Percutaneous nephrolithotomy (PCNL) is a popular technique for the management of large renal stones. The technique has trended toward decreasing invasiveness by employing smaller tract sizes, with options such as the mini-PCNL and ultra mini-PCNL, and by avoiding large nephrostomy tubes via the tubeless PCNL and totally tubeless PCNL techniques. These changes have allowed PCNL to be performed in ambulatory settings, with some reporting 60%-90% of PCNLs being performed outpatient.^1,2

As this trend continues, one important consideration is the role of anesthesia in optimizing outcomes. While PCNL can be performed under regional or spinal anesthesia, it is traditionally performed in the prone position under general anesthesia with endotracheal tube (ETT) placement with the aid of neuromuscular blockade and narcotics. This allows for safe access minimizing risks of injury to surrounding structures.

A commonly used neuromuscular blocking agent is rocuronium, an intermediate-acting nondepolarizing neuromuscular blocker.³ Rocuronium is used during intubation and can be used throughout the surgical procedure to provide moderate or deep neuromuscular blockade.³ Factors affecting a patient’s response to rocuronium include presence of neuromuscular disease, obesity, hepatic or renal disease, electrolyte abnormalities, and certain medications, including antibiotics and antidepressants.⁴ Proper use of neuromuscular blockade is important, given risks for residual neuromuscular weakness seen in 20%-40% of recovery room patients leading to postoperative pulmonary complications, which can manifest as atelectasis from impaired contraction of ventilatory muscles, inability to cough, impaired swallowing, and aspiration.^3-5

Similarly the use of intraoperative narcotics has been reviewed extensively. A common narcotic used is fentanyl, a mu agonist used for analgesia and during general anesthesia.⁶ With central and peripheral targets, it can cause respiratory depression, cough suppression, nausea, vomiting, dizziness, and constipation.⁶ The use of narcotics perioperatively has also been linked to opioid tolerance and opioid-induced hyperalgesia which may make subsequent narcotic use ineffective.⁶ This has led to several ERAS (enhanced recovery after surgery) protocols across various subspecialties in the ambulatory setting.

In an effort to reduce total intraoperative paralytic and narcotic use, limiting total anesthetic time and operative time and choosing alternatives to ETT placement with paralytic can be explored. One proposed method is performing the PCNL procedure in the supine position. The supine position allows for the option of spontaneous breathing with a laryngeal airway mask without the need for paralytic (per the discretion of the anesthesiologist), and has been shown in some studies to have shorter procedure times when compared to prone position.⁷

In our practice, a retrospective analysis of a total of 223 PCNL cases demonstrated 86 (39%) were performed in the supine position and 137 (61%) were in the prone position. Data including demographics, BMI, American Society of Anesthesiologists score, tract size (24Fr or 16.5Fr), stone burden, staghorn presence, use of laryngeal airway mask or ETT placement, total anesthesia time, total procedure time, and total intraoperative dose of paralytic (rocuronium in mg) and narcotic (fentanyl in μg) were assessed. Patients with anatomical abnormalities such as pelvic kidney, malrotated kidney, horseshoe kidney, transplant kidney, and those with urinary diversion were all excluded from analysis.

Multivariable linear regression models demonstrated that position and total stone burden were strong predictors of total anesthesia time and total operative time. After controlling for stone burden, tract size, presence of staghorn, and BMI, supine position had 14 minutes shorter anesthesia time (95% CI 1.23-26.8, R2 = 0.23, P = .032) and 12 minutes shorter operative time (95% CI −0.044-23.9, R = 0.22, P = .051) when compared to prone position. Multivariable linear regression models also demonstrated that position was a predictor of total paralytic dose and total narcotic dose. When controlling for stone burden, tract size, presence of staghorn, and BMI as well as total anesthesia time, supine patients received 20 mg less rocuronium (95% CI 13.2-26.8, R2 = 0.21, P < .001) and 38 μg less fentanyl (95% CI 14.5-62.2, R2 = 0.09, P = .002) when compared to patients in the prone position. These results suggest advantages intrinsic to patient positioning in the supine position that allow for less anesthesia use and duration (unpublished data).

The difference observed in operative time between the supine and prone groups may be related to intraoperative steps including time to access collecting system or time needed for stone evacuation, which may favor the supine position as the use of gravity may aid in removal. The difference in total anesthesia time between the 2 groups is greater than the difference in operative time between the groups, suggesting that factors outside of the operation itself, including patient positioning, may factor into prone positioning requiring longer anesthesia time.

The clinical significance of the dose reductions of both paralytic and narcotic seen during these PCNLs is still yet to be determined. There is evidence that postoperative pulmonary complications related to neuromuscular blockade are dose dependent.^3,4 On average, the normal loading dose of rocuronium for intubation in an average 60 kg person is approximately 30 mg. If the supine position can reduce the dose of rocuronium by 20 mg or even eliminate it entirely, it is hypothesized that several adverse events related to residual neuromuscular blockade can also be avoided. Similarly, a normal loading dose of fentanyl is approximately 25 to 100 μg in a standard 60 kg person. While our model suggests supine positioning reduced the fentanyl dose by 38 μg, this reduction can theoretically be even larger for those with large stone burden or in obese patients with BMI >30, which were also strong predictors of narcotic use.

Further evaluation of patients in a prospective fashion and postoperatively in the recovery room and in the days following surgery is warranted to understand whether this dose reduction decreases adverse effects associated with narcotics. Nevertheless, if performing PCNL in the supine position is noninferior to the prone position with respect to factors like stone-free rates and postoperative complications, then anesthetic dose reductions afforded by the supine position should be encouraged by both the surgical and anesthesia teams to promote shorter recovery room and operating room times, leading to improved efficiency and surgical volume in an ambulatory setting.