Intra-Arrest Arterial Blood Pressure and Return of Spontaneous Circulation in Out-of-Hospital Cardiac Arrest.

Background

Out-of-hospital cardiac arrest (OHCA) is a leading cause of prehospital mortality, with survival rates in the UK stubbornly remaining below 10%. Despite significant investment in public health measures like widespread CPR education and the increasing availability of automated external defibrillators (AEDs), the reality is that most patients do not survive to hospital discharge. For those patients who do get CPR and/or AED use by the public and are still in arrest by the time of the ambulance services, we are still tied to the principles of ALS. Those are great, but ALS is about ‘process’, by which I mean that it is not targeted to any physiological measure (apart from rhythm). We go through the processes of CPR, defibrillation, and drugs, but we don’t effectively measure (Ed – perhaps ETCO2 is a measure here) or know what effect they are having unless ROSC occurs and then we do try and get objective physiological data, and target ROSC care around that. That change is worthy of reflection.

Traditionally, advanced life support (ALS) protocols emphasise the importance of uniform chest compression parameters—standardising rate, depth, and hand position for all patients. However, this one-size-fits-all approach fails to consider individual anatomical and physiological variations. When we have intra-arterial monitoring or TOE then we quickly learn that this is not true, and that small changes in how CPR is performed can make big differences to how effective (cardiac output) is. There has been growing interest in the potential role of haemodynamic monitoring during resuscitation. Notably, recent studies measuring diastolic blood pressure (DBP) during CPR offers a potential proxy for coronary perfusion, a DBP is likely a critical factor in achieving a return of spontaneous circulation (ROSC).

I recently attended the excellent SPEAR course that really made me think hard about how we manage intra-arrest phase of cardiac arrest and I am largely convinced, although the evidence base is not as robust as I would like (and which the course organisers also highlight). The EAAA RAID group is driving research in this area and it’s good to see the evidence based developing. This week we are looking at a paper from EAAA (East Anglian Air Ambulance) that looks at the potential association between DBP and outcome in OOHCA. The abstract is below, but as always please read the full paper yourself and make your own mind up.

Abstract

Introduction – The optimal haemodynamic parameter for goal-directed resuscitation in out-of-hospital cardiac arrest (OHCA) remains uncertain. This study aimed to characterise the association between invasive blood pressure (IBP) measurements and return of spontaneous circulation (ROSC) in adult OHCA patients, to identify this parameter.
Methods – A retrospective observational study was conducted at East Anglian Air Ambulance (EAAA). Adult (≥18 years) medical OHCA patients attended by EAAA between 01/02/2015 and 01/02/2024, who had arterial IBP measurement during chest compressions were included. The initial, minimum, maximum, average (mean) and ▲ (maximum-initial) were calculated for systolic (SBP), diastolic (DBP) and mean arterial (MAP) components of IBP. Logistic regression and receiver operating characteristic curves tested the association between IBP variables and ROSC.
Results – During the study period, 4363 OHCA patients were attended and 80 met inclusion criteria. Thirty-four patients (42.5 %) achieved ROSC and 4 (5.0%) survived to discharge. The maximum, average and A DBP; and maximum and average MAP were positively associated with ROSC. Maximum DBP had an AUC of 0.83 (95 % CI 0.74-0.92) with an optimal cut-off of 35 mmHg (sensitivity 94.1 %; specificity 58.7%) for predicting ROSC. The odds ratio for ROSC was 1.05 (95 % CI 1.03-1.08) for every 1 mmHg increase in maximum DBP.
Conclusions – This study supports the use of arterial DBP as an important haemodynamic parameter for goal-directed resuscitation in adult OHCA. Maximising DBP may increase the chances of ROSC. These data suggest that a DBP threshold of 35 mmHg is optimal for identifying patients who may achieve ROSC with continued resuscitation.

The association between intra-arrest arterial blood pressure and return of spontaneous circulation in out-of-hospital cardiac arrest
Aziz, Shadman et al.
Resuscitation, Volume 205, 110426

What Kind of Study is This?

This was a retrospective observational study conducted by the East Anglian Air Ambulance (EAAA) service in the UK. The researchers analysed patient data from 2015 to 2024. They focused on adult medical OHCA patients where IBP measurements were obtained during CPR. The aim was to evaluate whether IBP metrics—especially DBP—were predictive of ROSC.

Tell Me About the Patients

The study analysed 80 patients out of 4,363 OHCA cases attended by the EAAA during the study period. Inclusion criteria were strict, focusing only on those with intra-arrest IBP monitoring, and excluded patients where measurements were taken post-ROSC.

• Demographics: The average age was 59 years, and 75% of the patients were male.
• Aetiologies: Most arrests were attributed to myocardial infarction (49%), followed by pulmonary embolism (13%).
• Bystander CPR: Present in 76% of cases.
• Initial Rhythm: 36% of patients presented with ventricular fibrillation (VF), the most common shockable rhythm.

ROSC was achieved in 42.5% (34 patients), but only 5% (4 patients) survived to hospital discharge.

What Were the Measured Outcomes in This Study?

The study’s primary outcome was ROSC, defined as evidence of signs of life such as a palpable pulse or a pulsatile blood pressure waveform during prehospital resuscitation. Secondary outcomes included survival to hospital discharge.

Key IBP parameters measured during CPR included:

• Systolic blood pressure (SBP)
• Diastolic blood pressure (DBP)
• Mean arterial pressure (MAP)
• Variability in DBP and MAP over time

What Are the Main Results?

The findings of this study underline the importance of haemodynamic parameters in predicting ROSC. Maximum and average DBP values were strongly associated with ROSC, with no patients achieving ROSC when maximum DBP remained below 28 mmHg. Maximum DBP emerged as the most reliable predictor, with an area under the curve (AUC) of 0.83. An optimal threshold of 35 mmHg was identified, balancing high sensitivity (94.1%) with moderate specificity (58.7%).

MAP values also showed a positive association with ROSC, albeit weaker than DBP. While systolic blood pressure was measured, it did not demonstrate a significant correlation with outcomes, reinforcing the notion that DBP is the most relevant parameter for coronary perfusion during cardiac arrest.

Diastolic Blood Pressure:

• Maximum DBP was significantly higher in patients achieving ROSC (65 mmHg vs 36 mmHg, p < 0.001).
• Average DBP was also higher in the ROSC group (37 mmHg vs 21 mmHg, p = 0.003).
• No ROSC was observed in patients with a maximum DBP below 28 mmHg.

Mean Arterial Pressure:

• Maximum and average MAP were significantly associated with ROSC.

Optimal Threshold:

• A maximum DBP threshold of 35 mmHg had the highest sensitivity (94.1%) and reasonable specificity (58.7%) for predicting ROSC.

Interestingly, the study found that time to achieve a higher DBP was less critical than the ability to reach and maintain an elevated DBP throughout resuscitation. This suggests that focusing on achieving a maximum DBP above the 35 mmHg threshold, rather than incremental improvements, may be key to improving outcomes.

How robust are the findings?

This study reinforces the case for invasive arterial BP monitoring into prehospital resuscitation. However, there are notable limitations. The retrospective design and small sample size (80 patients) restrict the generalisability of the findings. The study cohort was also biased towards patients with prolonged, refractory cardiac arrests, as intra-arrest IBP monitoring was only initiated in select cases. This raises questions about whether similar results would be observed in a broader OHCA population. Furthermore, the study focused exclusively on ROSC, which, while important, is not a perfect surrogate for meaningful long-term outcomes such as survival with good neurological function.

Another limitation is the reliance on univariate analysis, which does not account for confounding variables. While the baseline characteristics of ROSC and non-ROSC groups were similar, adjusting for factors like initial rhythm or time to resuscitation might have provided a clearer picture.

Should We Change Practice Based on This Study?

The findings are consistent with animal data and other observational studies, but we should be cautious about using this level of evidence to change practice. Notably the skill set needed to initiate intra-arrest BP monitoring is not widely available, and may not be that timely, even in HEMS services. Perhaps in urban areas it may be more available but for most populations it may not be practical.

That said, for capable teams who are able to gain access then aiming for a DBP threshold of 35 mmHg may guide CPR optimisation and vasopressor administration. However, broader implementation will require significant investment in training and resources, as well as further research to validate these findings in larger, more diverse populations.

For me, the big lesson here is that current ALS protocols may well not be the end point of our knowledge about how to manage the intra-arrest phase of the chain of survival and standard ALS protocols may need to evolve as the one-size-fits-all approach to chest compressions may not be ideal. The idea that tools like IBP monitoring can provide real-time feedback may be an option to customise CPR to achieve haemodynamic goals.

However, we would really need better quality data, ideally from an RCT before we could really know. So this paper is really interesting and hypothesis generating, and for some teams it may well change practice. But for general management of cardiac arrest we are not there yet.

Summary

This study demonstrates an association between diastolic blood pressure as a marker for effective resuscitation in OHCA. This may be an option for creating a more bespoke approach to intra-arrest monitoring, and I think some services will take this approach, but I’d like to see more and better data before it’s ready for prime-time.

Further reading

• Aziz S, Barratt J, Starr Z, Lachowycz K, Major R, Barnard EB, Rees P. The association between intra-arrest arterial blood pressure and return of spontaneous circulation in out-of-hospital cardiac arrest. Resuscitation. 2024;205:110426.
• Simon Carley, “Non-invasive or arterial pressure monitoring in PHEM?,” in St.Emlyn’s, September 29, 2024
• SPEAR course.
• Halden Hutchinson-Bazely, “Prehospital Partial Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) for Exsanguinating Subdiaphragmatic Hemorrhage,” in St.Emlyn’s, July 14, 2024,
• Gräsner JT, Wnent J, Herlitz J, et al. Survival after out-of-hospital cardiac arrest in Europe: Results of the EuReCa TWO study. Resuscitation. 2020;148:218–226.
• Yannopoulos D, Aufderheide TP, McKnite S, et al. Effects of incomplete chest wall decompression during cardiopulmonary resuscitation on coronary and cerebral perfusion pressures in a porcine model of cardiac arrest. Resuscitation. 2005;64(3):363–372.
• Berg RA, Sutton RM, Reeder RW, et al. Association between diastolic blood pressure during pediatric in-hospital cardiopulmonary resuscitation and survival. Circulation. 2018;137(17):1784–1795.
• Paradis NA, Martin GB, Rivers EP, et al. Coronary perfusion pressure and the return of spontaneous circulation in human cardiopulmonary resuscitation. JAMA. 1990;263(8):1106–1113.
• Koyama Y, Matsuyama T, Inoue Y. Association between haemodynamics during cardiopulmonary resuscitation and patient outcomes. Resuscitation. 2022;170:295–302.
• Morton S, Avery P, Payne J, et al. Arterial blood gases and arterial lines in the prehospital setting: A systematic literature review and survey of current United Kingdom helicopter emergency medical services. Air Medical Journal. 2022;41(2):201–208.
• Drumheller BC, Pinizzotto J, Overberger RC, et al. Goal-directed cardiopulmonary resuscitation for refractory out-of-hospital cardiac arrest in the emergency department: A feasibility study. Resuscitation Plus. 2021;7:100159.
• Butterfield ED, Price J, Bonsano M, et al. Prehospital invasive arterial blood pressure monitoring in critically ill patients attended by a UK helicopter emergency medical service: A retrospective observational review of practice. Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine. 2024;32(1):20.