Hypotension during subarachnoid anaesthesia: haemodynamic effects of colloid and metaraminol

British Journal of Anaesthesia 1996; 76: 734–736

Hypotension during subarachnoid anaesthesia: haemodynamic effects of colloid and metaraminol L. A. H. CRITCHLEY AND F. CONWAY

Summary We have studied 45 patients, aged 60–95 yr, receiving subarachnoid block for neck of femur fractures. Patient received either colloid (polygeline, Haemaccel) 8 ml kg91 (n : 15), metaraminol 5 ␮g kg91 and 1.7 ␮g kg91 min91 (n : 15) or a combination of both treatments to maintain systolic arterial pressure (SAP) between 75 and 100 % of baseline. If necessary, additional colloid 2
4 ml kg91 or metaraminol 3
2.5 ␮g kg91 was given. Arterial pressure was measured by automated oscillotonometry, central venous pressure (CVP) by a manometer and cardiac index (CI), stoke index (SI) and heart rate (HR) by transthoracic electrical bioimpedance. Systemic vascular resistance index (SVRI) was derived. Colloid was less effective than metaraminol (P  0.05). In the colloid group, SAP and SVRI decreased and CVP, CI and SI increased (P  0.001). In the metaraminol group, initial decreases in SAP, SVRI and CVP were restored after 10–15 min and HR decreased after 12 min (P  0.001). In the combined group, initial decreases in SAP and SVRI were restored after 4 and 16 min, and CVP, CI, SI and HR increased (P  0.001). Metaraminol was more effective than colloid because it increased SVRI, whereas colloid increased CVP without significantly increasing CI. (Br. J. Anaesth. 1996; 76: 734–736) Key words Anaesthetic techniques, subarachnoid. Complications, hypotension. Measurement techniques, transthoracic electrical impedance. Fluids, i.v. Sympathetic nervous system, metaraminol.

Hypotension is a common problem during subarachnoid block and elderly patients are particularly at risk. Different views exist on how this hypotension should be managed [1]. There are few data on the elderly, and only the effects of crystalloid preloading and the use of ephedrine have been investigated [2, 3]. Recently, we showed that i.v. fluids and ephedrine were not always effective in preventing hypotension during subarachnoid block in the elderly and we suggested that treatment with a predominantly alpha adrenergic receptor agonist would be more effective [4]. In the present study, we have compared the haemodynamic effects during subarachnoid block of colloid solution and the alpha agonist metaraminol.

Methods and results After obtaining local Ethnics Committee approval and written informed consent, we studied 45 ASA II and III Chinese patients undergoing surgical fixation of fractured neck of femur. Oral diazepam 5–10 mg was given 1 h before surgery. Subarachnoid block was performed using 0.5 % bupivacaine 2.5–3.0 ml (Marcain Spinal 0.5 % Heavy, Astra). We measured systolic (SAP) and mean (MAP) arterial pressures using automated oscillotonometry, central venous pressure (CVP) using a manometer and cardiac index (CI), stroke index (SI) and heart rate (HR) by transthoracic electrical bioimpedance using the BoMed NCCOM3-R7S (BoMed Medical Manufacturing Ltd, Irvine, CA, USA). We derived systemic vascular resistance index (SVRI). Data were collected at 1-min intervals (5-min intervals for CVP) for 3–5 min before and 0–25 min during subarachnoid block. For a more detailed description of our methodology, see previous publications [4, 5]. Patients were allocated to one of three regimens to prevent hypotension using block randomization with sequentially numbered sealed forms. Immediately after subarachnoid block, group I received a rapid infusion of colloid 8 ml kg91 (3.5 % polygeline, Haemaccel, Behringwerke, Germany), group II received an initial bolus of metaraminol 5 ␮g kg91 followed by an infusion of 1.7 ␮g kg91 min91 and group III received both colloid and metaraminol. Rescue treatment was given if SAP decreased to less than 75 % of baseline on two consecutive occasions. Group I received a rapid infusion of colloid 4 ml kg91 and, if necessary, repeated once to restore SAP. If hypotension persisted, metaraminol was given, as per group II. Groups II and III received up to three boluses of metaraminol 2.5 ␮g kg91 to restore SAP. If hypotension persisted, colloid 8 ml kg91 was given. Continuous haemodynamic data were analysed at 1-min intervals. Percentage changes compared with baseline were also calculated at 1-min intervals and their means compared. Numerical differences were used for CVP. Student’s t test, analysis of variance

LESTER A. H. CRITCHLEY, BMEDSCI, MB, CHB, FFARCSI, FRANCES CONWAY*, MB, BCH, FFARCSI, Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong. Accepted for publication: December 12, 1995. *Present address: St Vincent’s Hospital, Merrion Road, Dublin, Ireland.

Effects of colloid and metaraminol during subarachnoid block

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Figure 1 Mean (SEM) haemodynamic variables at baseline (0 min) and during the first 25 min of subarachnoid block for all patients in the three treatment groups: – – – : colloid alone; ----: metaraminol alone; and —— : metaraminol with colloid.

for factors and repeated measures and chi-square test were used for statistical analysis. P  0.05 was considered significant and results are given as mean (SD or range). The power of the study was assessed using Altman’s method [6]. Fifteen patients per group were required to detect changes of less than 10 % between haemodynamic data. We studied 11 male and 34 female patients, aged 78 (60–95) yr, weight 48 (7) kg and height 154 (8) cm. Maximum sensory level in pinprick was thoracic dermatome 6 (1–11). Patient characteristics, maximum sensory level and baseline haemodynamic data were similar in the three treatment groups. The colloid regimen failed to maintain an adequate SAP on eight occasions. The metaraminol regimen failed significantly less often (P  0.05), once in group II and once in group III, and resulted in an excessive SAP in four patients in group II and six patients in group III. Haemodynamic changes after subarachnoid block are shown in figure 1. In the colloid group, significant

decreases in SAP, MAP and SVRI and increases in CVP, CI and SI occurred (P  0.001). These changes were significant (P  0.05) after 1 min for SAP, MAP and SVRI, after 5 min for CVP and after 2 min for CI and SI. There was no significant change in HR. In the metaraminol group, significant decreases in SAP, MAP, SVRI, CVP and HR occurred (P  0.001). These changes were significant (P  0.05) at 1–14 min for SAP, at 1–15 min for MAP, at 2–10 min for SVRI, at 5–10 min for CVP and at 12–25 min for HR. There were no significant changes in CI or SI. In the combined group there were significant decreases in SAP, MAP, SVRI and HR, and increases in CVP, CI and SI (P  0.001). These changes were significant (P  0.05) at 1–4 min for SAP, at 1–10 min for MAP, at 1–16 min for SVRI, after 5 min for CVP, after 2 min for CI and SI, and after 14 min for HR. The magnitude of the haemodynamic effects of the three treatments during subarachnoid block are shown in table 1. Where treatment was effective,

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British Journal of Anaesthesia Table 1 Percentage changes (⌬) or numerical differences (Diff.) (mean (SD)) compared with baseline values for haemodynamic variables, for the established effects of subarachnoid block when treatment was successful in the three treatment groups (15–25 min) and when treatment was unsuccessful in the colloid group (10–15 min). SAP : Systolic arterial pressure, MAP : mean arterial pressure, SVRI : systemic vascular resistance index, CVP : central venous pressure, CI : cardiac index, SI : stroke index and HR : heart rate. *P  0.05, **P  0.01 compared with baseline Colloid

⌬SAP (%) ⌬MAP (%) ⌬SVRI (%) Diff. CVP (cm H2O) ⌬CI (%) ⌬SI (%) ⌬HR (%)

Metaraminol (n : 14)

Combined (n : 14)

(Successful) (n : 7)

(Unsuccessful) (n : 8)

2 (13) 93 (11) 92 (16) 0.2 (2.6) 0 (15) 14 (22)* 911 (12)**

6 (14) 1 (10) 92 (28) 3.4 (3.1)** 5 (18) 17 (19)** 910 (8)**

99 (7)* 911 (9)* 920 (12)** 2.5 (2.6)* 11 (14) 13 (15) 92 (5)

931 (6)** 929 (5)** 938 (12)** 4.5 (3.7)** 12 (17) 26 (25)* 910 (8)**

percentage changes were averaged between 15 and 25 min, and where additional colloid failed between 10 and 15 min.

Comment Current clinical practice is to use crystalloid, up to 2 litre, before and during subarachnoid block to prevent hypotension [1]. In the present study, we used colloid solution during the onset phase of subarachnoid block. This practice prevents excessive increases in CVP (table 1) and reduces the fluid volume required [4]. However, we found that even large volumes of colloid, up to 16 ml kg91, failed to correct hypotension in more than 50 % of our patients. Coe and Revanas [2] reported similar findings in patients with a high subarachnoid block (above T7) after preloading with crystalloid 16 ml kg91. In fact, administration of colloid appeared to decrease SVRI and yet cardiac output did not increase significantly despite increases in CVP, suggesting that elderly patients have a reduced ability to respond to i.v. fluids (table 1, fig. 1). In the present study, metaraminol was effective at maintaining SAP during subarachnoid block in 93 % of patients, the principal action of metaraminol being to maintain SVRI (table 1). However, metaraminol caused excessive treatment in some patients (33 %). In these patients subarachnoid block may have caused only a small decrease in SAP and the use of prophylactic treatment may have been unnecessary. CVP during high subarachnoid block decreases by 2.5 (1.5) cm H2O [5]. Metaraminol prevented this decrease (table 1), suggesting that metaraminol also acts by venoconstricting capacitance vessels. However, CVP did not increase sufficiently to increase cardiac output. Ephedrine is the most frequently studied vasopressor during subarachnoid block. Comparing the

present data with data from our previous study [4], we found ephedrine to be less effective than metaraminol at maintaining SVRI and that part of its action was to increase cardiac output and HR. Also, the efficacy of ephedrine depended on maintaining the patient well hydrated with i.v. fluids. In comparison, metaraminol was much less dependent on i.v. fluids. Administration of i.v. fluids during subarachnoid block is important, because it maintains preload and cardiac output. However, the use of large volumes of fluid to increase preload sufficiently to raise cardiac output and SAP is not always successful in the elderly patient. Therefore, this practice should not be encouraged because of the risk of fluid overload. Hypotension may be treated more effectively by using a vasopressor and we found that infusion of metaraminol was highly effective because it acted by increasing systemic vascular resistance.

References 1. McCrae AF, Wildsmith JA. Prevention and treatment of hypotension during central neural block. British Journal of Anaesthesia 1993; 70: 672–680. 2. Coe AJ, Revanas B. Is crystalloid preloading useful in spinal anaesthesia in the elderly? Anaesthesia 1990; 45: 241–243. 3. Hemmingsen C, Poulsen JA, Risbo A. Prophylactic ephedrine during spinal anaesthesia: double-blind study in patients in ASA groups I–III. British Journal of Anaesthesia 1989; 63: 340–342. 4. Critchley LA, Stuart JC, Conway F, Short TG. Hypotension during subarachnoid anaesthesia: haemodynamic effects of ephedrine. British Journal of Anaesthesia 1995; 74: 373–378. 5. Critchley LA, Stuart JC, Short TG, Gin T. Haemodynamic effects of subarachnoid block in elderly patients: measurement by transthoracic bioimpedance. British Journal of Anaesthesia 1994; 72: 464–470. 6. Altman DG. How large a sample? In: Altman DG, Gore S, eds. Statistics in Practice. London: British Medical Association, 1993; 6–8.