"THE MANTLE" bundle for minimizing cerebral hypoxia in severe traumatic brain injury

Abstract

To ensure neuronal survival after severe traumatic brain injury, oxygen supply is essential. Cerebral tissue oxygenation represents the balance between oxygen supply and consumption, largely reflecting the adequacy of cerebral perfusion. Multiple physiological parameters determine the oxygen delivered to the brain, including blood pressure, hemoglobin level, systemic oxygenation, microcirculation and many factors are involved in the delivery of oxygen to its final recipient, through the respiratory chain. Brain tissue hypoxia occurs when the supply of oxygen is not adequate or when for some reasons it cannot be used at the cellular level. The causes of hypoxia are variable and can be analyzed pathophysiologically following "the oxygen route." The current trend is precision medicine, individualized and therapeutically directed to the pathophysiology of specific brain damage; however, this requires the availability of multimodal monitoring. For this purpose, we developed the acronym "THE MANTLE," a bundle of therapeutical interventions, which covers and protects the brain, optimizing the components of the oxygen transport system from ambient air to the mitochondria.

Keywords: Brain hypoxia; Brain oxygenation; Cerebral ischemia; Cerebral oxygenation monitoring; Traumatic brain injury.

Fig. 1

A Oxygen, O₂ route. From atmospheric air or the gaseous mixture supplied by mechanical ventilation, O₂ travels following concentration gradients. Cerebral O₂ transport (CerO₂t) depends on the product of CBF and arterial O₂ content (CaO₂), determined by the following equation: CaO₂ = (Hgb × 1.34 x SaO₂) + (PaO₂ × 0.003), where: Hgb: concentration in gr/dl; 1.34: number of ml transported by each gram of Hgb; SaO₂: arterial O₂ saturation; PaO₂: arterial pressure of O₂. The affinity of oxygen for Hgb is expressed by analyzing the Hgb-oxygen saturation curve. The CBF is mainly determined by the cerebral perfusion pressure (CPP) and the radius of the cerebral resistance vessels (autoregulation curve). B O₂ diffusion at cellular level. If the physiological variables interact harmoniously, oxygen reaches the microcirculation at 98 mmHg, then diffuses into the cell through the interstitial space (PO₂i = 20–40 mmHg). Inside the cell, the O₂ pressure is 1.5 mmHg. The distance that the 0₂ must travel varies between 20 and 60 microns

Fig. 2

The MANTLE mnemonics. Jugular venous saturation of oxygen, SvjO₂; brain tissue oxygen pressure, PTiO₂; cerebral perfusion pressure, CPP; systolic arterial blood pressure, SABP; tidal volume, Vt; respiratory rate, RR; Plateau pressure, PP; driving pressure, DP; mechanical power, MP; intracranial pressure, ICP; oxygen pressure at half arterial oxygen pressure, p50; optic nerve sheath diameter, ONSD; pulsatility index, PI; Computed Tomography, CT