Perioperative Complications During Posterior Fossa Surgery in Sitting Position: A Single-Center Retrospective Study

Abstract

Background

Sitting position used to be a favored position for posterior fossa surgery. Its use has declined owing to the increased incidence of life-threatening complications. Our center continues to practice sitting craniotomy, although less frequently. This study aimed to determine the incidence of perioperative complications during sitting craniotomy.

Methods

Medical records of 206 patients who underwent posterior fossa surgery in sitting position over a 10-year period were analyzed. Data on demographics, perioperative complications, and neurological status were recorded. Statistical analysis was done using the chi-square and the Wilcoxon rank-sum tests, and a p-value of < 0.05 was considered significant.

Results

Out of 206 eligible patients, 188 had near-complete data. A declining trend was observed in the use of the sitting position. Thirty-nine patients presented with episodes of venous air embolism (VAE) with an incidence of 20.7%. No correlation was found between cerebrospinal fluid draining procedures or previous craniotomy and the development of VAE. None of the patients reported other perioperative complications except one who developed tension pneumocephalus. Intraoperative brainstem handling was the most common reason (72%) for postoperative mechanical ventilation. At discharge, 166 (88.3%) patients had good neurological outcomes, while poor outcomes were seen in 4 and mortality in 15 (7.9%), respectively.

Conclusion

The incidence of perioperative complications with the sitting position was not unusually high to prevent its routine use. Moreover, the development of VAE was not associated with increased complications or patient mortality risk. The use of sitting craniotomy, while debatable, continues to be safe in expert hands.

Keywords

venous air embolism - neurosurgery - sitting craniotomy

Introduction

The use of the sitting position for posterior fossa surgeries has declined over the years due to the increased risk of life-threatening perioperative complications like venous air embolism (VAE), tension pneumocephalus, quadriparesis, and macroglossia, leading to a compromised airway with several centers abandoning the practice in favor of horizontal positions.[1] [2] [3] [4] [5] [6] [7] [8] Our center continues to practice the sitting position during neurosurgery, albeit with less frequency over the years. The continuation of such practice is based on the advantages the sitting position offers to the patient, neurosurgeon, and neuroanesthesiologist, such as improved surgical access, clearer operative fields, and reduced blood loss.[1] [3] [9] The sitting position also results in improved respiratory mechanics.[10] [11] The technological and/or procedural advancements in neurosurgery and neuromonitoring have changed the incidence of possible complications and the practice of sitting craniotomy during the last decade.[12]

Therefore, we conducted this study to review the incidence of perioperative complications following posterior fossa surgery in the sitting position at our institute over a 10-year period and correlate it with patient outcomes.

Materials and Methods

After institutional ethics committee approval (IECPG 528/26.10.2020), a retrospective review of all patients from July 1, 2010 to June 30, 2020, who underwent craniotomy in the sitting position for posterior fossa lesions at the Neurosciences Center of All India Institute of Medical Sciences (AIIMS), New Delhi, India, was performed for this single-center, retrospective cohort study. Perioperative patient data, including age, diagnosis, surgery duration, VAE number and impact, hypotensive episodes, and vasopressor use, were retrieved from operating room (OR) registers and intraoperative anesthesia records. Postoperative data were retrieved from the Computerized Patient Records System (CPRS-VistA, Department of Veterans Affairs, Washington, D.C., United States) for course and duration of hospital stay, including duration of mechanical ventilation, need for tracheostomy, and postoperative complications.

VAE was defined as a sudden and sustained fall in end-tidal carbon dioxide (EtCO₂) ≥ 4 mm Hg, or the characteristic appearance of air bubbles on transesophageal echocardiography (TEE) in patients in whom TEE was inserted.

The patient outcome was defined in the form of the extended Glasgow Outcome Scale (GOS) score at discharge (GOSE-D).[13] [14] The GOSE-D scores between 7 and 8, 5 and 6, and 2 and 4 were considered to be of good, fair, and poor outcomes, respectively. Mortality outcome was defined as in-hospital death due to any cause following posterior fossa surgery without any intervening period of discharge to home.

Reintubation was defined as the need for tracheal intubation and reinstitution of mechanical ventilation due to any cause within 7 days of successful weaning and tracheal extubation postoperatively.

Statistical Analysis

Data analysis was analyzed using Stata 14 (College Station, Texas, United States). Categorical variables were compared using Fisher's exact test. Quantitative variables were compared using a paired t-test or a Wilcoxon rank-sum test. A p-value of < 0.05 was considered statistically significant.

Results

After perusing through OR records, 206 patients who underwent posterior fossa surgery in a sitting position during the 10 years were identified. Of these, near-complete intraoperative and postoperative records were available for 188 patients ([Fig. 1]), 114 (60.6%) male and 74 (39.4%) female. One hundred and eighteen patients (62.8%) underwent surgery between July 2010 and June 2015, while 70 (37.2%) underwent surgery from July 2015 to June 2020, which shows a declining trend in the use of sitting positions. The mean age of patients was 31.47 ± 15.69 years, and 49 (26.1%) patients belonged to the pediatric age group (< 18 years). Sixty-nine (36.7%) patients had a cerebrospinal fluid (CSF) draining procedure performed before definitive surgery, and 20 (10.6%) patients had undergone a previous craniotomy for the same disease. Twenty-four (12.8%) patients had systemic comorbidities. One patient was pregnant at 26 weeks at the time of surgery, and another patient had a concomitant aneurysm surgically clipped 10 days after tumor surgery. Mortality was seen in 15 (7.9%) patients.

Fig. 1 STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) flow diagram.

The breakup of the diagnosis of the patients is shown in [Fig. 2], and the presenting symptoms are presented in [Fig. 3].

Fig. 2 Primary diagnosis of patients who underwent surgery in the sitting position. SOL, space-occupying lesion.

Fig. 3 Neurological symptoms (includes patients with more than one symptom) at presentation.

Perioperative Data

All patients were monitored intraoperatively using electrocardiogram, pulse oximetry, core body temperature, noninvasive blood pressure, and EtCO₂. In addition, invasive arterial blood pressure monitoring was performed, and a right atrial catheter was placed in all patients for aspiration of possible VAE. The perioperative variables and anesthetic technique are described in [Table 1]. A TEE had been placed for the detection of VAE in 89 (47.3%) patients. Only 5 (2.7%) patients required vasopressors during the intraoperative period. The reasons for postoperative elective mechanical ventilation were brainstem handling in 103 (72%), prolonged duration of surgery in 25 (17.5%), the intraoperative vasopressor requirement (4), massive blood loss (3), poor respiratory efforts (3), and poor sensorium (5).

Table 1 Perioperative variables

Intraoperative variables		Postoperative variables
Parameter	Value (N = 188)	Parameter	Value (N = 188)
Intravenous (IV) induction [n (%)]	184 (97.9%)	Elective postoperative ventilation [n (%)]	143 (76.1%)
		Extubation on the operating table [n (%)]	45 (23.9%)
Use of flexo-metallic endotracheal tubes [n (%)]	152 (80.6%)	Ventilator days [median (IQR)] [survivors]	1 (1–2) [1 (0–2)]
Maintenance of anesthesia		Days in ICU [median (IQR)] [survivors]	2 (2–4) [2 (1–4)]
TIVA for maintenance [n (%)]	16 (8.5%)	Hospital stay [median (IQR)] [survivors]	7 (5–12) [7 (5–11)]
Isoflurane maintenance [n (%)]  Sevoflurane maintenance [n (%)]  Desflurane maintenance [n (%)]	42 (22.3%) 125 (66.5%) 5 (2.7%)	Postoperative new neurological deficits[b] [n (%)]
		Lateral gaze palsy Hemiparesis Facial palsy Poor sensorium Gag impairment	9 (4.8%) 7 (3.7%) 3 (1.6%) 6 (3.2%) 2 (1.1%)
Nitrous oxide (N2O) use [n (%)]	139 (73.9%)
Crystalloids (mL) [mean ± SD]	4219.9 ± 1617.3	Tracheostomy	16 (8.5%)
Colloids (mL) [mean ± SD] (n = 144)	740.6 ± 314.6
Blood loss (mL) [median (IQR)] (n = 174)	300 (200–600)	Intracranial hematoma	8 (4.3%)
PRBC transfused[a] (mL) [median (IQR)] (n = 47)	250 (250–500)	Hydrocephalus	11 (5.9%)
FFP transfused[a] (mL) [median (IQR)] (n = 9)	800 (400–800)
Platelet transfused[a] (mL) [median (IQR)] (n = 6)	150 (150–375)	CSF leak	3 (1.6%)
Facial nerve monitoring [n (%)]	6 (3.2%)	Difficult weaning	4 (2.1%)
Neural integrity monitoring [n (%)]	7 (3.7%)
Duration of surgery [mean ± SD] (min)	322.74 ± 100.36	Meningitis	7 (3.7%)
Total duration of anesthesia [mean ± SD] (min)	427.58 ± 107.53

Abbreviations: CSF, cerebrospinal fluid; FFP, fresh frozen plasma; ICU, intensive care unit; IQR, interquartile range; PRBC, packed red blood cells; SD, standard deviation; TIVA, total intravenous anesthesia.

^a Blood transfusion volume based on the empirical volume available in our center. Values for days spent on the ventilator, ICU, and hospital stay after excluding patients with mortality are italicized in brackets.

^b Postoperative deficits and complications include patients with more than one deficit or complication and patients who had mortality.

Reintubation was required in 5 patients due to respiratory distress (01), extradural hematoma (01), and neurological deterioration (03). The former two could be extubated, while the latter had mortality. Prolonged mechanical ventilation (more than 7 days) was required in 22 (11.7%). Of them, mortality was seen in 11 (5.9%), and 11 (5.9%) were tracheostomized. The reasons for tracheostomy were difficult weaning (06), poor sensorium (04), and new-onset lower cranial nerve dysfunction (01).

There was no incidence of macroglossia, quadriparesis, or peripheral nerve injury. Tension pneumocephalus was observed in one patient.

Venous Air Embolism

The overall incidence of VAE was 20.7% (39 out of 188). Nineteen of these patients had TEE placed, which helped in the diagnosis of VAE, while the remaining 20 were monitored with only EtCO₂. A sustained fall in EtCO₂ of more than or equal to (≥) 4 mm Hg was observed in 36 patients, which consisted of 16 patients in the TEE group and all patients in the EtCO₂ group. Hypotension secondary to VAE episode(s) was seen in 12 (30.8%) patients and was managed with fluid boluses or bolus doses of a short-acting vasoactive agent (mephentermine). Desaturation with the occurrence of VAE was noted in 3 patients, and multiple episodes of VAE were observed in 19 (10.1%) patients; however, only one patient required a change in the operating position to supine. There was no significant difference in the mortality rate and incidence of new neurological deficits between the VAE and non-VAE groups. Analysis for risk factors and complications because of VAE are shown in [Table 2].

Table 2 Risk factors and complications observed in patients who developed venous air embolism (VAE)

Parameter	VAE (n = 39)	No VAE (n = 149)	p-Value (statistical test)
Male:Female	20:19	94:55	0.2 (F.T.)
Age [mean ± SD] (y)	33.12 ± 15.94	31.04 ± 15.65	0.462 (TT)
Pediatric:Adult	10:29	39:110	0.99 (F.T.)
Shunting procedure (n = 69)	16	23	0.578 (FT)
Redo craniotomy (n = 20)	1	19	0.081(FT)
Use of N2O (n = 139)	31	108	0.42 (F.T.)
Blood loss (mL) [median (range)]	350 (100–1400) (n = 37)	300 (25–10000) (n = 137)	0.846 (W.T.)
Surgery duration [mean ± SD] (min)	336.92 ± 106.78	319.03 ± 98.65	0.322 (T.T.)
Total duration [mean ± SD] (min)	441.54 ± 108.26	423.93 ± 107.40	0.363 (T.T.)
Mortality	2	13	0.74 (F.T.)
New deficits	4	23	0.608 (FT)
Reintubation	1	4	0.99 (F.T.)
Tracheostomy	1	15	0.20 (F.T.)

Abbreviations: F.T., Fisher's exact test; N₂O, nitrous oxide; SD, standard deviation; T.T., paired t-test; W.T., Wilcoxon rank-sum test.

Patient Outcome

At the time of discharge, 166 (88.3%) patients had GOSE-D scores between 7 and 8, 3 patients had GOSE-D scores between 5 and 6, and 4 patients had GOSE-D scores between 2 and 4. Mortality was observed in 15 (7.9%) patients; the causes were posterior fossa bleed (03), postoperative infarcts (03), cerebral edema (02), meningitis (04), brain herniation (02), and adult respiratory distress syndrome in one patient. Analysis of risk factors for mortality is shown in [Table 3]. Intraoperative blood loss was found to be significantly associated with mortality (p = 0.0007) on univariate analysis. The duration of surgery and anesthesia was also increased, but it was not significant.

Table 3 Factors associated with mortality in the study population

Risk factor	Alive (n = 173)	Died (n = 15)	p-Value (statistical test)
Age (y)	31.25 ± 15.74	34.07 ± 15.40	0.50 (TT)
Male:Female	104:69	10:5	0.785 (F.T.)
CSF shunting procedure (n = 69)	63	6	0.786 (F.T.)
Previous craniotomy (n = 20)	17	3	0.20 (F.T.)
Anesthesia technique			0.99 (F.T.)
TIVA (n = 16) Inhalational (n = 172)	15 158	1 14
Use of N2O (n = 139)	127	12	0.763 (F.T.)
Intraoperative blood loss [median (range)] (mL)	300 (25–2300) (n = 160)	650 (100–10000) (n = 14)	0.0007 (W.T.)
Surgery duration [mean ± SD] (min)	318.64 ± 100.05	370.0 ± 94.64	0.057 (T.T.)
Total duration [mean ± SD] (min)	423.47 ± 107.77	475.0 ± 95.49	0.074 (T.T.)

Abbreviations: CSF, cerebrospinal fluid; F.T., Fisher's exact test; N₂O, nitrous oxide; SD, standard deviation; TIVA, total intravenous anesthesia; T.T., paired t-test; W.T., Wilcoxon rank-sum test.

Discussion

The use of the sitting position in neurosurgery has declined over the years in favor of horizontal positions in several centers.[1] [8] Like other centers, the number of patients being operated on in the sitting position at our center has also declined over the years. At our center, of the total number of patients operated in sitting position over a 10-year duration, more than 60% were operated during the first 5 years and less than 40% in the next 5 years. This observation was likely due to the change in the positioning preference of the operating neurosurgeons over the years.

The overall incidence of VAE in this study was 20.7%. The incidence of VAE in the sitting position varies based on the mode of detection, with rates as high as 75% when TEE monitoring is used.[1] [2] [15] [16] Even with the use of TEE, the incidence of VAE varies based on the study criteria, with rates as low as 25.6%.[10] In our study, the incidence of VAE was 21.3% in the subgroup where TEE was used. The risk factors that predispose patients to single or multiple episodes of VAE are still unclear. Ganslandt et al reported an increased incidence as the duration of surgery and anesthesia increased.[10] Although the mean duration of surgery and anesthesia is more extended in this study as well, neither was statistically significant for the occurrence of VAE. Few authors have reported a variable difference in the incidence of VAE in children.[6] [17] We, however, did not find any difference in the incidence of VAE between adults and children, which was similar to other previous observations.[18]

To the best of our knowledge, no previous study has compared the effect of CSF draining procedures, such as ventriculoperitoneal shunt or previous craniotomy, on the risk of intraoperative VAE. Our results indicate that a prior CSF draining procedure may not affect the risk of VAE or mortality. We also found that patients who appeared for repeat surgery had a lower but statistically insignificant incidence of VAE. Further studies with a larger sample size will be needed to investigate this further.

Intraoperative blood loss was significantly associated with mortality in our study (p = 0.0007). This blood loss, however, may be reflective of tumor size and grade, necessitating longer resection times, and may not have been a risk factor for mortality in itself. Episodes of VAE had no effect on mortality and on the development of postoperative new neurological deficits.[1] [2] [3] [4] [19]

The role of nitrous oxide (N₂O), specifically in the setting of neurosurgery in sitting position, is controversial. Our center continues to use gas, and the intraoperative use of N₂O was not associated with an increased risk of complications or mortality. Similar to previous studies, we also found that N₂O is not a major risk factor for the development of VAE.[6] [20]

Over 88% of patients who were included in this study had a good outcome with GOSE-D scores of 7 or 8. Despite the increased risks of perioperative complications, such as VAE, previous studies have failed to establish any difference in patient outcome between the sitting and horizontal positions when used in the setting of posterior fossa surgery.[1] [3] [19] Twenty seven patients had new neurological deficits in the postoperative period; however, there was no incidence of quadriparesis in our series of 188 patients.[2] [6]

Besides the inherent drawbacks of a retrospective study, our data are limited to only sitting position, and no comparison has been made with the other surgical positions. The incidence of VAE may be lower than reported in other studies due to underreporting of asymptomatic episodes of VAE; the grading of VAE episodes was not possible. Certain data, such as volume of blood loss and blood product transfused, may be empirical. The experience of the operating neurosurgeon has also not been considered in this study, which could have influenced some of the study results.

Conclusion

The incidence of VAE in this study was 20.7%, and the rate of other perioperative complications was similar between patients with and without the occurrence of intraoperative VAE. One patient developed tension pneumocephalus, and no patient developed macroglossia, quadriparesis, or peripheral nerve injury secondary to sitting craniotomy. The perioperative complications did not impact patient outcomes following the procedure, with most having a good outcome at discharge. Hence, the sitting position may continue to be employed whenever indicated in the practice of neurosurgery, and with strict vigilance on the part of the neuroanesthesiologist and neurosurgeon, the risk of perioperative complications could be minimal.

Conflict of Interest

None declared.

Acknowledgments

We would like to thank Dr. Maroof Ahmed Khan, Professor, and Mr. Hem Chandra Sati, Statistical Assistant, from the Department of Biostatistics, All India Institute of Medical Sciences, New Delhi, who helped with the statistical analysis of the data included in this study.

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Publication History

Article published online:
18 September 2025