Does Heart Rate Variablity (HRV) Predict Hypotension in Patients Undergoing Cervical Myelopathy Surgery ?

Does Heart Rate Variablity (HRV) Predict Hypotension on Induction in Patients Undergoing Surgery for Cervical Myelopathy ?

Cervical myelopathy is commonly associated with degenerative spinal disease. Dysfunction of the autonomic nervous system is also evident in many cases of cervical myelopathy. Autonomic dysfunction may result in haemodynamic instability and hypotension under anaesthesia. It is important to maintain adequate mean arterial pressure in order to perfuse the spinal cord and prevent cord ischemia. Heart rate variability, the physiological variations of the differences between heart beats, has been used to diagnose autonomic dysfunction. In patients with cervical myelopathy it may enable the anaesthetist to predict hypotension thereby allowing for early treatment and prevention of spinal cord ischemia.

Protocol

1. Standard perioperative management Routine standard preparation of the patients will be carried out as per the investigators institutional standard for all patients undergoing cervical spine surgery. All routine physiological monitoring (ECG, invasive arterial blood pressure, SPO2, end tidal CO2, temperature and depth of anaesthesia monitoring) will be performed. The induction of anesthesia will be performed with propofol (2-5 mg/kg), fentanyl (3mcg/Kg) and rocuronium (0.6 mg/kg) for intubation of the patient's trachea once peripheral nerve stimulation shows no muscle twitches.
2. Study protocol Before general anesthesia, following a 10 minute stabilization period with the patient lying supine and breathing at a rate of 12 - 15 breaths per minute, a 5 minute ECG recording will be obtained. ECG data will be downloaded onto a study laptop for later analysis using LabChart Software to determine HRV values. Hemodynamic data and depth of anaesthesia will be collected from the preinduction period until skin incision at 1 minute intervals. The study will be complete after skin incision.

Data Collection and Management Data Collection The following data will be collected: patient demographics, surgical data including position technique, number of levels, duration, anaesthetic data including agents used, hemodynamic measurements from preinduction to surgical incision, Japanese Orthopaedic Association Score. The incidence of hypotension and the number of interventions required to keep mean arterial blood pressure above 70 mmHg will be recorded.

Significance of the study Identifying patients at risk for hypotension can be useful to prevent hypotension and to prepare to treat hypotension sooner so that the risk of spinal cord ischemia can be minimized.

Inclusion Criteria:

• Adults patients, aged 18 - 70 years with the history of cervical myelopathy, presenting for anterior or posterior cervical decompression and fusion.

Exclusion Criteria:

1. Patients with arrhythmias or absence of sinus rhythm
2. Diabetic patients
3. Degenerative neurological disease e.g. Parkinson's disease
4. Complete SCI
5. Inherited autonomic dysfunction