Effects of Crystalloid Preloading (20 ml/kg) on Hemodynamics in Relation to Postural Changes in Patients Undergoing Neurosurgical Procedures in Sitting Position

INTRODUCTION

Sitting position for posterior fossa and cervical spine surgeries pose challenges to anesthesiologists in terms of hemodynamic instability. Sitting position for neurosurgery has both pros and cons, and there has been a constant debate since its introduction by De Martel.[1] The benefits of sitting position to the surgeons include optimum access to posterior midline lesions, improved access to tentorial hiatus, improved visibility, clear surgical field due to gravity assisted drainage of the blood.[2] Whereas for anesthesiologists, it offers greater access to the endotracheal tube, intravenous (IV) lines, lower airway pressure, decreased the need for blood transfusion, and clear view to observe the cranial nerve response. However, sitting position has several disadvantages such as hemodynamic disturbances, venous air embolism (VAE), paradoxical air embolism, pneumocephalus, and postoperative quadriplegia and quadriparesis.[3]

Hemodynamic disturbances like hypotension are very common in neurosurgical procedures in sitting position. The reported incidence of hypotension in the literature varies from 5% to 32%.[4567] The resulting hypotension may cause cerebral and myocardial ischemia. The gravitational effect can sequester as much as 1500 ml of blood in the lower limbs in sitting position, thus reducing preload to the heart. The vasodilator properties of inhaled anesthetic agents and depression of myocardial contractility can further aggravate hypotension in sitting position craniotomy. Besides, the positive pressure ventilation can reduce the venous return further contributing to the hypotension. Moreover, the patient-related factors such as body mass index (BMI) and intravascular volume status can influence the hemodynamic status during sitting position craniotomy.

Several studies[8910] have shown a decrease in mean arterial pressure (MAP), stroke volume index (SVI), and cardiac index (CI) in patients undergoing neurosurgical procedures in sitting position. None of the studies have prospectively studied the effects of crystalloid preloading on hemodynamic changes during positioning from supine to sitting position. Hence, this pilot study was designed to study the effect of crystalloid preloading on hemodynamic parameters such as MAP, SV, cardiac output (CO), CI, and inferior vena cava diameter (IVCD) during positioning the patient from supine to sitting position.

MATERIALS AND METHODS

It is a prospective observational study conducted in the tertiary care center, after obtaining institutional ethical approval. The study was registered with clinical trial registry India (CTRI number-CTRI/2014/11/005221). Written informed consent was taken from 20 patients, aged between 18 and 60 years with the American Society of Anesthesiologist (ASA) physical Status I and II. Patients with severe cardiac and renal disease, orthodeoxia, patent foramen ovale (PFO), and intracardiac shunts were excluded from the study. Patient data such as age, sex, weight, height, BMI, ASA physical status were collected during the preoperative visit, a day before surgery. Baseline investigations such as complete hemogram, blood urea, serum creatinine, random blood sugar, electrocardiogram, and chest X-ray were noted.

Preoperatively, all the patients posted for craniotomy in sitting position were assessed for any cardiac defects (PFO and other intracardiac shunts) by transthoracic echocardiography (TTE).

Inside the operation theater, standard monitors, i.e., electrocardiograph, noninvasive blood pressure, pulse oximeter (SpO₂) were attached. An 18-G IV cannula was secured, patients were anesthetized with standard induction protocol with fentanyl 2 μg/kg IV, propofol 1.5 mg/kg IV, and vecuronium 0.1 mg/kg IV and patients were intubated with the appropriate size endotracheal tube.

A volume of 20 ml/kg of normal saline was loaded until we began to position the patient. Following induction, the arterial line was secured using a 20G cannula in the radial artery and was connected to two BP transducer sets. One pressure transducer set was zeroed at the mastoid process to monitor Systolic BP, Diastolic BP and MAP. The second transducer was connected to FloTrac (Edward Lifesciences, LLC, Irvine, CA) sensor on Vigileo CO device (model no-MHM1E) for continuous monitoring of CO, CI, SV, SVI, and SV variation (SVV). A transesophageal echocardiography (TEE) probe was inserted (Esaote SpA) to rule out PFO by Color Doppler. A right subclavian vein was cannulated using a 7 Fr triple lumen central venous catheter. The tip of the catheter was placed at Superior vena cava (SVC) and right atrial junction using TEE and the presence of PFO was ruled out again with agitated saline technique. In patients in whom PFO was detected, the plan for sitting position was abandoned and surgery was continued in lateral or prone position.

The anesthesia was maintained with oxygen and air mixture (FiO2 of 40%), with 0.8–1 MAC of isoflurane titrated to entropy value of 40–60. An intermittent bolus of fentanyl and vecuronium were supplemented as and when required.

After the IV infusion of 20 ml/kg of saline, just before positioning, all the baseline parameters such as heart rate (HR), MAP, central venous pressure (CVP), CO, SVV, CI, and SV were noted. Maximum and minimum IVCD was noted 1 cm proximal to the IVC-portal vein junction using M-mode in TEE. These parameters were recorded again during positioning at 30°, 60° inclination of the operating table and after the final sitting position. Initially, a slight Trendelenburg position was given. Then, the head end of the table was given propped up position 20°–30°. by alternating Trendelenburg and propped up position, a standard 80°–90° sitting position was obtained after giving 10 min for stabilization with each degree of the position change.

Any fall in mean BP of >10% was considered as hypotension and was treated with intermittent boluses of 20 μg phenylephrine.

RESULTS

Twenty ASA I and II patients aged between 18 and 60 years were enrolled for the study. Eighteen patients were included in the final analysis. Two patients were excluded from the study after detection of PFO using TEE following induction of anesthesia. Twelve female and eight male patients were enrolled for the study [Table 1]. The mean age and body weight of the participants was 40.5 ± 6.9 years and 60.9 ± 7.3 kg, respectively.

Table 1 Patient demographics (n=20)

Vitals parameters during positioning of the patient

HR, MAP, and CVP were recorded at supine, 30°, 60°, final sitting position and 30 min after sitting position. There were no significant changes in the HR during positioning [Table 2].

Table 2 Vital parameters during positioning the patient (n=18)

The MAP showed a declining trend, but the changes were not significant (P > 0.05). When compared to the supine position MAP decreased by 6% in 30°, 7% in 60°, 8.4% in final sitting position. None of the patients required vasopressor boluses during positioning. Thirty minutes after final positioning the MAP decreased by around 11%. A significant fall in CVP was observed at 30°, 60°, final sitting position as compared to the supine position [Table 2].

Advanced hemodynamic parameters

The advanced hemodynamic parameters such as SV, SVV, SVI, CO, CI, SVR, and SVR Index (SVRI) were noted during positioning using FloTrac Vigileo sensor [Table 3].

Table 3 Hemodynamic parameters (n=18)

No significant changes in SV, SVV, CO, and CI were observed during positioning the patient from supine to final sitting position. The systemic vascular resistance and SVRI showed a declining trend with a significant reduction after 30 min of final position as compared to sitting position (P = 0.03 and 0.02, respectively).

Inferior vena cava diameter as a marker of preload and correlation with cardiac output

IVCD was measured as a marker of preload in patients during positioning. IVCD was measured during end inspiration and end expiration using M mode in TEE [Table 4]. IVC distensibility index was calculated using the parameters. There was no significant difference in IVCD and distensibility index during positioning the patient from supine to sitting position.

Table 4 Transesophageal echocardiography measured parameters (n=18)

The linear relationship between the differences in IVC distensibility at different time points from baseline with the difference in CO is given in Table 5. It shows that the difference in IVC distensibility index is not correlating with the difference in CO, which indicates the change in CO, is not linearly related to the change in IVC distensibility.

Table 5 Change in inferior vena cava distensibility from baseline to final sitting position with the change in cardiac output

DISCUSSION

Although neurosurgical procedures in sitting position have been diminishing since decades, it is still practiced in some centers as the advantages outweigh its disadvantages in certain cases.[1112] The aim of this study was to assess the hemodynamic changes during positioning, and correlation of the changes in IVCD in relation to the changes in CO.

One of the major complications during positioning is hypotension.[48] Hypotension while positioning can be carefully avoided by optimal preloading of fluids and slow verticalization of the body with pauses to elevate the legs alternatively to minimize the drastic pooling of blood in the lower extremities.

Hypotension, a fall in MAP of >10 mmHg was defined in the study conducted by Young et al. in 255 patients to compare the surgical and anesthetic complications in neurosurgical patients experiencing VAE in the sitting position.[6] In this study, we considered the cutoff value of 10% decrease in MAP as significant. MAP showed a falling trend while positioning from supine to sitting position but the fall in MAP was insignificant until this point. This can be attributed to the preloading of crystalloids before positioning. Fall in MAP by 11.5% after 30 min of final sitting position may be due to mannitol infusion that was given for brain relaxation.

In a study conducted by Marshall et al., they studied the hemodynamic effects of the seated position using four different commonly used anesthetic regimens (enflurane-nitrous oxide, halothane-nitrous oxide, fentanyl-droperidol-nitrous oxide, and morphine-nitrous oxide). In all the four groups observed, CI and SVI reduced significantly in the sitting position compared to supine position. In our study, although some reductions were observed in the SV, SVI, and CO while positioning the patient from supine to sitting position, the changes observed were not significant. Hemodynamic stability in our study may be due to 20 ml/kg of crystalloid preloading before positioning. The preloading of crystalloids and maintenance of adequate anesthetic depth may be responsible for significant fall in SVR and SVRI 30 min after final sitting position. Anesthetic depth was monitored using Entropy and maintained using 0.8–1 MAC of isoflurane titrated to entropy value of 40–60. Besides, intermittent boluses of fentanyl and vecuronium were given given while positioning the patient.

Respiratory variation in IVCD and IVC distensibility index are considered to better predict fluid responsiveness better in patients on mechanical ventilation.[13] In our study, IVCD measured in end inspiration, and end expiration are used as a marker of preload in patients during positioning. IVC distensibility index (maximum D-minimum diameter)/minimum diameter was calculated using the parameters. In a study conducted by Panebianco et al., they found no significant difference in the IVCD in relation to supine or semi-upright position.[14] In this study, we found no significant difference in IVCD and distensibility index during positioning the patient from supine to sitting position. In this study, difference in IVC distensibility index is not correlating with the difference in CO. This may be due to two reasons, careful positioning with the legs at the level of heart and adequate preloading before positioning the patient.

CVP being a poor predictor for fluid responsiveness, it is difficult to decide clinical management based on CVP.[15] In our study, when compared to the supine position CVP decreased by 17% at 30°, 11% at 60°, 12% at a final sitting, and 11% at 30 min after final sitting position. The fall in CVP continuously as the patient is moved from a supine to sitting position may be due to fall in SVR in sitting position. Although there is a decrease in CVP from supine to sitting position, no intervention has been done based on CVP due to other stable hemodynamic parameters.

The risk of VAE and paradoxical air embolism are frequently associated with sitting craniotomy surgeries.[16171819] The presence of PFO increases the risk of paradoxical air embolism.[202122] Many surgeons consider the presence of a PFO as an absolute contraindication to neurosurgery in the sitting position.[2324] The incidence of detection of VAE varies depending upon the technique used. Transesophageal echocardiography and transthoracic Doppler echocardiography are sensitive techniques to detect as small as 0.02 ml/kg and 0.06 ml/kg, respectively.[2526] In our study, TTE and transesophageal echocardiography are used to rule out PFO in the pre- and intra-operative period, respectively. Two patients were detected to have PFO when TEE was used. The Incidence of VAE reported in several studies range from 1% to 76% in sitting craniotomy surgeries.[27] The incidence of VAE detected in our study is 11% which is in the range from other studies.

CONCLUSION

A volume of 20 ml/Kg of crystalloid preloading before positioning the patient from supine to sitting position maintains the hemodynamic stability and avoids the vasopressor requirement.