PATIENT FACTORS:
Height:
There is evidence to support the opinion that the taller the patient, the lower the dermatome level of analgesia for a given dose of local anaesthetic (1, 2, 3, 4, 5, 40). Vertebral column length rather than height may be more important in determining anaesthetic spread (41).
Weight:
There is a correlation between height of blockade and the degree of obesity, A high level of block may be anticipated in obese patients (2, 7, 8, 9, 42).
Age:
There appears to be a correlation between age and the height of spinal anaesthesia (3, 10, 11, 43).
Cerebrospinal Fluid Volume:
In patients with a decreased volume of CSF (such as parturients, women in the 2nd or 3rd trimester of pregnancy (44), patients with ascites or patients with large intra-abdominal tumours), the spread of spinal anaesthetic solution is greater than normal (4). Other CSF parameters such as pressure, protein content, chloride concentration, pH and specific gravity, have no effect on spread (13, 15).
CONTROLLABLE FACTORS:
Solution, Density and Posture:
Hyperbaric local anaesthetic solutions spread preferentially to the dependant region if position is maintained for at least 5 minutes after injection (3, 8, 15, 16, 17, 18, 19, 20, 21). In contrast, hypobaric solutions spread preferentially to the non-dependant region. For example, if the patient is sitting then a hypobaric solution will spread preferentially cephalad (Figure 30.1). Changes in position can alter spread of analgesia for up to an hour after injection (47). (Chapter 30)
Volume, Dosage, Concentration and Temperature of Anaesthetic:
In general, the dermatomal level achieved is directly related to the volume of local anaesthetic solution used (31, 32, 33). When using an isobaric solution, it is the volume of the agent (rather than the posture of the patient) which is the most important determinant of the extent of spread (41); In contrast, with hyper- and hypo- baric solutions, posture becomes a more important factor.
If volume is constant and the dose (and, therefore, the concentration) of the anaesthetic solution is increased, there is a marginal increase in spread (46). If the anaesthetic solution is warmed to 37 degrees C, spread is increased (48); another study does not support this conclusion (49).
Technique of Injection:
Rapid injection of anaesthetic (0.5 to 1.0mI/sec) produces significantly greater spread than a slower rate of injection (0.02 to 0.2ml/sec) (37).
The direction of the bevel of the needle is also a factor. Spread is greater in the direction of the bevel (37). Barbotage has been found in one study to increase spread (50). Most other studies have failed to demonstrate this effect (34, 38, 39).
CONCLUSION:
The most significant factors affecting spread of anaesthesia are patient height, patient position and the baricity of the anaesthetic solution. Other factors are relevant but are of much lesser significance.
1. Moore D.C. Reg Anesth, 1982; 7:20-25.
2. Gordh T. Reg Anesth. 1979; 4:3-8.
3. Bengtsson M. Acta Anaesthesiol Scand 1983; 27:278-283.
4. Green N.M. Anesth Analg 1985; 64:715-730.
5. Attygalle D. Anaesthesia 1985; 40:1006-1008.
7. McCulloch W Br J Anaesth 1986; 58:610-614.
8. Gray D.C. Anesthesiology 1980; 53:234.
9. Pitkanen M.T, Anesth Analg. 1987; 66:127-131.
10. Cameron A.E. Anaesthesia. 1981;36:318-322,
11. Pitkanen MT. Br J Anaesth. 1984; 56:279-284.
13. Kalso E. Br J Anaesth. 1982; 54:1179-1184.
15. Kruger D. Reg Anesth. 1983; 6:1-3.
16. Gielen M. Reg Anesth. 1984; 9:62-67.
17. Wildsmith J. Br J Anaesth. 1981; 53:273-279.
18. Brown D.T. Br J Anaesth. 1980; 52:589-595.
19. Chambers Br J Anaesth. 1981; 53:279-282
20. Moller IW. Br J Anaesth. 1984; 56:1191-1194.
21. Cummings G.C. Br J Anaesth. 1984; 56;573-79.
32. Axelsson K. Acta Anaestheslol Scand. 1982; 26:439-445.
33. Axelsson K. Br J Anaesth. 1984; 56:271-277.
34. Nightingale P.J. Anaesthesia. 1983; 38:7-9.
37. Neigh J.L. Anesth AnaIg. 1970; 49:912-920.
38. Pitkanen M. Acta Anaesthesiol Scand, 1985; 29:590-593.
39. Levin E. Anesth Analg. 1981; 60 ;810-813.
40. Huffnagle S.L Reg Anesth. 1994; 19:330-334.
41. Hartwell B.L. Reg Anesth. 1991;16:17-19.
42. Talvainen T. Br J Anaesth. 1990; 64:542-546
43. Nydahl P.A. Anesth Analg. 1991;73:780-786.
46. King H.K. Reg Anesth. 1995; 20:45-49.
47. Horlocker T.T. Anesth Analg. 1994; 773-777.
48. Callesen T. Anaesthesia. 1991; 46:17-19.
49. Kristoffersen E. Br J Anaesth. 1990; 65:504-507.
50. Janik R. Reg Anesth. 1989; 14:26-30.