Should end-tidal carbon dioxide monitoring be mandatory for surgeries under spinal anaesthesia?

Sir,

Spinal anaesthesia is one of the most important and commonly performed anaesthetic techniques. It is generally considered to be safe, though complications such as hypotension, bradycardia, nausea and vomiting may occur.[1] Monitoring of heart rate, electrocardiogram, noninvasive blood pressure and pulse oximetry routinely is advocated, and capnometry only if the patient receives sedation.[2] There are no guidelines on the use of end-tidal carbon dioxide without sedation use. We emphasise the importance of end-tidal carbon dioxide monitoring in patients undergoing spinal anaesthesia without sedation.

A 70-year-old female patient, American Society of Anesthesiologists physical status II, with no history of any comorbidity, and investigations including complete Haemogram, serum sodium, potassium, blood urea, serum creatinine, electrocardiogram and chest X-ray within normal limits, was administered intrathecal 2.4 ml of 0.5% heavy bupivacaine for reduction and fixation of trochanteric fracture. Apart from monitoring ECG, non invasive blood pressure, and SpO2 we also monitored end-tidal carbon dioxide through nasal cannula that was used for oxygen administration at 3 lpm as a routine practice. No sedation was given as part of premedication or in the operating room. Sensory blockade level was T10 and motor blockade as per modified Bromage score was 4. After 20–25 min of start of surgery, there was disappearance of capnometry graph. The patient was not responding to painful stimuli and had become apnoeic. Mechanical ventilation using bag mask with Bain's circuit was done. Endotracheal intubation was not performed as there was no hypotension, bradycardia or desaturation. Spontaneous respiration returned after 4–5 min and full consciousness was regained after 7–8 min. Rest of the perioperative period was uneventful. Arterial blood gas analysis done in the postoperative period was within normal limits.

There are anecdotal reports of neurological complications such as apnoea and aphasia during spinal anaesthesia. Various mechanisms have been proposed, but the exact cause is still not clear.[34] Most common causes include sedation, neuraxial opioids or any comorbidity such as history of diabetes, epilepsy or loss of consciousness. Another cause could be a total spinal block where intercostal muscle paralysis occurs, and is associated with hypotension, bradycardia and a longer period of apnoea. None of the features of total spinal block were observed in our patient. The authors have also postulated a subdural spread of drug or inhibition of ascending pathways such as fibres of spinoreticular tracts by the anaesthetic agents during similar incidents.[5]

Monitors do not replace eternal vigilance offered by anaesthesiologists and may not prevent all adverse incidents and accidents; however, they give an early warning that the condition of patient is deteriorating. Capnography in our patient helped in averting a catastrophic event. Clinical examination of respiratory movements during anaesthesia may not be always feasible since the patient is draped, covered with warmer and screen is placed. In a patient on oxygen therapy, hypoxia may occur late. In our patient, that could be the reason for the oxygen saturation being maintained. Simultaneous administration of oxygen with capnometry leads to dilution of carbon dioxide by oxygen. A discrepancy of EtCO2 and PaCO2 can occur, although a flow rate ≥6 lpm through nasal cannula does not interfere with the accuracy of EtCO2 measurement.[6] The exact value of EtCO2 may not be reliable at lower flow rates, but the trend and graph provide adequate information.[7] In our case, continuous monitoring of capnography showing sudden disappearance raised a suspicion, and on clinical examination, the patient was found to be apnoeic. There are recommendations that capnometry be done in patients under regional anaesthesia if sedation is given.[2] During spinal anaesthesia, dreaded complications though rare do occur and assessment of ventilation using capnography may enhance patient's safety. Thus, we suggest end-tidal CO2 monitoring as a simple, practical and cost-effective equipment which may be used for all surgeries under spinal anaesthesia.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.