The asthmatic attack was relieved with your treatment, and the surgery was completed. Following emergence, the patient was found to be hypoventilating. What are the common causes of hypoventilation? What will be your approach to treat hypoventilation?
Answer:
The following are common causes of apnea or hypoventilation at the end of surgery:
Respiratory center depression by inhalational anesthetics, opioids, or mechanical hyperventilation (low PCO2)
Peripheral blockade by muscle relaxants
Hypothermia
This list of the common causes of postoperative hypoventilation can be used to guide the systematic approach for the diagnosis and management. Measuring the temperature can easily diagnose hypothermia, and residual neuromuscular blockade can be assessed by a response to peripheral nerve stimulator. If hypothermia and residual neuromuscular blockade are ruled out, then hypoventilation is likely due to residual anesthetics and opioids. This can be managed by waiting longer or by pharmacologic reversal (if deemed appropriate) of opioid or benzodiazepine effect.
Management of residual neuromuscular blockade requires extra care in patients with reactive airway disease. In a patient with severe asthma, avoiding the use of an anticholinesterase, such as neostigmine, to reverse a nondepolarizing relaxant may be beneficial because neostigmine may trigger bronchospasm by cholinergic and prosecretory effects. However, any hypoventilating patient without adequate recovery (defined as TOF ratio greater than 0.90 when measured with a peripheral nerve stimulator) should be reversed.
If reversal is required, larger than customary doses of glycopyrrolate or atropine should be administered to minimize the possibility of bronchospasm. Although atropine or glycopyrrolate given simultaneously with neostigmine may prevent bronchospasm, the duration of action of neostigmine can outlast that of a vagolytic agent, especially in the presence of renal insufficiency, and lead to delayed bronchospasm. Intraoperatively, it is advisable to use inhalation agents to potentiate relaxants and to use smaller amounts of intermediate-acting relaxants for surgery. Alternatively, sugammadex may be safely used for reversal of rocuronium-induced neuromuscular blockade (see section C.10).
Finally, if the patient does not appear to have any of the aforementioned causes of hypoventilation but is still inadequately ventilating, extubation should be delayed.
Reference(s):
- Brull SJ, Kopman AF. Current status of neuromuscular reversal and monitoring: challenges and opportunities. Anesthesiology. 2017;126:173-190.
- Carron M, Zarantonello F, Tellaroli P, et al. Efficacy and safety of sugammadex compared to neostigmine for reversal of neuromuscular blockade: a meta-analysis of randomized controlled trials. J Clin Anesth. 2016;35:1-12.
- Gropper MA, Cohen NH, Eriksson LI, et al, eds. Miller’s Anesthesia. 9th ed. Philadelphia, PA: Elsevier; 2020:2592-2593.
- Hazizaj A, Hatija A. Bronchospasm caused by neostigmine. Eur J Anaesthesiol. 2006;23:85-86.
- Woods BD, Sladen RN. Perioperative considerations for the patient with asthma and bronchospasm. Br J Anaesth. 2009;103(suppl 1):i57-i65.