84
Correspondence
Fig. 2
available in most hospitals has made brachial plexus block by the supraclavicular approach a safer and technically easier procedure.
St Barrholomew's Hospital, London ECIA 7BE
K.M. HILLMAN
Blood pressure measurement during lateral tilt The need to avoid the supine position during late pregnancy and labour is well recognised, particularly during the administration of epidural analgesia. In order to obviate the effects of aorto-caval occlusion while ensuring full spread of analgesic solution during the administration of continuous epidural analgesia, it is common practice to administer half the dose of local analgesic solution with the patient lying on one side and the remainder about 5 minutes later with the patient lying on the opposite side. The blood pressure is monitored before, during, and after administration of the block, the supine position being avoided until after delivery. Blood pressure is usually measured using the Riva Rocci method with the cuff placed over the brachial artery. In addition to the usual inaccuracies inherent in the Riva Rocci method, lateral tilt itself introduces an additional element of error not fully appreciated by many dealing with patients receiving epidural analgesia in labour. The distances across the chest in a woman of average build is approximately 27 cm. Thus, in the true lateral position the arterial pressure measured in the lowermost arm is equal to the
pressure measured in the uppermost arm plus the pressure exerted by a column of blood 27 cm high. As mercury is approximately 13 times as heavy as blood, this difference amounts to more than 20 mmHg. The more nearly the patient is to the supine position the less is the difference in arterial pressure between the two arms. If 15" tilt is used, the vertical distance between the arms 27 cm apart is 7.0 cm. This represents a difference in pressure equivalent to 5.4 mmHg. The aortic pressure is approximately the mean of the pressures measured in both arms. In order to make blood pressure measurements meaningful and to make comparisons valid, it is necessary to specify the position of the patient and to state whether the blood pressure was measured in the uppermost or lowermost arm when lateral tilt is used. University of Natal, PO Box 17309, Congella 4013, Durban, South Africa
E. MANKOWITZ
Correspondence
Fig. 2
available in most hospitals has made brachial plexus block by the supraclavicular approach a safer and technically easier procedure.
St Barrholomew's Hospital, London ECIA 7BE
K.M. HILLMAN
Blood pressure measurement during lateral tilt The need to avoid the supine position during late pregnancy and labour is well recognised, particularly during the administration of epidural analgesia. In order to obviate the effects of aorto-caval occlusion while ensuring full spread of analgesic solution during the administration of continuous epidural analgesia, it is common practice to administer half the dose of local analgesic solution with the patient lying on one side and the remainder about 5 minutes later with the patient lying on the opposite side. The blood pressure is monitored before, during, and after administration of the block, the supine position being avoided until after delivery. Blood pressure is usually measured using the Riva Rocci method with the cuff placed over the brachial artery. In addition to the usual inaccuracies inherent in the Riva Rocci method, lateral tilt itself introduces an additional element of error not fully appreciated by many dealing with patients receiving epidural analgesia in labour. The distances across the chest in a woman of average build is approximately 27 cm. Thus, in the true lateral position the arterial pressure measured in the lowermost arm is equal to the
pressure measured in the uppermost arm plus the pressure exerted by a column of blood 27 cm high. As mercury is approximately 13 times as heavy as blood, this difference amounts to more than 20 mmHg. The more nearly the patient is to the supine position the less is the difference in arterial pressure between the two arms. If 15" tilt is used, the vertical distance between the arms 27 cm apart is 7.0 cm. This represents a difference in pressure equivalent to 5.4 mmHg. The aortic pressure is approximately the mean of the pressures measured in both arms. In order to make blood pressure measurements meaningful and to make comparisons valid, it is necessary to specify the position of the patient and to state whether the blood pressure was measured in the uppermost or lowermost arm when lateral tilt is used. University of Natal, PO Box 17309, Congella 4013, Durban, South Africa
E. MANKOWITZ
