What is Capnography anesthesia point of view

Capnograph capnography anesthesia
Simple understanding capnograph for anesthesia residents

1. What is Capnography ? Capnography is the non-invasive real-time measurement, during inspiration and expiration, of the partial pressure of CO₂ from the airway. It provides continuous physiological information on ventilation, perfusion, and metabolism vital to proper airway management[1]. This enables the identification of adverse events[2] such as airway obstruction, hyperventilation (rapid or deep breathing), hypoventilation (slow or shallow breathing) or apnoea (temporary cessation of breathing).

2. Indications and Applications of Capnography Capnography is considered the gold standard measurement for respiratory rate monitoring[8] and it has a range of other clinical applications including monitoring metabolism and circulation[9]. A Guideline published in May 2021 by the Association of Anaesthetists states that waveform capnography should be used for monitoring the airway during anaesthesia , wherever anaesthesia takes place and until a patient has fully recovered from anaesthesia .

3. indications for capnography include: evaluation of maximum exhaled CO2 concentration as a reflection of the PaCO2 evaluation of the severity of pulmonary disease monitoring the integrity of the ventilator circuit and artificial airway monitoring the adequacy of pulmonary blood flow confirming tracheal rather than esophageal intubation Detect bronchospasm or other lung pathology Monitor rebreathing of carbon dioxide Signal alterations in metabolic status such as malignant hyperthermia

4. Types of Capnography : Sidestream – often used in non-intubated patients during procedural sedation, emergency transport and post-operative wake up (i.e. outside the OR) Microstream – a variation of sidestream capnography used for intubated and non-intubated patients, providing more accurate EtCO ₂ measurements[16]. Mainstream – used mainly in the operating room (OR) with intubated patients

5. Normal Capnography Phase I (inspiratory baseline) reflects inspired air, which is normally devoid of CO2. Phase II (expiratory upstroke) is the transition between dead space to alveolar gas. Phase III is the alveolar plateau. Traditionally, PCO2 of the last alveolar gas sampled at the airway opening is called the EtCO2. (normally 35-45 mmHg) Phase 0 is the inspiratory downstroke , the beginning of the next inspiration

6. Normal Capnography

7. An elderly gentleman with a history of COPD, CAD & CKD gets rushed into the trauma bay with respiratory distress and altered mental status. You gave him a trial of BiPAP for a few minutes without improvement. 1- You swiftly tubed the patient. It was not the easiest view, but you advance the ETT hoping for the best. Upon attaching the Bag Valve Mask to bag the patient, you saw this on capnography : the ETT is in the esophagus, as evidenced by the low-level EtCO2 that quickly tapers off.

8. 2. You remove the ETT, bag the patient up, and try again with a bougie . Afterward, you see… This suggests a problem with ETT position, most often in the right main bronchus. Notice the irregular plateau--the initial right lung ventilation, followed by CO2 escaping from the left lung. Beware that capnography can sometimes still appear normal despite the right main bronchus placement.

9. 3. You pull back the ETT a few cm and the CXR now confirms the tip is now above the carina. The patient’s capnography now looks like this: Almost looks normal but notice the “shark fin” appearance, this is due to delayed exhalation, often seen in airway obstruction and bronchospasms such as COPD or asthma exacerbation.

10. 4. You suction the patient and administer several bronchodilator nebs. The waveform now looks more normal:

11. 5. However, just as you were about to get back to the workstation to call the ICU, the monitor alarms and you see this: Noticing the ETT still in place with good chest rise, you quickly check for a pulse. There is none.

12. 6. You holler, push the code button and start ACLS with a team of clinicians. With CPR in progress, you notice this capnography : Initially, your patient’s EtCO2 was only 7, after coaching the compressor and improving CPR techniques, it increased to 14. You are also aware that EtCO2 at 20min of CPR has prognostic values. EtCO2 <10 mmHg at 20 minutes suggests little chance of achieving Return of spontaneous circulation ( ROSC ) and can be used as an adjunctive data point in the decision to terminate resuscitation.

13. 7. Fortunate for your patient, during the 3rd round of ACLS, you notice the following: This sudden jump in EtCO2 suggests ROSC. You stop the CPR and confirm that the patient indeed has a pulse.

14. 8. As you are putting in orders for post-resuscitation care, you notice this: This curare cleft comes from the patient inhaling in between ventilator-delivered breaths and is usually a sign of asynchronous breathing. However, in the post-arrest scenario, it is a positive prognostic sign as your patient is breathing spontaneously.

15. Noticing the low respiratory rate and high EtCO2 value, you recognize this is hypoventilation. The waveform reveals a high respiratory rate and relatively low EtCO2. you recognize this is hyperventilation .