Practical considerations for the use of a pulmonary artery thermistor catheter

The use of a pulmonary artery thermistor catheter for pressure measurement and thermodilution cardiac output determination was evaluated in 11 dogs. Pulmonary artery wedge pressure was a reliable index of left atrial pressure at end-expiratory pressures less than 10 cm. H2O. Fluctuations in pulmonary artery temperature occurred at a frequency equal to the respiratory rate and an amplitude of 0.010 to 0.086 degrees C. Changes in amplitude were associated with changes in ventilatory waveform, respiratory rate, and level of anesthesia. Intermittent and continuous positive-pressure ventilation generally dampened and reversed the pulmonary artery temperature pattern exhibited during spontaneous breathing. This suggested that when end expiration is used to time indicator injection, cardiac output will be underestimated during spontaneous breathing and overestimated during continuous or intermittent positive-pressure ventilation. When indicator was injected at the same point in the ventilatory cycle, successive values of cardiac output deviated from one another by 0.0 to 6.7 percent. Deviations as large as 14 percent resulted if sequential injections were out of phase by half a respiratory cycle. These deviations can be minimized by injecting indicator at the same point in the respiratory cycle, if it is not feasible to measure cardiac output during apnea. The clinical utility of a pulmonary artery thermistor catheter can be optimized through appreciation of its specific strengths and limitations.