ScvO2 values are obtained by measuring the oxygen saturation in venous blood returning to the heart, and reflect the balance between oxygen delivery and oxygen consumption.
Low (<70%) ScvO2 values were targeted by Rivers in his Early Goal Directed Therapy study: by improving the macrocirculation with fluids, vasoactive drugs, and packed red cells the aim is to improve oxygen delivery to tissues, and therefore a higher oxygen saturation is found in the venous blood returning to the heart in adequately resuscitated patients. The story is more complex, however, as mechanisms of oxygen supply (macrocirculatory flow), distribution (microcirculatory flow), and processing (mitochondrial function) must all function at an adequate level to maintain normal physiology.
Although low ScvO2 values may be a marker for macrocirculatory failure, high ScvO2 values may reflect microcirculatory or mitochondrial failure.
A multicentre study demonstrated a higher mortality on patients whose ScvO2 in the ED was high (90-100%) compared with those with a normal ScvO2.
Mortality associated with three groups according to their highest recorded ScvO2 in the ED was:
Hypoxia group (ScvO2 <70%) – 40% mortality (95% CI 29-53)
Normoxia group (ScvO2 71-89%) – 21% mortality (95% CI 17-25)
Hyperoxia group (ScvO2 90-100%) – 34% mortality (95% CI 25-44)
The study design could not control for many potential confounders, but this opens the door for further study, and reminds us that the unthinking pursuit of a single physiological target may miss the bigger clinical picture.
Multicenter Study of Central Venous Oxygen Saturation (ScvO2) as a Predictor of Mortality in Patients With Sepsis
Annals of Emergency Medicine 2010;55(1):40-46
In a study of febrile infants with a bulging fontanelle, only one out of 153 infants had bacterial meningitis. Other diagnoses included aseptic meningitis (26.7%), upper respiratory tract infection (18.3%), viral disease NOS (15.6%), roseola infantum (8.5%) and acute otitis media (6.5%).
In this study, most infants with fever and a bulging fontanelle had benign and self-limited disease.
Bulging fontanelle in febrile infants: is lumbar puncture mandatory?
Arch Dis Child. 2009 Sep;94(9):690-2
In a multicentre RCT of patients with septic shock who were receiving steroids (hydrocortisone) for the septic shock, intensive insulin therapy did not affect outcome but was (once again) associated with a higher incidence of hypoglycaemia. Also, the addition of (enteral) fludrocortisone did not provide benefit compared with hydrocortisone alone.
Corticosteroid Treatment and Intensive Insulin Therapy for Septic Shock in Adults
Data from 15,022 subjects at 165 sites at which the Surviving Sepsis Campaign (SSC) 6 hour and 24 hour care guideline bundles were introduced were submitted from 2005 to early 2008. As adherence to the guidelines increased (18.4 to 26.1%), hospital mortality decreased (37 to 30.8%). The study was partly funded by manufacturers of some of the monitoring and therapeutic components of the SSC guidelines.
The Surviving Sepsis Campaign: Results of an international guideline- based performance improvement program targeting severe sepsis
Crit Care Med. 2010 Feb;38(2):367-74
An insightful editorial points out several methodological weaknesses in this study, as well as the interesting point that the guidelines published in 2004 drew on evidence published predominantly between 2000 and 2003, and subsequent research has called a number of components into question. Examples are:
- The Corticosteroid Therapy of Septic Shock (CORTICUS) study did not confirm that low-dose corticosteroids were beneficial
- the Normoglycaemia in Intensive Care Evaluation and Survival Using Glucose Algorithm Regulation (NICE- SUGAR) study reported that targeting tight glycemic control may be harmful
- Early goal-directed therapy is the subject of no less than three ongoing clinical trials supported by national research funding agencies
- and the effect of drotrecogin alfa (activated) is being re-examined in both industry-sponsored and investigator-initiated trials.
While scientific skepticism is healthy, there is no doubt at least that in part due to the efforts of the SSC more clinicians than ever are aware of the importance of timely aggressive management of severe sepsis / septic shock.
The Surviving Sepsis Campaign: robust evaluation and high-quality primary research is still neede
Crit Care Med. 2010 Feb;38(2):683-4
Some persist in thinking and teaching that the ‘vasopressor’ noradrenaline (norepinephrine) increases mean arterial pressure (MAP) simply by increasing systemic vascular resistance, leading to concerns that it may increase blood pressure at the expense of tissue perfusion. This assertion is contested by many, who now have further support from this study.
In 16 patients with septic shock, various measures of peripheral perfusion were recorded while the dose of noradrenaline was increased to achieve target MAPs. The use of noradrenaline to achieve incremental targets for MAP was associated with increases in global oxygen delivery, cutaneous microvascular flow, and tissue oxygenation in patients with established septic shock; there were no associated changes in the preexisting abnormalities of sublingual microvascular flow. The authors state that these findings suggest that in patients with septic shock, improvements in global hemodynamics and tissue oxygen delivery can be achieved with noradrenaline, without exacerbating microcirculatory flow abnormalities.
The effect of increasing doses of norepinephrine on tissue oxygenation and microvascular flow in patients with septic shock
Crit Care Med. 2009 Jun;37(6):1961-6
Ventilator associated pneumonia (VAP) is a well recognised complication of ICU care, but colonisation and infection further up the respiratory tract may be a risk factor for VAP that is worth identifying and treating. Ventilator-associated tracheobronchitis (VAT) has similar diagnostic criteria to VAP, but without the radiographic infiltrates.
Ventilator-associated tracheobronchitis: the impact of targeted antibiotic therapy on patient outcomes
Chest. 2009 Feb;135(2):521-8