Hemodynamic Effects of Vasopressin in Early Septic Shock Stage

Immediately before vasopressin infusion, fluid responsiveness was evaluated by delta PP (ΔPP) with ΔPP module attached to the monitor (DX 20x20, Dixtal, São Paulo, Brazil). Continuous sedation was maintained to control spontaneous ventilatory efforts. ΔPP > 13% receive crystalloid (Ringer's lactate or normal saline 0.9%) challenges until the ΔPP were below this value. Patients in whom was not possible to measure ΔPP, received crystalloid aliquots of 500 ml until there was no increase in cardiac output greater than 10%. Vasopressors were used to maintain mean arterial pressure above 65 mmHg. The fraction of inspired oxygen was adjusted to maintain oxygen saturation between 92-94%.

Thirty minutes after initial stabilization (the pre-vasopressin), all hemodynamic and respiratory measurements were obtained (pre-vasopressin), namely mean arterial pressure (MAP), heart rate (HR), right atrial pressure (RAP) , mean pulmonary artery pressure (MPAP), occluded pulmonary artery pressure (OPAP), cardiac index (CI), stroke index (SI), systemic vascular resistance index (SVRI), pulmonary vascular resistance index (PVRI). Samples were collected for blood gas analysis and arterial and mixed venous blood lactate.

Direct analysis of the sublingual microcirculation was done at that time by videomicroscopy obtained by SDF (Microscan; MicroVision Medical, Amsterdam, Netherlands), following the protocol previously described. Briefly, after removal of secretions, the lens of SDF was placed in the sublingual space without exerting any pressure. All images were obtained by a qualified physician using the recommended techniques to ensure image quality. We obtained three sequential images of high quality stable for at least 20 seconds, of both sides of the tongue while avoiding artifacts pressure. All images were captured using a notebook and a video converter analog / digital (ADVC110, Canopus Co, San Jose, California).

After obtaining baseline data, vasopressin was infused at fixed dose of 0.04 U / min. After one hour of vasopressin(post-vasopressin), the same variables were collected. If required, the adrenergic vasopressors infusion was adjusted during the study to maintain the target MAP from 65 to 70 mmHg. If patients were receiving dobutamine, its dose was kept constant during the study procedures. If fluid replacement or adjustment of ventilatory parameters or sedation were needed during the study, the patient was excluded.

All images were subsequently analyzed using the AVA 3.0 ® software (Microvision Medical, Amsterdam, Netherlands), considering only vessels with a diameter less than 20 micrometers. A blinded investigator analyzed all the images in a random order. The microcirculatory flow index (MFI), the total vascular density (TVD), the proportion of perfused vessels (PPV), the perfused vessel density (PVD), and the heterogeneity index (HI) were calculated.

Briefly, the MFI is calculated from the imaginary division of the image captured and stabilized into four quadrants. Its calculation is the average of the subjective evaluation of the flow in the four quadrants, quantified 0-3, where 0 corresponds to absent flow, 1 intermittent flow, 2 and 3 sluggish flow and continuous flow, respectively. TVD is calculated from the assumption that it is proportional to the number of vessels crossing three horizontal lines and three vertical equidistant arbitrary placed in the overlay image. The program computes the number of vessels crossing the lines and vessels and the total is divided by the lines length. Perfusion subjective evaluation was done in each vessel, graduated from 0 to 3 (absent, intermittent, sluggish or continuous). The PPV is calculated from the total number of vessels counted in the TVD subtracted not perfused vessels (those with flow 0 or flow 1), according to the formula: PPV = TVD - not perfused vessels / TVD x100. The PVD is obtained by multiplying TVD and PPV. The HI is calculated from the difference between the highest and lowest MFI found in three images captured in each moment (before and after vasopressin), according to the formula: HI = highest MFI - lowest MFI / MFI average.