A gas analyzer has a test chamber for a gas sample, an inlet for the gas sample and a gas sensor sensitive to gas movement, for determining the concentration of a constituent gas in the gas sample. The inlet is adapted to be connected to an inspiration line of a respirator. A shield is arranged so it covers the inlet of the test chamber, causing the gas sample to remain relatively still inside the test chamber during the analysis, regardless of the main flow of the gas to be analyzed. The gas analyzer can accordingly be devised for direct connection to the gas to be analyzed.