| Popis: |
Study objective: To further define the relationship between cardiac output (CO) and end-tidal carbon dioxide tension (ETCO 2 ) at various levels of systemic flow. Design: Prospective, controlled laboratory investigation. Setting: Animal laboratory. Type of participants: Fourteen anesthetized, intubated sheep weighing 23 to 47 kg. Interventions: One hundred seventy-two simultaneous measurements of thermodilution CO and ETCO 2 were made during controlled arterial hemorrhage. After a 30-minute baseline control period, CO was sampled from approximately 0.6 to more than 8.0 L/min during a 60- to 90-minute period of controlled hemorrhage. Measurements: Thermodilution CO; arterial pressure using fluid-filled plastic 14-gauge catheters; ETCO 2 using an infrared analyzer. Main results: A plot of CO versus ETCO 2 suggested that the relationship was logarithmic rather than linear. Linear regression showed that ETCO 2 was significantly related (r = .91; P Conclusions: The relationship between CO and ETCO 2 is logarithmic. Decreased presentation of CO 2 to the lungs is the major, rate-limiting determinant of the ETCO 2 during low flow. As the CO increases during resuscitation from shock or cardiac arrest, respiration becomes the rate-limiting controller of the ETCO 2 (after the tissue washout of CO 2 has occured). Under such conditions, the ETCO 2 provides useful information about the adequacy of ventilation provided that there is little ventilation/perfusion mismatch. |
