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

Abstract

The central venous-arterial carbon dioxide tension gradient ('CO 2 gap') has been shown to correlate with cardiac output and tissue perfusion in septic shock. Compared to central venous oxygen saturation (S CV O 2), the CO 2 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 CO 2 gap was associated with an increased systemic oxygen extraction (O 2 ER >0.3) or occult tissue hypoperfusion in 201 patients in the immediate postoperative period. The median CO 2 gap of all patients was 8 mmHg (IQR 6 to 9), and a large CO 2 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 CO 2 gap <5 mmHg had a higher sensitivity (93%) and negative predictive value (74%) than a CO 2 gap <6 mmHg in excluding occult tissue hypoperfusion. Of the four variables that were predictive of an increased O 2 ER in the multivariate analysis-CO 2 gap, arterial pH, haemoglobin and arterial lactate concentrations-the CO 2 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 CO 2 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.

Evaluation of two different fluids regimens on central venous-to-arterial Carbon Dioxide difference (pCO 2 gap) - a randomized controlled trial

“…In patients with low ScvO 2 , an elevation of pCO 2 gap is reflecting a state of low CO and evaluation of pCO2 gap at this situation could be of value in integrating therapies that help improving CO. When ScvO 2 (≥ 70%), persistent elevation of pCO 2 gap is indication of impaired perfusion and in this way evaluation of pCO 2 gap could help in choosing the ideal decisions regarding fluids and inotropes [30,31].…”

Venous-to-arterial pCO2 difference in high-risk surgical patients

“…Because there is a linear association between CO 2 content and CO 2 pressure, the pCO 2 gap may be expressed as: pCO 2 gap = K * VCO 2 /CO. Therefore, the pCO 2 gap could be associated with CO 2 generation and CO. As CO 2 is much more soluble than O 2 , it represents a very sensitive marker of tissue hypoxia (6). Since the pCO 2 gap depends on CO and VCO 2 , it represents an indicator of the capacity of venous blood to eliminate CO 2 generated by peripheral tissues, and thus the adequacy of blood flow during shock states.…”

Hypothesis: Fever control, a niche for alpha-2 agonists in the setting of septic shock and severe acute respiratory distress syndrome?

“…Nevertheless, achieving adequate cardiac output does not necessarily translate into achieving adequate micro-circulation [23], i.e. mixed venous saturation or superior vena cava saturation >70-75% 8 [82], CO2 gap <5-6 mmHg [83][84][85], lactate trending <2mM and excellent capillary refill. Few drugs achieved popularity to improve the micro-circulation [86].…”