Study design and setting
This single-center retrospective control study was conducted at a tertiary emergency critical care center (Tokyo, Japan), which receives approximately 170 patients with OHCA every year. The medical records of OHCA patients transferred to our center between April 1, 2015, and March 31, 2022, were surveyed. The staffing shift during the study period was generally provided as follows: (i) day-time (> 2 board-certified emergency physicians, 3 medical interns, and 3 nurses) and (ii) night-time (1 board-certified emergency physician, 3 medical interns, and 2 nurses). Procedures and medications were equally available at all times. Pre-hospital factors were recorded as similar between day- and night-times, as the Japanese emergency service (EMS) system ensures constant quality assessment of pre-hospital care (including holidays). The method of chest compressions on arrival of patients at the ED was formally changed at the study center on May 1, 2020, at which point automated mechanical compression replaced manual compression. During the study period, CPR and post-cardiac arrest care (including targeted temperature management) were provided consistently in accordance with the 2015 or 2020 AHA Guidelines for CPR and European Resuscitation Council (ERC).
This study complied with the principles of the 1964 Declaration of Helsinki and its amendments. The study protocol was approved by the ethics committee of Tokyo Medical and Dental University Hospital of Medicine (M2022-249). The need for informed consent was waived due to the retrospective nature of the study. All patient data were retrospectively collected from electronic medical charts and anonymized before statistical analyses.
Study population
This study included consecutive OHCA patients who were transferred to the Tokyo Medical and Dental University Hospital between April 1, 2015, and March 31, 2022. We excluded patients who were less than 18 years old, had do-not-attempt-resuscitation orders, experienced cardiac arrest due to trauma, received open-chest CPR, did not undergo chest computed tomography (CT) examination, or had missing or insufficient data regarding the study variables (i.e., lack of information regarding CPR duration, witnessed status, or initial rhythm). In addition, patients were excluded if they had received CPR from an automated chest compression device after arrival to the ED before May 1, 2020, regardless of the setting, as this study aimed to evaluate whether the quality of CPR performed by emergency medical staff was comparable to mechanical chest compression devices. Patients who were not suitable for mechanical CPR (e.g., those with severe cachexia, morbid obesity, and chest wall deformity) were also excluded from the study.
The Lund University Cardiac Assist System 3 (LUCAS 3, Stryker, Kalamazoo, MI, USA) was used as the mechanical chest compression device at our hospital for in-hospital resuscitation after May 1, 2020. LUCAS 3 is a piston-based device that provides active compression and decompression via a suction cup placed at the center of the chest.
Data collection
The following data were collected retrospectively from medical records: age, sex, ED admission time, presence or absence of a witness to cardiac arrest, presence or absence of bystander CPR before the arrival of paramedics’ at the scene, shockable rhythm status, cause of cardiac arrest, whether or not ROSC was achieved, IHCPR duration, out-of-hospital CPR (OHCPR) duration, and patient status at the time of hospital discharge (i.e., survival or death). We also used the patients’ medical records and 64-slice CT imagery to collect data regarding CPR-related chest injuries (i.e., rib fractures, sternal fractures, pleural effusion/hemothorax, or pneumothorax). Our hospital has a general policy of routinely performing CT after CPR to identify the cause of cardiac arrest in non-traumatic cases. CT findings were interpreted by ≥ 2 board-certified emergency physicians and one radiologist.
Definitions
OHCA was defined as cardiac arrest that occurred out-of-hospital, during which the patient was unresponsive to stimulation, gasping or not breathing, and had carotid arteries that were not palpable for a maximum assessment interval of 10 seconds, as described previously. [9] Based on the hospitals’ shift schedules and the results of previous studies, [9, 10] we divided the patients into two groups on the basis of when they were admitted to the ED: during day-time (07:00–22:59) or night-time (23:00–06:59).
OHCPR duration was defined as the interval between EMS dispatch and ED arrival in cases with bystander CPR, [11] or as the interval between EMS arrival at the scene and ED arrival in cases without bystander CPR.
IHCPR duration was defined as the interval between ED arrival and termination of resuscitation or ROSC. [12] For this study, ROSC was defined as the return of spontaneous circulation that lasted at least 5 min. We defined CPR-related chest injuries as rib fractures, sternal fractures, pleural effusion/hemothorax, or pneumothorax, as described previously. [5]
Outcome Variables
The primary outcomes of this study were defined as rate of ROSC, frequency of CPR-related chest injuries, and duration of IHCPR. We defined secondary outcomes as rate of survival to ED discharge, rate of survival to hospital discharge, and rate of survival with good neurological outcomes to hospital discharge. Cerebral Performance Category (CPC) scores were used to classify neurological outcomes into five stages:1) full recovery or mild disability, 2) moderate disability but independent in activities of daily living, 3) severe disability with dependence for support in activities of daily living, 4) persistent vegetative state, and 5) death. CPC scores of 1 or 2 indicated good neurological outcomes, while CPC scores of 3 or 4 implied poor outcomes. [13]
Statistical analysis
Categorical variables were reported as numbers (percentages), while continuous variables were reported as means (standard deviation) or medians (interquartile range), as appropriate.
We divided the enrolled patients on the basis of whether they were admitted to the ED during day-time or night-time, and further divided them into two categories based on the IHCPR device used: the manual chest compression (mCC) group (from April 1, 2015, to April 31, 2020) and automatic chest compression device (ACCD) group (from May 1, 2020, to March 31, 2022). First, we used a multivariate ordered logistic regression model to evaluate the interaction between in-hospital ACCD use and admission time for the outcomes to evaluate whether the effect of in-hospital ACCD use was affected by admission time. We incorporated age, sex, witnessed status, bystander CPR status, initial rhythm (shockable or not), cause of cardiac arrest, and OHCPR duration as explanatory variables in the multivariate model, which were clinically plausible and well-known confounders in previous epidemiologic studies. Second, we used univariate and multivariate ordered logistic regression models to evaluate the impact of ACCD use during IHCPR on outcomes in the day- and night-time groups, respectively.
All statistical analyses were performed using the R software (version 4.1.1; R Foundation for Statistical Computing, Vienna, Austria). Moreover, we used a command to add statistical functions that are frequently used in biostatistics. All reported p values were two-sided, and p values < 0.05 were considered statistically significant.