Postoperative cognitive decline: the nurse's role in identifying this underestimated and misinterpreted condition

Definition

POD can be thought of as an acute cerebral failure and a multifactorial syndrome that highlights the role of cognitive reserve or brain resilience versus external harmful factors (Hshieh et al, 2018). It presents as an attention disorder that occurs acutely after surgery (within 72 hours) and cannot be explained by a pre-existing or evolving neurocognitive disorder.

The course of POD fluctuates. Clinical signs include an altered state of consciousness, inattentiveness, disorientation, inversion of the sleep-wake cycle, inappropriate behaviour and emotional instability. In some cases, clinical presentation is more severe with signs of perceptual disturbances (hallucinations), memory impairment, alterations in language and psychomotor disorders (European Delirium Association and American Delirium Society, 2014).

Sometimes, it manifests as a state of apathy, which can be unrecognised so it remains undiagnosed and untreated (Rudolph and Marcantonio, 2011).

Identifying POD: epidemiology, costs and diagnostic criteria

Inouye et al (2014), in a systematic review, reported the overall incidence of POD at 12% to 51%. They estimated the incidence of POD in three types of major surgical procedures: cardiac surgery (11–46%); noncardiac surgery (13–50%); and orthopaedic surgery (12–51%).

Delirium in general has been estimated to cost more than $164 billion a year in the USA (Leslie et al, 2008) and more than $182 billion a year in 18 European countries (Inouye et al, 2014). Weinrebe et al (2016), in line with this data, estimated hyperactive delirium to cost €1200 per case in total because of increased hospitalisation, medication use and time spent by doctors, nurses, and other healthcare professionals.

POD clinical presentation in elderly patients is complex, as these patients are likely to have multiple predisposing factors and be exposed to harmful insults that may precipitate the condition. Predisposing factors are independent variables that increase susceptibility and therefore the risk of elderly patients developing POD. They can be identified during a preoperative assessment that takes into account demographic variables, comorbidities, and surgical and anaesthetic variables (Table 1).

The criteria used to diagnose delirium are given in the Diagnostic and Statistical Manual of the Association of American Psychiatrists (Sachdev et al, 2014) and the International Statistical Classification of Diseases and Related Health Problems Diagnosis Code F05: Delirium due to Known Physiological Condition (ICD-10-CM, 2018).

To help practitioners recognise the condition correctly on the basis of robust, evidence-based clinical assessment, several validated tools are available (Table 2). Despite these, health professionals fail to recognise the onset of POD in more than 80% of cases (Marcantonio, 2012).

This could be because they are focusing on factors other than POD because elderly surgical patients can be complex, be of an advanced age, have comorbidities, pre-existing dementia and mild cognitive impairment, and may be experiencing mood changes. Second, health professionals are often reluctant to perform cognitive screening tests because they are thought to make patients and their families uncomfortable (Ribeiro Filho and Lourenço, 2009). Nurses are particularly reluctant to administer the tests when patients are about to undergo surgery as it is already a stressful time for them (Brooks et al, 2014). Finally, it is necessary to consider the intrinsic risk of false positives occurring because of tools' limitations, which could needlessly alarm patients and their families.

However, to make an accurate diagnosis of POD, knowledge about a patient's mental state during the perioperative period is essential.

Definition

POCD can be defined as a decline in perceptual, memory and information processing functions (Newman et al, 2007). It persists over time, and is characterised by declines in the recall of memory and a slowing down of the ability to process information.

There may be disturbances of attention but these are not characterised as main manifestations and patients generally remain fully conscious, unlike those with POD.

Krenk and Rasmussen (2011) described POCD as a decline in postoperative cognitive state observed when cognitive status is compared to how it was in the preoperative period.

Epidemiology and aetiology

The epidemiology of POCD is unclear because of the nature of studies performed, heterogeneity in methodology and different populations studied; however, the evidence appears to associate anaesthesia and surgery with POCD (Terrando et al, 2015).

The first international multicentre study on POCD conducted on patients undergoing noncardiac surgery provided the first methodological approach, which is used today to identify POCD (Moller et al, 1998). This study reported a POCD incidence of 25.8% and 9.9% respectively at 1 week and 3 months postoperatively (although the latter figure could be an underestimate because 22% of the sample had died by three months after the procedure); it found age could be the main risk factor for long-term cognitive decline.

In 2009, the International Study of Post-Operative Cognitive Dysfunction group investigated possible consequences for patients experiencing persistent cognitive decline and reported higher mortality rates, a risk of leaving the labour market prematurely and a need for financial support (Steinmetz et al, 2009).

Evered et al (2011) compared patients undergoing cardiac surgery with those undergoing noncardiac surgical procedures and minimally invasive procedures such as coronary arteriography. They found the incidence of POCD was 25.8–43% during the first postoperative week and 17% at 3 months; the 3-month data covered three study groups and were similar for all types of surgery. These results have important implications, as they potentially indicate that elderly patients experience POCD regardless of the type of surgical procedure and anaesthetic, shifting attention from type of surgery to patient susceptibility as a causal factor.

Although the aetiology of POCD has not yet been clarified and remains unknown in many respects, greater age and educational level, a slight cognitive decline before surgery, polypharmacy and severe comorbidity, longer duration of anaesthesia, previous surgical interventions, and respiratory and infectious complications have all been confirmed as risk factors (Moller et al, 1998; Krenk and Rasmussen, 2011).

In cardiac surgery, risk factors include micro-emboli, activation of the inflammatory response and disruption of the blood–brain barrier, and alteration of cerebral metabolism because of hypoxaemia and oedema (Carrascal and Guerrero, 2010). Acute pain in the immediate postoperative period, which often manifests with inflammation, can cause brain structural changes when it is protracted or not adequately managed (Nadelson et al, 2014). These changes result in hypofunctionality that manifests clinically with memory impairment secondary to attentional deficits, inability to inhibit automatic responses guided by external stimuli and inability to plan and implement strategies to perform a task.

Effective postoperative pain management is indispensable to the good recovery of a patient's functional ability and limits the triggering of processes associated with structural brain deterioration and worsening cognitive function during the postoperative period. (Nadelson et al, 2014). On the other hand, opioids administered during the perioperative period play a central role in pain and cognitive activity. Their side effects are well known and include a deterioration in sleep quality that has been associated with hyperalgesia, which in turn increases need for painkillers, triggering a vicious circle (Kosar et al, 2014). Deprivation of sleep leads to an imbalance in mental state that must be taken into consideration during the postoperative period, keeping in mind the intricate relationship between opioids, sleep disorders and pain.

The cause of cognitive decline after anaesthesia and surgery remains unknown, but reasoning and evidence indicate it may result from anaesthesia, surgery, the patient's baseline clinical condition or a combination of these (Evered and Silbert, 2018).

Preoperative period

During the preoperative period, nurses can consider predisposing factors eg demographic, comorbidities and type of surgery (Table 1) to estimate the risk of developing cognitive changes during the immediate and medium-term postoperative period.

To assess patients' cognition at baseline, the Montreal Cognitive Assessment test (MoCA) should be administered as it is reliable at detecting mild cognitive impairment (Kazmierski et al, 2014).

On admission, all risk factors identified should be minimised; drugs could be adjusted, anxiety should be reduced, a good wake–sleep cycle should be ensured, medical problems should be treated, and hydration and nutrition should be maintained.

Theatre and recovery room

In the theatre and recovery room, it is possible to minimise some risk factors correlated with delayed postoperative cognitive recovery, such as avoiding premedication with benzodiazepines, preventing hypoxia and postoperative hypotension. Comorbidities, surgical techniques, type of hypnotic, duration of anaesthesia and amount of opioids should be considered (Taipale et al, 2012).

The recovery nurse could assess patients when they become conscious and aware by administering the Short Orientation Memory Concentration Test (SOMCT) (Davous et al, 1987). This test allows the restoration of cognition to be monitored during the early postoperative phase. The patient's performance should be included in the handover to the ward nurse and considered as an index to monitor cognitive changes along the transition from theatre to ward.

Postoperative period

To identify the onset of POD on the ward, the 4AT could be used (De et al, 2017). If POD is present, the nurse should intervene by managing environmental stressors that can precipitate symptoms. This includes identifying infection and treating it aggressively, ensuring nutrition and hydration are adequate, providing visual and hearing aids for those with visual or auditory impairments, limiting strong light and loud noise, promoting proper sleep hygiene, and avoiding physical and pharmacological containment measures by treating dissociative episodes with small doses of neuroleptic agents (Hartjes et al, 2016).

After 72 hours, as cognitive changes can be subtle, the nurse should re-administer the MoCA and, if the score is positive (<26), the patient should be evaluated by an occupational therapist and assessed by specialists in moderate neurocognitive disorders before discharge. If the MoCA score is negative but there are changes in cognition levels, the presence of apathy, anxiety or depression should be considered, as they may manifest as an alteration of mental state.

These 4AT and MoCA tests are supported by the literature and are quick and easy to administer, appear to be sensitive and specific in identifying cognitive impairments and could be implemented into clinical practice easily after effective, simple education for practitioners.

If a patient's family members report that their relative has not been the same since surgery, they should be informed that, in 69% to 77% of these cases, changes are transient and related to drugs, sleep disorders and general postoperative stress; however, if the patient's mental state has not returned to normal within 3 months, more specialised assessments should be carried out by the GP and a specialist such as a neuropsychologist (Wofford and Vacchiano, 2011).