American Journal of Emergency Medicine (2012) 30, 1684-1690

Original Contribution

The influence of hemorrhagic shock on ventilation through needle cricothyroidotomy in pigs

Ivan Murad PhD ^a,b,?, Simone C.V. Abib PhD ^a, Daniela P.A. Lima PhD ^a, Paulo S.V.S. Ferreira ^a, Eduardo Q. dos Santos MD ^b, Thomas V. Bataglia MD ^b

^aSurgery Department, Paulista School of Medicine, Federal University of Sao Paulo

^bDepartment of Medicine, State University of Maringa, PR, Brazil

Received 27 November 2011; revised 12 January 2012; accepted 14 January 2012

Abstract

Background: The aim of this study was to examine the effects of controlled hemorrhage and shock on oxygenation and ventilation using needle cricothyroidotomy and jet ventilation in an animal model. Methods: Twenty-four male pigs were randomly allocated into 4 groups: SHOCK (animals in hemorrhagic shock only), CRICH (animals that underwent needle cricothyroidotomy only), SHOCK+ CRICH (animals in hemorrhagic shock + needle cricothyroidotomy), and SHAM (anesthetized animals submitted to surgical preparation only). All animals were surgically prepared and were observed for a period of 40 minutes (T0 - T40). Hemodynamic and Blood gas variables were compared using analysis of variance and Bonferroni post hoc testing at a level of significance of 95%.

Results: CRICH and SHOCK+CRICH developed respiratory acidosis, with a progressive decrease of arterial pH after T20, and they presented a significant increase of PaCO₂ levels after T10, when compared with SHAM and SHOCK (P b .001). When SHOCK+CRICH was compared with CRICH, it presented a larger increase of PaCO₂ after T10 (P = .036) and an even more significant increase after T20 (P = .009).

Conclusion: Hemorrhagic shock anticipated and intensified the retention of carbon dioxide and respiratory acidosis during manual jet ventilation through needle cricothyroidotomy in comparison with animals with jet ventilation but without shock. The results found in this work should be considered in future protocols for the assistance of victims of trauma in prehospital settings.

(C) 2012

Introduction

Ensuring a patent airway is the first priority of trauma management and resuscitation [1-5]. In some emergency situations, inserting a catheter with a needle through the

* Corresponding author. Rua Fernandez Vieira, 1068, 87010-340 Maringa, PR, Brazil. Tel.: +55 44 3222 5602; fax: +55 44 3011 9423.

E-mail address: [email protected] (I. Murad).

Cricothyroid membrane can offer the patient oxygen for a short period, until a definitive airway can be accomplished [1,6-8]. Needle cricothyroidotomy is a simple procedure, and the material needed (14G Jelco catheter; Medex Medical Ltd, England) is commonly available in prehospital settings [6,7]. Nevertheless, because of the small gage of the catheter, the main limitation of this method, compared with endotracheal tube, is that retention of carbon dioxide occurs [6-8]. Therefore, needle cricothyroidotomy is a temporizing emergency proce- dure that should be used for only 15 to 45 minutes [1,7,9].

0735-6757/$ - see front matter (C) 2012 http://dx.doi.org/10.1016/j.ajem.2012.01.017

The effectiveness of ventilation through 14G needle cricothyroidotomy has been extensively studied already. It has been demonstrated that it should be connected to an oxygen source or to a jet ventilator [10]. A literature review on needle and surgical cricothyroidotomy has shown that ventilation can be effective if a high pressure jet ventilator of at least 45 pounds per square inch (psi) is used [11,12]. Ventilation through needle cricothyroidotomy has also been analyzed in Porcine models, showing effective oxygenation and ventilation, either from an oxygen supply source or with the use of manual jet insufftation [13,14].

In prehospital scenarios, where more sophisticated devices may not be readily available, needle cricothyroidotomy can be a valuable temporizing measure in critical situations, such as when there is an association of airway obstruction and hemorrhagic shock in trauma patients, which may lead to abnormalities in the hemodynamic and acid-base balances. Clearly, there are limited experimental data in the literature regarding the safety and use of needle cricothyroidotomy in the setting of hemorrhagic shock. Therefore, this large animal study, based on a porcine model, was designed to examine the effects of controlled hemorrhage and shock on oxygenation and ventilation using needle cricothyroidotomy and jet ventilation. The study hypothesis is that animals subjected to hemorrhagic shock will demonstrate worsening hypercarbia and respiratory acidosis during jet ventilation in comparison with animals with jet ventilation but without shock.

Methods

Study design

This study was approved by the Animal Research Ethics Committee at Federal University of Sao Paulo, Paulista School of Medicine (protocol no. 01263/08). This study used a large animal (pigs) basic science model devised to examine the effects of controlled hemorrhage and shock on oxygenation and ventilation using needle cricothyroidotomy and jet ventilation. The model design was divided into 3 experimental stages: surgical preparation, bleeding and stabilization, needle cricothyroidotomy/jet ventilation, and data collection (Fig. 1).

Study protocol

Twenty-four C-76 Sus scrofa domesticus (Agroceres(R), Sao Paulo, Brazil) male pigs especially bred for research weighing 18.38 +- 1 kg, and supplied by a local farm situated in the State of Sao Paulo, Brazil, were randomly allocated into 4 groups (n = 6) in the following fashion: SHOCK (animals in hemorrhagic shock only), CRICH (animals that underwent needle cricothyroidotomy only), SHOCK+ CRICH (animals in hemorrhagic shock + needle cricothyr- oidotomy), and SHAM (anesthetized animals submitted to surgical preparation only).

Group Experimental Stages

Anesthesia. Surgical procedures. Stabilization.

Bleeding 20 mL/min until 40 mmHg

Stabilization

Monitoring and data collection at regular intervals, from T0 to T40

SHOCK

CRICH

Anesthesia. Surgical procedures. Stabilization.

Monitoring

Cricothyroidotomy at T0. Ventilation, Monitoring and data collection at regular intervals, from T0 to T40

SHOCK

Anesthesia. Surgical procedures. Stabilization.

Bleeding 20 mL/min until 40 mmHg

Stabilization

Cricothyroidotomy at T0. Ventilation, Monitoring and data collection at regular intervals, from T0 to T40

+ CRICH

SHAM

Anesthesia. Surgical procedures. Stabilization.

Monitoring

Monitoring and data collection at regular intervals, from T0 to T40

30 min 30 min 40 min

Preparation Baseline Bleeding T0 T40

Fig. 1 Study design.

All 24 animals were premedicated with intramuscular acepromazine (0.1 mg/kg) and ketamine (10 mg/kg). Anesthetic induction was performed with intravenous (IV) sodium pentobarbital (12.5 mg/kg). orotracheal intubation was carried out with a 6F tube, and the animals were maintained under isoftuorane 1.5% volume, with constant mechanical ventilation (Monterrey-Takaoka(R), Sao Paulo, Brazil) of 14 respiratory movements per minute, 10 mL/kg of tidal volume, at an oxygen concentration of 100%, and positive end-expiratory pressure of 5 mm Hg [15]. Every animal received Neuromuscular blocking (pancuronium bromide 0.15 mg/kg IV) 3 minutes before T0, and supplemental doses (0.05 mg/kg) were administered at the first sign of muscular contraction [16-18]. An 8F polyeth- ylene catheter was introduced into the left carotid artery through a cervical incision and was positioned in the thoracic aorta for arterial pressure monitoring. A 7F Swan-Ganz catheter (93A-131H-7F; Edwards, Baxter Edwards Critical Care, Irvine, Calif) was placed into the pulmonary artery through the right external jugular vein. The catheters were attached to a polygraph (Viridia 24C; Hewlett-Packard Corp, Andover, Miss) for the evaluation of pulmonary artery pressure (PAP), the hemodynamic parameters, and mean arterial pressure (MAP). Cardiac output (CO) was deter- mined using thermo dilution: bolus of saline solution (0.9%) at 20?C [19]. The animals belonging to SHOCK and SHOCK+CRICH had their left femoral artery dissected, and a polyethylene catheter was introduced to bleed the animals with a reversed infusion pump.

After anesthesia and the initial surgical procedures, the

animals had a period of 15 minutes for stabilization, when the baseline hemodynamic and blood gas parameters were measured [20]. The animals belonging to SHOCK and SHOCK+CRICH were then bled (20 mL/min) with a reverse infusion pump until they reached a MAP of 40 mm Hg (approximately 30 minutes). Total shed blood volume was measured. Then, the animals were monitored for 30 minutes further. No volume replacement either with crystalloids or blood was performed. Animals in the SHAM and CRICH were kept under observation from baseline until T0 (60 minutes).

At T0, cricothyroidotomy was performed in the animals belonging to CRICH and SHOCK+CRICH through a median cervical incision [21]. The cricothyroid membrane was identified, and the orotracheal tube was disconnected from the ventilator and occluded by the placement of a Kelly clamp. The cuff was then inftated below the vocal chords, and the orotracheal tube was positioned immedi- ately above the cricoid cartilage [20]. The surgical exposition allowed palpation and confirmation of the tube’s position. Needle cricothyroidotomy was performed with a 14G catheter (Jelco) connected to a 5-mL syringe to aspirate air. To ensure that the same extent of the catheter was inserted into the airway, as well as to avoid kinking, the catheter was fully introduced, except for its connecting device [6-8].

An oxygen source of 15 L/min (50 psi) was connected to a manual jet ventilator (Manu Jet III System; VBM Medizin- technik GmbH, Sulz, Germany) [7], with a pressure of 1.5 bar (21.71 psi) [22]. A 3-way connector was used to connect the catheter to the jet ventilator and to make expiration possible [7,23]. Cycles of 1 second of insufftation, during which the escape route was digitally occluded, and 4 seconds of passive expiration, when the exit was freed, were performed as recommended by the Advanced Trauma Life Support (ATLS) protocol in the 2 cricothyroidotomy groups [1,6]. Hemodynamic and blood gas measurements were taken during ventilation.

At the end of the experiment, euthanasia was carried out in the living animals with a bolus of sodium pentobarbital (30 mg/kg IV) [17].

Key outcome measures

Throughout the preparatory and experimental period, oxygen saturation, blood pressure, heart rate, and rhythm were monitored. procedure time was defined as from the moment jet ventilation started (T0). As from T0, MAP and PAP were measured at every 5 minutes, and CO, arterial pH (pHa), arterial saturation of oxygen (SaO₂), PaO₂, and PaCO₂ were measured at every 10 minutes through the catheter placed in the femoral artery. Blood samples were analyzed using ABL-5 (Radiometer Medical A/S, Copenhagen, Denmark).

Data analysis

All data were reported as mean +- standard error of the mean. One-way analysis of variance with repeated measures was used to analyze continuous variables over time for statistically significant group differences. When statistically significant differences were observed, Bonferroni post hoc testing was used to isolate differences between groups. Statistical significance was defined as P b .05. Calculations were done using SPSS (Statistical Package for Social Sciences; SPSS Inc, Chicago, Ill) for Windows, version 15.0.

Results

Animal characteristics and baseline values

Mean weights did not differ significantly among the 4 groups (P = .76): SHOCK (18.33 +- 0.09 kg), CRICH (18.38 +- 0.08 kg), SHOCK+CRICH (18.65 +- 0.09 kg), and

SHAM (18.15 +- 0.10 kg). Shed blood volume varied between 492 and 587 mL for SHOCK and between 506 and 597 mL for SHOCK+CRICH. No statistical difference was observed between these 2 groups (P = .63). One animal belonging to SHOCK+CRICH died at T40. There were no deaths among the other groups. Baseline hemodynamic and blood gas measurements did not differ significantly among groups.

Arterial oxygen saturation“>Mean arterial pressure

SHOCK and SHOCK+CRICH showed a drop in MAP as from shock induction and remained relatively stable at around 40 mm Hg (between 36 and 40 mm Hg) throughout the observation period, with no significant differences between the groups. Animals belonging to CRICH and SHAM presented MAP of about 72 mm Hg.

Pulmonary artery pressure

SHOCK and SHOCK+CRICH showed significant differ- ences in PAP (P b .001), when compared with SHAM and CRICH. SHOCK showed a significant decrease in PAP between T10 and T20 (P = .011), when compared with SHOCK+CRICH. However, as from T25, PAP for SHOCK

+CRICH started to drop, and at T40, it was significantly below that of SHOCK (P = .002).

Cardiac output

No differences were observed between CRICH and SHAM (P = .457) or between SHOCK and SHOCK+ CRICH (P = .903). In the 2 groups submitted to shock, however, CO was lower from T0, reaching 1.52 +- 0.17 L/min (SHOCK+CRICH) and 1.75 +- 0.03 L/min (SHOCK) at T40,

which is significantly lower in comparison with the groups without shock (P b .001).

Arterial pH

Except for SHAM, all the other groups presented a significant reduction of pHa, compared with baseline values. Both groups submitted to cricothyroidotomy and jet

ventilation developed respiratory acidosis, with a drop in pHa as from T20. However, at T40, the pHa drop for SHOCK+CRICH (7.19 +- 0.04) was more marked than that for CRICH (7.29 +- 0.01). SHOCK+CRICH showed lower pHa levels than SHOCK did as from T20 (P b .001), and at T40, SHOCK presented a less marked drop in pHa (7.34 +- 0.01). Fig. 2 illustrates pHa behavior in the groups.

Arterial base excess

As from T30, all groups except SHAM (-0.67 +- 0.42 mmol/L) presented a Base deficit. At T40, CRICH presented

-3.17 +- 1.05, SHOCK presented -4.00 +- 0.82, and SHOCK+

CRICH presented -5.50 +- 0.67 mmol/L, indicating a combined respiratory and metabolic acidosis. SHOCK+ CRICH presented a significant drop in relation to CRICH (P = .031).

Arterial oxygen saturation

SHOCK+CRICH showed a significant reduction in SaO₂ after T30, when compared with the other groups (P b .001). From T30, there was a just slight decrease in SaO₂ for CRICH compared with SHAM, but at T40, it reached statistical significance (P = .001). SHOCK presented no differences in relation to SHAM.

Arterial partial oxygen pressure

SHAM and SHOCK presented no significant alterations over the experimental time. CRICH initially presented a considerable elevation in PaO₂ (from around 361 mm Hg at T10 to 448 mm Hg at T20), but from T30, PaO₂ started to drop. SHOCK+CRICH presented an increase in PaO₂

	SHOCK SHOCK+CRICH CRICH SHAM

7,45

7,40

7,35

7,30

7,25

pHa

7,20

7,15

7,10

7,05

7,00

a b c

MB 0 10 20 30 40

Time (min)

600,00

	SHOCK SHOCK+CRICH CRICH SHAM

500,00

400,00

PaO2 (mmHg)

300,00

200,00

100,00

0,00

a

b

MB 0 10 20 30 40

Time (min)

SHOCK+CRICH and CRICH < SHAM (P = .001)

SHOCK+CRICH < SHOCK (P < .001)

SHOCK < SHAM (P = .044)

Fig. 2 Arterial pH behavior during the monitoring period.

1. SHOCK+CRICH and CRICH > SHOCK and SHAM ( P < .001)
2. SHOCK+CRICH < CRICH ( P < .001)

Fig. 3 PaO₂ behavior during the monitoring period.

90,00

80,00

70,00

PaCO2 (mmHg)

60,00

50,00

40,00

30,00

20,00

10,00

0,00

SHOCK

CRICH

SHOCK+CRICH

SHAM

MB 0 10 20 30 40

d

b c

a

Time (min)

emergency conditions has been found in the literature. Therefore, the experimental animal model used in this study could contribute in the elaboration of new therapeutic protocols in the assistance of victims of trauma in a Prehospital stage.

Swine possess a larynx that is similar to that of humans, both in shape and size [24]. Animals in this study were of the same breed and origin and had similar weight, making the groups comparable. Although no power analysis has been carried out to determine sample size, the number of animals used in this experiment was considerably higher than that used in similar reports typically found in the literature. Whereas in this experiment a total of 24 animals, divided into 4 groups of 6, were used, Yildiz et al [19] used 9 animals, Preussler et al [22] used 6 animals, and Manoach et al [17]

used 12 animals.

1. SHOCK+CRICH > SHOCK and SHAM (P < .001)
2. SHOCK+CRICH and CRICH > SHOCK and SHAM (P < .001)
3. SHOCK+CRICH > CRICH (P = .036)
4. SHOCK+CRICH > CRICH (P = .009)

Fig. 4 PaCO₂ behavior over the monitoring period.

between T10 and T30 in comparison with SHAM and SHOCK. This increase in PaO₂ found for SHOCK+CRICH was much lower than that found for CRICH and started to steadily fall from T20 until the end of the experiment. Fig. 3 illustrates PaO₂ behavior in the groups.

Arterial partial carbon dioxide pressure

The PaCO₂ levels for SHOCK and SHAM did not present any alterations, remaining stable throughout the study. SHOCK+CRICH and CRICH, however, presented a signif- icant increase of PaCO₂ levels from T10 (P b .001). CRICH showed a gradual increase from T10 (around 45 mm Hg) until reaching 59.50 +- 1.48 mm Hg at T40. SHOCK+ CRICH, on the contrary, presented an even more marked increase of PaCO₂ levels at T10 (around 48 mm Hg) until finally reaching 71.00 +- 2.86 mm Hg at T40 (P = .009). Fig. 4 illustrates PaCO₂ behavior in the groups.

Discussion

Needle cricothyroidotomy is an important tool in emergency settings and, in certain situations, may be the only means to offer oxygen to a trauma patient for a short period, until a definite airway access can be accomplished [1,6-8]. One possible feature of trauma situations is the association of airway obstruction and hemorrhagic shock. In this scenario, there is the risk that the presence of hemorrhagic shock may negatively affect oxygenation and ventilation when needle cricothyroidotomy and jet ventila- tion is used, and therefore compromise the procedure’s safety time. However, no study involving the association of these 2

Because of the need to standardize the groups to a maximum to obtain a cleaner comparison of hemodynamic and blood gas variables, and establish a model that could be easily reproduced, a controlled animal model of hemorrhagic shock was chosen. This considerably differs from actual prehospital care where noncontrolled shock, hemodynamic instability, and sometimes, blood pressures that are incom- patible with life are present. Despite this difference, large animal models have a unique role in furthering the understanding of complex physiology.

To mimic a clinical situation, the needle cricothyroidot- omy procedure did not start until hypovolemic shock had been established. To standardize the position of the catheter and the orotracheal tube in this series, the needle puncture was made through an incision. Several authors recommend that needle positioning should be confirmed using bronchos- copy [16,19,22,25] but that is not possible in the prehospital phase. The total airway obstruction model was performed with the association of tube occlusion and an inftated cuff. This was carried out to prevent gas dispersion through the oro/nasopharynx during ventilation, which would be a problem in precisely predicting the varying escape and ventilatory patterns of each animal. This was also the reason for using neuromuscular blocking (pancuronium bromide), in accordance with previous studies [17,19,22]. Although jet ventilation is formally contraindicated in cases of total airway obstruction, because of the risk of barotrauma, it was chosen to optimize experimental conditions. During jet ventilation, an exit route is necessary [26], and in the present study, a 3-way device was used between the catheter and the jet ventilator.

All blood gas and Hemodynamic variables were analyzed

within each group along the experiment from T0 and T40 and compared with the other groups at preestablished times. At baseline, the analysis showed that the parameters were standardized and without differentiation among groups, as in other studies with pigs [19,22].

The presence of hemorrhagic shock inftuenced all the hemodynamic and blood gas parameters measured in this study. It had a direct effect on MAP, PAP, CO, and arterial base

excess and had a worsening effect in all others parameters. A significant CO drop was observed in the 2 groups submitted to hemorrhagic shock, being more market for the animals in CRICH+SHOCK. This may be explained by the increase in the positive intrathoracic pressure, which may lead to a decreased pressure gradient between the thorax and the extrathoracic structures, even reverting it, causing a venous return drop. This drop reduces the ventricles’ ejection volume and, as a result, CO. Because of the maintenance anesthesia mechanical ventilation and stabilized shock, no difference in SaO₂ was observed between SHAM and SHOCK.

The fall in SaO₂ levels, on the contrary, observed in the cricothyroidotomy groups were expected and are in accordance with previous studies [16,17,28]. However, the drop in SaO₂ levels was, again, more evident for SHOCK

+CRICH in relation to CRICH from T30. Moreover, despite the statistical significance in PaO₂ values found among the different groups, the animals in this study were never hypoxic over the experimental time. However, the steady fall observed for SHOCK+CRICH from T20 may indicate that animals in this group were on their way to become hypoxic (Fig. 3)-a trend that needs to be confirmed in studies with longer observational time.

Both cricothyroidotomy groups also developed respira- tory and metabolic acidosis-a fact that has been known to occur and has been well documented in a series of human and animal studies [1,9,14,16,18,20,22,25,27,28]. The fall in pHa observed for SHOCK+CRICH animals (7.19) was more significant at T40 than that observed for CRICH (7.29). Likewise, the base deficit (arterial base excess) in the CRICH+SHOCK animals was more evident than that of CRICH. This was confirmed by the levels of PaCO₂ in the blood seen in the CRICH+SHOCK, which was significantly higher than that of CRICH from T20 (Fig. 4).

The present study has several limitations. Because of the difficulty and expense of using large animals, the porcine model used involved 3-month-old pigs. Immature swine have similar though not identical hemodynamic parameters to humans. Other studies, however, have also used young animals to study human physiology [14,19,22]. There was also extensive instrumentation, and the animals were subjected to anesthesia with multiple agents. These in- terventions, especially the anesthetics, can have significant effects on blood pressure, CO, oxygenation, and ventilation. Although this is a limitation in comparison with a clinical situation, all procedures in the present study were carried out in all animals in the same fashion before measurements, and their effect tended to be neutralized. Although considerable number of animals was used in this study (n = 24), only 6 animals were allocated to each group. Increasing the size of the groups would have increased the power of our study to detect differences in the respiratory and hemodynamic variables.

Furthermore, all procedures in this study were carried out

in a well-equipped surgical center within a controlled environment, without the high levels of stress normally found in the reality of prehospital care. In a patient with

hemorrhagic shock, lesions would frequently be present, and there would be efforts toward repleting the blood volume lost with either blood products or saline. This would probably cause a change in the hemodynamic parameters and the progression of metabolic acidosis from lactic acidemia.

Conclusions

The results obtained in this study clearly demonstrated that hemorrhagic shock anticipated and intensified the retention of carbon dioxide and respiratory acidosis during manual jet ventilation through needle cricothyroidotomy in comparison with animals with jet ventilation but without shock, confirming our initial assumption. However, although statistically significant differences were reached far earlier, it seems that clinically important changes did not appear until the 30- to 40-minute range. In the clinical practice, these results indeed suggest that the procedure’s safety time can be further compromised by the presence of hemorrhagic shock and that this information should be taken into consideration in prehospital emergency settings, particularly when trans- port times involved are in the 20- to 30-minute range.

Acknowledgments

The authors would like to thank Mr Antonio Carlos Correa for his assistance in writing the English version of this article. The authors would also like to thank Dr. Luiz Francisco Poli de Figueiredo for his invaluable contribution to this paper.

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