This study demonstrated favorable response rates regarding the efficacy of a single preoperative dose of DEX 8 mg intravenous infusion (IVI) to attenuate the PSA hypotension in geriatric patients undergoing orthopedic surgery. The research team observed higher minimal values of systolic, diastolic and mean arterial pressures in DEX group with minimal effects on heart rate. As far as the authors know, they were the first to raise that observation and proposed that theory.
The investigators observed that patients who were on steroids for different reasons and had spinal anesthesia had favorable post-spinal hemodynamic outcomes with minimal hypotension and accordingly minimal needs for vasoconstrictors. This proposed the theory of the value of administration of DEX for obtunding the PSA hypotension.
Different controlled trials failed to demonstrate the superiority of either general or neuroaxial anesthesia on the outcome in elderly patients. However, neuroaxial anesthesia benefits of minimizing surgical stress, reducing pulmonary compromise, superior pain control and reduction of total blood loss made it a well-accepted anesthetic option for geriatric patients (19). However, in elderly, SA is associated with 25–69% incidence of hypotension and decreased physiological reserve that if added to the associated cardiovascular ischemic and/or valvular disease makes even brief episodes of uncorrected hypotension hardly tolerable and might cause detrimental consequences on their cardiac and mental compromised conditions (20).
DEX is a potent synthetic glucocorticoid that has pure glucocorticoid activity (12). It increases PVR by a variety of mechanisms i.e., decreases vasodilator nitric oxide (NO), increases sympathetic activity and elevates plasma dopamine and plasma epinephrine. It also increases the sensitivity of vascular endothelium to different vasoconstrictors. (12) Moreover, it has an anti 5HT3 effects which might influence BJR (12). Those two effects hit exactly the two pathophysiological effects incriminated in eliciting post spinal hypotension (2), explained our results and confirmed our conclusion (Fig 4) (12,15,21,22). The timing and the administration of a preoperative single dose of dexamethasone IVI was based on a meta-analysis study conducted by De Oliveira et al., (7). The investigators believed that all patients were given the same dose of hyperbaric bupivacaine since all patients were given 3 ml of hyperbaric bupivacaine without additives
Methods to alleviate post spinal hypotension either physical e.g., leg wrapping, elastic stockings, optimizing patient's position, or pharmacological e.g., intravenous fluids and vasopressors have been used with varying degree of success (23). The usual measures of pre-load or co-load of either crystalloid or colloid remain controversial with many studies that confirmed that post-spinal hypotension remains significant regardless of the type or timing of the given fluids (23) and may cause hypervolemia (6). Infusion of crystalloid solutions results in its redistribution to extravascular compartment and induces atrial natriuretic peptide secretion which might augment lowering blood pressure because of its natriuretic, diuretic, and vasodilatory effects (24). Infusion of colloid solutions on the other hand, despite remaining in intravascular space for a longer duration, is not popular routinely due to its increased cost, possibility of derangement of coagulation, suppression of platelet activity and the risk of anaphylaxis (25). When it comes to vasoconstrictors, they cause tachycardia and hypertension which may worsen associated myocardial ischemia (26).
The study of Owczuk et al., documented that administration of intravenous ondansetron (5HT3 receptor blocker) prior to spinal anesthesia in geriatric patients attenuated the drop in the diastolic and mean arterial pressure without substantially affecting the systolic blood pressure(5). However, meta-analysis studies fail to confirm the validity of those conclusions based on low quality of evidence and insufficient evidence (27). Moreover, ondansetron might be responsible for lower spinal block level and early recovery from spinal anesthesia. (28)
In concordant with our study, Chu et al., (15) confirmed that dexamethasone (with 5-HT3 receptor blocking properties) similarly reduced the PONV risks as has been shown with other 5-HT3 receptor antagonists e.g. ondansetron. Concomitant with our results, Moeen et al.,(8) reported that intrathecal dexamethasone was as effective as intrathecal meperidine in attenuation of PSA shivering compared to placebo in patients scheduled for prostate surgery under spinal anesthesia with less adverse events. Adding to this, Shalu et al., concluded that administration of DEX 8 mg IV prolonged the duration of sensory block and postoperative analgesia in patients undergoing lower segment cesarean section under spinal anesthesia (9).
This study had some limitation namely; the relatively small sample size and the restriction of the study duration to 20 minutes post spinal. However, the investigators chose to restrict the time of study to the time of maximum hemodynamic instability and before other influences e.g., tourniquet, skin incision or, bleeding occur. The time frame of 20 minutes may be considered as inadequate for a drug such as corticosteroids, which acts with a transcriptional mechanism on nuclear receptors, and therefore takes several hours to reach the peak of action. However, this could be argued by the fact that dexamethasone was given 2 hours before commencement of spinal anesthesia and the onset of its action is within 10 minutes for the IV route (29). Glycemic profile in the hours after dexamethasone administration, the rate of infection and the postoperative delirium should have been reported.
On the other hand the small narrow differences may be considered as a limitation. However, the statistical significance was emphasized by the clinical significance of obtunding post-spinal hypotension without the need for infusing volume or the use of hemodynamic support e.g., ephedrine. The investigators even observed that patients who did develop hypotension needed lower doses of ephedrine and hypotension when developed was not associated with nausea and/or vomiting. The research team strongly suggests trying the use of dexamethasone in geriatric patients and other patient populations with higher risk of postspinal hypotension like obstetric patients. Moreover, ephedrine, by virtue of its synthetic origin, may rarely cause allergic reactions, such as contact allergic responses with topical use (e.g., during ophthalmologic surgery) (30), and delayed severe dermatitis following IV injection has been reported (31).
The study however had many merits; the most important of which was the redirection of the medical society towards using dexamethasone which offers a cheap, an available and a simple pharmacological strategy to prevent post-spinal hypotension, a common complication of spinal anesthesia, which can lead to serious events. Moreover, dexamethasone can be used also for the prevention of postoperative nausea and vomiting, the prevention of post spinal shivering and as antalgic adjuvant.
In conclusion, despite the small differences and a short time frame assessment in the study, the investigators found that the single administration of 8 mg dexamethasone IVI prior to spinal anesthesia in geriatric patients attenuated the decrease in arterial blood pressure, especially in whom excess fluid infusion or alpha-agonist administration is contraindicated due to the risk of cardiovascular decompensation.