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For both intubated and non-intubated patients, a capnography machine can provide a wealth of information about vital signs. In the life-or-death business of EMS, you need tools you can rely on. A capnography machine is a non-invasive measurement of exhaled carbon dioxide (CO2) displayed as a CO2 waveform concentration over time. In the 1980s, capnography machines became the standard of care in anesthesia in the United States and are now becoming the standard of care in EMS, emergency departments, and ICUs.
The capnography machine reflects metabolism and appears to be one of the earliest indicators of altered metabolic activity. Capnography machines are available for both spontaneously breathing patients and patients receiving positive pressure ventilation. For spontaneously breathing patients, exhaled CO2 can be measured using a nasal cannula-type device in which a cannula tip (and sometimes an additional collector located in the mouth) samples the breathing gas.
One of the most obvious uses of a capnography machine is cardiac arrest. The American Heart Association recommends the use of a continuous waveform capnography machine during any cardiac arrest for three reasons: to ensure the endotracheal tube remains in the trachea or other advanced airways in place; to assess the quality of CPR; to provide an early stage of ROSC index.
Monitoring CPR quality and detecting ROSC using a capnography machine should first be accomplished by connecting an EtCO2 monitoring device to a bag-valve-mask device. Once an advanced airway is placed, the additional purpose of the capnography machine is to ensure that the airway remains in place.
Resuscitation involves maximal patient movement and provides considerable opportunity for airway displacement. In fact, the level of patient movement seen in any patient transport inside or outside the hospital is sufficient to cause unrecognized airway displacement.
The utility of capnography machine in detecting ROSC has an additional purpose of monitoring perfusion and metabolism after cardiac arrest. Once ROSC is reached, capnography machine provides the earliest indicator of perfusion deterioration. The falling EtCO2 signals to the resuscitation team that the patient is recovering.
The capnography machine has an additional role of allowing the provider to control assisted ventilation. In post-arrest and head injury patients with suspected elevated intracranial pressure (ICP), controlled ventilation can significantly impact outcomes. For example, in patients with head injuries, sustained arterial CO2 levels of 50 mmHg or higher increase blood flow to the brain, thereby increasing ICP. Persistently low CO2 levels of 30 or lower also worsened neurological outcomes. Since EtCO2 reflects arterial CO2 in patients with reasonable perfusion, capnography machine is a valuable tool for avoiding accidental hyperventilation or hypoventilation.
