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Risk factors and outcomes of postoperative emergency response team activation: a matched case-control study
Matthew I Hardman*, S Chandralekha Kruthiventi*, Michelle R Schmugge*, Alexandre N Cavalcante, Jeffrey B Jensen, Darrell R Schroeder, Juraj Sprung, Toby N Weingarten, (* equal first authors)
Crit Care Resusc 2020; 22 (1): 6-14
- Matthew I Hardman* 1
- S Chandralekha Kruthiventi* 1
- Michelle R Schmugge* 1
- Alexandre N Cavalcante 1, 2
- Jeffrey B Jensen 1
- Darrell R Schroeder 3
- Juraj Sprung 1
- Toby N Weingarten 1
- (* equal first authors) 4
Toby Weingarten currently serves as a consultant to Medtronic in the role as chairman of the Clinical Endpoint Committee for the Prodigy Trial; has received research support from Respiratory Motion (study equipment) and unrestricted investigator-initiated grants from Merck (active) and Baxter (completed).
OBJECTIVE: To determine patient and perioperative characteristics associated with unexpected postoperative clinical deterioration as determined for the need of a postoperative emergency response team (ERT) activation.
DESIGN: Retrospective case–control study.
SETTING: Tertiary academic hospital.
PARTICIPANTS: Patients who underwent general anaesthesia discharged to regular wards between 1 January 2013 and 31 December 2015 and required ERT activation within 48 postoperative hours. Controls were matched based on age, sex and procedure.
MAIN OUTCOME MEASURES: Baseline patient and perioperative characteristics were abstracted to develop a multiple logistic regression model to assess for potential associations for increased risk for postoperative ERT.
RESULTS: Among 105 345 patients, 797 had ERT calls, with a rate of 7.6 (95% CI, 7.1–8.1) calls per 1000 anaesthetics (0.76%). Multiple logistic regression analysis showed the following risk factors for postoperative ERT: cardiovascular disease (odds ratio [OR], 1.61; 95% CI, 1.18–2.18), neurological disease (OR, 1.57; 95% CI, 1.11–2.22), preoperative gabapentin (OR, 1.60; 95% CI, 1.17–2.20), longer surgical duration (OR, 1.06; 95% CI, 1.02–1.11, per 30 min), emergency procedure (OR, 1.54; 95% CI, 1.09–2.18), and intraoperative use of colloids (OR, 1.50; 95% CI, 1.17–1.92). Compared with control participants, ERT patients had a longer hospital stay, a higher rate of admissions to critical care (55.5%), increased postoperative complications, and a higher 30-day mortality rate (OR, 3.36; 95% CI, 1.73–6.54).
CONCLUSION: We identified several patient and procedural characteristics associated with increased likelihood of postoperative ERT activation. ERT intervention is a marker for increased rates of postoperative complications and death.
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Emergency response teams (ERTs) are the effector arm of a rapid response system (RRS) and have been adopted by many health organisations to provide prompt evaluation and intervention for hospitalised patients. 2
In 2012, we examined our institutional experience with postoperative ERTs and made several observations about the association between patient and clinical factors and ERT outcomes. 3
Methods and materialsThe Mayo Clinic Institutional Review Board approved the review of health records for study purposes (protocol No. 16-004503). Consistent with Minnesota Statute 144.295, prior authorisation was provided by all study patients for research use of their health records. This study used a retrospective case–control design to review patient characteristics and perioperative data and assess potential factors surrounding the need for ERT activation within 48 hours after procedures performed with general anaesthesia. The study took place at the Mayo Clinic (Rochester, MN, USA) — a large academic quaternary care facility that keeps a record of all ERT activations.
Emergency response team activation callsAt Mayo Clinic, an ERT can be categorised as a rapid response team (RRT) or a code (cardiac arrest) team. The code team is activated for pulseless arrest and impending respiratory arrest or threatened airway. RRTs are activated on the basis of standard criteria, 10
- decline in oxyhaemoglobin saturation;
- profound bradycardia or tachycardia;
- concern for possible myocardial ischaemia; and
- acute neurological deficits or mental status changes (agitation, delirium).
Study populationThe Mayo Clinic Department of Anesthesiology and Perioperative Medicine maintains a log of all ERT activations that occur at the Mayo Clinic Rochester Campus. Using the ERT records, we identified all patients older than 18 years who required a postoperative ERT activation between 1 January 2013 and 31 December 2015. Patients were excluded if they did not undergo general anaesthetic (ie, had sedation only or regional anaesthesia) or were admitted directly to a higher level of care (eg, an intensive care unit [ICU]). To assess risk factors for ERT activation for each patient who required a postoperative ERT call, we randomly selected two matched control patients who did not require ERT activation within 48 postoperative hours on the basis of age, sex and exact type of procedure. Matched controls were selected from the entire surgical cohort during the study timeframe using automated interrogation of the electronic medical record. 11
Data abstractionA comprehensive chart review was undertaken of the preoperative, intraoperative and postoperative variables as previously described. 3
Classification of emergency response team interventionsThe abstracted ERT data included the probable primary cause of activation:
- cardiac causes — symptoms and signs of myocardial ischaemia, dysrhythmias, severe hypertension;
- hypotension — hypovolaemia, distributive shock including septic shock, bleeding, vasovagal reaction (syncope);
- neurological/psychiatric causes — sensorium changes (somnolence, delirium), psychiatric decompensation, seizure activity, acute motor or sensory deficit;
- pulmonary causes — oxyhaemoglobin desaturations, hypoventilation (bradypnoea, apnoea), tachypnoea;
- other causes of respiratory distress — eg, typically upper airway pathology such as bleeding, angioedema; and
- miscellaneous causes — drug or allergic reactions, fever, severe pain, sepsis without hypotension, acute postoperative bleeding without haemodynamic instability, glycaemic or electrolyte abnormalities.
Statistical analysesData were summarised as mean (standard deviation [SD]) or median (interquartile range [IQR]) for continuous variables and as frequency (percentage) for nominal variables. The denominator of patients admitted to the post-anaesthesia care unit was used in the estimation of incidence of ERT activation.
Analyses to identify preoperative and intraoperative characteristics associated with ERT activation were performed with multivariable conditional logistic regression that took into account the 1:2 matched set study design. Results from these analyses were summarised as odds ratio (OR) and 95% confidence interval (CI). Additional multivariable conditional logistic regression analysis was performed to assess the association between demographic and clinical characteristics and ERT activation by indication. Secondary analyses were performed to compare postoperative outcomes between ERT cases and controls. These comparisons were performed with the two-sample t test (or Wilcoxon rank sum test) for continuous variables and the X2 test (or Fisher exact test) for categorical variables. Statistical significance was considered achieved for a two-tailed P < 0.05. For analyses of ERT activation by indication, statistical significance was considered for two-tailed P < 0.01. Analyses were performed with statistical software (JMP Pro version 14.1.0 and SAS statistical software version 9.2; SAS Institute).
ResultsDuring the study period, 105 345 patients underwent procedures that required general anaesthesia and were discharged to a regular ward. Of those patients, 797 required ERT activation within 48 hours of anaesthesia, yielding an estimated rate of 7.6 (95% CI, 7.1–8.1) activations per 1000 anaesthetics. This rate stayed stable over the 3 years of study (7.4 activations per 1000 anaesthetics in 2013, 7.9 per 1000 anaesthetics in 2014, and 7.4 per 1000 anaesthetics in 2015). Among ERT patients, 238 (29.9%) underwent orthopaedic, 131 (16.4%) general, 115 (14.4%) colorectal, 92 (11.5%) urological, 82 (10.3%) gynaecological, 56 (7.0%) head and neck, 36 (4.5%) thoracic, 17 (2.1%) breast or plastic, 17 (2.1%) vascular, and 10 (1.3%) neurological operations. Three patients (0.4%) had bone marrow harvest.
Details of emergency response team triggers and interventionsFor 266 patients (34.4%), ERT activations occurred within the first 12 postoperative hours, and for 470 patients (59.0%), ERT activations occurred within the first 24 hours (Figure 1). The indications for ERT activations were cardiac (n = 245, 30.7%), hypotension (n = 216, 27.1%), neurological/psychiatric (n = 83, 10.4%), pulmonary (n = 172, 21.6%), and miscellaneous (n = 81, 10.2%) causes. Interventions (overall and according to ERT indication) performed and immediate outcomes are summarised in Table 1. Thirteen patients had cardiac arrest that required chest compressions, six received defibrillation, and 17 received tracheal intubation. Five patients died: two of ventricular fibrillation (one secondary to myocardial infarction and the other of an unidentified cause) and three of cardiac arrest (one after pulmonary embolism and two of an unidentified cause). ERT activation resulted in transfer to the ICU for 344 patients (43.2%). For 179 patients (22.5%), ERT was limited to evaluation, with continued observation on the ward.
Associations with the development of an emergency response teamFor assessment of the potential risk factors for ERT activation, these patients were matched 1:2 with control patients who did not require postoperative ERT (Table 2). The risk factors for ERT call included an existing cardiovascular or neurological disease, emergency procedures, longer procedures, preoperative use of gabapentin, and intraoperative use of colloids. The secondary multivariate association of clinical characteristics with ERT activation according to clinical indications was assessed (Table 3); the full model is presented in the Online Appendix, Supplementary table.
Patient outcomes in association with emergency response team activationCompared with control patients, ERT patients had longer hospital stay and higher rates of all major complications, especially pneumonia (14.1% v 4.6%; P < .001) (Table 4). The 30-day ERT mortality rate was 4.5% (n = 36), with patients with an RRT having a three-fold increased risk of death (OR, 3.36; 95% CI, 1.73–6.54). Of the deaths, cardiopulmonary arrests were most frequent (n = 16), followed by sepsis (n = 5), acute respiratory failure (n = 4), fulminant hepatic failure (n = 1), hypovolaemic shock (n = 1), and renal failure (n = 1). Eight patients died after discharge and from an unknown cause. Among control patients, 16 died within 30 postoperative days from cardiorespiratory arrest (n = 7), pulmonary embolism (n = 1), respiratory failure (n = 2), sepsis (n = 1), and after discharge with cause unknown (n = 5).
DiscussionIn this study, we used ERT activation as a surrogate for acute deterioration of health status, with the aim of identifying patient and procedural characteristics associated with postoperative ERT activation. Our main findings were that the rate of postoperative ERT activation from 2013 to 2015 was higher than in our previous report. 3
Emergency response team activation rates and disposition following eventsThe incidence of ERT calls was 7.6 per 1000 anaesthetics, compared with two per 1000 anaesthetics in our previous report 3
Predictors of emergency response team activationThe patient and periprocedural characteristics that may be used to predict ERT activation have been reported infrequently. 3
Gabapentin in our practice is used mostly as a part of the ERAS protocol. We previously demonstrated associations between preoperative gabapentin administration and increased rate of respiratory depression during anaesthesia recovery, 7
Emergency response team management and outcomesThe most frequent indications for ERT were cardiac causes and hypotension, which accounted for 58% of activations, at a rate similar to our previous study 3
LimitationsThis study has all inherent limitations related to its retrospective design. Many of the details of the clinical presentation were deduced from documentation of the ERT team, recorded in medical records during the time of acute patient decompensation, and thus reflecting a degree of subjectivity based on clinical judgements made during a time of crisis. Our use of ERT activation as a surrogate for acute clinical deterioration is somewhat arbitrary, but nevertheless, it represents an acceptable marker of substantial deviation from the expected postoperative course. Our designation of ERT indication was determined by review of retrospective data based on clinical notes and interventions. In some cases, multiple indications for ERT activation were present, and in these cases, the primary (ie, most life-threatening) indication was selected. This concern was most germane in distinguishing cardiac from hypotension causes. We are comfortable in our final adjudication that the ERT indications deemed for hypotension were truly limited to this cause. Our ERT disposition after activation, as well as the postoperative outcomes, represents outcomes of the large quaternary medical centre and, therefore, they may not be generalisable to other health institutions. Further, as indications for ERT activation may differ between institutions, our incidence rates may not be applicable to other practices. Because cases and controls were matched on exact surgical procedure, there was insufficient variability between anaesthetic techniques (general anaesthesia v combined regional/general anaesthesia) to meaningfully explore this variable. Lastly, data acquisition from our cohort reflects our practice from 2013 to 2015, and risk assessment and outcomes from ERT calls would be expected to change over time to mirror changes in clinical practice.
ConclusionWe identified several patient and procedure risk factors for postoperative ERT activation. More than 50% of ERT calls were considered severe enough to warrant transfer to the critical care environment for higher level monitoring and/or treatment. Because postoperative ERT activation is a marker of substantially increased morbidity and mortality, these patients deserve vigilant observation for the development of in-hospital complications.
Acknowledgements: A portion of this research has been presented as an abstract to the 9th Annual Meeting of the Society of Anesthesia and Sleep Medicine; Orlando (USA), 17–18 October 2019. Financial support was provided by the Department of Anesthesiology and Perioperative Medicine, Mayo Clinic.