Evaluation of role of Common Carotid Artery corrected flow time (FTc) in predicting post-induction hypotension in patients undergoing elective craniotomy under general anaesthesia.

Hypotension is a common complication when general anaesthesia (GA) is initiated. This drop in blood pressure can be triggered by various factors, notably low blood volume, advanced age, significant systemic disease (ASA III or higher), anaesthetic agents, compromised physiological responses, and impaired cardiac function. While intraoperative hypotension is known to worsen outcomes in both cardiac and non-cardiac surgeries, it carries particular significance in neurosurgical procedures. Even brief periods of post-induction hypotension, which may be tolerated in general surgery, can be harmful in neurosurgery and significantly affect patient recovery. Whether a patient’s brain can properly regulate blood flow or not, hypotension can have detrimental neurological consequences.

In patients with intact autoregulation, it can paradoxically increase intracranial pressure (ICP) due to reflex vasodilation and increased cerebral blood volume. In contrast, for those with impaired autoregulation, hypotension can lead to cerebral ischemia. Neurosurgical patients are particularly vulnerable to developing low blood volume due to factors such as poor oral intake related to reduced consciousness or cranial nerve deficits, vomiting caused by elevated ICP, the effects of medications like mannitol used to reduce brain swelling, and complications from conditions like diabetes insipidus (DI). Low blood volume can lead to hypotension during administration of anaesthesia. Anaesthesiologists play a vital role in managing intraoperative hypotension by early detection and management of hypotension.

The relationship between a neurosurgical patient’s preoperative fluid status and the degree of hypotension following anaesthesia induction is still unclear. Historically, the diagnosis of low blood volume depended on clinical assessments (e.g., tachycardia, weak pulse) and laboratory tests (e.g., haematocrit levels), which have limitations and invasive approaches like central venous pressure and pulse pressure variation.

More recently ultrasonography (USG) has been used for visualisation of major vessels and obtaining various parameters or indices for determination of fluid status of the patients.  Many parameters have emerged by analysing the flow, diameter of great vessels like IVC collapsibility index (IVCCI), caval/aorta diameter index, and corrected flow time (FTc, derived from carotid artery). Goyal et al evaluated the relationship between IVCCI and post-induction reduction in mean arterial blood pressure, and reported a good association with each other with an area under receiver operator curve (AUC) of 0.65 and an optimal cutoff for IVCCI of 37.5%. Fathy et al explored the role of caval /aorta diameter index and IVCCI with post general anaesthesia induction hypotension and found an AUC of 0.95 and 0.93 respectively.

Doppler-derived hemodynamic parameters, like Common Carotid Artery corrected flow time (FTc) have emerged as indicators of volume responsiveness in diverse clinical settings. The Common Carotid Artery corrected flow time (FTc), defined as the heart rate-normalized interval from systolic flow onset to aortic valve closure, reflects intravascular volume status. Carotid Artery Doppler ultrasonography offers the advantages of being non-invasive and technically facile due to the superficial location of the vessel. Critically, FTc is not influenced by respiratory mechanics, extending its applicability to spontaneously breathing patients. Kim et al.  demonstrated the predictive power of both FTc for fluid responsiveness, however their study did not explore their ability to anticipate post-induction hypotension.

As prediction of postinduction of hypotension is important, we designed a prospective observational study to determine the utility of the common carotid artery corrected flow time (FTc) for prediction of hypotension after induction of general anaesthesia in patients undergoing elective craniotomy surgeries. Any hypotension that occurred in up to 15 minutes of induction of general anaesthesia will be evaluated in this study.

We are going to do this study because there are very limited studies in evaluating role of FTc in patients undergoing neurosurgeries. After taking written informed consent from the participants, the FTc will be measured in right common carotid artery in supine position by a 6 to 13 MHz linear probe in the preop area 3 times and the mean will be used are main data. after that patient will be taken into operation room and after induction of general anaesthesia, in every 3 minute desired parameters will be recorded till 15 minutes post induction. If systolic blood pressure fall is less than 90 mmHg or less than 30 percent from baseline or mean arterial pressure less than 65mmHg or fall in mean arterial pressure is more than 20 percent from baseline than we will call it as post induction hypotension.