A comparative study of hemodynamic changes between prone and supine emergence from anesthesia in lumbar disc surgery.

BACKGROUND: Supine emergence from anesthesia in patients undergoing lumbar surgery in prone position leads to tachycardia, hypertension, coughing, laryngospasm and loss of monitoring as the patients are rolled back to supine position at the end of surgery. The prone extubation might facilitate a smoother emergence because the patients are not disturbed during emergence and secretions are drained away from patient's airway.
MATERIALS AND METHODS: The patients were randomly allocated to one of the two groups of 30 each at conclusion of surgery. First group was extubated in prone position and second in supine position at conclusion of surgery. Supine group patients were rolled back and prone group patients were left undisturbed. Extubation was done after complete reversal of neuromuscular block. Heart rates (HR), mean arterial pressure (MAP) were noted at various points of time. Coughing, laryngospasm, vomiting, monitor disconnection if any were also noted.
RESULTS: During emergence from anesthesia heart rate was significantly more in group S than group P at all intervals (P < 0.001). Mean arterial pressure was significantly higher in the supine group at 2, 3, and 4 min compared to prone group (P = 0.003). Compared to supine patients, prone patients had fewer incidences of coughing (P = 0. 0004), laryngospasm, vomiting and monitor disconnection.
CONCLUSION: In healthy normotensive patients, emergence from anesthesia in the prone position is associated with minimal hemodynamic change, and fewer incidences of coughing, laryngospasm, and monitor disconnections.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Supine extubation from anesthesia in patients undergoing lumbar disc surgery in the prone position is associated with hemodynamic and cardiovascular response consisting of increased circulating catecholamines, heart rate, blood pressure, myocardial oxygen demand and dysrhythmia.[123] These changes are probably generated by the movement of endotracheal tube during rolling of patients back to supine position in lighter depth of anesthesia at the conclusion of surgery and laryngoscopy.[4]

Several studies have been recommended to attenuate the cardiovascular responses during emergence in supine position, including deep extubation, the administration of dexmedetomidine, esmolol, fentanyl, i.v. or topical lidocaine.[5678] However, there are few studies comparing prone and supine extubation on hemodynamic and airway response during emergence from anesthesia.

Prone emergence was nearly always observed to be a calm and smooth transition from surgery to the awake, extubated state by avoiding the movement that causes tracheal irritation.[4] The present study was performed to compare the effect of prone and supine extubation on modifying the hemodynamic and airway responses during emergence from anesthesia.

MATERIALS AND METHODS

After obtaining institutional ethics committee approval and written informed consent from each patient, 60 patients undergoing elective lumbar disc surgery under general anesthesia in prone position aged between 18 and 60 years of either gender, belonging to American Society of Anaesthesiology (ASA) physical status I and II, with ± 20% of ideal body weight, were recruited for study. Patients with suspected difficult airway, risk factors for perioperative aspiration, chronic coughing, hypertension and diabetes mellitus, a recent history of respiratory tract infection, or chronic obstructive lung disease and obesity were excluded from the study. The patients were randomly divided into two groups using the computerized random number table at the conclusion of surgery: Group P, Patients were extubated in prone position, Group S, Patients were extubated in supine position.

Group P: Patients who were extubated in prone position at conclusion of surgery.

Supine S: Patients who were extubated in supine position at conclusion of surgery.

After shifting inside the operation theater, the patients were made to lie supine on the operating table, a peripheral vein was cannulated with 18 G cannula and an intravenous ringer lactate drip was started. The patients were connected to non-invasive blood pressure (NIBP) monitor, electrocardiogram (ECG) monitor and pulse oximeter. All patients were uniformly premedicated with midazolam (0.05 mg/kg) and inj. Glycopyrrolate 0.2 mg, and Inj. Fentanyl 2 μg/kg intravenously on operating table 5 minutes before induction and the patients were preoxygenated with 100% oxygen for 3 minutes.

All the patients were induced with intravenous Inj. propofol 2.5 mg/kg followed by Inj. vecuronium bromide 0.1mg/kg. Endotracheal intubation was performed under direct laryngoscopic view. We used appropriate sized flexometallic endotracheal tracheal tubes with high volume–low pressure cuffs (Mallinckrodt Inc.).

Anesthesia was maintained with isoflurane (0.4-0.8 vol%), nitrous oxide (70 vol% in oxygen) and vecuronium bromide. Patients were then rolled prone onto a level, standard operating table, lying on a pair of bolsters. The head was turned approximately 45° to the side and supported by a foam head ring. The endotracheal tube was secured only to the upper, lateral edge of the mouth. Eye lubrication was applied, but the eyes were not taped. In this manner, the upper eye, half of the face and tubes were readily visible and accessible during emergence.

Fifteen minutes before the conclusion of surgery, all patients received diclofenac 75 mg intramuscularly for postoperative analgesia. During skin closure, isoflurane was reduced to 0.2%, after surgery was completed and the drapes removed, isoflurane and nitrous oxide was discontinued and three sets of baseline data (P-2, P-1, P0) were recorded over 2 min. All data were collected by either of two authors. Operating room personnel were instructed to secure the stretcher beside the operating table and to surround the patient. Patients were randomized at P0 to either the supine group or prone group. The anesthesia team was instructed to retain all monitoring attachments. Patients in the prone group were left undisturbed to be in the same position whereas those in supine group were rolled back to supine position. HR and MAP were recorded each minute till extubation (P1, P2, P3 P4). Coughing, vomiting, laryngospasm and monitor connections were also recorded from conclusion of surgery (P0) till extubation. Supine patients were suctioned just before extubation under direct laryngoscopy but prone patients were not.

Residual muscle relaxation was reversed with neostigmine 0.05 μg/kg and glycopyrrolate 4 mg/kg IV. While extubating patients in prone position, we took all the precautions for the safe airway management, such as appropriate sized laryngeal mask airway was ready to maintain airway in prone position, patients were free from operating table to turn immediately if necessary, patient trolley from post-anesthesia care unit was ready by the side of operating table to turn the patient to supine position immediately, and all the preparations for re-intubation in case the need arises. All the anesthesia monitoring of patients continued for variable period after reversal. Patients in the supine group are rolled supine then reversed and extubated.

Statistical analysis

All the numerical variables are expressed as mean and standard deviation and categorical variables are presented as frequency (%). Statistical analyses were performed using the GraphPad prism software package v. 5 (GraphPad Inc., California, USA). Continuous patient's variables like HR and MAP were compared between treatment groups using unpaired t test with two-tailed P value. Non-parametric categorical data like incidence of coughing, vomiting and monitor disconnection was compared between two groups using Fisher's exact test with two-tailed P value. A P value of < 0.05 was considered as statistically significant and a P value of < 0.001 was considered as highly significant. A power of more than 80% and a 5% significance level to detect a mean heart rate difference of more than 20% was used for sample calculation.

RESULTS

All 50 patients completed the study without any adverse events. Table 1 indicates that there were no statistically significant differences observed among two groups with respect to demographic data, ASA physical status, total duration of surgery, and total duration of anesthesia. Although the supine group had more number of females compared to prone group, the difference between study groups was not statistically significant. Three patients required a second attempt for endotracheal intubation and none of the patients had difficult airway.

Table 1

Demographic characteristics, preinduction hemodynamic values*

Baseline values (P0) of heart rate and mean arterial pressure were comparable in prone and supine groups, and there was no statistically significant difference in baseline heart rate and mean arterial pressure between groups [Figures 1 and 2].

Figure 1

Mean change in heart rate from baseline at each minute after the initiation of treatment. Heart rate increased significantly at P1, P2, P3 and P4

Figure 2

Mean changes in mean arterial pressure at each minute after the initiation of treatment. Mean arterial pressure increased significantly in the supine group compared with prone group patients at P2 and P3 and also approached significance at P4

Results of unpaired t test shows heart rate was significantly higher in supine group above baseline at all intervals - P1, P2, P3, and P4 (P < 0.0001) and significantly higher increase in mean arterial pressure above the baseline at intervals P2, P3 and P4 (P = 0.003) compared with prone group patients [Figures 1 and 2]. The maximum increase in HR was 7.4 ± 2.7 beats per min for prone patients compare to 32 ± 3.7 for supine patients. The maximum increase in mean arterial pressure was 7.8 ± 2.2 mm Hg for prone patients compared to 15.2 ± 2.3 for supine patients [Figure 3].

Figure 3

Maximum percent changes in mean arterial pressure and heart rate (mean) from levels at the completion of surgery to levels associated with tracheal extubation in the prone group and supine group (n = 30 for each group). *P < 0.001

No patients suffered from laryngeal spasm after extubation. Analysis by Fisher's exact test with two-tailed P value shows that prone group patients had statistically significant lower median coughs per patients (P = 0. 0004) and lower monitor disconnects when compared to supine group [Figure 4]. The number of patients with pruritus, nausea, vomiting, or laryngeal irritation, including sore throat and hoarseness, did not differ among the four groups.

Figure 4

The bar graph demonstrates significantly higher monitor disconnections in the supine group in comparison to prone group (*P < 0.0001 by Fisher's exact test)

DISCUSSION

The result of our study demonstrates that patients emerging from anesthesia in prone position are less hemodynamically stimulated in comparison to supine emergence. Regarding prone extubation there are limited published literatures in indexed journal and even in standard anesthesia textbooks. Considering all these facts, our study was conducted on carefully selected patients with all the precautions to ensure the safety of patients in this unconventional technique. We excluded the patients with difficult airway, and paramount importance was given to airway management. Patients were achieved spontaneous regular respiration with complete reversal of neuromuscular block, and all patients were extubated awake and end point of wakefulness was eye opening to simple verbal commands before extubation.

This study demonstrated that tracheal extubation in prone position were able to attenuate increase in HR, MAP in comparison to supine emergence. Olympio MA et al. (2000)[4] showed that emergence in prone position is associated with less hemodynamic response, though the maximum increase in HR and MAP in prone group was less in our study.

Our study also demonstrates that the patients emerging in prone position had less number of coughs, vomiting, and monitor disconnections; these findings were in concurrence with previous studies.[910] Oropharyngeal suctioning was not done in prone group patients during emergence as secretions were drained away from airway prone position as compared to supine group patients, which contributed substantially in reducing hemodynamic response, coughing, and laryngospasm.

As airway management is challenging and difficult in prone position, we have conducted our study with utmost importance to maintain the airway during prone extubation. We extubated the patients only when patients were taking spontaneous regular respiration and sustained head lifting with complete reversal of residual neuromuscular block.

During and after tracheal extubation, plasma concentrations of adrenaline and noradrenaline are reported to increase.[11] Although the precise mechanism responsible for tachycardia and hypertension after tracheal extubation is unknown, these hemodynamic changes may be associated with the release of catecholamines occurring during this stressful period. This sympatho-adrenal stimulation is reduced significantly by extubating in prone position due to avoidance of direct laryngoscopy and oropharyngeal suctioning, and minimizing movement of tracheal tube before emergence.

In the present study we primarily considered hemodynamic changes, cough and monitor disconnection as these are most common adverse effects of emergence and extubation in the supine position after surgery in prone position due to increased movement of endotracheal tube during rolling of the patient to the supine position in lighter plane of anesthesia at the conclusion of surgery.

There are clear differences in respiratory physiology between the supine and prone position, including an increase in FRC and alterations in the distribution of both ventilation and perfusion throughout the lungs. It is thought that this leads to improved ventilation/perfusion matching and consequently improved oxygenation in the surgical patient. These physiologic changes may facilitate recovery from anesthesia in prone position by improving oxygenation and preventing atelectasis.[12]

The prone position is associated with a variety of complications, some of which may be prevented with care on the part of the anesthetist, like pressure on neck vessels due to excessive neck rotation[13] which can be prevented by limiting neck rotation less than 45°, cervical spine injury due to excessive neck extension or during rolling of a patient under anesthesia which can be prevented by extubating patient in prone position.[14]

We studied patients in ASA physical status I and II without any known cardiovascular disease. This population was chosen to ensure the safety of the initial evaluation of the effects of prone emergence as number of literature on the safety of prone emergence are limited. Further studies on the prone emergence in patients with coronary artery disease (CAD) and diabetes mellitus is required

As the lumbar disc surgeries are performed in the prone position and there is a choice for anesthesiologists to plan extubation and emergence in prone position, as prone position itself keeps the airway patent and drains the secretions away from patient airway, this omits the necessity of oropharyngeal suctioning and subsequent stimulation of airway. However, prone position is the most difficult position for airway management, considering all these patients with difficult airway, obesity, and reactive airway are not suitable for emergence in prone position. The relative ease of airway management in supine position merits its use in these cases.

CONCLUSION

In conclusion, in ASA physical status I and II, patients undergoing surgery in the prone position, prone extubation is a simple, effective, and practical method for blunting cardiovascular and airway responses to tracheal extubation and also allows the continuous monitoring of patient during critical periods of emergence. However, further studies are required to evaluate the advantage, beneficial effects, and safety of prone emergence in comparison to supine emergence in patients with CAD and cerebrovascular disease.