Konrad Reinhart, MD; Tobias Rudolph...

Konrad Reinhart, MD; Tobias Rudolph, MD; Donald L Bredle Phd; Lutz Hannemann. MD; and Stephen M Cain, PhD

Because central venous [Osub2] saturation (superior vena cava, [Scvosub2]) can be monitored with les patient risk than mixed venous [Osub2] saturation (pulmonary artery, [S[unkeyable]O.sub.2]), we examined the correlations between [S[unkeyable]O.sub.2] and [ScvOsub2] throughout a broad range of cardiorespiratory conditions, including hypoxia, hemorrhage, and resuscitation in anesthetized dogs. The correlation coefficient (r) between [S[unkeyable]O.sub.2] and [ScvOsub2] in 179 simultaneously drawn kindred samples from 22 dogs was 097 In another nine dogs, the pair sites were continuously and simultaneously monitored with fiberoptic catheters; r was 096 with a mean difference of 37 [+ or -] 29 percent (SD) saturation. In each dog the changes in [ScvOsub2] closely paralleled the changes in [S[unkeyable]O.sub.2]. Although absolute values of [ScvOsub2] are not sufficiently identical to [S[unkeyable]O.sub.2] to calculate [Osub2] uptake or pulmonary switch precisely, close tracking of changes in the sum of two units sites across a wide range of hemodynamic conditions warrant further consideration of [ScvOsub2] for patient monitoring of turns in [O.sub.2] supply/demand.

(Chest 1989;95:1216-21)

The novel addition of fiberoptic sensors in pulmonary artery (PA) catheters has made possible the continuous monitoring of mixed venous oxygen saturation ([S[unkeyable]O.sub.2])[1-4] This can be helpful in patient management, because changes in [S[unkeyable]O.sub.2] indicate changes in the balance of [Osub2] accommodate with and demand[5-7] and thereby provide an index of tissue oxygenation, on a level without the determination of cardiac output or calculation of actual values for [Osub2] delivery and consumption. However, the use of PA catheters is not without risk to the patient, and the risk/benefit ration is generally a matter for vigorous debate.[8-10] Central venous catheters (superior vena cava), forward the other hand, are les rich have less risk of complications, and are used in the critically ill more routinely than PA catheters.[11] Central venous [Osub2] saturation ([ScvOsub2]) monitoring has been advocated as a simple rule of assessing changes in cardiac function in patients with MI.[12] Others, however, have questioned the usefulness of [ScvOsub2] measurements, particularly in onset because [ScvO.sub.2] tended to diverge from [S[unkeyable]O.sub.2.][13,14]

To proof the hypothesis that [ScvO.sub.2] parallels [S[unkeyable]O.sub.2] sufficiently well from one side of to the other wide ranges of altered [Osub2] delivery to monitor cardiorespiratory status in critically ill patients, we made simultaneous measurements of [ScvOsub2] and [S[unkeyable]O.sub.2] in anesthetized dogs while decreasing [Osub2] delivery from lowering inspired [O.sub.2] fraction and on hemorrhage. In addition, we used specially made fiberoptic catheters to monitor as well-as; not only-but also; not only-but; not alone-but variables continuously and to remark on-line the rapidity with which each variable changed with alterations of [Osub2] delivery.

METHODS

Thirty-eight hybrid dogs of either sex (av wt 18 [+ or -] 2 kg) were anesthetized with pentobarbital sodium (30 mg/kg IV), with supplemental doses given as wanted They were intubated and ventilated with a Harvard respirator at ten breaths/min and a tidal turn sufficient to maintain arterial [Pcosub2] at 35 to 40 mm Hg The animals were paralyzed with succinylcholine chloride. Systemic and PA constraining forces heart rate, and ECG were continuously recorded.

In the first series of experiments (n=24) double-lumen PA catheters were custom made from plastic tubing of 12- and 30-mm outside diameters. The distal tip of the catheter was floated into a pulmonary artery by means of observing the pressure wave form. The proximal orifice was 14 to 165 cm from the tip, and its location in the superior vena cava was verified at autopsy. In brace cases in which the proximal orifice was in the right atrium, the data were discarded. Simultaneous family samples were drawn anaerobically and slowly and immediately analyzed for [Osub2] saturation with an instrumentation Laboratory 282 CO-oximeter.

In the secondary series of 14 dogs, mixed central venous [Osub2] saturations were continuously monitored with fiberoptic catheters introduced within the right external jugular vein. The PA catheter was a Swan Ganz oximetry TD catheter (75 F American Edwards Lab). After inflating the balloon with 10 ml of air, we placed the catheter tip in a pulmonary artery at observing the pressure waveform until a typical wedge tracing appeared. A custom-made catheter (4F Baxter Edwards) which used the same fiberoptics as the Edwards PA catheter, was advanced into the external jugular vein between 18 and 21 cm depending in succession the size of the dog. The placement of the catheter tip in the superior vena cava was verified at autopsy. In individual dog the tip was in the right atrium, and we were unable to advance the next to the first catheter into the vena cava of four other dogs. Data from these animals were exclud from analysis.