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Study Objective: A number of studies have shown that expired CO2 concentration is closely related to cardiac output, but that cardiac output was not controlled as an independent variable. In addition, the partial pressure of end-tidal CO2 (PETCO2) during extremely low cardiac output has not been reported. The objective of the present study was to measure PETCO2 during well-controlled, very low blood flow rates under conditions of constant minute ventilation., Design: Ten anesthetized, intubated, and mechanically ventilated swine (weight, 43 to 102 kg) were placed on two ventricular assist devices in order to control cardiac output. Minute ventilation was measured and kept constant. Ventricular assist device output (measured with an ultrasonic flow probe); PETCO2; and aortic, pulmonary artery, and central venous pressures were recorded continuously., Interventions: After electrical induction of ventricular fibrillation, pump output was decreased in steps., Measurements and Main Results: Cardiac index ranged from 0 to 5,371 mL/min/m2; 59% of PETCO2 measurements were made at cardiac indexes of less than 1,313 mL/min/m2 (30 mL/min/kg). The relationship of PETCO2 levels to cardiac index was determined with linear regression analysis; P < .05 was statistically significant. PETCO2 correlated significantly with cardiac index (P < .0001). The best-fit line by least-squares analysis produced the equation: PETCO2 = 4.98 + 0.012 [cardiac index] (r2 = .82)., Conclusion: Under conditions of constant minute ventilation, PETCO2 correlated closely with cardiac index over a large range of blood flow rates, including extremely low rates.

Current standards for ventilation during cardiopulmonary resuscitation are not supported by recent and ongoing investigation. This is particularly true in victims with an unprotected airway. Currently used flow rates and inspiratory times predispose to gastric insufflation and its complications. Potential changes and corrections that may benefit the victim of cardiac arrest are reviewed.

Current American Heart Association standards for ventilation during two-rescuer CPR recommend that a 0.8- to 1.2-L breath be delivered in 0.5 second after every fifth chest compression. Delivering a high-volume breath over a brief inspiratory time (TI) may lead to hypoventilation and gastric insufflation in victims with an unprotected airway. We reasoned that lengthening TI would lower peak inspiratory pressure and peak inspiratory flow rate, and thus improve lung inflation. To study this possibility, a mechanical model of the airway and upper gastrointestinal tract was designed. A ventilator delivering a sinusoidal wave form was used to simulate artificial ventilation. A 0.8-L breath was delivered at 0.5, 1.0, or 1.5 seconds at three lung compliances (CLs). Also, the effect of lengthening TI was studied with increased airway resistance. Lengthening TI improved lung inflation and decreased gastric insufflation at all CLs, but more so with normal CL than with decreased CL. This study demonstrates the need for evaluating alternative ventilatory patterns with longer TI during CPR.