Clinical Predictors of a Low Central Venous Oxygen Saturation after Major Surgery: A Prospective Prevalence Study

The relationship between perioperative central venous oxygen saturation and postoperative complications in highly invasive gastroenterological surgery

Purpose

Operations for malignant diseases of the bile duct, pancreas, and esophagus are the most invasive gastroenterological surgeries. The frequency of complications after these surgeries is high, which affects the postoperative course and mortality. In patients who undergo these types of surgeries, continuous monitoring of the perioperative central venous oxygen saturation (ScvO2) is possible via a central venous catheter. We aimed to investigate the relationship between continuously monitored perioperative ScvO2 values and postoperative complications.

Methods

The medical records of 115 patients who underwent highly invasive gastroenterological surgeries and ScvO2 monitoring from April 2012 to March 2014 were analyzed. Sixty patients met the inclusion criteria, and their ScvO2 levels were continuously monitored perioperatively. The relationship between ScvO2 levels and major postoperative complications, defined as Clavien-Dindo grade ≥ III, was examined using uni- and multivariate analysis.

Results

Thirty patients developed major postoperative complications. The adequate cut-off value derived from receiver operating curves of the postoperative average ScvO2 levels for predicting major complications was 75%. Multivariate analysis revealed that low average postoperative ScvO2 levels (p = 0.016) and blood loss ≥ 1000 mL (p = 0.039) were significant predictors of major postoperative complications.

Conclusions

Low perioperative ScvO2 values were associated with an increased risk of major postoperative complications. Continuous ScvO2 monitoring will help prevent postoperative complications.

Prospective, observational study of carbon dioxide gaps and free energy change and their association with fluid therapy following cardiac surgery

Background Venoarterial carbon dioxide pressure (p_v-a CO₂ ) and content (C_v-a CO₂ ) differences, including the ratio to arteriovenous oxygen content difference (C_a-v O₂ ), and free energy changes (-∆∆G_a-v ) may reflect tissue hypoperfusion. The associations with changes in cardiac output (CO) or oxygen consumption (VO₂ ) following fluid bolus administration were investigated. Methods Single-centre, observational study of 89 adult post-operative cardiac surgical patients admitted to ICU. The p_v-a CO₂ , C_v-a CO₂ and their ratios to C_a-v O₂ as well as the -∆∆G_a-v were determined before and after a 250-500 mL fluid bolus using arterial, central venous and mixed venous blood gas analyses. Responses associated with changes ≥ or <15% in CO or oxygen consumption (VO₂ ) were compared. Results In 234 boluses, the mixed venous to arterial p_v-a CO₂ and its ratio to C_a-v O₂ were independently associated with an increase in CO; odds ratio 1.3 (95% CI 1.1-1.5) and 1.7 (95% CI 1.5-1.9) respectively, P < .001) and VO₂ ; odds ratio 2.1 (95% CI 1.3-3.1), P < .001 for C_a-v O₂ . No measures of p_v-a CO₂ , C_v-a CO₂ or related ratios to the C_a-v O₂ were associated with an increase in CO ≥15% following a single volume bolus. The mixed venous and central venous C_v-a CO₂ to C_a-v O₂ ratios were different for the first bolus episode only; mean differences 0.81 (95% CI 0.13-1.5), P = .02 and 0.44 (95% CI 0.06-0.82), P = .02, respectively, for increased VO₂  ≥ 15%. The -∆∆G_a-v did not change. Conclusion The venoarterial carbon dioxide gradients and related calculations to assess the adequacy of tissue perfusion before a fluid bolus were not associated with subsequent increases in CO of oxygen consumption. Editorial Comment In some shock conditions, regional tissue hypoperfusion can be obvious and arterio-venous differences for CO₂ or O₂ may reflect this. This is not always the case; sometimes there are A-V differences or even a high lactate level without any obvious regional tissue hypoperfusion. Fluid therapy is a cornerstone in shock resuscitation treatment, but determining optimal fluid therapy is challenging, particularly as fluid overload may be detrimental. Fluid challenges are used as an "ex juvantebus" method to dose fluid therapy, but it is not clear if a positive response reflects a state of hypoperfusion or the existence of a cardiac reserve. Still, a better understanding on how to target and guide fluid therapy is welcome, and studies digging into the problem are needed. Here, invasively monitored post-operative cardiac surgery patients are assessed as a model to investigate if carbon dioxide gaps and free energy charge may be useful in detecting possible tissue hypoperfusion.

Central venous oxygen saturation/lactate ratio: a novel predictor of outcome following emergency open laparotomy

INTRODUCTION

Emergency laparotomy is associated with high rates of morbidity and mortality. The need for highly sensitive readily prognostic biomarkers is necessary to improve the outcome. We investigated the usefulness of post-operative arterial lactate and ScvO₂/lactate ratio as predictors of outcome after post-operative emergency open laparotomy. To the best of our knowledge, the novel ScvO₂/lactate ratio was not investigated before in emergency open laparotomy patients.

METHODS

It is a prospective observational cohort study. We investigated the usefulness of post-operative arterial lactate and ScvO₂/lactate ratio as predictors of early mortality in 40 patients following emergency open laparotomy admitted to the ICU.

RESULTS

Admission and 24 h lactate levels were predictor of mortality with cut-off point > 3.95 mmol/L, sensitivity 100%, and specificity 93.3%, and cut-off > 3.5 mmol/L, sensitivity 100%, and specificity 96.7%, respectively. In this study, ScvO₂/lactate ratio on admission was predictor of at day 7 with cut-off point < 13.95, sensitivity 100%, and specificity 96.7% p < 0.0001. Lactate at 12 and 24 h was also predictor of survival p < 0.0001. Serial arterial lactate was highly correlated to ICU length of stay; admission APACHE II and day 1; and 2 MODS and SOFA scores (p < 0.001).

CONCLUSION

Serial blood lactate as well as the novel ScvO₂/lactate ratio can be useful for early predictors of mortality at 7 days. Serial lactate levels correlate to admission ICU scores APACHE II; MODS and SOFA in post-operative emergency open laparotomy patients.

Pitfalls in haemodynamic monitoring in the postoperative and critical care setting

Haemodynamic monitoring is a vital part of daily practice in anaesthesia and intensive care. Although there is evidence to suggest that goal-directed therapy may improve outcomes in the perioperative period, which haemodynamic targets we should aim at to optimise patient outcomes remain elusive and controversial. This review highlights the pitfalls in commonly used haemodynamic targets, including arterial blood pressure, central venous pressure, cardiac output, central venous oxygen saturation and dynamic haemodynamic indices. Evidence suggests that autoregulation in regional organ circulation may change either due to chronic hypertension or different disease processes such as traumatic brain injury, cerebrovascular ischaemia or haemorrhage; this will influence the preferred blood pressure target. Central venous pressure can be influenced by multiple pathophysiological factors and, unless central venous pressure is very low, it is rarely useful as a predictor for fluid responsiveness. Central venous oxygen saturation can be easily increased by a high arterial oxygen tension, making it useless as a surrogate marker of good cardiac output or systemic oxygen delivery in the presence of hyperoxaemia. Many dynamic haemodynamic indices have been reported to predict fluid responsiveness, but they all have their own limitations. There is also insufficient evidence to support that giving fluid until the patient is no longer fluid responsive can improve patient-centred outcomes. With the exception in the context of preventing contrast-induced nephropathy, large randomised controlled studies suggest that excessive fluid treatment may prolong duration of mechanical ventilation without preventing acute kidney injury in the critically ill.

Central Venous-to-Arterial Carbon Dioxide Gradient as a Marker of Occult Tissue Hypoperfusion after Major Surgery

The central venous-arterial carbon dioxide tension gradient (‘CO2 gap’) has been shown to correlate with cardiac output and tissue perfusion in septic shock. Compared to central venous oxygen saturation (SCVO2), the CO2 gap is less susceptible to the effect of hyperoxia and may be particularly useful as an adjunctive haemodynamic target in the perioperative period. This study investigated whether a high CO2 gap was associated with an increased systemic oxygen extraction (O2ER >0.3) or occult tissue hypoperfusion in 201 patients in the immediate postoperative period. The median CO2 gap of all patients was 8 mmHg (IQR 6 to 9), and a large CO2 gap was very common (>6 mmHg in 139 patients [69%], 95% CI 63 to 75; >5 mmHg in 170 patients [85%], 95% CI 79 to 89). A CO2 gap <5 mmHg had a higher sensitivity (93%) and negative predictive value (74%) than a CO2 gap <6 mmHg in excluding occult tissue hypoperfusion. Of the four variables that were predictive of an increased O2ER in the multivariate analysis—CO2 gap, arterial pH, haemoglobin and arterial lactate concentrations—the CO2 gap (odds ratio 4.41 per mmHg increment, 95% CI 1.7 to 11.2, P=0.002) was most important and explained about 34% of the variability in the risk of occult tissue hypoperfusion. In conclusion, a normal CO2 gap (<5 mmHg) had a high sensitivity and negative predictive value in excluding inadequate systemic oxygen delivery and may be useful as an adjunct to other haemodynamic targets in avoiding occult tissue hypoperfusion in the perioperative setting when high inspired oxygen concentrations are used.