
==== Front
Intensive Care Med
Intensive Care Med
Intensive Care Medicine
0342-4642
1432-1238
Springer Berlin Heidelberg Berlin/Heidelberg

39115566
7570
10.1007/s00134-024-07570-w
Original
Long-term survival comparison of patients admitted to the intensive care unit following in-hospital cardiac arrest in perioperative and ward settings. A multicentre retrospective cohort study
http://orcid.org/0000-0003-1681-0107
Ueno Ryo ryo.ueno@monash.edu

123
Chan Rachel 4
Reddy Mallikarjuna Ponnapa 567
Jones Daryl 238
Pilcher David 2910
Subramaniam Ashwin 261112
1 grid.414366.2 0000 0004 0379 3501 Department of Intensive Care, Box Hill Hospital, Eastern Health, Box Hill, VIC Australia
2 grid.1002.3 0000 0004 1936 7857 Department of Epidemiology and Preventive Medicine, Australian and New Zealand Intensive Care Research Centre, Monash University, Melbourne, VIC Australia
3 https://ror.org/05dbj6g52 grid.410678.c 0000 0000 9374 3516 Department of Intensive Care, Austin Health, Heidelberg, VIC Australia
4 https://ror.org/04h7nbn38 grid.413314.0 0000 0000 9984 5644 Department of Anaesthesia and Pain Medicine, The Canberra Hospital, Canberra, Australia
5 https://ror.org/03vb6df93 grid.413243.3 0000 0004 0453 1183 Department of Anaesthesia and Pain Medicine, Nepean Hospital, Sydney, NSW Australia
6 https://ror.org/02n5e6456 grid.466993.7 0000 0004 0436 2893 Department of Intensive Care, Peninsula Health, Frankston, VIC Australia
7 https://ror.org/04h7nbn38 grid.413314.0 0000 0000 9984 5644 Department of Intensive Care, North Canberra Hospital, Canberra, Australia
8 https://ror.org/01ej9dk98 grid.1008.9 0000 0001 2179 088X University of Melbourne, Parkville, VIC Australia
9 https://ror.org/007847151 grid.489411.1 0000 0004 5905 1670 Centre for Outcome and Resource Evaluation, Australian and New Zealand Intensive Care Society, Melbourne, VIC Australia
10 https://ror.org/01wddqe20 grid.1623.6 0000 0004 0432 511X Department of Intensive Care, Alfred Hospital, Melbourne, VIC Australia
11 https://ror.org/046gme853 grid.413901.e 0000 0001 0706 710X Department of Intensive Care, Dandenong Hospital, Dandenong, VIC Australia
12 https://ror.org/02bfwt286 grid.1002.3 0000 0004 1936 7857 Peninsula Clinical School, Monash University, Frankston, VIC Australia
8 8 2024
8 8 2024
2024
50 9 14961505
21 4 2024
23 7 2024
© The Author(s) 2024
2024
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Purpose

Perioperative in-hospital cardiac arrests (Perioperative IHCAs) may have better outcomes than IHCAs in the ward (Ward IHCAs), due to enhanced monitoring and faster response. However, quantitative comparisons of their long-term outcomes are lacking, posing challenges for prognostication.

Methods

This retrospective multicentre study included adult intensive care unit (ICU) admissions from theatre/recovery or wards with a diagnosis of cardiac arrest between January 2018 and March 2022. We used data from 175 ICUs in the ANZICS adult patient database. The primary outcome was a survival time of up to 4 years. We used the Cox proportional hazards model adjusted for Sequential Organ Failure Assessment (SOFA) score, age, sex, comorbidities, hospital type, treatment limitation on admission to the ICU, and ICU treatments. Subgroup analyses examined age (≥ 65 years), intubation within the first 24 h, elective vs. emergency admission, and survival on discharge.

Results

Of 702,675 ICU admissions, 5,659 IHCAs were included (Perioperative IHCA 38%; Ward IHCA 62%). Perioperative IHCA group were younger, less frail, and less comorbid. Perioperative IHCA were most frequent in patients admitted to ICU after cardiovascular, gastrointestinal, or trauma surgeries. Perioperative IHCA group had longer 4-year survival (59.9% vs. 33.0%, p < 0.001) than the Ward IHCA group, even after adjustments (adjusted hazard ratio [HR]: 0.63, 95% confidence interval [CI] 0.57–0.69). This was concordant across all subgroups. Of note, older patients with Perioperative IHCA survived longer than both younger and older patients with Ward IHCA.

Conclusion

Patients admitted to the ICU following Perioperative IHCA had longer survival than Ward IHCA. Future studies on IHCA should distinguish these patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00134-024-07570-w.

Keywords

Long-term outcome
Intensive care medicine
Perioperative medicine
Cardiac arrest
Monash UniversityOpen Access funding enabled and organized by CAUL and its Member Institutions

issue-copyright-statement© Springer-Verlag GmbH Germany, part of Springer Nature and European Society of Intensive Care Medicine 2024
==== Body
pmcTake-home message

Little is known about the long-term outcome of in-hospital cardiac arrest patients requiring admission to the intensive care unit (ICU), particularly concerning the variability associated with the location of cardiac arrest. Using a national dataset from 175 ICUs across Australia, our study compared the long-term survival of perioperative and ward cardiac arrest patients, demonstrating better survival in the perioperative group across various subgroups.	

Introduction

In-hospital cardiac arrests (IHCA) have been defined by the Utstein registry as the delivery of chest compressions and/or defibrillation to patients admitted to the hospital [1]. The incidence of IHCA ranges between 1 and 10 per 1000 patient admissions across various countries [2, 3]. IHCA has been associated with a high incidence of mortality and morbidity, with survival to discharge ranging between 15 and 40%, and moderate to severe cerebral disability among survivors at 90 days [4–7]. In terms of long-term outcomes, only 13.4% were alive at 1 year according to a large systematic review and meta-analysis that included 1,358,478 patients from 39 studies which ranged over 30 years [5]. However, most of the studies did not specify the location or setting of the IHCA.

There are two types of IHCAs: IHCAs occurring in the operating theatre or recovery (Perioperative IHCA) and IHCA occurring in the non-surgical area such as regular ward (Ward IHCAs). Most IHCA studies have not differentiated between Perioperative and Ward IHCAs [8–10]. Early detection of IHCAs such as those in a monitored location has been associated with improved outcomes [11–13]. Accordingly, patients with Perioperative IHCA have been shown in a few studies to have better short-term outcomes than patients with Ward IHCA [7, 14]. However, these studies are limited due to being conducted in small, single centre [7] or lacking long-term outcomes [14]. In addition, there were few studies that examined the vulnerable subgroups of Perioperative IHCA patients, such as elderly subgroup, emergency surgery subgroup, or a subgroup needing intubation or admission to the intensive care unit (ICU) [14, 15]. The absence of long-term outcome poses a challenge in prognosticating such heterogeneous ICU patients post-Perioperative IHCA.

Therefore, this study aims to compare the long-term survival and discharge destinations of ICU patients admitted after Perioperative IHCA and Ward IHCA using a large multicentre database in Australia. We hypothesised that Perioperative IHCA patients would have a higher long-term survival rate than Ward IHCA patients, given the monitored environment, differences in the patient cohort and adequate skilled staff in the operating theatre.

Methods

Study design and patient selection

We performed a retrospective multicentre study of all critically ill adult (age ≥ 16 years) patients admitted to Australian ICUs between 1st January 2018 and 31st March 2022. Patients were classified as having IHCA if they were admitted from the ward or operating theatre/recovery and met either of the criteria: having a primary diagnosis of cardiac arrest or having a different primary diagnosis but being labelled as experiencing a cardiac arrest within 24 h before ICU admission. We only included patients who had IHCA before the ICU admission; hence, patients who had IHCA in the ICU were not included in this study. Patients were excluded if they were readmitted to the ICU during the same hospitalisation; were admitted for palliative care or organ donation; or were admitted following an out-of-hospital cardiac arrest (i.e. ICU admission source was from the emergency department, another hospital, or directly from home). Our dataset treated initial ICU admission and ICU readmission within the same hospitalisation as separate events. To prevent double-counting 1-year mortality, we only included the first admission episode within the same hospital stay [16–18].

Data sources and measurement

Data were extracted from the Australian and New Zealand Intensive Care Society (ANZICS) adult patient database (APD), a clinical quality registry dataset managed by the ANZICS Centre for Outcomes and Resources Evaluation. The database compiles data from 98% of all adult ICUs in Australia [19, 20]. During the study period in Australia, ICU admission records were linked with the death records in the Australian national death registers using a secure linkage key.

Variables

We extracted data on patient demographics (age, sex, height, weight, comorbidities, hospital admission source, frailty status using the clinical frailty scale [CFS]), ICU type (public rural, public tertiary, public metropolitan and private), the worst physiological parameters within the first 24 h of ICU admission (Acute Physiology and Chronic Health Evaluation [APACHE] III, Australian and New Zealand Risk of Death [ANZROD] and Sequential Organ Failure Assessment [SOFA] scores), ICU organ supports (a receipt of inotropes, invasive mechanical ventilation, non-invasive ventilation and renal replacement therapy), the presence of a treatment limitation order at ICU admission [21].

ICU admission source

ANZICS-APD has a pre-specified algorithm to determine the source of ICU admission for non-operative and post-operative patients as summarised elsewhere [22]. In summary, patients were considered postoperative if they were directly admitted to the ICU from the operating theatre or recovery after surgery. ANZICS-APD mandates that IHCA in the cardiac catheterization lab should be labelled as Perioperative IHCA if the patient was anaesthetised.

Outcomes

The primary outcome was survival time up to 4 years after ICU admission. Secondary outcomes included ICU and hospital mortality, ICU and hospital length of stays, ICU complications (delirium), future readmission, discharge destination at hospital discharge, and survival at 1, 2, 3 and 4 years of follow-up.

Statistical analysis

We summarised categorical data using counts and percentages, and continuous data using mean ± standard deviation (SD) or median (interquartile range, IQR) as appropriate depending on the distribution. We compared between groups using the Chi-square, student’s t, or log-rank tests as appropriate. We estimated overall survival over time using the Kaplan–Meier method. We censored time-to-event data on 1st April 2022 to ensure that there was at least 1-day follow-up for all patients. Based on the ICU admission dates, the maximum possible calculated follow-up study period was 51 months. We assessed the impact of IHCA location (operation theatre/recovery versus ward) on survival time up to 4 years between groups using a Cox proportional hazards model and adjusted for age, sex, comorbidities, ICU admission source, treatment limitations on ICU admission, acute illness severity at ICU admission (assessed using the SOFA score), hospital type and ICU organ support (invasive ventilation on day 1, renal replacement therapy and inotrope use). We reported the survival time using adjusted hazard ratios (HR) and 95% confidence intervals (95% CI). The interaction between variables and collinearity between confounders was assessed with the variance inflation factor. We repeated the primary analysis for several subgroups, which were pre-defined in our protocol. First, we stratified patients based on age, using 65 years as an arbitrary threshold. Second, we investigated the effect of IHCA only in patients needing early invasive mechanical ventilation (defined as mechanical ventilation within day 1). Third, we focussed on those who survived to hospital discharge. Finally, we stratified Perioperative IHCA into patients undergoing elective or emergency surgery and compared that with Ward IHCA (defined as medical patients). In addition to these pre-planned analyses, we performed a post hoc analysis to investigate the very elderly subgroup of patients by splitting the age group into three categories (< 65 years old, between 65 and 80 years old and > 80 years old). There was minimal missing data (< 5%) and the data were generally complete. As such, we considered that the missing-completely-at-random assumption was valid, and imputation was deemed unnecessary. We analysed data using R4·2·2 (The R Foundation, Boston, MA), and to increase the robustness of our analysis, a two-sided p value of < 0.001 was used to indicate statistical significance.

Ethics approval

The Alfred Hospital Ethics Committee (local reference 215/22) approved this study, and the ANZICS Centre for Outcome and Resource Evaluation Management Committee approved to release of the data from the ANZICS adult patient database. This study did not receive any funding.

Results

During the study period, 702,675 adult patients were admitted to Australian ICUs, of whom 18,008 had either a primary diagnosis of cardiac arrest or a different primary diagnosis but were labelled as having a cardiac arrest within 24 h before ICU admission. After applying the inclusion and exclusion criteria, 5,659 patients from a total of 175 ICUs were included in the final analysis (supplementary Fig. 1). This represented 0.8% of all ICU admissions reported to the ANZICS-APD. Of these, 38% (2152) of patients had Perioperative IHCAs, whilst the remaining 62% (3507) had Ward IHCAs.

The baseline comparisons between the Perioperative IHCA and Ward IHCA are summarised in Table 1. Perioperative IHCA patients were younger (mean [SD] 63.8 [17] vs. 68 [14.8], p < 0.001), and seldom frail (median [IQR] 3 [2–4] vs. 4 [3–5], p < 0.001). Perioperative IHCA patients infrequently had comorbidities such as chronic cardiovascular, respiratory, or renal conditions, metastatic cancer, and immunosuppression, and had lower illness severity scores (SOFA (median [IQR] 6 [4–9] vs. 7 [4–10], p < 0.001) and ANZROD score (mean [SD] 25% [28] vs. 47% [32], p < 0.001). Perioperative IHCA patients were more frequently intubated (75% vs. 64.7%; p < 0.001) and more likely to receive vasopressor support (74.3% vs. 67.8%; p < 0.001). There was no difference in the receipt of renal replacement therapy between the two groups. The top ten admission diagnoses for Perioperative IHCA and Ward IHCA patients are presented in the supplementary Table 1. In both Perioperative and Ward IHCA groups, cardiovascular pathology was the most common ICU admission diagnosis.Table 1 Demographic characteristics for Perioperative IHCA and Ward IHCA patients

	Perioperative IHCA patients (n = 2152)	Ward IHCA patients
(n = 3507)	p value	
Age, years	63.8 (17)	68 (14.8)	 < 0.001	
Female	39 (839)	38.5 (1,351)	0.75	
BMI	29.2 (8)	29.3 (8)	0.84	
Clinical Frailty Scale	3 [2, 4]	4 [3, 5]	 < 0.001	
Treatment limitation at ICU admission	8.9 (192)	15.7 (548)	 < 0.001	
APACHE II score	21 (9)	26 (11)	 < 0.001	
APACHE III/IV score	71 (33)	89 (39)	 < 0.001	
ANZROD (mean, median, IQR)	0.25, 0.11 [0.03,0.4]	0.47, 0.45 [0.15, 0.79]	 < 0.001	
Worst lactate in first 24 h of ICU admission	3 [1.7, 6.2]	3.8 [1.9, 7.6]	 < 0.001	
SOFA score on day 1	6 [4, 9]	7 [4, 10]	 < 0.001	
Hospital classification			 < 0.001	
 Public, tertiary	58.5 (1258)	47.6 (1,670)		
 Public, metropolitan	13.2 (283)	20.5 (718)		
 Public, rural	9.9 (213)	11.8 (413)		
 Private	18.5 (398)	20.1 (706)		
Sources of ICU admission			 < 0.001	
 Elective surgery	37.6 (793)	0.2a (8)		
 Emergency surgery	62.4 (1317)	0 (0)		
 Medical ward	0 (0)	99.8 (3,471)		
Sources of hospital admission			0.08	
 Home	82.1 (1761)	81.8 (2846)		
 Transfer from other hospital ward or ED	16.6 (356)	16 (560)		
 Nursing home/rehabilitation/mental health	1.3 (28)	2.1 (75)		
Comorbidities				
 Chronic respiratory disease	6.3 (136)	8.9 (311)	0.001	
 Chronic heart disease	11.5 (247)	15.7 (552)	 < 0.001	
 Chronic liver disease	1.9 (41)	2.4 (85)	0.23	
 Chronic renal disease	4.9 (105)	10.1 (354)	 < 0.001	
 Immunosuppression	2.4 (51)	3.2 (113)	0.08	
 Lymphoma	1.2 (25)	1.3 (44)	0.85	
 Metastatic cancer	2.6 (57)	4.2 (148)	0.003	
 Leukaemia	0.9 (20)	2 (70)	0.003	
Treatment in the ICU				
 Vasopressor	74.3 (1409)	67.8 (2,109)	 < 0.001	
 Non-invasive ventilation	8.6 (160)	13.3 (405)	 < 0.001	
 Invasive ventilation	75 (1557)	64.7 (2202)	 < 0.001	
 Renal replacement therapy	13.8 (249)	14.7 (437)	0.42	
Data are presented as % (n), mean (SD) and median [IQR]

APACHE Acute Physiology and Chronic Health Evaluation score, ANZROD Australian and New Zealand Risk of Death, BMI body mass index, ED emergency department, ICU intensive care medicine, IHCA in-hospital cardiac arrest, IQR interquartile range, SD standard deviation, SOFA score Sequential Organ Failure Assessment score

a8 patients had cardiac arrest in the ward after being discharged from theatre recovery. They are classified as Ward IHCA following study protocol

Primary outcome

Perioperative IHCA patients had higher overall survival at each year of follow-up when compared with the Ward IHCA patients (at 1, 2, 3, and 4 years were 68.7% vs. 47.1%, 65% vs. 42.1%, 62% vs. 37.8% and 59.9% vs. 33% respectively; p < 0.001 for all; Table 2 and Fig. 1). The survival time was longer for Perioperative IHCAs compared to Ward IHCAs (18 months [SD 16.7] vs. 12 months [SD 15.6]; p < 0.001). Perioperative IHCA patients were associated with longer survival times of up to 4 years after adjusting for age, sex, acute physiology, hospital type, ICU treatment, treatment limitation, and comorbidities (adjusted HR: 0.63, 95% CI 0.57–0.69, Table 3).Table 2 Primary and secondary outcomes for Perioperative IHCA and Ward IHCA patients

	Perioperative IHCA patients	Ward IHCA patients	p value	
Survival Outcomes, % [95%CI]				
 Survival up to 4 years	59.9 [57.4–62.5]	33 [30.6–35.5]	 < 0.001	
 Survival up to 3 years	62 [59.7–64.3]	37.8 [36–39.7]	 < 0.001	
 Survival up to 2 years	65 [62.9–67.2]	42.1 [40.4–43.8]	 < 0.001	
 Survival up to 1 year	68.7 [66.8–70.8]	47.1 [45.4–48.8]	 < 0.001	
 Survival months, mean (SD)	18 (16.7)	12 (15.6)	 < 0.001	
In-hospital survival				
 Survival in the ICU	79.5 (1,713)	64.2 (2,255)	 < 0.001	
 Survival in hospital	75.4 (1,622)	56.9 (1,995)	 < 0.001	
Other outcomes				
 ICU length of stay, hours	60 [26, 135]	52 [22, 115]	 < 0.001	
 Hospital length of stay, hours	221 [105, 434]	224 [106, 451]	0.73	
 Readmission to the ICU, % (n)	6.8 (118/1713a)	7.2 (163/2255)	0.18	
Complications in ICU				
 Delirium during ICU, % (n)	10.7 (130)	6.3 (147)	 < 0.001	
Hospital outcome			 < 0.001	
 Discharged home	55 (1183)	39.9 (1398)		
 Transfer to other acute hospital	9.5 (204)	8.2 (286)		
 Rehabilitation	8.3 (178)	6.4 (225)		
 Nursing home/palliative care	2.3 (49)	2.1 (72)		
other	0.4 (8)	0.5 (16)		
CI confidence interval, ICU intensive care unit, SD standard deviation

Data are presented as % (n) and median [IQR] unless specified

aDenominator was ICU survivors

Fig. 1 Unadjusted Kaplan–Meier survival curve for Perioperative IHCA and Ward IHCA patients

Table 3 Cox proportional hazards analysis

Predictors	HR (95%-CI)	
Ward IHCA patients	reference	
Perioperative IHCA patients	0.63 (0.57–0.69)	
Male (compared to female)	1.01 (0.93–1.1)	
Age (per each year increment)	1.02 (1.01–1.02)	
SOFA score on day 1	1.18 (1.60–1.19)	
Treatment limitation on admission to the ICU	2.15 (1.94–2.38)	
Hospital type		
 Public, metropolitan	reference	
 Private	0.77 (0.66–0.89)	
 Public, rural	0.92 (0.79–1.07)	
 Public, tertiary	0.85 (0.76–0.95)	
Comorbidities		
 Chronic respiratory disease	1.21 (1.06–1.38)	
 Chronic heart disease	1.1 (0.98–1.23)	
 Chronic liver disease	1.39 (1.12–1.72)	
 Chronic renal disease	1.07 (0.94–1.22)	
 Immunosuppression	1.24 (1.01–1.52)	
 Lymphoma	1.25 (0.92–1.7)	
 Metastatic cancer	1.47 (1.23–1.76)	
 Leukaemia	1.13 (0.88–1.47)	
ICU treatment		
 Vasopressor therapy	0.94 (0.84–1.04)	
 Mechanical ventilation within 24 h of ICU admission	1.15 (1.02–1.28)	
 Renal replacement therapy	1.13 (1.01–1.26)	
ICU intensive care unit, IHCA in-hospital cardiac arrest, SOFA score Sequential Organ Failure Assessment score

Subgroup analyses

First, we stratified our IHCA patients based on age. 3,418 (60.4%) of patients were aged ≥ 65 years; of which 1,158 (33.9%) had Perioperative IHCA. The older patients with Perioperative IHCA (aged ≥ 65 years) had longer survival times than both the younger and older Ward IHCA patients (Fig. 2). In older subgroups, Perioperative IHCA patients had longer survival times when compared to the Ward IHCA patients (adjusted HR: 0.58; 95% CI: 0.52–0.65; supplementary Table 2). In our post hoc analysis with three age categories (< 65 years old, 65–80 years old, > 80 years old), very elderly (> 80) patients with Perioperative IHCA initially had better survival than any age group of Ward IHCA patients for the first 1 year. However, very old Perioperative IHCA patients (> 80 years old) eventually had worse survival than the youngest (< 65 years old) Ward IHCA patients (supplementary Fig. 2). Second, we stratified patients based on the need for early intubation within 24 h of ICU admission. Perioperative IHCA patients had longer survival up to 4 years, even if these patients required intubation, when compared to the Ward IHCA patients who did not require intubation (Fig. 2, supplementary Table 3). Third, Perioperative IHCA patients were categorised as those receiving elective and emergency surgeries. When compared to elective surgery, the patients who had emergency surgery (adjusted HR: 1.34; 95% CI: 1.13–1.6) and Ward IHCA (predominantly medical patients; adjusted HR: 1.97; 95% CI: 1.68–2.31) had shorter survival times (Fig. 2, supplementary Table 4). Finally, amongst the subgroup of patients who survived hospitalisation, we found that patients admitted to ICU after a Perioperative IHCA were still associated with longer survival times (adjusted HR: 0.58, 95% CI 0.49–0.7) (Fig. 2, supplementary Table 5).Fig. 2 Kaplan–Meier survival curves of Perioperative and Ward IHCA patients: a stratified by age; b whether were a receipt of mechanical ventilation within 24 h; c based on Perioperative IHCA dichotomised for elective and emergency surgeries and Ward IHCA patients, who were predominantly medical patients; and (d) those who were discharged alive from hospital

Secondary outcomes

The raw secondary outcomes are summarised in Table 2. Perioperative IHCAs had a lower mortality rate in ICU (20.5% vs. 35.8%; p < 0.001) and hospital (24.6% vs. 43.1%; p < 0.001), stayed longer in the ICU (60 [26–135] hours vs. 52 [22–115] hours; p =  < 0.001), but had similar length of stay in hospital (220 [105–433] hours vs. 224 [105–451] hours p = 0.73). Perioperative IHCA group more frequently had delirium (10.7% vs. 6.3%; p < 0.001) when compared to ward IHCA patients. Both groups had similar readmission rate. Perioperative IHCA patients were more frequently discharged home, but there was no difference amongst those discharged to nursing homes or rehabilitation when compared to Ward IHCA patients.

Discussion

Summary of the findings

In this retrospective observational study from Australia that included 5,659 IHCAs, patients admitted to ICU after Perioperative IHCA had better long-term survival than patients admitted to ICU after Ward IHCA. The result remained unchanged after adjusting for age, sex, acute physiology, hospital type, ICU treatment, treatment limitation and comorbidities. A similar trend was observed in all subgroups.

Comparison with published literature

Our mortality data were better than other reported studies. This might be partly due to temporal trends in improved outcome for IHCA patients [23, 24], but mostly due to selection bias. A large systematic review including both ICU and non-ICU patients found only 13.4% of the patients who survived IHCA were alive at 1 year [5]. A recent prospective single-centre Swiss study that included 146 IHCAs observed that about a third of the patients survived to 5 years with favourable neurological and functional status [7]. In contrast, our study found that almost two-thirds of the patients admitted to ICU post-IHCA were alive at 1 year. This data is congruent with other IHCA registry focussing on ICU patients [25, 26]. It is important to acknowledge that the ANZICS-APD only reports on patients admitted to the ICU and do not have any information if IHCA patients die before ICU admission.

One of the largest studies to compare Perioperative and Ward IHCA in ICU was a retrospective analysis from 174 ICUs in the United Kingdom (UK) [14]. This study investigated intubated patients admitted to ICU with a diagnosis of either out-of-hospital- or ward- or perioperative-cardiac arrest. This study found lower hospital mortality in Perioperative IHCA patients when compared to the Ward IHCA patients (56.1% vs. 75.2%). In this UK study, the study period was between 1995 and 2005. Our study used Australian data between 2018 and 2022, and confirmed the similar trend in the long-term outcome. The gap between Perioperative and Ward IHCA still exists despite all the advances in prevention (e.g. rapid response system, early involvement of ICU), resuscitation (e.g. more availability of defibrillator, development of advanced life support training) and post-arrest care (e.g. extracorporeal life support, target-temperature-management) over the last 20 years.

In terms of intubated subgroup, recent large studies have shown that survival and functional outcomes were worse amongst patients who were intubated during IHCA compared with those not intubated [27, 28]. Similarly in our study, patients in both IHCA groups who received early invasive mechanical ventilation had poorer long-term survival. However, Perioperative IHCA patients had longer survival even if they were intubated within 24 h of ICU admission, compared with Ward IHCAs who did not require intubation. The patients who did not receive early mechanical ventilation may have developed a faster return of spontaneous circulation. A time-dependent propensity analysis of data from an IHCA registry showed tracheal intubation during each of the first 15 min of resuscitation compared with no intubation during that minute was associated with decreased survival to hospital discharge [27]. However, the Perioperative IHCA patients who received invasive mechanical ventilation had better survival than their Ward IHCA counterparts, suggesting that there is a higher chance of minimising prolonged hypoxaemia when compared to Ward IHCA patients, which could result in improved survival times.

Study implications

The observed survival advantage of Perioperative IHCA patients might be attributed to a few factors, some were assessed in our study, and some were not. First, patient demographics need to be addressed. Perioperative IHCAs group had fewer risk factors at baseline. ICU admission criteria might be different between Perioperative and Ward IHCA patients. However, Perioperative IHCA patients still had better survival after adjustment for age, sex, acute physiology, hospital type, ICU treatment, treatment limitation, and comorbidities. Perioperative IHCAs even had better outcomes than all Ward IHCA patients even if they were old, intubated or after emergency surgery. These results were particularly interesting as all three are important risk factors [16]. We must acknowledge that Perioperative IHCA might be likely to come back from operation theatre intubated for delayed extubation. Hence, the reasons for intubation may vary between the ward and perioperative groups. Also, surgical patients may have high acute physiology scores directly due to the surgical insult itself with subsequent prolonged ventilation and vasopressor use. Second, another important factor is a monitored environment. Various studies showed that a monitored environment with faster response is key for survival in IHCA patients [11, 12]. Although we lack data on monitoring and response time for the ward IHCA population, we can assume that Perioperative IHCAs had much better values for both, compared to Ward IHCA patients. Third, post-arrest care, we observed that Perioperative IHCAs received intubation and vasopressors more frequently, and had slightly longer ICU stays. More than 40% of our Perioperative IHCA patients had cardiovascular surgery. Hence, such patients required longer ICU stay as part of the postoperative bundle of care. Also, Perioperative IHCAs had fewer treatment limitations than Ward IHCAs. This is the treatment limitation on admission to the ICU, instead of the one placed later during the admission. However, the Perioperative IHCAs group had better survival even after adjustment for ICU treatments and limitation of medical treatment. Finally, anaphylaxis—we might consider that Perioperative IHCAs performed better as they simply had a short period of cardiopulmonary resuscitation (CPR) due to anaphylaxis, which usually has better outcomes [29]. However, ANZICS-APD rules state that a patient is considered a non-operative patient if the procedure was cancelled due to such complications [20]. The source of ICU admission for such patients should be the patient’s location before the operation—i.e. either ward, outpatient or emergency department. Hence, anaphylactic patients are likely to be excluded from our study or considered as ward patients. Perioperative IHCAs had better outcomes despite this.

Strengths

Using large, high-quality data across 175 ICUs in this national dataset allowed us to assess long-term outcomes in this relatively rare population. Linkage with the national death index allowed us to investigate long-term survival, providing a foundation for informed decision-making for patients and caregivers regarding perioperative code status. Furthermore, the large sample size allowed both adjustment for confounders and assessment of specific subgroups of interest, facilitating the extrapolation of our result to the diverse patient population.

Limitations

This study has limitations. First, we did not include patients who were not admitted to the ICU or were too unwell for surgery. We cannot generalise our results to these groups or suggest ICU triage or surgical intervention for them. Second, our registry lacked specific data on pre-IHCA treatment details, anaesthetic management details, direct causes of IHCA, cardiopulmonary resuscitation and post-resuscitation care. Especially, information on direct causes of IHCA is crucial for developing effective prevention strategies. However, we had other important prognosticators such as patient characteristics, laboratory values, diagnosis and surgery types. Third, we lacked long-term outcomes such as functional status and quality of life for IHCA survivors. Fourth, sources of ICU admission were based on the ANZICS-APD algorithm. This provides consistency and objectivity but may misclassify some postoperative patients as ward patients. Perioperative IHCAs were those who were admitted to ICU directly from operation theatre or recovery, instead of those who had surgery at any point during their hospital stay. Another rare limitation is the possible inclusion of out-of-hospital cardiac arrest patients who were admitted to the general ward or transferred to the theatre before ICU admission. Finally, variability in practice (e.g. treatment limitation) should be considered in other countries, although our data are generalisable to Australia.

Future directions

Clinically, future medicine should aim to narrow the gap between perioperative and ward settings. Examples include, but not limited to, enhanced monitoring (e.g. telemetry, smart-band, expansion of ICU), availability of critical care staffs (e.g. rapid response system with more accurate triggering system), standardised care bundle to detect abnormalities, and increased number of advanced life support training (supplementary Table 8).

Future research should include evaluation of long-term functional outcomes for IHCA survivors with both national and international benchmarking of findings. A pilot study collecting functional outcomes in all ICU survivors 3 months after discharge is being undertaken by the ANZICS CORE Registry in 2024 [30]. Also, detailed cardiac arrest database such as National Audit Project [31] will provide further input, especially about the direct causes for cardiac arrest. International collaboration to merge such datasets would be required [32–35]. Also, IHCA researchers should pay closer attention to the differences between Perioperative IHCAs and Ward IHCAs.

Conclusion

In this retrospective multicentre study, patients admitted to ICU following Perioperative IHCA had better long-term survival than patients with Ward IHCA. Future studies on IHCA should distinguish these patients and aim to narrow the gap between them.

Supplementary Information

Below is the link to the electronic supplementary material.Supplementary file1 (DOCX 259 KB)

Acknowledgements

The authors and the ANZICS CORE management committee would like to thank clinicians, data collectors and researchers at the following centres for their contribution (see supplementary Table 6).

Author contributions

Study conception and design: RU, RC, DJ, DP, AS. Data collection: RU, AS, DP. Data analysis: RU, DP. Data interpretation: RU, AS. Writing initial draft: RU, RC, AS. Writing editing: RU, RC, MR, DJ, DP, AS.

Funding

Open Access funding enabled and organized by CAUL and its Member Institutions.

Availability of data and materials

The data dictionary and the ANZICS Centre for Outcome and Resource Evaluation Management Committee policies are available online. Data from the ANZICS-APD are shared with conditional approval by the ANZICS Centre for Outcome and Resource Evaluation Management Committee, but it is not publicly available.

Declarations

Conflicts of interest

All authors declare no support from any organisation for the submitted work, and no competing interests with regards to the submitted work.

Ethics approval and consent to participate

We received approval from the Alfred Hospital Ethics Committee (Reference 215/22) and the Australia and New Zealand Intensive Care Society (ANZICS) Centre for Outcome and Resource Evaluation Management Committee to issue the data from the ANZICS adult patient database (APD) for this study.

Consent for publication

Not applicable.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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