Impact of a low postoperative central venous oxygen saturation on postoperative morbidity

Background

Patients undergoing major surgery have an increased oxygen debt that may affect postoperative outcomes. Current strategies of perioperative hemodynamic optimisation necessitate use of a pulmonary artery catheter. In patients with severe sepsis, early goal directed therapy using a central venous catheter and targeted to ScvO₂ of 70% improves survival. This strategy is untested in perioperative patients.

Aim

To investigate whether a low postoperative ScvO₂ is associated with increased postoperative morbidity.

Methods

Observational study from August to December 2003 in a 22-bed ICU-HDU of a tertiary referral cancer centre. ScvO₂ was analysed from blood collected from a central venous catheter at 2 and 12 hours after surgery in 83 patients undergoing major resections for cancer. Patients were divided into two groups: normal (ScvO₂ ≥ 70% at both intervals) and low (ScvO₂ < 70% at one or both intervals). Central venous pH and base excess were also noted. The ICU team managing clinical care was unaware of the ScvO₂ values. Outcomes studied were ventilator days, length of ICU and hospital stay, ICU and hospital mortality, incidence of anastomotic leak and incidence of complications (any of sepsis, cardiovascular or respiratory complications, ICU stay ≥ 2 days or ventilator days ≥ 2 days). Data were analysed using the unpaired t test and chi-square test. Binary logistic regression (stepwise forward conditional) was performed to determine the parameters contributing to morbidity.

Results

Fifty-one patients (62%) had a low ScvO₂ at one or both time intervals. Patients in the low group had significantly lower ScvO₂ at 2 hours (63.9 ± 8.9 vs 76.8 ± 5.8, P = 0.000) and 12 hours (68.7 ± 6.1 vs 76.2 ± 4.1, P = 0.000), respectively. APACHE II scores within 24 hours of ICU admission were similar (8.9 ± 2.7 vs 9.9 ± 2.7, P = 0.1). There was no difference in ICU or hospital mortality (both 3 vs 0, P = 0.16) between the low and normal groups, respectively. pH and base excess were not different. Patients in the low group had more days on ventilator (3.5 ± 6.1 days vs 0.59 ± 1.5 days, P = 0.009), and longer ICU stay (5.6 ± 6.7 days vs 1.75 ± 2.6 days, P = 0.009) and hospital stay (17.8 ± 10.5 days vs 13.7 ± 5.06 days, P = 0.002). They required more colloid infusion postoperatively (682 ± 398 ml vs 228.4 ± 279 ml). There was no difference in the number of patients requiring inotropes (1 vs 0, P = 0.1). Significantly more patients in the low group developed postoperative complications (56.8% vs 18.7%, P = 0.009) and anastomotic dehiscence (26% vs 9%, P = 0.03). On logistic regression, only ScvO₂ at 12 hours (P = 0.012) affected morbidity.

Conclusions

A low ScvO₂ was associated with major postoperative morbidity. The results of this observational, hypothesis-generating study justify a prospective trial of perioperative goal directed therapy.