Anatomical Investigations for Appropriate Needle Positioning for Thoracic Paravertebral Blockade inChildren

Abstract

Objective:

Clinicians hesitate to perform thoracic paravertebral blockade (TPVB) in children due to the potential high risk of adverse effects. No paediatric anatomical guidelines for TPVB exist. This study aimed to estimate the appropriate depth and distance for safe needle positioning in children.

Methods:

The depth (D) from the skin to the paravertebral space and the distance (A) from the spinous process to the needle entry point on the skin were measured using chest computed tomography (CT) in children aged between 1 and 9 years. Correlations between age, gender, weight, height, body mass index (BMI) and each of the anatomical measurements were analysed.

Results:

Each measurement correlated significantly with age, weight and height, but not with BMI (n = 373 children). Measurements A and D could be calculated by: A = 13.56 + (0.33 × age [years]) + (0.06 × weight [kg]) + 0.47 × (gender [female = 0, male = 1]); and D = 17.49 - (0.35 × age [years]) + (0.55 × weight [kg]).

Conclusion:

These anatomical guidelines for TPVB are recommended to help prevent anaesthetic complications such as pneumothorax, when ultra -sonography and CT are unavailable.

Keywords

Anaesthetics Thoracic paravertebral block Children Anatomy Pain control Needle insertion depth

Introduction

Thoracic paravertebral blockade (TPVB) can be useful in paediatric patients for providing preoperative anaesthesia or postoperative pain control for surgery that does not require bilateral blockade.¹ Many clinicians, however, avoid TPVB due to its potential for adverse effects, which include pneumo -thorax (prevalence rate, 0.5%), vascular puncture (prevalence rate, 3.8%), hypotension (prevalence rate, 4.6%) or pleural puncture (prevalence rate, 1.1%).² Of particular concern is pneumothorax, which, despite its low prevalence, causes physical and mental distress to both the clinician and patient. The Serious Harm and Morbidity (SHAM) score is used to grade the severity of potential complications of placebo-controlled interventions in local anaesthesia research and it is, perhaps, of note that pneumothorax is listed as a potential complication with a grade 4 SHAM score, which represents a major risk.³

In order to perform TPVB while minimizing the risk of pneumothorax, the clinician must have the relevant anatomical knowledge. The present study aimed to identify the depth of needle insertion required to reach the paravertebral space, and the distance from the spinous process to the insertion point on the skin, using chest computed tomography (CT) scanning of paediatric patients. These measurements could then be used to locate the paravertebral space accurately, thus preventing the complications associated with TPVB using the loss-of-resistance (LOR) technique for needle insertion. This study also aimed to identify any correlations between these anatomical measurements and demographic characteristics such as gender, height, weight or body mass index (BMI).

Patients and methods

Study Population

Consecutive paediatric patients (aged 1 – 9 years) who underwent chest CT regardless of their disease or procedure at the Soonchunhyang University Hospital Cheonan, College of Medicine, Soonchunhyang University, Cheonan, Republic of Korea, between January 2010 and March 2011, and at the Uijeongbu St Mary's Hospital, College of Medicine, The Catholic University of Korea, Uijeongbu, Republic of Korea, between September 2003 and May 2009 were included in this study. Patients with severe spinal deformities were excluded from the study.

The study was approved by the Institutional Review Boards of the Soonchunhyang University Hospital Cheonan (No. 2010-83) and the Uijeongbu St Mary's Hospital (No. UC11RIMI0012); due to the retrospective nature of the study, the requirement for written informed consent was waived.

CT Measurements of the Thoracic Spine

All CT examinations were performed with the patient in the supine position, using the LightSpeed^® VCT (GE Healthcare, Tokyo, Japan) chest CT scanner at the Soonchunhyang University Hospital Cheonan and the SOMATOM^® Sensation 16 chest CT scanner (Siemens, Erlangen, Germany) at the Uijeongbu St Mary's Hospital. In patients who were overly anxious about the procedure, 50 mg/kg chloral hydrate was administered (POCRAL SYR^® 10%, Han Lim Pharmaceutical Company, Kyounggi-do, Republic of Korea). A representative CT scout cutting plane is shown in Fig. 1. A set of five measurements were taken from each patient, from the first level down to the twelfth level of the thoracic spine (T1 – T12), in each selected cutting plane that had the longest transverse process of the serial cutting planes of the same level of the thoracic spine (Fig. 2); these included: (A) distance from the spinous process (midpoint) to the needle entry point on the skin; (B) distance from the spinous process to the lateral tip of the transverse process; (C) depth from the skin to the junction with the transverse process on the insertion line; (D) depth from the skin to the paravertebral space (i.e. final point of the needle position); (E) depth from the skin to the anterior margin of the rib. The final position of the needle was set as the place where the line bisecting the lateral margin of the pedicle and the lateral margin of the transverse process met the anterior margin of the transverse process, as shown in Fig. 2. For each age group (1 – 9 years), the mean measurements of A (T_a) and D (T_d) were determined for each level (T1 – T12) of the thoracic spine (data not shown). The overall mean values of T_a and T_d for all 12 levels of the thoracic spine were obtained from these values and named T_A and T_D, respectively. If the sectional plane of the thoracic spine on the screen did not present the same shape as shown in Fig. 1, the measurement of that thoracic spine was excluded. CT data collected at the Soonchunhyang University Hospital Cheonan and Uijeongbu St Mary's Hospital were analysed using DEJA-VIEW (v2010.9.14.1, Dongeun Information Technology Company, Bucheon, South Korea) and M-VIEW (v5.4.9.34, Marotech, Seoul, South Korea) software, respectively.

Figure 1:

Representative computed tomography image showing the scout cutting plane of the thoracic spine

Figure 2:

Schematic diagram showing the five anatomical measurements taken from each paediatric patient from the first level down to the twelfth level of the thoracic spine (T1 – T12): (A) distance from spinous process (midpoint) to needle entry point on skin; (B) distance from spinous process to lateral tip of transverse process; (C) depth from skin to junction with transverse process on insertion line; (D) depth from skin to paravertebral space (i.e. final point of needle positioning); (E) depth from skin to anterior margin of rib

Statistical Analyses

Statistical analyses were performed using SAS/STAT^® v9.2 (SAS Institute Inc., Cary, NC, USA). All measurements were reported as mean ± SD. The body weight and height of all patients were recorded and the BMI (kg/m²) was calculated for each individual. Associations between the anatomical measurements made at each level of the thoracic spine and demographic characteristics were analysed using Pearson's correlation coefficient. Weight, height and BMI were compared between males and females using an unpaired Student's t-test. A P-value of < 0.05 was considered to be statistically significant. In addition, relationships between the anatomical distances measured and the demographic characteristics were analysed using simple and multiple regression analyses.

Results

A total of 373 paediatric patients (236 males, 137 females) participated in this study and underwent chest CT examinations. In 457 sectional planes of the thoracic spine, the shape was not the same as that shown in Fig. 1, therefore these were excluded from the analysis. Each set of five measurements (A – E) was, therefore, taken from a total of 4019 sectional planes selected from the images of the thoracic spine at 12 levels. Overall, there were no significant differences between male and female patients in weight, height or BMI, although there were some significant differences within individual age groups (P < 0.05, Table 1). The overall mean values of T_a and T_d for all 12 levels of the thoracic spine (T_A and T_D, respectively) are presented in Table 2. There were significant differences in T_A between male and female patients aged 1, 5 and 7 years (P < 0.05 for each comparison). Gender-related differences in T_D were only observed in 1-year-old children (P = 0.0261).

Table 1:

Demographic data stratified according to age (1-9 years) in paediatric patients (n = 373) who underwent anatomical measurements of the thoracic spine using chest computed tomography

Age, years	Weight, kg		Statistical significance^a	Height, cm		Statistical significance^a	BMI, kg/m²		Statistical significance^a
Age, years	Males	Females	Statistical significance^a	Males	Females	Statistical significance^a	Males	Females	Statistical significance^a
1, n=35	10.89 ± 2.87	10.62 ± 1.29	NS	77.68 ± 11.89	77.33 ± 18.18	NS	17.29 ± 1.56	17.72 ± 25.91	NS
2, n = 31	14.20 ± 1.98	13.51 ± 2.66	NS	91.84 ± 8.58	91.68 ± 5.91	NS	16.16 ± 1.57	15.85 ± 2.29	NS
3, n = 50	15.23 ± 1.93	15.12 ± 1.96	NS	99.52 ± 4.63	101.24 ± 5.18	NS	15.84 ± 1.69	14.85 ± 1.97	NS
4, n = 64	17.72 ± 2.97	16.64 ± 1.91	NS	109.02 ± 6.04	103.35 ± 7.21	P = 0.0101	15.16 ± 2.42	15.91 ± 2.97	NS
5, n = 44	20.57 ± 3.48	18.09 ± 2.92	P = 0.0296	114.73 ± 5.50	108.19 ± 6.36	P = 0.0204	15.86 ± 2.56	15.73 ± 1.78	NS
6, n = 37	22.57 ± 3.48	20.94 ± 1.82	NS	118.47 ± 5.95	121.03 ± 7.66	NS	16.05 ± 1.31	14.29 ± 0.70	P = 0.0208
7, n = 40	27.76 ± 6.62	23.36 ± 2.13	P = 0.0082	127.51 ± 9.39	130.61 ± 7.54	NS	17.14 ± 3.04	13.91 ± 1.33	P = 0.0154
8, n = 40	28.15 ± 8.20	28.27 ± 8.16	NS	127.81 ± 7.65	130.83 ± 6.07	NS	16.80 ± 3.22	18.54 ± 2.74	NS
9, n = 32	35.63 ± 9.47	29.80 ± 6.14	NS	136.07 ± 10.25	133.03 ± 3.25	NS	19.96 ± 5.49	14.99 ± 2.10	NS

Data presented as mean ± SD.

Statistical analyses comparing male and female patients at each age were performed using an unpaired Student's t-test.

BMI, body mass index; NS, no statistically significant between-group differences (P ≥ 0.05).

Table 2:

Overall mean values were calculated (TA and TD), using individual values for each of the 12 levels of the thoracic spine. These measurements were the distance from the spinous process (midpoint) to the needle entry point on the skin (Ta) and the depth from the skin to the paravertebral space (Td). Measurements are given for each age group (1-9 years) in paediatric patients who underwent anatomical spinal measurements using, chest computed tomography (n = 373)

Age, years	T_A		Statistical significance^a	T_D		Statistical significance^a
Age, years	Males n = 236	Females n = 137	Statistical significance^a	Males n = 236	Females n = 137	Statistical significance^a
1	14.71 ± 0.90	13.99 ± 0.77	P = 0.0212	23.30 ± 2.20	21.52 ± 2.15	P = 0.0261
2	15.43 ± 0.90	14.87 ± 1.06	NS	24.77 ± 2.00	24.02 ± 2.93	NS
3	16.04 ± 0.80	15.79 ± 0.82	NS	24.29 ± 2.11	24.61 ± 2.52	NS
4	16.36 ± 0.78	16.04 ± 1.15	NS	25.53 ± 2.59	25.40 ± 2.45	NS
5	16.86 ± 0.72	16.17 ± 1.10	P = 0.0166	26.75 ± 1.77	25.50 ± 2.92	NS
6	17.79 ± 0.80	17.38 ± 0.68	NS	28.53 ± 3.58	27.06 ± 2.76	NS
7	18.09 ± 1.10	17.26 ± 1.22	P = 0.0403	30.45 ± 3.63	28.38 ± 2.19	NS
8	18.35 ± 1.08	17.60 ± 1.41	NS	31.77 ± 5.50	30.86 ± 5.97	NS
9	18.08 ± 0.96	17.77 ± 1.13	NS	33.10 ± 5.49	29.76 ± 6.05	NS

Data presented as mean ± SD.

Statistical analyses comparing male and female patients at each age were performed using an unpaired Student's t-test.

TA, overall mean value for Ta at all 12 levels of the thoracic spine; TD, overall mean value for Td at all 12 levels of the thoracic spine; NS, no statistically significant between-group differences (P ≥ 0.05).

Age, weight and height correlated significantly with each anatomical measurement (A – E; P < 0.05 for each comparison); no significant correlations between gender and BMI and anatomical measurements were observed (data not shown). Simple regression analysis demonstrated that age, gender, weight and height, but not BMI, were significantly associated with anatomical measurements A – E (Table 3). Multicolinearity was indicated for height, therefore this variable was excluded from the multiple regression analysis; as such, multiple regression equations were estimated only for age, gender and weight. The multiple regression equations were significant for age, gender and weight (P = 0.0041, Table 3) for anatomical measurements A and B, for age and weight for anatomical measurements C and D (P = 0.0032), and for weight only for anatomical measurement E (P < 0.0001).

Table 3:

Simple and multiple regression analyses of the relationship between the five anatomical thoracic spinal measures (A - E) and demographic characteristics in paediatric patients who underwent chest computed tomography (n = 373)

Anatomical measure			Constant	Age, years	Sex	Weight, kg	Height, cm	BMI, kg/m²
A	Simple	Statistical significance		P < 0.0001	P = 0.0001	P < 0.0001	P < 0.0001	NS
	Multiple	Parameter	13.5636	0.3338	0.4682	0.0637	ND	ND
		Statistical significance		P < 0.0001	P < 0.0001	P < 0.0001	ND	ND
B	Simple	Statistical significance		P < 0.0001	P = 0.0022	P < 0.0001	P < 0.0001	NS
	Multiple	Parameter	17.0647	0.5334	0.4317	0.0824	ND	ND
		Statistical significance		P < 0.0001	P = 0.0041	P < 0.0001	ND	ND
C	Simple	Statistical significance		P < 0.0001	P = 0.033	P < 0.0001	P < 0.0001	NS
	Multiple	Parameter	10.8505	-0.5673	ND	0.5116	ND	ND
		Statistical significance		P < 0.0001	ND	P < 0.0001	ND	ND
D	Simple	Statistical significance		P < 0.0001	P = 0.0145	P < 0.0001	P < 0.0001	NS
	Multiple	Parameter	17.4948	-0.3546	ND	0.5468	ND	ND
		Statistical significance		P = 0.0032	ND	P < 0.0001	ND	ND
E	Simple	Statistical significance		P < 0.0001	P = 0.0062	P < 0.0001	P < 0.0001	NS
	Multiple	parameter	26.8267	ND	ND	0.5044	ND	ND
		Statistical significance		ND	ND	P < 0.0001	ND	ND

BMI, body mass index; A, distance from spinous process (midpoint) to needle entry point on skin; B, distance from spinous process to lateral tip of transverse process; C, depth from skin to junction with transverse process on insertion line; D, depth from skin to paravertebral space (i.e. final point of needle positioning); E, depth from skin to anterior margin of rib; ND, not determined; NS, no statistically significant between-group differences (P ≥ 0.05).

Based on the results of the present study, the following predictive equations were calculated:

A = 13.56 + (0.33 × age [years]) + (0.06 × weight [kg]) + (0.47 × gender [female = 0, male = 1])

B = 17.06 + (0.53 × age [years]) + (0.08 × weight [kg]) + (0.43 × gender [female = 0, male = 1])

C = 10.85 – (0.57 × age [years]) + (0.51 × weight [kg])

D = 17.49 – (0.35 × age [years]) + (0.55 × weight [kg])

E = 26.83 + (0.50 × weight [kg])

Using the above equations, calculation of the appropriate insertion point of the needle for a 4-year-old boy weighing 20 kg would proceed as follows:

A = 13.56 + (0.33 × 4) + (0.06 × 20) + 0.47 = 16.55 mm

B = 17.06 + (0.53 × 4) + (0.08 × 20) + 0.43 = 21.21 mm

C = 10.85 – (0.57 × 4) + (0.51 × 20) = 18.77 mm

D = 17.49 – (0.35 × 4) + (0.55 × 20) = 27.09 mm

E = 26.83 + (0.5 × 20) = 36.83 mm

According to these calculations, in a 4-year-old boy weighing 20 kg, the needle should be advanced ∼16 mm lateral to the midline, and the needle depth when connection with the transverse process is made should be ∼19 mm. Once such contact is made, if the needle is adjusted, redirected and advanced using the LOR method, the needle tip would be expected to enter the paravertebral space. Using these equations, it is possible to infer that it could be dangerous to insert the needle from the side over 20 mm to the midline or to advance the needle ≥ 36 mm, due to the increased risk of pneumothorax.

Discussion

The advantage of TPVB over epidural block is that it results in a more profound sensory block associated with a low risk of hypotension or undesired motor paralysis of the lower extremities, superior pulmonary function, and lower neuroendocrine stress response and postoperative respiratory morbidity compared with epidural block.^{4 – 7} In addition, TPVB does not interfere with normal micturition and is unlikely to damage the spinal cord directly, or lead to haematoma formation.⁸ TPVB is performed on one side of the body, is a relatively easy technique to undertake and affords a lower frequency of postoperative vomiting.^9,10 Taken together, these advantages suggest that TPVB may be an attractive therapeutic option in patients requiring thoracic anaesthesia.

In paediatric patients, TPVB is used mostly for preoperative anaesthesia during renal surgery or thoracotomy, and for postoperative pain control.¹¹ A previous study in children reported that there was no requirement for narcotics or other analgesics while TPVB was maintained after thoracotomy.¹² For most children, administration of local anaesthetics at a dose of 0.5 ml/kg via the paravertebral route blocked at least six or more dermatomes.¹³ Naja et al.¹⁴ reported that paediatric patients treated with TPVB prior to hernia surgery required lower doses of analgesics, experienced better pain control and were discharged sooner from hospital compared with those treated with systemic anaesthesia and analgesics. In another study in paediatric patients undergoing renal surgery, the analgesic effects of a single TPVB injection were sustained for a mean of 600 min without additional analgesics, thus indicating the effective analgesic action of TPVB even without continuous administration.¹⁵ TPVB in children has also been used quite successfully for outpatient anaesthesia.¹⁶

Since its first description in 1994, the procedure of real-time ultrasound-guided regional anaesthesia has been widely used.¹⁷ The use of ultrasound in nerve blockade procedures can increase the success rate, shorten the duration of the block and reduce the use of local anaesthetics, so as to decrease the rate of anaesthesia-associated complications.^{18 – 22} The use of ultrasound is strongly recommended for peripheral blockade in children and infants.²³ Even though it is expected to be beneficial, the justification for peripheral blockade is, however, limited in the case of neuroaxial block for which the target nerve is not directly visible.²³ While ultrasound-assisted TPVB is considered to be much easier to perform than peripheral blockade, with fewer complications, TPVB is not always available due to a lack of skilled and experienced personnel. Guidelines for improving the safety of TPVB may, therefore, be required. The results of the present study may provide data for such guidelines.

An equation to estimate the depth of the paravertebral space in children using a similar method to the current study has been reported.²⁴ In a subsequent study by the same authors, it was observed that the values obtained using CT were smaller than those measured during thoracic paravertebral block, using the LOR technique.²⁵ It was suggested that the underlying reason for this discrepancy was that CT was performed with the patient lying in a supine position, which caused the subcutaneous tissues to compress, making the measured values appear smaller than the actual values. The authors concluded that their original equation may, therefore, have underestimated the depth of the paravertebral space; consequently they described a new equation for its estimation.²⁵ Using the revised equation²⁵ to calculate the needle position for the example of a 4-year-old boy of 20 kg described in the present study, the resulting value for D (28.34 mm) was larger than that (27.09 mm) obtained using the equation described herein (skin to paravertebral space [mm] in Lönnqvist et al.²⁵ = 18.6172 + (0.4861 × body weight [kg]) + (2.72 × method [method: 0 = estimated depth from CT, 1 = actual depth by LOR sensation)]. This difference also appears to be caused by a reduction in values due to the compression of subcutaneous tissues. Moreover, the values calculated using CT in the study by Lönnqvist et al.²⁴ were larger than those determined in the present study. The reason for this discrepancy is unclear but it could be because the age of patients was also considered in the present study. Alternatively it could be that the values obtained in the present study were measured right up to the front side of the transverse process (Fig. 2), whereas values were measured up to the paravertebral space in the previous investigation.

Three aspects of the current study differ from the previous study by Lönnqvist et al.²⁴ First, more specific values are reported in the present study due to the inclusion of age and gender in addition to weight, which showed the highest correlation with anatomical measurements. The main advantage of using the previously described equation is its simplicity, but the sample size used to develop it was small (including only 52 patients) and the study could not detect differences by age and gender, particularly for children, since the age range was too wide (0 – 22 years).²⁴ Secondly, the present study measured all levels of the thoracic vertebrae whereas the measurements in Lönnqvist et al.²⁴ were made at the seventh vertebra in 46 patients, the fifth vertebra in one patient, and the sixth vertebra in five patients. Finally, unlike the previous investigation, the present study provides guidelines to limit the lateral safety zone for the needle insertion point and the depth of insertion. These guidelines may help prevent burdensome complications (such as pneumothorax) when ultrasonography or CT equipment are unavailable.

Limitations of the current study included the small number of patients in each age group and the fact that the immediate rear side of the transverse process was measured, which made the values obtained smaller than those determined during the actual procedure. Another limitation was that in order to perform the procedure blind, it had to be carried out by advancing the needle diagonally rather than in a straight line, vertical to the skin. The measured value thus had to be smaller than the actual value. Finally, no comparison between the actual measured value and the CT measurement was performed in the same patient.

In conclusion, the equations developed in the present study provide guidelines to limit the lateral safety zone for the needle insertion point and the depth of insertion during TPVB in children. These guidelines could help prevent complications such as pneumothorax in situations where no ultrasonography or CT equipment is available.

Footnotes

Conflicts of interest: The authors had no conflicts of interest to declare in relation to this article.

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