider, for example, the validation of the ventilation-perfusion scan for the diagnosis of pulmonary embolism (13). Investigators did not first start performing ventilation-perfusion scans, then collect data later and try to understand what those data meant. They compared the new technology of ventilation-perfusion scanning with pulmonary angiography, the gold standard, so that they were able to define sensitivity, specificity, positive and negative predictive values, and likelihood ratios for the new method. Such an approach has never been used with regard to SjO2 monitoring; therefore, we do not know patients’ risk, if any, of developing cerebral ischemia if SjO2 is 60 or 45%. Neither do we know the risk of cerebral ischemia if the SjO2 is 70 or 85%, because investigators have shown that cerebral blood flow may be very low in this situation also (4). Conversely, we know that cerebral ischemia in head trauma patients is almost always associated with increased ICP, as recently confirmed in a basic neuropathological investigation (1). Furthermore, axonal stretch injury rather than neuronal ischemic damage is prevalent in such patients (1, 9). Did or did not the use of SjO2 monitoring modify the management of our patients? In 94 patients, ventilation was increased because of hypercapnia and/or intracranial hypertension. So, if care is taken to avoid derangements of arterial blood gases, arterial blood pressure, and ICP, what else can be done for the patient that would be changed by SjO2 monitoring (8) ? Vascular catheter infection is a major problem in critically ill patients. Recent figures from United States intensive care units show that approximately 2400 to 20,000 patients die annually of central venous catheter-related bloodstream infections (10). No doubt, bacterial colonization plays a major pathogenic role, and no one should be reassured that in a small study such as ours “only” 15% of jugular bulb catheters showed microbial colonization. Furthermore, at least four prospective studies have found that the risk of infection is increased significantly with insertion of such catheters into the internal jugular vein rather than the subclavian vein (10). This risk is particularly worrying in situations in which two jugular bulb catheters are to be positioned, as some authors have suggested (12). In fact, Stocchetti and Rossi do not mention the problem of SjO2 monitoring differences in simultaneous bilateral samples. Three studies have shown that these differences are on the order of 10 to 20% and can be as high as 44%(8, 12, 14), so that one may have a normal SjO2 on one side and an abnormally low or an abnormally high SjO2 on the other. Stocchetti et al. (14) concluded that, despite this limitation, unilateral monitoring is the cheapest way of observing cerebral blood flow-metabolism coupling. Metz et al. concluded that unilateral monitoring has an unpredictable risk for misleading or missing data (12) and suggested bilateral cannulation (11). We concluded that available data did not indicate the use of SjO2 monitoring for clinical purposes, but only for research (8). Thus, it seems that the world of expert opinion is not an inferior one, as Stocchetti and Rossi suggest, but rather that there are as many worlds as there are experts. The final problem that Stocchetti and Rossi mention—namely, the feasibility of a randomized clinical trial—is of great importance, and here our points of view diverge profoundly. In this respect, the pulmonary artery catheter article, in which Connors et al. (3) demonstrated increased mortality and cost in patients monitored with pulmonary artery catheters, should be a lesson to neurosurgeons who are involved in neurocritical care. That article proves that the old adage that more is better is methodologically unsound (6) and that unproved strategies based on invasive procedures, though widely used, may harm patients. After the Connors et al. article was published, Dalen and Bone (5) called for either a moratorium on the use of pulmonary artery catheters or a randomized clinical trial to study their safety and effectiveness. Four years after publication of the Dalen and Bone article, the latter option has been taken up by the National Institutes of Health’s National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome Network. That group is comparing pulmonary artery catheter monitoring with central venous catheter monitoring (2). Therefore, waiting for the evidence is a better choice for both patients and physicians than “the extrication [of data] from widespread use of a technology that has not been adequately assessed”(7). Nicola Latronico Frank Rasulo