Volumetric Capnography – A Brief HistoryVolumetric Capnography – A Brief HistoryMichael B. Jaffe PhD, Philips-Respironics, Wallingford, CTMichael B. Jaffe PhD, Philips-Respironics, Wallingford, CT

One of the earliest infrared measurements of CO2 in the expired human breath was reported by John Tyndall in 1865. However, it took another century before these measurements reached the bedside. Similarly, some of the earliest measurements of vital capacity by John Hutchinson reported in 1846 preceded the development of devices which permitted convenient measurement of flow (and hence volume) by over 75 years. The importance of measuring volume with carbon dioxide has long been recognized by physiologists and clinicians. Early methods such as the Haldane method and its various derivatives, used chemical absorbents, and served as the reference method for a volumetric measure of CO2 for many years. Various investigators sought to extend these discrete chemical absorption-based methods to “continuous” analysis (e.g. Rein (1933) [1]). One of the earliest descriptions of the volumetric capnogram and a method to determine “airway” dead-space is that of Aitken and Clark-Kennedy (1928) [2] . Fowler (1948)[3] in describing the single breath test for nitrogen (SBT-N2) curve sought to use uniform terminology to clarify the “meaning of dead-space”, and, thus, divided this curve into four phases: I, II, III, and IV. Different methods to sample “alveolar” CO2 gas were developed, including single and multiple breath methods. Elam (1955), using newly developed CO2 gas monitors, was first to publish capnographic profiles of human respiration in the anesthesiology literature [4]. It was not until Fletcher (1980) [5] presented the concepts of dead-space and CO2 elimination in a unified framework known as the single breath CO2 curve that this approach began to gain clinical recognition. In 1976 the Model 930 CO2 analyzer (for use with the 900 Servoventilators) offered the first commercial volumetric capnograph, featuring mainstream CO2 and ventilator derived flow.In the early 1990’s the first efforts to integrate CO2 and flow from the airway manifested with the introduction of the on-airway D-lite sensor (Instrumentarium, Helsinki, Finland) combining in a single adapter piece a flow-restrictor element for flow and a port to allow sidestream gas sampling. The sidestream approach requires sophisticated computer algorithms to align and compensate the flow and CO2 signals [6]. The mid-1990s saw the introduction of the first “all-mainstream” devices for on-airway volumetric capnography (Novametrix, Wallingford,CT)[7]. These devices evolved from separate flow and CO2 sensors connected to separate devices (e.g., Ventrak 1550/Capnogard) and became integrated CO2/flow-airway adapters interfaced to the same host system (e.g. CO2SMO+, NICO). The development of this family of flow/CO2 adapters (neonatal, pediatric and adult) required a number of key technological developments such as a novel thick-film IR source, a robust, fixed orifice flow sensor, and extremely sensitive low-cost differential pressure sensors[8]. With the increased recognition of the clinical value of volumetric capnography, it will likely evolve to become the standard of care for all mechanically ventilated patients.

1. Arch f. exp. Path. U. Pharml. 1933; 171: 363.2. J. Physiol. 1928; 65: 389–411.3. Am. J. Physiol. 1948; 154: 405-416.4. Anesthesiology 1955; 16: 876–885.5. Fletcher, R. Thesis. Lund, Sweden, 1980.6. J Clin Monit. 1993; 9(5):374-80.7. Anesth. Analg., 2008, 107: 890–904.8.IEEE Eng Med Biol Mag. 2010 ;29:44-52.9.Haldane, J.S. (1912). Methods of Air Analysis. London: Griffin.10.Tyndall J. Heat - A mode of motion. 6th ed. New York. D. Appleton and Company, 1890.11.Tyndall, J. On Radiation. The "Rede" Lecture, delivered May 16, 1865.

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8/11/11 MBJ

Mainstream CO2 and ventilator derived flow Model 930 CO2 analyzer (for use with the 900 Servoventilators); the first commercial volumetric capnograph (Siemens-Elema)

Method of deducing the alveolar CO2 curve and the dead space from the experimental CO2 curve . The flat part BC of the experimental curve OABC is prolonged to the left to D until the area FDCG equals the area OABCG, DF and CG being perpendicular to OG. OF then represents the volume of the dead space. DC is prolonged to the right to E, over a distance equal to OF (when measured horizontally). The whole line DE then represents the changing concentration of alveolar CO2 throughout expiration. (Aiken and Clark-Kennedy, 1928) (2)

Simultaneous carbon dioxide and flow curve showing criteria for reading alveolar concentration of carbon dioxide from recorded plateau (from Elam JA 1955) (4)

Geometric representation of Bohr's formula applied to an expiration (Fowler, 1948) (3)

Used uniform terminology to divided SBN2 curve into four phases: I, II, III, and IV and proposed method for determination of airway deadspace.

A single adapter piece a flow-restrictor element for flow and a port to allow sidestream gas sampling. This sidestream approach requires sophisticated computer algorithms to align and compensate the flow and CO2 signals [6].

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Combined mainstream CO2/flow sensors (left to right) neonatal, adult and pediatric (Respironics).

The three phases of SBT-CO2. Phase I is the CO2 free part of the breath, the ineffective tidal volume. At the start of phase II, CO2 appears and the effective volume start. Phases II and III together are the effective tidal volume, VTeff. Relative slope of phase III can be measured between 0.2 and 0.4 l effective volume. (Fletcher, 1980) (5)

Ventrak (1994) CO2SMO Plus! (1996) NICO(1998)

Chemical absorption -reduction of the gas volume was measured and indicated the quantity of the gas absorbed. (Haldane, 1912) (9)

Tyndall's experimental apparatus, shown here consisted of a long tube that he filled with various gases. (Tyndall 1865) (10,11)

Pre-1920

Novametrix/Respironics