We present a case of delayed tracheal extubation after cardiac surgery due to ventilator auto-triggering caused by cardiogenic oscillations. We did not recognize the auto-triggering during the first SBT because there were a few spontaneous inspiratory efforts due to relative deep sedation; hence, the cardiogenic oscillation-triggered breaths simply looked like shallow, fast breathing. However, during the second SBT, we were able to notice that his HR and RR were the same by carefully observing his vital signs; at that point, we suspected ventilator auto-triggering caused by cardiogenic oscillations. We could definitively diagnose auto-triggering by changing the trigger setting from flow-trigger to pressure-trigger. Clinicians should consider the possibility of auto-triggering caused by cardiogenic oscillations when performing a SBT before the appearance of sufficient spontaneous breathing.
Patient-ventilator dyssynchrony including auto-triggering, which is caused by circuit leaks, water condensation in the circuit, or cardiogenic oscillations, is reported to occur in 26-82% patients [2]. Cardiogenic auto-triggering tends to occur in patients with brain death and those who have just undergone cardiac surgery [3, 4]. Patients with brain death tends to have hyperdynamic cardiovascular state [5], which may cause cardiogenic ventilator auto-triggering. Indeed, auto-triggering is reported to occur more often in patients with hyperdynamic cardiovascular state after cardiac surgery [4]. If not detected, this phenomenon can cause prolonged duration of mechanical ventilation, prolonged ICU and hospital stays, and higher ICU and hospital mortality [6,7,8]. Thus, clinicians must be aware of this possibility, particularly in critically ill patients.
The mechanism of cardiogenic oscillation is not completely clear, but there are several possible contributory factors. Pulmonary artery pulsatility is reported to be the main cause of cardiogenic oscillations [9]. Additionally, changes in heart volume during systole and diastole may change intrathoracic pressure, which may change airway pressure or cause compression and expansion of the lung [10]. Thus, enlargement of the heart may be associated with cardiogenic oscillation. In the present case, this patient’s postoperative cardiothoracic ratio (CTR) was 67%, indicating enlargement of heart. Indeed, cardiogenic oscillations are reported to occur in patients with larger CTR values [4].
Our PubMed search could not reveal any reports describing a relationship between cardiac oscillation and chronic constrictive pericarditis or radical pericardiectomy. However, hyperdynamic cardiovascular state after radical pericardiectomy may be associated with cardiac oscillation, because, as mentioned above, cardiac oscillation tends to occur in patients with hyperdynamic cardiovascular state [4]. Indeed, this patient’s cardiac output after surgery was more than 4.2 L/min.
One way to terminate false triggering is to change ventilator settings from the very sensitive “flow trigger” mechanism to the less sensitive “pressure trigger” mechanism [11]. In the present case, we could definitively diagnose auto-triggering by changing from the flow-trigger to the pressure-trigger setting. On the other hand, clinicians have to be careful for mistriggering, which can cause prolonged duration of mechanical ventilation, when using pressure trigger. Thus, clinicians have to select which triggering setting to use according to the patient’s situation.