Background: Previous studies have shown "beat-to-beat" variation in systemic BP with highfrequency jet ventilation (HFJV). However, it is not clear if such changes are paralleled by changes in cardiac output.
Objective: To characterize the effect of HFJV near or equal to the heart rate (HR) on beat-to-beat cardiac output in an adult human subject with ARDS.
Design: Case study.
Setting: ICU, university teaching hospital.
Patients: One patient with end-stage liver disease complicated by sepsis, severe pancreatitis, ARDS, and multisystem organ failure.
Methods: The patient was intubated, sedated, paralyzed, and ventilated with controlled mechanical ventilation (CMV). Ventilatory mode was then switched to HFJV at fixed frequencies (f) near but not equal to the HR (f=100, 110, and 120 beats/min; HR=108/min). HFJV was then synchronized to the ECG such that f and HR were equal. Continuous cardiac output (COc) was monitored during change of ventilator mode from CMV to fixed-rate HFJV to synchronized HFJV, then followed through progressive delays in jet triggering within the cardiac cycle during the synchronous HFJV mode. COc was monitored by arterial pulse-contour analysis, allowing assessment of beat-to-beat changes in cardiac output.
Measurements and main results: A cyclic variation in COc equal to the beat frequency difference between f and HR was observed (harmonic interaction) during fixed-rate HFJV. This COc oscillation was abolished during synchronous HFJV. COc was significantly greater during systolic synchronous HFJV as compared to diastolic synchronous HFJV or fixed-rate HFJV (10.1 to 9.0 [p<0.05] and to 8.6 [p<0.05] L/min, systolic synchronous to diastolic synchronous and to fixed-rate HFJV, respectively).
Conclusions: This study demonstrates instantaneous variations in cardiac output in a human subject with fixed rates of HFJV near to the HR in humans. These variations are abolished by synchronous HFJV but cardiac output was dependent on the timing of the HFJV inspiration in relation to the cardiac cycle. COc is a potentially valuable method to monitor sudden changes in cardiac output and facilitate attempts to maximize cardiac output during synchronized HFJV.