Blood Gas Analyzer

Overview

A blood gas analyzer measures the chemistry that keeps critical-care decisions moving: how acidic the blood is, how much carbon dioxide and oxygen it carries, and the concentrations of the key electrolytes. It runs on a tiny whole-blood sample drawn directly into a syringe or capillary, returns results in under two minutes, and lives at the bedside or in a stat lab rather than a central chemistry line, because in resuscitation the answer is needed now.

A presented sample sits on the Universal Inlet Port, where the Aspiration Probe draws a metered slug into the flow path. The Peristaltic Pump moves that slug, along with calibrants and wash fluids from the Reagent & Calibration System, across the Sensor Cartridge, a replaceable block of electrodes held at body temperature by the Thermostat Block. For oxygenation parameters that electrodes cannot give, the CO-Oximeter Module reads hemoglobin and its fractions optically, and the Control Electronics assembles everything into a report shown on the Display Panel.

How it works

The measurements are electrochemical. Each parameter has its own electrode in the Sensor Cartridge: a glass Glass pH Electrode develops a voltage that tracks pH, a Severinghaus pCO2 Electrode (Severinghaus) reads CO2 as a pH shift behind a gas-permeable membrane, and a Clark-style pO2 Electrode (Clark) reduces oxygen to produce a current proportional to its partial pressure. The electrolyte channels use ion-selective membranes, all read against a single stable Reference Electrode. Because gas solubility and electrode response both shift with temperature, the cartridge is clamped to 37 °C so results reflect conditions inside the patient.

Accuracy depends on relentless calibration. Between samples the Reagent & Calibration System flushes tonometered buffers of known pH and gas content across the same electrodes, and the controller re-zeros and re-slopes each channel so slow membrane drift never reaches the result. The CO-oximeter works differently: it hemolyzes a sub-sample and measures absorbance across several wavelengths, separating oxygenated, deoxygenated, carboxy- and met-hemoglobin by their distinct spectra. Spent fluid is pushed to waste, the probe is rinsed to prevent carryover, and the analyzer reports its self-check status before accepting the next patient sample.