logistic reasons; amendment pending with IRB

Rationale: Spinal anesthesia is a safe, frequently used anesthetic technique. The main side effect of spinal anesthesia is hypotension, occuring in up to 85 % of selected cases. This hypotension is often treated with fluid infusion. However, especially in elderly patients, high volume fluid infusion can lead to fluid overload.

The effects of spinal anesthesia on preload and fluid responsiveness are not exactly known. Hence, therapy for hypotension after spinal anesthesia might not be adequate. With transthoracic echocardiography, vena cava inferior diameter and collapsibility can be used to monitor fluid responsiveness and guide fluid management.

Objective: This study has two main objectives. The first is to explore the effects of spinal anesthesia on hemodynamic parameters of fluid status, especially vena cava inferior diameter and collapsibility. The second goal is to test the interrater variability transthoracic echocardiography exams when performed by (trained) anesthesiologists.

Furthermore, the correlation between vena cava inferior collapsibility and the occurence and degree of hypotension (defined as a decrease from baseline of >20% or a systolic pressure < 90 mmHg) after spinal anesthesia will be explored.

Inclusion Criteria:

• Adult age (>18 years)
• Written informed consent
• Minor surgery under the umbilicus, e.g. herniorrhaphy, transurethral resection of bladder or prostate, orthopaedic procedures
• ASA class I or II

Exclusion Criteria:

• No informed consent
• ASA class III or higher
• Obstetric surgery
• Emergency procedures
• Pre-existing neurological injury or disease
• Contra-indications for spinal anesthesia (e.g. coagulation abnormalities)

adult patients undergoing spinal anesthesia for minor surgery below the umbilicus