Effects of variation in systemic blood pressure on intraosseous pressure, PO2, and PCO2

The relationship between intraosseous catheter tip placement, flow rates, and infusion pressures in a high bone density cadaveric swine (Sus scrofa) model

Background

Intraosseous (IO) infusion is a life-preserving technique when intravenous access is unobtainable. Successful IO infusion requires sufficiently high flow rates to preserve life but at low enough pressures to avoid complications. However, IO catheter tips are often misplaced, and the relative flow rates and pressures between IO catheter tips placed in medullary, trabecular, and cortical bone are not well described, which has important implications for clinical practice.

Objectives

We developed the Zone Theory of IO Catheter Tip Placement based on bone density and proximity to the venous central sinus and then tested the influence of catheter tip placement locations on flow rates and pressures in a cadaveric swine model.

Methods

Three cross-trained participants infused 500 mL of crystalloid fluid into cadaveric swine humerus and sternum (N = 210 trials total) using a push‒pull method with a 60 cm3 syringe. Computed tomography scans were scored by radiologists and categorized as zone 1 (medullary space), zone 2 (trabecular bone), or zone 3 (cortical bone) catheter tip placements. Differences between zones in flow rates, mean pressures, and peak pressures were assessed using analysis of variance and analysis of covariance to account for participant and site differences at the p < 0.05 threshold.

Results

Zone 1 and zone 2 placements were essentially identical in flow rates, mean pressures, and peak pressures (each p > 0.05). Zone 1 and zone 2 placements were significantly higher in flow rates and lower in pressures than zone 3 placements (each p < 0.05 or less).

Conclusion

Within the limitations of an unpressurized cadaveric swine model, the present findings suggest that IO catheter tip placements need not be perfect to acquire high flow rates at low pressures, only accurate enough to avoid the dense cortical bone of zone 3. Future research using in vivo animal and human models is needed to better define the clinical impact of IO catheter placement on infusion flow rates and pressures.

Relationships of intraosseous and systemic pressure waveforms in a Swine model

BACKGROUND

Despite some focus on the use of intraosseous (IO) catheters to obtain laboratory samples, very little is known about the potential for obtaining other forms of clinical data. Largely unstudied is the relationship between IO pressures (IOPs) and systemic hemodynamic pressures such as mean arterial pressure (MAP) and central venous pressures (CVP).

OBJECTIVES

The objective was to explore the relationship between hemodynamic parameters (blood pressures) measured through an IO catheter and intravascular catheters placed in the arterial and central venous circulation.

METHODS

Eight pigs (Sus scrofa) weighing 30 to 45 kg were sedated with a short-acting agent, intubated with a cuffed endotracheal tube, and anesthetized with 2% to 3% isoflurane. Intravascular catheters were placed into the femoral or carotid artery and the femoral or jugular vein for MAP and CVP measurements. IO catheters, 15 mm for the sternum and 25 mm for the long bones, were placed percutaneously into the proximal tibia, proximal femur, proximal humerus, right proximal ulna, and/or sternum. Pressures were recorded during normotension, hypotension, and hypertension.

RESULTS

Averaged across all eight animals, the means (ranges) for baseline systemic pressures were as follows: MAP = 66.5 (55.6 to 76.7) mm Hg, tibia IOP = 17.4 (9.3 to 34.5) mm Hg, femur IOP =18.4 (3.3 to 33.1) mm Hg, humerus IOP = 15.7 (2.8 to 28.9) mm Hg, ulna IOP = 16.0 (7.9 to 25.6) mm Hg, sternum IOP = 5.7 (-0.5 to 47.9) mm Hg, and CVP = 2.7 mm Hg (-3.3 to 7.9) mm Hg. The best median correlation occurred between femur IOP and mean MAP (r = 0.65). The four highest correlations between IOP and MAP were associated with mean femur IOP. Only one IO site had a correlation coefficient over 0.50 for CVP. The long bones tended to correlate better with the MAP and the sternum tended to correlate better with the CVP. Nonlinearity was observed in the actively rising pressure phases, which can be explained by a hysteresis model.

CONCLUSIONS

The relationship between IOP and MAP or CVP is variable by site, with the MAP and CVP tending to be estimated by the femur and sternum, respectively. The relationship to actively rising pressures is nonlinear and a hysteresis model is proposed to explain the phase change. Further experimentation is needed to refine the IOP relationship to the MAP and CVP and assess the potential of these measurements to provide clinically relevant information.

Modulation of the intramedullary pressure responses by calcium dobesilate in a rabbit knee model of osteoarthritis

BACKGROUND AND PURPOSE

The presence of bone marrow edema in patients with osteoarthritis is associated with pain and disease progression. Management of bone edema with the synthetic prostacyclin iloprost may be complicated by side effects. Calcium dobesilate, a treatment for chronic venous disease, shares some pharmacological actions with iloprost but appears to be better tolerated. Anecdotal reports have suggested that calcium dobesilate may be useful for medical management of osteoarthritis, possibly by reducing bone marrow edema, and this study was performed to investigate possible benefits of treatment.

METHODS

The effects of a 6-week period of oral calcium dobesilate administration on tibial intramedullary pressure dynamics and physical joint characteristics were evaluated in 20 rabbits with unilaterally induced knee osteoarthritis that were randomly allocated to either a treatment group or a placebo control group. Treatment or placebo started 8 weeks after induction of osteoarthritis, and was followed by a 4-week washout period.

RESULTS

Calcium dobesilate did not affect joint thickness or range of motion, nor individual pressure measurements, compared to placebo. Pressure ranges in the operated limb were greater than in the intact limb after 8 weeks, and approached those of the intact limb after 6 weeks of treatment with calcium dobesilate but not with placebo. Inter-limb differences were lower (p = 0.02) in the dobesilate group following the washout period.

INTERPRETATION

Calcium dobesilate had a detectable effect on pressure dynamics in the subchondral bone of osteoarthritic joints in this model. The significance of these effects for pain and function should be established.

Core decompression of the equine navicular bone: an in vivo study in healthy horses

OBJECTIVE

To determine the physiologic response of the equine navicular bone to core decompression surgery in healthy horses.

STUDY DESIGN

Experimental in vivo study.

MATERIALS

Healthy adult horses (n=6).

METHODS

Core decompression was completed by creating three 2.5-mm-diameter drill channels into the navicular bone under arthroscopic control. The venous (P(V)), arterial (P(A)), articular (P(DIPJ)), and intraosseous pressures (IOP) were recorded before and after decompression drilling. Each IOP measurement consisted of a baseline (IOP(B)) and a stress test (intramedullary injection of saline solution, IOP(S)) recording. Lameness was assessed subjectively and using force plate gait analysis. Fluorochrome bone labeling was performed. Horses were euthanatized at 12 weeks. Navicular bone mineral density (BMD) was measured, and bone histology evaluated.

RESULTS

Peak IOP (IOP(max)) after stress testing was significantly (P<.05) reduced immediately after core decompression; however, the magnitude of these effects was decreased at 3 and 6 weeks after decompression. A significant (P<.05) correlation existed between IOP(max) and BMD. No lameness was observed beyond the first week after surgery. Substantial remodeling and neovascularization was evident adjacent the surgery sites.

CONCLUSION

Navicular bone core decompression surgery reduced IOP(max), and, with the exception of a mild short-lived lameness, caused no other adverse effects in healthy horses during the 12-week study period.

Femoral head blood flow during hip resurfacing

Preserving femoral head vascularity during hip resurfacing may avoid femoral neck fractures and late femoral loosening. The posterior approach and notching of the femoral neck influence femoral head perfusion. However, it is not known if standard preparation of the femoral head during hip resurfacing can disrupt blood flow. Ten patients (10 hips) with advanced osteoarthritis having metal-on-metal hip resurfacing by means of a vascular-preserving surgical approach had femoral head blood flow measurements using laser Doppler flowmetry. Nine hips had a mean decrease of 70% in femoral head blood flow after standard reaming and preparation. The data suggest femoral head reaming during hip resurfacing substantially impacts blood flow to the femoral head and infers the extra osseous blood supply is still important in the arthritic femoral head. To avoid damaging the retinacular vessels, surgeons should direct the cylindrical reamer superolaterally staying as close as possible to the inferomedial neck.

Dose-dependent inversion of the effect of prostaglandin E1 on intraosseous pressure: adequate dose for reducing blood loss during operation on bone

Tibial intraosseous pressure and blood flow, along with arterial pressure, were measured in anesthetized rabbits before and during intravenous infusion of prostaglandin E1 at doses of 0, 100, 300, 1000, and 2000 ng/kg per min. The mean arterial pressure decreased dose-dependently. The intra-osseous pressure increased during infusion at doses of 300 and 1000 ng/kg per min, but decreased during infusion at the dose of 2000 ng/kg per min. Bone blood flow increased during infusion only at a dose of 1000 ng/kg per min. Calculated vascular and arteriolar resistances in bone decreased dose-dependently during infusion at doses of up to 1000 ng/kg per min, but no change was seen when the dose was increased from 1000 to 2000 ng/kg per min. These findings indicated that: (1) there was a turning point in the effect of prostaglandin E1 at a certain dose between 1000 and 2000 ng/kg per min, at which the arterioles in bone were fully dilated; (2) at a dose of 1000 ng/kg per min or lower, responsive dilatation in the arterioles of bone under mild arterial hypotension increased the influx of blood into the bone, thereby increasing the intraosseous pressure; and (3) at doses higher than 1000 ng/kg per min, dose-dependent arterial hypotension without further dilatation in the arterioles of bone decreased the influx of blood.

Intraosseous blood gases during hypothermia: correlation with arterial, mixed venous, and sagittal sinus blood

OBJECTIVE

Especially in pediatric patients with severe hypothermia, intraosseous access may be more readily available than intravascular access during an early phase of treatment and therefore, may be helpful to optimize management. The purpose of this study was to determine whether intraosseous blood gases are comparable with arterial, mixed venous, and sagittal sinus blood gases during different degrees of hypothermia.

DESIGN

Prospective, descriptive laboratory investigation using a porcine model.

SETTING

University hospital laboratory.

SUBJECTS

Twelve anesthetized, 12- to 16-wk-old domestic pigs weighing 30-35 kg.

INTERVENTIONS

Volume-controlled ventilated animals were instrumented with arterial, pulmonary artery, sagittal sinus, and 16-gauge intraosseous catheters. Blood samples were obtained from each site every 15 mins during surface cooling with crushed ice until mean +/- SEM core temperature decreased from 38.5+/-0.1 degrees C [101.3+/-0.2 degrees F] to 27+/-0.5 degrees C [80.5+/-0.9 degrees F] over 2 hrs.

MEASUREMENTS AND MAIN RESULTS

Intraindividual correlation of Pco2 and pH values were determined as the difference (delta) between intraosseous and reference blood samples. With hypothermia, absolute values of Pco2 decreased and pH increased in samples from all sites. At 27 degrees C, intraosseous--arterial delta P(CO2) and delta pH (mean +/- 95% confidence intervals) were 2.6+/-10.6 torr [0.35+/-1.4 kPa] and -0.11+/-0.07 units; intraosseous - mixed venous were 0.4+/-12.2 torr [0.05+/-1.6 kPa] and -0.06+/-0.08 units; and intraosseous - sagittal sinus were -7.3+/-16 torr [-0.97+/-2.1 kPa] and 0.001+/-0.14 units, respectively. Intraosseous Pco2 was not comparable to end-tidal values (deltaP(CO2) 17.4+/-14.6 torr [2.3+/-1.9 kPa]), and intraosseous lactate did not correlate with arterial, mixed venous, or sagittal sinus values.

CONCLUSIONS

During hypothermia, intraosseous P(CO2) values were predictable for mixed venous Pco2 and arterial P(CO2). Intraosseous pH values also correlated with mixed venous and sagittal sinus blood samples. Accordingly, interpretation of blood gas values obtained from bone marrow aspirates may be helpful to adjust ventilation and optimize fluid and drug therapy during the early treatment of patients with severe hypothermia.

Intraosseous infusions in the adult

Intraosseous infusions are used in children when intravenous access is difficult or impossible. The intraosseous route is also applicable to adults, but is not widely used. In this article, the anatomy and physiology of bone marrow is described and techniques and sites of intraosseous needle placement are discussed. Fluid and drug administration by the intraosseous route is also discussed. Intraosseous anaeasthesia and diagnostic testing is possible through intraossoeous needles. Potential complications and contraindications are considered.

Partial pressures of oxygen and carbon dioxide in bone and their correlation with bone-blood flow: effect of decreased arterial supply and venous congestion on intraosseous oxygen and carbon dioxide in an animal model

Pathological changes in bone have been related to a preceding impediment of the arterial or venous bone circulation and hypoxia. In this study, we analyzed the feasibility of mass spectrometry in measuring intraosseous oxygen and carbon dioxide. The partial pressures were also measured in intraosseous blood samples, and blood flow in bone was measured with the radioactive microspheres technique. The average partial pressure of oxygen in the lateral femoral condyle was 34 +/- 1.6 mm Hg when measured in intraosseous blood samples and 36.3 +/- 2.3 mm Hg when measured with the on-line mass spectrometer, with significant correlation between the methods. The absolute value of the partial pressure of carbon dioxide measured in situ with mass spectrometry was correlated with the value in the withdrawn blood. There was no significant difference in partial pressures of oxygen and carbon dioxide between the two sides or between repetitive measurements. Arterial occlusion resulted in severe hypoxia, whereas more moderate changes followed venous occlusion.