The present review indicates that between 4-7% of SAH experience a CA. Among OHCA patients between 4-7% have an arrest related to SAH probably higher than in IHCA were the only study available reported only 0.5% of IHCAs are due to SAH. Patients with SAH and CA are commonly of female gender and younger than the average CA patients. Even though resuscitation attempts are initially successful and ROSC is achieved, survival is dismal following prolonged resuscitation attempts. Survival is possible in brief cardiac arrests only requiring defibrillation.
It is well known that some patients with SAH die due to sudden death [1
]. In a meta-analysis from 2002 the incidence of sudden death in patients with SAH was reported to be between 11-14% [1
]. This is higher than the reported rate of CA among hospital cohorts of SAH patients suggesting that a considerable proportion of SAH patients die outside of the hospital. How many of these undergo resuscitation attempts are difficult to determine since none of the studies included in the present review included autopsy data of patients terminated in the field and data of those resuscitated and admitted to the hospital. On the other hand, the practise in most Asian Emergency Medical Service systems seems to be that all patients found in OHCA are transported to the hospital with ongoing CPR [18
]. Therefore the prevalence of SAH in OHCA of 6-18% reported by Inamasu and Mitsuma may be representative of the SAH prevalence OHCA patients in Japan [4
]. These rates are higher than reported in Europe and may reflect the high incidence of SAH in Japan [14
Cardiac involvement ranging from benign ECG changes to cardiogenic shock and ventricular arrhythmias have been reported following SAH [19
]. Interestingly in the studies included in the present review PEA and asystole were the most frequently reported initial CA rhythms [4
]. This may because most SAH induced arrest is due the sudden rise of ICP resulting in respiratory arrest followed by hypoxia and asystole. It is also possible that some patients found in asystole may have initially have had VF. Several patients with an initial rhythm of VF were in fact included in the study by Toussaint and colleagues [3
]. It is probable that there is underreporting in the literature of successfully resuscitated SAH patients with VF as the initial rhythm.
Despite a high likelihood of ROSC few patients survive to be discharged from the hospital [4
]. Survival of SAH patients seems to be related to the duration of the cardiac arrest, which is not surprising since the latency to ROSC is an important predictor of outcome in CA patients overall [15
]. Few patients requiring prolonged resuscitation i.e. latency to ROSC longer than 20 minutes survive. Indeed most reported survivors have had their arrest in the hospital or in the ambulance. The outcome of patients with SAH who experience a cardiac arrest in the hospital is reported by Toussaint and colleagues and recently by Walmuller and colleagues [3
]. As previously discussed underreporting of outcomes of SAH patients experiencing cardiac arrest in the hospital is likely.
In most studies SAH patients that experienced a cardiac arrest had more a severe type of SAH with large bleeds and intraventricular clots. These patients were admitted deeply comatose with World Federation of Neurosurgical Surgeon (WFNS) grades of 4–5, a patient group that even without a secondary hit in form of a cardiac arrest with additional ishaemia, have a very high mortality [21
]. In one study 13% of SAH patients presenting with a WFNS grade of V had a favourable outcome at 6 months [21
]. It has been suggested, however, that the outcome of patients with poor grade SAH has improved during recent years [22
In studies included in this review neurosurgical care was mainly directed to patients with short delays to ROSC, likely because of poor clinical condition and lack of brain stem reflexes in those with a prolonged cardiac arrest [8
]. An important aspect is the possibility of organ donation in SAH patients who are declared brain dead or, in some countries as a part of non-heart beating organ donation programs [23
Very little can be said about the effect of ALS measures in patients with CA due to SAH. The use of adrenaline seems to be common. Adrenaline may cause hypertension after ROSC and this might even be harmful due to the high risk of rebleed in SAH patients. Firm conclusions abut these issues are difficult to make and very challenging if not impossible to study given the overall rarity of SAH causing CA and because diagnosing SAH in the pre-hospital setting.
The results of this review support the vigilant use of CT scanning in patients following OHCA [24
]. Especially, since headache is a common symptom prior to the arrest but it is not 100% sensitive, as shown in the study by Inamasu and colleagues where 50% of the OHCA patients with SAH did not have symptoms prior to the arrest [13
The present review has some limitations. Firstly, few of the included studies had been conducted according to the Utstein Guidelines hindering the comparison of results. Secondly, most studies originated from Japan and it may be debated how well these results are applicable to centres in other parts of the world. Thirdly, this review included 3 papers by Inamasu and colleagues originating from the same hospital and from partly overlapping time periods. It is therefore possible that the patient material is partly the same leading overrepresentation of their findings.