Respiratory insufficiency is common in patients recovering from anesthesia, and failure to recognize it or lack of timely intervention can lead to hypoxia, severe brain damage, and even death [13]. Therefore, effective monitoring and rapid recovery of respiratory function in patients undergoing abdominal surgery are particularly crucial. In this study, compared with conventional resuscitation, the impact of ultrasound assessment of lung and diaphragm function and precise intervention on postoperative respiratory function in patients undergoing abdominal surgery was observed. Our data showed that the extubation time and PACU length-of-stay of patients in the ultrasound group were obviously shortened, and the incidence of hypoxemia after extubation was significantly reduced.
Currently, it is considered that postoperative residual curarization (PORC) exists if the train-of-four-ratio (TOFr) is lower than 0.9 [14]. However, due to complex procedures, special equipment requirements, easy interference, and inconvenient detection, the clinical use of neuromuscular monitors is limited, and the incidence rate of PORC is still high [15,16]. Furthermore, due to the unpredictability of the metabolism of blocking drugs, PORC may occur when the effects of AChEIs disappear. In an observational study, 18% of patients achieved TOFr < 0.9 20 minutes after dosing [17]. In the absence of neuromuscular monitoring, diaphragmatic ultrasonography can be used to assess postoperative diaphragmatic recovery, and it is more comfortable than TOF for conscious patients, which can help anesthesiologists to detect PORC patients in the PACU [18]. There are two commonly used methods for clinical evaluation of diaphragm function, that is, DTF and diaphragm position method.
The displacement of the diaphragm reflects the movement of the central tendon and the joint action of the diaphragm with the abdomen and the thorax[19]; while the part of the diaphragm attached to the 8th to 10th intercostal space is relatively fixed during the respiratory movement and can truly reflect the overall thickness variation of the diaphragm during the respiratory cycle[20]. Vivier et al. [21] demonstrated that DTF is directly related to respiratory load. However, because the left side is affected by the air contained in the gastrointestinal tract and other hollow organs, it is easy to interfere with the ultrasonic image of the diaphragm, so this study adopted the DTF method that can provide images of the diaphragm itself and selected the right diaphragm as the measurement site[22]. In this study, 8 patients in the ultrasound group had DTF < 30% at 15 minutes (T2) after extubation, and 12.3% had postoperative residual muscle relaxation, which was consistent with previous research results [17]. The results of this study showed that the DTF of the patient was the lowest at T1, and began to increase at T1-T3, suggesting that the patient's spontaneous breathing recovered after the operation, and the diaphragm and other respiratory muscle groups gradually recovered their contraction function. In the meantime, DTF at T3 was still lower than T0 (P<0.01), indicating that the contractile function of the diaphragm had not recovered to the preoperative awake state before the patient returned to the ward after spontaneous breathing, suggesting that the deep breathing function was impaired after the operation, which was consistent with the research results of Kim et al. [23].
In this study, it was found that compared with T0, the postoperative LUSS of the patients at T1, T2, and T3 were all increased significantly, and most of the patients admitted to the PACU after surgery showed varying degrees of ventilation defects, similar to the findings of Hedenstierna et al. [24]. Among these patients, LUS most commonly manifests as B line signs in the gravity-dependent lung area and irregularities and ruptures of the pleura. The above-mentioned LUS signs appear not only due to the effect of gravity, which causes the liquid to distribute to the lowered part, resulting in changes in gas-liquid distribution, but also considered to be related to the changes in the respiratory system of patients after induction of general anesthesia, which leads to lung inflation defects[21].In addition, during laparoscopic surgery, the increase in intra-abdominal pressure pushes the diaphragm muscle cephalad, causing changes in lung volume that exacerbate the formation of atelectasis in the gravity-dependent area of the lung [25]. Monastesse et al[9] pointed out that although the pulmonary ventilation defect caused by pneumoperitoneum was not as severe as that induced by general anesthesia, a significant increase in LUSS after pneumoperitoneum could be observed. Our research results showed that the LUSS at T1 was 5.22±2.89, which was the highest score at each time point, suggesting that the pulmonary ventilation defect was the most serious at this time, which was consistent with the maximum suppression of the diaphragm thickening rate. The LUSS at the T1-T3 time point gradually decreased, and the difference between the LUSS at the T3 time point and the T0 time point was still statistically significant (P<0.01), suggesting that the pulmonary ventilation defect caused by general anesthesia abdominal surgery is recoverable, but during the anesthesia recovery period still can not return to pre-anesthesia level.
Previous studies have evaluated the feasibility of diaphragmatic ultrasonography or LUS in the PACU, but the clinical significance of combined evaluation of the two in improving postoperative respiratory function in patients under general anesthesia has not been confirmed. Our study found that the total number of intervention cases, the number of intervention cases at early T1 and T2 time points after extubation in the group DL were greater than those in the group N (P<0.05), and the extubation time and PACU length-of-stay were significantly shorter than those in the group N (P<0.01), and the incidence of hypoxemia was significantly reduced (P<0.01). These findings suggest that adding LUS and diaphragm ultrasound real-time assessment results to routine interventions that rely on auscultation and SpO2 can help anesthesiologists perform precise interventions. Diaphragm ultrasound can dynamically monitor diaphragm function in real time. Early detection of PORC and timely addition of muscle relaxant antagonists will help the recovery of respiratory muscle function. LUS images can help anesthesiologists identify the status of lung ventilation, and guide lung recruitment therapy according to lung conditions. They can also quickly identify the cause of hypoxemia, and perform bedside precise treatment for patients with extravascular pulmonary edema before clinical pulmonary edema symptoms, relieving impairment of respiratory function caused by surgery and anesthesia and thus promoting rapid recovery.In this study, inconsistent with the results of the incidence of hypoxemia, there was no significant difference in SpO2 at each time point and the lowest SpO2 after extubation between the two groups of patients(Table 2), which may be related to the ability of auxiliary oxygen supply to cover up the abnormal respiratory function of patients after SpO2 detection. Studies have shown that when the inhaled oxygen concentration is 25% to 30%, even if the patient has hypoventilation, the SpO2 remains above 95% [26]. In this experiment, arterial blood gas analysis was used to evaluate the tissue oxygenation status, and PaO2/FiO2≤300mmHg (1mmHg=0.133kPa) was defined as hypoxemia[7]. The accuracy was greater than SpO2 under the condition of auxiliary oxygen supply [27].
We expected that ultrasound assessment and intervention would reduce the incidence of postoperative pulmonary complications in patients. However, the results of this study indicated that the number of postoperative pulmonary complications in the group DL was less than that in the group N, but the difference was not statistically significant (P>0.1). It may be related to the missed diagnosis caused by insufficient sample size or routine radiological examination for all patients. If it is to be determined whether ultrasound assessment and intervention can reduce postoperative pulmonary complications, it is necessary to increase the sample size or improve related examinations.
This study still has the following limitations. Firstly, the feasibility of ultrasound assessment of diaphragm function has been confirmed, but it is easily interfered by factors such as BMI and sedation level. This experiment was not compared with other methods for assessing diaphragmatic function.Secondly, diaphragm and lung examination has high repeatability and feasibility, but its accuracy and effectiveness depend on the experience of the operator. Lastly, the subjects of this study are those without diaphragmatic muscle function impairment and lung disease before operation. The clinical significance of ultrasound-assisted intervention for patients with preoperative respiratory insufficiency needs further research.
In summary, LUS and diaphragm ultrasound can provide effective monitoring of postoperative respiratory function in patients undergoing abdominal surgery. During the general anesthesia recovery period, the real-time display of the pulmonary ventilation status and the recovery of diaphragm function is beneficial to clarify the patient's lung condition, quickly identify the cause, timely detect PORC and carry out precise treatment, further improving the recovery of respiratory function of patients and promoting rapid recovery.