Feasibility of laryngeal mask anesthesia combined with nerve block in adult patients undergoing internal fixation of rib fractures: a prospective observational study

Rib fracture is one of the most common injuries following blunt trauma, occurring in approximately 10% of all trauma patients. Surgical stabilization of rib fractures has been shown to be beneficial in those patients with flail chest and multiple severe displaced fractures [1]. In the past, general anesthesia with endotracheal intubation (ETI) was considered mandatory for rib fracture surgery. However, it might cause ventilator-induced lung injury (VILI) [2] and the patients might also have delayed awakening or even need re-intubation owing to residual general anesthetics [3]. Currently, the enhanced recovery after surgery (ERAS) protocol is well established as a standard of care for several surgeries. LMA anesthesia combined with a nerve block could offer an enhanced recovery owing to the possibility of a fast and coughless extubation and effective postoperative analgesia with less opioid [4]. Therefore, we designed this prospective observational study to evaluate the feasibility of general anesthesia with an LMA associated to regional anesthesia in elderly patients undergoing internal fixation of rib fractures.

Twenty patients were enrolled in this study, and their characteristics are listed in Table 1. Of the 20 patients, eight (40%) received single-level TPB, while the remaining 12 (60%) received double-level TPB. Moreover, 13 (65%) patients additionally received ESPB. All patients achieved satisfactory blockade and received LMA anesthesia. No patient required ETI anesthesia owing to the poor position of the LMA or insufficient ventilation. A flow chart of patients recruited for the study is depicted in Fig. 2.

The postoperative PaO₂ was significantly improved compared to the preoperative value (91.2 ± 16.0 vs. 83.7 ± 15.9 mmHg, p = 0.004). Nevertheless, there was no significant difference between preoperative and postoperative PaCO₂ (42.1 ± 3.7 vs. 43.2 ± 3.7 mmHg, p = 0.165).

In most patients, the mean arterial pressure was stable, except for eight (40%) patients, whose MAPs were less than 60 mmHg transiently and were treated by phenylephrine. Patients’ SpO₂ before anesthesia was 98% (93.25, 98) % and remained above 95% [99% (98, 100) %] during the operation, except for one patient whose SpO₂ declined from 100 to 87% transiently but recovered to 98% within 5 min. The duration from LMA insertion to spontaneous breathing recovery was 27.3 ± 19.4 min. Vt, RR, and EtCO₂ during spontaneous breathing were in the range of 205–875 ml, 7–23 breaths/min, 36–63 mmHg, respectively, except for one patient whose EtCO₂ exceeded 60 mmHg, ranging from 57 mmHg to 63 mmHg. The time to removal of LMA was 6 ± 3 min.

The postoperative NRS scores at T1, T2, and T3 were 3(2,4), 1(1,3), and 0(0,1), respectively. In this study, the highest score was 5 in four patients (20%). Two patients had a score of 5 at 6 h and the other two at 12 h after surgery. All four patients received one intramuscular injection of 50 mg pethidine for rescue analgesia, and pain was relieved. PONV did not occur within 48 h after surgery in all cases.

Sufentanil was administered at a dose of 9.9 ± 3.4 μg. None of the patients developed agitation or sore throat after anesthesia. Perioperative regurgitation, aspiration, and nerve block-related complications were not observed in any of the patients.

In this study, we found that LMA anesthesia combined with nerve blocks such as TPB and ESPB could offer satisfactory analgesia, stable hemodynamic function, good oxygenation, acceptable EtCO₂, and thereby a smooth recovery.

Although thoracic epidural anesthesia is a gold standard for thoracic analgesia, it can frequently induce hypotension. It is also associated with serious complications such as epidural hematoma and neuropathy [6]. Therefore, various nerve blocks can be used as alternatives to epidural anesthesia, such as the serratus anterior plane block (SAPB), intercostal nerve block (INB), and ESPB. Nevertheless, there are some limitations to the above-mentioned methods. In SAPB, the local anesthetic agent is distributed along the midaxillary line near the surgical incision, which may impede the surgeon from transecting the muscular layers. INB requires multiple injections, subjecting the patient to more pain and increases the risk of inadvertent intercostal vessel or pleural puncture. As ESPB is administered in the intermuscular space, the incidence of a complete block is about 1/3 [7]. As TPB can provide a reliable effect equivalent to that obtained with unilateral epidural anesthesia with lesser hemodynamic depression, we chose TPB for method of regional anesthesia in our study. Meanwhile, all patients maintained steady hemodynamic function with occasional administration of phenylephrine.

The intercostal (IC) and paralaminar (PL) approaches are commonly used in TPB. Yasuko Taketa et al. [8] considered that a single injection of 20 ml 0.375% ropivacaine via the PL approach could acquire 4–5 dermatomes of sensory blockade. They found that the blocked dermatomes of sensory loss were more in the PL group than in the IC group. The average number of blocked dermatomes was three in the IC group and four in the PL group. In addition, the PL approach was regarded as a better choice to block the dorsal ramus of the thoracic nerves [9]. The TPB through a PL approach may obtain a wider block effect compared to the IC approach and should be applied preferentially. Our approach regarding the TPB is the similar to Taketa’s PL approach and is also consistent with the transversal IAP approach described by Krediet et al. [10] Moreover, we chose the TPVS of the second fractured rib for injection when the surgical segments were not more than four sequential ribs because we found that the area of blockade in the caudal direction was more extensive than that in the cephalic direction.

In thoracic surgery, postoperative pulmonary complications (PPCs) are problems that should be addressed. Recruitment maneuver and airway suction might be beneficial to patients during ETI anesthesia. The leak pressure of the LMA Supreme™ was 27.1 ± 5.2 cmH₂O according to Russo’s study [11]. Thus, the LMA Supreme™ could settle for recruitment maneuver during anesthesia. Early extubation and good analgesia in our study promoted patients to have enough strength to cough and expectorate postoperatively, also beneficial to lung recruitment. In particular, the early recovery of spontaneous breathing reduced PPCs including pneumonia and acute respiratory distress syndrome [12]. Positive pressure ventilation not only changes the pressure gradient of the thoracic cavity and interferes with the distribution of intrapulmonary ventilation, but also leads to an imbalance in the ventilation/perfusion (V/Q) ratio with excessive or inadequate tidal volume. Barotrauma and volume injury caused by mechanical ventilation can also cause VILI. The information above indicates that the spontaneous breathing might be beneficial to lung protection [12, 13]. In our study, the postoperative PaO₂ was improved compared to the preoperative values.

The patients showed various degrees of carbon dioxide retention during spontaneous breathing. The EtCO₂ of most patients was below 50 mmHg at the end of surgery. The highest EtCO₂ value in our study was 63 mmHg and occurred in a male patient whose final EtCO₂ was 58 mmHg at the end of the surgery. After extubation all patients were fully awake and their PaCO₂ was normal on the second day after surgery. The concept of permissive hypercapnia has been accepted for a long time. O′ Toole et al. [14] believed that hypercapnia could produce an anti-inflammatory effect by inhibiting nuclear factor-kappa B (NF-κB). Other scholars thought that hypercapnia had a protective effect on VILI [15, 16]. Hypercapnia can also improve pulmonary compliance by a non-surfactant mechanism and enhance pulmonary vascular resistance by strengthening hypoxic pulmonary vasoconstriction to decrease the pulmonary shunt [17].

Most patients with rib fractures experienced dyspnea. The satisfactory effect of TPB could improve patient oxygenation, as respiratory amplitude increases when the patients do not feel pain [18]. The patients’ Vt and RR during spontaneous breathing can meet the needs of intraoperative oxygenation, even in LMA anesthesia with 50% oxygen. Koo et al. concluded that an oxygen concentration of 50% could decrease the risk of atelectasis caused by high oxygen concentration [19]. Our results showed that all patients maintained their SpO₂ at good level during the operation, including three patients whose preoperative SpO₂ was lower than 93%. The minimum SpO₂ was 87% and occurred transiently in one case. Preoperative chest computed tomography showed a large amount of pleural effusion, incomplete atelectasis, and consolidation of the inferior lobe on the injured thorax. The decline in SpO₂ was attributed to a notable decrease in tidal volume caused by sufentanil. However, it increased to 98% in a few minutes and remained at 100% until the end of surgery.

The serratus anterior and latissimus dorsi muscles were innervated by the long thoracic and thoracodorsal nerves, respectively. TPB cannot paralyze these muscles. We found that one effective dose (ED₉₅) of rocuronium could weaken muscle twitching when the surgeons transected the muscles using a high-frequency electrotome. Murphy et al. [3] pointed out that the residual effect of muscle relaxants was one of the causes of postoperative respiratory failure, and critical respiratory events observed in 18.0% of patients undergoing thoracic surgeries. Althausen et al. reported that the incidence of re-intubation after surgical stabilization of the flail chest was 4.55% (1/22) [20]. The half dosage of muscular relaxants for ETI anesthesia in our study facilitated the patients to recover spontaneous breathing during surgery. Therefore, the patients were not monitored for neuromuscular blockade or administer muscle relaxant antagonists. Since SpO₂ was maintained above 96% during spontaneous respiration at 40% oxygen concentration, each patient was extubated with the confirmation of consciousness, blinking, good swallowing function, and fist clenching in the post-anesthesia care unit. Besides, the patients maintained a good level of cough strength after extubation and did not need re-intubation.

In our study, the analgesic effect of the nerve block was sufficient and maintained for approximately six hours after the operation. This was consistent with the duration of postoperative analgesia of TPB (303.97 ± 76.08 min) reported by Das et al. [21] Due to the PCA and intravenous infusion of flurbiprofen, most patients felt an acceptable level of pain. This indicated that the multi-mode analgesia protocol was effective and necessary for postoperative analgesia. This result also suggests that better postoperative analgesia can be achieved by TPB catheterization in a future study, as reported by Ge et al. [22].

There were several limitations to this study. Owing to the small sample size, the capacity to evaluate potential risks such as regurgitation, aspiration, and nerve block related complications was limited. Patient selection and lack of a control group also contribute to the limitations. Since the initial focus was on whether the anesthetic technique could meet the needs of rib surgery, we excluded patients with complicated extubation conditions such as respiratory failure, obesity, difficult airway, myasthenia gravis, asthma, and chronic obstructive emphysema. Although early extubation occurred and PPCs such as pneumonia and acute respiratory distress syndrome were not observed, these findings are not sufficient to declare superiority when compared with ETI anesthesia. The results in our study might provide a basis for further randomized controlled trials to assess the safety and effectiveness of this anesthesia technique.

We demonstrated that LMA anesthesia combined with nerve blocks could be feasibly applied in our selective patient population undergoing internal fixation of rib fractures. This practice could provide stable hemodynamic and respiratory function, and the advantage of a smooth recovery. Our protocol could represent a draft of an ERAS anesthetic protocol for this type of surgery.