The Midnight Gap: Nighttime is associated with detrimental outcome in out-of-hospital cardiac arrests in Poland

The Midnight Gap: Nighttime is associated with detrimental outcome in out-of-hospital cardiac arrests in Poland | medRxiv /* */ /* */ <!-- <!-- /*! * yepnope1.5.4 * (c) WTFPL, GPLv2 */ (function(a,b,c){function d(a){return"[object Function]"==o.call(a)}function e(a){return"string"==typeof a}function f(){}function g(a){return!a||"loaded"==a||"complete"==a||"uninitialized"==a}function h(){var a=p.shift();q=1,a?a.t?m(function(){("c"==a.t?B.injectCss:B.injectJs)(a.s,0,a.a,a.x,a.e,1)},0):(a(),h()):q=0}function i(a,c,d,e,f,i,j){function k(b){if(!o&&g(l.readyState)&&(u.r=o=1,!q&&h(),l.onload=l.onreadystatechange=null,b)){"img"!=a&&m(function(){t.removeChild(l)},50);for(var d in y[c])y[c].hasOwnProperty(d)&&y[c][d].onload()}}var j=j||B.errorTimeout,l=b.createElement(a),o=0,r=0,u={t:d,s:c,e:f,a:i,x:j};1===y[c]&&(r=1,y[c]=[]),"object"==a?l.data=c:(l.src=c,l.type=a),l.width=l.height="0",l.onerror=l.onload=l.onreadystatechange=function(){k.call(this,r)},p.splice(e,0,u),"img"!=a&&(r||2===y[c]?(t.insertBefore(l,s?null:n),m(k,j)):y[c].push(l))}function j(a,b,c,d,f){return q=0,b=b||"j",e(a)?i("c"==b?v:u,a,b,this.i++,c,d,f):(p.splice(this.i++,0,a),1==p.length&&h()),this}function k(){var a=B;return a.loader={load:j,i:0},a}var l=b.documentElement,m=a.setTimeout,n=b.getElementsByTagName("script")[0],o={}.toString,p=[],q=0,r="MozAppearance"in l.style,s=r&&!!b.createRange().compareNode,t=s?l:n.parentNode,l=a.opera&&"[object Opera]"==o.call(a.opera),l=!!b.attachEvent&&!l,u=r?"object":l?"script":"img",v=l?"script":u,w=Array.isArray||function(a){return"[object Array]"==o.call(a)},x=[],y={},z={timeout:function(a,b){return b.length&&(a.timeout=b[0]),a}},A,B;B=function(a){function b(a){var a=a.split("!"),b=x.length,c=a.pop(),d=a.length,c={url:c,origUrl:c,prefixes:a},e,f,g;for(f=0;f<d;f++)g=a[f].split("="),(e=z[g.shift()])&&(c=e(c,g));for(f=0;f<b;f++)c=x[f](c);return c}function g(a,e,f,g,h){var i=b(a),j=i.autoCallback;i.url.split(".").pop().split("?").shift(),i.bypass||(e&&(e=d(e)?e:e[a]||e[g]||e[a.split("/").pop().split("?")[0]]),i.instead?i.instead(a,e,f,g,h):(y[i.url]?i.noexec=!0:y[i.url]=1,f.load(i.url,i.forceCSS||!i.forceJS&&"css"==i.url.split(".").pop().split("?").shift()?"c":c,i.noexec,i.attrs,i.timeout),(d(e)||d(j))&&f.load(function(){k(),e&&e(i.origUrl,h,g),j&&j(i.origUrl,h,g),y[i.url]=2})))}function h(a,b){function c(a,c){if(a){if(e(a))c||(j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}),g(a,j,b,0,h);else if(Object(a)===a)for(n in m=function(){var b=0,c;for(c in a)a.hasOwnProperty(c)&&b++;return b}(),a)a.hasOwnProperty(n)&&(!c&&!--m&&(d(j)?j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}:j[n]=function(a){return function(){var b=[].slice.call(arguments);a&&a.apply(this,b),l()}}(k[n])),g(a[n],j,b,n,h))}else!c&&l()}var h=!!a.test,i=a.load||a.both,j=a.callback||f,k=j,l=a.complete||f,m,n;c(h?a.yep:a.nope,!!i),i&&c(i)}var i,j,l=this.yepnope.loader;if(e(a))g(a,0,l,0);else if(w(a))for(i=0;i (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0];var j=d.createElement(s);var dl=l!='dataLayer'?'&l='+l:'';j.src='//www.googletagmanager.com/gtm.js?id='+i+dl;j.type='text/javascript';j.async=true;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-P4HH5NV'); Skip to main content Home About Submit ALERTS / RSS Search for this keyword Advanced Search The Midnight Gap: Nighttime is associated with detrimental outcome in out-of-hospital cardiac arrests in Poland View ORCID Profile Anna Żądło , View ORCID Profile Monika Bednarek-Chałuda , View ORCID Profile Izabela A. Karpińska , View ORCID Profile Grzegorz Cebula , View ORCID Profile Tomasz Tokarek doi: https://doi.org/10.1101/2025.05.09.25327222 Anna Żądło 1 Department of Medical Education, Centre of Innovative Medical Education, Jagiellonian University Medical College , Cracow, Poland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Anna Żądło For correspondence: anna.zadlo{at}uj.edu.pl Monika Bednarek-Chałuda 2 Department of Disaster and Emergency Medicine, Chair of Anesthesiology and Intensive Care, Jagiellonian University Medical College , Cracow, Poland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Monika Bednarek-Chałuda Izabela A. Karpińska 3 2nd Department of General Surgery, and Doctoral School of Medical and Health Sciences, Jagiellonian University Medical College , Cracow, Poland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Izabela A. Karpińska Grzegorz Cebula 4 Department of Medical Education, Centre of Innovative Medical Education, Jagiellonian University Medical College , Cracow, Poland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Grzegorz Cebula Tomasz Tokarek 5 Department of Medical Education, Jagiellonian University Medical College , Cracow, Poland; Center for Invasive Cardiology, Electrotherapy and Angiology , Nowy Scz, Poland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Tomasz Tokarek Abstract Full Text Info/History Metrics Data/Code Preview PDF Abstract Objective Out-of-hospital cardiac arrest (OHCA) has low survival rates with worse outcomes at night due to delayed emergency medical services (EMS) response, resource limitations, and workforce fatigue. Timely resuscitation is crucial, but logistical challenges exacerbate disparities. Since randomized trials are unfeasible, all-comers registries provide essential data to bridge evidence gaps and improve EMS protocols. This study aimed to investigate the impact of day versus night shifts on OHCA outcomes, focusing on ROSC rates, 30-day survival, and timing metrics within EMS operations. Methods This study analyzed OHCA cases in Poland from September to November 2022 using paramedics records and national death registry data. Patients were grouped by time of cardiac arrest (on-hours: 7:00 AM–6:59 PM; off-hours: 7:00 PM–6:59 AM) and matched 1:1 using propensity score analysis (1194 pairs). Results Our findings revealed significant disparities in OHCA outcomes between day and night shifts. ROSC rates were notably lower at night (20.9% vs. 34.8%; P = 0.01 ), as was 30-day survival (47.0% vs. 59.3%; P = 0.01 ). EMS response times were significantly longer during nighttime hours (median and interquartile range: 12.4(7.4-14.6) vs. 11.2(6.2-13.5)(minutes); P = 0.01 ) Conclusions Patients with OHCA during off-hours were exposed to longer EMS response time as compared to procedures conducted during regular working hours. Furthermore, OHCA during night shift might be associated with a lower rate of ROSC and decreased 30-day survival What’s New? Out-of-hospital cardiac arrest (OHCA) remains a critical public health challenge with significant implications for morbidity and mortality. Despite advancements in emergency medical services systems and resuscitation techniques, survival rates following OHCA remain low, particularly during nighttime hours. This study provided a clinical view from a national perspective on the impact of day versus night shifts on the clinical outcomes in patients with OHCA. Propensity score match analysis was performed to evade risk of bias in the preselection process. This study suggested detrimental outcome in OHCA treatment during nighttime as compared to regular working hours. Patients from nighttime group were associated with longer response times as well as decreased rate of return of spontaneous circulation and 30-day survival as compared to daytime. These findings underscore the importance of systemic approach to improve OHCA outcome. Introduction Out-of-hospital cardiac arrest (OHCA) remains a critical public health challenge with significant implications for morbidity and mortality. Despite advancements in emergency medical services (EMS) systems and resuscitation techniques, survival rates following OHCA remain low, particularly during nighttime hours 1 . Previous research has highlighted differences in patient outcomes based on the time of day, with variations in return of spontaneous circulation (ROSC) and survival rates 2 – 4 . Factors such as extended response times, reduced witnessed cardiopulmonary resuscitation (CPR) rates, and limited access to specialized care during nighttime hours have been shown to negatively impact outcomes 4 , 5 . Moreover, workforce fatigue, resource limitations, and logistical challenges during night shifts may further contribute to the observed disparities 6 . Due to ethical constraints, randomized clinical trials in this setting are limited therefore, all-comers registries might serve as a valuable source of real-world data to address gaps in evidence. Thus, we sought to analyze the impact of day versus night shifts on OHCA outcomes in data from an unselected cohort of consecutive patients. Methods This retrospective observational study collected data on cardiac arrest using mandatory electronic records maintained by emergency medical team personnel, including paramedics, nurses, and physicians. The study was conducted in Poland over a three-month period, with data gathered at the scene of each OHCA by emergency medical teams. Information regarding 30-day survival in follow up was gathered from the national death registry. The analysis focused on OHCA cases that occurred between September 1 and November 30, 2022. The patient flow chart is presented in Figure 1 . All procedures were performed following local standards and Advance Life Support guidelines wherever applicable. All periprocedural complications were collected prospectively. All adverse events were diagnosed at the EMS team leader discretion in accordance with definitions in current ERC guidelines 7 . However, data beyond the hospital discharge were not collected. The sample was specifically selected to enable comparisons with the multicenter EuReCa study 8 . Patients were grouped by the time of their cardiac arrest using the Utstein framework 9 – 11 . Data marked as “unknown” or “not recorded” were excluded. All ambulance service patients who experienced OHCA during the study period were included (n=7237). Propensity score matching (PSM) analysis was performed to match patients with cardiac arrest occurring during day to those with cardiac arrest occurred during night (On-hours: Monday to Sunday, 7:00 AM – 6:59 PM vs. Off-hours: Monday to Sunday, 7:00 PM – 6:59 AM). The stabilized weights were calculated using propensity scores obtained from a logistic regression model. The covariates included in the final propensity score model were: age, sex, CPR before EMS arrival, cause of cardiac arrest, location of cardiac arrest, presence of a witness on scene, shockable initial rhythm occurrence, and Automated External Defibrillator (AED) utilization. The nearest neighbor matching was performed. To minimize the standardized differences between groups, no match tolerance was applied. The 1:1 ratio was chosen to minimize bias without sacrificing test power in accordance with previous recommendations 12 . Analyzed variables between groups included ROSC, 30-day survival, time of arrival, time on-scene and overall operation time. Continuous variables ware presented as median and interquartile range (IQR) for non-normally distributed variables, respectively. Categorical variables were presented as numbers and percentages. To check the normality of the distribution of the continuous variables we used the Shapiro-Wilk and the Kolmogorov-Smirnov with the Lilliefors correction tests. Comparison between groups was established using a Mann–Whitney U test for continuous variables and Chi-square test or Chi-square test with Fisher’s correction for categorical variables. For all inferential statistics statistical significance was defined as P=0.05 . All calculations were done with SPSS 10.0 ® statistical software (SPSS Inc, Chicago IL, USA). Statistical criteria for selecting the optimal number of untreated subjects matched to each treated subject when using many-to-one matching on the propensity score. The study was approved by the institutional ethical board. The study was provided in accordance with ethical principles for clinical research based on the Declaration of Helsinki with later amendments. Download figure Open in new tab Figure 1 Study Population Results The characteristics of the study population are presented in Table 1 . A total of 1194 matched pairs treated during day- and nighttime were evaluated. After PSM no significant differences in baseline patients’ characteristics were observed between groups ( Table 2 ). The results obtained from this analysis are set out in Table 3 , showing a significantly higher ROSC rate (34.8% vs. 20.9%; P = 0.01 ) and improved 30-day survival outcomes (59.3% vs. 47.0%; P = 0.01 ) during the day-as compared to nighttime. Patients in daytime group experienced shorter time to arrival (median and interquartile range (IQR):11.2(6.2-13.5) vs. 12.4(7.4-14.6) (minutes); P = 0.01 ) and longer on-scene times (median and IQR: 108.3(56.2-103.1) vs.107.1(59.9 – 106.7)(minutes); P = 0.03 ). Furthermore, overall operation time was found to be shorter at night 108.6 (65.0-113.5) vs (112.8(58.8-106.7) minutes; P = 0.02 ) longer on-scene times (108.2min vs. 107.1min; P = 0.03 ). View this table: View inline View popup Table 1 Characteristics of the study population before propensity score matching. View this table: View inline View popup Table 2 Baseline characteristics of the study population after propensity score matching. View this table: View inline View popup Table 3 Comparison of OHCA outcomes and response times between groups. Limitations While our findings provide valuable insights, there are certain limitations that must be acknowledged. The most important is the nonrandomized design with all related bias. The risk of confounding factors cannot be excluded. However, a PSM calculation was provided to imitate randomization procedure and evade risk of bias in the preselection process. The presented analysis has not included all patients with OHCA during the study period. Some patients with highest risk burden and the most severe condition might die without EMS call, thus they were not included in the database. There are notable gaps in data completeness: while ROSC data is available for nearly all patients, 30-day survival data is limited to about 250 pairs of matched patients. This discrepancy could affect the robustness of our findings. The analysis relies on paramedic reports for ROSC and the national death registry for 30-day survival rates, initially connected by PESEL number and anonymized before analysis. Any ROSC is marked in paramedic reports, while 30-day survival was chosen for its standardized timeline from the Utstein framework 10 . The use of the PESEL number to connect paramedic reports and National Death Registry to monitor deaths excluded some patients who had not yet been assigned identification numbers, resulting in missing data and underrepresentation of cases in terms of 30-day survival. PESEL is a unique 11-digit national identification number assigned to all Polish citizens and residents, used for identity verification in administrative, legal, and medical systems. This limitation impacts the completeness and accuracy of survival data, potentially affecting the study’s conclusions. There might be additional risk of patients overlapping across the cohorts, mainly in those registered between shifts. Furthermore, senior staff availability and experience of medical team might be considered as possible alterable aspects influencing outcomes. Despite all these described limitations, our study presented experience from a large, unselected cohort of patients; thus, outcomes might be adapted to the general population. Discussion Presented results suggested detrimental outcome in OHCA treatment during nighttime as compared to regular working hours. Nighttime group was associated with longer response times as well as decreased rate of ROSC and 30-day survival as compared to daytime. These results are in line with previous research and underscore the critical importance of timely responses in OHCA management 13 – 17 . Multiple factors likely contribute to this disparity, including workforce fatigue, variations in available resources like dispatcher assistance 18 , 19 , medical staff competence and the extent of witness involvement 15 , 20 . The findings of Bartlett at all. (2022) described how sleepiness effected at EMS work at night 21 . Reaction time is longer, cognitive decisions are harder to make, and more mistakes occur. Furthermore, the presence of specialized hospital care in emergency department and personnel during the day likely increases survival outcomes, whereas nighttime care may encounter challenges such as limited staffing, specialist availability and diagnostic support 22 . Variations in response time might also influence the outcome. In terms of on-scene time, the slight reduction at night (108.2min vs.107.1min; P = 0.03 ) suggested different treatment strategies. Daytime operations might allow for more comprehensive on-site interventions due to better resource availability and presence of more experienced medical staff. While reduced traffic congestion at night might appear advantageous, the reality of navigation difficulties, and possible delays in dispatch can counteract these benefits, resulting in longer response intervals. This study demonstrated that EMS operations during night shifts are less effective, emphasizing the need for systemic changes to improve after-hours response capabilities. According to the Central Statistical Office (Główny Urząd Statystyczny), as of December 31, 2023, emergency medical teams in Poland consisted of nearly 12,900 personnel. Paramedics represented the largest group, with over 11,200 members, followed by more than 1,000 emergency medical system nurses, over 300 physicians, and nearly 300 other staff members 23 . The operational structure of EMS in Poland characterized working under a 7-7 shift system, alternating day and night shifts. The standard daily working time for EMS personnel on a full-time contract is 7 hours and 35 minutes. However, the equivalent working time system is commonly used in practice, offering greater flexibility in scheduling while ensuring compliance with the statutory weekly working limits. Following each night shift, a minimum rest period of 11 hours is required, whereas after a 24-hour shift, a minimum of 24 hours of rest must be provided. However, these regulations do not apply to B2B contracts, which are commonly chosen by a significant number of EMS personnel. A more stable work environment, regulated shifts, and standardized rest periods could improve overall system effectiveness and response quality. In the United Kingdom, EMS personnel work under a variety of shift patterns to ensure continuous 24/7 service, tailored to operational demands, environmental factors, and resource availability. One of the most commonly used schedules is the “2-2-4” system, where staff complete two consecutive 12-hour day shifts (e.g., 06:00–18:00), in accordance with the guidelines outlined by the Health and Safety Executive in Managing Shiftwork – Health and Safety Guidance 24 . The B2B contract offers flexibility in choosing shift rotations, allowing individuals to tailor their work schedules based on personal preferences 25 . However, it is worth considering established guidelines, such as those provided by the American College of Emergency Physicians. Their key recommendations suggest implementing a forward-rotating shift schedule (day to evening to night), managing shift lengths and consecutive work periods to prevent fatigue, and structuring night shifts either as isolated shifts or in longer blocks spanning several weeks 25 . Furthermore, witnessed CPR might improve survival in cardiac arrest 15 , 20 . However, available data revealed that bystander CPR is infrequent, particularly at night, further exacerbating poor outcomes. Implementing a national first responder system, expanding public CPR training programs, and increasing access to AEDs could allow to close the gap in outcomes between day and night 26 , 27 . Despite longer overall operation time during daytime both mortality and ROSC rates seem to be beneficial as compared to outcomes from night shift. Since there was no difference in baseline characteristics presented results cannot be easily explained by impact of bystander or prevalence of shockable rhythm and AED utilization. This outcome might by partialy elucidated by lower quality of chest compression/ALS manoeuvers and general fatigue of medical staff at night. In addition, level of experience and dexterity in ALS procedures might have impact on this outcome. However, such data was not collected in this registry. Furthermore, hesitation in ambulance call especially in older population might result in more aggravated condition and higher risk burden of cardiac arrest. Previously published studies suggested diurnal variability in myocardial perfusion, particularly early in the morning and peak in platelet aggregation during night hours 28 . Both patient-related and systemic factors might be responsible for presented phenomenon. These findings underscore the importance of systemic approach 29 to improve OHCA outcome. Addressing workforce issues such as implementing more sustainable work schedules, strengthening dispatcher-assisted CPR efforts, Public-Access Defibrillation and public education on AED usage, particularly during nighttime hours, could further support early intervention. Additionally, ensuring hospital readiness and coordination at night would help minimize delays and improve patient outcomes. Patients experiencing OHCA during off-hours faced longer EMS response time as compared to procedures conducted during regular working hours. Furthermore, OHCA occurring during night shift might be associated with a lower rate of ROSC and decreased 30-day survival as compared to patients treated during daytime. Author Contributions (CRediT) Anna Żą dło: Conceptualization, Methodology, Investigation, Data Curation, Writing – Original Draft Grzegorz Cebula: Conceptualization, Investigation, Data Curation Monika Bednarek-Chałuda: Writing – Review & Editing, Data Curation Izabela A. Karpi ń ska: Methodology, Investigation, Data Curation, Writing – Original Draft Tomasz Tokarek: Conceptualization, Methodology, Investigation, Data Curation, Writing – Review & Editing Conflict of Interes1t None declared. Funding Statement This study was supported by internal research funds allocated under the announcement of the Deputy Rector’s Representative for Science and International Cooperation of the Jagiellonian University Medical College for projects financed from the Ministry of Education and Science (MEiN) subsidy N41/DBS/001329. Ethics Approval Statement Approved by the Bioethics Committee for Research Studies of the Jagiellonian University Medical College (approval no. 118.0043.1.299.2024) on September 26, 2024. Data Availability All data produced in the present study are available upon reasonable request to the authors Footnotes Email: anna.zadlo{at}uj.edu.pl , Email: monika.bednarek{at}uj.edu.pl , Email: iza.karpinska{at}doctoral.uj.edu.pl , Email: grzegorz.cebula{at}uj.edu.pl , Email: tomasz.tokarek{at}uj.edu.pl References 1. ↵ Berdowski J , Berg RA , Tijssen JGP , Koster RW . Global incidences of out-of-hospital cardiac arrest and survival rates: Systematic review of 67 prospective studies . Resuscitation . 2010 ; 81 : 1479 – 1487 . Doi: 10.1016/j.resuscitation.2010.08.006 OpenUrl CrossRef PubMed Web of Science 2. ↵ Koike S , Tanabe S , Ogawa T , et al. 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