Lithotripsy under low dose spinal anaesthesia with dexmedetomidine in a patient with hypertrophic obstructive cardiomyopathy.

Sir,

A 48 year old obese male patient was scheduled to undergo ureteroscopic lithotripsy for ureteric calculus. On routine evaluation, chest X-ray was suggestive of cardiac enlargement and electrocardiogram (ECG) showed left ventricular hypertrophy (LVH) with strain pattern with prominent T wave inversions [Figure 1]. Echocardiography revealed normal systolic left ventricular function with ejection fraction 60%, interventricular septum (IVS) of 2.8 cm (asymmetric septal hypertrophy), left ventricular posterior wall thickness of 1.4 cm and aortic jet velocity of 15 m/secs with LVH. Systolic anterior motion of mitral valve leaflet was present, but there was no gradient across the left ventricular outflow tract (LVOT). Patient was receiving tablet telmisartan 80 mg daily. His vitals included a pulse rate of 72/min and arterial blood pressure (BP) of 120/85 mmHg. Haematological investigations were within the normal limits. High risk informed consent was obtained. Pre-operatively patient was infused with 1 L of ringer lactate solution before shifting to operation theatre over a period of 30 min. In the theatre, ECG, invasive blood pressure monitoring and central venous pressure (CVP) monitoring was done along with routine monitoring and emergency drugs were kept ready. Spinal anaesthesia using 3 ml of 0.25% hyperbaric bupivacaine (1.5 ml of 0.5% bupivacaine + 1.5 ml of 5% dextrose including 10 mcg dexmedetomidine) was administered in L3-L4 space. The sensory level block of T10 for pain and motor block of Bromage grade II were obtained. Oxygen was given via Polymask at the rate of 4 L/min. During the procedure haemodynamics were stable and no abnormal ECG changes were noticed. Intra-operative fluids were given to maintain CVP in the range of 12-13 mmHg. After turning the patient to supine position, there was slight 10-15 mmHg fall in systolic pressure which was corrected with fluids alone. Whole procedure lasted for 90 min, later patient was shifted to recovery room and observed for 2 h, which was uneventful.

Figure 1

Electrocardiogram with left ventricular hypertrophy and T wave inversions

Hypertrophic obstructive cardiomyopathy (HOCM) involves hypertrophy of the left and/or right ventricle and may be classified as symmetric or asymmetric, obstructive or non-obstructive.[1] Subaortic HOCM is characterised by asymmetric hypertrophy of the IVS, resulting in dynamic obstruction of the LVOT.[2] Anaesthetic management of these patients presents considerable challenges and requires maintenance of desired haemodynamic parameters and management of specific complications. These patients are highly prone to arrhythmias and patients with unrecognised HOCM may have sudden and unexpected systemic hypotension (e.g., due to blood loss and hypovolemia) and trigger dynamic LVOT obstruction. Aims of anaesthetic management are to maintain normal sinus rhythm, haemodynamic stability, maintaining adequate preload and afterload to minimise or prevent outflow obstruction. Avoiding vasodilators and avoiding agents that increase contractility are pivotal in the management of these patients. General anaesthesia is preferred[12] but low dose spinal anaesthesia was chosen for this case because the procedure was endoscopic, lower abdominal, with minimal anticipated blood loss and fluid shifts.[34] Marked hypotension associated with conventional spinal anaesthesia can be deleterious especially in cardiac patients with limited cardiac reserve.

Low-dose local anaesthetic is commonly administered to limit the level of block in order to minimise the haemodynamic changes.[5] However, sometimes they may not provide an adequate level of sensory block. Thus, intra-thecal additive is frequently administered with local anaesthetic to improve analgesic effect. Previous clinical studies showed that intravenous dexmedetomidine administration prolonged the sensory and motor blocks of bupivacaine spinal analgesia.[34] Low-dose diluted bupivacaine 5 mg provided sufficient anaesthetic level when opioid was added with local anaesthetic (4). However, opioid - induced side-effects, such as pruritus, nausea, or vomiting, could be an obstacle for routine use. Intrathecal dexmedetomidine, low dose bupivacaine spinal anaesthesia can provide the effective spinal anaesthesia and post-operative analgesia with minimal side-effect compared with the local anaesthetic group (3). In patients with HOCM for endoscopic urological procedures, low-dose spinal anaesthesia combined with dexmedetomidine provides haemodynamic stability and care should be taken to maintain intravenous volume and phenylephrine infusion for hypotension, guided by invasive monitoring.