Increases in Both Buccal and Sublingual Partial Pressure of Carbon Dioxide Reflect Decreases of Tissue Blood Flows in a Porcine Model During Hemorrhagic Shock

Real-Time Measurements of Oral Mucosal Carbon Dioxide (POMCO2) Reveals an Inverse Correlation With Blood Pressure in a Porcine Model of Coagulopathic Junctional Hemorrhage

INTRODUCTION

Shock states that occur during, for example, profound hemorrhage can cause global tissue hypoperfusion leading to organ failure. There is an unmet need for a reliable marker of tissue perfusion during hemorrhage that can be followed longitudinally. Herein, we investigated whether longitudinal POMCO2 tracks changes in hemodynamics in a swine model of coagulopathic uncontrolled junctional hemorrhage.

MATERIALS AND METHODS

Female Yorkshire-crossbreed swine (n = 7, 68.1 ± 0.7 kg) were anesthetized and instrumented for continuous measurement of mean arterial pressure (MAP). Coagulopathy was induced by the exchange of 50 to 60% of blood volume with 6% Hetastarch over 30 minutes to target a hematocrit of <15%. A 4.5-mm arteriotomy was made in the right common femoral artery with 30 seconds of free bleeding. POMCO2 was continuously measured from baseline through hemodilution, hemorrhage, and a subsequent 3-h intensive care unit period. Rotational thromboelastometry and blood gases were measured.

RESULTS

POMCO2 and MAP showed no significant changes during the hemodilution phase of the experiment, which produced coagulopathy evidenced by prolonged clot formation times. However, POMCO2 increased because of the uncontrolled hemorrhage by 11.3 ± 3.1 mmHg and was inversely correlated with the drop (17.9 ± 5.9 mmHg) in MAP (Y = -0.4122*X + 2.649, P = .02, r2 = 0.686). In contrast, lactate did not significantly correlate with the changes in MAP (P = .35) or POMCO2 (P = .37).

CONCLUSIONS

Despite the logical appeal of measuring noninvasive tissue CO2 measurement as a surrogate for gastrointestinal perfusion, prior studies have only reported snapshots of this readout. The present investigation shows real-time longitudinal measurement of POMCO2 to confirm that MAP inversely correlates to POMCO2 in the face of coagulopathy. The simplicity of measuring POMCO2 in real time can provide an additional practical option for military or civilian medics to monitor trends in hypoperfusion during hemorrhagic shock.

Vital sign patterns before shock-related cardiopulmonary arrest

OBJECTIVE

Traditional vital sign thresholds reflect an increased risk of mortality, which may occur hours, days, or weeks following illness/injury, limiting immediate clinical significance to guide rescue therapy to avoid arrest. Our objective is to explore vital sign patterns prior to arrest due to shock.

DESIGN

This retrospective observational analysis utilized physiological data from adult helicopter patients suffering provider-witnessed arrest. Pre-arrest values for systolic blood pressure (SBP), mean arterial pressure (MAP), heart rate (HR), shock index, and end-tidal carbon dioxide (EtCO2) were modeled against time using polynomial linear regression. The "terminal inflection point" beyond which arrest was imminent was identified where slope equals 1.0 (shock index) or -1.0 (SBP, MAP, HR, EtCO2) and was then compared to initial values.

SETTING

Air ambulance services.

PATIENTS

70 helicopter patients over age fourteen suffering cardiac arrest.

RESULTS

SBP and MAP demonstrated a gentle decline followed by acceleration beyond the inflection point (SBP 80.7 mmHg, MAP 61.9 mmHg). HR demonstrated an increase followed by a terminal drop, but inflection point values fell within normal range. Shock index increased gradually from a mean of 0.9 to the inflection point of 1.1. Initial EtCO2 values declined gradually from normal (34.4 mmHg) to the inflection point (24.7 mmHg), then dropped precipitously into arrest. All inflection points occurred 2-5 min prior to arrest.

CONCLUSIONS

Vital sign patterns were defined for SBP, MAP, HR, shock index, and EtCO2 with clear inflection points identified 2-5 min prior to arrest. These patterns may help guide therapy to reverse deterioration and prevent arrest.

Patients with chronic mesenteric ischemia have an altered sublingual microcirculation

Background

Little is known about the microcirculatory alterations in patients with chronic mesenteric ischemia (CMI). We hypothesized that patients with CMI have an impaired microcirculatory function and show an oral microcirculatory response after caloric challenge compared to healthy controls.

Methods

All patients and controls received the standard workup for CMI. Sublingual micro-circulation was evaluated before (T0) and 20 minutes after (T1) feeding. The total vessel density (TVD; mm/mm²), perfused vessel density (PVD; mm/mm²), proportion of perfused vessels (PPV; %) and microvascular flow index (MFI; AU) were assessed.

Results

We included 12 patients (63.2 years [IQR 48.8–70.4 years], 67% males) and 12 controls (32.7 years [IQR 27.7–38.1 years], 42% males). At baseline, patients with CMI had a decreased PPV of the sublingual small vessels (median 84.8% vs 95.7%, P=0.006), PPV of all vessels (PPV median 85.4% vs 95.3%, P=0.007) and microvascular flow index of all vessels (MFIa; median 3.00 vs 2.80, P=0.039) compared to healthy controls. After caloric challenge, PVD increased significantly in both small vessels (perfused vessel density of the small vessels [PVDs]) and all vessels (perfused vessel density of all vessels [PVDa]; PVDs [T0]) median 16.3 [IQR 13.3–22.1] vs [T1] median 19.9 [IQR 14.2–26.2], P=0.008; PVDa [T0] median 19.1 [IQR 16.2–23.6] vs [T1] median 22.2 [IQR 16.5–28.9], P=0.02; proportion of perfused vessels of the small vessels (PPVs; [T0] median 84.8% [IQR 75.3–90.4] vs [T1] median 91.0% [IQR 80.1–93.8], P=0.010). In contrast, no significant changes in microcirculatory parameters were observed after caloric challenge in healthy controls.

Conclusion

Patients with CMI have an impaired sublingual microcirculation at baseline and show a significant response in the sublingual microcirculation after caloric challenge, whereas healthy controls have a normal microcirculation at baseline and show no reactive response upon a caloric challenge as seen in CMI patients. Sublingual microcirculation visualization may offer a rapid noninvasive method to identify patients at risk for having CMI.

Recent Advances of Mucosal Capnometry and the Perspectives of Gastrointestinal Monitoring in the Critically Ill. A Pilot Study

Mucosal capnometry involves the monitoring of partial pressure of carbon dioxide (PCO2) in mucous membranes. Different techniques have been developed and applied for this purpose, including sublingual or buccal sensors, or special gastrointestinal tonometric devices. The primary use of these procedures is to detect compensated shock in critically ill patients or patients undergoing major surgery. Compensatory mechanisms, in the early phases of shock, lead to the redistribution of blood flow towards the vital organs, within ostensibly typical macro-haemodynamic parameters. Unfortunately, this may result in microcirculatory disturbances, which can play a pivotal role in the development of organ failure. In such circumstances mucosal capnometry monitoring, at different gastrointestinal sites, can provide a sensitive method for the early diagnosis of shock. The special PCO2 monitoring methods assess the severity of ischaemia and help to define the necessary therapeutic interventions and testing of these monitors have justified their prognostic value. Gastrointestinal mucosal capnometry monitoring also helps in determining the severity of ischaemia and is a useful adjunctive in the diagnosis of occlusive splanchnic arterial diseases. The supplementary functional information increases the diagnostic accuracy of radiological techniques, assists in creating individualized treatment plans, and helps in follow-up the results of interventions. The results of a pilot study focusing on the interrelation of splanchnic perfusion and gastrointestinal function are given and discussed concerning recent advances in mucosal capnometry.

Microcirculatory alterations during haemorrhagic shock and after resuscitation in a paediatric animal model

BACKGROUND

Haemorrhagic shock is frequent in paediatric trauma patients and after cardiac surgery, especially after cardiopulmonary bypass. It has demonstrated to be related to bad outcome.

OBJECTIVES

To evaluate changes on microcirculatory parameters during haemorrhagic shock and resuscitation in a paediatric animal model. To determine correlation between microcirculatory parameters and other variables routinely used in the monitoring of haemorrhagic shock.

METHODS

Experimental study on 17 Maryland pigs. Thirty minutes after haemorrhagic shock induction by controlled bleed animals were randomly assigned to three treatment groups receiving 0.9% normal saline, 5% albumin with 3% hypertonic saline, or 5% albumin with 3% hypertonic saline plus a bolus of terlipressin. Changes on microcirculation (perfused vessel density (PVD), microvascular blood flow (MFI) and heterogeneity index (HI)) were evaluated and compared with changes on macrocirculation and tisular perfusion parameters.

RESULTS

Shock altered microcirculation: PVD decreased from 13.5 to 12.3 mm mm(-2) (p=0.05), MFI decreased from 2.7 to 1.9 (p<0.001) and HI increased from 0.2 to 0.5 (p<0.001). After treatment, microcirculatory parameters returned to baseline (PVD 13.6 mm mm(-2) (p<0.05), MFI 2.6 (p<0.001) and HI 0.3 (p<0.05)). Microcirculatory parameters showed moderate correlation with other parameters of tissue perfusion. There were no differences between treatments.

CONCLUSIONS

Haemorrhagic shock causes important microcirculatory alterations, which are reversed after treatment. Microcirculation should be assessed during haemorrhagic shock providing additional information to guide resuscitation.

Monitoring Microcirculatory Blood Flow with a New Sublingual Tonometer in a Porcine Model of Hemorrhagic Shock

Tissue capnometry may be suitable for the indirect evaluation of regional hypoperfusion. We tested the performance of a new sublingual capillary tonometer in experimental hemorrhage. Thirty-six anesthetized, ventilated mini pigs were divided into sham-operated (n = 9) and shock groups (n = 27). Hemorrhagic shock was induced by reducing mean arterial pressure (MAP) to 40 mmHg for 60 min, after which fluid resuscitation started aiming to increase MAP to 75% of the baseline value (60-180 min). Sublingual carbon-dioxide partial pressure was measured by tonometry, using a specially coiled silicone rubber tube. Mucosal red blood cell velocity (RBCV) and capillary perfusion rate (CPR) were assessed by orthogonal polarization spectral (OPS) imaging. In the 60 min shock phase a significant drop in cardiac index was accompanied by reduction in sublingual RBCV and CPR and significant increase in the sublingual mucosal-to-arterial PCO2 gap (PSLCO2 gap), which significantly improved during the 120 min resuscitation phase. There was significant correlation between PSLCO2 gap and sublingual RBCV (r = -0.65, p < 0.0001), CPR (r = -0.64, p < 0.0001), central venous oxygen saturation (r = -0.50, p < 0.0001), and central venous-to-arterial PCO2 difference (r = 0.62, p < 0.0001). This new sublingual tonometer may be an appropriate tool for the indirect evaluation of circulatory changes in shock.

Cutaneous ear lobe Pco₂ at 37°C to evaluate microperfusion in patients with septic shock

BACKGROUND

Tissue hypercarbia is related to hypoperfusion and microcirculatory disturbances in patients with septic shock. Transcutaneous Pco₂ devices using a heated sensor to arterialize the tissue have been used as an alternative method for estimation of Paco₂. This study investigates whether a cutaneous sensor attached to an ear lobe and regulated to 37°C could be used to measure cutaneous Pco₂ (Pcco₂) and evaluate microperfusion in patients with septic shock.

METHODS

Fifteen stable patients in an ICU were studied as a control group. Forty-six patients with septic shock who were ventilated were enrolled as the study group. The difference of the gradients between Pcco₂ and Paco₂ (Pc-aco₂) and between Pcco₂ and end-tidal Pco₂(Pc-etco₂) were evaluated for 36 h. Variations of the Pc-aco₂ and Pc-etco₂ during fluid challenge were compared with microcirculatory skin blood flow (mBFskin) assessed by laser Doppler flowmetry.

RESULTS

The baseline levels for Pc-aco₂ and Pc-etco₂ were significantly higher in the patients with septic shock than in the control group (14.8 [12.6] vs 6 [2.7] mm Hg and 25 [16.3] vs 9 [3.8] mm Hg, P < .0001, respectively). During the following 36 h, the Pc-aco₂ and Pc-etco₂ for the surviving patients with septic shock decreased significantly compared with the nonsurvivors (P < .01). The evolution of macrohemodynamic parameters showed no differences between survivors and nonsurvivors. At hour 24, a Pc-aco₂ > 16 mm Hg and a Pc-etco₂ > 26 mm Hg were related to poor outcome. Pc-aco₂ and Pc-etco₂ variations during fluid challenge were inversely correlated with changes in mBFskin (r² = 0.7).

CONCLUSIONS

Ear lobe cutaneous Pco₂ at 37°C represents a noninvasive technique to assess tissue Pco₂ measurement. Pc-aco₂ and Pc-etco₂ were related to outcome and provide continuous information on microperfusion in patients with septic shock.

The cerebral microcirculation is protected during experimental hemorrhagic shock

OBJECTIVE

Decreases in buccal microcirculation are indicative of the severity of hemorrhage, but incidental observations suggest that this may not apply to the cerebral microcirculation. We therefore hypothesized that the cerebral microcirculation may be preserved in hemorrhagic shock in which systemic and buccal microcirculatory flow are reduced. We propose to relate changes in the macrocirculation to the buccal and cerebral microcirculations during hemorrhage and after fluid resuscitation.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

Fifteen male Sprague-Dawley rats were anesthetized and endotracheally intubated. Craniotomy exposed the parietal cortex for orthogonal polarization spectral imaging. Mean arterial pressure, cardiac output, arterial blood gases, and lactate were measured concurrently with determination of microcirculatory indices in buccal and cerebral areas. Animals were randomly assigned to bleeding either 35% or 25% of estimated total blood volume and compared with sham bled animals. Hypovolemia was maintained for 60 mins in test animals, after which saline in amounts to 2 times the blood loss, was administered over 30 mins. Cerebral and buccal microvascular indices were measured in vessels smaller than 20 mum, representing capillaries.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure and cardiac output were reduced and arterial blood lactate was increased in relationship to the magnitude of blood loss. Saline infusion increased mean arterial pressure and cardiac output. Buccal microcirculation decreased after bleeding but was restored after saline infusion. However, the cerebral microcirculation was essentially unaffected by hemorrhage and saline infusion.

CONCLUSION

In contrast to the systemic decreases in pressure and flow characteristics of hemorrhagic shock, including decreases in microcirculations of buccal mucosa, cerebral microvascular flow was preserved during moderate and severe blood losses.

Buccal capnometry for quantitating the severity of hemorrhagic shock

We have recently demonstrated that measurement of buccal mucosal PCO2 (PBUCO2) is a reliable alternative to sublingual mucosal PCO2 for measuring the severity of hemorrhagic shock. We hypothesized that measurement of PBUCO2 would serve as a continuous and a more sensitive and specific measurement for predicting survival during hemorrhagic shock than conventional measurements and thereby better guide initial management. Four groups of five pentobarbital anesthetized Sprague-Dawley rats were randomly assigned to be bled over 30 min in amounts estimated to be 25%, 30%, 35%, or 40% of total blood volume. With an optical PCO2 sensor applied noninvasively to the mucosa of the left inner cheek, PBUCO2 was continuously measured together with arterial pressure, end-tidal PCO2, and intermittent measurement of cardiac output, arterial blood lactate, and base deficit. Surviving animals had free access to water and food but no other treatment during the 72-h interval after recovery from anesthesia. After an estimated 40% blood loss, all animals died within 1 h. In the remaining animals, arterial pressure, end-tidal carbon dioxide, cardiac index, blood lactate, and base deficit each failed to discriminate among animals with 35%, 30%, and 25% acute blood losses. This contrasted with PBUCO2, which discriminated between the magnitude of massive blood loss and untreated survival. Buccal mucosal PCO2 was predictive of outcome after rapid bleeding when compared with arterial pressure, end-tidal carbon dioxide, cardiac index, arterial blood lactate, and base deficit. This measurement is therefore likely to serve as a useful guide for the immediate management of hemorrhagic shock.

Effects of epinephrine and vasopressin on cerebral microcirculatory flows during and after cardiopulmonary resuscitation

OBJECTIVES

Both epinephrine and vasopressin increase aortic and carotid arterial pressure when administered during cardiopulmonary resuscitation. However, we recently demonstrated that epinephrine reduces cerebral cortical microcirculatory blood flow. Accordingly, we compared the effects of nonadrenergic vasopressin with those of epinephrine on cerebral cortical microvascular flow together with cortical tissue Po2 and Pco2 as indicators of cortical tissue ischemia.

DESIGN

Randomized, prospective animal study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Domestic pigs.

MEASUREMENTS AND MAIN RESULTS

The tracheae of ten domestic male pigs, weighing 40 +/- 2 kg, were noninvasively intubated, and the animals were mechanically ventilated. A frontoparietal bilateral craniotomy was created. Microcirculatory blood flow was quantitated with orthogonal polarization spectral imaging. Blood flow velocity in pial and cortical penetrating vessels measuring <20 microm was graded from 0 (no flow) to 3 (normal). Cerebral cortical tissue carbon dioxide and oxygen tensions (Pbco2 and Pbo2) were measured concurrently using miniature optical sensors. Ventricular fibrillation, induced with an alternating current delivered to the right ventricular endocardium, was untreated for 3 mins. Animals were then randomized to receive central venous injections of equipressor doses of epinephrine (30 microg/kg) or vasopressin (0.4 units/kg) at 1 min after the start of cardiopulmonary resuscitation. After 4 mins of cardiopulmonary resuscitation, defibrillation was attempted. Spontaneous circulation was restored in each animal. However, postresuscitation microvascular flows and Pbo2 were greater and Pbco2 less after vasopressin when compared with epinephrine. We observed that a significantly greater number of cortical microvessels were perfused after vasopressin.

CONCLUSIONS

Cortical microcirculatory blood flow was markedly reduced after epinephrine, resulting in a greater severity of brain ischemia after the restoration of spontaneous circulation in contrast to the more benign effects of vasopressin.

Role of buccal PCO2 in the management of fluid resuscitation during hemorrhagic shock

Arterial pressure is a widely used measurement for estimating the severity of hemorrhagic shock and to guide its management. However, this capability is reduced when very low arterial pressure values cannot be reliably measured by noninvasive methods. Moreover, hypoperfusion may be masked by compensatory hemodynamic changes, and therefore, in the presence of near normal blood pressure, tissue hypoperfusion may progress undetected. Accordingly, hypercarbia is a general phenomenon of perfusion failure, which occurs in coincidence of the onset of hypotension and is promptly reversed with restoration of normal blood flows. Increases in buccal mucosa PCO2 are highly correlated with increases in gastric wall and sublingual mucosa PCO2 and decreases in tissue blood flows during hemorrhagic shock. In both clinical and experimental settings, tissue PCO2 measured in the oral mucosa proved to be a practical and reliable measurement for the diagnosis of circulatory failure states and an indicator of its severity. In contrast to intraarterial pressure, buccal PCO2 discriminated between short- and long-term survival after large-volume blood loss. Buccal PCO2 measurement therefore emerges as a useful predictor for survival and outcome and a useful guide to manage fluid resuscitation during hemorrhagic shock.

Measurement of acid-base resuscitation endpoints: lactate, base deficit, bicarbonate or what?

PURPOSE OF REVIEW

Inadequate oxygen delivery to the tissues frequently results in significant metabolic acidosis. The resultant cellular and organ dysfunction can increase morbidity, mortality and hospital stay. Early diagnosis of shock can lead to early resuscitation efforts that can prevent ongoing tissue injury. This review focuses on the metabolic, hemodynamic and regional perfusion endpoints utilized in the diagnosis of metabolic acidosis resulting from shock. Resuscitation strategies aimed at supranormal oxygen delivery will be discussed.

RECENT FINDINGS

Serum pH, lactate, base deficit and bicarbonate have all been extensively studied as clinical markers of metabolic acidosis in shock. While their trend helps guide resuscitation, no single marker or specific value can be utilized to guide resuscitation for all patients. Hemodynamic parameters and regional tissue endpoints are designed to identify compensated shock before it progresses to uncompensated shock. Resuscitation strategies initiated in the early phases of shock can reduce complications and death. Efforts to resuscitate patients to supranormal oxygen delivery endpoints have demonstrated mixed success, with several notable complications.

SUMMARY

Despite the large number of endpoints available to the clinician, none are universally applicable and none have independently demonstrated improved survival when guiding resuscitation. Patients who respond well to initial resuscitation efforts demonstrate a survival advantage over nonresponders.

Sublingual capnometry: a non-invasive measure of microcirculatory dysfunction and tissue hypoxia

With improvement in supportive care patients rarely die from their presenting illness but rather from its sequela, namely sequential multi-organ failure. Tissue hypoxia is believed to be the causation of multi-organ dysfunction syndrome (MODS). The expedient detection and correction of tissue hypoxia may therefore limit the development of MODS. The standard oxygenation and hemodynamic variables (blood pressure, arterial oxygenation, cardiac output) which are monitored in critically ill patients are 'upstream' markers and provide little information as to the adequacy of tissue oxygenation. Global 'downstream' markers such as mixed venous oxygen saturation and blood lactate are insensitive indicators of tissue hypoxia. Sublingual PCO(2) is a regional marker of microvascular perfusion and tissue hypoxia that holds great promise for the risk stratification and end-point of goal directed resuscitation in critically ill patients. This paper reviews the technology and application of sublingual PCO(2) monitoring.

Increases in tissue Pco2 during circulatory shock reflect selective decreases in capillary blood flow*

OBJECTIVES

Tissue Pco2 reflects metabolic alterations due to circulatory failure during circulatory shock. This study addresses simultaneous changes in gastric and buccal tissue Pco2 with changes in microcirculatory blood flow in a rat model of circulatory shock induced by cecal ligation and puncture.

DESIGN

Prospective controlled laboratory study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Male breeder Sprague-Dawley rats.

INTERVENTIONS

Induction of polymicrobial, abdominal sepsis by cecal ligation and puncture.

MEASUREMENTS AND MAIN RESULTS

Tissue Pco2 was continuously measured with the aid of a miniature carbon dioxide electrode. Using orthogonal polarization spectral imaging, recordings of the microcirculation were taken at baseline and hourly intervals until death and compared with sham-operated animals. Gastric and buccal tissue Pco2 values progressively increased in animals after cecal ligation and puncture and terminated in death. Microcirculatory blood flow in vessels >20 microm was well preserved during progression of shock, whereas there was an early and progressive decrease in microcirculatory blood flow in vessels <20 microm, mostly representing capillaries. Tissue Pco2, the tissue Pco2-Paco2 gradient, and blood flow in vessels <20 microm were highly correlated. This contrasted with sham control animals in which no significant hemodynamic, blood gas, lactate, microcirculatory, and tissue Pco2 abnormalities were observed.

CONCLUSIONS

These observations suggest that microcirculatory failure in capillaries appears as an early defect in close association with anaerobic metabolism during progression of circulatory shock in an animal model of septic peritonitis.

Buccal capnometry to guide management of massive blood loss

In both clinical and experimental settings, tissue Pco2 measured in the oral mucosa is a practical and reliable measurement of the severity of hypoperfusion. We hypothesized that a threshold level of buccal tissue Pco2 (Pco2 BU) would prognosticate the effects of volume repletion on survival. Twenty pentobarbital-anesthetized Sprague-Dawley male breeder rats, each weighing ∼0.5 kg, were randomly assigned to one of four groups. Animals were bled over an interval of 30 min in amounts estimated to be 25, 30, 35, or 40% of total blood volume. One-half hour after the completion of bleeding, each animal received an infusion of Ringer lactate solution over the ensuing 30 min in amounts equivalent to two times the volume of blood loss. Pco2 BU was measured continuously with an optical Pco2 sensor applied noninvasively to the mucosa of the left cheek. Arterial pressure and end-tidal CO2 were measured over the same interval. Neurological deficit and 72-h survival were recorded. Aortic pressures were restored to near baseline values for each of the four groups after fluid resuscitation. This contrasted with the improvement of Pco2 BU, which differentiated between animals with short and long durations of postintervention survival. After electrolyte fluid resuscitation in rats subjected to rapid bleeding, noninvasive measurement of Pco2 BU was predictive of outcomes. Neither noninvasive end-tidal Pco2 nor invasive aortic pressure measurements achieved such discrimination. Accordingly, Pco2 BU fulfills the criterion of a noninvasive and reliable measurement to guide fluid management of hemorrhagic shock.