In vivo analysis techniques : sampling

IN VIVO ANALYSIS TECHNIQUES : SAMPLING

blood
cerebrospinal fluid
exhaled air :

capnography : monitoring of the concentration of exhaled CO₂ in order to assess the physiologic status of patients with acute respiratory problems or who are receiving mechanical ventilation and to determine the adequacy of ventilation in anesthetized patients.

capnograph : a system for monitoring the concentration of exhaled CO₂, consisting of a sensor placed in the breathing circuit or a tube that carries part of the exhaled gases to the analyzing device, a mass spectrometer or an infrared spectrometer, and devices to provide continuous visual (cathode ray tube) and graphic (printer) displays.

capnogram

₂

A : CO₂ cleared from the anatomic dead space;
B : dead space and alveolar CO₂
C : alveolar plateau
D : end-tidal CO₂ tension (PETCO₂)

urine has to be collected after > 3 hrs without urinating and after perineal washing without soap. The first 100÷150 mL are not collected (required for urethral clearing) : only the following 10 mL are collected in a sterile recipient and eventually frozen before forwarding to laboratory.
stools are collected into a non-necessarily sterile recipient.
nasopharyngeal or oropharyngeal exudate. Collection is made by a synthetic (non-cottoned !) tampon introduced through nose or mouth respectively after 2 hrs without food : contacts with tongue and cheeks must be avoided. 2 samples are usually collected.
sputum. When sputum is not collectable (30%), mucus collection can be stimulated by administration of saline solutions (risk of contaminations) or made by invasive methods.
gastric tonometry is relatively non-invasive technique to assess gastric perfusion and to monitor oxygen metabolism in visceral system. The technique utilizes the P_CO2 of the gastric fluid to calculate intramucosal pH (pH_i). The calculation is assessed by a modified Henderson-Hasselbalch equation. The combination of a high intramural PCO2 and mucosal acidosis may result from decreased splanchnic perfusion. The values of pH_i and regional P_CO2 (rP_CO2) based on gastric tonometry reflect indirect index of visceral blood flow. In clinical practice the P_CO2 of the gastric fluid is collected from saline sampled in the penetrable by carbon dioxide balloon. The silicon balloon is a part of tonometric probe placed in the gastric lumen. Device TONOCAP (Datex-Ohmeda, Helsinki, Finland) allows for full automatic measurement of the carbon dioxide regional pressure (rP_CO2). Presented experimental and clinical studies confirmed the usefulness of gastric tonometry in visceral blood perfusion assessment during perioperative and critical ill stage. Finally, the technique allows to decrease the number of complications, treatment expenses and mortality.