Please see Bibliography of References for a list of abstracts, manuscripts and posters.

Microvascular Dysfunction

Thenar oxygen saturation (StO₂) and invasive oxygen delivery measurements in patients with cardiovascular insufficiency what are we measuring?

Mesquida J, Baigorri F, Masip J, Martinez ML, Gruartmoner G, Artigas A. Int Care Med. 2009;35(Suppl 1):S81.

Background: Several studies have demonstrated that tissue oxygen saturation (StO₂) correlates with either mixed or central venous oxygen saturation (SvO₂ and ScvO₂, respectively). Furthermore, our group showed that, in septic patients, low StO₂ values (<75%) predict low ScvO₂ values (<70%) with high specificity [1]. Unfortunately, this technique appears to be poorly sensitive, and normal StO₂ values cannot rule out low ScvO₂. We hypothesized that StO₂ could be a reflection of DO₂, where low StO₂ is always due to low DO₂, and high StO₂ reflects normal or high DO₂, although it could be inadequate to meet the global requirements (reflected by low ScvO₂).

Aims: To analyze the correlation between StO₂ (and its changes derived from a transient ischemic challenge) and global oxygen delivery (DO₂) parameters measured invasively using a pulmonary artery catheter (PAC).

Methods: Observational study, performed in a 26-bed medical-surgical ICU, at a university hospital. We recruited adult patients with cardiovascular insufficiency that required a PAC placement for hemodynamic monitoring and resuscitation. We collected demographic data, and hemodynamic and oxymetric data derived from the PAC. Simultaneously, we measured StO₂ and its changes derived from a vascular occlusion test (VOT).

Results: Twenty-two patients were studied. All the patients had a mean arterial pressure (MAP) above 65 mmHg. The DO₂ index (iDO₂) range in the studied population was 212–674 mLO₂/(min m²). The mean SvO₂ value was 57 ± 9%, mean cardiac index (CI) 2.7 ± 1 L/(min m²), and blood lactate 4.5 ± 3.1 mmol/L. The correlations found between StO₂ and invasive oxygen delivery-related variables are shown in Table 1. The StO₂-deoxygenation slope (DeOx) during the VOT showed a significant correlation with SvO₂ (r 0.6, p 0.02).

TABLE 1 StO₂ AND INVASIVE O₂ –DELIVERY MEASUREMENTS

	Hb	SvO2	CaO2	CvO2	iDO2	O2ER	CI
Pearson’s correlation	0.45	0.41	0.6	0.6	0.45	-0.7	0.7
P (two-tailed)	0.04*	0.06	0.003*	0.001*	0.03*	0.03*	0.7

Hb hemoglobin, CaO₂ arterial oxygen content, CvO₂ venous oxygen content, O2ER oxygen extraction ratio, CI, cardiac index

Conclusions: We did not find any correlation between StO₂ and global flow measurements, such as cardiac index (CI), but we found a correlation between StO₂ and iDO₂. This correlation seems related to the arterial oxygen content, and not to global flow. Normal StO₂ values could not rule out low iDO₂ and low IC states. Therefore, StO₂ seems to be poorly sensitive to exclude hypoperfusion states.

Reference(s): 1. Mesquida J, Masip J, Gili G, Artigas A, Baigorri F (2009) Thenar oxygen saturation measured by near infrared spectroscopy as a noninvasive predictor of low central venous oxygen saturation in septic patients. Intensive Care Med (Epub ahead of print).