Chest tubes are used routinely in the intensive care setting to clear blood and air from the mediastinal and pleural spaces after cardiac and thoracic surgery and trauma. Chest tube clogging can develop when shed blood comes in contact with the inside of drainage catheters, occurring in up to 36% of prospectively evaluated heart surgery patients [2, 15]. Chest tube stripping, milking and open suction have been utilized in an attempt to prevent chest tube clogging, but its safety and efficacy are not shown when reviewed in meta-analysis of randomized trials [8]. In particular, a major issue for chest tube stripping and milking is the potential for the high negative pressures generated to injure the heart or great vessels, further exacerbating bleeding. Thus alternatives are needed to allow protocols to be implemented to prevent chest tube clogging. ATC was developed as a low risk alternative to these approaches [9]. In preclinical studies ATC was more effective in evacuating blood, even when smaller diameter tubes were compared to larger diameter tubes [16, 17]. Clinically ATC is readily integrated into the operating room and ICU without disruption of the usual workflow [13].
To quantify the clinical sequelae of chest tube clogging, a composite clinical endpoint of retained blood interventions was proposed in prior publications [1, 3,4,5]. Retained blood as an endpoint is defined as any postoperative intervention to remove blood, blood clot or bloody fluid after cardiac surgery [4]. This includes taking a patient back to wash out mediastinal clot or hemothorax, inserting an additional chest tube in the ICU, thoracentesis or pericardial drainage for bloody effusions. Sirch, et al., previously demonstrated a 43% relative risk reduction in retained blood in an all comers population of cardiac surgery patients treated with ATC, and Maltais, et al., reported a 59% reduction in retained blood in a mechanical assist cohort of patients [5, 11]. Likewise in this study, we noted a 59% relative risk reduction in retained blood in matched patients.
The primary driver of the reduction in the retained blood composite endpoint were interventions to drain pleural effusion by thoracentesis. In this series over the course of 30 days, 22% of Phase 0 patients required at least one pleural intervention which was reduced to 8.1% in patients in Phase 2. The majority of early pleural effusions are known to be bloody and inflammatory after cardiac surgery [18, 19]. By minimizing retained blood in the pericardium and pleural spaces there could be less of an inflammatory process driving fluid exudation from the inflamed mesothelium during recovery [4]. Although there was a trend toward reduced take back for re-exploration for bleeding for washout of mediastinal clot the sample sizes was too small for statistical comparison [20].
In this study, as also seen by Sirch, et al., the volume of bleeding (measured as chest tube output) was significantly less in Phase 2 patients at 24 h and in total [5]. While this may seem counter intuitive, it suggest there may be an advantage of more rapidly clearing shed mediastinal blood to prevent on going microvascular bleeding from the cut surfaces in the early hours after surgery. Tissue plasminogen activator (t-PA) is known to significantly accumulate in shed mediastinal blood, which can promote on going microvascular bleeding within the postsurgical space if not promptly evacuated by chest tubes [21]. Therefore perhaps having shed mediastinal blood more effectively evacuated could leave less t-PA remaining in contact with these tissues, facilitating a more rapid achievement of microvascular hemostasis in this time period.
Retained blood is recognized as an important trigger for POAF in susceptible individuals after heart surgery [22,23,24]. Blood not evacuated from the pericardial space coagulates, generating thrombin that recruits neutrophils which promote a localized inflammatory response on the surface of the atrium that is highly pro-oxidant and inflammatory [6]. In patients who have susceptible atrial substrate this oxidative response can trigger POAF [23]. In the present study, there was a 32.4% reduction in POAF. This is consistent with the studies by Sirch, where patients treated with ATC had a 30% reduction in POAF, and St. Onge, where there was a 34% reduction in POAF [5, 12]. This could have a significant impact on hospital resource utilization, as POAF is known to significantly increase hospital costs [25].
AKI is a well-recognized complication of cardiac surgery in the postoperative period [14]. In this study, patients with ATC had lower postoperative creatinine levels as well as a significant reduction in the need for postoperative dialysis. The calculated KDIGO stage I AKI rate was 30% during Phase 0, controls, dropping to 17% in Phase 2 (P = 0.0014). There was a trend towards a reduction in KDIGO stage II and III AKI, but the sample sizes were too small for this analysis. This study was not designed to specifically study these endpoints or the mechanism by which this may occur. However, several mechanisms can be considered such as a reduction in hypotension from tamponade or hypoxia from effusions might put less stress on the kidneys during recovery. Additionally, perhaps if there is less retained blood there is less reabsorption of oxidized products of which are known to contribute to AKI [26]. AKI imposes a sizable financial burden for hospitals and thus reducing this outcome could contribute to a reduction of overall hospital costs [27]. Further studies are indicated to more specifically evaluate this endpoint and the possible mechanisms of how ATC might be an additional adjunct to help minimize AKI after heart surgery.
Patients with ATC had a reduction in hospital resource utilization including a reduction in ICU hours, ICU stays of over 3 days, and reduced incidence of prolonged intubation (defined as > 24 h). There was a statistically significant reduction in infections, primarily driven by a reduction in pneumonia and sepsis. Patients in Phase 2 had a 1 day reduced total and hospital postoperative length of stay, again, which could have significant hospital resource use implications (measured in costs, not charges) [5, 12]. This suggests that ATC is economically justifiable for hospitals, even after including the costs of acquiring the technology. In the United States, ATC costs approximately $395 per unit, and in this study it was implemented as a preventative measure in all patients. Our program performs 700 cardiac cases on a yearly basis. Assuming that 700 cases a year utilizing 1.2 ATC per case, the yearly costs to implement ATC is $331,800. A median net savings of $1831 per patient over 700 patients would result in a net recuperation of $1,281,700 per year for the hospital. A mean net savings of $2696 per patient over 700 patients would result in a net recuperation of $1,887,200 per year for the hospital. Both of these sums provide a considerable margin for cost effectiveness from a hospital purchasing perspective. This important administrative consideration is crucial in the current healthcare environment which endeavors to increase healthcare value by reducing complications and costs [28, 29].
There are several limitations to this study. First, data were generated from a nonrandomized, prospectively collected observational cardiac surgical database supplemented by retrospective chart reviews. These cases, however, represented a 100% census of all cardiac surgical procedures occurring during the duration of this study, which could have limited the potential for selection bias. Second, the endpoint of retained blood relies on the analysis of patients who had interventions performed, rather than by direct imaging for retained blood. This has the disadvantage of being more dependent on the subjective decision of the operating surgeon to intervene to evacuate retained blood. On the other hand, this strictly represents the experience of only two operating surgeons who have internally consistent practice patterns. Imaging may be more likely to include retained blood of uncertain clinical significance, while relying on the definition that requires specific invasive intervention for retained blood may represent a more clinically meaningful endpoint with quality improvement ramifications. Finally, although we implemented an ATC protocol for all patients undergoing cardiac surgery in our program, it is important to note that sub populations of patients such as those having CABG only, on pump vs off pump CABG, valve surgery, reoperations and more complex combined procedures have different risks and patterns of postoperative bleeding and thus may have differing clinical responses to such a clinical protocol. Further studies are needed that are statistically powered to examine these different cardiac surgery populations so that the outcomes with this approach can be better defined and protocols more specifically developed to best serve these patients.