Erroneous Pressure Reading from an Unpowered Intra-aortic Balloon Pump: Case Report : ASAIO Journal

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Erroneous Pressure Reading from an Unpowered Intra-aortic Balloon Pump: Case Report

Belway, Dean*; Corrigan, Andrea*; Manchuk, Derek; Bittira, Bindu

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doi: 10.1097/MAT.0000000000001695
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Abstract

Intra-aortic balloon (IAB) counterpulsation is an established treatment modality for patients with acute cardiac failure. Hemodynamic support with an intra-aortic balloon pump (IABP) can improve survival and aid recovery in select high-risk patients.1,2 Advances in IABP technology have simplified use and reliability. Although clinical complications may often occur, reports of equipment malfunctions are relatively rare. Nevertheless, electromechanical malfunction is a risk with potentially devastating consequences. We present a case of an unanticipated pressure output signal from a powered off Cardiosave IABP console resulting in an erroneous mean arterial blood pressure (MAP) waveform being displayed during cardiopulmonary bypass (CPB).

Case Report

A 48 year old patient with acute valvular regurgitation secondary to infective endocarditis had an IABP inserted in the catheterization laboratory for hemodynamic support and was referred for double valve surgery. Subsequently, while awaiting surgery, the pressure waveform from the IAB's central lumen was lost, likely because of clot formation. The patient’s radial arterial pressure was then directly transduced to the IABP console. This configuration was maintained in the operating room (OR), such that the patient’s radial arterial pressure waveform was displayed on the IABP console and also slaved back to the external anesthetic monitor. The IABP was set to “Auto Operation Mode,” the pressure source setting on the IABP was set to “Direct,” both monitors were rezeroed, and a good quality, equivalent arterial pressure waveform was noted on both the external monitor and IABP console. Pulsatile arterial blood pressure was continuously displayed until initiation of CPB. After full flow was reached, the IABP was placed on standby, resulting in a loss of pulsatile pressure but MAP displayed. An aortic cross-clamp was placed, the heart arrested, and the IABP was then powered off. At this time, a MAP of 63 was displayed on the external anesthesia monitor. The surgery proceeded for approximately 83 minutes. When a request was made to lower extracorporeal flow, it was observed that there was no change in displayed MAP. It was then recognized that the displayed MAP was an erroneous reading; the IABP console was repowered, pressure zeroed, and factual invasive arterial blood pressure (BP) monitoring resumed. Surgery was then completed. The patient suffered no adverse effects and made a full recovery.

The patient provided written informed consent for publication and IREB approval was not required.

Discussion

An IABP is an electromechanical system used to increase cardiac output and augment coronary perfusion.3 The use of an IABP requires synchronization to the cardiac cycle, most commonly via the patient’s ECG or systolic upstroke of the arterial BP. Loss of trigger source occasions an alarm message along with an audio tone to prompt corrective action.

Valvular heart surgery requires the use of CPB. CPB diverts blood from the surgical field while providing continuous systemic blood flow, the adequacy of which is assessed by monitoring MAP and other physiologic variables. The patient’s heart is arrested and pulsatility is lost until removal of the aortic cross clamp and return of native cardiac function.

The Cardiosave Hybrid is the latest model IABP commercially available from Maquet in Canada. Our institution recently upgraded from the CS100 to the Cardiosave. In addition to the traditional ability to accept an arterial pressure input from an external monitor, the Cardiosave can also provide a low level pressure output to an external monitor via an electric signal from the IAB Sensor module to the physiologic pressure transducer input of the external monitor (Figure 1). A low level interface cable with a 9 pin circular plug is connected to the Low Level BP Output jack on the rear panel of the console and to the 12 pin input of the bedside or anesthetic monitor (Low Level Output Cable – Interface to Philips monitor 0012-00-1589-03) (Figure 2). This ability to provide a pressure output signal to an external bedside monitor was not available on the CS100.

F1
Figure 1.:
The rear panels of A) the CS-100 and B) the Cardiosave IABP consoles are shown for comparison purposes. The arrow indicates the low level BP Output jack of the Cardiosave IABP console for providing a pressure output signal to an external monitor. IABP, intra-aortic balloon pump.
F2
Figure 2.:
Low level interface cable with a 9 pin circular plug for connection to the low Level BP Output jack on the rear panel of the IABP console and to the 12 pin input of the external monitor (Low Level Output Cable – Interface to Philips monitor 0012-00-1589-03). IABP, intra-aortic balloon pump.

The use of an IABP in the OR requires care to avoid loss of trigger when electrosurgical unit (ESU) is used. Although the IABP has built in ESU interference suppression, some ESU noise may interfere with the ECG signal.4 When placed in Auto Operation Mode, the IABP will automatically select Pressure as the trigger source when ESU interference is detected. Therefore, it is common to select Auto Operation Mode so that counterpulsation will not be interrupted with cautery use. In the specific setting of CPB, all trigger sources are lost for the period of aortic cross clamping. Although the IABP does have an Internal Trigger Mode that can be used to provide pulsatility during CPB, this is not a standard practice. At our institution, on initiation of CPB the IABP is commonly placed in standby. Likewise, while alarms can be disabled during the period of aortic cross clamping and re-enabled after resumption of native ECG activity, this is not the practice at our institution. We power off the IABP console during CPB to avoid nuisance audio alarms because of loss of trigger and prolonged time in standby. Then on resumption of native cardiac activity we power on the IABP console, rezero pressures, and resume counterpulsation, if indicated.

The low level pressure output of the Cardiosave is designed to emulate that of a typical Arterial Pressure Transducer.5 The signal is provided from an Analog to Digital Signal Converter on the Front End Board at a standard sensitivity of 5 µV/V/mmHg excitation.5 The voltage for this converter is provided by the transducer itself. While the Cardiosave is powered on and operating this system is constantly sampling and providing the signal for output to the bedside monitor. When the Cardiosave is powered off, the excitation voltage from the transducer is still present but the Cardiosave is no longer sampling. The last signal received while the Cardiosave was sampling will be present at the low level output until the power from the transducer is removed. Consequently, the external monitor will continue to display this signal, both as a continuous waveform and numeric, which can be misinterpreted as the patient MAP. To our knowledge this has never previously been described.

We were able to reproduce this finding on every one of our Cardiosave consoles across different ORs and different external monitors. Each time the Cardiosave was powered off, the last MAP reading to be displayed on the external monitor continued to be displayed (Figures 3–5). We noted that this signal persisted until the interface cable was disengaged from the external monitor or IABP console. This is an unexpected finding. Clinicians presume that a powered off electromechanical device will stop transmitting a signal.

F3
Figure 3.:
Pulsatile arterial pressure waveform typical of IABP-assisted diastolic augmentation is seen. IABP, intra-aortic balloon pump.
F4
Figure 4.:
After the Cardiosave IABP is powered off a nonpulsatile arterial pressure waveform continues to be displayed on the external monitor. IABP, intra-aortic balloon pump.
F5
Figure 5.:
The last signal received while the Cardiosave IABP was sampling, displayed as a nonpulsatile arterial pressure waveform with numeric MAP, persists on the external monitor even after loss of the ECG. This signal continues until the interface cable is disengaged from the external monitor or from the IABP console. IABP, intra-aortic balloon pump; MAP, mean arterial blood pressure.

The unique clinical scenarios surrounding the present case contributed to our suspicions of an equipment malfunction. Preoperatively, the loss of IABP central lumenal pressure resulted in the availability of only one invasive arterial line. Intraoperatively, with the lack of coronary artery bypass grafting, there was no requirement for manipulation of extracorporeal flows that might otherwise have earlier alerted us to the problem of a false MAP. Additionally, other routine measures of adequate perfusion, including cerebral oximetry, venous saturation and lactate, remained normal throughout the period of aortic cross clamping and the CPB run, consistent with the displayed MAP value. The absence of any fluctuations from the displayed MAP value of 63 mmHg, as would be expected during a CPB run, alerted us to a potential error in MAP display averting potentially patient harm. Nevertheless, the presence of an unanticipated continuous low level pressure output signal at the low level BP Output jack on the rear panel of the Cardiosave console after the console has been powered off has important implications that, if unrecognized, could result in serious patient injury.

These findings have prompted us to ensure that all patients with an IABP brought to the OR for surgery have at least two arterial lines, one of which is not off the IABP. Moreover, our policies have been revised to recommend that the IABP console be powered off once at CPB full flow rather than after aortic cross clamping to allow observation of changes in MAP associated with manipulation of extracorporeal flows. Finally, operators have been reminded to transduce to a working external monitor or to disconnect the pressure transducer cable from the Cardiosave or external monitor to remove the voltage from the system if powering off the Cardiosave during CPB.

In summary, we describe a case of unanticipated pressure output signal from a powered off Cardiosave IABP console that resulted in an erroneous arterial pressure display throughout double valve surgery. As a result of this event, our policies have been revised to ensure that all patients with an IABP brought to the OR for surgery have at least two arterial lines, one of which is not off the IABP. Despite the relative infrequency of reports of electromechanical failure involving IABP technology, electromechanical malfunction remains a risk with potentially devastating consequences.

Acknowledgments

The authors gratefully acknowledge Irma Saulova, BSc, MLIS, DPA, for her assistance in searching the literature.

References

1. Pilarczyk K, Boening A, Jakob H, et al.: Preoperative intra-aortic counterpulsation in high-risk patients undergoing cardiac surgery: a meta-analysis of randomized controlled trials†. Eur J Cardiothorac Surg. 49: 5–17, 2016.
2. Gatti G, Morra L, Castaldi G, et al.: Preoperative intra-aortic counterpulsation in cardiac surgery: insights from a retrospective series of 588 consecutive high-risk patients. J Cardiothorac Vasc Anesth. 32: 2077–2086, 2018.
3. Dudzinsk JE, Gnall E, Kowey PR: A Review of percutaneous mechanical support devices and strategies. Rev Cardiovasc Med. 19: 21–26, 2018.
4. Datascope.Corp. Maquet. CS300 Operating Instructions, Datascope Corp 2005 p. 8–3, 0070-10-0654-01.
5. Getinge Group Corp. Cardiosave Hybrid Operating Instructions, English | 0070-00-0638-01, 2015, Maquet Getinge Group, Mahwah, NJ.
Keywords:

case report; equipment malfunctions; intra-aortic balloon pump

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