The goal of this clinical trial is to find out whether height-based dosing of spinal anaesthesia provides better hemodynamic stability and anesthetic outcome than conventional fixed dosing in elderly patients undergoing lower limb orthopaedic surgery.The main questions this study aims to answer are:

1. Does height-based spinal anaesthetic dosing reduce the risk of hypotension and bradycardia during surgery as compared to conventional fixed dosing?
2. Does it improve anaesthetic outcomes, such as the onset and duration of sensory and motor block?

Data collection would begin after the approval of ethical review committee of the institution. This investigation will encompass patients who are scheduled to undergo lower limb orthopaedic surgical procedures within the Department of Anaesthesia, SMBBIT, Karachi. Following a comprehensive description of the study and their acceptance to participate (written consent), the subject will be recruited as detailed in the inclusion criteria.

Data will be collected using a defined data collection proforma to record baseline demographics and clinical characteristics including age, height, gender, and residential status. Height will be measured in the supine position as the patients will be undergoing lower limb surgeries. The patient will be placed flat on a firm examination table or operating-room bed without a pillow, with legs extended and neutral. To accurately measure height in centimetres, a measuring tape or stadiometer will be placed along the length of the patient's body from the heel to the vertex of the head, using trained staff to ensure precise placement, and the reading will be recorded to the nearest decimal point.

The subjects will be allocated to one of two groups through a computer-generated random number sequence with concealed allocation to mitigate selection bias and safeguard the integrity of the randomization process. Allocation concealment will be accomplished by the Sequentially Numbered, Opaque, Sealed Envelope (SNOSE) method, conducted by a blinded independent researcher not involved in subject recruitment, surgical procedure, or clinical assessment. In the operating room, baseline pulse rate and mean arterial pressure will be measured before spinal anaesthesia is induced. Intravenous access will be established, and patients will be preloaded with Ringer Lactate (10 ml/kg) prior to induction of spinal anaesthesia.

Spinal anaesthesia will be provided in the sitting position, aseptically at the level of L3-4 vertebra. Group A will receive 0.07 mg/cm of 0.5% Hyperbaric Bupivacaine in conjunction with 2 mg (0.5 ml) of preservative-free Dexamethasone administered intrathecally, whereas patients in Group B will be administered 12.5 mg (2.5 ml) of 0.5% Hyperbaric Bupivacaine alongside 2 mg (0.5 ml) of preservative-free Dexamethasone. Subsequent to the administration of spinal anaesthesia, patients will be positioned in the supine orientation; sensory blockade will be evaluated utilizing the pinprick method with a blunt-tipped 23-gauge needle at the T10 dermatome level, while motor blockade will be assessed employing the Bromage scale. The specific time at which the most effective sensory and motor blockade is achieved will be documented in accordance with the established operational definition.

The hemodynamic (heart rate and mean arterial pressure) will be continuously monitored. The procedure and the principal investigator (in consultation with a faculty consultant with >5 years' experience) will mark the findings of "bradycardia" and "hypotension" based on the operational definition on the proforma. The early postoperative period will be followed in all patients in order to know sensory and motor blockade duration by operational definition, and each result will be written. The principal investigator will record collected data on a predesigned proforma. Confidentiality will be ensured along with data security measures allowing only authorized personnel access to all information. The study is produced to be directly relevant with its aims, and rigorous exclusion criteria will be used in minimizing potential biases or confounders.

Data will be entered into a secure database and analyzed using SPSS version 26. Continuous variables (including age, height, weight, BMI, heart rate, mean arterial pressure, onset of sensory block, and duration of sensory block) will be summarized as mean ± standard deviation or median with interquartile range, as appropriate. Comparisons between the two study groups will be performed using the independent sample t-test for continuous variables. Chi-square test or Fisher's exact test will be used for categorical variables, depending on expected cell counts. A p-value ≤ 0.05 will be considered statistically significant.

Inclusion Criteria:

Individuals aged 60 to 80 years. Either gender (male or female). Patients who are ASA physical status I-III. Individuals scheduled to undergo elective lower limb orthopaedic surgeries (e.g., fracture fixation, total knee replacement, open reduction and internal fixation).

Patients planned to receive spinal anaesthesia as the primary anaesthetic technique.

Those who provide informed written consent for participation in the study.

Exclusion Criteria:

Individuals exhibiting a stature inferior to 150 cm. Patients receiving anti-hypertensive drugs or those on beta blockers or beta-agonists.

Patients with a history of neurological disease like CVA or Parkinsonism. Patients presenting with sepsis (≥ 2 positive SIRS criteria with positive aseptically obtained blood or wound culture).

Patients with a history of coagulation disorders like haemophilia or vWD or those with a history of anti-platelet drug intake in the last 2 weeks.

Individuals possessing a documented history of hypersensitivity reactions to pharmacological agents utilized in the research.

Patients who will be diagnosed with a skin infection at the spinal needle puncture site.

Patients undergoing emergency orthopaedic procedures requiring immediate intervention

Patient Confidentiality: Sharing IPD could compromise patient confidentiality and anonymity.

Informed consent: Participants are not providing informed consent for their data to be shared and it could raise ethical concerns.

This study is single blind, assessor is kept blind because participants are difficult to mask due to well distinguished treatment plan.