Effects of arterial oxygen tension and cardiac output on venous saturation: a mathematical modeling approach

OBJECTIVES: Hemodynamic support is aimed at providing adequate O-2 delivery to the tissues; most interventions target O-2 delivery increase. Mixed venous O-2 saturation is a frequently used parameter to evaluate the adequacy of O-2 delivery. METHODS: We describe a mathematical model to compare the effects of increasing O-2 delivery on venous oxygen saturation through increases in the inspired O-2 fraction versus increases in cardiac output. The model was created based on the lungs, which were divided into shunted and non-shunted areas, and on seven peripheral compartments, each with normal values of perfusion, optimal oxygen consumption, and critical O-2 extraction rate. O-2 delivery was increased by changing the inspired fraction of oxygen from 0.21 to 1.0 in steps of 0.1 under conditions of low (2.0 L.min(-1)) or normal (6.5 L.min(-1)) cardiac output. The same O-2 delivery values were also obtained by maintaining a fixed O-2 inspired fraction value of 0.21 while changing cardiac output. RESULTS: Venous oxygen saturation was higher when produced through increases in inspired O-2 fraction versus increases in cardiac output, even at the same O-2 delivery and consumption values. Specifically, at high inspired O-2 fractions, the measured O-2 saturation values failed to detect conditions of low oxygen supply. CONCLUSIONS: The mode of O-2 delivery optimization, specifically increases in the fraction of inspired oxygen versus increases in cardiac output, can compromise the capability of the "venous O-2 saturation" parameter to measure the adequacy of oxygen supply. Consequently, venous saturation at high inspired O-2 fractions should be interpreted with caution.

ACCM/PALS haemodynamic support guidelines for paediatric septic shock: an outcomes comparison with and without monitoring central venous oxygen saturation

Introduction: The ACCM/PALS guidelines address early correction of paediatric septic shock using conventional measures. In the evolution of these recommendations, indirect measures of the balance between systemic oxygen delivery and demands using central venous or superior vena cava oxygen saturation ( ScvO(2) >= 70%) in a goal-directed approach have been added. However, while these additional goal-directed endpoints are based on evidence-based adult studies, the extrapolation to the paediatric patient remains unvalidated. Objective: The purpose of this study was to compare treatment according to ACCM/PALS guidelines, performed with and without ScvO(2) goal-directed therapy, on the morbidity and mortality rate of children with severe sepsis and septic shock. Design, participants and interventions: Children and adolescents with severe sepsis or fluid-refractory septic shock were randomly assigned to ACCM/PALS with or without ScvO(2) goal-directed resuscitation. Measurements: Twenty-eight-day mortality was the primary endpoint. Results: Of the 102 enrolled patients, 51 received ACCM/PALS with ScvO(2) goal-directed therapy and 51 received ACCM/PALS without ScvO(2) goal-directed therapy. ScvO(2) goal-directed therapy resulted in less mortality ( 28-day mortality 11.8% vs. 39.2%, p = 0.002), and fewer new organ dysfunctions ( p = 0.03). ScvO(2) goal-directed therapy resulted in more crystalloid ( 28 ( 20-40) vs. 5 ( 0-20) ml/kg, p < 0.0001), blood transfusion ( 45.1% vs. 15.7%, p = 0.002) and inotropic ( 29.4% vs. 7.8%, p = 0.01) support in the first 6 h. Conclusions: This study supports the current ACCM/PALS guidelines. Goal-directed therapy using the endpoint of a ScvO(2) = 70% has a significant and additive impact on the outcome of children and adolescents with septic shock.

Multicentre study on peri- and postoperative central venous oxygen saturation in high-risk surgical patients

Introduction Low central venous oxygen saturation (ScvO2) has been associated with increased risk of postoperative complications in high-risk surgery. Whether this association is centre-specific or more generalisable is not known. The aim of this study was to assess the association between peri- and postoperative ScvO2 and outcome in high-risk surgical patients in a multicentre setting. Methods Three large European university hospitals (two in Finland, one in Switzerland) participated. In 60 patients with intra-abdominal surgery lasting more than 90 minutes, the presence of at least two of Shoemaker's criteria, and ASA (American Society of Anesthesiologists) class greater than 2, ScvO2 was determined preoperatively and at two hour intervals during the operation until 12 hours postoperatively. Hospital length of stay (LOS) mortality, and predefined postoperative complications were recorded. Results The age of the patients was 72 ± 10 years (mean ± standard deviation), and simplified acute physiology score (SAPS II) was 32 ± 12. Hospital LOS was 10.5 (8 to 14) days, and 28-day hospital mortality was 10.0%. Preoperative ScvO2 decreased from 77% ± 10% to 70% ± 11% (p < 0.001) immediately after surgery and remained unchanged 12 hours later. A total of 67 postoperative complications were recorded in 32 patients. After multivariate analysis, mean ScvO2 value (odds ratio [OR] 1.23 [95% confidence interval (CI) 1.01 to 1.50], p = 0.037), hospital LOS (OR 0.75 [95% CI 0.59 to 0.94], p = 0.012), and SAPS II (OR 0.90 [95% CI 0.82 to 0.99], p = 0.029) were independently associated with postoperative complications. The optimal value of mean ScvO2 to discriminate between patients who did or did not develop complications was 73% (sensitivity 72%, specificity 61%). Conclusion Low ScvO2 perioperatively is related to increased risk of postoperative complications in high-risk surgery. This warrants trials with goal-directed therapy using ScvO2 as a target in high-risk surgery patients.

Incidence of low central venous oxygen saturation during unplanned admissions in a multidisciplinary intensive care unit: an observational study

INTRODUCTION: It has been shown that early central venous oxygen saturation (ScvO2)-guided optimization of hemodynamics can improve outcome in septic patients. The early ScvO2 profile of other patient groups is unknown. The aim of this study was to characterize unplanned admissions in a multidisciplinary intensive care unit (ICU) with respect to ScvO2 and outcome. METHODS: Ninety-eight consecutive unplanned admissions to a multidisciplinary ICU (median age 63 [range 19 to 83] years, median Simplified Acute Physiology Score [SAPS II] 43 [range 11 to 92]) with a clinical indication for a central venous catheter were included in the study. ScvO2 was assessed at ICU arrival and six hours later but was not used to guide treatment. Length of stay in ICU (LOSICU) and in hospital (LOShospital) and 28-day mortality were recorded. RESULTS: ScvO2 was 70% +/- 12% (mean +/- standard deviation) at admission and 71% +/- 10% six hours later (p = 0.484). Overall 28-day mortality was 18%, LOSICU was 3 (1 to 28) days, and LOShospital was 19 (1 to 28) days. Patients with an ScvO2 of less than 60% at admission had higher mortality than patients with an ScvO2 of more than 60% (29% versus 17%, p < 0.05). Changes in ScvO2 during the first six hours were not predictive of LOSICU, LOShospital, or mortality. CONCLUSION: Low ScvO2 in unplanned admissions and high SAPS II are associated with increased mortality. Standard ICU treatment increased ScvO2 in patients with a low admission ScvO2, but the increase was not associated with LOSICU or LOShospital.

Percutaneous central venous catheterization through the external jugular vein in children: improved success rate with body maneuvers and fluoroscopy assistance

Background/Purpose: Central venous catheterization is among the most common procedures performed by pediatric surgeons. Significant morbidity and even mortality can ensue from the widespread approach to the deep veins of the neck and femoral region. The external jugular vein (EJV) is a low-morbidity alternative for percutaneous catheterization in children, but it has yielded a low success rate in previous reports The authors show an improved success rate with this option. Methods: We performed an analysis of 33 patients` charts in which central venous catheterization using Seldinger technique through the EJV was attempted in 2005. Age, diagnosis, maneuvers used for success, fluoroscopy usefulness, and types of inserted catheters were evaluated. Results: The procedure was successful in 26 (78.8%) patients without complications. Diagnosis was neoplasia in almost half of the patients (42%). In half of the successful cases, body maneuvers were used, namely, twisting the head of the patient to the side of the vein and stretching the ipsilateral arm and shoulder. All but one procedure were completed under fluoroscopic guidance. In 6 (23%) patients, a long-term catheter was inserted. Conclusions: The EJV is an excellent option for central venous catheterization in children. The execution of simple maneuvers along with fluoroscopic assistance might allow for an improved success rate not only for short-term but also for long-term catheter insertion. (C) 2008 Elsevier Inc. All rights reserved.

Salvage of long-term central venous catheters during an outbreak of Pseudomonas putida and Stenotrophomonas maltophilia infections associated with contaminated heparin catheter-lock solution

objective. To describe the management of patients with long-term central venous catheters (CVCs) during an outbreak of infection due to Pseudomonas putida and Stenotrophomonas maltophilia associated with contaminated heparin catheter-lock solution. design. Descriptive study. setting. Private, 250-bed tertiary-care hospital. methods. In March 2003, we identified 2 febrile cancer patients with P. putida bacteremia. Over 2 days, 7 cases of bacteremia were identified; lots of syringes prefilled with heparin catheter-lock solution, supplied by a compounding pharmacy, were recalled and samples were cultured. More cases of bacteremia appeared during the following days, and any patient who had had a catheter lock infused with the suspect solution was asked to provide blood samples for culture, even if the patient was asymptomatic. Isolates that were recovered from culture were typed by pulsed-field gel electrophoresis. Antimicrobial salvage treatment of long-term CVCs was attempted. results. A total of 154 patients had had their catheter lock infused with solution from the lots that were suspected of being contaminated. Only 48 of these patients had CVCs. By day 7 of the outbreak, 18 of these patients had become symptomatic. Twenty-six of the remaining 30 asymptomatic patients then also provided blood samples for culture, 10 of whom developed fever shortly after samples were collected. Thirty-two patients were identified who had P. putida bacteremia; 9 also had infection due to S. maltophilia. Samples from 1 of the 3 lots of prefilled syringes in use at the time of the outbreak also grew P. putida on culture. Molecular typing identified 3 different clones of P. putida from patients and heparin catheter-lock solution, and 1 clone of S. maltophilia. A total of 27 patients received antimicrobial therapy regimens, some of which included decontamination of the catheter lock with anti- infective lock solution. Of 27 patients, 19 (70%) retained their long-term CVC during the 6-month follow-up period. conclusions. To our knowledge, this is one of the largest prospective experiences in the management of bloodstream infection associated with long-term CVCs. The infections were caused by gram-negative bacilli and were managed without catheter removal, with a high response rate. We emphasize the risks of using intravenous formulations of medications supplied by compounding pharmacies that produce large quantities of drugs.

Use of a thermodilution catheter to measure core body temperature, central venous pressure and cardiac output during anaesthesia and surgery in the dog

The use of thermodilution and other methods of monitoring in dogs during surgery and critical care was evaluated. Six Greyhounds were anaesthetised and then instrumented by placing a thermodilution catheter into the pulmonary artery via the jugular vein. A catheter in the dorsal pedal artery also permitted direct measurement of arterial pressures. Core body temperature (degreesC) and central venous pressure (mmHg) were measured, while cardiac output (mL/min/kg) and mean arterial pressure (mmHg) were calculated. A mid-line surgical incision was performed and the physiological parameters were monitored for a total of two hours. All physiological parameters generally declined, although significant increases (P<0.05) were noted for cardiac output following surgical incision. Central venous pressure was maintained at approximately 0mmHg by controlling an infusion of sterile saline. Core body temperature decreased from 37.1+/-0.6degreesC (once instrumented) to 36.6+/-0.60degreesC (at the end of the study), despite warming using heating pads. Physiological parameters indicative of patient viability will generally decline during surgery without intervention. This study describes an approach that can be undertaken in veterinary hospitals to accurately monitor vital signs in surgical and critical care patients.

Effect of central venous catheter type on infections: a prospective clinical trial

This study reports on a block clinical trial of two types of central venous catheters (CVCs): antiseptic-impregnated catheters (AIC) and non-impregnated catheters (non-AIC), on catheter tip colonization and bacteraemia. In total, 500 catheters were inserted in 390 patients over the 18 month study period, 260 (52.0%) AIC and 240 (48.0%) non-AIC. Of these, 460 (92.0%) tips (237 AIC and 223 non-AIC) were collected. While significantly fewer AIC, 14 (5.9%), than non-AIC, 30 (13.5%), catheters were colonized (P < 0.01), there was no difference in the rates of bacteraemias in the two groups (0.8% vs. 2.7%, respectively, P = 0.16). There were 6.87 (95% CI 3.38-14.26) and 16.92 (95% CI 10.61-27.12) colonized AIC and non-AIC catheters, respectively, per 1000 catheter days, a difference that was significant (P < 0.01). However, no difference emerged between bacteraemias in AIC and non-AIC catheters per 1000 catheter days measured at 0.98 (95% CI 0.24-5.54) and 3.38 (95% CI 1.29-9.34), respectively (P = 0.10). Of the 444 CVCs that were sited in the subclavian or jugular veins and had tips collected, significantly more catheters were colonized in the jugular group, 19 (20%), compared with the subclavian group, 24 (6.9%; P less than or equal to 0.01). Overall, the low rates of colonization and bacteraemia may be explained by the population studied, the policies used and the employment of a clinical nurse dedicated to CVC management. (C) 2003 The Hospital Infection Society. Published by Elsevier Science Ltd. All rights reserved.

High vancomycin resistance among biofilms produced by Staphylococcus species isolated from central venous catheters

Biofilm production is an important mechanism that allows microbes to escape host defences and antimicrobial therapy. Vancomycin has been used largely for the treatment of methicillin-resistant staphylococcal infections. Here, we determined the minimal inhibitory concentration (MIC) and minimal biofilm eradication concentration (MBEC) for 82 Staphylococcus species isolated from central venous catheters (CVC). Our results showed that the 41 strong and moderate-biofilm-producing isolates presented a higher MBEC/MIC ratio for vancomycin than the 24 weak-biofilm-producing isolates, illustrating the importance of biofilm production ability and the difficulty in treating biofilm-related infections. The MBEC was significantly higher in moderate-biofilm-producing isolates than in weak-biofilm-producing isolates (p < 0.001) and in strong-biofilm-producing isolates than in weak-biofilm-producing isolates (p = 0.001). The correlation between the MIC and the MBEC was poor. Based on our results, we recommend that bacterial biofilms be suspected in all cases of CVC infection.

Effectiveness of heparin versus 0.9% saline solution in maintaining the permeability of central venous catheters: a systematic review

Abstract OBJECTIVE Determining which is the most effective solution (heparin flush compared to 0.9% saline flush) for reducing the risk of occlusions in central venous catheters (CVC) in adults. METHOD The systematic review followed the principles proposed by the Cochrane Handbook; critical analysis, extraction and synthesis of data were performed by two independent researchers; statistical analysis was performed using the RevMan program 5.2.8. RESULTS Eight randomized controlled trials and one cohort study were included and the results of the meta-analysis showed no difference (RR=0.68, 95% CI=0.41-1.10; p=0.12). Analysis by subgroups showed that there was no difference in fully deployed CVC (RR=1.09, CI 95%=0.53-2.22;p=0.82); Multi-Lumen CVC showed beneficial effects in the heparin group (RR=0.53, CI 95%=0.29-0.95; p=0.03); in Double-Lumen CVC for hemodialysis (RR=1.18, CI 95%=0.08-17.82;p=0.90) and Peripherally inserted CVC (RR=0.14, CI 95%=0.01-2.60; p=0.19) also showed no difference. CONCLUSION Saline solution is sufficient for maintaining patency of the central venous catheter, preventing the risks associated with heparin administration.

Percutaneous central venous catheterization in premature infants: a method for facilitating insertion of silastic catheters via peripheral veins.

Peripheral venous cannulation is the preferred method of inserting central venous silastic catheters in premature infants. The standard techniques are placement of the catheter using a breakaway introducer needle or introduction of the catheter through a cannula. In extremely low birth weight infants (<1000 g) successful cannulation is impeded by the small size of the vessels. After repeated attempts, both procedures can be time-consuming and stressful to the infant. We present a modified insertion technique of the standard 2-French silastic catheter with an increased success rate, thus reducing insertion time, stress to the infant, and costs. The method uses the tip of a 20-gauge cannula as dilator/introducer for the 2-French catheter. This tip is inserted into the vessel with a standard 24-gauge cannula. After successful insertion of the dilator/introducer cannula, the standard 2-French catheter can then be advanced easily.

Mise en place d'un cathéter veineux central chez l'adulte. 1. Indications, précautions et complications [Bases of central venous catheterization]

La pose d'un cathéter veineux central est un geste fréquent dans un service de médecine interne. En suivant la formation des médecins-assistants, nous nous sommes aperçus que certaines questions, doutes ou craintes concernant cette procédure nous sont régulièrement adressées: «Est-ce qu'un cathéter sous-clavier peut être posé avec une thrombocytopénie modérée?»; «Quel site de ponction présente le moins de risques pour le patient?»; «Après combien de jours un cathéter doit-il être changé?». Cet article se propose de répondre à ces questions et à d'autres, en partant d'une mini-revue de la littérature actuelle. Central venous catheterization is a frequently performed procedure in internal medicine units. Residents in training frequently share the same questions, doubts and fears about this procedure : "Should I perform a subclavian catheterization in a patient with mild thrombopenia?"; "Which site has the lesser complication rate?"; "After how long does a catheter need to be replaced?". This mini-review of the current literature tries to answer this and other questions

Spurious hyperphosphatemia in a patient with alteplase-locked central venous catheter.

Alteplase has been shown to be effective in preventing central venous access clotting in patients on hemodialysis. Because of a high phosphorus content in its excipient, it can inadvertently contaminate blood samples, leading the physician in care of the patient to erroneously increase dialysis time or change diet in order to control the pseudo-hyperphosphatemia.

Mismatch of arterial and central venous blood gas analysis during haemorrhage.

BACKGROUND AND OBJECTIVE: Arterial base excess and lactate levels are key parameters in the assessment of critically ill patients. The use of venous blood gas analysis may be of clinical interest when no arterial blood is available initially. METHODS: Twenty-four pigs underwent progressive normovolaemic haemodilution and subsequent progressive haemorrhage until the death of the animal. Base excess and lactate levels were determined from arterial and central venous blood after each step. In addition, base excess was calculated by the Van Slyke equation modified by Zander (BE(z)). Continuous variables were summarized as mean +/- SD and represent all measurements (n = 195). RESULTS: Base excess according to National Committee for Clinical Laboratory Standards for arterial blood was 2.27 +/- 4.12 versus 2.48 +/- 4.33 mmol(-l) for central venous blood (P = 0.099) with a strong correlation (r(2) = 0.960, P < 0.001). Standard deviation of the differences between these parameters (SD-DIFBE) did not increase (P = 0.355) during haemorrhage as compared with haemodilution. Arterial lactate was 2.66 +/- 3.23 versus 2.71 +/- 2.80 mmol(-l) in central venous blood (P = 0.330) with a strong correlation (r(2) = 0.983, P < 0.001). SD-DIFLAC increased (P < 0.001) during haemorrhage. BE(z) for central venous blood was 2.22 +/- 4.62 mmol(-l) (P = 0.006 versus arterial base excess according to National Committee for Clinical Laboratory Standards) with strong correlation (r(2) = 0.942, P < 0.001). SD-DIFBE(z)/base excess increased (P < 0.024) during haemorrhage. CONCLUSION: Central venous blood gas analysis is a good predictor for base excess and lactate in arterial blood in steady-state conditions. However, the variation between arterial and central venous lactate increases during haemorrhage. The modification of the Van Slyke equation by Zander did not improve the agreement between central venous and arterial base excess.

Small access (30F) clinical central venous smart cannulation: is it adequate?

OBJECTIVES: To assess the performance of 45F vs. 36F smartcanula in CPB with gravity drainage alone. METHODS: Twenty patients were randomly assigned to two groups receiving for venous drainage a smartcanula which is collapsed over a mandrel for trans-atrial insertion into the inferior vena cava and expanded in situ to either 45F or 36F. RESULTS: Valve replacement/repair was realized in 7/10 and/or CABG in 6/10 for 36F (69+/-13 years) vs. 5/10 and 5/10, respectively, for 45F (63+/-11 years: NS). Body weight and surface area (BSA) were 83+/-9 kg (1.9+/-0.2 m2, max 2.2 m2) for 36F vs. 79+/-6 kg: NS (1.9+/-0.1 m2 (NS), max 2.1 m2) for 45F. Insertion and access orifice diameter (area) was 6 mm and 10 mm (78.5 mm2) for the 36F vs. 6 mm and 13 mm (132 mm2) for the 45F (+69%). Calculated target pump flow (2.4 l/min/m2) was 4.7+/-0.4 l/min for 36F vs. 4.5+/-0.3 l/min for 45F. Achieved pump flow accounted for 5.0+/-0.3 l/min for 36F (8% above target) vs. 4.8+/-0.3 l/min for 45F (8% above target): NS. The water balance during the pump run (clear volume added minus hemofilter and urine output) was 2.2+/-0.3 l for 36F vs. 2.0 l for 45F: NS. CONCLUSION: Due to its 'open' wall (the vena cava provides the seal), its reduced wall thickness (range: 0.0-0.4 mm), and its self-expanding design, the 36F smartcanula requiring a 30F access orifice has sufficient drainage capacity by gravity alone for full CPB in adults with a BSA up to 2.2 mm2.