Comparison of Cinical Outcomes Between Nurse Practitioner and Registrar led Medical Emergency Teams – A Propensity Matched Analysis


 Objective: Medical emergency teams (MET) are mostly led by physicians. Some hospitals are currently using nurse practitioners (NP) to lead MET calls. These are no studies comparing clinical outcomes between these two care models. To determine if NP led MET calls are associated with lower risk of acute patient deterioration, when compared to intensive care (ICU) registrar (ICUR) led MET calls.Methods: The composite primary outcome included recurrence of MET call, occurrence of Code blue or ICU admission within 24 hours. Secondary outcomes were mortality within 24 hours of MET call, length of hospital stay, hospital mortality and proportion of patients discharged home. Propensity score matching was used to reduce selection bias from confounding factors between the ICUR and NP group.Results: A total of 1343 MET calls were included (1070 NP, 273 ICUR led). On Univariable analysis, the incidence of the primary outcome was higher in ICUR led MET calls (26.7% vs 20.6%, p = 0.03). Of the secondary outcome measures, mortality within 24 hours (3.4% vs 7.7%, p = 0.002) and hospital mortality (12.7% vs 20.5%, p = 0.001) was higher in ICUR led MET calls. Propensity score matched analysis of 263 pairs revealed the composite primary outcome was comparable between both groups but NP led group was associated with reduced risk of hospital mortality (OR 0.57, 95%CI 0.35-0.91, p = 0.02) and higher likelihood of discharge home (OR 1.55, 95% CI 1.09-2.2, p=0.015). Conclusion: Acute patient deterioration was comparable between ICUR and NP led MET Calls. NP led MET calls were associated with lower hospital mortality and higher likelihood of discharge home.


Introduction
Over the last two decades, establishment of Rapid Response Systems (RRS) in healthcare services has led to a reduction of in-hospital mortality and incidence of in-hospital cardiac arrests (1). Reductions in the incidence of cardiac arrests has been linked with an increase in "dose" of medical emergency team (MET) calls (2). While the composition of the team responding to MET calls varies between different jurisdictions, it is largely led by physicians (3,4). Physicians attending these MET calls generally have other de ned roles. Attendance at MET calls was known to cause signi cant disruption to the critical care physicians' usual activities (5,6). To reduce disruptions to the critical care staff with de ned roles, a small proportion of health care services have introduced trained Nurse Practitioners (NP) speci cally employed to lead MET call response. The need for judicious allocation of increasingly limited resources and growing expertise with the evolving role of NPs has resulted in examination of the role of NPs in leading MET response (7)(8)(9)(10)(11)(12). To our knowledge, clinical outcomes between NP led MET calls and intensive care unit registrar (ICUR) led MET calls have not been compared. The aim was to compare clinical outcomes including subsequent acute deterioration as evidenced by recurrence of MET call, occurrence of code blue or ICU admission within 24 hours of rst MET call between NP and ICUR led MET calls (NPMET study). We hypothesized that the primary composite outcome comprising recurrence of MET call, occurrence of code blue or admission to ICU within 24 hours of the MET calls would not be different between NP and ICUR led MET calls.

Ethics approval
The NPMET study was identi ed as a quality assurance activity and was approved by study site Research Ethics Committee (approval no. QA17PH44).

Rapid Response System (rrs)
RRS at the study site comprises two-tiered efferent limb, (1) comprising single criterion triggered MET response for patients meeting physiological observation thresholds or staff concern triggers (Appendix E Propensity score matching was used to reduce selection bias from confounding factors between the ICUR and NP group. The individual propensities for being in the ICUR led group were estimated with the use of a multivariable logistic regression model that included age, Charlson Comorbidity Index (CCI), weekend (Saturday and Sunday) occurrence of MET call, out of hours occurrence of MET call, "not for resuscitation" plan prior to MET call, triggering of MET call due to oxygen saturation < 90% and diagnoses (medical vs surgical) as the predictor variables. This propensity score was used to match patients managed by ICUR to those managed by NP using a one-to-one nearest neighboring matching with a caliper width of 0.15 times the standard deviation. Primary and secondary outcomes were compared between ICUR and NP led groups using conditional logistic regression taking into account the matched design with results reported as odds ratios (OR) and 95% con dence intervals (95% CI). Sensitivity analysis was also performed using a multivariable logistic regression model that included the same covariates as the propensity score model to ensure robustness of the primary analysis.
All reported p-values are two-sided, and a p-value less than 0.05 was considered to indicate statistical signi cance. Baseline characteristics of both NP led and ICUR led cohort are presented ( Table 1). As shown in Table 1, age, gender, and CCI scores were comparable between both groups. Cardiovascular diagnoses and medical patients were signi cantly more common in ICUR led MET calls, while surgical patients were higher in NP led MET calls ( Table 1).

Results
Out of 1343 patients, 1322 (98.4%) had triggers recorded in MET call documentation ( Table 2). Out of hours MET calls were higher in ICUR led MET calls whereas weekend MET calls were distributed similarly in both groups ( Table 2). The triggers for MET calls were comparable between both groups but for oxygen saturation < 90%, which was more common in ICUR led MET calls (15% vs 9.9%, p = 0.02). Of the observations compared at the onset of MET calls, heart rate (105 vs 99, p = 0.02) and oxygen saturation level (91% vs 93%, p = 0.002) were different between the groups (Table 2).
There was no statistically signi cant difference in hospital length of stay prior to MET call, MET calls occurring within 24 hours of admission and not for resuscitation status between both groups ( Table 2). The severity of illness, length of ICU stay and ICU mortality of patients admitted to ICU were comparable between both groups ( Table 2).
A comparison of interventions performed during attendance for MET call are presented in Table 3. Intravenous cannulation (24.1% vs 15.4%, p = 0.002), uid bolus administration (33.4% vs 26.5%, p = 0.03) and performing ECG (58.6% vs 42.6%, p < 0.001) were more frequent during NP led MET calls. Occurrence of change in resuscitation status was similar in both groups (16.2% in NP led vs 13.6% in ICUR led, p = 0.3). The primary and secondary outcomes in both groups are presented in Table 4. NP led MET calls were associated with lesser occurrence of the composite outcome as compared to ICUR led MET calls (20.6% Vs 26.7%; p = 0.03). There were fewer ICU admissions within 24 hours of index MET call in NP led MET calls as compared to ICUR led MET calls (7.7% Vs 15%; p < 0.0001).

Discussion
This study showed no difference in acute deterioration, a reduction in hospital mortality, and an increased likelihood of discharge home for NP led MET calls. To our knowledge, NPMET is the rst study making contemporaneous comparison of patient centred outcomes between NP and ICUR led MET calls. All other studies either used a retrospective cohort using a before and after design, focused on recognition of systemic in ammatory response syndrome, measured post ICU discharge interventions instead of MET call leadership, did not have ICUR led cohort or measured active surveillance for deteriorating patients rather than MET call leadership (7-13).
The organisation and governance of MET teams in different organisations are variable and is largely dependent on the availability of personnel (4). To the best of our knowledge, there are no studies that directly compared the e cacy of service delivery on clinical outcomes. NPMET study showed that a NP led model of care in MET calls might offer better clinical outcomes than ICUR led MET calls. There could be several reasons for the association of NP led MET calls with lower risk of hospital mortality and higher probability of discharge to home. NPs leading MET calls had prior experience of attending MET calls for over 7 years. Although they were not leading these MET calls, this experience could have contributed to better patient management that may have led to improvement in clinical outcomes. ICUR led MET calls were attended by registrars with varying experience in assessing and treating acutely ill or deteriorating patients in an unfamiliar ward environment. This is unavoidable in the existing system, where ICURs are expected to gain competence in managing MET calls, while extrapolating knowledge of management of deteriorating patients from the ICU to a ward environment.
It is possible that the differences in the outcomes could also be due to differences in interventions that were performed during the MET calls. Interventions such as IV cannulations, administration of uid bolus, and performance of ECGs were signi cantly higher in NP led MET calls. While the retrospective nature of our study does not allow us to further de ne the in uence of these interventions on the outcomes, it is possible that early correction of the physiological abnormalities during an acute deterioration could have contributed to better outcomes in these MET calls (14).