This trial aims to compare the incidence of postoperative residual curarisation (PORC) and postoperative pulmonary complications (PPCs) in the SUG and NEO group by means of diaphragm ultrasonography and LUS, so as to conclude whether SUG can outperform NEO in preventing occurrence of PORC and PPCs.

The incidence of postoperative residual curarisation (PORC) is about 2%-64% worldwide, which may be an underling risk factor of postoperative pulmonary complications (PPCs), causing many undesirable effects on patients. Thus, reversal drugs of neuromuscular blocking agents (NMBAs) such as neostigmine (NEO) and sugammadex (SUG) have been administrated, and SUG maybe perform better in preventing PORC. Different supplementary methods to help identify PORC or PPCs have also been reported, such as adductor of pollicis acceleromyography and lung ultrasound (LUS). Recently, diaphragm ultrasonography has been used to evaluate PORC, as a novel approach.In this prospective, double-blind, randomized controlled trial, we will enroll 414 patients of American Society of Anesthesiologists physical status I-III, aged over 60 years, who will be scheduled to undergo arthroplasty surgery under general anesthesia. Participants will be randomized into NEO and SUG group receiving neostigmine and sugammadex as reversal drug respectively. The primary outcomes will be the incidence of PPCs in NEO and SUG group respectively. The secondary outcome is the incidence of PORC in the two groups.We hypothesize that: 1) the incidence of PPCs is lower after reversal with SUG than with NEO, 2) using the method of diaphragm ultrasonography, the incidence PORC is lower after reversal with SUG than with NEO, 3) the incidence of PPCs can be predicted by LUS and by evaluating whether there is PORC through diaphragmatic ultrasound.

Inclusion Criteria:

1. American Society of Anesthesiologists (ASA) physical status I-III
2. Aged over 60 years
3. Anesthesia induction with rocuronium as NMBAs, maintenance with volatile sevoflurane
4. Scheduled to undertake joint surgery
5. Signed the informed consent form

Exclusion Criteria:

1. Those with a history of hepatic or renal disease, chronic or acute alcoholism, allergy or hypersensitivity to sugammadex or neostigmine, current medication with effects on the central nervous system, a history of dysfunction of neuromuscular system
2. Those with diaphragm insufficiency or massive pleural effusion
3. Women who are pregnant or nursing
4. Those undergoing upper abdominal laparotomy, after which we cannot obtain a satisfactory ultrasound imaging or do not have space for placement of ultrasonic probe
5. Declined to participate