Mechanical circulatory support in cardiogenic shock due to drug intoxication may rely on the use of IABP, CPB, or ECMO.
15.4.1 Aortic Counterpulsation
IABP is the most currently used form of mechanical support to circulation. The alternated infl ation and defl ation of the balloon, synchronized with the cardiac cycle, improve peak diastolic pressure and coronary blood fl ow while reducing end- systolic pressure, afterload, and myocardial oxygen consumption. It is the least
expensive form of mechanical circulatory support and it is easy and fast to deploy.
It has been used alone to treat cardiotoxic poisonings induced by quinidine [ 15 ], propranolol [ 16 ], dextropropoxyphene [ 17 ], antihistamine [ 18 ], and a combination of verapamil and atenolol [ 19 ]. It has also been used in combination with ECLS in the case of organophosphate poisoning [ 20 ].
In this context, however, IABP shows some important limitations: in the fi rst place, it requires some residual cardiac function to be effective and is totally inef- fective when systolic arterial pressure is less than 40 mmHg or during a cardiac arrest. Another drawback is the impossibility of providing oxygenation, which might be needed in severe poisonings impairing the respiratory function.
15.4.2 Cardiopulmonary Bypass via Central Cannulation
CPB provides full circulatory support and oxygenation. It requires a full median sternotomy, so that a venous return cannula is inserted in the right atrium, while the arterial infl ow cannula is inserted in the ascending aorta. Sporadic experiences are reported in literature [ 21 , 22 ]: indeed, the strong limits to this technique are linked to its high invasiveness, the required setting of implantation (operatory room), and, therefore, the longer times required before ECLS can be provided. In case of cardiac arrest, it is not possible to deliver uninterrupted chest compressions before CPB is started. A prolonged assistance is inevitably associated with infective sequelae and higher rates of bleeding issues (a high anticoagulation regimen is required).
15.4.3 ECMO
Features and indications of ECMO support in the setting of refractory cardiogenic shock from drug intoxication do not differ from what has already been discussed in the previous chapters of this book. The possibilities of a complete cardiopulmonary support, a rapid deployment, and an implantation almost anywhere inside the hos- pital make ECMO the support of choice in the setting of refractory cardiogenic shock from drug intoxication. Peripheral cannulation through the femoral vessels allows continuation of chest compressions if the patient is in cardiac arrest.
Requirements in terms of anticoagulation are minor; if compared with CPB, the infective risk is smaller and postoperative pain is avoided.
Nonetheless, the rate of complications is all but negligible, rising exponentially with the duration of support. Knowing this, and remembering the outcomes reported without ECLS [ 4 ], we once again underline that ECMO support should be reserved to very sick patients in whom the risk of death overcomes the risk of ECMO-related complications. On the other hand, as we will see later in this chapter, if we examine the outcomes reported in literature for ECMO support in cardiogenic shock, we will fi nd that drug intoxication is one of the most favorable scenarios. Indeed, in this context the planned strategy for ECMO support is almost inevitably bridging to recovery.
The evidence on the subject relies mostly on isolated case reports and three case series. The fi rst reported case series by Babatasi et al. dates 2001 [ 23 ]: six patients with cardiac arrest following acute severe self-administration of an overdose of beta-blockers, calcium antagonists, or antiarrhythmics were supported on femoro- femoral venoarterial ECMO. The fi rst two patients died of multiorgan failure due to a delay in the installation of the assistance, while the remaining four patients sur- vived without sequelae.
In 2009, Daubin and colleagues published the largest case series to date [ 24 ]:
over a period of 10 years, out of 721 patients admitted for drug intoxication, 17 patients with refractory cardiogenic shock ( n = 10) or cardiac arrest ( n = 7) ful- fi lled the institution’s criteria for ECMO implantation. In all of them, cannula- tion was achieved through the groin vessels and assistance was venoarterial.
Thirteen patients survived and were discharged without signifi cant cardiovascu- lar or neurological sequelae. In 2012, Masson published the fi rst retrospective cohort analysis comparing survival among critically ill poisoned patients treated with or without ECLS [ 25 ]. Sixty-two patients with cardiogenic shock ( n = 42) or cardiac arrest ( n = 20) following poisoning from drug intoxications were admit- ted in two centers over a time span of 10 years: 14 were treated with ECLS and the remaining 48 with conventional therapies. Global survival was 56 % (35 patients): 86 % in the ECLS group and 48 % in the non-ECLS group ( p = 0.02).
Notably, none of the patients with persistent cardiac arrest survived with conven- tional therapy.
A recent review by De Lange et al. [ 26 ] extensively examined the literature on the subject: a total of 46 publications were found that dealt with ECMO support in drug poisoning. The authors concluded commenting that, in the absence of contra- indications, the organ support provided by ECMO makes it especially useful in patients with severe poisoning, as the clinical impact of the intoxication is often temporary; therefore, ECMO can be used as a “bridge to recovery” and is a good salvage therapy for patients who are severely poisoned with acute respiratory dis- tress syndrome (ARDS) or refractory circulatory shock.
The overall rate of complications (typically bleeding at the surgical entry site or intracranial hemorrhage) did not differ from reported complications for ECMO sup- port in general.
The heart being the most severely affected organ in this subset of patients, it is important to remember that, though supporting the circulation, ECMO may have detrimental effects on the left ventricle. In fact, in a not negligible proportion of cases, the combination of severely reduced left ventricular function, blood return to the left atrium via the bronchial circulation, and increased afterload from the arterial cannula result in a dangerous rise in left atrial and ventricular pressures and pulmo- nary congestion [ 27 ]. The increase in wall stress due to left ventricular distention decreases myocardial perfusion and increases oxygen consumption leading to isch- emia and reducing the likelihood of ventricular recovery [ 28 ]. In literature, a case of septal atriotomy to accomplish mechanical decompression of the left heart in patients with ECMO support for drug intoxication has already been described [ 24 ], but other methods are also available [ 29 ].
If the patient cannot be weaned from the ECMO support, the initial “bridge to recovery” strategy can turn into a “bridge to ventricular assist device (VAD)” or a
“bridge to transplantation” strategy.
To date, no cases of switch from ECMO to VAD in drug poisoning have been reported. Nonetheless, it is technically feasible to alter the ECMO circuit in order to turn it into a left VAD for a potential midterm support by means of a left thora- cotomy that allows the insertion of an outfl ow cannula in the apex of the left ven- tricle [ 29 ].
A case of ECMO as bridge to transplantation in a case of fl ecainide and betaxolol poisoning has been reported in 2010 [ 30 ].