Anaesthetic vigilance during endoscopic spine surgery: Impending signs of intraoperative hydroperitoneum and pleural effusion

Dear Editor,

A 29-year-old male weighing 74 kg presented with L4-L5 disc prolapse with compression of the left traversing root. He was scheduled for endoscopic interlaminar discectomy. After uneventful induction and intubation, the patient was positioned prone on an Allen’s spine system (ASS). Volume-controlled ventilation was initiated with a tidal volume of 500 mL, a respiratory rate of 12 breaths per minute, a fraction of inspired oxygen (FiO₂) of 50%, and zero positive end-expiratory pressure (PEEP). End-tidal carbon dioxide (ETCO₂) was maintained at 35 mmHg, and the peak airway pressure (Ppeak) was 15 cmH₂O.

Around 60 minutes into surgery with continuous irrigation, Ppeak gradually rose to 20 cmH₂O at the same tidal volume [Table 1]. Within the next 20 minutes, Ppeak increased sharply to 30 cmH₂O, and the expired tidal volume dropped to 180 mL. ETCO₂rose to 43 mmHg, peripheral oxygen saturation (SpO₂) decreased to 96% (FiO₂ 50%), the blood pressure was 102/60 mmHg, and the heart rate increased to 118 beats per minute. The anaesthesia depth was 1 minimum alveolar concentration (MAC) (expired sevoflurane 2%). An additional 1 mg of vecuronium was administered, and FiO₂ was increased to 100%. The surgeon was immediately alerted about the changes.

Table 1.

A 5-minute timeline table of spirometry changes during the sequence of events

TIMELINE (5 min)	11:10 AM	11:15 AM	11:20 AM	11:25 AM	11:30 AM	11: 35 AM
Peak airway pressure (cmH20)	17	20	30	31	31	31
Plateau pressure (cmH2O)	16	20	29	30	30	30
Mean airway pressure (cmH20)	9	10	12	13	15	16
Inspired/expired minute ventilation (L/min)	6.7/6.7	7.3/7.3	7.3/7.4	4.5/4.5	4.4/4.4	2.6/2.6
Inspired/expired tidal volume (ml)	482/474	520/519	531/527	315/310	310/313	182/180
RR bpm	14	14	14	14	14	14
Positive endexpiratory pressure (cmH20)	5	5	4	5	6	6
I:E	1:2	1:2	1:2	1:2	1:2	1:2
Compliance (ml/cmH2O)	66	53	29	12	13	7
Airway resistance (cmH20/L/s)	17	18	21	31	29	52

The timeline shows a rise in airway pressure, decreased compliance and delivered tidal volume. bpm: Breaths per minute; I/E: Inspiratory/Expiratory ratio

There was no occlusion in the breathing circuit or endotracheal tube, but the abdomen was visibly distended. Irrigation fluid input–output estimation revealed a discrepancy of approximately 3 litres. Equipment and tubing were checked and found to be intact.

Immediately, C-arm fluoroscopy was performed, which showed bilateral lung opacities with elevation of the right hemidiaphragm up to the 6^th rib. With a suspicion of hydroperitoneum, the procedure was promptly terminated after skin closure, and the patient was turned supine. Ultrasonography confirmed fluid in the peritoneal cavity and bilateral pleural spaces.

A 16G needle was used to drain the fluid: 3 litres from the abdomen, 300 mL from the right pleural space, and 80 mL from the left pleural space. Following drainage, Ppeak decreased to 20 cmH₂O. Haemodynamics and oxygenation remained stable. The patient was made to undergo computed tomography of the abdomen and thorax, which confirmed moderate bilateral pleural effusion and hydroperitoneum [Figure 1]. He was admitted to the intensive care unit, where bilateral pleural drains and a right-sided abdominal drain were inserted. He remained sedated and mechanically ventilated with PEEP of 10 cmH₂O. All drains were removed after 24 hours.

Figure 1.

(a) Axial section of CT thorax showing bilateral moderate pleural effusion. (b) Axial section of CT abdomen at L5 vertebra shows fluid in peritoneal space and area of breach from erector spinae muscles to the peritoneum (Image acquisition done after draining 3 litres of fluid from the abdomen). CT: Computed tomogram

He was gradually weaned and successfully extubated after 48 hours following a spontaneous breathing trial.

Endoscopic spine surgery is widely performed for lumbar disc herniation owing to its minimally invasive nature, reduced tissue trauma, and faster recovery.[1,2].Direct injury to the posterior abdominal wall during surgical instrumentation can create a pathway for pressurised irrigation fluid to enter the peritoneal cavity. The irrigation fluid pressure is typically maintained between 30 and 100 mmHg and is sometimes left unmonitored, as in our case.[3] In contrast, the intra-abdominal pressure is much lower (5–7 mmHg).[4] Consequently, irrigation fluid tracks easily along the pressure gradient into the peritoneum rather than returning through the suction port of the endoscope. Progressive accumulation of fluid in the peritoneal cavity increases intra-abdominal pressure, which restricts downward movement of the diaphragm. This is reflected initially as a rise in Ppeak. With further accumulation and increase in pressure, fluid can migrate into the pleural and interstitial spaces, resulting in impaired alveolar gas exchange. If abdominal distension continues, it may progress to abdominal compartment syndrome, manifesting as severe hypotension.[5] Early identification of rising peak airway pressure on spirometry is therefore critical as it often precedes changes in ETCO₂, SpO₂, and hypotension. Compared with the case reported by Park et al.,[5] our patient exhibited less severe respiratory compromise and did not develop hypotension. Early recognition of spirometry changes and the use of the ASS could be the reason. The ASS allows the abdomen to hang freely in the prone position, thereby improving lung compliance and reducing compression on the inferior vena cava.[6] During endoscopic spine surgery, continuous monitoring of spirometry and irrigation fluid balance is essential. Immediate intervention can effectively prevent progression to respiratory failure and abdominal compartment syndrome.

Declaration of Patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient consented to the images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed.

Disclosure of use of artificial intelligence (AI)-assistive or generative tools

No AI tools were used for preparation or editing the manuscript

Author contributions

DGP, IG, VJR, DS: Directly involved in patient’s care, critical thinking during patient management and responsible for drafting the manuscript. DGP: Obtaining informed consent, sourcing of clinical images and preparation of table, responsible for overall integrity of manuscript content and final approval of the manuscript.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.