Cattedra di Anestesiologia e Rianimazione, I Università, II Facoltà di Medicina e Chirurgia, Roma, Italy
Introduction: The microvascular tone regulation can be very useful
to be assessed to titrate therapy in critical conditions. In the
present study, we use near infrared (NIR) spectroscopy in the frequency domain on critically ill patients and healthy subjects, to
obtain the measurement of microcirculatory compliance and the
regulation of vascular tone.
Methods: Two groups of subjects have been studied: the first
group was composed by 17 healthy subjects (H) at rest, in the
second group five critically ill patients were treated with noradrenalin infusion (N). In the N group the measurements have been performed at different noradrenalin doses: the first dose (d1) was
established by the head physician, then the dose was doubled (d2)
and finally reduced at the half of the first dose (d3).
The probe of the spectrometer used in this study (ISS incorporated, Urbana, IL, USA), have been applied on the forearm skin, in a
zone corresponding to brachioradial muscle. A serial of a pneumatic cuff compressions have been performed at the arm. Measurements
of the total hemoglobin [Hbt] in tissue and blood
volume, derived from [Hbt] have been obtained. The linear coefficient correlating blood volume to cuff compressions was considered
as a measurement of venous and capillary compliance.
Results: The [Hbt] and Hb in the blood of the two groups are
shown in Table 1, the Hb content in the blood was lower in N than
in H group. There was no difference about [Hbt] between the
groups. In the H group in no subject [Hbt] change, at cuff pressure
of 10 mmHg, was evidenced while only five subjects out of 17
showed a [Hbt] increase at 20 mmHg. In the N group, three subjects out of five (60%) showed a [Hbt] increase at 20 mmHg pressure.
The capillary and venular bed compliance is shown in Table 1.
Conclusions: From our results is shown clearly that in critically ill
subjects the microvascular bed volume rose, in fact even if the Hb
in blood was low the [Hbt] in tissue did not change.
References:
1. De Blasi RA, Ferrari M, Natali A, et al.: A non invasive measurament of forearm blood flow and oxygen consumption by near–infrared
spectroscopy. J Appl Physiolol 1994, 76(3):1388-1393.
2. Fantini S, Franceschini MA, Maier JS, et al.: Frequency domain multichannel optical detector for non-invasive tissue spectroscopy and
oxymetry. Opt Eng 1995, 34:32-42.
3. Shrier I, Magder S: Pressure–flow relationship in a vitro model of compartment syndrome. J Appl Physiolol 1995, 79:214-221
