**5. Direct methods**

### **5.1. Measuring microcirculatory perfusion**

Video microscopic techniques involve highly sensitive video microscopes that allow direct measurement of capillary density, perfusion and flow dynamics. Video microscopic techniques have shown a correlation between increased mortality in ICU patients [29]. These techniques, which included orthogonal polarisation spectral (OPS), sidestream dark-field (SDF) imaging and incident dark-field (IDF) imaging (CytoCam) provide in vivo visualisation of the microcirculation. OPS and SDF imaging have become clinically useless due to the large size, motion and pressure artefacts, operator-dependent output, and the need for offline analysis, which takes time to produce data.

in tissue metabolism (VCO2) increases tissue perfusion and decreases PCO<sup>2</sup>

inverse relationship between microvascular perfusion and the PCO<sup>2</sup>

should be used during treatment to make it more clinically useful [37].

**6.5. Microcirculation and hyperbaric oxygen therapy**

irreversible tissue damage [40–42].

**7.1. Microcirculatory dysfunction**

**7. Microcirculation and disease**

is increased, there is an inadequate relationship between metabolism

gradient (PCO<sup>2</sup>

gaps may signify either flow stagnation or tissue hypoxia [35]. Importantly, there is an

Microcirculatory alterations in critically ill patients may play a role in the development of organ dysfunction. Video microscopic techniques and tissue PCO2 measurements can be used to evaluate microvascular perfusion. But, microcirculation monitoring is not yet part of

Lactate in the human body is a metabolic product of anaerobic glycolysis, produced from the reduction of pyruvate by the enzyme lactate dehydrogenase, and reflects inadequate oxygen delivery. Normally, a total amount of 1500 mmol of lactate is produced daily in adult, and blood lactate levels are sustained less than 2 mmol/L. However, in the state of hypoperfusion and hypoxia, pyruvate rapidly accumulate, and its metabolism is shifted almost entirely to lactate production. The tissue hypoxia is a cause of lactate elevation and characterised by supply-dependent oxygen consumption [36]. Single measurement of lactate can only serve as a risk-stratification biomarker. Lactate clearance with its association with clinical outcome

Hyperbaric oxygen therapy (HBOT) is a clinical treatment in which a patient breathes pure oxygen for a limited period of time at an increased pressure. This therapy has been suggested to improve oxygen supply to tissues and therefore improves microcirculation [38]. HBOT in patients with diabetic foot ulcer was associated with a greater reduction in the ulcer wound area than standard therapy and significantly improves the ulcers in a short term [39]. Also, HBOT which is applied in acute ischemic stroke, femoral head necrosis, and carbon monoxide intoxication aims to increase oxygen supply to the ischemic tissue and to reduce the extent of

Microcirculation plays a critical role in the physiological process such as oxygen supply to tissues and nutritional exchange and has a key role in modulation of inflammation and coagulation. These functions are mainly controlled by endothelial cells, which produce biologic signals to regulate local blood flow, cell adhesion, permeability, and coagulation activation. The most important function of the microcirculation is the regulation of flow within the different organs [43].

is constant, and PtCO<sup>2</sup>

routine clinical practice.

**6.4. Lactate**

PCO<sup>2</sup>

and tissue perfusion. Normal tissue-arterial CO<sup>2</sup>

represents a good assessment of tissue perfusion.

. When PaCO<sup>2</sup>

57

consequently

gap) <7 mmHg. Elevated

gap. PtCO<sup>2</sup>

Microcirculation and Hyperbaric Oxygen Treatment http://dx.doi.org/10.5772/intechopen.75609
