Delirium is a common and potentially serious complication after major surgery. A previous history of depression is a known risk factor for experiencing delirium in patients admitted to the hospital, but the generalised risk has not been estimated in surgical patients.
We conducted a systematic review and meta-analysis of studies reporting the incidence or relative risk (or relative odds) of delirium in the immediate postoperative period for adults with pre-operative depression. We included studies that defined depression as either a formal pre-existing diagnosis or having clinically important depressive symptoms measured using a patient-reported instrument before surgery. Multilevel random effects meta-analyses were used to estimate the pooled incidences and pooled relative risks. We also conducted subgroup analyses by various study-level characteristics to identify important moderators of pooled estimates.
Forty-two studies (n = 4,664,051) from five continents were included. The pooled incidence of postoperative delirium for patients with pre-operative depression was 29% (95%CI 17–43%, I2 = 99.0%), compared with 15% (95%CI 6–28%, I2 = 99.8%) in patients without pre-operative depression and 21% (95% CI 11–33%, I2 = 99.8%) in the cohorts overall. For patients with pre-operative depression, the risk of delirium was 1.91 times greater (95%CI 1.68–2.17, I2 = 42.0%) compared with patients without pre-operative depression.
Patients with a previous diagnosis of depression or clinically important depressive symptoms before surgery have substantially greater risk of experiencing delirium after surgery. Clinicians and patients should be informed of these increased risks. Robust screening and other risk mitigation strategies for postoperative delirium are warranted, especially for patients with pre-operative depression.
The 7th National Audit Project (NAP7) confirmed haemorrhage as a leading cause of maternal cardiac arrest[1]. In this audit of cardiac arrest in patients under the care of an anaesthetist, nearly half of the obstetric cases involved a general anaesthetic, and anaesthetic care was judged to be a key factor in 68% of cases. The specific drugs used for induction of anaesthesia were not recorded [1]. We speculate that over-generous use of opioids may be implicated. In the hypovolaemic obstetric patient, it is important to minimise the haemodynamic effects of induction. Most anaesthetists are familiar with techniques that achieve smooth induction for patients with cardiac disease. During and after training, anaesthetists come across more opportunities to care for such patients compared with managing major trauma. This may explain why, anecdotally at least, they tend to opt for a ‘cardiac anaesthetic induction’ comprising high-dose opioids with a reduced dose of induction drug when providing anaesthesia to patients who are haemodynamically unstable [2].
Liberal use of opioids in a hypovolaemic patient may, however, worsen haemodynamic status. Due to a reduced volume of distribution and clearance, plasma concentrations of fentanyl during haemorrhage can double. Activation of the sympathetic nervous system maintains cardiac output in the face of hypovolaemia through an increase in heart rate and systemic vascular resistance [3]. Fentanyl, through its sympatholytic action, can obtund these mechanisms, exacerbating haemodynamic instability, especially at high doses. It is for this reason that rapid sequence induction in a patient with shock is undertaken using limited doses of opioids, e.g. 1 μg.kg-1 of fentanyl [4]. Once effective volume resuscitation has been established and blood pressure has increased, fentanyl can be titrated in aliquots to dilate the microcirculation and restore tissue perfusion, as evidenced by a reduction in serum lactate and base deficit [5].
To promote haemodynamic stability, we suggest that the anaesthetic management of an obstetric patient with haemorrhage should be more akin to that of a patient with trauma and shock by judicious use of opioids and induction with drugs such as ketamine. A ‘cardiac anaesthetic’ should instead be reserved for those with cardiac pathology.
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