Red blood cell transfusion and skeletal muscle tissue oxygenation in anaemic haematologic outpatients

Anaemia is state of decreased blood oxygen carrying capacity.¹ Acute anaemia is associated with increased tissue oxygen extraction.² On the other hand, with chronic anaemia human body has time to at least partially adapt to decreased blood oxygen carrying capacity.^3,4

Near-infrared spectroscopy (NIRS) is non-invasive method to assess tissue oxygenation (StO₂) and estimate tissue haemoglobin (THb) levels.⁵ We have studied skeletal muscle StO₂ in critically ill patients with preserved oxygen (i.e., cardiogenic shock) and with impaired oxygen extraction (i.e., septic shock).^6-9 In addition to measuring resting StO₂, we performed vascular occlusion tests to stop arterial blood flow, to estimate oxygen consumption, and at the end of the occlusion, it was also possible to estimate vascular reactivity and maximal reperfusion capability.¹⁰

Under acute blood loss in trauma patients, the skeletal muscle StO₂ measured by NIRS correlates with blood haemoglobin (Hb) and delivery of oxygen, and can easily detect latent stage of haemorrhagic shock.¹¹ Unexpectedly, chronically anaemic haematology patients with preserved oxygen extraction capability did not show low skeletal StO₂ and THb index despite their severe anaemia, which is what would be predicted from normal physiological responses.¹²

It is known that there are structural and functional changes to RBCs during storage. Recent study detected deleterious effects of RBC storage on microvascular responses to transfusion in stable anaemic trauma patients.¹³

The aim of the present study was to re-challenge the current data that anaemia in chronically anaemic haematology patients is not associated with low skeletal muscle StO₂, and that the age of RBCs does not influence tissue responses. We investigated these aspects using improved technology NIRS devices, for deeper tissue penetration and removal of the superficial signal from the skin.

The study was approved by the National Medical Ethics Committee of the Republic of Slovenia (N° 117/06/12, 29.06.2012). All of the patients were informed of the goals of the study, and signed their written consent. This study was carried out according to the Helsinki-Tokyo Declaration.

Near-infrared spectroscopy measurements and analysis

The thenar skeletal muscle StO₂ and THb concentrations were measured with tissue spectrometer (Equanox 7600; Nonin Medical, Minnesota, USA). The electrode (8004CA, Equanox Advance Sensor, Nonin Medical) was placed on the thenar eminence to measure the maximum resting StO₂. During measurements, there were no additional treatment procedures in place, except for the RBC transfusion. All of the patients were positioned in a semirecumbent position.

In this resting period before the transfusion and after StO₂ signal stabilisation, the basal StO₂(%) and THb(g/l) were determined. Then vascularocclusion test was performed, as reported previously.⁶ In short, a sphygmomanometer cuff was placed over the brachium, and the pressure cuff inflation was taken to 60 mmHg over systolic blood pressure, to stop the blood flow in brachial artery. The StO₂ decreased during this arterial occlusion, which was measured as the downslope StO₂ (%/min). After reaching a StO₂ of 40% (the minimum StO₂) the cuff was released, and the StO₂ and THb continuously measured for an additional 5 min (Figure 1). During this reperfusion, the StO₂ increased rapidly, as the upslope StO₂ (%/min), and usually reached values higher than the basal StO₂, to give the maximum StO₂ (%). The same procedure was carried out 30 min after the RBC transfusion.

These time-dependent StO₂ values were continuously saved using the RealTerm software (http://realterm.sourceforge.net), which allowed a 1-Hz sampling rate. The data acquired were fur-ther analysed off-line using the Microsoft Excel 2010 software (Microsoft, WA, USA).

All of the NIRS measurements were carried out without knowing the exact age of RBCs.

Our findings confirm the low resting thenar skeletal muscle StO₂ in chronic anaemic haematology patients, and also the positive effects of RBCs on maximum StO₂ after vascular occlusion test-after reperfusion. Age of RBCs was negatively related to change of basal, upslope and maximum StO₂; age of RBCs ≥ 10days was found to predict divergent response of skeletal muscle StO₂ different responses of skeletal muscle StO₂.

In these patients, the resting StO₂ (53% ± 7%) was lower than that expected for normal healthy volunteers (83% ± 4%).⁶ Studies that have including patients with acute anaemia have also reported low skeletal muscle StO₂. On the other hand, surprisingly, Yurku et al. did not detect such expected low StO₂ of thenar eminence in anaemic haematology outpatients¹², although their RBC transfusions were successful in improving these variables. The explanation for these contradictory data probably lies with the NIRS probe they used (length 15 mm; penetration, ca.7 mm). Their kind of probe mainly detects changes in skin and subdermal tissue, which is, however, not the main issue in clinical use of NIRS.¹⁴ The thenar skin and subdermal tissue are 3–4 mm thick, and these layers are eventhicker for oedematous patients. By using probes with deeper penetration or devices that can filter out superficial layers and bones, the organ/skeletal muscle StO₂ can be better monitored, which is also more interesting for daily clinical practice (i.e., the device used in the present study). The importance of the probe and site has been shown previously.^15,16 Superficial structures are more prone to changes in peripheral circulation and ambient temperature.¹⁷

Our data that show here that skeletal muscle StO₂ in the resting period is influenced by age of the RBCs is supported by Leal-Noval et al., who showed increases in cerebral oxygenation in patients with severe traumatic brain injury if the RBCs were stored for < 19 days. Their data suggested an inverse association between increments in brain oxygen tension and RBC storage time.¹⁸

Kiraly et al. using 25 mm NIRS showed probe, that transfusion of older RBCs ( > 21 days) resulted in decreased skeletal muscle StO₂ in critically injured trauma patients. They reported a moderate correlation between increasing age of blood and decrease of oxygenation.¹⁹

Recent study also confirmed the deleterious effects of RBC storage on microvascular responses to transfusion in trauma patients.¹³ The transfusion of relatively older RBC units was associated with a decline in both StO₂ and perfused capillary vascular density. They even predicted a mean decrease in StO₂ during the duration of the transfusion that was related to the RBC age (-0.1064 × age of transfusion in days).

Other studies carried out in septic patients did not confirm the present data that the age of the blood has an impact on the tissue saturation measured in the resting period.^20,21 Patients in sepsis/septic shock have imbalanced autoregulation of the blood flow in their peripheral tissues.¹⁰ Volume resuscitated anaemic septic patients already have relatively high resting skeletal muscle StO₂. Roberson et al. did not find any differences in StO₂ of the brain and of the thenar muscle of healthy volunteers after transfusion of one unit of RBCs that was either 7 or 42 days old.²²

In the present study, the divergent responses of resting thenar skeletal muscle StO₂ after receiving old blood could not be simply explained by an elevation of their blood Hb content only in the patients treated with fresh blood, which will lead to the increases in the oxygen delivery to the tissue, because there was no relationship between Hb or THb and age of RBCs. There is another explanation possible. In most tissues ratio of the arteriole to capillary to venous compartments is approximately 10:20:70.²³ In case of a ratio change due to benefits for the arterial or capillary parts in comparison to the venous part, we might expect an elevation of StO₂ in the resting period, without considering the equal increases in THb concentrations. The differences between these vascular compartments might be changed to the benefit of the arterial and capillary systems in the patients treated with fresh blood because of less disturbance of nitric oxide (NO) metabolism in these fresher RBCs, with fewer degraded RBC products and a lower free Hb content, which are all NO-scavenging substances.²⁴

It was shown that NO metabolism becomes disturbed in blood with storage duration > 14 days.²⁴ Using competition kinetics analysis, it was also recently demonstrated that compared with freshly prepared RBCs, the consumption rates of NO increase approximately 40-fold and NO-dependant vasodilatation is inhibited 2–4-fold in 42-day-old RBCs.¹³

This decreased vascular reactivity (upslope and maximum StO₂) found in patients treated with older blood can also be explained in terms of more disturbance of NO metabolism in older blood.²⁴ NO has an important effect on vascular homeostasis, which is known as NO-based vasodilatation.²⁴ Post-ischaemic hyperaemia, which develops with vascular occlusion, is one of the most important and reproducible indicators of microcirculatory responses.²⁵

Bennett-Guerrero et al. studied effects of storage on the deformability of RBCs, on RBC-dependent vasoregulation, and on the changes in S-nitrosohaemoglobin (SNO-Hb) concentrations.²⁶ They observed significant drop in SNO-Hb concentrations in RBCs only 3h after blood donation, which might have been a reason for decreased vasodilatation after RBC transfusions. Reynolds et al. determined that there is possible regeneration of SNO-Hb in the received RBCs in vivo, which enables RBC-dependent vasodilatation and optimisation of blood perfusion through the peripheral tissues.²⁷

The present study poses some new questions. Further studies should focus on the effects of NO scavenging in RBCs that are stored for longer; also, whether aged RBCs can also be used as a therapeutic option, such as for septic patients, who have excessively induced NO synthesis.

The resting skeletal muscle StO₂ in chronically anaemic haematology patients is low. The RBC storage time affects the skeletal muscle tissue oxygenation of these patients.