A large Venous-Arterial PCO(2) Is Associated with Poor Outcomes in Surgical Patients. Anesthesiol Res Pract. 2011;2011:759792. [PMID: 22007204 PMCID: PMC3189458 DOI: 10.1155/2011/759792]

Effects of volume management on free flap perfusion and metabolism in a large animal model study

Free flap failure represents a substantial clinical burden. The role of intraoperative volume management remains controversial, with valid studies lacking. Here, using a large animal model, we investigated the influence of volume management on free flap perfusion and metabolism. Autotransfer of a musculocutaneous gracilis flap was performed on 31 German domestic pigs, with arterial anastomosis and catheterization of the pedicle vein for sequential blood sampling. Flap reperfusion was followed by induction of a hemorrhagic shock with maintenance for 30 min and subsequent circulation stabilization with crystalloid solution, crystalloid solution and catecholamine, autotransfusion or colloidal solution. Flap perfusion and oxygenation were periodically assessed using hyperspectral imaging. Flap metabolism was assessed via periodic blood gas analyses. Hyperspectral imaging revealed no difference in either superficial or deep tissue oxygen saturation, tissue hemoglobin or tissue water content between the test groups at any time point. Blood gas analyses showed that lactate levels were significantly increased in the group that received crystalloid solution and catecholamine, after circulatory stabilization and up to 2 h after. We conclude that, in hemorrhagic shock, volume management impacts acid-base balance in free flaps. Crystalloid solutions with norepinephrine increase lactate levels, yet short-term effects on flap perfusion seem minimal, suggesting that vasopressors are not detrimental.

Role of central venous - Arterial pCO2 difference in determining microcirculatory hypoperfusion in off-pump coronary artery bypass grafting surgery

Background:

Cardiac surgery is frequently associated with macro and microcirculatory hypoperfusion. Patients with normal central venous oxygen saturation (Scvo2) also suffer from hypoperfusion. We hypothesized that monitoring central venous-arterial pco2 difference (dCO₂) could also serve as additional marker in detecting hypoperfusion in cardiac surgery patient.

Methods:

This is a prospective observational study. Patients undergoing off-pump coronary artery bypass grafting included in this study. The dCO2 was measured postoperatively. The patients with a ScvO2 ≥70% were divided in to 2 groups, the high-dCO2 group (≥8 mmHg) and the low-dCO2 group (<8 mmHg).

Results:

The 65 patient had scvO₂ ≥70%. Out of these, 20 patients were assigned to the high dCO₂ group and 45 patients to the low dCO₂ group. Patients with high dco2 had higher lactate levels after ICU admission. They also had significantly prolonged need for mechanical ventilation (14.90 ± 10.33 vs 10 ± 9.65, P = 0.0402), ICU stay (5.05 ± 2.52 d vs 3.75 ± 2.36 d, P = 0.049) and hospital stay (12.25 ± 5.90 d vs 8.57 ± 5.55 d P = 0.018). The overall rate of post-operative complications was similar in both the group.

Conclusion:

The present study demonstrates dCO₂ as an easy to assess and routinely available tool to detect global and microcirculatory hypoperfusion in off-pump CABG patients, with assumed adequate fluid status and ScvO₂ as a hemodynamic goal. We observed that high dCO₂ (>8 mmHg) was associated with decreased DO₂I, increased oxygen extraction ratio, the longer need for mechanical ventilation and longer ICU stay.

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

Alteration of tissue perfusion is a main contributor to organ dysfunction in high-risk surgical patients. The difference between venous carbon dioxide and arterial carbon dioxide pressure (pCO₂ gap) has been described as a parameter reflecting tissue hypoperfusion in critically ill patients who are insufficiently resuscitated. The pCO₂ gap/CavO₂ ratio has also been described as an indicator of the respiratory quotient, thus the relationship between DO₂ and VO₂. Most of the knowledge about the pCO₂ gap and the pCO₂ gap/CavO₂ ratio has come from studies in the literature on animal models or intensive care unit (ICU) patients. To date, publications pertaining to the operative setting are sparse. In the present review, we will first discuss the physiological background of the pCO₂ gap and CO₂-O₂ derived parameters used in the operating room. Few studies have focused on the clinical relevance of the pCO₂ gap in high-risk non-cardiac surgical patients. Prospective observational studies with a small sample size and retrospective studies have shown that the pCO₂ gap may be a useful complementary tool to identify patients who remain insufficiently optimized hemodynamically. In a few studies, a high pCO₂ gap was associated with postoperative complications following non-cardiac high-risk surgery. Results of observational studies conducted in patients undergoing cardiac surgery are contradictory. We focused on the divergence between non-cardiac surgery, cardiac surgery, and septic critically ill patients. When analyzing the literature, we can find some explanations for the discrepancies in the published results between cardiac and non-cardiac surgery. Finally, we will discuss the clinical utility of the pCO₂ gap in high-risk surgical patients.

Monitoring of Tissue Oxygenation: an Everyday Clinical Challenge

Purpose of review

The aim of this article is to study the overview of pathophysiology and clinical application of central venous oxygen saturation monitoring in critically ill patients and during the perioperative period.

Recent findings

There are several clinical studies and animal experiments evaluating the effects of goal-directed hemodynamic stabilization on critically ill patients. Recent systematic reviews and meta-analyses found that advanced hemodynamic endpoints-targeted management has a positive effect on outcome in high-risk surgical patients. As all interventions aim to improve tissue oxygenation, it is of utmost importance to monitor the balance between oxygen delivery and consumption. For this purpose, central venous blood gas analysis provides an easily available tool in the everyday clinical practice. The adequate interpretation of central venous oxygen saturation renders the need of careful evaluation of several physiological and pathophysiological circumstances. When appropriately evaluated, central venous oxygen saturation can be a valuable component of a multimodal individualized approach, in which components of oxygen delivery are put in the context of the patients' individual oxygen consumption. In addition to guide therapy, central venous oxygen saturation may also serve as an early warning sign of inadequate oxygen delivery, which would otherwise remain hidden from the attending physician.

Summary

With the incorporation of central venous oxygen saturation in the everyday clinical routine, treatment could be better tailored for the patients' actual needs; hence, it may also improve outcome.

Central Venous to Arterial CO2 Difference After Cardiac Surgery in Infants and Neonates

OBJECTIVES

Venous to arterial CO2 difference correlates with cardiac output in critically ill adults, but its utility in pediatric patients is unclear. We sought to correlate venous to arterial CO2 difference with other cardiac output surrogates (arteriovenous oxygen saturation difference, central venous oxygen saturation, and lactate) and investigate its capacity to predict poor outcomes associated with low cardiac output (low cardiac output syndrome) in infants after cardiac surgery with cardiopulmonary bypass.

DESIGN

Retrospective chart review. Poor outcome was defined as any inotrope score greater than 15; death, cardiac arrest, extracorporeal membrane oxygenation; and unplanned surgical reintervention.

SETTING

Pediatric cardiovascular ICU.

PATIENTS

One hundred thirty-nine infants less than 90 days who underwent cardiopulmonary bypass, from October 2012 to May 2015.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

Two hundred ninety-six arterial and venous blood gas pairs from admission (n = 139), 6 (n = 62), 12 (n = 73), and 24 hours (n = 22) were included in analysis. For all pairs, venous to arterial CO2 difference was moderately correlated with arteriovenous oxygen saturation difference (R = 0.53; p < 0.01) and central venous oxygen saturation (R = -0.43; p < 0.01), but not lactate. At admission, venous to arterial CO2 difference was also moderately correlated with central venous oxygen saturation (R = -0.40; p < 0.01) and arteriovenous oxygen saturation difference (R = 0.55; p < 0.01), but not lactate. Thirty-four of 139 neonates (24.5%) had poor outcome. Median admission venous to arterial CO2 difference was 5.9 mm Hg (3.8-9.2 mm Hg). Patients with poor outcome had median admission venous to arterial CO2 difference 8.3 (5.6-14.9) versus 5.4 mm Hg (3.0-8.4 mm Hg) in those without poor outcome. Venous to arterial CO2 difference (area under the curve = 0.69; p < 0.01), serum lactate (area under the curve = 0.64; p = 0.02), and central venous oxygen saturation (area under the curve = 0.74; p < 0.01) were predictive of poor outcome. After controlling for covariates, admission venous to arterial CO2 difference remained significantly associated with poor outcome (odds ratio, 1.3; 95% CI, 1.1-1.45), including independent association with mortality (odds ratio, 1.2; 95% CI, 1.07-1.31).

CONCLUSIONS

Venous to arterial CO2 difference is correlated with important surrogates of cardiac output, and is associated with poor outcome and mortality related to low cardiac output syndrome after cardiac surgery in infants. Prospective validation of these findings, including confirmation that venous to arterial CO2 difference can identify low cardiac output syndrome in real time, is warranted.

SAPS 3 score as a predictive factor for postoperative referral to intensive care unit

BACKGROUND

Patients undergoing intermediate-risk surgery are typically taken to the ward postoperatively. However, some may develop complications requiring intensive care later. We aimed to evaluate the characteristics of patients undergoing intermediate-risk surgery who required late postoperative admission to the intensive care unit (ICU) and determine the predictors for this.

METHODS

The study included patients undergoing intermediate-risk surgery with preoperative indication for ICU but who were taken to the ward postoperatively, because they appeared to be responding well. However, they required late ICU admission. ICU care and preoperative SAPS 3 score were evaluated. Palliative surgeries and patients readmitted to ICU were excluded.

RESULTS

The study included 100 patients, 27 % of whom had late postoperative admission to the ICU. The preoperative SAPS 3 score was higher (45.4 ± 7.8 vs. 35.9 ± 7.4, P < 0.001) in patients who required delayed admission to the ICU postoperatively. Furthermore, they had undergone longer surgery (4.2 ± 1.9 vs. 2.7 ± 1.5 h, P < 0.001), and a greater proportion were gastrointestinal surgeries (14.8 vs. 5.5 %, P = 0.03) and intraoperative transfusion (18.5 vs. 5.5 % P = 0.04). In multivariate analysis, preoperative SAPS 3 and surgery duration independently predicted postoperative ICU admission, respectively (OR 1.25; 95 % CI 1.1-1.4 and OR 3.33; 95 % CI 1.7-6.3).

CONCLUSION

The identification of high-risk surgical patients is essential for proper treatment; time of surgery and preoperative SAPS 3 seem to provide a useful indication of risk and may help better to characterize patients undergoing intermediate-risk surgery that demand ICU care.

[Venous saturation : Between oxygen delivery and consumption]

Venous saturation is an important parameter to assess the ratio between oxygen delivery and oxygen consumption for both intensive care medicine and during perioperative care. Mixed venous saturation (SvO₂) is the most reliable parameter in this setting. Due to the high invasiveness of measuring mixed venous saturation, the less invasive central venous saturation (ScvO₂) has been entrenched for determining the balance of oxygen delivery and consumption. However, central venous saturation is inferior compared to mixed venous saturation as it does not cover the lower part of the body, including splanchnic perfusion. Nevertheless, studies have shown that central venous saturation is a reliable marker for goal-directed therapy in intensive care medicine, especially in patients with septic or hemorrhagic shock. Furthermore, central venous saturation has deep impact as a prognostic factor concerning morbidity and mortality. It has to be mentioned that not only decreased venous saturations but also elevated venous saturations are associated with poor outcome. Besides mixed venous and central venous saturation, intensivists and anesthesiologists focus on the central venous-arterial pCO₂ difference (dCO₂). An elevated dCO₂ is associated with poor outcome in patients after cardiac surgery or patients with sepsis. Yet, further investigations have to be performed to implement the dCO₂ as a reliable marker in daily routine.

Monitoring CO2 in shock states

The primary end point when treating acute shock is to restore blood circulation, mainly by reaching macrocirculatory parameters. However, even if global haemodynamic goals can be achieved, microcirculatory perfusion may remain impaired, leading to cellular hypoxia and organ damage. Interestingly, few methods are currently available to measure the adequacy of organ blood flow and tissue oxygenation. The rise in tissue partial pressure of carbon dioxide (CO2) has been observed when tissue perfusion is decreased. In this regard, tissue partial pressure of CO2 has been proposed as an early and reliable marker of tissue hypoxia even if the mechanisms of tissue partial pressure in CO2 rise during hypoperfusion remain unclear. Several technologies allow the estimation of CO2 content from different body sites: vascular, tissular (in hollow organs, mucosal or cutaneous), and airway. These tools remain poorly evaluated, and some are used but are not widely used in clinical practice. The present review clarifies the physiology of increasing tissue CO2 during hypoperfusion and underlines the specificities of the different technologies that allow bedside estimation of tissue CO2 content.

Arterial vs venous blood gas differences during hemorrhagic shock

AIM: To characterize differences of arterial (ABG) and venous (VBG) blood gas analysis in a rabbit model of hemorrhagic shock.

METHODS: Following baseline arterial and venous blood gas analysis, fifty anesthetized, ventilated New Zealand white rabbits were hemorrhaged to and maintained at a mean arterial pressure of 40 mmHg until a state of shock was obtained, as defined by arterial pH ≤ 7.2 and base deficit ≤ -15 mmol/L. Simultaneous ABG and VBG were obtained at 3 minute intervals. Comparisons of pH, base deficit, pCO₂, and arteriovenous (a-v) differences were then made between ABG and VBG at baseline and shock states. Statistical analysis was applied where appropriate with a significance of P < 0.05.

RESULTS: All 50 animals were hemorrhaged to shock status and euthanized; no unexpected loss occurred. Significant differences were noted between baseline and shock states in blood gases for the following parameters: pH was significantly decreased in both arterial (7.39 ± 0.12 to 7.14 ± 0.18) and venous blood gases (7.35 ± 0.15 to 6.98 ± 0.26, P < 0.05), base deficit was significantly increased for arterial (-0.9 ± 3.9 mEq/L vs -17.8 ± 2.2 mEq/L) and venous blood gasses (-0.8 ± 3.8 mEq/L vs -15.3 ± 4.1 mEq/L, P < 0.05). pCO₂ trends (baseline to shock) demonstrated a decrease in arterial blood (40.0 ± 9.1 mmHg vs 28.9 ± 7.1 mmHg) but an increase in venous blood (46.0 ± 10.1 mmHg vs 62.8 ± 15.3 mmHg), although these trends were non-significant. For calculated arteriovenous differences between baseline and shock states, only the pCO₂ difference was shown to be significant during shock.

CONCLUSION: In this rabbit model, significant differences exist in blood gas measurements for arterial and venous blood after hemorrhagic shock. A widened pCO₂ a-v difference during hemorrhage, reflective of poor tissue oxygenation, may be a better indicator of impending shock.