Oxygen delivery optimization using lithium indicator dilution and pulse power analysis during major surgery in high-risk patients

Introduction

Increasing oxygen delivery in high-risk surgical patients led to a dramatic reduction in both mortality and morbidity. Yet, it is still not widely practised due to logistical difficulties associated with its use. We aimed to evaluate whether pulse power analysis calibrated by the lithium dilution technique, a pragmatic minimally invasive technique, can be used to optimize the oxygen delivery index (DO₂I) in high-risk patients during major surgery.

Methods

Lithium indicator dilution and pulse power analysis were used to measure cardiac output and to calculate DO₂I (LiDCO-plus system). We prospectively evaluated the oxygen delivery pattern and perfusion variables of 26 high-risk patients (LiDCO group) submitted to major surgeries and goal-directed therapy during surgery and 8 hours postoperatively, aiming to maximize the DO₂I to levels higher than 600 ml/min/m² using dobutamine and either 'restrictive' (4 ml/kg/min) or 'liberal' (12 ml/kg/min) strategies of intraoperative fluid management (partial results). Postoperatively both groups received 1.5 ml/kg/min lactated ringer. Fluid challenge with 250 ml colloid was done in the presence of signs of hypovolemia and additional fluids were given if necessary. Patients were considered responders if they achieved the therapeutic goal. A historical group of 42 high-risk surgical patients in whom the therapeutic goals were to keep a mean arterial pressure between 80 and 110 mmHg, a central venous pressure between 6 and 12 cmH₂O, hematocrit > 30% and urine output > 0.5 ml/kg/hour in the first 24 hours after ICU admission was used as control.

Results

Median doses of 10 μg/kg/min and 7.5 μg/kg/min dobutamine were used intraoperatively and postoperatively, respectively. A total of 75% and 84% of the patients were responders during surgery and postoperatively. However, a much better pattern of DO₂I during surgery was seen in the liberal group than in the restrictive group (Figure 1). The values for arterial lactate and central venous oxygen saturation (ScvO₂) on ICU admission and 24 hours later for both groups are shown in Table 1. Significantly lower arterial lactate and higher ScvO₂ were seen in optimized patients (P < 0.05 vs control group). Major complications occurred in 50% of the patients in the historical control group (21/42) and in 15% of the LiDCO group (4/26) (RR 0.15, 95% CI 0.037–0.600, P < 0.05).

Figure 1

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Table 1 abstract

Conclusion

The use of a therapeutic approach guided by DO₂I calculated by the LiDCO plus system, intraoperatively and postoperatively, seems to be a feasible and practical approach to guide oxygen delivery optimization therapy during major surgery in high-risk patients. Better perfusion and a much lower rate of complications were seen in optimized patients.