Can nonstandardised, simplified autonomic function tests be used for risk profiling in the anaesthesia population?
Local as well as general anaesthesia have marked effects on autonomic function, which may lead to unexpected haemodynamic instability during surgery.1 Moreover, in patients with preexisting autonomic dysfunction (e.g. because of health risk factors and/or diseases such as diabetes mellitus or heart failure) anaesthesia is a prominent risk factor for perioperative complications.1 This letter discusses the implementation of simplified cardiovascular autonomic function tests in preoperative patient risk assessment to identify patients at risk of intraoperative hypotension and peri- and postoperative cardiovascular complications.
Traditional Ewing tests (deep breathing, Valsalva manoeuvre, sustained handgrip, quick standing) and heart rate (HR) variability analysis are internationally used to identify patients with impaired autonomic function.1–2 However, these tests are complex to implement because of the recommended standardisation of environmental factors and abstention from smoking, eating, and drinking.1–3 In recent publications by our group, we pointed out that cardiovascular autonomic function tests (traditional Ewing tests and HR variability) can also be performed under nonstandardised conditions. In both healthy volunteers and patients with diabetes mellitus and cardiovascular comorbidity, we showed that the results and reproducibility of cardiovascular autonomic function tests during nonstandardised test conditions were comparable with those of standardised conditions.3
When we discuss the best tests to use, we should take into account that impairment of the autonomic nervous system is typically first reflected by the parasympathetic autonomic function tests.2 This may suggest that the parasympathetic nervous system is affected earlier then the sympathetic nervous system but this assumption is still under debate.2
The Ewing tests based on HR responses (deep breathing, Valsalva manoeuvre, quick standing) were developed to analyse parasympathetic function, whereas the Ewing tests to analyse sympathetic function (sustained handgrip, quick standing) are based on blood pressure (BP) responses.2 However, the validity of Ewing tests for evaluation of sympathetic function is questionable. The tests based on BP responses often show poor reproducibility [e.g. intraclass correlation coefficients from 0.32 to 0.48 (P > 0.09)], whereas other autonomic function tests (particularly the deep breathing test and Valsalva manoeuvre) show moderate-to-good reproducibility [e.g. intraclass correlation coefficients from 0.76 to 0.89 (P < 0.001)].3
Recent literature suggests that the best Ewing test to determine cardiovascular autonomic neuropathy is the deep breathing test, with the Valsalva manoeuvre as second best.4 The deep breathing test as well as the Valsalva manoeuvre demonstrated the best reproducibility in our data.3 Therefore, we propose to use the deep breathing test and Valsalva manoeuvre, in combination with heart or pulse rate variability analysis to determine cardiovascular autonomic neuropathy.
Increasing evidence shows that Ewing autonomic function tests may be replaced by sole measurements of HR variability as a valuable predictor of cardiovascular events in the perioperative setting and as an outcome predictor in the intensive care setting.1,3 In 2007, Fujiwara et al.5 published several studies focusing on the association of impaired HR variability and haemodynamic alterations during anaesthesia. In a study of Hanss et al.,6 preoperative total power of HR variability was predictive for low BP and bradycardia after induction of anaesthesia in high-risk patients. Furthermore, in another study of Hanss et al.,7 the preoperative total power of HR variability in high-risk cardiac patients predicted postoperative cardiac events and extended length of hospital stay.
Interestingly, recent evidence suggests adverse outcome when intraoperative hypotension is present during anaesthesia and surgery.8–9 Although the association between autonomic dysfunction and postoperative outcome is likely, postoperative complications might be independent of the occurrence of intraoperative hypotension.
Consequently, preoperative cardiovascular autonomic function tests using simplified test conditions are a valuable instrument to identify patients at risk of perioperative cardiovascular complications.