Effect of Intravenous Calcium Gluconate on Prevention of Post Spinal Hypotension during Spinal Anaesthesia for Caesarean Section: A Randomized Double-Blind Controlled Study.

BACKGROUND: Calcium, a physiological ion, causes vasoconstriction and has a positive ionotropic action on heart. Its use to prevent post-spinal hypotension has been suggested but never formally evaluated for patients undergoing caesarean section. This study investigated the hemodynamic effects of calcium administration in parturients with the primary aim of comparing the incidence of post-spinal hypotension. METHODS: Sixty healthy full-term pregnant patients scheduled for caesarean section were randomly allocated to two equal groups to receive either calcium gluconate or normal Saline bolus over 20min by syringe infusion pump under electrocardiography monitoring immediately after the patient was turned supine following spinal anaesthesia. Blood pressure and heart rate were recorded at baseline, and at regular intervals following spinal. Maternal calcium levels were estimated before and after infusion. Neonatal blood gas analysis and calcium level were analyzed. Total mephentermine requirement was recorded in both groups. RESULTS: The heart rate values remained comparable to baseline value in group calcium gluconate while in group normal Saline, it decreased significantly at 8,12 and 16min. Blood pressure decreased significantly as compared to the baseline value from 4min onwards in both the groups. However, it was comparable in the two groups at all time points(0.622). Nineteen patients(63.33%) required mephentermine infusion in group calcium gluconate as compared to 23 patients(76.6%) in group normal Saline for maintenance of systolic blood pressure.(p=0.791) Umbilical venous pH (p=0.038) and partial pressure of carbon dioxide(p=0.038) were significantly better in group calcium gluconate. CONCLUSIONS: Calcium used for prophylaxis of hypotension in healthy parturients undergoing caesarean section reduced the vasopressor requirements and total mephenteramine dose, but the difference did not attain statistical significance.

Comparison of phenylephrine hydrochloride and mephentermine sulphate for prevention of post spinal hypotension.

This study compared the effects of intravenous infusions of phenylephrine and mephentermine on the prevention of maternal hypotension and neonatal outcome in patients receiving spinal anaesthesia for caesarean section. Sixty ASA 1-2 patients with term, uncomplicated singleton pregnancy undergoing caesarean section under spinal anaesthesia were randomly divided into two groups of 30 each, to receive a prophylactic intravenous infusion of either phenylephrine or mephentermine. The incidence of hypotension was statistically similar in the two groups. However, in patients receiving phenylephrine, 7 (23%) developed bradycardia and 6 (20%), reactive hypertension. Neonatal outcome, in terms of Apgar scores and umbilical artery pH, was similar in both the groups. To conclude, phenylephrine and mephentermine infusions are equally effective in preventing post spinal hypotension in patients undergoing caesarean section and are associated with a similar neonatal outcome.

Combination of low doses of intrathecal ketamine and midazolam with bupivacaine improves postoperative analgesia in orthopaedic surgery.

BACKGROUND: Intrathecal ketamine produces a short period of analgesia with stable haemodynamics. Midazolam with bupivacaine prolongs the duration of analgesia when administered intrathecally but does not prevent hypotension. The objective of this study was to assess the effect of a combination of intrathecal bupivacaine, ketamine and midazolam on the duration of analgesia and haemodynamic parameters. METHODS: A prospective, randomized, double-blind study was carried out in 60 ASA I and II patients undergoing lower limb surgery under spinal anaesthesia. Patients were divided into three groups of 20 each. Patients in all the three groups received 3 mL of hyperbaric bupivacaine (0.5%) intrathecally. In addition, patients in Groups II and III received intrathecal ketamine (0.1 mg kg-1) and the same dose of ketamine along with midazolam (0.02 mg kg-1), respectively. All patients were evaluated for block characteristics, duration of pain-free period, total rescue analgesic requirement in the 24-h postoperative period, total dose of mephenteramine to treat hypotension and any central or neurological complication. RESULTS: No patients in Group II required mephenteramine while 40% of patients in Group I and 10% in Group III required mephenteramine to maintain blood pressure after spinal anaesthesia. The mean +/- standard deviation duration of pain-free period was 331.5 +/- 89.9, 369.7 +/- 124.2 and 730.5 +/- 81.5 min in Group I, II and III, respectively. The pain-free interval was significantly greater in Group III compared to Groups I and II (P < 0.001). No patient had any complications. CONCLUSION: A low dose of midazolam and ketamine with bupivacaine intrathecally results in prolonged analgesia and less haemodynamic fluctuations. However, the safety of this combination needs to be proved before its use in clinical practice.

Potency of mephentermine for prevention of post-spinal hypotension.

This study was designed to determine the minimum effective dose (ED50) of mephentermine for prevention of post-spinal hypotension in women undergoing elective caesarean section. Dixon's up-down method of sequential allocation was used to determine the patient's dose of vasopressor drug. In our previous study, mephentermine appeared to be much more potent than ephedrine, so the present study was conducted using a lower initial dose and smaller dose interval for this vasopressor. Following administration of spinal anaesthesia, a prophylactic infusion of mephentermine was started with 5 mg infused over a period of 30 minutes as the initial dose and a dose interval of 1 mg. The ED50 of mephentermine of 3.7 mg (95% confidence interval 2.4 to 5.7 mg) was much less than that of ephedrine, as calculated in our previous study using the same methodology. Using these values gives a potency ratio of ephedrine to mephentermine of 1:6.8 (95% confidence interval 6.0 to 7.5).

Comparison of potency of ephedrine and mephentermine for prevention of post-spinal hypotension in caesarean section.

The dosages and potency of intravenous mephentermine for prevention of post-spinal hypotension are not available in English literature. This study was designed to determine the minimum effective dose (ED50) of mephentermine and to compare its potency with that of ephedrine for prevention of post-spinal hypotension in parturients undergoing caesarean section. Dixon's up-down method of sequential allocation was used for vasopressor doses. Following administration of spinal anaesthesia, patients received a prophylactic infusion with 50 mg infused over a period of 30 minutes as the initial dose and dose intervals of 5 mg, of either ephedrine or mephentermine. The ED50 of ephedrine was 25.0 mg (95% CI 15.5 to 40.4 mg). For mephentermine, the up-down method was abandoned due to the success of the minimum dose possible but the ED50 appeared to be less than 5 mg. In conclusion, the minimum effective dose of mephentermine is much less than that of ephedrine for prevention of post-spinal hypotension. Another trial with a lower starting dose and smaller dose interval of mephentermine is required to determine the potency ratio of mephentermine and ephedrine.

Randomised trial of intravenous infusion of ephedrine or mephentermine for management of hypotension during spinal anaesthesia for Caesarean section.

This study compared the effects of intravenous infusions of ephedrine and mephentermine for maintenance of maternal arterial pressure and neonatal outcome in pregnant women receiving subarachnoid block for lower segment Caesarean section. Sixty patients who developed hypotension following subarachnoid block for Caesarean section were randomly divided into two groups of 30 each to receive an intravenous infusion of ephedrine or mephentermine. Hypotension was defined as a decrease in systolic blood pressure of > or = 20% from the baseline value or an absolute value of <100 mmHg, whichever was higher. The vasopressor infusion was titrated to maintain systolic blood pressure between 'hypotension' and baseline values. Baseline haemodynamic parameters, haemodynamic changes subsequent to the start of vasopressor infusion, duration of hypotension and amount of vasopressor required were statistically similar for both groups. Neonatal APGAR scores and acid-base profiles were also comparable. To conclude, mephentermine can be used as safely and effectively as ephedrine for the management of hypotension during spinal anaesthesia in patients undergoing elective Caesarean section.

[Suitability of mephentermine for the management of arterial hypotension in pregnancy]. / Die eignung von Mephentermin zur Behandlung der arteriellen Hypotonie in der Schwangerschaft.

10 late pregnant women with hypotension were examined before and after the intravenous injection of 30 mg mephentermin with the method of quantitative sphygmometry, the bloodless graphic registration of the arterial blood pressure and direct electronic timing of pulse wave velocity. Systolic and diastolic blood pressure increase significantly. The cause of this rise in arterial blood pressure is the increase of stroke volume exclusively. Heart rate and total peripheral resistance remain constant. This hemodynamic mode of action is a favourable one in regard to protection of uteroplacental blood flow. Therefore mephentermin is suitable for treatment of hypotension in pregnancy.

Influence of some sympathomimetic amines on the experimental gastric ulcers in rats.

In reserpine-induced ulcers in rats, the centrally acting sympathomimetic ámines (amphetamine, mephentermine and ephedrine) produced a significant protection. Only amphetamine had a beneficial effect in restraint ulcers. Tyramine, a preponderant peripherally acting sympathominetic amine, was inefficient in both experimental models. It is suggested that the protective activity is due to the influence of these amines on the adrenergic structures, mainly at central level.