Rapid Response Systems and MET Calls — Written Clinical Reasoning

SAQ 1 — Integrated Post-MET-Call Management and Afferent-Limb Analysis (20 marks, 30 minutes)

Prompt: Outline your integrated management of Mr Chen in the post-MET-call period, addressing: (a) the interpretation of the MET call record and your reassessment of the response so far; (b) the working diagnosis, the source identification, and the ongoing resuscitation including the fluid strategy in the context of his ischaemic heart disease; (c) the management of his hyperkalaemia and his new atrial fibrillation; (d) the escalation decision and the ceiling-of-care conversation; (e) the afferent-limb analysis — at what points should the escalation have occurred, and what does the trajectory tell you about the detection system; and (f) the post-MET plan you would communicate to the team. [1]

Model Answer

(a) Interpretation of the MET record and reassessment (3 marks): [1]

The MET call record shows a NEWS2 that rose from 2 to 8 over four hours, crossing the medium-risk threshold (5 to 6) at approximately 19:00 and the high-risk emergency threshold (7 or more) at approximately 21:00, with the MET call made at 22:00. The call was therefore made approximately one hour after the emergency threshold was crossed, and approximately three hours after the intermediate threshold. The MET interventions (high-flow oxygen, fluid challenge, broad-spectrum antibiotics) were appropriate for the working diagnosis of septic shock, but the patient has not responded adequately — he remains hypotensive at 88 over 54 after 500 mL, oliguric at 20 mL per hour, and his NEWS2 is still elevated. My reassessment is that he is in refractory septic shock with multi-organ involvement (acute kidney injury, hyperkalaemia, new atrial fibrillation, encephalopathy) and that ward-level therapy has failed; the escalation to ICU is indicated. [1]

(b) Working diagnosis, source, and fluid strategy (4 marks): [1]

The working diagnosis is septic shock, most likely from progression of the cellulitis to deeper soft-tissue infection (necrotising fasciitis or myonecrosis) or a nosocomial pneumonia. I examine the limb urgently for signs of necrotising infection (spreading erythema, pain out of proportion, crepitus, blistering, skin necrosis) and request a chest X-ray. I send blood cultures (taken before the antibiotic escalation) and review the white cell count and inflammatory markers. I arrange a surgical review of the limb immediately if there is any suspicion of necrotising infection, because source control is time-critical and delays mortality [6].

The fluid strategy must be modified for his ischaemic heart disease. The Surviving Sepsis Campaign 2021 recommends 30 mL per kilogram of crystalloid in the first three hours for sepsis with hypoperfusion [6], but his ischaemic heart disease and likely diastolic dysfunction make him vulnerable to fluid overload and pulmonary oedema from an uncritical bolus. My approach is 250 mL aliquots of balanced crystalloid over 15 minutes, with reassessment between each for fluid responsiveness (a rise in blood pressure, a fall in heart rate, an improvement in capillary refill) and for signs of overload (a rise in JVP, new basal crackles, a fall in SpO2). If he is not fluid-responsive after two aliquots, I start an early vasopressor — noradrenaline via a central line — to restore the mean arterial pressure to above 65 mmHg, and I use a focused bedside echocardiogram or a passive leg raise to guide the fluid if available. The principle: the comorbidity does not override the guideline, but it modifies the aliquot size, the reassessment frequency, and the threshold for vasopressor support.

(c) Hyperkalaemia and new atrial fibrillation (3 marks): [1]

The hyperkalaemia (potassium 5.6) is a medical emergency, particularly with the new arrhythmia. I give calcium gluconate 10 mL of 10 per cent intravenously over 5 to 10 minutes for myocardial membrane stabilisation, followed by insulin-dextrose (10 units of Actrapid in 50 mL of 50 per cent dextrose over 15 minutes) and a salbutamol nebuliser to shift potassium into cells. I monitor the blood glucose during and after the insulin-dextrose for late hypoglycaemia. I recheck the potassium and the ECG within 30 minutes. Given his acute kidney injury and oliguria, he is unlikely to excrete the potassium spontaneously; if the hyperkalaemia is refractory or recurs, he will need renal replacement therapy, which is itself an indication for ICU admission. [1]

The new atrial fibrillation is almost certainly secondary to the sepsis, the fever, and the electrolyte disturbance. My priority is to treat the sepsis and correct the potassium; the AF will usually revert as the acute illness resolves. I would NOT give a beta-blocker or a calcium-channel blocker in his hypotensive state. If the AF persists and is itself the haemodynamic problem, the options are amiodarone 300 mg intravenously over one hour or, if peri-arrest, synchronised DC cardioversion. The teaching point: treat the cause of the arrhythmia first. [1]

(d) Escalation and the ceiling-of-care conversation (3 marks): [1]

I call ICU now — he has met the criteria (refractory hypotension, need for vasopressor support, likely need for renal replacement therapy, multi-organ failure). The ceiling-of-care decision weighs three factors: the reversibility of the acute illness (the sepsis is potentially reversible, which favours escalation), his baseline function (independent, retired engineer — favouring escalation), and his expressed wishes. I ask the family, gently and early, whether he has an advance care directive and what he would want. A previously independent 68-year-old with potentially reversible sepsis is a candidate for a time-limited trial of ICU care — a defined period of 48 to 72 hours of maximal support, with a clear review point. I do not frame this as all-or-nothing; the trial is a defined commitment after which we reassess with the family [1].

(e) Afferent-limb analysis (4 marks): [1]

The trajectory is the signal. The NEWS2 crossed 5 at approximately 19:00, which is the medium-risk threshold mandating an urgent ward-registrar review within 30 minutes and hourly monitoring. It crossed 7 at approximately 21:00, which is the high-risk emergency threshold mandating an emergency critical care assessment within minutes. The MET call was made at 22:00 — one hour after the emergency threshold and three hours after the intermediate threshold. The afferent limb fired late at both thresholds. [1]

This is a classic afferent-limb failure, and it is the dominant failure mode of the Rapid Response System. The MERIT study showed the MET was called to only about 30 per cent of patients who met criteria [1]; this patient's late call is a milder version of the same failure. The fixes are: the education of the ward staff in recognising the intermediate threshold and acting on it (not waiting for the emergency threshold); the visible observation chart that displays the trend; the bedside signage that flags a rising score; and the feedback to the ward team after the event, which closes the quality-improvement loop. The observation that the respiratory rate was the rising parameter (as it is in the majority of deteriorations) reinforces the specific teaching that the respiratory rate is the earliest and most neglected vital sign [2].

(f) The post-MET plan (3 marks): [1]

I set and communicate the following post-MET plan to the nursing staff, the treating consultant, the ICU team, and the family: [1]

1. Goals of care: active treatment of the reversible septic shock with a time-limited trial of ICU support.
2. Ceiling of treatment: ICU-level support including vasopressors and renal replacement therapy, with mechanical ventilation if required, for a defined 48 to 72 hour trial with a review point.
3. Monitoring: continuous cardiac and SpO2 monitoring, hourly observations, hourly urine output via catheter.
4. Ongoing management: continued broad-spectrum antibiotics, noradrenaline infusion titrated to MAP above 65, serial lactate and potassium, daily creatinine, and the surgical review for source control.
5. Named responsible consultant: the treating general medical consultant, with the ICU consultant co-leading during the ICU admission.
6. Review timeline: ICU review within 30 minutes, registrar review at 30 minutes and then hourly, consultant review within the hour and at the 48 to 72 hour trial endpoint.
7. Communication: the family is informed of the deterioration, the plan, and the review point, and the conversation is documented. [1]

SAQ 2 — Evidence Synthesis for a Hospital Executive (10 marks)

Prompt: A hospital executive is considering implementing a Rapid Response System and asks you: (a) to describe the four-limb model and where the investment should be prioritised; (b) to summarise the MERIT study and the meta-analytic evidence honestly; and (c) to explain why the mortality signal is less consistent than the cardiac arrest signal, and what that means for the evaluation. [1]

Model Answer

(a) The four-limb model and the investment priority (4 marks): [1]

The Rapid Response System, as defined at the 2005 consensus conference, comprises four interdependent limbs [2]: the afferent limb (detection — the ward staff, the track-and-trigger system, and the calling criteria), the efferent limb (the response team — the MET, RRT, or critical care outreach), the administrative or governance limb (resources, staffing, policy, culture), and the quality improvement limb (audit, outcome review, education, feedback). The investment must attend to all four, but the evidence and the experience of implementation consistently identify the afferent limb as the weakest link. A perfectly constituted team is useless if the ward staff do not measure, score, recognise, or escalate the deterioration — the MERIT finding that the team was called to only 30 per cent of patients who met criteria is the afferent-limb failure [1]. My priority for the executive is the ward education: the simulation training, the case-based teaching, the visible observation charts, the bedside escalation signage, and the cultural message that it is always acceptable to call. The team is the visible part; the education is the part that determines whether the team is called.

(b) MERIT and the meta-analytic evidence (4 marks): [1]

The MERIT study (Hillman 2005), the only cluster-randomised controlled trial, found that introducing the MET system increased emergency team calls from 3.1 to 8.7 per 1000 admissions but did not significantly reduce the composite primary outcome of cardiac arrest, unexpected death, or unplanned ICU admission (5.31 versus 5.86, p equal to 0.640) [1]. The trial was underpowered, there was contamination (control hospitals increased their own calls), the implementation period was short, and the composite included unplanned ICU admission, which may rise with appropriate escalation. The meta-analytic evidence is more favourable: Chan's 2010 review of 18 studies showed a 33.8 per cent reduction in non-ICU cardiopulmonary arrests (RR 0.66) but no significant reduction in overall hospital mortality (RR 0.96) [4], and Maharaj's 2015 review of 29 studies suggested reductions in both adult mortality (RR 0.87) and arrests (RR 0.65), though limited by heterogeneity and before-and-after design [5]. The honest synthesis is that the cardiac arrest reduction is the consistent signal and the mortality benefit is plausible but not conclusively demonstrated.

(c) Why the mortality signal is diluted (2 marks): [1]

The mortality signal is diluted by two factors. First, the patients for whom escalation is appropriately withheld — the ceiling-of-care decision means that a proportion of MET calls lead to a refocusing on comfort rather than ICU, and these patients die in both the intervention and the control arms. The MERIT observation that the MET system increased the rate of not-for-resuscitation orders is part of this dilution: the system surfaces the goals-of-care conversation, which appropriately redirects some patients away from escalation. Second, the before-and-after design of most studies means that secular trends in mortality (from other quality improvements) are confounded with the RRS effect. For the evaluation, the executive should measure the non-ICU cardiac arrest rate (the primary outcome the system is designed to reduce), the MET call rate per 1000 admissions (the afferent-limb activity), the proportion of patients meeting criteria who were called (the afferent-limb sensitivity), and the outcome of calls. The mortality rate is a secondary marker, useful in aggregate but not the primary test of the system's function [2].