Original article
Combined Central Venous Oxygen Saturation and Lactate as Markers of Occult Hypoperfusion and Outcome Following Cardiac Surgery

https://doi.org/10.1053/j.jvca.2011.07.021Get rights and content

Objective

To assess the association between postoperative central venous oxygen saturation (ScvO2) and arterial lactate with outcome after cardiac surgery.

Design

Prospective observational study.

Setting

University-affiliated tertiary care hospital.

Participants

Patients after coronary artery bypass and/or valve surgery.

Interventions

None.

Measurements and Main Results

Postoperative ScvO2 and arterial lactate were obtained on arrival to the intensive care unit (ICU). ScvO2 and lactate were drawn again at 8 and 24 hours, respectively, after ICU admission. Moderate global tissue hypoxia (GTH) was defined as ScvO2 <70% and lactate ≥2 to <4 mmol/L, and severe GTH was defined as ScvO2 <70% and lactate ≥4 mmol/L. Occult hypoperfusion was defined as moderate-to-severe GTH with mean arterial pressure ≥65 mmHg, central venous pressure ≥8 mmHg, and urine output ≥0.5 mL/kg/h. ScvO2 on ICU admission negatively correlated with postoperative 24-hour lactate (p = 0.009), which was a strong predictor of time on mechanical ventilation, total complications, and ICU and hospital lengths of stay (p < 0.001 for all comparisons). On admission to the ICU, 19 patients (32%) exhibited occult hypoperfusion. Patients with severe GTH (n = 8) had longer ICU lengths of stay (p = 0.04) and a trend toward longer length of mechanical ventilation (p = 0.17) and number of complications per patient (p = 0.09) compared with those without GTH (n = 10).

Conclusions

The incidence of GTH is high after cardiac surgery. Postoperative ScvO2 and lactate may be valuable measurements to identify patients with occult hypoperfusion and subsequently guide hemodynamic optimization to positively affect postoperative outcomes in patients after cardiac surgery.

Section snippets

Methods

This prospective, observational study was approved by the hospital's institutional review board for human research and written informed consent was obtained for each patient.

Eligible adult patients who were to undergo coronary artery bypass grafting (CABG) and/or valve surgery using cardiopulmonary bypass (CPB) from October 2007 through June 2008 at a 912-bed academic tertiary care hospital were assessed for enrollment based on inclusion and exclusion criteria of the study. Inclusion criteria

Results

Of the 129 screened patients, 60 patients fulfilled eligibility requirements (17 women, 43 men). Thirty-one patients had CABG surgery, 17 had valve surgery, and 12 patients underwent both surgeries. One death occurred during the study period. Patients' mean age was 65 ± 11 years.

Discussion

The unyielding imbalance between oxygen demand and oxygen supply is an initiator for the cascade of events leading to multiple organ failure.1, 2, 3, 4 Prompt amelioration of this hypoperfused state is, therefore, key. Conventional indicators of perfusion, such as blood pressure or UO, have been proved repeatedly to be inaccurate.5, 6, 7 Therefore, the need for a tool to assess hypoperfusion accurately is paramount in curbing the incidence of organ dysfunction in these patients.

SvO2, ScvO2, and

Conclusions

The incidence of occult hypoperfusion after cardiac surgery was remarkably high, and the use of ScvO2 and lactate facilitated rapid identification of these patients. Although admission ScvO2 and lactate were not independently associated with increased morbidity, patients who developed severe GTH (ScvO2 <70% and lactate ≥4 mmol/L) had significantly prolonged ICU stays. This trial supports the use of ScvO2 and lactate in combination to identify patients with hypoperfusion otherwise undetected by

Acknowledgments

The authors acknowledge the contributions of Nic Bartell for database development, Michael Dore and Ian Jarrett for obtaining laboratory data, and Kimberly Putney for careful review of the manuscript. The authors thank the patients, families, nurses, and cardiovascular surgeons at St Luke's Episcopal Hospital, whose cooperation and participation made this study possible.

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